Cellular Mechanisms Underlying the Effects of Milrinone and Cilostazol to Suppress Arrhythmogenesis Associated with Brugada Syndrome

PubMed Central

Szél, Tamás; Koncz, István; Antzelevitch, Charles

2013-01-01

Background: Brugada syndrome is an inherited disease associated with vulnerability to ventricular tachycardia and sudden cardiac death in young adults. Milrinone and cilostazol, oral phosphodiesterase (PDE) type III inhibitors, have been shown to increase ICa and modestly increase heart rate by elevating the level of intracellular cyclic AMP. Objective: The present study examines the effectiveness of these PDE inhibitors to suppress arrhythmogenesis in an experimental model of Brugada syndrome. Methods: Action potential (AP) and ECG recordings were obtained from epicardial and endocardial sites of coronary-perfused canine right ventricular wedge preparations. The Ito agonist NS5806 (5 μM) and Ca2+ channel blocker verapamil (2 μM) were used to pharmacologically mimic Brugada phenotype. Results: The combination induced all-or-none repolarization at some epicardial sites but not others, leading to ST-segment elevation as well as an increase in both epicardial and transmural dispersion of repolarization. Under these conditions, phase 2 reentry developed as the epicardial AP dome propagated from sites where it was maintained to sites at which it was lost, generating closely coupled extrasystoles and ventricular tachycardia. Addition of the PDE inhibitor milrinone (2.5 μM) or cilostazol (5-10 μM) to the coronary perfusate restored the epicardial AP dome, reduced dispersion and abolished phase 2 reentry—induced extrasystoles and ventricular tachycardia. Conclusions: Our study identifies milrinone as a more potent alternative to cilostazol for reversing the repolarization defects responsible for the electrocardiographic and arrhythmic manifestations of Brugada syndrome. Both drugs normalize ST segment elevation, and suppress arrhythmogenesis in experimental models of Brugada syndrome. PMID:23911896

Modulation of KCNQ1 alternative splicing regulates cardiac IKs and action potential repolarization.

PubMed

Lee, Hsiang-Chun; Rudy, Yoram; Po-Yuan, Phd; Sheu, Sheng-Hsiung; Chang, Jan-Gowth; Cui, Jianmin

2013-08-01

Slow delayed-rectifier potassium current (IKs) channels, made of the pore-forming KCNQ1 and auxiliary KCNE1 subunits, play a key role in determining action potential duration (APD) in cardiac myocytes. The consequences of drug-induced KCNQ1 splice alteration remain unknown. To study the modulation of KCNQ1 alternative splicing by amiloride and the consequent changes in IKs and action potentials (APs) in ventricular myocytes. Canine endocardial, midmyocardial, and epicardial ventricular myocytes were isolated. Levels of KCNQ1a and KCNQ1b as well as a series of splicing factors were quantified by using the reverse transcriptase-polymerase chain reaction and Western blot. The effect of amiloride-induced changes in the KCNQ1b/total KCNQ1 ratio on AP was measured by using whole-cell patch clamp with and without isoproterenol. With 50 μmol/L of amiloride for 6 hours, KCNQ1a at transcriptional and translational levels increased in midmyocardial myocytes but decreased in endo- and epicardial myocytes. Likewise, changes in splicing factors in midmyocardial were opposite to that in endo- and epicardial myocytes. In midmyocardial myocytes amiloride shortened APD and decreased isoproterenol-induced early afterdepolarizations significantly. The same amiloride-induced effects were demonstrated by using human ventricular myocyte model for AP simulations under beta-adrenergic stimulation. Moreover, amiloride reduced the transmural dispersion of repolarization in pseudo-electrocardiogram. Amiloride regulates IKs and APs with transmural differences and reduces arrhythmogenicity through the modulation of KCNQ1 splicing. We suggested that the modulation of KCNQ1 splicing may help prevent arrhythmia. Copyright © 2013 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

Cellular mechanisms underlying the effects of milrinone and cilostazol to suppress arrhythmogenesis associated with Brugada syndrome.

PubMed

Szél, Tamás; Koncz, István; Antzelevitch, Charles

2013-11-01

Brugada syndrome is an inherited disease associated with vulnerability to ventricular tachycardia and sudden cardiac death in young adults. Milrinone and cilostazol, oral phosphodiesterase (PDE) type III inhibitors, have been shown to increase L-type calcium channel current (ICa) and modestly increase heart rate by elevating the level of intracellular cyclic adenosine monophosphate. To examine the effectiveness of these PDE inhibitors to suppress arrhythmogenesis in an experimental model of Brugada syndrome. Action potential (AP) and electrocardiographic recordings were obtained from epicardial and endocardial sites of coronary-perfused canine right ventricular wedge preparations. The Ito agonist NS5806 (5 μM) and Ca(2+) channel blocker verapamil (2 μM) were used to pharmacologically mimic Brugada phenotype. The combination induced all-or-none repolarization at some epicardial sites but not others, leading to ST-segment elevation as well as an increase in both epicardial and transmural dispersion of repolarization. Under these conditions, phase 2 reentry developed as the epicardial AP dome propagated from sites where it was maintained to sites at which it was lost, generating closely coupled extrasystoles and ventricular tachycardia. The addition of the PDE inhibitor milrinone (2.5 μM) or cilostazol (5-10 μM) to the coronary perfusate restored the epicardial AP dome, reduced dispersion, and abolished phase 2 reentry-induced extrasystoles and ventricular tachycardia. Our study identifies milrinone as a more potent alternative to cilostazol for reversing the repolarization defects responsible for the electrocardiographic and arrhythmic manifestations of Brugada syndrome. Both drugs normalize ST-segment elevation and suppress arrhythmogenesis in experimental models of Brugada syndrome. © 2013 Heart Rhythm Society. All rights reserved.

Effects of 4-aminopyridine on cardiac repolarization, PR interval, and heart rate in patients with spinal cord injury.

PubMed

Isoda, Wakana C; Segal, Jack L

2003-02-01

To determine the effects of 4-aminopyridine (4-AP) on heart rate and PR, QT, and QTc intervals in patients with longstanding spinal cord injury (SCI). Randomized, active-treatment-controlled, dose level-blinded study, with allocation concealed. University-affiliated, tertiary care medical center. Sixty otherwise healthy male and female outpatients with traumatic SCI of more than 1 year's duration. Intervention. Oral administration and dose titration to tolerance of an immediate-release formulation of 4-AP. The PR interval, heart rate, QT interval, and QTc interval obtained from standard 12-lead electrocardiograms (ECGs) at baseline (before administration of 4-AP) and after 1 month of treatment were compared. The QTc intervals were derived by using Bazett's formula (equation) incorporated into standard computerized analyses of 12-lead ECG printouts. The paired t test was performed to test for the significance of differences between means and variances. No statistically significant differences were noted in heart rate or between ECG time intervals measured at baseline and after 1 month of treatment with 4-AP among all patients with SCI or between subgroups stratified by injury level (tetraplegia, paraplegia) or sex. During the 1-month period that 4-AP was administered, the heart rate and PR, QT, and QTc intervals all remained unchanged and stayed well within normal range in comparison to literature-derived control values. 4-Aminopyridine does not appear to influence the length of cardiac time intervals or heart rate and, hence, is unlikely to cause potentially life-threatening ventricular dysrrhythmias when administered long-term and taken orally in dosages of up to 30 mg/day. Specifically, cardiac repolarization (QTc interval) is unaffected in patients with SCI who continuously receive 4-AP for up to 1 month.

Human induced pluripotent stem cell‐derived versus adult cardiomyocytes: an in silico electrophysiological study on effects of ionic current block

PubMed Central

Paci, M; Hyttinen, J; Rodriguez, B

2015-01-01

Background and Purpose Two new technologies are likely to revolutionize cardiac safety and drug development: in vitro experiments on human‐induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs) and in silico human adult ventricular cardiomyocyte (hAdultV‐CM) models. Their combination was recently proposed as a potential replacement for the present hERG‐based QT study for pharmacological safety assessments. Here, we systematically compared in silico the effects of selective ionic current block on hiPSC‐CM and hAdultV‐CM action potentials (APs), to identify similarities/differences and to illustrate the potential of computational models as supportive tools for evaluating new in vitro technologies. Experimental Approach In silico AP models of ventricular‐like and atrial‐like hiPSC‐CMs and hAdultV‐CM were used to simulate the main effects of four degrees of block of the main cardiac transmembrane currents. Key Results Qualitatively, hiPSC‐CM and hAdultV‐CM APs showed similar responses to current block, consistent with results from experiments. However, quantitatively, hiPSC‐CMs were more sensitive to block of (i) L‐type Ca2+ currents due to the overexpression of the Na+/Ca2+ exchanger (leading to shorter APs) and (ii) the inward rectifier K+ current due to reduced repolarization reserve (inducing diastolic potential depolarization and repolarization failure). Conclusions and Implications In silico hiPSC‐CMs and hAdultV‐CMs exhibit a similar response to selective current blocks. However, overall hiPSC‐CMs show greater sensitivity to block, which may facilitate in vitro identification of drug‐induced effects. Extrapolation of drug effects from hiPSC‐CM to hAdultV‐CM and pro‐arrhythmic risk assessment can be facilitated by in silico predictions using biophysically‐based computational models. PMID:26276951

The spike generator in the labellar taste receptors of the blowfly is differently affected by 4-aminopyridine and 5-hydroxytryptamine.

PubMed

Sollai, Giorgia; Solari, Paolo; Corda, Valentina; Masala, Carla; Crnjar, Roberto

2012-12-01

In taste chemoreception of invertebrates the interaction of taste stimuli with specific membrane receptors and/or ion channels located in the apical membrane of taste receptor cells results in the generation of a receptor potential which, in turn, activates the 'encoder' region to produce action potentials which propagate to the CNS. This study investigates, in the labellar chemosensilla of the blowfly, Protophormia terraenovae, the voltage-gated K(+) currents involved in the action potential repolarization and repetitive firing of the neurons by way of the K(v) channel inhibitors, 4-aminopyridine and 5-hydroxytryptamine. The receptor potential and the spike activity were simultaneously recorded from the 'salt', 'sugar' and 'deterrent' cells, by means of the extracellular side-wall technique, in response to 150 mM NaCl, 100 mM sucrose and 1 mM quinine HCl, before, 0÷10 min after apical administration of 4-AP (0.01-10 mM) or 5-HT (0.1-100 mM). The results show that the receptor potential in all three cells is neither affected by 4-AP nor by 5-HT. Instead, spike activity is significantly decreased, by way of blocking different K(v) channel types: an inactivating A-type K(+) current (KA) modulating repetitive firing of the cells and responsible for the after hyperpolarization, and a sustained K(+) current that resembles the delayed rectifier (DKR) and contributes to action potential repolarization. Copyright © 2012 Elsevier Ltd. All rights reserved.

Effects of seasonal acclimatization on temperature dependence of cardiac excitability in the roach, Rutilus rutilus.

PubMed

Badr, A; El-Sayed, M F; Vornanen, M

2016-05-15

Temperature sensitivity of electrical excitability is a potential limiting factor for performance level and thermal tolerance of excitable tissues in ectothermic animals. To test whether the rate and rhythm of the heart acclimatize to seasonal temperature changes, thermal sensitivity of cardiac excitation in a eurythermal teleost, the roach (Rutilus rutilus), was examined. Excitability of the heart was determined from in vivo electrocardiograms and in vitro microelectrode recordings of action potentials (APs) from winter and summer roach acclimatized to 4 and 18°C, respectively. Under heat ramps (3°C h(-1)), starting from the acclimatization temperatures of the fish, heart rate increased to maximum values of 78±5 beats min(-1) (at 19.8±0.5°C) and 150±7 beats min(-1) (at 28.1±0.5°C) for winter and summer roach, respectively, and then declined in both groups. Below 20°C, heart rate was significantly higher in winter than in summer roach (P<0.05), indicating positive thermal compensation. Cardiac arrhythmias appeared with rising temperature as missing QRS complexes, increase in variability of heart rate, episodes of atrial tachycardia, ventricular bradycardia and complete cessation of the heartbeat (asystole) in both winter and summer roach. Unlike winter roach, atrial APs of summer roach had a distinct early repolarization phase, which appeared as shorter durations of atrial AP at 10% and 20% repolarization levels in comparison to winter roach (P<0.05). In contrast, seasonal acclimatization had only subtle effects on ventricular AP characteristics. Plasticity of cardiac excitation appears to be necessary for seasonal improvements in performance level and thermal resilience of the roach heart. © 2016. Published by The Company of Biologists Ltd.

Identification and characterization of a transient outward K+ current in human induced pluripotent stem cell-derived cardiomyocytes

PubMed Central

Cordeiro, Jonathan M.; Nesterenko, Vladislav V.; Sicouri, Serge; Goodrow, Robert J.; Treat, Jacqueline A.; Desai, Mayurika; Wu, Yuesheng; Doss, Michael Xavier; Antzelevitch, Charles; Di Diego, José M.

2013-01-01

Background The ability to recapitulate mature adult phenotypes is critical to the development of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) as models of disease. The present study examines the characteristics of the transient outward current (Ito) and its contribution to the hiPSC-CM action potential (AP). Method Embryoid bodies were made from a hiPS cell line reprogrammed with Oct4, Nanog, Lin28 and Sox2. Sharp microelectrodes were used to record APs from beating-clusters (BC) and patch-clamp techniques were used to record Ito in single hiPSC-CM. mRNA levels of Kv1.4, KChIP2 and Kv4.3 were quantified from BCs. Results BCs exhibited spontaneous beating (60.5 ± 2.6 bpm) and maximum-diastolic-potential (MDP) of 67.8 ± 0.8 mV (n = 155). A small 4-aminopyridine-sensitive phase-1-repolarization was observed in only 6/155 BCs. A robust Ito was recorded in the majority of cells (13.7 ± 1.9 pA/pF at +40 mV; n = 14). Recovery of Ito from inactivation (at −80 mV) showed slow kinetics (τ1 = 200 ± 110 ms (12%) and τ2 = 2380 ± 240 ms (80%)) accounting for its minimal contribution to the AP. Transcript data revealed relatively high expression of Kv1.4 and low expression of KChIP2 compared to human native ventricular tissues. Mathematical modeling predicted that restoration of IK1 to normal levels would result in a more negative MDP and a prominent phase-1-repolarization. Conclusion The slow recovery kinetics of Ito coupled with a depolarized MDP account for the lack of an AP notch in the majority of hiPSC-CM. These characteristics reveal a deficiency for the development of in vitro models of inherited cardiac arrhythmia syndromes in which Ito-induced AP notch is central to the disease phenotype. PMID:23542310

Cardiac structural changes and electrical remodeling in a thiamine-deficiency model in rats.

PubMed

Roman-Campos, D; Campos, A C; Gioda, C R; Campos, P P; Medeiros, M A A; Cruz, J S

2009-06-05

Thiamine is an important cofactor present in many biochemical reactions, and its deprivation can lead to heart dysfunction. Little is known about the influence of thiamine deprivation on the electrophysiological behavior of the isolated heart cells and information about thiamine deficiency in heart morphology is controversial. Thus, we decided to investigate the major repolarizing conductances and their influence in the action potential (AP) waveform as well as the changes in the heart structure in a set of thiamine deficiency in rats. Using the patch-clamp technique, we investigated inward (I(K1)) and outward K(+) currents (I(to)), T-type and L-type Ca(2+) currents and APs. To evaluate heart morphology we used hematoxylin and eosin in transversal heart sections. Thiamine deficiency caused a marked decrease in left ventricle thickness, cardiomyocyte number, cell length and width, and membrane capacitance. When evaluating I(to) we did not find difference in current amplitude; however an acceleration of I(to) inactivation was observed. I(K1) showed a reduction in the amplitude and slope conductance, which implicated a less negative resting membrane potential in cardiac myocytes isolated from thiamine-deficient rats. We did not find any difference in L-type Ca(2+) current density. T-type Ca(2+) current was not observed. In addition, we did not observe significant changes in AP repolarization. Based on our study we can conclude that thiamine deficiency causes heart hypotrophy and not heart hypertrophy. Moreover, we provided evidence that there is no major electrical remodeling during thiamine deficiency, a feature of heart failure models.

Computational model based approach to analysis ventricular arrhythmias: Effects of dysfunction calcium channels

NASA Astrophysics Data System (ADS)

Gulothungan, G.; Malathi, R.

2018-04-01

Disturbed sodium (Na+) and calcium (Ca2+) handling is known to be a major predisposing factor for life-threatening cardiac arrhythmias. Cardiac contractility in ventricular tissue is prominent by Ca2+ channels like voltage dependent Ca2+ channels, sodium-calcium exchanger (Na+-Ca2+x) and sacroplasmicrecticulum (SR) Ca2+ pump and leakage channels. Experimental and clinical possibilities for studying cardiac arrhythmias in human ventricular myocardium are very limited. Therefore, the use of alternative methods such as computer simulations is of great importance. Our aim of this article is to study the impact on action potential (AP) generation and propagation in single ventricular myocyte and ventricular tissue under different dysfunction Ca2+ channels condition. In enhanced activity of Na+-Ca2+x, single myocyte produces AP duration (APD90) and APD50 is significantly smaller (266 ms and 235 ms). Its Na+-Ca2+x current at depolarization is increases 60% from its normal level and repolarization current goes more negative (nonfailing= -0.28 pA/pF and failing= -0.47 pA/pF). Similarly, same enhanced activity of Na+-Ca2+x in 10 mm region of ventricular sheet, raises the plateau potential abruptly, which ultimately affects the diastolic repolarization. Compare with normal ventricular sheet region of 10 mm, 10% of ventricular sheet resting state is reduces and ventricular sheet at time 250 ms is goes to resting state very early. In hypertrophy condition, single myocyte produces APD90 and APD50 is worthy of attention smaller (232 mS and 198 ms). Its sodium-potassium (Na+-K+) pump current is 75% reduces from its control conditions (0.13 pA/pF). Hypertrophy condition, 50% of ventricular sheet is reduces to minimum plateau potential state, that starts the repolarization process very early and reduces the APD. In a single failing SR Ca2+ channels myocyte, recovery of Ca2+ concentration level in SR reduces upto 15% from its control myocytes. At time 290 ms, 70% of ventricular sheet is in dysfunction resting potential state in the range -83 mV and ventricular sheet at time 295 ms is goes to 65% dysfunction resting state. Therefore we concluded that shorter APD, instability resting potential and affected calcium induced calcium release (CICR) due to dysfunction Ca2+ channels is potentially have a substantial effect on cardiac contractility and relaxation. Computational study on ventricular tissue AP and its underlying ionic channel currents could help to elucidate possible arrhythmogenic mechanism on a cellular level.

Aging-Related Hyperexcitability in CA3 Pyramidal Neurons Is Mediated by Enhanced A-Type K+ Channel Function and Expression.

PubMed

Simkin, Dina; Hattori, Shoai; Ybarra, Natividad; Musial, Timothy F; Buss, Eric W; Richter, Hannah; Oh, M Matthew; Nicholson, Daniel A; Disterhoft, John F

2015-09-23

Aging-related impairments in hippocampus-dependent cognition have been attributed to maladaptive changes in the functional properties of pyramidal neurons within the hippocampal subregions. Much evidence has come from work on CA1 pyramidal neurons, with CA3 pyramidal neurons receiving comparatively less attention despite its age-related hyperactivation being postulated to interfere with spatial processing in the hippocampal circuit. Here, we use whole-cell current-clamp to demonstrate that aged rat (29-32 months) CA3 pyramidal neurons fire significantly more action potentials (APs) during theta-burst frequency stimulation and that this is associated with faster AP repolarization (i.e., narrower AP half-widths and enlarged fast afterhyperpolarization). Using a combination of patch-clamp physiology, pharmacology, Western blot analyses, immunohistochemistry, and array tomography, we demonstrate that these faster AP kinetics are mediated by enhanced function and expression of Kv4.2/Kv4.3 A-type K(+) channels, particularly within the perisomatic compartment, of CA3 pyramidal neurons. Thus, our study indicates that inhibition of these A-type K(+) channels can restore the intrinsic excitability properties of aged CA3 pyramidal neurons to a young-like state. Significance statement: Age-related learning deficits have been attributed, in part, to altered hippocampal pyramidal neuronal function with normal aging. Much evidence has come from work on CA1 neurons, with CA3 neurons receiving comparatively less attention despite its age-related hyperactivation being postulated to interfere with spatial processing. Hence, we conducted a series of experiments to identify the cellular mechanisms that underlie the hyperexcitability reported in the CA3 region. Contrary to CA1 neurons, we demonstrate that postburst afterhyperpolarization is not altered with aging and that aged CA3 pyramidal neurons are able to fire significantly more action potentials and that this is associated with faster action potential repolarization through enhanced expression of Kv4.2/Kv4.3 A-type K(+) channels, particularly within the cell bodies of CA3 pyramidal neurons. Copyright © 2015 the authors 0270-6474/15/3513206-13$15.00/0.

Aging-Related Hyperexcitability in CA3 Pyramidal Neurons Is Mediated by Enhanced A-Type K+ Channel Function and Expression

PubMed Central

Simkin, Dina; Hattori, Shoai; Ybarra, Natividad; Musial, Timothy F.; Buss, Eric W.; Richter, Hannah; Oh, M. Matthew

2015-01-01

Aging-related impairments in hippocampus-dependent cognition have been attributed to maladaptive changes in the functional properties of pyramidal neurons within the hippocampal subregions. Much evidence has come from work on CA1 pyramidal neurons, with CA3 pyramidal neurons receiving comparatively less attention despite its age-related hyperactivation being postulated to interfere with spatial processing in the hippocampal circuit. Here, we use whole-cell current-clamp to demonstrate that aged rat (29–32 months) CA3 pyramidal neurons fire significantly more action potentials (APs) during theta-burst frequency stimulation and that this is associated with faster AP repolarization (i.e., narrower AP half-widths and enlarged fast afterhyperpolarization). Using a combination of patch-clamp physiology, pharmacology, Western blot analyses, immunohistochemistry, and array tomography, we demonstrate that these faster AP kinetics are mediated by enhanced function and expression of Kv4.2/Kv4.3 A-type K+ channels, particularly within the perisomatic compartment, of CA3 pyramidal neurons. Thus, our study indicates that inhibition of these A-type K+ channels can restore the intrinsic excitability properties of aged CA3 pyramidal neurons to a young-like state. SIGNIFICANCE STATEMENT Age-related learning deficits have been attributed, in part, to altered hippocampal pyramidal neuronal function with normal aging. Much evidence has come from work on CA1 neurons, with CA3 neurons receiving comparatively less attention despite its age-related hyperactivation being postulated to interfere with spatial processing. Hence, we conducted a series of experiments to identify the cellular mechanisms that underlie the hyperexcitability reported in the CA3 region. Contrary to CA1 neurons, we demonstrate that postburst afterhyperpolarization is not altered with aging and that aged CA3 pyramidal neurons are able to fire significantly more action potentials and that this is associated with faster action potential repolarization through enhanced expression of Kv4.2/Kv4.3 A-type K+ channels, particularly within the cell bodies of CA3 pyramidal neurons. PMID:26400949

Components of action potential repolarization in cerebellar parallel fibres.

PubMed

Pekala, Dobromila; Baginskas, Armantas; Szkudlarek, Hanna J; Raastad, Morten

2014-11-15

Repolarization of the presynaptic action potential is essential for transmitter release, excitability and energy expenditure. Little is known about repolarization in thin, unmyelinated axons forming en passant synapses, which represent the most common type of axons in the mammalian brain's grey matter.We used rat cerebellar parallel fibres, an example of typical grey matter axons, to investigate the effects of K(+) channel blockers on repolarization. We show that repolarization is composed of a fast tetraethylammonium (TEA)-sensitive component, determining the width and amplitude of the spike, and a slow margatoxin (MgTX)-sensitive depolarized after-potential (DAP). These two components could be recorded at the granule cell soma as antidromic action potentials and from the axons with a newly developed miniaturized grease-gap method. A considerable proportion of fast repolarization remained in the presence of TEA, MgTX, or both. This residual was abolished by the addition of quinine. The importance of proper control of fast repolarization was demonstrated by somatic recordings of antidromic action potentials. In these experiments, the relatively broad K(+) channel blocker 4-aminopyridine reduced the fast repolarization, resulting in bursts of action potentials forming on top of the DAP. We conclude that repolarization of the action potential in parallel fibres is supported by at least three groups of K(+) channels. Differences in their temporal profiles allow relatively independent control of the spike and the DAP, whereas overlap of their temporal profiles provides robust control of axonal bursting properties.

Neurotransmitter Release Can Be Stabilized by a Mechanism That Prevents Voltage Changes Near the End of Action Potentials from Affecting Calcium Currents

PubMed Central

Clarke, Stephen G.; Scarnati, Matthew S.

2016-01-01

At chemical synapses, presynaptic action potentials (APs) activate voltage-gated calcium channels, allowing calcium to enter and trigger neurotransmitter release. The duration, peak amplitude, and shape of the AP falling phase alter calcium entry, which can affect neurotransmitter release significantly. In many neurons, APs do not immediately return to the resting potential, but instead exhibit a period of depolarization or hyperpolarization referred to as an afterpotential. We hypothesized that presynaptic afterpotentials should alter neurotransmitter release by affecting the electrical driving force for calcium entry and calcium channel gating. In support of this, presynaptic calcium entry is affected by afterpotentials after standard instant voltage jumps. Here, we used the mouse calyx of Held synapse, which allows simultaneous presynaptic and postsynaptic patch-clamp recording, to show that the postsynaptic response is affected significantly by presynaptic afterpotentials after voltage jumps. We therefore tested the effects of presynaptic afterpotentials using simultaneous presynaptic and postsynaptic recordings and AP waveforms or real APs. Surprisingly, presynaptic afterpotentials after AP stimuli did not alter calcium channel responses or neurotransmitter release appreciably. We show that the AP repolarization time course causes afterpotential-induced changes in calcium driving force and changes in calcium channel gating to effectively cancel each other out. This mechanism, in which electrical driving force is balanced by channel gating, prevents changes in calcium influx from occurring at the end of the AP and therefore acts to stabilize synaptic transmission. In addition, this mechanism can act to stabilize neurotransmitter release when the presynaptic resting potential changes. SIGNIFICANCE STATEMENT The shape of presynaptic action potentials (APs), particularly the falling phase, affects calcium entry and small changes in calcium influx can produce large changes in postsynaptic responses. We hypothesized that afterpotentials, which often follow APs, affect calcium entry and neurotransmitter release. We tested this in calyx of Held nerve terminals, which allow simultaneous recording of presynaptic calcium currents and postsynaptic responses. Surprisingly, presynaptic afterpotentials did not alter calcium current or neurotransmitter release. We show that the AP falling phase causes afterpotential-induced changes in electrical driving force and calcium channel gating to cancel each other out. This mechanism regulates calcium entry at the end of APs and therefore stabilizes synaptic transmission. This also stabilizes responses when the presynaptic resting potential changes. PMID:27911759

Neurotransmitter Release Can Be Stabilized by a Mechanism That Prevents Voltage Changes Near the End of Action Potentials from Affecting Calcium Currents.

PubMed

Clarke, Stephen G; Scarnati, Matthew S; Paradiso, Kenneth G

2016-11-09

At chemical synapses, presynaptic action potentials (APs) activate voltage-gated calcium channels, allowing calcium to enter and trigger neurotransmitter release. The duration, peak amplitude, and shape of the AP falling phase alter calcium entry, which can affect neurotransmitter release significantly. In many neurons, APs do not immediately return to the resting potential, but instead exhibit a period of depolarization or hyperpolarization referred to as an afterpotential. We hypothesized that presynaptic afterpotentials should alter neurotransmitter release by affecting the electrical driving force for calcium entry and calcium channel gating. In support of this, presynaptic calcium entry is affected by afterpotentials after standard instant voltage jumps. Here, we used the mouse calyx of Held synapse, which allows simultaneous presynaptic and postsynaptic patch-clamp recording, to show that the postsynaptic response is affected significantly by presynaptic afterpotentials after voltage jumps. We therefore tested the effects of presynaptic afterpotentials using simultaneous presynaptic and postsynaptic recordings and AP waveforms or real APs. Surprisingly, presynaptic afterpotentials after AP stimuli did not alter calcium channel responses or neurotransmitter release appreciably. We show that the AP repolarization time course causes afterpotential-induced changes in calcium driving force and changes in calcium channel gating to effectively cancel each other out. This mechanism, in which electrical driving force is balanced by channel gating, prevents changes in calcium influx from occurring at the end of the AP and therefore acts to stabilize synaptic transmission. In addition, this mechanism can act to stabilize neurotransmitter release when the presynaptic resting potential changes. The shape of presynaptic action potentials (APs), particularly the falling phase, affects calcium entry and small changes in calcium influx can produce large changes in postsynaptic responses. We hypothesized that afterpotentials, which often follow APs, affect calcium entry and neurotransmitter release. We tested this in calyx of Held nerve terminals, which allow simultaneous recording of presynaptic calcium currents and postsynaptic responses. Surprisingly, presynaptic afterpotentials did not alter calcium current or neurotransmitter release. We show that the AP falling phase causes afterpotential-induced changes in electrical driving force and calcium channel gating to cancel each other out. This mechanism regulates calcium entry at the end of APs and therefore stabilizes synaptic transmission. This also stabilizes responses when the presynaptic resting potential changes. Copyright © 2016 the authors 0270-6474/16/3611559-14$15.00/0.

Identification of local myocardial repolarization time by bipolar electrode potential.

PubMed

Namba, Tsunetoyo; Todo, Takahiro; Yao, Takenori; Ashihara, Takashi; Haraguchi, Ryo; Nakazawa, Kazuo; Ikeda, Takanori; Ohe, Tohru

2007-01-01

The aim of this study was to investigate whether bipolar electrode potentials (BEPs) reflect local myocardial repolarization dynamics, using computer simulation. Simulated action potential and BEP mapping of myocardial tissue during fibrillation was performed. The BEP was modified to make all the fluctuations have the same polarity. Then, the modified BEP (mBEP) was transformed to "dynamic relative amplitude" (DRA) designed to make all the fluctuations have the similar amplitude. The repolarization end point corresponded to the end of the repolarization-related small fluctuation that clearly appeared in the DRA of mBEP. Using the DRA of mBEP, we could reproduce the repolarization dynamics in the myocardial tissue during fibrillation. The BEP may facilitate identifying the repolarization time. Furthermore, BEP mapping has the possibility that it would be available for evaluating repolarization behavior in myocardial tissue even during fibrillation. The accuracy of activation-recovery interval was also reconfirmed.

A mathematical model of action potential heterogeneity in adult rat left ventricular myocytes.

PubMed Central

Pandit, S V; Clark, R B; Giles, W R; Demir, S S

2001-01-01

Mathematical models were developed to reconstruct the action potentials (AP) recorded in epicardial and endocardial myocytes isolated from the adult rat left ventricle. The main goal was to obtain additional insight into the ionic mechanisms responsible for the transmural AP heterogeneity. The simulation results support the hypothesis that the smaller density and the slower reactivation kinetics of the Ca(2+)-independent transient outward K(+) current (I(t)) in the endocardial myocytes can account for the longer action potential duration (APD), and more prominent rate dependence in that cell type. The larger density of the Na(+) current (I(Na)) in the endocardial myocytes results in a faster upstroke (dV/dt(max)). This, in addition to the smaller magnitude of I(t), is responsible for the larger peak overshoot of the simulated endocardial AP. The prolonged APD in the endocardial cell also leads to an enhanced amplitude of the sustained K(+) current (I(ss)), and a larger influx of Ca(2+) ions via the L-type Ca(2+) current (I(CaL)). The latter results in an increased sarcoplasmic reticulum (SR) load, which is mainly responsible for the higher peak systolic value of the Ca(2+) transient [Ca(2+)](i), and the resultant increase in the Na(+)-Ca(2+) exchanger (I(NaCa)) activity, associated with the simulated endocardial AP. In combination, these calculations provide novel, quantitative insights into the repolarization process and its naturally occurring transmural variations in the rat left ventricle. PMID:11720973

A human ventricular cell model for investigation of cardiac arrhythmias under hyperkalaemic conditions.

PubMed

Carro, Jesús; Rodríguez, José Félix; Laguna, Pablo; Pueyo, Esther

2011-11-13

In this study, several modifications were introduced to a recently proposed human ventricular action potential (AP) model so as to render it suitable for the study of ventricular arrhythmias. These modifications were driven by new sets of experimental data available from the literature and the analysis of several well-established cellular arrhythmic risk biomarkers, namely AP duration at 90 per cent repolarization (APD(90)), AP triangulation, calcium dynamics, restitution properties, APD(90) adaptation to abrupt heart rate changes, and rate dependence of intracellular sodium and calcium concentrations. The proposed methodology represents a novel framework for the development of cardiac cell models. Five stimulation protocols were applied to the original model and the ventricular AP model developed here to compute the described arrhythmic risk biomarkers. In addition, those models were tested in a one-dimensional fibre in which hyperkalaemia was simulated by increasing the extracellular potassium concentration, [K(+)](o). The effective refractory period (ERP), conduction velocity (CV) and the occurrence of APD alternans were investigated. Results show that modifications improved model behaviour as verified by: (i) AP triangulation well within experimental limits (the difference between APD at 50 and 90 per cent repolarization being 78.1 ms); (ii) APD(90) rate adaptation dynamics characterized by fast and slow time constants within physiological ranges (10.1 and 105.9 s); and (iii) maximum S1S2 restitution slope in accordance with experimental data (S(S1S2)=1.0). In simulated tissues under hyperkalaemic conditions, APD(90) progressively shortened with the degree of hyperkalaemia, whereas ERP increased once a threshold in [K(+)](o) was reached ([K(+)](o)≈6 mM). CV decreased with [K(+)](o), and conduction was blocked for [K(+)](o)>10.4 mM. APD(90) alternans were observed for [K(+)](o)>9.8 mM. Those results adequately reproduce experimental observations. This study demonstrated the value of basing the development of AP models on the computation of arrhythmic risk biomarkers, as opposed to joining together independently derived ion channel descriptions to produce a whole-cell AP model, with the new framework providing a better picture of the model performance under a variety of stimulation conditions. On top of replicating experimental data at single-cell level, the model developed here was able to predict the occurrence of APD(90) alternans and areas of conduction block associated with high [K(+)](o) in tissue, which is of relevance for the investigation of the arrhythmogenic substrate in ischaemic hearts.

The Role of Transmural Repolarization Gradient in the Inversion of Cardiac Electric Field: Model Study of ECG in Hypothermia.

PubMed

Arteyeva, Natalia V; Azarov, Jan E

2017-01-01

The changes in ventricular repolarization gradients lead to significant alterations of the electrocardiographic body surface T waves up to the T wave inversion. However, the contribution of a specific gradient remains to be elucidated. The objective of the present investigation was to study the role of the transmural repolarization gradient in the inversion of the body surface T wave with a mathematical model of the hypothermia-induced changes of ventricular repolarization. By means of mathematical simulation, we set the hypothermic action potential duration (APD) distribution on the rabbit ventricular epicardium as it was previously experimentally documented. Then the parameters of the body surface potential distribution were tested with the introduction of different scenarios of the endocardial and epicardial APD behavior in hypothermia resulting in the unchanged, reversed or enlarged transmural repolarization gradient. The reversal of epicardial repolarization gradients (apicobasal, anterior-posterior and interventricular) caused the inversion of the T waves regardless of the direction of the transmural repolarization gradient. However, the most realistic body surface potentials were obtained when the endocardial APDs were not changed under hypothermia while the epicardial APDs prolonged. This produced the reversed and increased transmural repolarization gradient in absolute magnitude. The body surface potentials simulated under the unchanged transmural gradient were reduced in comparison to those simulated under the reversed transmural gradient. The simulations demonstrated that the transmural repolarization gradient did not play a crucial role in the cardiac electric field inversion under hypothermia, but its magnitude and direction contribute to the T wave amplitude. © 2016 Wiley Periodicals, Inc.

Electrophysiological properties of computational human ventricular cell action potential models under acute ischemic conditions.

PubMed

Dutta, Sara; Mincholé, Ana; Quinn, T Alexander; Rodriguez, Blanca

2017-10-01

Acute myocardial ischemia is one of the main causes of sudden cardiac death. The mechanisms have been investigated primarily in experimental and computational studies using different animal species, but human studies remain scarce. In this study, we assess the ability of four human ventricular action potential models (ten Tusscher and Panfilov, 2006; Grandi et al., 2010; Carro et al., 2011; O'Hara et al., 2011) to simulate key electrophysiological consequences of acute myocardial ischemia in single cell and tissue simulations. We specifically focus on evaluating the effect of extracellular potassium concentration and activation of the ATP-sensitive inward-rectifying potassium current on action potential duration, post-repolarization refractoriness, and conduction velocity, as the most critical factors in determining reentry vulnerability during ischemia. Our results show that the Grandi and O'Hara models required modifications to reproduce expected ischemic changes, specifically modifying the intracellular potassium concentration in the Grandi model and the sodium current in the O'Hara model. With these modifications, the four human ventricular cell AP models analyzed in this study reproduce the electrophysiological alterations in repolarization, refractoriness, and conduction velocity caused by acute myocardial ischemia. However, quantitative differences are observed between the models and overall, the ten Tusscher and modified O'Hara models show closest agreement to experimental data. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Period doubling cascades of limit cycles in cardiac action potential models as precursors to chaotic early Afterdepolarizations.

PubMed

Kügler, Philipp; Bulelzai, M A K; Erhardt, André H

2017-04-04

Early afterdepolarizations (EADs) are pathological voltage oscillations during the repolarization phase of cardiac action potentials (APs). EADs are caused by drugs, oxidative stress or ion channel disease, and they are considered as potential precursors to cardiac arrhythmias in recent attempts to redefine the cardiac drug safety paradigm. The irregular behaviour of EADs observed in experiments has been previously attributed to chaotic EAD dynamics under periodic pacing, made possible by a homoclinic bifurcation in the fast subsystem of the deterministic AP system of differential equations. In this article we demonstrate that a homoclinic bifurcation in the fast subsystem of the action potential model is neither a necessary nor a sufficient condition for the genesis of chaotic EADs. We rather argue that a cascade of period doubling (PD) bifurcations of limit cycles in the full AP system paves the way to chaotic EAD dynamics across a variety of models including a) periodically paced and spontaneously active cardiomyocytes, b) periodically paced and non-active cardiomyocytes as well as c) unpaced and spontaneously active cardiomyocytes. Furthermore, our bifurcation analysis reveals that chaotic EAD dynamics may coexist in a stable manner with fully regular AP dynamics, where only the initial conditions decide which type of dynamics is displayed. EADs are a potential source of cardiac arrhythmias and hence are of relevance both from the viewpoint of drug cardiotoxicity testing and the treatment of cardiomyopathies. The model-independent association of chaotic EADs with period doubling cascades of limit cycles introduced in this article opens novel opportunities to study chaotic EADs by means of bifurcation control theory and inverse bifurcation analysis. Furthermore, our results may shed new light on the synchronization and propagation of chaotic EADs in homogeneous and heterogeneous multicellular and cardiac tissue preparations.

Characterization of two distinct depolarization-activated K+ currents in isolated adult rat ventricular myocytes

PubMed Central

1991-01-01

Depolarization-activated outward K+ currents in isolated adult rat ventricular myocytes were characterized using the whole-cell variation of the patch-clamp recording technique. During brief depolarizations to potentials positive to -40 mV, Ca(2+)-independent outward K+ currents in these cells rise to a transient peak, followed by a slower decay to an apparent plateau. The analyses completed here reveal that the observed outward current waveforms result from the activation of two kinetically distinct voltage-dependent K+ currents: one that activates and inactivates rapidly, and one that activates and inactivates slowly, on membrane depolarization. These currents are referred to here as Ito (transient outward) and IK (delayed rectifier), respectively, because their properties are similar (although not identical) to these K+ current types in other cells. Although the voltage dependences of Ito and IK activation are similar, Ito activates approximately 10-fold and inactivates approximately 30-fold more rapidly than IK at all test potentials. In the composite current waveforms measured during brief depolarizations, therefore, the peak current predominantly reflects Ito, whereas IK is the primary determinant of the plateau. There are also marked differences in the voltage dependences of steady-state inactivation of these two K+ currents: IK undergoes steady-state inactivation at all potentials positive to -120 mV, and is 50% inactivated at -69 mV; Ito, in contrast, is insensitive to steady-state inactivation at membrane potentials negative to -50 mV. In addition, Ito recovers from steady-state inactivation faster than IK: at -90 mV, for example, approximately 70% recovery from the inactivation produced at -20 mV is observed within 20 ms for Ito; IK recovers approximately 25-fold more slowly. The pharmacological properties of Ito and IK are also distinct: 4-aminopyridine preferentially attenuates Ito, and tetraethylammonium suppresses predominantly IK. The voltage- and time- dependent properties of these currents are interpreted here in terms of a model in which Ito underlies the initial, rapid repolarization phase of the action potential (AP), and IK is responsible for the slower phase of AP repolarization back to the resting membrane potential, in adult rat ventricular myocytes. PMID:1865177

The effect of cardiac electric anisotropy on epicardial potential fields during ventricular repolarization.

PubMed

Spaggiari, S; Baruffi, S; Macchi, E; Traversa, M; Arisi, G; Taccardi, B

1986-11-01

We tried to establish whether some of the manifestations of electrical anisotropy previously observed on the canine ventricular epicardium during the spread of excitation were also present during repolarization, with the appropriate polarity. To this end we determined the potential distribution on the ventricular surface of exposed dog hearts during ventricular excitation and repolarization. The ventricles were paced by means of epicardial or intramural electrodes. During the early stages of ventricular excitation following epicardial pacing we observed typical, previously described potential patterns, with negative, elliptical equipotential lines surrounding the pacing site, and two maxima aligned along the direction of subepicardial fibers. Intramural pacing gave rise to similar patterns. The axis joining the maxima, however, was oriented along the direction of intramural fibers. The repolarization potential pattern relating to epicardial excitation exhibited some features similar to those observed during the spread of excitation, namely the presence of families of elliptical equipotential lines around the pacing site, with pairs of potential extrema along the major or minor axes of the ellipses or both. The location of the extrema and the distribution of the epicardial potential gradients during repolarization suggested the presence of anisotropic current generators mainly oriented along the direction of deep myocardial fibers, with some contribution from more superficial sources which were oriented along the direction of subepicardial fibers. Deep stimulation elicited more complicated epicardial patterns whose interpretation is still obscure. We conclude that the electrical anisotropy of the heart affects the distribution of repolarization potentials and probably the strength of electrical generators during ventricular repolarization.

Transmural ultrasound imaging of thermal lesion and action potential changes in perfused canine cardiac wedge preparations by high intensity focused ultrasound ablation.

PubMed

Wu, Ziqi; Gudur, Madhu S R; Deng, Cheri X

2013-01-01

Intra-procedural imaging is important for guiding cardiac arrhythmia ablation. It is difficult to obtain intra-procedural correlation of thermal lesion formation with action potential (AP) changes in the transmural plane during ablation. This study tested parametric ultrasound imaging for transmural imaging of lesion and AP changes in high intensity focused ultrasound (HIFU) ablation using coronary perfused canine ventricular wedge preparations (n = 13). The preparations were paced from epi/endocardial surfaces and subjected to HIFU application (3.5 MHz, 11 Hz pulse-repetition-frequency, 70% duty cycle, duration 4 s, 3500 W/cm(2)), during which simultaneous optical mapping (1 kframes/s) using di-4-ANEPPS and ultrasound imaging (30 MHz) of the same transmural surface of the wedge were performed. Spatiotemporally correlated AP measurements and ultrasound imaging allowed quantification of the reduction of AP amplitude (APA), shortening of AP duration at 50% repolarization, AP triangulation, decrease of optical AP rise, and change of conduction velocity along tissue depth direction within and surrounding HIFU lesions. The threshold of irreversible change in APA correlating to lesions was determined to be 43 ± 1% with a receiver operating characteristic (ROC) area under curve (AUC) of 0.96 ± 0.01 (n = 13). Ultrasound imaging parameters such as integrated backscatter, Rayleigh (α) and log-normal (σ) parameters, cumulative extrema of σ were tested, with the cumulative extrema of σ performing the best in detecting lesion (ROC AUC 0.89 ± 0.01, n = 13) and change of APA (ROC AUC 0.79 ± 0.03, n = 13). In conclusion, characteristic tissue and AP changes in HIFU ablation were identified and spatiotemporally correlated using optical mapping and ultrasound imaging. Parametric ultrasound imaging using cumulative extrema of σ can detect HIFU lesion and APA reduction.

Transmural Ultrasound Imaging of Thermal Lesion and Action Potential Changes in Perfused Canine Cardiac Wedge Preparations by High Intensity Focused Ultrasound Ablation

PubMed Central

Wu, Ziqi; Gudur, Madhu S. R.; Deng, Cheri X.

2013-01-01

Intra-procedural imaging is important for guiding cardiac arrhythmia ablation. It is difficult to obtain intra-procedural correlation of thermal lesion formation with action potential (AP) changes in the transmural plane during ablation. This study tested parametric ultrasound imaging for transmural imaging of lesion and AP changes in high intensity focused ultrasound (HIFU) ablation using coronary perfused canine ventricular wedge preparations (n = 13). The preparations were paced from epi/endocardial surfaces and subjected to HIFU application (3.5 MHz, 11 Hz pulse-repetition-frequency, 70% duty cycle, duration 4 s, 3500 W/cm2), during which simultaneous optical mapping (1 kframes/s) using di-4-ANEPPS and ultrasound imaging (30 MHz) of the same transmural surface of the wedge were performed. Spatiotemporally correlated AP measurements and ultrasound imaging allowed quantification of the reduction of AP amplitude (APA), shortening of AP duration at 50% repolarization, AP triangulation, decrease of optical AP rise, and change of conduction velocity along tissue depth direction within and surrounding HIFU lesions. The threshold of irreversible change in APA correlating to lesions was determined to be 43±1% with a receiver operating characteristic (ROC) area under curve (AUC) of 0.96±0.01 (n = 13). Ultrasound imaging parameters such as integrated backscatter, Rayleigh (α) and log-normal (σ) parameters, cumulative extrema of σ were tested, with the cumulative extrema of σ performing the best in detecting lesion (ROC AUC 0.89±0.01, n = 13) and change of APA (ROC AUC 0.79±0.03, n = 13). In conclusion, characteristic tissue and AP changes in HIFU ablation were identified and spatiotemporally correlated using optical mapping and ultrasound imaging. Parametric ultrasound imaging using cumulative extrema of σ can detect HIFU lesion and APA reduction. PMID:24349337

Late Na+ current and protracted electrical recovery are critical determinants of the aging myopathy

PubMed Central

Signore, Sergio; Sorrentino, Andrea; Borghetti, Giulia; Cannata, Antonio; Meo, Marianna; Zhou, Yu; Kannappan, Ramaswamy; Pasqualini, Francesco; O'Malley, Heather; Sundman, Mark; Tsigkas, Nikolaos; Zhang, Eric; Arranto, Christian; Mangiaracina, Chiara; Isobe, Kazuya; Sena, Brena F.; Kim, Junghyun; Goichberg, Polina; Nahrendorf, Matthias; Isom, Lori L.; Leri, Annarosa; Anversa, Piero; Rota, Marcello

2015-01-01

The aging myopathy manifests itself with diastolic dysfunction and preserved ejection fraction. We raised the possibility that, in a mouse model of physiological aging, defects in electromechanical properties of cardiomyocytes are important determinants of the diastolic characteristics of the myocardium, independently from changes in structural composition of the muscle and collagen framework. Here we show that an increase in the late Na+ current (INaL) in aging cardiomyocytes prolongs the action potential (AP) and influences temporal kinetics of Ca2+ cycling and contractility. These alterations increase force development and passive tension. Inhibition of INaL shortens the AP and corrects dynamics of Ca2+ transient, cell contraction and relaxation. Similarly, repolarization and diastolic tension of the senescent myocardium are partly restored. Thus, INaL offers inotropic support, but negatively interferes with cellular and ventricular compliance, providing a new perspective of the biology of myocardial aging and the aetiology of the defective cardiac performance in the elderly. PMID:26541940

Difference of acute dissociation and 1-day culture on the electrophysiological properties of rat dorsal root ganglion neurons.

PubMed

Song, Yuanlong; Zhang, Miaomiao; Tao, Xiaoqing; Xu, Zifen; Zheng, Yunjie; Zhu, Minjie; Zhang, Liangpin; Qiao, Jinhan; Gao, Linlin

2018-01-19

The dissociated dorsal root ganglion (DRG) neurons with or without culture were widely used for investigation of their electrophysiological properties. The culture procedures, however, may alter the properties of these neurons and the effects are not clear. In the present study, we recorded the action potentials (AP) and the voltage-gated Na + , K + , and Ca 2+ currents with patch clamp technique and measured the mRNA of Nav1.6-1.9 and Cav2.1-2.2 with real-time PCR technique from acutely dissociated and 1-day (1-d) cultured DRG neurons. The effects of the nerve growth factor (NGF) on the expression of Nav1.6-1.9 and Cav2.1-2.2 were evaluated. The neurons were classified as small (DRG-S), medium (DRG-M), and large (DRG-L), according to their size frequency distribution pattern. We found 1-d culture increased the AP size but reduced the excitability, and reduced the voltage-gated Na + and Ca 2+ currents and their corresponding mRNA expression in all types of neurons. The lack of NGF in the culture medium may contribute to the reduced Na + and Ca 2+ current, as the application of NGF recovered some of the reduced transcripts (Nav1.9, Cav2.1, and Cav2.2). 1-d culture showed neuron-type specific effects on some of the AP properties: it increased the maximum AP depolarizing rate (MDR) and hyperpolarized the resting membrane potential (RP) in DRG-M and DRG-L neurons, but slowed the maximum AP repolarizing rate (MRR) in DRG-S neurons. In conclusion, the 1-d cultured neurons had different properties with those of the acutely dissociated neurons, and lack of NGF may contribute to some of these differences.

The Impact of Ancestry and Common Genetic Variants on QT Interval in African Americans

PubMed Central

Smith, J. Gustav; Avery, Christy L.; Evans, Daniel S.; Nalls, Michael A.; Meng, Yan A.; Smith, Erin N.; Palmer, Cameron; Tanaka, Toshiko; Mehra, Reena; Butler, Anne M.; Young, Taylor; Buxbaum, Sarah G.; Kerr, Kathleen F.; Berenson, Gerald S.; Schnabel, Renate B.; Li, Guo; Ellinor, Patrick T.; Magnani, Jared W.; Chen, Wei; Bis, Joshua C.; Curb, J. David; Hsueh, Wen-Chi; Rotter, Jerome I.; Liu, Yongmei; Newman, Anne B.; Limacher, Marian C.; North, Kari E.; Reiner, Alexander P.; Quibrera, P. Miguel; Schork, Nicholas J.; Singleton, Andrew B.; Psaty, Bruce M.; Soliman, Elsayed Z.; Solomon, Allen J.; Srinivasan, Sathanur R.; Alonso, Alvaro; Wallace, Robert; Redline, Susan; Zhang, Zhu-Ming; Post, Wendy S.; Zonderman, Alan B.; Taylor, Herman A.; Murray, Sarah S.; Ferrucci, Luigi; Arking, Dan E.; Evans, Michele K.; Fox, Ervin R.; Sotoodehnia, Nona; Heckbert, Susan R.; Whitsel, Eric A.; Newton-Cheh, Christopher

2013-01-01

Background Ethnic differences in cardiac arrhythmia incidence have been reported, with a particularly high incidence of sudden cardiac death (SCD) and low incidence of atrial fibrillation in individuals of African ancestry. We tested the hypotheses that African ancestry and common genetic variants are associated with prolonged duration of cardiac repolarization, a central pathophysiological determinant of arrhythmia, as measured by the electrocardiographic QT interval. Methods and Results First, individual estimates of African and European ancestry were inferred from genome-wide single nucleotide polymorphism (SNP) data in seven population-based cohorts of African Americans (n=12 097) and regressed on measured QT interval from electrocardiograms. Second, imputation was performed for 2.8 million SNPs and a genome-wide association (GWA) study of QT interval performed in ten cohorts (n=13 105). There was no evidence of association between genetic ancestry and QT interval (p=0.94). Genome-wide significant associations (p<2.5×10−8) were identified with SNPs at two loci, upstream of the genes NOS1AP (rs12143842, p=2×10−15) and ATP1B1 (rs1320976, p=2×10−10). The most significant SNP in NOS1AP was the same as the strongest SNP previously associated with QT interval in individuals of European ancestry. Low p-values (p<10−5) were observed for SNPs at several other loci previously identified in GWA studies in individuals of European ancestry, including KCNQ1, KCNH2, LITAF and PLN. Conclusions We observed no difference in duration of cardiac repolarization with global genetic indices of African ancestry. In addition, our GWA study extends the association of polymorphisms at several loci associated with repolarization in individuals of European ancestry to include African Americans. PMID:23166209

Impact of ancestry and common genetic variants on QT interval in African Americans.

PubMed

Smith, J Gustav; Avery, Christy L; Evans, Daniel S; Nalls, Michael A; Meng, Yan A; Smith, Erin N; Palmer, Cameron; Tanaka, Toshiko; Mehra, Reena; Butler, Anne M; Young, Taylor; Buxbaum, Sarah G; Kerr, Kathleen F; Berenson, Gerald S; Schnabel, Renate B; Li, Guo; Ellinor, Patrick T; Magnani, Jared W; Chen, Wei; Bis, Joshua C; Curb, J David; Hsueh, Wen-Chi; Rotter, Jerome I; Liu, Yongmei; Newman, Anne B; Limacher, Marian C; North, Kari E; Reiner, Alexander P; Quibrera, P Miguel; Schork, Nicholas J; Singleton, Andrew B; Psaty, Bruce M; Soliman, Elsayed Z; Solomon, Allen J; Srinivasan, Sathanur R; Alonso, Alvaro; Wallace, Robert; Redline, Susan; Zhang, Zhu-Ming; Post, Wendy S; Zonderman, Alan B; Taylor, Herman A; Murray, Sarah S; Ferrucci, Luigi; Arking, Dan E; Evans, Michele K; Fox, Ervin R; Sotoodehnia, Nona; Heckbert, Susan R; Whitsel, Eric A; Newton-Cheh, Christopher

2012-12-01

Ethnic differences in cardiac arrhythmia incidence have been reported, with a particularly high incidence of sudden cardiac death and low incidence of atrial fibrillation in individuals of African ancestry. We tested the hypotheses that African ancestry and common genetic variants are associated with prolonged duration of cardiac repolarization, a central pathophysiological determinant of arrhythmia, as measured by the electrocardiographic QT interval. First, individual estimates of African and European ancestry were inferred from genome-wide single-nucleotide polymorphism (SNP) data in 7 population-based cohorts of African Americans (n=12,097) and regressed on measured QT interval from ECGs. Second, imputation was performed for 2.8 million SNPs, and a genome-wide association study of QT interval was performed in 10 cohorts (n=13,105). There was no evidence of association between genetic ancestry and QT interval (P=0.94). Genome-wide significant associations (P<2.5 × 10(-8)) were identified with SNPs at 2 loci, upstream of the genes NOS1AP (rs12143842, P=2 × 10(-15)) and ATP1B1 (rs1320976, P=2 × 10(-10)). The most significant SNP in NOS1AP was the same as the strongest SNP previously associated with QT interval in individuals of European ancestry. Low probability values (P<10(-5)) were observed for SNPs at several other loci previously identified in genome-wide association studies in individuals of European ancestry, including KCNQ1, KCNH2, LITAF, and PLN. We observed no difference in duration of cardiac repolarization with global genetic indices of African American ancestry. In addition, our genome-wide association study extends the association of polymorphisms at several loci associated with repolarization in individuals of European ancestry to include individuals of African ancestry.

Rate dependency of delayed rectifier currents during the guinea-pig ventricular action potential

PubMed Central

Rocchetti, Marcella; Besana, Alessandra; Gurrola, Georgina B; Possani, Lourival D; Zaza, Antonio

2001-01-01

The action potential clamp technique was exploited to evaluate the rate dependency of delayed rectifier currents (IKr and IKs) during physiological electrical activity. IKr and IKs were measured in guinea-pig ventricular myocytes at pacing cycle lengths (CL) of 1000 and 250 ms.A shorter CL, with the attendant changes in action potential shape, was associated with earlier activation and increased magnitude of both IKr and IKs. Nonetheless, the relative contributions of IKr and IKs to total transmembrane current were independent of CL.Shortening of diastolic interval only (constant action potential shape) enhanced IKs, but not IKr.IKr was increased by a change in the action potential shape only (constant diastolic interval).In ramp clamp experiments, IKr amplitude was directly proportional to repolarization rate at values within the low physiological range (< 1.0 V s−1); at higher repolarization rates proportionality became shallower and finally reversed.When action potential duration (APD) was modulated by constant current injection (I-clamp), repolarization rates > 1.0 V s−1 were associated with a reduced effect of IKr block on APD. The effect of changes in repolarization rate was independent of CL and occurred in the presence of IKs blockade.In spite of its complexity, the behaviour of IKr was accurately predicted by a numerical model based entirely on known kinetic properties of the current.Both IKr and IKs may be increased at fast heart rates, but this may occur through completely different mechanisms. The mechanisms identified are such as to contribute to abnormal rate dependency of repolarization in prolonged repolarization syndromes. PMID:11483703

Mechanism linking T-wave alternans to the genesis of cardiac fibrillation.

PubMed

Pastore, J M; Girouard, S D; Laurita, K R; Akar, F G; Rosenbaum, D S

1999-03-16

Although T-wave alternans has been closely associated with vulnerability to ventricular arrhythmias, the cellular processes underlying T-wave alternans and their role, if any, in the mechanism of reentry remain unclear. -T-wave alternans on the surface ECG was elicited in 8 Langendorff-perfused guinea pig hearts during fixed-rate pacing while action potentials were recorded simultaneously from 128 epicardial sites with voltage-sensitive dyes. Alternans of the repolarization phase of the action potential was observed above a critical threshold heart rate (HR) (209+/-46 bpm) that was significantly lower (by 57+/-36 bpm) than the HR threshold for alternation of action potential depolarization. The magnitude (range, 2.7 to 47.0 mV) and HR threshold (range, 171 to 272 bpm) of repolarization alternans varied substantially between cells across the epicardial surface. T-wave alternans on the surface ECG was explained primarily by beat-to-beat alternation in the time course of cellular repolarization. Above a critical HR, membrane repolarization alternated with the opposite phase between neighboring cells (ie, discordant alternans), creating large spatial gradients of repolarization. In the presence of discordant alternans, a small acceleration of pacing cycle length produced a characteristic sequence of events: (1) unidirectional block of an impulse propagating against steep gradients of repolarization, (2) reentrant propagation, and (3) the initiation of ventricular fibrillation. Repolarization alternans at the level of the single cell accounts for T-wave alternans on the surface ECG. Discordant alternans produces spatial gradients of repolarization of sufficient magnitude to cause unidirectional block and reentrant ventricular fibrillation. These data establish a mechanism linking T-wave alternans of the ECG to the pathogenesis of sudden cardiac death.

A reliability analysis of cardiac repolarization time markers.

PubMed

Scacchi, S; Franzone, P Colli; Pavarino, L F; Taccardi, B

2009-06-01

Only a limited number of studies have addressed the reliability of extracellular markers of cardiac repolarization time, such as the classical marker RT(eg) defined as the time of maximum upslope of the electrogram T wave. This work presents an extensive three-dimensional simulation study of cardiac repolarization time, extending the previous one-dimensional simulation study of a myocardial strand by Steinhaus [B.M. Steinhaus, Estimating cardiac transmembrane activation and recovery times from unipolar and bipolar extracellular electrograms: a simulation study, Circ. Res. 64 (3) (1989) 449]. The simulations are based on the bidomain - Luo-Rudy phase I system with rotational fiber anisotropy and homogeneous or heterogeneous transmural intrinsic membrane properties. The classical extracellular marker RT(eg) is compared with the gold standard of fastest repolarization time RT(tap), defined as the time of minimum derivative during the downstroke of the transmembrane action potential (TAP). Additionally, a new extracellular marker RT90(eg) is compared with the gold standard of late repolarization time RT90(tap), defined as the time when the TAP reaches 90% of its resting value. The results show a good global match between the extracellular and transmembrane repolarization markers, with small relative mean discrepancy (or=0.92), ensuring a reasonably good global match between the associated repolarization sequences. However, large local discrepancies of the extracellular versus transmembrane markers may ensue in regions where the curvature of the repolarization front changes abruptly (e.g. near front collisions) or is negligible (e.g. where repolarization proceeds almost uniformly across fiber). As a consequence, the spatial distribution of activation-recovery intervals (ARI) may provide an inaccurate estimate of (and weakly correlated with) the spatial distribution of action potential durations (APD).

Ranolazine improves abnormal repolarization and contraction in left ventricular myocytes of dogs with heart failure by inhibiting late sodium current

PubMed Central

Undrovinas, Albertas I.; Belardinelli, Luiz; Undrovinas, Nidas A.; Sabbah, Hani N.

2005-01-01

Background Ventricular repolarization and contractile function are frequently abnormal in ventricular myocytes from human failing hearts as well as canine hearts with experimentally induced heart failure (HF). These abnormalities have been attributed to dysfunction involving various steps of the excitation-contraction coupling process, leading to impaired intracellular sodium and calcium homeostasis. We previously reported that the slow inactivating component of the Na+ current (late INa) is augmented in myocytes from failing hearts, and this appears to play a significant role in abnormal ventricular myocytes repolarization and function. We tested the effect of ranolazine, a novel drug being developed to treat angina, on 1) action potential duration (APD), 2) peak transient and late INa (INaT and INaL respectively), 3) early afterdepolarizations (EADs), and 4) twitch contraction (TC) including aftercontractions and contracture. Methods: Myocytes were isolated from the left ventricle of normal dogs and of dogs with chronic HF caused by multiple sequential intracoronary microembolizations. INaT and INaL were recorded using conventional whole-cell patch-clamp techniques. APs were recorded using the β-escin perforated patch-clamp configuration at frequencies of 0.25 and 0.5 Hz. TCs were recorded using an edge movement detector at stimulation frequencies ranging from 0.5 to 2.0 Hz. Results Ranolazine significantly (p < 0.05) and reversibly shortened the APD of myocytes stimulated at either 0.5 or 0.25 Hz in a concentration-dependent manner. At a stimulation frequency of 0.5 Hz, 5, 10 and 20 μM ranolazine shortened the APD90 (APD measured at 90% repolarization) from 516 ± 51 to 304 ± 22, 212 ± 34 and 160 ± 11 ms, respectively, and markedly decreased beat-to-beat variability of APD90, EADs and dispersion of APDs. Ranolazine preferentially blocked INaL relative to INaT in a state-dependent manner; with a ~ 38-fold greater potency against INaL to produce tonic block (IC50 = 6.5 μ M) than INaT (IC50 =294 μM). When we evaluated inactivated state blockade of INaL from the steady-state inactivation mid-potential shift using a theoretical model, ranolazine was found to bind more tightly to the inactivated state than the resting state of the sodium channel underlying INaL, with apparent dissociation constants Kdr=7.47μ M and Kdi=1.71μ M, respectively. TCs of myocytes stimulated at 0.5 Hz were characterized by an initial spike followed by a dome-like aftercontraction, which was observed in75% of myocytes from failing hearts and coincided with the long AP plateau and EADs. Ranolazine at 5, and 10 μM reversibly shortened duration of TCs and abolished the aftercontraction. When the rate of myocyte stimulation was increased from 1.0 to 2.0 Hz, there was a progressive increase in diastolic “tension”, i.e., contracture. Ranolazine at 5, and 10 μM reversibly prevented this frequency-dependent contracture. PMID:16686675

Pharmacological modulations of cardiac ultra-rapid and slowly activating delayed rectifier currents: potential antiarrhythmic approaches.

PubMed

Islam, Mohammed A

2010-01-01

Despite the emerging new insights into our understandings of the cellular mechanisms underlying cardiac arrhythmia, medical therapy for this disease remains unsatisfactory. Atrial fibrillation (AF), the most prevalent arrhythmia, is responsible for significant morbidity and mortality. On the other hand, ventricular fibrillation results in sudden cardiac deaths in many instances. Prolongation of cardiac action potential (AP) is a proven principle of antiarrhythmic therapy. Class III antiarrhythmic agents prolong AP and QT interval by blocking rapidly activating delayed rectifier current (I(Kr)). However, I(Kr) blocking drugs carry the risk of life-threatening proarrhythmia. Recently, modulation of atrial-selective ultra-rapid delayed rectifier current (I(Kur)), has emerged as a novel therapeutic approach to treat AF. A number of I(Kur) blockers are being evaluated for the treatment of AF. The inhibition of slowly activating delayed rectifier current (I(Ks)) has also been proposed as an effective and safer antiarrhythmic approach because of its distinguishing characteristics that differ in remarkable ways from other selective class III agents. Selective I(Ks) block may prolong AP duration (APD) at rapid rates without leading to proarrhythmia. This article reviews the pathophysiological roles of I(Kur) and I(Ks) in cardiac repolarization and the implications of newly developed I(Kur) and I(Ks) blocking agents as promising antiarrhythmic approaches. Several recent patents pertinent to antiarrhythmic drug development have been discussed. Further research will be required to evaluate the efficacy and safety of these agents in the clinical setting.

Human ex-vivo action potential model for pro-arrhythmia risk assessment.

PubMed

Page, Guy; Ratchada, Phachareeya; Miron, Yannick; Steiner, Guido; Ghetti, Andre; Miller, Paul E; Reynolds, Jack A; Wang, Ken; Greiter-Wilke, Andrea; Polonchuk, Liudmila; Traebert, Martin; Gintant, Gary A; Abi-Gerges, Najah

2016-01-01

While current S7B/E14 guidelines have succeeded in protecting patients from QT-prolonging drugs, the absence of a predictive paradigm identifying pro-arrhythmic risks has limited the development of valuable drug programs. We investigated if a human ex-vivo action potential (AP)-based model could provide a more predictive approach for assessing pro-arrhythmic risk in man. Human ventricular trabeculae from ethically consented organ donors were used to evaluate the effects of dofetilide, d,l-sotalol, quinidine, paracetamol and verapamil on AP duration (APD) and recognized pro-arrhythmia predictors (short-term variability of APD at 90% repolarization (STV(APD90)), triangulation (ADP90-APD30) and incidence of early afterdepolarizations at 1 and 2Hz to quantitatively identify the pro-arrhythmic risk. Each drug was blinded and tested separately with 3 concentrations in triplicate trabeculae from 5 hearts, with one vehicle time control per heart. Electrophysiological stability of the model was not affected by sequential applications of vehicle (0.1% dimethyl sulfoxide). Paracetamol and verapamil did not significantly alter anyone of the AP parameters and were classified as devoid of pro-arrhythmic risk. Dofetilide, d,l-sotalol and quinidine exhibited an increase in the manifestation of pro-arrhythmia markers. The model provided quantitative and actionable activity flags and the relatively low total variability in tissue response allowed for the identification of pro-arrhythmic signals. Power analysis indicated that a total of 6 trabeculae derived from 2 hearts are sufficient to identify drug-induced pro-arrhythmia. Thus, the human ex-vivo AP-based model provides an integrative translational assay assisting in shaping clinical development plans that could be used in conjunction with the new CiPA-proposed approach. Copyright © 2016 Elsevier Inc. All rights reserved.

Human ex-vivo action potential model for pro-arrhythmia risk assessment

PubMed Central

Page, Guy; Ratchada, Phachareeya; Miron, Yannick; Steiner, Guido; Ghetti, Andre; Miller, Paul E; Reynolds, Jack A; Wang, Ken; Greiter-Wilke, Andrea; Polonchuk, Liudmila; Traebert, Martin; Gintant, Gary A; Abi-Gerges, Najah

2016-01-01

While current S7B/E14 guidelines have succeeded in protecting patients from QT-prolonging drugs, the absence of a predictive paradigm identifying pro-arrhythmic risks has limited the development of valuable drug programs. We investigated if a human ex-vivo action potential (AP)-based model could provide a more predictive approach for assessing pro-arrhythmic risk in man. Human ventricular trabeculae from ethically consented organ donors were used to evaluate the effects of dofetilide, d,l-sotalol, quinidine, paracetamol and verapamil on AP duration (APD) and recognized pro-arrhythmia predictors (short-term variability of APD at 90% repolarization (STV(APD90)), triangulation (ADP90-APD30) and incidence of early afterdepolarizations at 1 and 2 Hz to quantitatively identify the pro-arrhythmic risk. Each drug was blinded and tested separately with 3 concentrations in triplicate trabeculae from 5 hearts, with one vehicle time control per heart. Electrophysiological stability of the model was not affected by sequential applications of vehicle (0.1% dimethyl sulfoxide). Paracetamol and verapamil did not significantly alter anyone of the AP parameters and were classified as devoid of pro-arrhythmic risk. Dofetilide, d,l-sotalol and quinidine exhibited an increase in the manifestation of pro-arrhythmia markers. The model provided quantitative and actionable activity flags and the relatively low total variability in tissue response allowed for the identification of pro-arrhythmic signals. Power analysis indicated that a total of 6 trabeculae derived from 2 hearts are sufficient to identify drug-induced pro-arrhythmia. Thus, the human ex-vivo AP-based model provides an integrative translational assay assisting in shaping clinical development plans that could be used in conjunction with the new CiPA-proposed approach. PMID:27235787

A Parsimonious Model of the Rabbit Action Potential Elucidates the Minimal Physiological Requirements for Alternans and Spiral Wave Breakup

PubMed Central

2016-01-01

Elucidating the underlying mechanisms of fatal cardiac arrhythmias requires a tight integration of electrophysiological experiments, models, and theory. Existing models of transmembrane action potential (AP) are complex (resulting in over parameterization) and varied (leading to dissimilar predictions). Thus, simpler models are needed to elucidate the “minimal physiological requirements” to reproduce significant observable phenomena using as few parameters as possible. Moreover, models have been derived from experimental studies from a variety of species under a range of environmental conditions (for example, all existing rabbit AP models incorporate a formulation of the rapid sodium current, INa, based on 30 year old data from chick embryo cell aggregates). Here we develop a simple “parsimonious” rabbit AP model that is mathematically identifiable (i.e., not over parameterized) by combining a novel Hodgkin-Huxley formulation of INa with a phenomenological model of repolarization similar to the voltage dependent, time-independent rectifying outward potassium current (IK). The model was calibrated using the following experimental data sets measured from the same species (rabbit) under physiological conditions: dynamic current-voltage (I-V) relationships during the AP upstroke; rapid recovery of AP excitability during the relative refractory period; and steady-state INa inactivation via voltage clamp. Simulations reproduced several important “emergent” phenomena including cellular alternans at rates > 250 bpm as observed in rabbit myocytes, reentrant spiral waves as observed on the surface of the rabbit heart, and spiral wave breakup. Model variants were studied which elucidated the minimal requirements for alternans and spiral wave break up, namely the kinetics of INa inactivation and the non-linear rectification of IK.The simplicity of the model, and the fact that its parameters have physiological meaning, make it ideal for engendering generalizable mechanistic insight and should provide a solid “building-block” to generate more detailed ionic models to represent complex rabbit electrophysiology. PMID:27749895

A Parsimonious Model of the Rabbit Action Potential Elucidates the Minimal Physiological Requirements for Alternans and Spiral Wave Breakup.

PubMed

Gray, Richard A; Pathmanathan, Pras

2016-10-01

Elucidating the underlying mechanisms of fatal cardiac arrhythmias requires a tight integration of electrophysiological experiments, models, and theory. Existing models of transmembrane action potential (AP) are complex (resulting in over parameterization) and varied (leading to dissimilar predictions). Thus, simpler models are needed to elucidate the "minimal physiological requirements" to reproduce significant observable phenomena using as few parameters as possible. Moreover, models have been derived from experimental studies from a variety of species under a range of environmental conditions (for example, all existing rabbit AP models incorporate a formulation of the rapid sodium current, INa, based on 30 year old data from chick embryo cell aggregates). Here we develop a simple "parsimonious" rabbit AP model that is mathematically identifiable (i.e., not over parameterized) by combining a novel Hodgkin-Huxley formulation of INa with a phenomenological model of repolarization similar to the voltage dependent, time-independent rectifying outward potassium current (IK). The model was calibrated using the following experimental data sets measured from the same species (rabbit) under physiological conditions: dynamic current-voltage (I-V) relationships during the AP upstroke; rapid recovery of AP excitability during the relative refractory period; and steady-state INa inactivation via voltage clamp. Simulations reproduced several important "emergent" phenomena including cellular alternans at rates > 250 bpm as observed in rabbit myocytes, reentrant spiral waves as observed on the surface of the rabbit heart, and spiral wave breakup. Model variants were studied which elucidated the minimal requirements for alternans and spiral wave break up, namely the kinetics of INa inactivation and the non-linear rectification of IK.The simplicity of the model, and the fact that its parameters have physiological meaning, make it ideal for engendering generalizable mechanistic insight and should provide a solid "building-block" to generate more detailed ionic models to represent complex rabbit electrophysiology.

Seasonal acclimatization of the cardiac potassium currents (IK1 and IKr) in an arctic marine teleost, the navaga cod (Eleginus navaga).

PubMed

Abramochkin, Denis V; Vornanen, Matti

2015-12-01

Several freshwater fishes of north-temperate latitudes exhibit marked seasonal changes in cardiac action potential (AP) waveform as an outcome of temperature-dependent changes in the density of delayed rectifiers (IKr, IKs) and inward rectifier (IK1) potassium currents. Thus far, ionic mechanisms of cardiac excitability in arctic marine fishes have not been examined. To this end we examined ventricular AP and the role of two major potassium currents (IK1, IKr) in repolarization of cardiac AP in winter-acclimatized (WA, caught in March) and summer-acclimatized (SA, caught in September) navaga cod (Eleginus navaga) of the White Sea. The duration of ventricular AP of WA navaga at 3 °C (APD50 = 659.5 ± 32.8 ms) was similar to the AP duration of SA navaga at 12 °C (APD50 = 543.9 ± 14.6 ms) (p > 0.05) indicating complete thermal compensation of AP duration. This acclimation effect was associated with strong up-regulation of the cardiac potassium currents in winter. Densities of ventricular IK1 (at -120 mV) and IKr (at +50 mV) of the WA navaga at 3 °C were 2.9 times and 2.8 times, respectively, higher than those of the SA navaga at 12 °C, thus indicating marked thermal overcompensation. Qualitatively similar results were obtained from atrial myocytes. Seasonal changes in IK1 and IKr are more than sufficient to explain the complete thermal compensation of ventricular AP duration. The excellent acclimation capacity of cardiac excitability of the navaga cod is probably needed to maintain high cardiac performance at subzero temperatures in winter and to increase thermal resilience of cardiac function under seasonally variable arctic temperature conditions.

In silico assessment of drug safety in human heart applied to late sodium current blockers

PubMed Central

Trenor, Beatriz; Gomis-Tena, Julio; Cardona, Karen; Romero, Lucia; Rajamani, Sridharan; Belardinelli, Luiz; Giles, Wayne R; Saiz, Javier

2013-01-01

Drug-induced action potential (AP) prolongation leading to Torsade de Pointes is a major concern for the development of anti-arrhythmic drugs. Nevertheless the development of improved anti-arrhythmic agents, some of which may block different channels, remains an important opportunity. Partial block of the late sodium current (INaL) has emerged as a novel anti-arrhythmic mechanism. It can be effective in the settings of free radical challenge or hypoxia. In addition, this approach can attenuate pro-arrhythmic effects of blocking the rapid delayed rectifying K+ current (IKr). The main goal of our computational work was to develop an in-silico tool for preclinical anti-arrhythmic drug safety assessment, by illustrating the impact of IKr/INaL ratio of steady-state block of drug candidates on “torsadogenic” biomarkers. The O’Hara et al. AP model for human ventricular myocytes was used. Biomarkers for arrhythmic risk, i.e., AP duration, triangulation, reverse rate-dependence, transmural dispersion of repolarization and electrocardiogram QT intervals, were calculated using single myocyte and one-dimensional strand simulations. Predetermined amounts of block of INaL and IKr were evaluated. “Safety plots” were developed to illustrate the value of the specific biomarker for selected combinations of IC50s for IKr and INaL of potential drugs. The reference biomarkers at baseline changed depending on the “drug” specificity for these two ion channel targets. Ranolazine and GS967 (a novel potent inhibitor of INaL) yielded a biomarker data set that is considered safe by standard regulatory criteria. This novel in-silico approach is useful for evaluating pro-arrhythmic potential of drugs and drug candidates in the human ventricle. PMID:23696033

Properties and ionic mechanisms of action potential adaptation, restitution, and accommodation in canine epicardium.

PubMed

Decker, Keith F; Heijman, Jordi; Silva, Jonathan R; Hund, Thomas J; Rudy, Yoram

2009-04-01

Computational models of cardiac myocytes are important tools for understanding ionic mechanisms of arrhythmia. This work presents a new model of the canine epicardial myocyte that reproduces a wide range of experimentally observed rate-dependent behaviors in cardiac cell and tissue, including action potential (AP) duration (APD) adaptation, restitution, and accommodation. Model behavior depends on updated formulations for the 4-aminopyridine-sensitive transient outward current (I(to1)), the slow component of the delayed rectifier K(+) current (I(Ks)), the L-type Ca(2+) channel current (I(Ca,L)), and the Na(+)-K(+) pump current (I(NaK)) fit to data from canine ventricular myocytes. We found that I(to1) plays a limited role in potentiating peak I(Ca,L) and sarcoplasmic reticulum Ca(2+) release for propagated APs but modulates the time course of APD restitution. I(Ks) plays an important role in APD shortening at short diastolic intervals, despite a limited role in AP repolarization at longer cycle lengths. In addition, we found that I(Ca,L) plays a critical role in APD accommodation and rate dependence of APD restitution. Ca(2+) entry via I(Ca,L) at fast rate drives increased Na(+)-Ca(2+) exchanger Ca(2+) extrusion and Na(+) entry, which in turn increases Na(+) extrusion via outward I(NaK). APD accommodation results from this increased outward I(NaK). Our simulation results provide valuable insight into the mechanistic basis of rate-dependent phenomena important for determining the heart's response to rapid and irregular pacing rates (e.g., arrhythmia). Accurate simulation of rate-dependent phenomena and increased understanding of their mechanistic basis will lead to more realistic multicellular simulations of arrhythmia and identification of molecular therapeutic targets.

Bradycardia alters Ca2+ dynamics enhancing dispersion of repolarization and arrhythmia risk

PubMed Central

Kim, Jong J.; Němec, Jan; Papp, Rita; Strongin, Robert; Abramson, Jonathan J.

2013-01-01

Bradycardia prolongs action potential (AP) durations (APD adaptation), enhances dispersion of repolarization (DOR), and promotes tachyarrhythmias. Yet, the mechanisms responsible for enhanced DOR and tachyarrhythmias remain largely unexplored. Ca2+ transients and APs were measured optically from Langendorff rabbit hearts at high (150 × 150 μm2) or low (1.5 × 1.5 cm2) magnification while pacing at a physiological (120 beats/min) or a slow heart rate (SHR = 50 beats/min). Western blots and pharmacological interventions were used to elucidate the regional effects of bradycardia. As a result, bradycardia (SHR 50 beats/min) increased APDs gradually (time constant τf→s = 48 ± 9.2 s) and caused a secondary Ca2+ release (SCR) from the sarcoplasmic reticulum during AP plateaus, occurring at the base on average of 184.4 ± 9.7 ms after the Ca2+ transient upstroke. In subcellular imaging, SCRs were temporally synchronous and spatially homogeneous within myocytes. In diastole, SHR elicited variable asynchronous sarcoplasmic reticulum Ca2+ release events leading to subcellular Ca2+ waves, detectable only at high magnification. SCR was regionally heterogeneous, correlated with APD prolongation (P < 0.01, n = 5), enhanced DOR (r = 0.9277 ± 0.03, n = 7), and was gradually reversed by pacing at 120 beats/min along with APD shortening (P < 0.05, n = 5). A stabilizer of leaky ryanodine receptors (RyR2), 3-(4-benzylcyclohexyl)-1-(7-methoxy-2,3-dihydrobenzo[f][1,4]thiazepin-4(5H)-yl)propan-1-one (K201; 1 μM), suppressed SCR and reduced APD at the base, thereby reducing DOR (P < 0.02, n = 5). Ventricular ectopy induced by bradycardia (n = 5/15) was suppressed by K201. Western blot analysis revealed spatial differences of voltage-gated L-type Ca2+ channel protein (Cav1.2α), Na+-Ca2+ exchange (NCX1), voltage-gated Na+ channel (Nav1.5), and rabbit ether-a-go-go-related (rERG) protein [but not RyR2 or sarcoplasmic reticulum Ca2+ ATPase 2a] that correlate with the SCR distribution and explain the molecular basis for SCR heterogeneities. In conclusion, acute bradycardia elicits synchronized subcellular SCRs of sufficient magnitude to overcome the source-sink mismatch and to promote afterdepolarizations. PMID:23316064

NS5806 partially restores action potential duration but fails to ameliorate calcium transient dysfunction in a computational model of canine heart failure.

PubMed

Maleckar, Mary M; Lines, Glenn T; Koivumäki, Jussi T; Cordeiro, Jonathan M; Calloe, Kirstine

2014-11-01

The study investigates how increased Ito, as mediated by the activator NS5806, affects excitation-contraction coupling in chronic heart failure (HF). We hypothesized that restoring spike-and-dome morphology of the action potential (AP) to a healthy phenotype would be insufficient to restore the intracellular Ca(2) (+) transient (CaT), due to HF-induced remodelling of Ca(2+) handling. An existing mathematical model of the canine ventricular myocyte was modified to incorporate recent experimental data from healthy and failing myocytes, resulting in models of both healthy and HF epicardial, midmyocardial, and endocardial cell variants. Affects of NS5806 were also included in HF models through its direct interaction with Kv4.3 and Kv1.4. Single-cell simulations performed in all models (control, HF, and HF + drug) and variants (epi, mid, and endo) assessed AP morphology and underlying ionic processes with a focus on calcium transients (CaT), how these were altered in HF across the ventricular wall, and the subsequent effects of varying compound concentration in HF. Heart failure model variants recapitulated a characteristic increase in AP duration (APD) in the disease. The qualitative effects of application of half-maximal effective concentration (EC50) of NS5806 on APs and CaT are heterogeneous and non-linear. Deepening in the AP notch with drug is a direct effect of the activation of Ito; both Ito and consequent alteration of IK1 kinetics cause decrease in AP plateau potential. Decreased APD50 and APD90 are both due to altered IK1. Analysis revealed that drug effects depend on transmurality. Ca(2+) transient morphology changes-increased amplitude and shorter time to peak-are due to direct increase in ICa,L and indirect larger SR Ca(2+) release subsequent to Ito activation. Downstream effects of a compound acting exclusively on sarcolemmal ion channels are difficult to predict. Remediation of APD to pre-failing state does not ameliorate dysfunction in CaT; however, restoration of notch depth appears to impart modest benefit and a likelihood of therapeutic value in modulating early repolarization. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.

Impact of Hypokalemia on Electromechanical Window, Excitation Wavelength and Repolarization Gradients in Guinea-Pig and Rabbit Hearts

PubMed Central

Osadchii, Oleg E.

2014-01-01

Normal hearts exhibit a positive time difference between the end of ventricular contraction and the end of QT interval, which is referred to as the electromechanical (EM) window. Drug-induced prolongation of repolarization may lead to the negative EM window, which was proposed to be a novel proarrhythmic marker. This study examined whether abnormal changes in the EM window may account for arrhythmogenic effects produced by hypokalemia. Left ventricular pressure, electrocardiogram, and epicardial monophasic action potentials were recorded in perfused hearts from guinea-pig and rabbit. Hypokalemia (2.5 mM K+) was found to prolong repolarization, reduce the EM window, and promote tachyarrhythmia. Nevertheless, during both regular pacing and extrasystolic excitation, the increased QT interval invariably remained shorter than the duration of mechanical systole, thus yielding positive EM window values. Hypokalemia-induced arrhythmogenicity was associated with slowed ventricular conduction, and shortened effective refractory periods, which translated to a reduced excitation wavelength index. Hypokalemia also evoked non-uniform prolongation of action potential duration in distinct epicardial regions, which resulted in increased spatial variability in the repolarization time. These findings suggest that arrhythmogenic effects of hypokalemia are not accounted for by the negative EM window, and are rather attributed to abnormal changes in ventricular conduction times, refractoriness, excitation wavelength, and spatial repolarization gradients. PMID:25141124

Delayed onset of changes in soma action potential genesis in nociceptive A-beta DRG neurons in vivo in a rat model of osteoarthritis

PubMed Central

Wu, Qi; Henry, James L

2009-01-01

Background Clinical data on osteoarthritis (OA) suggest widespread changes in sensory function that vary during the progression of OA. In previous studies on a surgically-induced animal model of OA we have observed that changes in structure and gene expression follow a variable trajectory over the initial days and weeks. To investigate mechanisms underlying changes in sensory function in this model, the present electrophysiological study compared properties of primary sensory nociceptive neurons at one and two months after model induction with properties in naïve control animals. Pilot data indicated no difference in C- or Aδ-fiber associated neurons and therefore the focus is on Aβ-fiber nociceptive neurons. Results At one month after unilateral derangement of the knee by cutting the anterior cruciate ligament and removing the medial meniscus, the only changes observed in Aβ-fiber dorsal root ganglion (DRG) neurons were in nociceptor-like unresponsive neurons bearing a hump on the repolarization phase; these changes consisted of longer half width, reflecting slowed dynamics of AP genesis, a depolarized Vm and an increased AP amplitude. At two months, changes observed were in Aβ-fiber high threshold mechanoreceptors, which exhibited shorter AP duration at base and half width, shorter rise time and fall time, and faster maximum rising rate/maximum falling rate, reflecting accelerated dynamics of AP genesis. Conclusion These data indicate that Aβ nociceptive neurons undergo significant changes that vary in time and occur later than changes in structure and in nociceptive scores in this surgically induced OA model. Thus, if changes in Aβ-fiber nociceptive neurons in this model reflect a role in OA pain, they may relate to mechanisms underlying pain associated with advanced OA. PMID:19785765

Systematic characterization of the ionic basis of rabbit cellular electrophysiology using two ventricular models.

PubMed

Romero, Lucía; Carbonell, Beatriz; Trenor, Beatriz; Rodríguez, Blanca; Saiz, Javier; Ferrero, José M

2011-10-01

Several mathematical models of rabbit ventricular action potential (AP) have been proposed to investigate mechanisms of arrhythmias and excitation-contraction coupling. Our study aims at systematically characterizing how ionic current properties modulate the main cellular biomarkers of arrhythmic risk using two widely-used rabbit ventricular models, and comparing simulation results using the two models with experimental data available for rabbit. A sensitivity analysis of AP properties, Ca²⁺ and Na⁺ dynamics, and their rate dependence to variations (±15% and ±30%) in the main transmembrane current conductances and kinetics was performed using the Shannon et al. (2004) and the Mahajan et al. (2008a,b) AP rabbit models. The effects of severe transmembrane current blocks (up to 100%) on steady-state AP and calcium transients, and AP duration (APD) restitution curves were also simulated using both models. Our simulations show that, in both virtual rabbit cardiomyocytes, APD is significantly modified by most repolarization currents, AP triangulation is regulated mostly by the inward rectifier K⁺ current (I(K1)) whereas APD rate adaptation as well as [Na⁺](i) rate dependence is influenced by the Na⁺/K⁺ pump current (I(NaK)). In addition, steady-state [Ca²⁺](i) levels, APD restitution properties and [Ca²⁺](i) rate dependence are strongly dependent on I(NaK), the L-Type Ca²⁺ current (I(CaL)) and the Na⁺/Ca²⁺ exchanger current (I(NaCa)), although the relative role of these currents is markedly model dependent. Furthermore, our results show that simulations using both models agree with many experimentally-reported electrophysiological characteristics. However, our study shows that the Shannon et al. model mimics rabbit electrophysiology more accurately at normal pacing rates, whereas Mahajan et al. model behaves more appropriately at faster rates. Our results reinforce the usefulness of sensitivity analysis for further understanding of cellular electrophysiology and validation of cardiac AP models. Copyright © 2011 Elsevier Ltd. All rights reserved.

Constitutional rho-kinase regulates atrioventricular nodal conduction and ventricular repolarization of the canine heart.

PubMed

Sugiyama, Atsushi; Takahara, Akira; Yatomi, Yutaka; Satoh, Yoshioki; Nakamura, Yuji; Hashimoto, Keitaro

2003-06-01

Given the limited information, physiological roles of Rho-kinase in the cardiac conduction system and ventricular repolarization process were assessed in comparison with those in the coronary vascular tone. A specific Rho-kinase inhibitor Y-27632 was administered to the nutrient coronary artery of the canine isolated, blood-perfused atrioventricular node preparation under the monitoring of the ventricular monophasic action potentials. Administration of Y-27632 moderately suppressed the atrioventricular nodal conduction, slightly but significantly accelerated the repolarization process, and potently increased the coronary blood flow, whereas it hardly affected the intraventricular conduction. The estimated concentrations of Y-27632 causing the currently observed effects were enough to inhibit Rho-kinase. These results suggest that constitutional Rho-kinase functions to moderately facilitate the atrioventricular nodal conduction, slightly delay ventricular repolarization process, and significantly increase the coronary vascular tone.

A simultaneous multichannel monophasic action potential electrode array for in vivo epicardial repolarization mapping.

PubMed

Sahakian, A V; Peterson, M S; Shkurovich, S; Hamer, M; Votapka, T; Ji, T; Swiryn, S

2001-03-01

While the recording of extracellular monophasic action potentials (MAPs) from single epicardial or endocardial sites has been performed for over a century, we are unaware of any previous successful attempt to record MAPs simultaneously from a large number of sites in vivo. We report here the design and validation of an array of MAP electrodes which records both depolarization and repolarization simultaneously at up to 16 epicardial sites in a square array on the heart in vivo. The array consists of 16 sintered Ag-AgCl electrodes mounted in a common housing with individual suspensions allowing each electrode to exert a controlled pressure on the epicardial surface. The electrodes are arranged in a square array, with each quadrant of four having an additional recessed sintered Ag-AgCl reference electrode at its center. A saline-soaked sponge establishes ionic contact between the reference electrodes and the tissue. The array was tested on six anesthetized open-chested pigs. Simultaneous diagnostic-quality MAP recordings were obtained from up to 13 out of 16 ventricular sites. Ventricular MAPs had amplitudes of 10-40 mV with uniform morphologies and stable baselines for up to 30 min. MAP duration at 90% repolarization was measured and shown to vary as expected with cycle length during sustained pacing. The relationship between MAP duration and effective refractory period was also confirmed. The ability of the array to detect local differences in repolarization was tested in two ways. Placement of the array straddling the atrioventricular (AV) junction yielded simultaneous atrial or ventricular recordings at corresponding sites during 1:1 and 2:1 AV conduction. Localized ischemia via constriction of a coronary artery branch resulted in shortening of the repolarization phase at the ischemic, but not the nonischemic, sites. In conclusion, these results indicate that the simultaneous multichannel MAP electrode array is a viable method for in vivo epicardial repolarization mapping. The array has the potential to be expanded to increase the number of sites and spatial resolution.

Quantitative analysis of the Ca2+ -dependent regulation of delayed rectifier K+ current IKs in rabbit ventricular myocytes.

PubMed

Bartos, Daniel C; Morotti, Stefano; Ginsburg, Kenneth S; Grandi, Eleonora; Bers, Donald M

2017-04-01

[Ca 2+ ] i enhanced rabbit ventricular slowly activating delayed rectifier K + current (I Ks ) by negatively shifting the voltage dependence of activation and slowing deactivation, similar to perfusion of isoproterenol. Rabbit ventricular rapidly activating delayed rectifier K + current (I Kr ) amplitude and voltage dependence were unaffected by high [Ca 2+ ] i . When measuring or simulating I Ks during an action potential, I Ks was not different during a physiological Ca 2+ transient or when [Ca 2+ ] i was buffered to 500 nm. The slowly activating delayed rectifier K + current (I Ks ) contributes to repolarization of the cardiac action potential (AP). Intracellular Ca 2+ ([Ca 2+ ] i ) and β-adrenergic receptor (β-AR) stimulation modulate I Ks amplitude and kinetics, but details of these important I Ks regulators and their interaction are limited. We assessed the [Ca 2+ ] i dependence of I Ks in steady-state conditions and with dynamically changing membrane potential and [Ca 2+ ] i during an AP. I Ks was recorded from freshly isolated rabbit ventricular myocytes using whole-cell patch clamp. With intracellular pipette solutions that controlled free [Ca 2+ ] i , we found that raising [Ca 2+ ] i from 100 to 600 nm produced similar increases in I Ks as did β-AR activation, and the effects appeared additive. Both β-AR activation and high [Ca 2+ ] i increased maximally activated tail I Ks , negatively shifted the voltage dependence of activation, and slowed deactivation kinetics. These data informed changes in our well-established mathematical model of the rabbit myocyte. In both AP-clamp experiments and simulations, I Ks recorded during a normal physiological Ca 2+ transient was similar to I Ks measured with [Ca 2+ ] i clamped at 500-600 nm. Thus, our study provides novel quantitative data as to how physiological [Ca 2+ ] i regulates I Ks amplitude and kinetics during the normal rabbit AP. Our results suggest that micromolar [Ca 2+ ] i , in the submembrane or junctional cleft space, is not required to maximize [Ca 2+ ] i -dependent I Ks activation during normal Ca 2+ transients. © 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.

Cytosolic increased labile Zn2+ contributes to arrhythmogenic action potentials in left ventricular cardiomyocytes through protein thiol oxidation and cellular ATP depletion.

PubMed

Degirmenci, Sinan; Olgar, Yusuf; Durak, Aysegul; Tuncay, Erkan; Turan, Belma

2018-07-01

Intracellular labile (free) Zn 2+ -level ([Zn 2+ ] i ) is low and increases markedly under pathophysiological conditions in cardiomyocytes. High [Zn 2+ ] i is associated with alterations in excitability and ionic-conductances while exact mechanisms are not clarified yet. Therefore, we examined the elevated-[Zn 2+ ] i on some sarcolemmal ionic-mechanisms, which can mediate cardiomyocyte dysfunction. High-[Zn 2+ ] i induced significant changes in action potential (AP) parameters, including depolarization in resting membrane-potential and prolongations in AP-repolarizing phases. We detected also the time-dependent effects such as induction of spontaneous APs at the time of ≥ 3 min following [Zn 2+ ] i increases, a manner of cellular ATP dependent and reversible with disulfide-reducing agent dithiothreitol, DTT. High-[Zn 2+ ] i induced inhibitions in voltage-dependent K + -channel currents, such as transient outward K + -currents, I to , steady-state currents, I ss and inward-rectifier K + -currents, I K1 , reversible with DTT seemed to be responsible from the prolongations in APs. We, for the first time, demonstrated that lowering cellular ATP level induced significant decreaeses in both I ss and I K1 , while no effect on I to . However, the increased-[Zn 2+ ] i could induce marked activation in ATP-sensitive K + -channel currents, I KATP , depending on low cellular ATP and thiol-oxidation levels of these channels. The mRNA levels of Kv4.3, Kv1.4 and Kv2.1 were depressed markedly with increased-[Zn 2+ ] i with no change in mRNA level of Kv4.2, while the mRNA level of I KATP subunit, SUR2A was increased significantly with increased-[Zn 2+ ] i , being reversible with DTT. Overall we demonstrated that high-[Zn 2+ ] i, even if nanomolar levels, alters cardiac function via prolonged APs of cardiomyocytes, at most, due to inhibitions in voltage-dependent K + -currents, although activation of I KATP is playing cardioprotective role, through some biochemical changes in cellular ATP- and thiol-oxidation levels. It seems, a well-controlled [Zn 2+ ] i can be novel therapeutic target for cardiac complications under pathological conditions including oxidative stress. Copyright © 2018 Elsevier GmbH. All rights reserved.

Flecainide-induced proarrhythmia is attributed to abnormal changes in repolarization and refractoriness in perfused guinea-pig heart.

PubMed

Osadchii, Oleg E

2012-11-01

Flecainide is nonselective Na(+) channel blocker which may also inhibit I(Kr), the rapid component of the delayed rectifier. This study was designed to explore if proarrhythmic responses to flecainide noted in cardiac patients may be partly attributed to abnormal changes in repolarization and refractoriness. Monophasic action potential duration (APD) and effective refractory periods (ERP) were assessed at distinct epicardial and endocardial sites along with volume-conducted ECG recordings in isolated perfused guinea-pig heart preparations. Flecainide was found to prolong ventricular repolarization, with effect being greater at the left ventricular compared with the right ventricular epicardium. This change translated to reversal of the normal right ventricular-to-left ventricular transepicardial APD difference determined before drug infusion. An inverse correlation between local epicardial APD and corresponding activation time values seen at baseline was eliminated in flecainide-treated hearts, indicating the activation-to-repolarization uncoupling. Over transmural plane, flecainide produced a greater ERP lengthening at endocardium than epicardium, thus markedly increasing ERP dispersion across ventricular wall. Spontaneous short-lasting episodes of monomorphic ventricular tachycardia were observed in 45% of heart preparations upon flecainide infusion. In conclusion, in nonischemic guinea-pig heart, flecainide-induced proarrhythmia may be partly attributed to abnormal spatial gradients in repolarization and refractoriness and impaired transepicardial activation-to-repolarization coupling.

Selective activation of heteromeric SK channels contributes to action potential repolarization in mouse atrial myocytes.

PubMed

Hancock, Jane M; Weatherall, Kate L; Choisy, Stéphanie C; James, Andrew F; Hancox, Jules C; Marrion, Neil V

2015-05-01

Activation of small conductance calcium-activated potassium (SK) channels is proposed to contribute to repolarization of the action potential in atrial myocytes. This role is controversial, as these cardiac SK channels appear to exhibit an uncharacteristic pharmacology. The objectives of this study were to resolve whether activation of SK channels contributes to atrial action potential repolarization and to determine the likely subunit composition of the channel. The effect of 2 SK channel inhibitors was assessed on outward current evoked in voltage clamp and on action potential duration in perforated patch and whole-cell current clamp recording from acutely isolated mouse atrial myocytes. The presence of SK channel subunits was assessed using immunocytochemistry. A significant component of outward current was reduced by the SK channel blockers apamin and UCL1684. Block by apamin displayed a sensitivity indicating that this current was carried by homomeric SK2 channels. Action potential duration was significantly prolonged by UCL1684, but not by apamin. This effect was accompanied by an increase in beat-to-beat variability and action potential triangulation. This pharmacology was matched by that of expressed heteromeric SK2-SK3 channels in HEK293 cells. Immunocytochemistry showed that atrial myocytes express both SK2 and SK3 channels with an overlapping expression pattern. Only proposed heteromeric SK2-SK3 channels are physiologically activated to contribute to action potential repolarization, which is indicated by the difference in pharmacology of evoked outward current and prolongation of atrial action potential duration. The effect of blocking this channel on the action potential suggests that SK channel inhibition during cardiac function has the potential to be proarrhythmic. Copyright © 2015 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

Layer 5 Callosal Parvalbumin-Expressing Neurons: A Distinct Functional Group of GABAergic Neurons

PubMed Central

Zurita, Hector; Feyen, Paul L. C.; Apicella, Alfonso Junior

2018-01-01

Previous studies have shown that parvalbumin-expressing neurons (CC-Parv neurons) connect the two hemispheres of motor and sensory areas via the corpus callosum, and are a functional part of the cortical circuit. Here we test the hypothesis that layer 5 CC-Parv neurons possess anatomical and molecular mechanisms which dampen excitability and modulate the gating of interhemispheric inhibition. In order to investigate this hypothesis we use viral tracing to determine the anatomical and electrophysiological properties of layer 5 CC-Parv and parvalbumin-expressing (Parv) neurons of the mouse auditory cortex (AC). Here we show that layer 5 CC-Parv neurons had larger dendritic fields characterized by longer dendrites that branched farther from the soma, whereas layer 5 Parv neurons had smaller dendritic fields characterized by shorter dendrites that branched nearer to the soma. The layer 5 CC-Parv neurons are characterized by delayed action potential (AP) responses to threshold currents, lower firing rates, and lower instantaneous frequencies compared to the layer 5 Parv neurons. Kv1.1 containing K+ channels are the main source of the AP repolarization of the layer 5 CC-Parv and have a major role in determining both the spike delayed response, firing rate and instantaneous frequency of these neurons. PMID:29559891

Layer 5 Callosal Parvalbumin-Expressing Neurons: A Distinct Functional Group of GABAergic Neurons.

PubMed

Zurita, Hector; Feyen, Paul L C; Apicella, Alfonso Junior

2018-01-01

Previous studies have shown that parvalbumin-expressing neurons (CC-Parv neurons) connect the two hemispheres of motor and sensory areas via the corpus callosum, and are a functional part of the cortical circuit. Here we test the hypothesis that layer 5 CC-Parv neurons possess anatomical and molecular mechanisms which dampen excitability and modulate the gating of interhemispheric inhibition. In order to investigate this hypothesis we use viral tracing to determine the anatomical and electrophysiological properties of layer 5 CC-Parv and parvalbumin-expressing (Parv) neurons of the mouse auditory cortex (AC). Here we show that layer 5 CC-Parv neurons had larger dendritic fields characterized by longer dendrites that branched farther from the soma, whereas layer 5 Parv neurons had smaller dendritic fields characterized by shorter dendrites that branched nearer to the soma. The layer 5 CC-Parv neurons are characterized by delayed action potential (AP) responses to threshold currents, lower firing rates, and lower instantaneous frequencies compared to the layer 5 Parv neurons. Kv1.1 containing K + channels are the main source of the AP repolarization of the layer 5 CC-Parv and have a major role in determining both the spike delayed response, firing rate and instantaneous frequency of these neurons.

Dofetilide promotes repolarization abnormalities in perfused Guinea-pig heart.

PubMed

Osadchii, Oleg E

2012-12-01

Dofetilide is class III antiarrhythmic agent which prolongs cardiac action potential duration because of selective inhibition of I (Kr), the rapid component of the delayed rectifier K(+) current. Although clinical studies reported on proarrhythmic risk associated with dofetilide treatment, the contributing electrophysiological mechanisms remain poorly understood. This study was designed to determine if dofetilide-induced proarrhythmia may be attributed to abnormalities in ventricular repolarization and refractoriness. The monophasic action potential duration and effective refractory periods (ERP) were assessed at distinct epicardial and endocardial sites along with volume-conducted ECG recordings in isolated, perfused guinea-pig heart preparations. Dofetilide was found to produce the reverse rate-dependent prolongation of ventricular repolarization, increased the steepness of action potential duration rate adaptation, and amplified transepicardial variability in electrical restitution kinetics. Dofetilide also prolonged the T peak-to-end interval on ECG, and elicited a greater prolongation of endocardial than epicardial ERP, thereby increasing transmural dispersion of refractoriness. At epicardium, dofetilide prolonged action potential duration to a greater extent than ERP, thus extending the critical interval for ventricular re-excitation. This change was associated with triangulation of epicardial action potential because of greater dofetilide-induced prolonging effect at 90 % than 30 % repolarization. Premature ectopic beats and spontaneous short-lasting episodes of monomorphic ventricular tachycardia were observed in 44 % of dofetilide-treated heart preparations. Proarrhythmic potential of dofetilide in guinea-pig heart is attributed to steepened electrical restitution, increased transepicardial variability in electrical restitution kinetics, amplified transmural dispersion of refractoriness, increased critical interval for ventricular re-excitation, and triangulation of epicardial action potential.

Genetic engineering of somatic cells to study and improve cardiac function.

PubMed

Kirkton, Robert D; Bursac, Nenad

2012-11-01

To demonstrate the utility of genetically engineered excitable cells for studies of basic electrophysiology and cardiac cell therapy. 'Zig-zag' networks of neonatal rat ventricular myocytes (NRVMs) were micropatterned onto thin elastomeric films to mimic the slow action potential (AP) conduction found in fibrotic myocardium. Addition of genetically engineered excitable human embryonic kidney cells (HEK-293 cells) ('Ex-293' cells stably expressing Kir2.1, Na(v)1.5, and Cx43 channels) increased both cardiac conduction velocity by 370% and twitch force amplitude by 64%. Furthermore, we stably expressed mutant Na(v)1.5 [A1924T (fast sodium channel mutant (substitution of alanine by threonine at amino acid 1924)] channels with hyperpolarized steady-state activation and showed that, despite a 71.6% reduction in peak I(Na), these cells propagated APs at the same velocity as the wild-type Na(v)1.5-expressing Ex-293 cells. Stable expression of Ca(v)3.3 (T-type voltage-gated calcium) channels in Ex-293 cells (to generate an 'ExCa-293' line) significantly increased their AP duration and reduced repolarization gradients in cocultures of these cells and NRVMs. Additional expression of an optogenetic construct [ChIEF (light-gated Channelrhodopsin mutant)]enabled light-based control of AP firing in ExCa-293 cells. We show that, despite being non-contractile, genetically engineered excitable cells can significantly improve both electrical and mechanical function of engineered cardiac tissues in vitro. We further demonstrate the utility of engineered cells for tissue-level studies of basic electrophysiology and cardiac channelopathies. In the future, this novel platform could be utilized in the high-throughput design of new genetically encoded indicators of cell electrical function, validation, and improvement of computer models of AP conduction, and development of novel engineered somatic cell therapies for the treatment of cardiac infarction and arrhythmias.

Early afterdepolarizations promote transmural reentry in ischemic human ventricles with reduced repolarization reserve

PubMed Central

Dutta, Sara; Mincholé, Ana; Zacur, Ernesto; Quinn, T. Alexander; Taggart, Peter; Rodriguez, Blanca

2016-01-01

Aims Acute ischemia is a major cause of sudden arrhythmic death, further promoted by potassium current blockers. Macro-reentry around the ischemic region and early afterdepolarizations (EADs) caused by electrotonic current have been suggested as potential mechanisms in animal and isolated cell studies. However, ventricular and human-specific arrhythmia mechanisms and their modulation by repolarization reserve remain unclear. The goal of this paper is to unravel multiscale mechanisms underlying the modulation of arrhythmic risk by potassium current (IKr) block in human ventricles with acute regional ischemia. Methods and results A human ventricular biophysically-detailed model, with acute regional ischemia is constructed by integrating experimental knowledge on the electrophysiological ionic alterations caused by coronary occlusion. Arrhythmic risk is evaluated by determining the vulnerable window (VW) for reentry following ectopy at the ischemic border zone. Macro-reentry around the ischemic region is the main reentrant mechanism in the ischemic human ventricle with increased repolarization reserve due to the ATP-sensitive potassium current (IK(ATP)) activation. Prolongation of refractoriness by 4% caused by 30% IKr reduction counteracts the establishment of macro-reentry and reduces the VW for reentry (by 23.5%). However, a further decrease in repolarization reserve (50% IKr reduction) is less anti-arrhythmic despite further prolongation of refractoriness. This is due to the establishment of transmural reentry enabled by electrotonically-triggered EADs in the ischemic border zone. EADs are produced by L-type calcium current (ICaL) reactivation due to prolonged low amplitude electrotonic current injected during the repolarization phase. Conclusions Electrotonically-triggered EADs are identified as a potential mechanism facilitating intramural reentry in a regionally-ischemic human ventricles model with reduced repolarization reserve. PMID:26850675

Knockout of the BK β2 subunit abolishes inactivation of BK currents in mouse adrenal chromaffin cells and results in slow-wave burst activity

PubMed Central

Martinez-Espinosa, Pedro L.; Yang, Chengtao; Gonzalez-Perez, Vivian; Xia, Xiao-Ming

2014-01-01

Rat and mouse adrenal medullary chromaffin cells (CCs) express an inactivating BK current. This inactivation is thought to arise from the assembly of up to four β2 auxiliary subunits (encoded by the kcnmb2 gene) with a tetramer of pore-forming Slo1 α subunits. Although the physiological consequences of inactivation remain unclear, differences in depolarization-evoked firing among CCs have been proposed to arise from the ability of β2 subunits to shift the range of BK channel activation. To investigate the role of BK channels containing β2 subunits, we generated mice in which the gene encoding β2 was deleted (β2 knockout [KO]). Comparison of proteins from wild-type (WT) and β2 KO mice allowed unambiguous demonstration of the presence of β2 subunit in various tissues and its coassembly with the Slo1 α subunit. We compared current properties and cell firing properties of WT and β2 KO CCs in slices and found that β2 KO abolished inactivation, slowed action potential (AP) repolarization, and, during constant current injection, decreased AP firing. These results support the idea that the β2-mediated shift of the BK channel activation range affects repetitive firing and AP properties. Unexpectedly, CCs from β2 KO mice show an increased tendency toward spontaneous burst firing, suggesting that the particular properties of BK channels in the absence of β2 subunits may predispose to burst firing. PMID:25267913

Kinetics of atrial repolarization alternans in a free-behaving ovine model.

PubMed

Jousset, Florian; Tenkorang, Joanna; Vesin, Jean-Marc; Pascale, Patrizio; Ruchat, Patrick; Rollin, Anne Garderes; Fromer, Martin; Narayan, Sanjiv M; Pruvot, Etienne

2012-09-01

Kinetics of Atrial Repolarization Alternans. Repolarization alternans (Re-ALT), a beat-to-beat alternation in action potential repolarization, promotes dispersion of repolarization, wavebreaks, and reentry. Recently, Re-ALT has been shown to play an important role in the transition from rapid pacing to atrial fibrillation (AF) in humans. The detailed kinetics of atrial Re-ALT, however, has not been reported so far. We developed a chronic free-behaving ovine pacing model to study the kinetics of atrial Re-ALT as a function of pacing rate. Thirteen sheep were chronically implanted with 2 pacemakers for the recording of broadband right atrial unipolar electrograms and delivery of rapid pacing protocols. Beat-to-beat differences in the atrial T-wave apex amplitude as a measure of Re-ALT and activation time were analyzed at incremental pacing rates until the effective refractory period (ERP) defined as stable 2:1 capture. Atrial Re-ALT appeared intermittently but without periodicity, and increased in amplitude as a function of pacing rate until ERP. Intermittent 2:1 atrial capture was observed at pacing cycle lengths 40 ms above ERP, and increased in duration as a function of pacing rate. Episodes of rapid pacing-induced AF were rare, and were preceded by Re-ALT or complex oscillations of atrial repolarization, but without intermittent capture. We show in vivo that atrial Re-ALT developed and increased in magnitude with rate until stable 2:1 capture. In rare instances where capture failure did not occur, Re-ALT and complex oscillations of repolarization surged and preceded AF initiation. (J Cardiovasc Electrophysiol, Vol. 23, pp. 1003-1012, September 2012). © 2012 Wiley Periodicals, Inc.

Prolonged intra-myocardial growth hormone administration ameliorates post-infarction electrophysiologic remodeling in rats.

PubMed

Kontonika, Marianthi; Barka, Eleonora; Roumpi, Maria; La Rocca, Vassilios; Lekkas, Panagiotis; Daskalopoulos, Evangelos P; Vilaeti, Agapi D; Baltogiannis, Giannis G; Vlahos, Antonios P; Agathopoulos, Simeon; Kolettis, Theofilos M

2017-02-01

Experimental studies indicate improved ventricular function after treatment with growth hormone (GH) post-myocardial infarction, but its effect on arrhythmogenesis is unknown. Here, we assessed the medium-term electrophysiologic remodeling after intra-myocardial GH administration in (n = 33) rats. GH was released from an alginate scaffold, injected around the ischemic myocardium after coronary ligation. Two weeks thereafter, ventricular tachyarrhythmias were induced by programmed electrical stimulation. Monophasic action potentials were recorded from the infarct border, coupled with evaluation of electrical conduction and repolarization from a multi-electrode array. The arrhythmia score was lower in GH-treated rats than in alginate-treated rats or controls. The shape and the duration of the action potential at the infarct border were preserved, and repolarization-dispersion was attenuated after GH; moreover, voltage rise was higher and activation delay was shorter. GH normalized also right ventricular parameters. Intra-myocardial GH preserved electrical conduction and repolarization-dispersion at the infarct border and decreased the incidence of induced tachyarrhythmias in rats post-ligation. The long-term antiarrhythmic potential of GH merits further study.

Mechanistic Basis for Type 2 Long QT Syndrome Caused by KCNH2 Mutations that Disrupt Conserved Arginine Residue in the Voltage Sensor

PubMed Central

McBride, Christie M.; Smith, Ashley M.; Smith, Jennifer L.; Reloj, Allison R.; Velasco, Ellyn J.; Powell, Jonathan; Elayi, Claude S.; Bartos, Daniel C.; Burgess, Don E.

2013-01-01

KCNH2 encodes the Kv11.1 channel, which conducts the rapidly activating delayed rectifier K+ current (IKr) in the heart. KCNH2 mutations cause type 2 long QT syndrome (LQT2), which increases the risk for life-threatening ventricular arrhythmias. LQT2 mutations are predicted to prolong the cardiac action potential (AP) by reducing IKr during repolarization. Kv11.1 contains several conserved basic amino acids in the fourth transmembrane segment (S4) of the voltage sensor that are important for normal channel trafficking and gating. This study sought to determine the mechanism(s) by which LQT2 mutations at conserved arginine residues in S4 (R531Q, R531W or R534L) alter Kv11.1 function. Western blot analyses of HEK293 cells transiently expressing R531Q, R531W or R534L suggested that only R534L inhibited Kv11.1 trafficking. Voltage-clamping experiments showed that R531Q or R531W dramatically altered Kv11.1 current (IKv11.1) activation, inactivation, recovery from inactivation and deactivation. Coexpression of wild type (to mimic the patients’ genotypes) mostly corrected the changes in IKv11.1 activation and inactivation, but deactivation kinetics were still faster. Computational simulations using a human ventricular AP model showed that accelerating deactivation rates was sufficient to prolong the AP, but these effects were minimal compared to simply reducing IKr. These are the first data to demonstrate that coexpressing wild type can correct activation and inactivation dysfunction caused by mutations at a critical voltage-sensing residue in Kv11.1. We conclude that some Kv11.1 mutations might accelerate deactivation to cause LQT2 but that the ventricular AP duration is much more sensitive to mutations that decrease IKr. This likely explains why most LQT2 mutations are nonsense or trafficking-deficient. PMID:23546015

Mechanistic basis for type 2 long QT syndrome caused by KCNH2 mutations that disrupt conserved arginine residues in the voltage sensor.

PubMed

McBride, Christie M; Smith, Ashley M; Smith, Jennifer L; Reloj, Allison R; Velasco, Ellyn J; Powell, Jonathan; Elayi, Claude S; Bartos, Daniel C; Burgess, Don E; Delisle, Brian P

2013-05-01

KCNH2 encodes the Kv11.1 channel, which conducts the rapidly activating delayed rectifier K+ current (I Kr) in the heart. KCNH2 mutations cause type 2 long QT syndrome (LQT2), which increases the risk for life-threatening ventricular arrhythmias. LQT2 mutations are predicted to prolong the cardiac action potential (AP) by reducing I Kr during repolarization. Kv11.1 contains several conserved basic amino acids in the fourth transmembrane segment (S4) of the voltage sensor that are important for normal channel trafficking and gating. This study sought to determine the mechanism(s) by which LQT2 mutations at conserved arginine residues in S4 (R531Q, R531W or R534L) alter Kv11.1 function. Western blot analyses of HEK293 cells transiently expressing R531Q, R531W or R534L suggested that only R534L inhibited Kv11.1 trafficking. Voltage-clamping experiments showed that R531Q or R531W dramatically altered Kv11.1 current (I Kv11.1) activation, inactivation, recovery from inactivation and deactivation. Coexpression of wild type (to mimic the patients' genotypes) mostly corrected the changes in I Kv11.1 activation and inactivation, but deactivation kinetics were still faster. Computational simulations using a human ventricular AP model showed that accelerating deactivation rates was sufficient to prolong the AP, but these effects were minimal compared to simply reducing I Kr. These are the first data to demonstrate that coexpressing wild type can correct activation and inactivation dysfunction caused by mutations at a critical voltage-sensing residue in Kv11.1. We conclude that some Kv11.1 mutations might accelerate deactivation to cause LQT2 but that the ventricular AP duration is much more sensitive to mutations that decrease I Kr. This likely explains why most LQT2 mutations are nonsense or trafficking-deficient.

A KCNQ1 Mutation Causes a High Penetrance for Familial Atrial Fibrillation

PubMed Central

Bartos, Daniel C.; Anderson, Jeffrey B.; Bastiaenen, Rachel; Johnson, Jonathan N.; Gollob, Michael H; Tester, David J.; Burgess, Don E.; Homfray, Tessa; Behr, Elijah R.; Ackerman, Michael J.; Guicheney, Pascale; Delisle, Brian P.

2012-01-01

Background Atrial fibrillation (AF) is the most common cardiac arrhythmia, and its incidence is expected to grow. A genetic predisposition for AF has long been recognized, but its manifestation in these patients likely involves a combination of rare and common genetic variants. Identifying genetic variants that associate with a high penetrance for AF would represent a significant breakthrough for understanding the mechanisms that associate with disease. Method and Results Candidate gene sequencing in five unrelated families with familial AF identified the KCNQ1 missense mutation p.Arg231His (R231H). In addition to AF, several of the family members have abnormal QTc intervals, syncope, or experienced sudden cardiac arrest or death. KCNQ1 encodes the voltage-gated K+ channel that conducts the slowly activating delayed rectifier K+ current in the heart. Functional and computational analyses suggested that R231H increases KCNQ1 current (IKCNQ1) to shorten the atrial action potential (AP) duration. R231H is predicted to minimally affect ventricular excitability, but it prevented the increase in IKCNQ1 following PKA activation. The unique properties of R231H appeared to be caused by a loss in voltage-dependent gating. Conclusions The R231H variant causes a high penetrance for interfamilial early-onset AF. Our study indicates R231H likely shortens atrial refractoriness to promote a substrate for reentry. Additionally, R231H might cause abnormal ventricular repolarization by disrupting PKA activation of IKCNQ1. We conclude genetic variants, which increase IKs during the atrial AP, decrease the atrial AP duration, and/or shorten atrial refractoriness, present a high risk for interfamilial AF. PMID:23350853

Regulatory mechanisms and the role of calcium and potassium channels controlling supercontractile crop muscles in adult Phormia regina.

PubMed

Solari, Paolo; Stoffolano, John G; Fitzpatrick, Joanna; Gelperin, Alan; Thomson, Alan; Talani, Giuseppe; Sanna, Enrico; Liscia, Anna

2013-09-01

Bioassays and electrophysiological recordings were conducted in the adult blowfly Phormia regina to provide new insights into the regulatory mechanisms governing the crop filling and emptying processes of the supercontractile crop muscles. The cibarial pump drives ingestion. Simultaneous multisite extracellular recordings show that crop lobe (P5) distension during ingestion of a 4.7 μl sugar meal does not require muscle activity by any of the other pumps of the system. Conversely, pumping of fluids toward the anterior of the crop system during crop emptying is brought about by active muscle contraction, in the form of a highly coordinated peristaltic wave starting from P5 and progressively propagating to P6, P4 and P3 pumps, with P5 contracting with a frequency about 3.4 times higher than the other pumps. The crop contraction rate is also modulated by hemolymph-borne factors such as sugars, through ligand recognition at a presumptive receptor site rather than by an osmotic effect, as assessed by both behavioural and electrophysiological experiments. In this respect, sugars of equal osmolarity produce different effects, glucose being inhibitory and mannose ineffective for crop muscles, while trehalose enhances crop activity. Finally, voltage and current clamp experiments show that the muscle action potentials (mAPs) at the P4 pump are sustained by a serotonin-sensitive calcium conductance. Serotonin enhances calcium entry into the muscle cells and this could lead, as an indirect modulatory effect, to activation of a Ca(2+)-activated K(+) conductance (IK(Ca)), which sustains the following mAP repolarization phase in such a way that further mAPs can be generated early and the frequency consequently increased. Copyright © 2013 Elsevier Ltd. All rights reserved.

How the knowledge of genetic "makeup" and cellular data can affect the analysis of repolarization in surface electrocardiogram.

PubMed

Shimizu, Wataru

2010-01-01

This review article sought to describe patterns of repolarization on the surface electrocardiogram in inherited cardiac arrhythmias and to discuss how the knowledge of genetic makeup and cellular data can affect the analysis based on the data derived from the experimental studies using arterially perfused canine ventricular wedge preparations. Molecular genetic studies have established a link between a number of inherited cardiac arrhythmia syndromes and mutations in genes encoding cardiac ion channels or membrane components during the past 2 decades. Twelve forms of congenital long QT syndrome have been so far identified, and genotype-phenotype correlations have been investigated especially in the 3 major genotypes-LQT1, LQT2, and LQT3. Abnormal T waves are reported in the LQT1, LQT2, and LQT3, and the differences in the time course of repolarization of the epicardial, midmyocardial, and endocardial cells give rise to voltage gradients responsible for the manifestation of phenotypic appearance of abnormal T waves. Brugada syndrome is characterized by ST-segment elevation in leads V1 to V3 and an episode of ventricular fibrillation, in which 7 genotypes have been reported. An intrinsically prominent transient outward current (I(to))-mediated action potential notch and a subsequent loss of action potential dome in the epicardium, but not in the endocardium of the right ventricular outflow tract, give rise to a transmural voltage gradient, resulting in ST-segment elevation, and a subsequent phase 2 reentry-induced ventricular fibrillation. In conclusion, transmural electrical heterogeneity of repolarization across the ventricular wall profoundly affects the phenotypic manifestation of repolarization patterns on the surface electrocardiogram in inherited cardiac arrhythmias. Copyright © 2010 Elsevier Inc. All rights reserved.

Evaluation of nefazodone-induced cardiotoxicity in human induced pluripotent stem cell-derived cardiomyocytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sujeong, E-mail: crystalee@gmail.com; Lee, Hyang-Ae, E-mail: hyangaelee@gmail.com; Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, 110-799

2016-04-01

The recent establishment of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), which express the major cardiac ion channels and recapitulate spontaneous mechanical and electrical activities, may provide a possible solution for the lack of in vitro human-based cardiotoxicity testing models. Cardiotoxicity induced by the antidepressant nefazodone was previously revealed to cause an acquired QT prolongation by hERG channel blockade. To elucidate the cellular mechanisms underlying the cardiotoxicity of nefazodone beyond hERG, its effects on cardiac action potentials (APs) and ion channels were investigated using hiPSC-CMs with whole-cell patch clamp techniques. In a proof of principle study, we examined the effectsmore » of cardioactive channel blockers on the electrophysiological profile of hiPSC-CMs in advance of the evaluation of nefazodone. Nefazodone dose-dependently prolonged the AP duration at 90% (APD{sub 90}) and 50% (APD{sub 50}) repolarization, reduced the maximum upstroke velocity (dV/dt{sub max}) and induced early after depolarizations. Voltage-clamp studies of hiPSC-CMs revealed that nefazodone inhibited various voltage-gated ion channel currents including I{sub Kr}, I{sub Ks}, I{sub Na}, and I{sub Ca}. Among them, I{sub Kr} and I{sub Na} showed relatively higher sensitivity to nefazodone, consistent with the changes in the AP parameters. In summary, hiPSC-CMs enabled an integrated approach to evaluate the complex interactions of nefazodone with cardiac ion channels. These results suggest that hiPSC-CMs can be an effective model for detecting drug-induced arrhythmogenicity beyond the current standard assay of heterologously expressed hERG K{sup +} channels. - Highlights: • Nefazodone prolonged APD and decreased upstroke velocity of APs in hiPSC-CMs. • Nefazodone inhibited cardiac ion channels, especially I{sub Kr} and I{sub Na}, in hiPSC-CMs. • Nefazodone-induced AP changes are mainly the result of I{sub Kr} and I{sub Na} inhibition. • hiPSC-CMs are sensitive model to validate nefazodone-induced cardiotoxicity. • hiPSC-CMs provide an integrated approach for evaluating mechanism of drug actions.« less

Cellular mechanism underlying hypothermia-induced ventricular tachycardia/ventricular fibrillation in the setting of early repolarization and the protective effect of quinidine, cilostazol, and milrinone.

PubMed

Gurabi, Zsolt; Koncz, István; Patocskai, Bence; Nesterenko, Vladislav V; Antzelevitch, Charles

2014-02-01

Hypothermia has been reported to induce ventricular tachycardia and fibrillation (VT/VF) in patients with early repolarization (ER) pattern. This study examines the cellular mechanisms underlying VT/VF associated with hypothermia in an experimental model of ER syndrome and examines the effectiveness of quinidine, cilostazol, and milrinone to prevent hypothermia-induced arrhythmias. Transmembrane action potentials were simultaneously recorded from 2 epicardial and 1 endocardial site of coronary-perfused canine left ventricular wedge preparations, together with a pseudo-ECG. A combination of NS5806 (3-10 μmol/L) and verapamil (1 μmol/L) was used to pharmacologically model the genetic mutations responsible for ER syndrome. Acetylcholine (3 μmol/L) was used to simulate increased parasympathetic tone, which is known to promote ER. In controls, lowering the temperature of the coronary perfusate to induce mild hypothermia (32°C-34°C) resulted in increased J-wave area on the ECG and accentuated epicardial action potential notch but no arrhythmic activity. In the setting of ER, hypothermia caused further accentuation of the epicardial action potential notch, leading to loss of the action potential dome at some sites but not others, thus creating the substrate for development of phase 2 reentry and VT/VF. Addition of the transient outward current antagonist quinidine (5 μmol/L) or the phosphodiesterase III inhibitors cilostazol (10 μmol/L) or milrinone (5 μmol/L) diminished the ER manifestations and prevented the hypothermia-induced phase 2 reentry and VT/VF. Hypothermia leads to VT/VF in the setting of ER by exaggerating repolarization abnormalities, leading to development of phase 2 reentry. Quinidine, cilostazol, and milrinone suppress the hypothermia-induced VT/VF by reversing the repolarization abnormalities.

Triggered intracellular calcium waves in dog and human left atrial myocytes from normal and failing hearts.

PubMed

Aistrup, Gary L; Arora, Rishi; Grubb, Søren; Yoo, Shin; Toren, Benjamin; Kumar, Manvinder; Kunamalla, Aaron; Marszalec, William; Motiwala, Tej; Tai, Shannon; Yamakawa, Sean; Yerrabolu, Satya; Alvarado, Francisco J; Valdivia, Hector H; Cordeiro, Jonathan M; Shiferaw, Yohannes; Wasserstrom, John Andrew

2017-11-01

Abnormal intracellular Ca2+ cycling contributes to triggered activity and arrhythmias in the heart. We investigated the properties and underlying mechanisms for systolic triggered Ca2+ waves in left atria from normal and failing dog hearts. Intracellular Ca2+ cycling was studied using confocal microscopy during rapid pacing of atrial myocytes (36 °C) isolated from normal and failing canine hearts (ventricular tachypacing model). In normal atrial myocytes (NAMs), Ca2+ waves developed during rapid pacing at rates ≥ 3.3 Hz and immediately disappeared upon cessation of pacing despite high sarcoplasmic reticulum (SR) load. In heart failure atrial myocytes (HFAMs), triggered Ca2+ waves (TCWs) developed at a higher incidence at slower rates. Because of their timing, TCW development relies upon action potential (AP)-evoked Ca2+ entry. The distribution of Ca2+ wave latencies indicated two populations of waves, with early events representing TCWs and late events representing conventional spontaneous Ca2+ waves. Latency analysis also demonstrated that TCWs arise after junctional Ca2+ release has occurred and spread to non-junctional (cell core) SR. TCWs also occurred in intact dog atrium and in myocytes from humans and pigs. β-adrenergic stimulation increased Ca2+ release and abolished TCWs in NAMs but was ineffective in HFAMs making this a potentially effective adaptive mechanism in normals but potentially arrhythmogenic in HF. Block of Ca-calmodulin kinase II also abolished TCWs, suggesting a role in TCW formation. Pharmacological manoeuvres that increased Ca2+ release suppressed TCWs as did interventions that decreased Ca2+ release but these also severely reduced excitation-contraction coupling. TCWs develop during the atrial AP and thus could affect AP duration, producing repolarization gradients and creating a substrate for reentry, particularly in HF where they develop at slower rates and a higher incidence. TCWs may represent a mechanism for the initiation of atrial fibrillation particularly in HF. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2017. For permissions please email: journals.permissions@oup.com.

Quantitative analysis of the Ca2+‐dependent regulation of delayed rectifier K+ current I Ks in rabbit ventricular myocytes

PubMed Central

Bartos, Daniel C.; Morotti, Stefano; Ginsburg, Kenneth S.; Grandi, Eleonora

2017-01-01

Key points [Ca2+]i enhanced rabbit ventricular slowly activating delayed rectifier K+ current (I Ks) by negatively shifting the voltage dependence of activation and slowing deactivation, similar to perfusion of isoproterenol.Rabbit ventricular rapidly activating delayed rectifier K+ current (I Kr) amplitude and voltage dependence were unaffected by high [Ca2+]i.When measuring or simulating I Ks during an action potential, I Ks was not different during a physiological Ca2+ transient or when [Ca2+]i was buffered to 500 nm. Abstract The slowly activating delayed rectifier K+ current (I Ks) contributes to repolarization of the cardiac action potential (AP). Intracellular Ca2+ ([Ca2+]i) and β‐adrenergic receptor (β‐AR) stimulation modulate I Ks amplitude and kinetics, but details of these important I Ks regulators and their interaction are limited. We assessed the [Ca2+]i dependence of I Ks in steady‐state conditions and with dynamically changing membrane potential and [Ca2+]i during an AP. I Ks was recorded from freshly isolated rabbit ventricular myocytes using whole‐cell patch clamp. With intracellular pipette solutions that controlled free [Ca2+]i, we found that raising [Ca2+]i from 100 to 600 nm produced similar increases in I Ks as did β‐AR activation, and the effects appeared additive. Both β‐AR activation and high [Ca2+]i increased maximally activated tail I Ks, negatively shifted the voltage dependence of activation, and slowed deactivation kinetics. These data informed changes in our well‐established mathematical model of the rabbit myocyte. In both AP‐clamp experiments and simulations, I Ks recorded during a normal physiological Ca2+ transient was similar to I Ks measured with [Ca2+]i clamped at 500–600 nm. Thus, our study provides novel quantitative data as to how physiological [Ca2+]i regulates I Ks amplitude and kinetics during the normal rabbit AP. Our results suggest that micromolar [Ca2+]i, in the submembrane or junctional cleft space, is not required to maximize [Ca2+]i‐dependent I Ks activation during normal Ca2+ transients. PMID:28008618

Glucose ingestion causes cardiac repolarization disturbances in type 1 long QT syndrome patients and healthy subjects.

PubMed

Hyltén-Cavallius, Louise; Iepsen, Eva W; Christiansen, Michael; Graff, Claus; Linneberg, Allan; Pedersen, Oluf; Holst, Jens J; Hansen, Torben; Torekov, Signe S; Kanters, Jørgen K

2017-08-01

Both hypoglycemia and severe hyperglycemia constitute known risk factors for cardiac repolarization changes potentially leading to malignant arrhythmias. Patients with loss of function mutations in KCNQ1 are characterized by long QT syndrome (LQTS) and may be at increased risk for glucose-induced repolarization disturbances. The purpose of this study was to test the hypothesis that KCNQ1 LQTS patients are at particular risk for cardiac repolarization changes during the relative hyperglycemia that occurs after an oral glucose load. Fourteen KCNQ1 LQTS patients and 28 control participants matched for gender, body mass index, and age underwent a 3-hour oral 75-g glucose tolerance test with ECGs obtained at 7 time points. Fridericia corrected QT interval (QTcF), Bazett corrected QT interval (QTcB), and the Morphology Combination Score (MCS) were calculated. QTc and MCS increased in both groups. MCS remained elevated until 150 minutes after glucose ingestion, and the maximal change from baseline was larger among KCNQ1 LQTS patients compared with control subjects (0.28 ± 0.27 vs 0.15 ± 0.13; P <.05). Relative hyperglycemia induced by ingestion of 75-g glucose caused cardiac repolarization disturbances that were more severe in KCNQ1 LQTS patients compared with control subjects. Copyright © 2017 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

Evaluation of the acute electrophysiologic effects of intravenous dronedarone, an amiodarone-like agent, with special emphasis on ventricular repolarization and acquired torsade de pointes arrhythmias.

PubMed

Verduyn, S C; Vos, M A; Leunissen, H D; van Opstal, J M; Wellens, H J

1999-02-01

In the anesthetized dog with complete chronic AV block (CAVB), we evaluated and compared the acute electrophysiologic effects of dronedarone i.v. (Dron, 2 times 2.5 mg/kg/10 min) and amiodarone i.v. (Amio, 2 times 5 mg/kg/10 min). This canine model with a high sensitivity for acquired torsade de pointes (TdP) provides an ideal substrate to evaluate ventricular repolarization abnormalities. Six ECG leads and two endocardial monophasic action potential (MAP) recordings in the left and right ventricle (LV and RV) were simultaneously recorded to measure QT time, action-potential duration (APD), interventricular dispersion (deltaAPD = LV(APD) - RV(APD)), early afterdepolarizations (EADs), ectopic beats (EBs), and TdP. Measurements were made at the spontaneous idioventricular rhythm (IVR) and 1,000-ms steady-state pacing. To investigate its short-term, antiarrhythmic properties, Dron was given after almokalant (0.12 mg/kg)-induced TdP. Furthermore, in another set of experiments, oral Dron (20 mg/kg, b.i.d) was given for 3 weeks to conscious CAVB dogs. Dron, i.v., shortened ventricular repolarization (QT, 435 +/- 60 to 360 +/- 55; LV(APD) 395 +/- 75 to 335 +/- 60 ms; p < 0.05), whereas IVR and ventricular effective refractory period (VERP, 225 +/- 30 to 230 +/- 30 ms) remained similar. Therefore the VERP/QT ratio increased (0.55 +/- 0.04 to 0.61 +/- 0.03; p < 0.05). Similar results were obtained with Amio, i.v.. Almokalant-induced TdP was characterized by an increased repolarization duration, deltaAPD, and EADs. Dron, i.v., suppressed the EADs, EBs, and TdP by a reduction and homogenization of repolarization (LV(APD), 505 +/- 110 to 455 +/- 80 ms, and deltaAPD, 110 +/- 55 to 65 +/- 40 ms). Long-term oral Dron increased the PP interval, CL-IVR, and QT(c) time. In contrast to oral treatment, Dron i.v. shortens ventricular repolarization parameters, resulting in suppression of EAD-dependent acquired TdP. The increased VERP/QT ratio after Dron i.v. may indicate an important second antiarrhythmic property.

Effect of action potential duration on Tpeak-Tend interval, T-wave area and T-wave amplitude as indices of dispersion of repolarization: Theoretical and simulation study in the rabbit heart.

PubMed

Arteyeva, Natalia V; Azarov, Jan E

The aim of the study was to differentiate the effect of dispersion of repolarization (DOR) and action potential duration (APD) on T-wave parameters being considered as indices of DOR, namely, Tpeak-Tend interval, T-wave amplitude and T-wave area. T-wave was simulated in a wide physiological range of DOR and APD using a realistic rabbit model based on experimental data. A simplified mathematical formulation of T-wave formation was conducted. Both the simulations and the mathematical formulation showed that Tpeak-Tend interval and T-wave area are linearly proportional to DOR irrespectively of APD range, while T-wave amplitude is non-linearly proportional to DOR and inversely proportional to the minimal repolarization time, or minimal APD value. Tpeak-Tend interval and T-wave area are the most accurate DOR indices independent of APD. T-wave amplitude can be considered as an index of DOR when the level of APD is taken into account. Copyright © 2017 Elsevier Inc. All rights reserved.

Geraniol blocks calcium and potassium channels in the mammalian myocardium: useful effects to treat arrhythmias.

PubMed

de Menezes-Filho, José Evaldo Rodrigues; Gondim, Antônio Nei Santana; Cruz, Jader Santos; de Souza, Américo Azevedo; Santos, José Nilson Andrade Dos; Conde-Garcia, Eduardo Antônio; de Sousa, Damião Pergentino; Santos, Michel Santana; de Oliveira, Evaleide Diniz; de Vasconcelos, Carla Maria Lins

2014-12-01

Geraniol is a monoterpene present in several essential oils, and it is known to have a plethora of pharmacological activities. In this study, we explored the contractile and electrophysiological properties of geraniol and its antiarrhythmic effects in the heart. The geraniol effects on atrial contractility, L-type Ca(2+) current, K(+) currents, action potential (AP) parameters, ECG profile and on the arrhythmia induced by ouabain were evaluated. In the atrium, geraniol reduced the contractile force (~98%, EC = 1,510 ± 160 μM) and diminished the positive inotropism of CaCl2 and BAY K8644. In cardiomyocytes, the IC a,L was reduced by 50.7% (n = 5) after perfusion with 300 μM geraniol. Moreover, geraniol prolonged the AP duration (APD) measured at 50% (n = 5) after repolarization, without changing the resting potential. The increased APD could be attributed to the blockade of the transient outward K(+) current (Ito ) (59.7%, n = 4), the non-inactivation K(+) current (Iss ) (39.2%, n = 4) and the inward rectifier K(+) current (IK 1 ) (33.7%, n = 4). In isolated hearts, geraniol increased PRi and QTi without affecting the QRS complex (n = 6), and it reduced both the left ventricular pressure (83%) and heart rate (16.5%). Geraniol delayed the time to onset of ouabain-induced arrhythmias by 128%, preventing 30% of the increase in resting tension (n = 6). Geraniol exerts its negative inotropic and chronotropic responses in the heart by decreasing both L-type Ca(2+) and voltage-gated K(+) currents, ultimately acting against ouabain-induced arrhythmias. © 2014 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).

The human ether-a-go-go-related gene (hERG) current inhibition selectively prolongs action potential of midmyocardial cells to augment transmural dispersion.

PubMed

Yasuda, C; Yasuda, S; Yamashita, H; Okada, J; Hisada, T; Sugiura, S

2015-08-01

The majority of drug induced arrhythmias are related to the prolongation of action potential duration following inhibition of rapidly activating delayed rectifier potassium current (I(Kr)) mediated by the hERG channel. However, for arrhythmias to develop and be sustained, not only the prolongation of action potential duration but also its transmural dispersion are required. Herein, we evaluated the effect of hERG inhibition on transmural dispersion of action potential duration using the action potential clamp technique that combined an in silico myocyte model with the actual I(Kr) measurement. Whole cell I(Kr) current was measured in Chinese hamster ovary cells stably expressing the hERG channel. The measured current was coupled with models of ventricular endocardial, M-, and epicardial cells to calculate the action potentials. Action potentials were evaluated under control condition and in the presence of 1, 10, or 100 μM disopyramide, an hERG inhibitor. Disopyramide dose-dependently increased the action potential durations of the three cell types. However, action potential duration of M-cells increased disproportionately at higher doses, and was significantly different from that of epicardial and endocardial cells (dispersion of repolarization). By contrast, the effects of disopyramide on peak I(Kr) and instantaneous current-voltage relation were similar in all cell types. Simulation study suggested that the reduced repolarization reserve of M-cell with smaller amount of slowly activating delayed rectifier potassium current levels off at longer action potential duration to make such differences. The action potential clamp technique is useful for studying the mechanism of arrhythmogenesis by hERG inhibition through the transmural dispersion of repolarization.

Effects of sildenafil on cardiac repolarization.

PubMed

Chiang, Chern-En; Luk, Hsiang-Ning; Wang, Tsui-Min; Ding, Philip Yu-An

2002-08-01

Sudden death has occasionally been reported in patients taking sildenafil. The objective of this study was to investigate the effect of sildenafil on cardiac repolarization. We used conventional microelectrode recording technique in isolated guinea pig papillary muscles and canine Purkinje fibers, whole-cell patch clamp techniques in guinea pig ventricular myocytes, and in vivo ECG measurements in guinea pigs. Action potential duration at 90% repolarization (APD(90)) was not affected by sildenafil in the therapeutic ranges (< or =1 microM), but shortened by higher concentration (> or =10 microM) in both guinea pig papillary muscles and canine Purkinje fibers. D-Sotalol prolonged APD(90) in the same preparations with concentrations > or =1 microM in a reverse frequency-dependent manner. Co-administration of sildenafil (10 and 30 microM) abolished the APD-prolonging effects of D-sotalol (30 microM) and amiodarone (100 microM). Sildenafil, with concentrations up to 30 microM, had no significant effect on both the rapid (I(Kr)) and the slow (I(Ks)) components of the delayed rectifier potassium currents in guinea pig ventricular myocytes. Sildenafil dose-dependently blocked L-type Ca(2+) current (I(Ca,L)), but had no effect on persistent Na(+) current in guinea pig ventricular myocytes. ECG recordings in intact guinea pigs revealed significant shortening of QTc interval by sildenafil (10 and 30 mg/kg orally). The QT-prolonging effects by D,L-sotalol (50 mg/kg) and amiodarone (100 mg/kg) were abolished by sildenafil (30 mg/kg). Sildenafil does not prolong cardiac repolarization. Instead, in supra-therapeutic concentrations, it accelerates cardiac repolarization, presumably through its blocking effect on I(Ca,L).

Reduced intrinsic heart rate is associated with reduced arrhythmic susceptibility in guinea-pig heart.

PubMed

Osadchii, Oleg E

2014-12-01

In the clinical setting, patients with slower resting heart rate are less prone to cardiovascular death compared with those with elevated heart rate. However, electrophysiological adaptations associated with reduced cardiac rhythm have not been thoroughly explored. In this study, relationships between intrinsic heart rate and arrhythmic susceptibility were examined by assessments of action potential duration (APD) rate adaptation and inducibility of repolarization alternans in sinoatrial node (SAN)-driven and atrioventricular (AV)-blocked guinea-pig hearts perfused with Langendorff apparatus. Electrocardiograms, epicardial monophasic action potentials, and effective refractory periods (ERP) were assessed in normokalemic and hypokalemic conditions. Slower basal heart rate in AV-blocked hearts was associated with prolonged ventricular repolarization during spontaneous beating, and with attenuated APD shortening at increased cardiac activation rates during dynamic pacing, when compared with SAN-driven hearts. During hypokalemic perfusion, the inducibility of repolarization alternans and tachyarrhythmia by rapid pacing was found to be lower in AV-blocked hearts. This difference was ascribed to prolonged ERP in the setting of reduced basal heart rate, which prevented ventricular capture at critically short pacing intervals required to induce arrhythmia. Reduced basal heart rate is associated with electrophysiological changes that prevent electrical instability upon an abrupt cardiac acceleration.

Flecainide attenuates rate adaptation of ventricular repolarization in guinea-pig heart.

PubMed

Osadchii, Oleg E

2016-01-01

Flecainide is class Ic antiarrhythmic agent that was found to increase the risk of sudden cardiac death. Arrhythmic responses to flecainide could be precipitated by exercise, suggesting a role played by inappropriate rate adaptation of ventricular repolarization. This study therefore examined flecainide effect on adaptation of the QT interval and ventricular action potential duration (APD) to abrupt reductions of the cardiac cycle length. ECG and ventricular epicardial and endocardial monophasic APD were recorded in isolated, perfused guinea-pig heart preparations upon a sustained cardiac acceleration (rapid pacing for 30 s), and following a single perturbation of the cycle length evoked by extrasystolic stimulation. Sustained increase in heart rate was associated with progressive bi-exponential shortening of the QT interval and APD. Flecainide prolonged ventricular repolarization, delayed its rate adaptation, and decreased the amplitude of QT interval and APD shortening upon rapid cardiac pacing. During extrasystolic stimulation, flecainide attenuated APD shortening in premature ventricular beats, with effect being greater upon using a longer basic drive cycle length (S1-S1=550 ms versus S1-S1=300 ms). Flecainide-induced arrhythmia may be partly accounted for by attenuated adaptation of ventricular repolarization to sudden changes in cardiac cycle length provoked by transient tachycardia or ectopic beats.

Excess centrosomes perturb dynamic endothelial cell repolarization during blood vessel formation

PubMed Central

Kushner, Erich J.; Ferro, Luke S.; Yu, Zhixian; Bautch, Victoria L.

2016-01-01

Blood vessel formation requires dynamic movements of endothelial cells (ECs) within sprouts. The cytoskeleton regulates migratory polarity, and centrosomes organize the microtubule cytoskeleton. However, it is not well understood how excess centrosomes, commonly found in tumor stromal cells, affect microtubule dynamics and interphase cell polarity. Here we find that ECs dynamically repolarize during sprouting angiogenesis, and excess centrosomes block repolarization and reduce migration and sprouting. ECs with excess centrosomes initially had more centrosome-derived microtubules but, paradoxically, fewer steady-state microtubules. ECs with excess centrosomes had elevated Rac1 activity, and repolarization was rescued by blockade of Rac1 or actomyosin blockers, consistent with Rac1 activity promoting cortical retrograde actin flow and actomyosin contractility, which precludes cortical microtubule engagement necessary for dynamic repolarization. Thus normal centrosome numbers are required for dynamic repolarization and migration of sprouting ECs that contribute to blood vessel formation. PMID:27099371

Ventricular filling slows epicardial conduction and increases action potential duration in an optical mapping study of the isolated rabbit heart.

PubMed

Sung, Derrick; Mills, Robert W; Schettler, Jan; Narayan, Sanjiv M; Omens, Jeffrey H; McCulloch, Andrew D

2003-07-01

Mechanical stimulation can induce electrophysiologic changes in cardiac myocytes, but how mechanoelectric feedback in the intact heart affects action potential propagation remains unclear. Changes in action potential propagation and repolarization with increased left ventricular end-diastolic pressure from 0 to 30 mmHg were investigated using optical mapping in isolated perfused rabbit hearts. With respect to 0 mmHg, epicardial strain at 30 mmHg in the anterior left ventricle averaged 0.040 +/- 0.004 in the muscle fiber direction and 0.032 +/- 0.006 in the cross-fiber direction. An increase in ventricular loading increased average epicardial activation time by 25%+/- 3% (P < 0.0001) and correspondingly decreased average apparent surface conduction velocity by 16%+/- 7% (P = 0.007). Ventricular loading did not significantly alter action potential duration at 20% repolarization (APD20) but did at 80% repolarization (APD80), from 179 +/- 7 msec to 207 +/- 5 msec (P < 0.0001). The dispersion of APD20 was decreased with loading from 19 +/- 2 msec to 13 +/- 2 msec (P = 0.024), whereas the dispersion of APD80 was not significantly changed. These electrophysiologic changes with ventricular loading were not affected by the nonspecific stretch-activated channel blocker streptomycin (200 microM) and were not attributable to changes in myocardial perfusion or the presence of an electromechanical decoupling agent (butanedione monoxime) during optical mapping. Acute loading of the left ventricle of the isolated rabbit heart decreased apparent epicardial conduction velocity and increased action potential duration by a load-dependent mechanism that may not involve stretch-activated channels.

Heart rate profile during exercise in patients with early repolarization.

PubMed

Cay, Serkan; Cagirci, Goksel; Atak, Ramazan; Balbay, Yucel; Demir, Ahmet Duran; Aydogdu, Sinan

2010-09-01

Both early repolarization and altered heart rate profile are associated with sudden death. In this study, we aimed to demonstrate an association between early repolarization and heart rate profile during exercise. A total of 84 subjects were included in the study. Comparable 44 subjects with early repolarization and 40 subjects with normal electrocardiogram underwent exercise stress testing. Resting heart rate, maximum heart rate, heart rate increment and decrement were analyzed. Both groups were comparable for baseline characteristics including resting heart rate. Maximum heart rate, heart rate increment and heart rate decrement of the subjects in early repolarization group had significantly decreased maximum heart rate, heart rate increment and heart rate decrement compared to control group (all P < 0.05). The lower heart rate increment (< 106 beats/min) and heart rate decrement (< 95 beats/min) were significantly associated with the presence of early repolarization. After adjustment for age and sex, the multiple-adjusted OR of the risk of presence of early repolarization was 2.98 (95%CI 1.21-7.34) (P = 0.018) and 7.73 (95%CI 2.84-21.03) (P < 0.001) for the lower heart rate increment and heart rate decrement compared to higher levels, respectively. Subjects with early repolarization have altered heart rate profile during exercise compared to control subjects. This can be related to sudden death.

Timing of myocardial trpm7 deletion during cardiogenesis variably disrupts adult ventricular function, conduction, and repolarization.

PubMed

Sah, Rajan; Mesirca, Pietro; Mason, Xenos; Gibson, William; Bates-Withers, Christopher; Van den Boogert, Marjolein; Chaudhuri, Dipayan; Pu, William T; Mangoni, Matteo E; Clapham, David E

2013-07-09

Transient receptor potential (TRP) channels are a superfamily of broadly expressed ion channels with diverse physiological roles. TRPC1, TRPC3, and TRPC6 are believed to contribute to cardiac hypertrophy in mouse models. Human mutations in TRPM4 have been linked to progressive familial heart block. TRPM7 is a divalent-permeant channel and kinase of unknown function, recently implicated in the pathogenesis of atrial fibrillation; however, its function in ventricular myocardium remains unexplored. We generated multiple cardiac-targeted knockout mice to test the hypothesis that TRPM7 is required for normal ventricular function. Early cardiac Trpm7 deletion (before embryonic day 9; TnT/Isl1-Cre) results in congestive heart failure and death by embryonic day 11.5 as a result of hypoproliferation of the compact myocardium. Remarkably, Trpm7 deletion late in cardiogenesis (about embryonic day 13; αMHC-Cre) produces viable mice with normal adult ventricular size, function, and myocardial transcriptional profile. Trpm7 deletion at an intermediate time point results in 50% of mice developing cardiomyopathy associated with heart block, impaired repolarization, and ventricular arrhythmias. Microarray analysis reveals elevations in transcripts of hypertrophy/remodeling genes and reductions in genes important for suppressing hypertrophy (Hdac9) and for ventricular repolarization (Kcnd2) and conduction (Hcn4). These transcriptional changes are accompanied by action potential prolongation and reductions in transient outward current (Ito; Kcnd2). Similarly, the pacemaker current (If; Hcn4) is suppressed in atrioventricular nodal cells, accounting for the observed heart block. Trpm7 is dispensable in adult ventricular myocardium under basal conditions but is critical for myocardial proliferation during early cardiogenesis. Loss of Trpm7 at an intermediate developmental time point alters the myocardial transcriptional profile in adulthood, impairing ventricular function, conduction, and repolarization.

T-wave alternans and beat-to-beat variability of repolarization: pathophysiological backgrounds and clinical relevance.

PubMed

Floré, Vincent; Willems, Rik

2012-12-01

In this review, we focus on temporal variability of cardiac repolarization. This phenomenon has been related to a higher risk for ventricular arrhythmia and is therefore interesting as a marker of sudden cardiac death risk. We review two non-invasive clinical techniques quantifying repolarization variability: T-wave alternans (TWA) and beat-to-beat variability of repolarization (BVR). We discuss their pathophysiological link with ventricular arrhythmia and the current clinical relevance of these techniques.

Spatial variability in T-tubule and electrical remodeling of left ventricular epicardium in mouse hearts with transgenic Gαq overexpression-induced pathological hypertrophy

PubMed Central

Tao, Wen; Shi, Jianjian; Dorn, Gerald W.; Wei, Lei; Rubart, Michael

2012-01-01

Pathological left ventricular hypertrophy (LVH) is consistently associated with prolongation of the ventricular action potentials. A number of previous studies, employing various experimental models of hypertrophy, have revealed marked differences in the effects of hypertrophy on action potential duration (APD) between myocytes from endocardial and epicardial layers of the LV free wall. It is not known, however, whether pathological LVH is also accompanied by redistribution of APD among myocytes from the same layer in the LV free wall. In the experiments here, LV epicardial action potential remodeling was examined in a mouse model of decompensated LVH, produced by cardiac-restricted transgenic Gαq overexpression. Confocal linescanning-based optical recordings of propagated action potentials from individual in situ cardiomyocytes across the outer layer of the anterior LV epicardium demonstrated spatially non-uniform action potential prolongation in transgenic hearts, giving rise to alterations in spatial dispersion of epicardial repolarization. Local density and distribution of anti-Cx43 mmune reactivity in Gαq hearts were unchanged compared to wild-type hearts, suggesting preservation of intercellular coupling. Confocal microscopy also revealed heterogeneous disorganization of T-tubules in epicardial cardiomyocytes in situ. These data provide evidence of the existence of significant electrical and structural heterogeneity within the LV epicardial layer of hearts with transgenic Gαq overexpression-induced hypertrophy, and further support the notion that a small portion of electrically well connected LV tissue can maintain dispersion of action potential duration through heterogeneity in the activities of sarcolemmal ionic currents that control repolarization. It remains to be examined whether other experimental models of pathological LVH, including pressure overload LVH, similarly exhibit alterations in T-tubule organization and/or dispersion of repolarization within distinct layers of LV myocardium. PMID:22728217

Electrophysiological determinants of hypokalaemia-induced arrhythmogenicity in the guinea-pig heart.

PubMed

Osadchii, O E; Olesen, S P

2009-12-01

Hypokalaemia is an independent risk factor contributing to arrhythmic death in cardiac patients. In the present study, we explored the mechanisms of hypokalaemia-induced tachyarrhythmias by measuring ventricular refractoriness, spatial repolarization gradients, and ventricular conduction time in isolated, perfused guinea-pig heart preparations. Epicardial and endocardial monophasic action potentials from distinct left ventricular (LV) and right ventricular (RV) recording sites were monitored simultaneously with volume-conducted electrocardiogram (ECG) during steady-state pacing and following a premature extrastimulus application at progressively reducing coupling stimulation intervals in normokalaemic and hypokalaemic conditions. Hypokalaemic perfusion (2.5 mm K(+) for 30 min) markedly increased the inducibility of tachyarrhythmias by programmed ventricular stimulation and rapid pacing, prolonged ventricular repolarization and shortened LV epicardial and endocardial effective refractory periods, thereby increasing the critical interval for LV re-excitation. Hypokalaemia increased the RV-to-LV transepicardial repolarization gradients but had no effect on transmural dispersion of APD(90) and refractoriness across the LV wall. As determined by local activation time recordings, the LV-to-RV transepicardial conduction and the LV transmural (epicardial-to-endocardial) conduction were slowed in hypokalaemic heart preparations. This change was attributed to depressed diastolic excitability as evidenced by increased ventricular pacing thresholds. These findings suggest that hypokalaemia-induced arrhythmogenicity is attributed to shortened LV refractoriness, increased critical intervals for LV re-excitation, amplified RV-to-LV transepicardial repolarization gradients and slowed ventricular conduction in the guinea-pig heart.

Cardiac Delayed Rectifier Potassium Channels in Health and Disease.

PubMed

Chen, Lei; Sampson, Kevin J; Kass, Robert S

2016-06-01

Cardiac delayed rectifier potassium channels conduct outward potassium currents during the plateau phase of action potentials and play pivotal roles in cardiac repolarization. These include IKs, IKr and the atrial specific IKur channels. In this article, we will review their molecular identities and biophysical properties. Mutations in the genes encoding delayed rectifiers lead to loss- or gain-of-function phenotypes, disrupt normal cardiac repolarization and result in various cardiac rhythm disorders, including congenital Long QT Syndrome, Short QT Syndrome and familial atrial fibrillation. We will also discuss the prospect of using delayed rectifier channels as therapeutic targets to manage cardiac arrhythmia. Copyright © 2016 Elsevier Inc. All rights reserved.

Cardiac Delayed Rectifier Potassium Channels in Health and Disease

PubMed Central

Chen, Lei; Sampson, Kevin J.; Kass, Robert S.

2016-01-01

Cardiac delayed rectifier potassium channels conduct outward potassium currents during the plateau phase of action potentials and play pivotal roles in cardiac repolarization. These include IKs, IKr and the atrial specific IKur channels. In this chapter, we will review the molecular identities and biophysical properties of these channels. Mutations in the genes encoding delayed rectifiers lead to loss- or gain-of-function phenotypes, disrupt normal cardiac repolarization and result in various cardiac rhythm disorders, including congenital Long QT Syndrome, Short QT Syndrome and familial atrial fibrillation. We will also discuss the possibility and prospect of using delayed rectifier channels as therapeutic targets to manage cardiac arrhythmia. PMID:27261823

Anti-addiction Drug Ibogaine Prolongs the Action Potential in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes.

PubMed

Rubi, Lena; Eckert, Daniel; Boehm, Stefan; Hilber, Karlheinz; Koenig, Xaver

2017-04-01

Ibogaine is a plant alkaloid used as anti-addiction drug in dozens of alternative medicine clinics worldwide. Recently, alarming reports of life-threatening cardiac arrhythmias and cases of sudden death associated with the ingestion of ibogaine have accumulated. Using whole-cell patch clamp recordings, we assessed the effects of ibogaine and its main metabolite noribogaine on action potentials in human ventricular-like cardiomyocytes derived from induced pluripotent stem cells. Therapeutic concentrations of ibogaine and its long-lived active metabolite noribogaine significantly retarded action potential repolarization in human cardiomyocytes. These findings represent the first experimental proof that ibogaine application entails a cardiac arrhythmia risk for humans. In addition, they explain the clinically observed delayed incidence of cardiac adverse events several days after ibogaine intake. We conclude that therapeutic concentrations of ibogaine retard action potential repolarization in the human heart. This may give rise to a prolongation of the QT interval in the electrocardiogram and cardiac arrhythmias.

Histone Deacetylase Inhibitors Prolong Cardiac Repolarization through Transcriptional Mechanisms.

PubMed

Spence, Stan; Deurinck, Mark; Ju, Haisong; Traebert, Martin; McLean, LeeAnne; Marlowe, Jennifer; Emotte, Corinne; Tritto, Elaine; Tseng, Min; Shultz, Michael; Friedrichs, Gregory S

2016-09-01

Histone deacetylase (HDAC) inhibitors are an emerging class of anticancer agents that modify gene expression by altering the acetylation status of lysine residues of histone proteins, thereby inducing transcription, cell cycle arrest, differentiation, and cell death or apoptosis of cancer cells. In the clinical setting, treatment with HDAC inhibitors has been associated with delayed cardiac repolarization and in rare instances a lethal ventricular tachyarrhythmia known as torsades de pointes. The mechanism(s) of HDAC inhibitor-induced effects on cardiac repolarization is unknown. We demonstrate that administration of structurally diverse HDAC inhibitors to dogs causes delayed but persistent increases in the heart rate corrected QT interval (QTc), an in vivo measure of cardiac repolarization, at timepoints far removed from the Tmax for parent drug and metabolites. Transcriptional profiling of ventricular myocardium from dogs treated with various HDAC inhibitors demonstrated effects on genes involved in protein trafficking, scaffolding and insertion of various ion channels into the cell membrane as well as genes for specific ion channel subunits involved in cardiac repolarization. Extensive in vitro ion channel profiling of various structural classes of HDAC inhibitors (and their major metabolites) by binding and acute patch clamp assays failed to show any consistent correlations with direct ion channel blockade. Drug-induced rescue of an intracellular trafficking-deficient mutant potassium ion channel, hERG (G601S), and decreased maturation (glycosylation) of wild-type hERG expressed by CHO cells in vitro correlated with prolongation of QTc intervals observed in vivo The results suggest that HDAC inhibitor-induced prolongation of cardiac repolarization may be mediated in part by transcriptional changes of genes required for ion channel trafficking and localization to the sarcolemma. These data have broad implications for the development of these drug classes and suggest that the optimal time to assess potentially transcriptionally mediated physiologic effects will be delayed relative to an epigenetic drug's Tmax/Cmax. © The Author 2016. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Bifurcation diagrams of frequency dependence of repolarization during long QT syndrome using the Luo-Rudy model of cardiac repolarization

NASA Astrophysics Data System (ADS)

Bondarenko, V. E.; Doedel, E. J.; Rasmusson, R. L.

2000-02-01

We applied bifurcation analysis to the Luo-Rudy model of the guinea pig cardiac ventricular cell to investigate the behavior of repolarization in response to a simulated form of inherited arrhythmia, long QT syndrome. In this paper, we simulate pathological changes in cardiac repolarization through reductions in IKr. Decreased expression of this current has been linked to an inherited form of long QT syndrome which results in a high mortality, presumably due to sudden cardiac death from ventricular fibrillation.

Ventricular repolarization variability for hypoglycemia detection.

PubMed

Ling, Steve; Nguyen, H T

2011-01-01

Hypoglycemia is the most acute and common complication of Type 1 diabetes and is a limiting factor in a glycemic management of diabetes. In this paper, two main contributions are presented; firstly, ventricular repolarization variabilities are introduced for hypoglycemia detection, and secondly, a swarm-based support vector machine (SVM) algorithm with the inputs of the repolarization variabilities is developed to detect hypoglycemia. By using the algorithm and including several repolarization variabilities as inputs, the best hypoglycemia detection performance is found with sensitivity and specificity of 82.14% and 60.19%, respectively.

Ventricular filling slows epicardial conduction and increases action potential duration in an optical mapping study of the isolated rabbit heart

NASA Technical Reports Server (NTRS)

Sung, Derrick; Mills, Robert W.; Schettler, Jan; Narayan, Sanjiv M.; Omens, Jeffrey H.; McCulloch, Andrew D.; McCullough, A. D. (Principal Investigator)

2003-01-01

INTRODUCTION: Mechanical stimulation can induce electrophysiologic changes in cardiac myocytes, but how mechanoelectric feedback in the intact heart affects action potential propagation remains unclear. METHODS AND RESULTS: Changes in action potential propagation and repolarization with increased left ventricular end-diastolic pressure from 0 to 30 mmHg were investigated using optical mapping in isolated perfused rabbit hearts. With respect to 0 mmHg, epicardial strain at 30 mmHg in the anterior left ventricle averaged 0.040 +/- 0.004 in the muscle fiber direction and 0.032 +/- 0.006 in the cross-fiber direction. An increase in ventricular loading increased average epicardial activation time by 25%+/- 3% (P < 0.0001) and correspondingly decreased average apparent surface conduction velocity by 16%+/- 7% (P = 0.007). Ventricular loading did not significantly alter action potential duration at 20% repolarization (APD20) but did at 80% repolarization (APD80), from 179 +/- 7 msec to 207 +/- 5 msec (P < 0.0001). The dispersion of APD20 was decreased with loading from 19 +/- 2 msec to 13 +/- 2 msec (P = 0.024), whereas the dispersion of APD80 was not significantly changed. These electrophysiologic changes with ventricular loading were not affected by the nonspecific stretch-activated channel blocker streptomycin (200 microM) and were not attributable to changes in myocardial perfusion or the presence of an electromechanical decoupling agent (butanedione monoxime) during optical mapping. CONCLUSION: Acute loading of the left ventricle of the isolated rabbit heart decreased apparent epicardial conduction velocity and increased action potential duration by a load-dependent mechanism that may not involve stretch-activated channels.

Intramural activation and repolarization sequences in canine ventricles. Experimental and simulation studies.

PubMed

Taccardi, Bruno; Punske, Bonnie B; Sachse, Frank; Tricoche, Xavier; Colli-Franzone, Piero; Pavarino, Luca F; Zabawa, Christine

2005-10-01

There are no published data showing the three-dimensional sequence of repolarization and the associated potential fields in the ventricles. Knowledge of the sequence of repolarization has medical relevance because high spatial dispersion of recovery times and action potential durations favors cardiac arrhythmias. In this study we describe measured and simulated 3-D excitation and recovery sequences and activation-recovery intervals (ARIs) (measured) or action potential durations (APDs) (simulated) in the ventricular walls. We recorded from 600 to 1400 unipolar electrograms from canine ventricular walls during atrial and ventricular pacing at 350-450 ms cycle length. Measured excitation and recovery times and ARIs were displayed as 2-D maps in transmural planes or 3-D maps in the volume explored, using specially developed software. Excitation and recovery sequences and APD distributions were also simulated in parallelepipedal slabs using anisotropic monodomain or bidomain models based on the Lou-Rudy version 1 model with homogeneous membrane properties. Simulations showed that in the presence of homogeneous membrane properties, the sequence of repolarization was similar but not identical to the excitation sequence. In a transmural plane perpendicular to epicardial fiber direction, both activation and recovery pathways starting from an epicardial pacing site returned toward the epicardium at a few cm distance from the pacing site. However, APDs were not constant, but had a dispersion of approximately 14 ms in the simulated domain. The maximum APD value was near the pacing site and two minima appeared along a line perpendicular to fiber directions, passing through the pacing site. Electrical measurements in dog ventricles showed that, for short cycle lengths, both excitation and recovery pathways, starting from an epicardial pacing site, returned toward the epicardium. For slower pacing rates, pathways of recovery departed from the pathway of excitation. Highest ARI values were observed near the pacing site in part of the experiments. In addition, maps of activation-recovery intervals showed mid-myocardial clusters with activation-recovery intervals that were slightly longer than ARIs closer to the epi- or endocardium, suggesting the presence of M cells in those areas. Transmural dispersion of measured ARIs was on the order of 20-25 ms. Potential distributions during recovery were less affected by myocardial anisotropy than were excitation potentials.

Correlation between human ether‐a‐go‐go‐related gene channel inhibition and action potential prolongation

PubMed Central

Saxena, P; Hortigon‐Vinagre, M P; Beyl, S; Baburin, I; Andranovits, S; Iqbal, S M; Costa, A; IJzerman, A P; Kügler, P; Timin, E

2017-01-01

Background and Purpose Human ether‐a‐go‐go‐related gene (hERG; Kv11.1) channel inhibition is a widely accepted predictor of cardiac arrhythmia. hERG channel inhibition alone is often insufficient to predict pro‐arrhythmic drug effects. This study used a library of dofetilide derivatives to investigate the relationship between standard measures of hERG current block in an expression system and changes in action potential duration (APD) in human‐induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs). The interference from accompanying block of Cav1.2 and Nav1.5 channels was investigated along with an in silico AP model. Experimental Approach Drug‐induced changes in APD were assessed in hiPSC‐CMs using voltage‐sensitive dyes. The IC50 values for dofetilide and 13 derivatives on hERG current were estimated in an HEK293 expression system. The relative potency of each drug on APD was estimated by calculating the dose (D150) required to prolong the APD at 90% (APD90) repolarization by 50%. Key Results The D150 in hiPSC‐CMs was linearly correlated with IC50 of hERG current. In silico simulations supported this finding. Three derivatives inhibited hERG without prolonging APD, and these compounds also inhibited Cav1.2 and/or Nav1.5 in a channel state‐dependent manner. Adding Cav1.2 and Nav1.2 block to the in silico model recapitulated the direction but not the extent of the APD change. Conclusions and Implications Potency of hERG current inhibition correlates linearly with an index of APD in hiPSC‐CMs. The compounds that do not correlate have additional effects including concomitant block of Cav1.2 and/or Nav1.5 channels. In silico simulations of hiPSC‐CMs APs confirm the principle of the multiple ion channel effects. PMID:28681507

The proliferative and chronotropic effects of Brillantaisia nitens Lindau (Acanthaceae) extracts on pluripotent stem cells and their cardiomyocytes derivatives.

PubMed

Nembo, Erastus Nembu; Dimo, Theophile; Bopda, Orelien Sylvain Mtopi; Hescheler, Jürgen; Nguemo, Filomain

2014-10-28

Brillantaisia nitens Lindau (Acanthaceae) leaves are commonly used in traditional medicine in Africa for the treatment of many disorders including heart diseases and malaria. In this study, we therefore evaluated the effect of the methylene chloride/methanol leaf extract of Brillantaisia nitens on the proliferation of mouse pluripotent stem cells and their cardiomyocyte derivatives. In this study, we combined two emerging technologies, pluripotent stem cell-derived cardiomyocytes and modern electrophysiology systems (impedance-based real-time) to assess the cytotoxicity of Brillantaisia nitens extract (BNE). Undifferentiated pluripotent cells and cardiomyocytes were exposed to different concentrations of BNE. Cell viability and contraction were monitored by impedance using the xCELLigence system for short- and long-term treatment whereas the excitability of single cardiomyocytes was captured by patch clamp technique after BNE acute exposure. Brillantaisia nitens extract inhibited the proliferation and increased cytotoxicity of embryonic stem cells in a concentration-dependent manner. With the increase in concentration of BNE, beating rate and the contractile amplitude of cardiomyocytes changed significantly. Spontaneous rhythmic activity of cardiomyocytes was completely suppressed after 48 and 24h exposures to relatively low (4.16 mg/ml) and high (8.32 mg/ml) concentrations of BNE, respectively. Moreover, acute application of 4.16 mg/ml of BNE led to a significant alteration of action potential (AP) parameters such as beating frequency, amplitude and AP duration at 90% of repolarization. Brillantaisia nitens extract inhibits the proliferative capacity of pluripotent stem cells and reduces electrical activity of cardiomyocytes, confirming its depressant action on the heart. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Distinct gene-specific mechanisms of arrhythmia revealed by cardiac gene transfer of two long QT disease genes, HERG and KCNE1.

PubMed

Hoppe, U C; Marbán, E; Johns, D C

2001-04-24

The long QT syndrome (LQTS) is a heritable disorder that predisposes to sudden cardiac death. LQTS is caused by mutations in ion channel genes including HERG and KCNE1, but the precise mechanisms remain unclear. To clarify this situation we injected adenoviral vectors expressing wild-type or LQT mutants of HERG and KCNE1 into guinea pig myocardium. End points at 48-72 h included electrophysiology in isolated myocytes and electrocardiography in vivo. HERG increased the rapid component, I(Kr), of the delayed rectifier current, thereby accelerating repolarization, increasing refractoriness, and diminishing beat-to-beat action potential variability. Conversely, HERG-G628S suppressed I(Kr) without significantly delaying repolarization. Nevertheless, HERG-G628S abbreviated refractoriness and increased beat-to-beat variability, leading to early afterdepolarizations (EADs). KCNE1 increased the slow component of the delayed rectifier, I(Ks), without clear phenotypic sequelae. In contrast, KCNE1-D76N suppressed I(Ks) and markedly slowed repolarization, leading to frequent EADs and electrocardiographic QT prolongation. Thus, the two genes predispose to sudden death by distinct mechanisms: the KCNE1 mutant flagrantly undermines cardiac repolarization, and HERG-G628S subtly facilitates the genesis and propagation of premature beats. Our ability to produce electrocardiographic long QT in vivo with a clinical KCNE1 mutation demonstrates the utility of somatic gene transfer in creating genotype-specific disease models.

The Application of Root Mean Square Electrocardiography (RMS ECG) for the Detection of Acquired and Congenital Long QT Syndrome

PubMed Central

Lux, Robert L.; Sower, Christopher Todd; Allen, Nancy; Etheridge, Susan P.; Tristani-Firouzi, Martin; Saarel, Elizabeth V.

2014-01-01

Background Precise measurement of the QT interval is often hampered by difficulty determining the end of the low amplitude T wave. Root mean square electrocardiography (RMS ECG) provides a novel alternative measure of ventricular repolarization. Experimental data have shown that the interval between the RMS ECG QRS and T wave peaks (RTPK) closely reflects the mean ventricular action potential duration while the RMS T wave width (TW) tracks the dispersion of repolarization timing. Here, we tested the precision of RMS ECG to assess ventricular repolarization in humans in the setting of drug-induced and congenital Long QT Syndrome (LQTS). Methods RMS ECG signals were derived from high-resolution 24 hour Holter monitor recordings from 68 subjects after receiving placebo and moxifloxacin and from standard 12 lead ECGs obtained in 97 subjects with LQTS and 97 age- and sex-matched controls. RTPK, QTRMS and RMS TW intervals were automatically measured using custom software and compared to traditional QT measures using lead II. Results All measures of repolarization were prolonged during moxifloxacin administration and in LQTS subjects, but the variance of RMS intervals was significantly smaller than traditional lead II measurements. TW was prolonged during moxifloxacin and in subjects with LQT-2, but not LQT-1 or LQT-3. Conclusion These data validate the application of RMS ECG for the detection of drug-induced and congenital LQTS. RMS ECG measurements are more precise than the current standard of care lead II measurements. PMID:24454918

The application of root mean square electrocardiography (RMS ECG) for the detection of acquired and congenital long QT syndrome.

PubMed

Lux, Robert L; Sower, Christopher Todd; Allen, Nancy; Etheridge, Susan P; Tristani-Firouzi, Martin; Saarel, Elizabeth V

2014-01-01

Precise measurement of the QT interval is often hampered by difficulty determining the end of the low amplitude T wave. Root mean square electrocardiography (RMS ECG) provides a novel alternative measure of ventricular repolarization. Experimental data have shown that the interval between the RMS ECG QRS and T wave peaks (RTPK) closely reflects the mean ventricular action potential duration while the RMS T wave width (TW) tracks the dispersion of repolarization timing. Here, we tested the precision of RMS ECG to assess ventricular repolarization in humans in the setting of drug-induced and congenital Long QT Syndrome (LQTS). RMS ECG signals were derived from high-resolution 24 hour Holter monitor recordings from 68 subjects after receiving placebo and moxifloxacin and from standard 12 lead ECGs obtained in 97 subjects with LQTS and 97 age- and sex-matched controls. RTPK, QTRMS and RMS TW intervals were automatically measured using custom software and compared to traditional QT measures using lead II. All measures of repolarization were prolonged during moxifloxacin administration and in LQTS subjects, but the variance of RMS intervals was significantly smaller than traditional lead II measurements. TW was prolonged during moxifloxacin and in subjects with LQT-2, but not LQT-1 or LQT-3. These data validate the application of RMS ECG for the detection of drug-induced and congenital LQTS. RMS ECG measurements are more precise than the current standard of care lead II measurements.

Local transmural action potential gradients are absent in the isolated, intact dog heart but present in the corresponding coronary-perfused wedge.

PubMed

Boukens, Bastiaan J; Meijborg, Veronique M F; Belterman, Charly N; Opthof, Tobias; Janse, Michiel J; Schuessler, Richard B; Coronel, Ruben; Efimov, Igor R

2017-05-01

The left ventricular (LV) coronary-perfused canine wedge preparation is a model commonly used for studying cardiac repolarization. In wedge studies, transmembrane potentials typically are recorded; whereas, extracellular electrical recordings are commonly used in intact hearts. We compared electrically measured activation recovery interval (ARI) patterns in the intact heart with those recorded at the same location in the LV wedge preparation. We also compared electrically recorded and optically obtained ARIs in the LV wedge preparation. Five Langendorff-perfused canine hearts were paced from the right atrium. Local activation and repolarization times were measured with eight transmural needle electrodes. Subsequently, left ventricular coronary-perfused wedge preparations were prepared from these hearts while the electrodes remained in place. Three electrodes remained at identical positions as in the intact heart. Both electrograms and optical action potentials were recorded (pacing cycle length 400-4000 msec) and activation and repolarization patterns were analyzed. ARIs found in the subepicardium were shorter than in the subendocardium in the LV wedge preparation but not in the intact heart. The transmural ARI gradient recorded at the cut surface of the wedge was not different from that recorded internally. ARIs recorded internally and at the cut surface in the LV wedge preparation, both correlated with optically recorded action potentials. ARI and RT gradients in the LV wedge preparation differed from those in the intact canine heart, implying that those observations in human LV wedge preparations also should be extrapolated to the intact human heart with caution. © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

Electrophysiological properties of myocytes isolated from the mouse atrioventricular node: L-type ICa, IKr, If, and Na-Ca exchange

PubMed Central

Choisy, Stéphanie C; Cheng, Hongwei; Orchard, Clive H; James, Andrew F; Hancox, Jules C

2015-01-01

The atrioventricular node (AVN) is a key component of the cardiac pacemaker-conduction system. This study investigated the electrophysiology of cells isolated from the AVN region of adult mouse hearts, and compared murine ionic current magnitude with that of cells from the more extensively studied rabbit AVN. Whole-cell patch-clamp recordings of ionic currents, and perforated-patch recordings of action potentials (APs), were made at 35–37°C. Hyperpolarizing voltage commands from −40 mV elicited a Ba2+-sensitive inward rectifier current that was small at diastolic potentials. Some cells (Type 1; 33.4 ± 2.2 pF; n = 19) lacked the pacemaker current, If, whilst others (Type 2; 34.2 ± 1.5 pF; n = 21) exhibited a clear If, which was larger than in rabbit AVN cells. On depolarization from −40 mV L-type Ca2+ current, ICa,L, was elicited with a half maximal activation voltage (V0.5) of −7.6 ± 1.2 mV (n = 24). ICa,L density was smaller than in rabbit AVN cells. Rapid delayed rectifier (IKr) tail currents sensitive to E-4031 (5 μmol/L) were observed on repolarization to −40 mV, with an activation V0.5 of −10.7 ± 4.7 mV (n = 8). The IKr magnitude was similar in mouse and rabbit AVN. Under Na-Ca exchange selective conditions, mouse AVN cells exhibited 5 mmol/L Ni-sensitive exchange current that was inwardly directed negative to the holding potential (−40 mV). Spontaneous APs (5.2 ± 0.5 sec−1; n = 6) exhibited an upstroke velocity of 37.7 ± 16.2 V/s and ceased following inhibition of sarcoplasmic reticulum Ca2+ release by 1 μmol/L ryanodine, implicating intracellular Ca2+ cycling in murine AVN cell electrogenesis. PMID:26607172

T wave inversions in athletes: a variety of scenarios.

PubMed

Stein, Ricardo; Malhotra, Aneil

2015-01-01

Athletic intensive exercise is associated with repolarization changes affecting the ST-segment and T-wave morphology. The prevalence and distribution of these alterations are influenced by several demographic factors. One of the most challenging conundrums for both the cardiologist and the sports medicine physician is the correct interpretation of these repolarization changes to prevent an erroneous diagnosis with potentially serious consequences. A 12-lead electrocardiogram (ECG) demonstrating inverted T-waves may represent the first and only sign of such inherited heart muscle diseases, and may precede the detection of any structural changes in the heart, however, T-wave inversion in leads V1-V4 in black athletes may represent ethnic variation which is exaggerated by exercise. Copyright © 2015 Elsevier Inc. All rights reserved.

Minimal T-wave representation and its use in the assessment of drug arrhythmogenicity.

PubMed

Shakibfar, Saeed; Graff, Claus; Kanters, Jørgen K; Nielsen, Jimmi; Schmidt, Samuel; Struijk, Johannes J

2017-05-01

Recently, numerous models and techniques have been developed for analyzing and extracting features from the T wave which could be used as biomarkers for drug-induced abnormalities. The majority of these techniques and algorithms use features that determine readily apparent characteristics of the T wave, such as duration, area, amplitude, and slopes. In the present work the T wave was down-sampled to a minimal rate, such that a good reconstruction was still possible. The entire T wave was then used as a feature vector to assess drug-induced repolarization effects. The ability of the samples or combinations of samples obtained from the minimal T-wave representation to correctly classify a group of subjects before and after receiving d,l-sotalol 160 mg and 320 mg was evaluated using a linear discriminant analysis (LDA). The results showed that a combination of eight samples from the minimal T-wave representation can be used to identify normal from abnormal repolarization significantly better compared to the heart rate-corrected QT interval (QTc). It was further indicated that the interval from the peak of the T wave to the end of the T wave (Tpe) becomes relatively shorter after I K r inhibition by d,l-sotalol and that the most pronounced repolarization changes were present in the ascending segment of the minimal T-wave representation. The minimal T-wave representation can potentially be used as a new tool to identify normal from abnormal repolarization in drug safety studies. © 2016 Wiley Periodicals, Inc.

Intermittent atrial tachycardia promotes repolarization alternans and conduction slowing during rapid rates, and increases susceptibility to atrial fibrillation in a free-behaving sheep model.

PubMed

Monigatti-Tenkorang, Joanna; Jousset, Florian; Pascale, Patrizio; Vesin, Jean-Marc; Ruchat, Patrick; Fromer, Martin; Narayan, Sanjiv M; Pruvot, Etienne

2014-04-01

Paroxysmal atrial fibrillation (AF) may be triggered by intermittent atrial tachycardia, and ultimately lead to persistent AF. However, the mechanisms by which intermittent atrial tachycardia promotes sustained AF are not well understood. Eight sheep were chronically implanted with 2 pacemakers for the recording of broadband right atrial unipolar electrograms, and for the delivery of electrophysiological stimulation protocols and intermittent right atrial tachycardia. Right atrial kinetics of activation recovery interval (ARI) as a surrogate for action potential duration, of conduction time and velocity, and of repolarization alternans were analyzed at incremental pacing rates during the remodeling process induced by weeks of intermittent atrial tachycardia until the development of sustained AF. Intermittent atrial tachycardia decreased ARI and blunted its rate adaptation, facilitated atrial capture, and slowed conduction at high rates, and increased susceptibility to pacing-induced AF. In spite of blunted ARI rate adaptation, right atrial repolarization alternans was maintained during remodeling, and further increased in magnitude just before rapid pacing-induced AF. This study suggests that weeks of intermittent right atrial tachycardia result in a gradual electrical remodeling favorable for wavebreaks and reentry that may facilitate fibrillation. © 2014 Wiley Periodicals, Inc.

Effect of clebopride, antidopaminergic gastrointestinal prokinetics, on cardiac repolarization.

PubMed

Kim, Ki-Suk; Shin, Won-Ho; Park, Sang-joon; Kim, Eun-Joo

2007-01-01

The inhibition of the potassium current I(Kr) and QT prolongation has been known to be associated with drug-induced torsades de pointes arrhythmias (TdP) and sudden cardiac death. In this study, the authors investigated the cardiac electrophysiological effects of clebopride, a class of antidopaminergic gastrointestinal prokinetic, that has been reported to prolong the QT interval by using the conventional microelectrode recording techniques in isolated rabbit Purkinje fiber and whole-cell patch clamp techniques in human ether-à-go-go-related gene (hERG)-stably transfected Chinese hamster ovarian (CHO) cells. Clebopride at 10 microM significantly decreased the Vmax of phase 0 depolarization (p < .05) and significantly prolonged the action potential duration at 90% repolarization (APD90) (p < .01), whereas the action potential duration at 50% repolarization (APD50) was not prolonged. For hERG potassium channel currents, the IC50 value was 0.62 +/- 0.30 microM. Clebopride was found to have no effect on sodium channel currents. When these results were compared with Cmax (1.02 nM) of clinical dosage (1 mg, [p.o.]), it can be suggested that clebopride is safe at the clinical dosage of 1 mg from the electrophysiological aspect. These findings indicate that clebopride, an antidopaminergic gastrointestinal prokinetic drug, may provide a sufficient "safety factor" in terms of the electrophysiological threshold concentration. But, in a supratherapeutic concentration that might possibly be encountered during overdose or impaired metabolism, clebopride may have torsadogenic potency.

Action potential-based MEA platform for in vitro screening of drug-induced cardiotoxicity using human iPSCs and rat neonatal myocytes.

PubMed

Jans, Danny; Callewaert, Geert; Krylychkina, Olga; Hoffman, Luis; Gullo, Francesco; Prodanov, Dimiter; Braeken, Dries

2017-09-01

Drug-induced cardiotoxicity poses a negative impact on public health and drug development. Cardiac safety pharmacology issues urged for the preclinical assessment of drug-induced ventricular arrhythmia leading to the design of several in vitro electrophysiological screening assays. In general, patch clamp systems allow for intracellular recordings, while multi-electrode array (MEA) technology detect extracellular activity. Here, we demonstrate a complementary metal oxide semiconductor (CMOS)-based MEA system as a reliable platform for non-invasive, long-term intracellular recording of cardiac action potentials at high resolution. Quinidine (8 concentrations from 10 -7 to 2.10 -5 M) and verapamil (7 concentrations from 10 -11 to 10 -5 M) were tested for dose-dependent responses in a network of cardiomyocytes. Electrophysiological parameters, such as the action potential duration (APD), rates of depolarization and repolarization and beating frequency were assessed. In hiPSC, quinidine prolonged APD with EC 50 of 2.2·10 -6 M. Further analysis indicated a multifactorial action potential prolongation by quinidine: (1) decreasing fast repolarization with IC 50 of 1.1·10 -6 M; (2) reducing maximum upstroke velocity with IC 50 of 2.6·10 -6 M; and (3) suppressing spontaneous activity with EC 50 of 3.8·10 -6 M. In rat neonatal cardiomyocytes, verapamil blocked spontaneous activity with EC 50 of 5.3·10 -8 M and prolonged the APD with EC 50 of 2.5·10 -8 M. Verapamil reduced rates of fast depolarization and repolarization with IC 50 s of 1.8 and 2.2·10 -7 M, respectively. In conclusion, the proposed action potential-based MEA platform offers high quality and stable long-term recordings with high information content allowing to characterize multi-ion channel blocking drugs. We anticipate application of the system as a screening platform to efficiently and cost-effectively test drugs for cardiac safety. Copyright © 2017 Elsevier Inc. All rights reserved.

Kv2 Channel Regulation of Action Potential Repolarization and Firing Patterns in Superior Cervical Ganglion Neurons and Hippocampal CA1 Pyramidal Neurons

PubMed Central

Liu, Pin W.

2014-01-01

Kv2 family “delayed-rectifier” potassium channels are widely expressed in mammalian neurons. Kv2 channels activate relatively slowly and their contribution to action potential repolarization under physiological conditions has been unclear. We explored the function of Kv2 channels using a Kv2-selective blocker, Guangxitoxin-1E (GxTX-1E). Using acutely isolated neurons, mixed voltage-clamp and current-clamp experiments were done at 37°C to study the physiological kinetics of channel gating and action potentials. In both rat superior cervical ganglion (SCG) neurons and mouse hippocampal CA1 pyramidal neurons, 100 nm GxTX-1E produced near-saturating block of a component of current typically constituting ∼60–80% of the total delayed-rectifier current. GxTX-1E also reduced A-type potassium current (IA), but much more weakly. In SCG neurons, 100 nm GxTX-1E broadened spikes and voltage clamp experiments using action potential waveforms showed that Kv2 channels carry ∼55% of the total outward current during action potential repolarization despite activating relatively late in the spike. In CA1 neurons, 100 nm GxTX-1E broadened spikes evoked from −70 mV, but not −80 mV, likely reflecting a greater role of Kv2 when other potassium channels were partially inactivated at −70 mV. In both CA1 and SCG neurons, inhibition of Kv2 channels produced dramatic depolarization of interspike voltages during repetitive firing. In CA1 neurons and some SCG neurons, this was associated with increased initial firing frequency. In all neurons, inhibition of Kv2 channels depressed maintained firing because neurons entered depolarization block more readily. Therefore, Kv2 channels can either decrease or increase neuronal excitability depending on the time scale of excitation. PMID:24695716

New micro waveforms firstly recorded on electrocardiogram in human.

PubMed

Liu, Renguang; Chang, Qinghua; Chen, Juan

2015-10-01

In our study, not only the P-QRS-T waves but also the micro-wavelets before QRS complex (in P wave and PR segment) and after QRS complex (ST segment and upstroke of T wave) were first to be identified on surface electrocardiogram in human by the "new electrocardiogram" machine (model PHS-A10) according to conventional 12-lead electrocardiogram connection methods. By comparison to the conventional electrocardiogram in 100 cases of healthy individuals and several patients with arrhythmias, we have found that the wavelets before P wave theoretically reflected electrical activity of sinus node and the micro-wavelets before QRS complex may be related to atrioventricular conduction system (atrioventricular node, His bundle and bundle branch) potentials. Noninvasive atrioventricular node and His bundle potential tracing will contribute to differentiation of the origin of wide QRS and the location of the atrioventricular block. We also have found that the wavelets after QRS complex may be associated with phase 2 and 3 repolarization of ventricular action potential, which will further reveal ventricular repolarization changes. Copyright © 2015 Elsevier Ltd. All rights reserved.

A case of brugada syndrome presenting with ventricular fibrillation storm and prominent early repolarization.

PubMed

Iizuka, Chifumi; Sato, Masahito; Kitazawa, Hitoshi; Ikeda, Yoshio; Okabe, Masaaki; Kugiyama, Kiyotaka; Aizawa, Yoshifusa

2016-01-01

A 21-year-old man developed ventricular fibrillation (VF) while drinking alcohol and was admitted to our hospital. An electrocardiogram (ECG) on admission revealed remarkably prominent slurs on the terminal part of QRS complexes in the left precordial leads and a coved type ST elevation at higher intercostal spaces. After hypothermia therapy, he underwent implantation of an implantable cardioverter-defibrillator (ICD). Standard twelve-lead follow-up ECGs revealed early repolarization pattern and an intermittent coved type ST elevation. When the coved type ST elevation appeared, the early repolarization pattern in the inferior and left precordial leads was attenuated. Prominent early repolarization pattern was the most likely trigger of the VF storm in this Brugada patient. Copyright © 2016 Elsevier Inc. All rights reserved.

Can non‐clinical repolarization assays predict the results of clinical thorough QT studies? Results from a research consortium

PubMed Central

Park, Eunjung; Gintant, Gary A; Bi, Daoqin; Kozeli, Devi; Pettit, Syril D; Skinner, Matthew; Willard, James; Wisialowski, Todd; Koerner, John; Valentin, Jean‐Pierre

2018-01-01

Background and Purpose Translation of non‐clinical markers of delayed ventricular repolarization to clinical prolongation of the QT interval corrected for heart rate (QTc) (a biomarker for torsades de pointes proarrhythmia) remains an issue in drug discovery and regulatory evaluations. We retrospectively analysed 150 drug applications in a US Food and Drug Administration database to determine the utility of established non‐clinical in vitro IKr current human ether‐à‐go‐go‐related gene (hERG), action potential duration (APD) and in vivo (QTc) repolarization assays to detect and predict clinical QTc prolongation. Experimental Approach The predictive performance of three non‐clinical assays was compared with clinical thorough QT study outcomes based on free clinical plasma drug concentrations using sensitivity and specificity, receiver operating characteristic (ROC) curves, positive (PPVs) and negative predictive values (NPVs) and likelihood ratios (LRs). Key Results Non‐clinical assays demonstrated robust specificity (high true negative rate) but poor sensitivity (low true positive rate) for clinical QTc prolongation at low‐intermediate (1×–30×) clinical exposure multiples. The QTc assay provided the most robust PPVs and NPVs (ability to predict clinical QTc prolongation). ROC curves (overall test accuracy) and LRs (ability to influence post‐test probabilities) demonstrated overall marginal performance for hERG and QTc assays (best at 30× exposures), while the APD assay demonstrated minimal value. Conclusions and Implications The predictive value of hERG, APD and QTc assays varies, with drug concentrations strongly affecting translational performance. While useful in guiding preclinical candidates without clinical QT prolongation, hERG and QTc repolarization assays provide greater value compared with the APD assay. PMID:29181850

Left ventricular epicardial activation increases transmural dispersion of repolarization in healthy, long QT, and dilated cardiomyopathy dogs.

PubMed

Bai, Rong; Lü, Jiagao; Pu, Jun; Liu, Nian; Zhou, Qiang; Ruan, Yanfei; Niu, Huiyan; Zhang, Cuntai; Wang, Lin; Kam, Ruth

2005-10-01

Benefits of cardiac resynchronization therapy (CRT) are well established. However, less is understood concerning its effects on myocardial repolarization and the potential proarrhythmic risk. Healthy dogs (n = 8) were compared to a long QT interval (LQT) model (n = 8, induced by cesium chloride, CsCl) and a dilated cardiomyopathy with congestive heart failure (DCM-CHF, induced by rapid ventricular pacing, n = 5). Monophasic action potential (MAP) recordings were obtained from the subendocardium, midmyocardium, subepicardium, and the transmural dispersion of repolarization (TDR) was calculated. The QT interval and the interval from the peak to the end of the T wave (T(p-e)) were measured. All these characteristics were compared during left ventricular epicardial (LV-Epi), right ventricular endocardial (RV-Endo), and biventricular (Bi-V) pacing. In healthy dogs, TDR prolonged to 37.54 ms for Bi-V pacing and to 47.16 ms for LV-Epi pacing as compared to 26.75 ms for RV-Endo pacing (P < 0.001), which was parallel to an augmentation in T(p-e) interval (Bi-V pacing, 64.29 ms; LV-Epi pacing, 57.89 ms; RV-Endo pacing, 50.29 ms; P < 0.01). During CsCl exposure, Bi-V and LV-Epi pacing prolonged MAPD, TDR, and T(p-e) interval as compared to RV-Endo pacing. The midmyocardial MAPD (276.30 ms vs 257.35 ms, P < 0.0001) and TDR (33.80 ms vs 27.58 ms, P=0.002) were significantly longer in DCM-CHF dogs than those in healthy dogs. LV-Epi and Bi-V pacing further prolonged the MAPD and TDR in this model. LV-Epi and Bi-V pacing result in prolongation of ventricular repolarization time, and increase of TDR accounted for a parallel augmentation of the T(p-e) interval, which provides evidence that T(p-e) interval accurately represents TDR. These effects are magnified in the LQT and DCM-CHF canine models in addition to their intrinsic transmural heterogeneity in the intact heart. This mechanism may contribute to the development of malignant ventricular arrhythmias, such as torsades de pointes (TdP) in congestive heart failure (CHF) patients treated with CRT.

Coronary Artery Disease Alters Ventricular Repolarization Dynamics in Type 2 Diabetes

NASA Technical Reports Server (NTRS)

Vrtovec, Bojan; Sinkovec, Matjaz; Starc, Vito; Radovancevic, Branislav; Schlegel, Todd T.

2005-01-01

Ventricular repolarization dynamics (VRD) is an important predictor of outcome in diabetes. We examined the potential impact of coronary artery disease (CAD) on VRD in type 2 diabetic patients. We recorded 5-min high-resolution resting electrocardiograms (ECG) in 38 diabetic patients undergoing elective coronary angiography, and in 38 age- and gender- matched apparently healthy subjects (Controls). Using leads I and II, time-domain indices of VRD were calculated. Coronary angiography was regarded as positive if a 350% stenosis was found. Angiography was positive in 21 diabetic patients (55%). Patients with CAD had a significantly higher degree of VRD than Controls (SDNN(QT): 15.81+/-7.22 ms vs. 8.94+/-6.04 ms; P <0.001, rMSSD(QT): 21.02k7.07 ms vs. 11.18k7.45 ms; P <0.001). VRD in diabetic patients with negative angiograms did not differ from VRD in Controls (SDNN(QT): 8.94+/-6.04 ms vs. 7.44+/-5.72 ms; P=0.67, rMSSD(QT): 11.18+/-7.45 ms vs. 10.22+/-5.35 ms; P=O. 82). CAD increases VRD in patients with type 2 diabetes. Therefore, changes in ventricular repolarization in diabetic patients may be due to silent CAD rather than to diabetes per se.

The Role of Spatial Dispersion of Repolarization in Inherited and Acquired Sudden Cardiac Death Syndromes

PubMed Central

Antzelevitch, Charles

2007-01-01

This review examines the role of spatial electrical heterogeneity within ventricular myocardium on the function of the heart in health and disease. The cellular basis for transmural dispersion of repolarization (TDR) is reviewed and the hypothesis that amplification of spatial dispersion of repolarization underlies the development of life-threatening ventricular arrhythmias associated with inherited ion channelopathies is evaluated. The role of TDR in the long QT, short QT and Brugada syndromes as well as catecholaminergic polymorphic ventricular tachycardia (CPVT) are critically examined. In the long QT Syndrome, amplification of TDR is often secondary to preferential prolongation of the action potential duration (APD) of M cells, whereas in the Brugada Syndrome, it is thought to be due to selective abbreviation of the APD of right ventricular (RV) epicardium. Preferential abbreviation of APD of either endocardium or epicardium appears to be responsible for amplification of TDR in the short QT syndrome. In catecholaminergic polymorphic VT, reversal of the direction of activation of the ventricular wall is responsible for the increase in TDR. In conclusion, the long QT, short QT, Brugada and catecholaminergic polymorphic VT syndromes are pathologies with very different phenotypes and etiologies, but which share a common final pathway in causing sudden cardiac death. PMID:17586620

Therapeutic effects of a taurine-magnesium coordination compound on experimental models of type 2 short QT syndrome.

PubMed

An, Meng-Yao; Sun, Kai; Li, Yan; Pan, Ying-Ying; Yin, Yong-Qiang; Kang, Yi; Sun, Tao; Wu, Hong; Gao, Wei-Zhen; Lou, Jian-Shi

2018-03-01

Short QT syndrome (SQTS) is a genetic arrhythmogenic disease that can cause malignant arrhythmia and sudden cardiac death. The current therapies for SQTS have application restrictions. We previously found that Mg· (NH 2 CH 2 CH 2 SO 3 )2· H 2 O, a taurine-magnesium coordination compound (TMCC) exerted anti-arrhythmic effects with low toxicity. In this study we established 3 different models to assess the potential anti-arrhythmic effects of TMCC on type 2 short QT syndrome (SQT2). In Langendorff guinea pig-perfused hearts, perfusion of pinacidil (20 μmol/L) significantly shortened the QT interval and QTpeak and increased rTp-Te (P<0.05 vs control). Subsequently, perfusion of TMCC (1-4 mmol/L) dose-dependently increased the QT interval and QTpeak (P<0.01 vs pinacidil). TMCC perfusion also reversed the rTp-Te value to the normal range. In guinea pig ventricular myocytes, perfusion of trapidil (1 mmol/L) significantly shortened the action potential duration at 50% (APD 50 ) and 90% repolarization (APD 90 ), which was significantly reversed by TMCC (0.01-1 mmol/L, P<0.05 vs trapidil). In HEK293 cells that stably expressed the outward delayed rectifier potassium channels (I Ks ), perfusion of TMCC (0.01-1 mmol/L) dose-dependently inhibited the IKs current with an IC 50 value of 201.1 μmol/L. The present study provides evidence that TMCC can extend the repolarization period and inhibit the repolarizing current, I Ks , thereby representing a therapeutic candidate for ventricular arrhythmia in SQT2.

Reconstruction of the action potential of ventricular myocardial fibres

PubMed Central

Beeler, G. W.; Reuter, H.

1977-01-01

1. A mathematical model of membrane action potentials of mammalian ventricular myocardial fibres is described. The reconstruction model is based as closely as possible on ionic currents which have been measured by the voltage-clamp method. 2. Four individual components of ionic current were formulated mathematically in terms of Hodgkin—Huxley type equations. The model incorporates two voltage- and time-dependent inward currents, the excitatory inward sodium current, iNa, and a secondary or slow inward current, is, primarily carried by calcium ions. A time-independent outward potassium current, iK1, exhibiting inward-going rectification, and a voltage- and time-dependent outward current, ix1, primarily carried by potassium ions, are further elements of the model. 3. The iNa is primarily responsible for the rapid upstroke of the action potential, while the other current components determine the configuration of the plateau of the action potential and the re-polarization phase. The relative importance of inactivation of is and of activation of ix1 for termination of the plateau is evaluated by the model. 4. Experimental phenomena like slow recovery of the sodium system from inactivation, frequency dependence of the action potential duration, all-or-nothing re-polarization, membrane oscillations are adequately described by the model. 5. Possible inadequacies and shortcomings of the model are discussed. PMID:874889

Re-polarization of nuclear spins using selective SABRE-INEPT.

PubMed

Knecht, Stephan; Kiryutin, Alexey S; Yurkovskaya, Alexandra V; Ivanov, Konstantin L

2018-02-01

A method is proposed for significant improvement of NMR pulse sequences used in high-field SABRE (Signal Amplification By Reversible Exchange) experiments. SABRE makes use of spin order transfer from parahydrogen (pH 2 , the H 2 molecule in its singlet spin state) to a substrate in a transient organometallic Ir-based complex. The technique proposed here utilizes "re-polarization", i.e., multiple application of an NMR pulse sequence used for spin order transfer. During re-polarization only the form of the substrate, which is bound to the complex, is excited by selective NMR pulses and the resulting polarization is transferred to the free substrate via chemical exchange. Owing to the fact that (i) only a small fraction of the substrate molecules is in the bound form and (ii) spin relaxation of the free substrate is slow, the re-polarization scheme provides greatly improved NMR signal enhancement, ε. For instance, when pyridine is used as a substrate, single use of the SABRE-INEPT sequence provides ε≈260 for 15 N nuclei, whereas SABRE-INEPT with re-polarization yields ε>2000. We anticipate that the proposed method is useful for achieving maximal NMR enhancement with spin hyperpolarization techniques. Copyright © 2017 Elsevier Inc. All rights reserved.

Re-polarization of nuclear spins using selective SABRE-INEPT

NASA Astrophysics Data System (ADS)

Knecht, Stephan; Kiryutin, Alexey S.; Yurkovskaya, Alexandra V.; Ivanov, Konstantin L.

2018-02-01

A method is proposed for significant improvement of NMR pulse sequences used in high-field SABRE (Signal Amplification By Reversible Exchange) experiments. SABRE makes use of spin order transfer from parahydrogen (pH2, the H2 molecule in its singlet spin state) to a substrate in a transient organometallic Ir-based complex. The technique proposed here utilizes "re-polarization", i.e., multiple application of an NMR pulse sequence used for spin order transfer. During re-polarization only the form of the substrate, which is bound to the complex, is excited by selective NMR pulses and the resulting polarization is transferred to the free substrate via chemical exchange. Owing to the fact that (i) only a small fraction of the substrate molecules is in the bound form and (ii) spin relaxation of the free substrate is slow, the re-polarization scheme provides greatly improved NMR signal enhancement, ε . For instance, when pyridine is used as a substrate, single use of the SABRE-INEPT sequence provides ε ≈ 260 for 15N nuclei, whereas SABRE-INEPT with re-polarization yields ε > 2000 . We anticipate that the proposed method is useful for achieving maximal NMR enhancement with spin hyperpolarization techniques.

A novel predictive pharmacokinetic/pharmacodynamic model of repolarization prolongation derived from the effects of terfenadine, cisapride and E-4031 in the conscious chronic av node--ablated, His bundle-paced dog.

PubMed

Nolan, Emily R; Feng, Meihua Rose; Koup, Jeffrey R; Liu, Jing; Turluck, Daniel; Zhang, Yiqun; Paulissen, Jerome B; Olivier, N Bari; Miller, Teresa; Bailie, Marc B

2006-01-01

Terfenadine, cisapride, and E-4031, three drugs that prolong ventricular repolarization, were selected to evaluate the sensitivity of the conscious chronic atrioventricular node--ablated, His bundle-paced Dog for defining drug induced cardiac repolarization prolongation. A novel predictive pharmacokinetic/pharmacodynamic model of repolarization prolongation was generated from these data. Three male beagle dogs underwent radiofrequency AV nodal ablation, and placement of a His bundle-pacing lead and programmable pacemaker under anesthesia. Each dog was restrained in a sling for a series of increasing dose infusions of each drug while maintained at a constant heart rate of 80 beats/min. RT interval, a surrogate for QT interval in His bundle-paced dogs, was recorded throughout the experiment. E-4031 induced a statistically significant RT prolongation at the highest three doses. Cisapride resulted in a dose-dependent increase in RT interval, which was statistically significant at the two highest doses. Terfenadine induced a dose-dependent RT interval prolongation with a statistically significant change occurring only at the highest dose. The relationship between drug concentration and RT interval change was described by a sigmoid E(max) model with an effect site. Maximum RT change (E(max)), free drug concentration at half of the maximum effect (EC(50)), and free drug concentration associated with a 10 ms RT prolongation (EC(10 ms)) were estimated. A linear correlation between EC(10 ms) and HERG IC(50) values was identified. The conscious dog with His bundle-pacing detects delayed cardiac repolarization related to I(Kr) inhibition, and detects repolarization change induced by drugs with activity at multiple ion channels. A clinically relevant sensitivity and a linear correlation with in vitro HERG data make the conscious His bundle-paced dog a valuable tool for detecting repolarization effect of new chemical entities.

Early changes in myocardial repolarization and coronary perfusion after cardiopulmonary bypass surgery for ASD repair in children.

PubMed

Aburawi, Elhadi H; Souid, Abdul-Kader; Liuba, Petru; Zoubeidi, Taoufik; Pesonen, Erkki

2013-09-10

In adults, impaired myocardial repolarization and increased risk of arrhythmia are known consequences of open heart surgery. Little is known, however, about post-operative consequences of cardiopulmonary bypass surgery in children. The aim of this study was to assess ventricular repolarization and coronary perfusion after bypass surgery for atrial septal defect (ASD) repair in children. Twelve patients with ASD were assessed one day before and 5-6 days after ASD repair. Myocardial repolarization (corrected QT interval, QTc, QT dispersion, QTd, and PQ interval) was determined on 12-lead electrocardiograms. Coronary flow in proximal left anterior descending artery (peak flow velocity in diastole, PFVd) was assessed by transthoracic Doppler echocardiography. Ten of the 12 (83%) children had normal myocardial repolarization before and after surgery. After surgery, QTc increased 1-9% in 5 (42%) patients, decreased 2-11% in 5 (42%) patients and did not change in 2 (16%) patients. Post-op QTc positively correlated with bypass time (R=0.686, p=0.014) and changes in PFVd (R=0.741, p=0.006). After surgery, QTd increased 33-67% in 4 (33%) patients, decreased 25-50% in 6 patients (50%) and did not change in 2 (16%) patients. After surgery, PQ interval increased 5-30% in 4 (33%) patients, decreased 4-29% in 6 (50%) patients and did not change in 1 (8%) patient. Post-op PQ positively correlated with bypass time (R=0.636, p=0.027). As previously reported, PFVd significantly increased after surgery (p<0.001). Changes in QTc, PQ and PFVd are common in young children undergoing surgery for ASD repair. Post-op QTc significantly correlates with bypass time, suggesting prolonged cardiopulmonary bypass may impair ventricular repolarization. Post-op QTc significantly correlates with PFVd changes, suggesting increased coronary flow may also impair ventricular repolarization. The clinical significance and reversibility of these alternations require further investigations.

Rivaroxaban modulates electrical and mechanical characteristics of left atrium

PubMed Central

2013-01-01

Background Rivaroxaban reduces stroke in patients with atrial fibrillation (AF). Left atrium (LA) plays a critical role in the pathophysiology of AF. However, the electromechanical effects of rivaroxaban on LA are not clear. Results Conventional microelectrodes and a whole-cell patch-clamp were used to record the action potentials (APs) and ionic currents in rabbit LA preparations and isolated single LA cardiomyocytes before and after the administration of rivaroxaban. Rivaroxaban (10, 30, 100, and 300 nM) concentration-dependently reduced LA (n = 7) AP durations at 90% repolarization (APD90) from 76 ± 2 to 79 ± 3, 67 ± 4 (P < 0.05, vs. control), 59 ± 5, (P < 0.01, vs. control), and 56 ± 4 ms (P < 0.005, vs. control), respectively. Rivaroxaban (10, 30, 100, and 300 nM) concentration-dependently increased the LA (n = 7) diastolic tension by 351 ± 69 (P < 0.05, vs. control), 563 ± 136 (P < 0.05, vs. control), 582 ± 119 (P < 0.05, vs. control), and 603 ± 108 mg (P < 0.005, vs. control), respectively, but did not change LA contractility. In the presence of L-NAME (100 μM) and indomethacin (10 μM), additional rivaroxaban (300 nM) treatment did not significantly further increase the LA (n = 7) diastolic tension, but shortened the APD90 from 73 ± 2 to 60 ± 6 ms (P < 0.05, vs. control). Rivaroxaban (100 nM) increased the L-type calcium current and ultra-rapid delayed rectifier potassium current, but did not change the transient outward potassium current in isolated LA cardiomyocytes. Conclusions Rivaroxaban modulates LA electrical and mechanical characteristics with direct ionic current effects. PMID:23497194

Increase in Cardiac Ischemia-Reperfusion Injuries in Opa1+/- Mouse Model

PubMed Central

Fauconnier, Jérémy; Cellier, Laura; Tamareille, Sophie; Gharib, Abdallah; Chevrollier, Arnaud; Loufrani, Laurent; Grenier, Céline; Kamel, Rima; Sarzi, Emmanuelle; Lacampagne, Alain; Ovize, Michel; Henrion, Daniel; Reynier, Pascal; Lenaers, Guy; Mirebeau-Prunier, Delphine

2016-01-01

Background Recent data suggests the involvement of mitochondrial dynamics in cardiac ischemia/reperfusion (I/R) injuries. Whilst excessive mitochondrial fission has been described as detrimental, the role of fusion proteins in this context remains uncertain. Objectives To investigate whether Opa1 (protein involved in mitochondrial inner-membrane fusion) deficiency affects I/R injuries. Methods and Results We examined mice exhibiting Opa1delTTAG mutations (Opa1+/-), showing 70% Opa1 protein expression in the myocardium as compared to their wild-type (WT) littermates. Cardiac left-ventricular systolic function assessed by means of echocardiography was observed to be similar in 3-month-old WT and Opa1+/- mice. After subjection to I/R, infarct size was significantly greater in Opa1+/- than in WTs both in vivo (43.2±4.1% vs. 28.4±3.5%, respectively; p<0.01) and ex vivo (71.1±3.2% vs. 59.6±8.5%, respectively; p<0.05). No difference was observed in the expression of other main fission/fusion protein, oxidative phosphorylation, apoptotic markers, or mitochondrial permeability transition pore (mPTP) function. Analysis of calcium transients in isolated ventricular cardiomyocytes demonstrated a lower sarcoplasmic reticulum Ca2+ uptake, whereas cytosolic Ca2+ removal from the Na+/Ca2+ exchanger (NCX) was increased, whilst SERCA2a, phospholamban, and NCX protein expression levels were unaffected in Opa1+/- compared to WT mice. Simultaneous whole-cell patch-clamp recordings of mitochondrial Ca2+ movements and ventricular action potential (AP) showed impairment of dynamic mitochondrial Ca2+ uptake and a marked increase in the AP late repolarization phase in conjunction with greater occurrence of arrhythmia in Opa1+/- mice. Conclusion Opa1 deficiency was associated with increased sensitivity to I/R, imbalance in dynamic mitochondrial Ca2+ uptake, and subsequent increase in NCX activity. PMID:27723783

Effects of tacrolimus on action potential configuration and transmembrane ion currents in canine ventricular cells.

PubMed

Szabó, László; Szentandrássy, Norbert; Kistamás, Kornél; Hegyi, Bence; Ruzsnavszky, Ferenc; Váczi, Krisztina; Horváth, Balázs; Magyar, János; Bányász, Tamás; Pál, Balázs; Nánási, Péter P

2013-03-01

Tacrolimus is a commonly used immunosuppressive agent which causes cardiovascular complications, e.g., hypertension and hypertrophic cardiomyopathy. In spite of it, there is little information on the cellular cardiac effects of the immunosuppressive agent tacrolimus in larger mammals. In the present study, therefore, the concentration-dependent effects of tacrolimus on action potential morphology and the underlying ion currents were studied in canine ventricular cardiomyocytes. Standard microelectrode, conventional whole cell patch clamp, and action potential voltage clamp techniques were applied in myocytes enzymatically dispersed from canine ventricular myocardium. Tacrolimus (3-30 μM) caused a concentration-dependent reduction of maximum velocity of depolarization and repolarization, action potential amplitude, phase-1 repolarization, action potential duration, and plateau potential, while no significant change in the resting membrane potential was observed. Conventional voltage clamp experiments revealed that tacrolimus concentrations ≥3 μM blocked a variety of ion currents, including I(Ca), I(to), I(K1), I(Kr), and I(Ks). Similar results were obtained under action potential voltage clamp conditions. These effects of tacrolimus developed rapidly and were fully reversible upon washout. The blockade of inward currents with the concomitant shortening of action potential duration in canine myocytes is the opposite of those observed previously with tacrolimus in small rodents. It is concluded that although tacrolimus blocks several ion channels at higher concentrations, there is no risk of direct interaction with cardiac ion channels when applying tacrolimus in therapeutic concentrations.

Neuropathic pain in experimental autoimmune neuritis is associated with altered electrophysiological properties of nociceptive DRG neurons.

PubMed

Taha, Omneya; Opitz, Thoralf; Mueller, Marcus; Pitsch, Julika; Becker, Albert; Evert, Bernd Oliver; Beck, Heinz; Jeub, Monika

2017-11-01

Guillain-Barré syndrome (GBS) is an acute, immune-mediated polyradiculoneuropathy characterized by rapidly progressive paresis and sensory disturbances. Moderate to severe and often intractable neuropathic pain is a common symptom of GBS, but its underlying mechanisms are unknown. Pathology of GBS is classically attributed to demyelination of large, myelinated peripheral fibers. However, there is increasing evidence that neuropathic pain in GBS is associated with impaired function of small, unmyelinated, nociceptive fibers. We therefore examined the functional properties of small DRG neurons, the somata of nociceptive fibers, in a rat model of GBS (experimental autoimmune neuritis=EAN). EAN rats developed behavioral signs of neuropathic pain. This was accompanied by a significant shortening of action potentials due to a more rapid repolarization and an increase in repetitive firing in a subgroup of capsaicin-responsive DRG neurons. Na + current measurements revealed a significant increase of the fast TTX-sensitive current and a reduction of the persistent TTX-sensitive current component. These changes of Na + currents may account for the significant decrease in AP duration leading to an overall increase in excitability and are therefore possibly directly linked to pathological pain behavior. Thus, like in other animal models of neuropathic and inflammatory pain, Na + channels seem to be crucially involved in the pathology of GBS and may constitute promising targets for pain modulating pharmaceuticals. Copyright © 2017 Elsevier Inc. All rights reserved.

ParamAP: Standardized Parameterization of Sinoatrial Node Myocyte Action Potentials.

PubMed

Rickert, Christian; Proenza, Catherine

2017-08-22

Sinoatrial node myocytes act as cardiac pacemaker cells by generating spontaneous action potentials (APs). Much information is encoded in sinoatrial AP waveforms, but both the analysis and the comparison of AP parameters between studies is hindered by the lack of standardized parameter definitions and the absence of automated analysis tools. Here we introduce ParamAP, a standalone cross-platform computational tool that uses a template-free detection algorithm to automatically identify and parameterize APs from text input files. ParamAP employs a graphic user interface with automatic and user-customizable input modes, and it outputs data files in text and PDF formats. ParamAP returns a total of 16 AP waveform parameters including time intervals such as the AP duration, membrane potentials such as the maximum diastolic potential, and rates of change of the membrane potential such as the diastolic depolarization rate. ParamAP provides a robust AP detection algorithm in combination with a standardized AP parameter analysis over a wide range of AP waveforms and firing rates, owing in part to the use of an iterative algorithm for the determination of the threshold potential and the diastolic depolarization rate that is independent of the maximum upstroke velocity, a parameter that can vary significantly among sinoatrial APs. Because ParamAP is implemented in Python 3, it is also highly customizable and extensible. In conclusion, ParamAP is a powerful computational tool that facilitates quantitative analysis and enables comparison of sinoatrial APs by standardizing parameter definitions and providing an automated work flow. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Anodal sensory nerve action potentials: From physiological understanding to potential clinical applicability.

PubMed

Leote, Joao; Pereira, Pedro; Cabib, Christopher; Cipullo, Federica; Valls-Sole, Josep

2016-06-01

Low-intensity electrical stimuli of digital nerves may generate a double peak potential (DPp), composed of a cathodal (caAP) and an anodal (anAP) potential in orthodromic recordings. We studied the effects on caAP and anAP of stimuli of variable intensity, duration, and frequency. We also applied a conditioning stimulus to study potential differences in recovery time. The anAP was obtained in 33 of 40 healthy subjects (82.5%) and 4 of 20 patients with various types of sensory neuropathies (20%). Changes in stimulus duration and intensity had reciprocal effects on the amplitude of the anAP and the caAP. There were significant differences in recovery time between caAP and anAP after a conditioning stimulus. The caAP and anAP are 2 interdependent waveforms generated by different effects of the same stimulus over axons at the verge of depolarization. Muscle Nerve 53: 897-905, 2016. © 2015 Wiley Periodicals, Inc.

Electrophysiological properties of myocytes isolated from the mouse atrioventricular node: L-type ICa, IKr, If, and Na-Ca exchange.

PubMed

Choisy, Stéphanie C; Cheng, Hongwei; Orchard, Clive H; James, Andrew F; Hancox, Jules C

2015-11-01

The atrioventricular node (AVN) is a key component of the cardiac pacemaker-conduction system. This study investigated the electrophysiology of cells isolated from the AVN region of adult mouse hearts, and compared murine ionic current magnitude with that of cells from the more extensively studied rabbit AVN. Whole-cell patch-clamp recordings of ionic currents, and perforated-patch recordings of action potentials (APs), were made at 35-37°C. Hyperpolarizing voltage commands from -40 mV elicited a Ba(2+)-sensitive inward rectifier current that was small at diastolic potentials. Some cells (Type 1; 33.4 ± 2.2 pF; n = 19) lacked the pacemaker current, If, whilst others (Type 2; 34.2 ± 1.5 pF; n = 21) exhibited a clear If, which was larger than in rabbit AVN cells. On depolarization from -40 mV L-type Ca(2+) current, IC a,L, was elicited with a half maximal activation voltage (V0.5) of -7.6 ± 1.2 mV (n = 24). IC a,L density was smaller than in rabbit AVN cells. Rapid delayed rectifier (IK r) tail currents sensitive to E-4031 (5 μmol/L) were observed on repolarization to -40 mV, with an activation V0.5 of -10.7 ± 4.7 mV (n = 8). The IK r magnitude was similar in mouse and rabbit AVN. Under Na-Ca exchange selective conditions, mouse AVN cells exhibited 5 mmol/L Ni-sensitive exchange current that was inwardly directed negative to the holding potential (-40 mV). Spontaneous APs (5.2 ± 0.5 sec(-1); n = 6) exhibited an upstroke velocity of 37.7 ± 16.2 V/s and ceased following inhibition of sarcoplasmic reticulum Ca(2+) release by 1 μmol/L ryanodine, implicating intracellular Ca(2+) cycling in murine AVN cell electrogenesis. © 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

Preservation of cardiac function by prolonged action potentials in mice deficient of KChIP2.

PubMed

Grubb, Søren; Aistrup, Gary L; Koivumäki, Jussi T; Speerschneider, Tobias; Gottlieb, Lisa A; Mutsaers, Nancy A M; Olesen, Søren-Peter; Calloe, Kirstine; Thomsen, Morten B

2015-08-01

Inherited ion channelopathies and electrical remodeling in heart disease alter the cardiac action potential with important consequences for excitation-contraction coupling. Potassium channel-interacting protein 2 (KChIP2) is reduced in heart failure and interacts under physiological conditions with both Kv4 to conduct the fast-recovering transient outward K(+) current (Ito,f) and with CaV1.2 to mediate the inward L-type Ca(2+) current (ICa,L). Anesthetized KChIP2(-/-) mice have normal cardiac contraction despite the lower ICa,L, and we hypothesized that the delayed repolarization could contribute to the preservation of contractile function. Detailed analysis of current kinetics shows that only ICa,L density is reduced, and immunoblots demonstrate unaltered CaV1.2 and CaVβ₂ protein levels. Computer modeling suggests that delayed repolarization would prolong the period of Ca(2+) entry into the cell, thereby augmenting Ca(2+)-induced Ca(2+) release. Ca(2+) transients in disaggregated KChIP2(-/-) cardiomyocytes are indeed comparable to wild-type transients, corroborating the preserved contractile function and suggesting that the compensatory mechanism lies in the Ca(2+)-induced Ca(2+) release event. We next functionally probed dyad structure, ryanodine receptor Ca(2+) sensitivity, and sarcoplasmic reticulum Ca(2+) load and found that increased temporal synchronicity of the Ca(2+) release in KChIP2(-/-) cardiomyocytes may reflect improved dyad structure aiding the compensatory mechanisms in preserving cardiac contractile force. Thus the bimodal effect of KChIP2 on Ito,f and ICa,L constitutes an important regulatory effect of KChIP2 on cardiac contractility, and we conclude that delayed repolarization and improved dyad structure function together to preserve cardiac contraction in KChIP2(-/-) mice. Copyright © 2015 the American Physiological Society.

Hysteresis effect implicates calcium cycling as a mechanism of repolarization alternans.

PubMed

Walker, Mariah L; Wan, Xiaoping; Kirsch, Glenn E; Rosenbaum, David S

2003-11-25

T-wave alternans is due to alternation of membrane repolarization at the cellular level and is a risk factor for sudden cardiac death. Recently, a hysteresis effect has been reported in patients whereby T-wave alternans, once induced by rapid heart rate, persists even when heart rate is subsequently slowed. We hypothesized that alternans hysteresis is an intrinsic property of cardiac myocytes, directly related to an underlying mechanism for repolarization alternans that involves intracellular calcium cycling. Stepwise pacing was used to induce alternans in Langendorff-perfused guinea pig hearts from which optical action potentials were recorded simultaneously at 256 ventricular sites with voltage-sensitive dyes and in whole-cell patch-clamped cardiac myocytes treated with or without BAPTA-AM (1,2-bis[2-aminophenoxy]ethane-N,N,N',N'-tetraacetic acid tetrakis [acetoxymethyl ester]). Alternans hysteresis was observed in every isolated heart: threshold heart rate for alternans was 280+/-12 bpm, but during subsequent deceleration of pacing, alternans persisted to significantly slower heart rates (238+/-5 bpm, P<0.05). Optical mapping showed that this effect also applied to the threshold for spatially discordant alternans (313+/-2.2 bpm during acceleration versus 250+/-6.6 bpm during deceleration, P<0.05). Alternans hysteresis was also observed in isolated cardiac myocytes. Moreover, calcium chelation by BAPTA-AM raised the threshold for alternans and inhibited hysteresis in a dose-dependent manner with no effect on baseline action potential duration. Alternans hysteresis is an intrinsic property of cardiac myocytes that can lead to persistence of arrhythmogenic discordant alternans even after heart rate is slowed. These results also support an important underlying role of calcium cycling in the mechanism of alternans.

Myocyte repolarization modulates myocardial function in aging dogs

PubMed Central

Sorrentino, Andrea; Signore, Sergio; Borghetti, Giulia; Meo, Marianna; Cannata, Antonio; Zhou, Yu; Wybieralska, Ewa; Luciani, Marco; Kannappan, Ramaswamy; Zhang, Eric; Matsuda, Alex; Webster, Andrew; Cimini, Maria; Kertowidjojo, Elizabeth; D'Alessandro, David A.; Wunimenghe, Oriyanhan; Michler, Robert E.; Royer, Christopher; Goichberg, Polina; Leri, Annarosa; Barrett, Edward G.; Anversa, Piero; Hintze, Thomas H.

2016-01-01

Studies of myocardial aging are complex and the mechanisms involved in the deterioration of ventricular performance and decreased functional reserve of the old heart remain to be properly defined. We have studied a colony of beagle dogs from 3 to 14 yr of age kept under a highly regulated environment to define the effects of aging on the myocardium. Ventricular, myocardial, and myocyte function, together with anatomical and structural properties of the organ and cardiomyocytes, were evaluated. Ventricular hypertrophy was not observed with aging and the structural composition of the myocardium was modestly affected. Alterations in the myocyte compartment were identified in aged dogs, and these factors negatively interfere with the contractile reserve typical of the young heart. The duration of the action potential is prolonged in old cardiomyocytes contributing to the slower electrical recovery of the myocardium. Also, the remodeled repolarization of cardiomyocytes with aging provides inotropic support to the senescent muscle but compromises its contractile reserve, rendering the old heart ineffective under conditions of high hemodynamic demand. The defects in the electrical and mechanical properties of cardiomyocytes with aging suggest that this cell population is an important determinant of the cardiac senescent phenotype. Collectively, the delayed electrical repolarization of aging cardiomyocytes may be viewed as a critical variable of the aging myopathy and its propensity to evolve into ventricular decompensation under stressful conditions. PMID:26801307

The prognostic value of early repolarization with ST-segment elevation in African Americans.

PubMed

Perez, Marco V; Uberoi, Abhimanyu; Jain, Nikhil A; Ashley, Euan; Turakhia, Mintu P; Froelicher, Victor

2012-04-01

Increased prevalence of classic early repolarization, defined as ST-segment elevation (STE) in the absence of acute myocardial injury, in African Americans is well established. The prognostic value of this pattern in different ethnicities remains controversial. Measure association between early repolarization and cardiovascular mortality in African Americans. The resting electrocardiograms of 45,829 patients were evaluated at the Palo Alto Veterans Affairs Hospital. Subjects with inpatient status or electrocardiographic evidence of acute myocardial infarction were excluded, leaving 29,281 subjects. ST-segment elevation, defined as an elevation of >0.1 mV at the end of the QRS, was electronically flagged and visually adjudicated by 3 observers blinded to outcomes. An association between ethnicity and early repolarization was measured by using multivariate logistic regression. We analyzed associations between early repolarization and cardiovascular mortality by using the Cox proportional hazards regression analysis. Subjects were 13% women and 13.3% African Americans, with an average age of 55 years and followed for an average of 7.6 years, resulting in 1995 cardiovascular deaths. There were 479 subjects with lateral STE and 185 with inferior STE. After adjustment for age, sex, heart rate, and coronary artery disease, African American ethnicity was associated with lateral or inferior STE (odds ratio 3.1; P = .0001). While lateral or inferior STE in non-African Americans was independently associated with cardiovascular death (hazard ratio 1.6; P = .02), it was not associated with cardiovascular death in African Americans (hazard ratio 0.75; P = .50). Although early repolarization is more prevalent in African Americans, it is not predictive of cardiovascular death in this population and may represent a distinct electrophysiologic phenomenon. Copyright © 2012 Heart Rhythm Society. All rights reserved.

Detection and evaluation of ventricular repolarization alternans: an approach to combined ECG, thoracic impedance, and beat-to-beat heart rate variability analysis.

PubMed

Kriščiukaitis, Algimantas; Šimoliūnienė, Renata; Macas, Andrius; Petrolis, Robertas; Drėgūnas, Kęstutis; Bakšytė, Giedrė; Pieteris, Linas; Bertašienė, Zita; Žaliūnas, Remigijus

2014-01-01

Beat-to-beat alteration in ventricles repolarization reflected by alternans of amplitude and/or shape of ECG S-T,T segment (TWA) is known as phenomena related with risk of severe arrhythmias leading to sudden cardiac death. Technical difficulties have caused limited its usage in clinical diagnostics. Possibilities to register and analyze multimodal signals reflecting heart activity inspired search for new technical solutions. First objective of this study was to test whether thoracic impedance signal and beat-to-beat heart rate reflect repolarization alternans detected as TWA. The second objective was revelation of multimodal signal features more comprehensively representing the phenomena and increasing its prognostic usefulness. ECG, and thoracic impedance signal recordings made during 24h follow-up of the patients hospitalized in acute phase of myocardial infarction were used for investigation. Signal morphology variations reflecting estimates were obtained by the principal component analysis-based method. Clinical outcomes of patients (survival and/or rehospitalization in 6 and 12 months) were compared to repolarization alternans and heart rate variability estimates. Repolarization alternans detected as TWA was also reflected in estimates of thoracic impedance signal shape and variation in beat-to-beat heart rate. All these parameters showed correlation with clinical outcomes of patients. The strongest significant correlation showed magnitude of alternans in estimates of thoracic impedance signal shape. The features of ECG, thoracic impedance signal and beat-to-beat variability of heart rate, give comprehensive estimates of repolarization alternans, which correlate, with clinical outcomes of the patients and we recommend using them to improve diagnostic reliability. Copyright © 2014 Lithuanian University of Health Sciences. Production and hosting by Elsevier Urban & Partner Sp. z o.o. All rights reserved.

Electrocardiographic Characteristics of Potential Organ Donors and Associations with Cardiac Allograft Utilization

PubMed Central

Khush, Kiran K.; Menza, Rebecca; Nguyen, John; Goldstein, Benjamin A.; Zaroff, Jonathan G.; Drew, Barbara J.

2012-01-01

Background Current regulations require that all cardiac allograft offers for transplantation must include an interpreted 12-lead electrocardiogram (ECG). However, little is known about the expected ECG findings in potential organ donors, or the clinical significance of any identified abnormalities in terms of cardiac allograft function and suitability for transplantation. Methods and Results A single experienced reviewer interpreted the first ECG obtained after brainstem herniation in 980 potential organ donors managed by the California Transplant Donor Network from 2002-2007. ECG abnormalities were summarized, and associations between specific ECG findings and cardiac allograft utilization for transplantation were studied. ECG abnormalities were present in 51% of all cases reviewed. The most common abnormalities included voltage criteria for left ventricular hypertrophy (LVH), prolongation of the corrected QT interval (QTc), and repolarization changes (ST/T wave abnormalities). Fifty seven percent of potential cardiac allografts in this cohort were accepted for transplantation. LVH on ECG was a strong predictor of allograft non-utilization. No significant associations were seen between QTc prolongation, repolarization changes and allograft utilization for transplantation, after adjusting for donor clinical variables and echocardiographic findings. Conclusions We have performed the first comprehensive study of ECG findings in potential donors for cardiac transplantation. Many of the common ECG abnormalities seen in organ donors may result from the heightened state of sympathetic activation that occurs after brainstem herniation, and are not associated with allograft utilization for transplantation. PMID:22615333

Channel sialic acids limit hERG channel activity during the ventricular action potential.

PubMed

Norring, Sarah A; Ednie, Andrew R; Schwetz, Tara A; Du, Dongping; Yang, Hui; Bennett, Eric S

2013-02-01

Activity of human ether-a-go-go-related gene (hERG) 1 voltage-gated K(+) channels is responsible for portions of phase 2 and phase 3 repolarization of the human ventricular action potential. Here, we questioned whether and how physiologically and pathophysiologically relevant changes in surface N-glycosylation modified hERG channel function. Voltage-dependent hERG channel gating and activity were evaluated as expressed in a set of Chinese hamster ovary (CHO) cell lines under conditions of full glycosylation, no sialylation, no complex N-glycans, and following enzymatic deglycosylation of surface N-glycans. For each condition of reduced glycosylation, hERG channel steady-state activation and inactivation relationships were shifted linearly by significant depolarizing ∼9 and ∼18 mV, respectively. The hERG window current increased significantly by 50-150%, and the peak shifted by a depolarizing ∼10 mV. There was no significant change in maximum hERG current density. Deglycosylated channels were significantly more active (20-80%) than glycosylated controls during phases 2 and 3 of action potential clamp protocols. Simulations of hERG current and ventricular action potentials corroborated experimental data and predicted reduced sialylation leads to a 50-70-ms decrease in action potential duration. The data describe a novel mechanism by which hERG channel gating is modulated through physiologically and pathophysiologically relevant changes in N-glycosylation; reduced channel sialylation increases hERG channel activity during the action potential, thereby increasing the rate of action potential repolarization.

Wolff-Parkinson-White syndrome concomitant with idiopathic ventricular fibrillation associated with inferior early repolarization.

PubMed

Takahashi, Naohiko; Shinohara, Tetsuji; Hara, Masahide; Saikawa, Tetsunori

2012-01-01

We encountered a 39-year-old man with documented ventricular fibrillation (VF). His ECGs showed intermittent Wolff-Parkinson-White (WPW) syndrome pattern. During electrophysiological study, no ventricular preexcitation was observed. An accessory pathway located at the posterior mitral annulus was identified, and successfully eliminated by radiofrequency catheter ablation. VF was not induced. His ECGs in the absence of delta waves demonstrated early repolarization in the inferior leads. This case raises the possibility that patients with manifest WPW syndrome may have an arrhythmogenic substrate associated with early repolarization, and the characteristic J waves can be masked by the presence of ventricular preexcitation.

Actions and mechanisms of action of novel analogues of sotalol on guinea-pig and rabbit ventricular cells.

PubMed Central

Connors, S. P.; Gill, E. W.; Terrar, D. A.

1992-01-01

1. The actions and mechanisms of action of novel analogues of sotalol which prolong cardiac action potentials were investigated in guinea-pig and rabbit isolated ventricular cells. 2. In guinea-pig and rabbit cells the compounds significantly prolonged action potential duration at 20% and 90% repolarization levels without affecting resting membrane potential. In guinea-pig but not rabbit cells there was an increase in action potential amplitude and in rabbit cells there was no change in the shape or position of the 'notch' in the action potential. 3. Possible mechanisms of action were studied in more detail in the case of compound II (1-(4-methanesulphonamidophenoxy)-3-(N-methyl 3,4 dichlorophenylethylamino)-2-propanol). Prolongation of action potential duration continued to occur in the presence of nisoldipine, and calcium currents recorded under voltage-clamp conditions were not reduced by compound II (1 microM). Action potential prolongation by compound II was also unaffected in the presence of 10 microM tetrodotoxin. 4. Compound II (1 microM) did not influence IK1 assessed from the current during ramp changes in membrane potential (20 mV s-1) over the range -90 to -10 mV. 5. Compound II (1 microM) blocked time-dependent delayed rectifier potassium current (IK) activated by step depolarizations and recorded as an outward tail following repolarization. When a submaximal concentration (50 nM) was applied there was no change in the apparent reversal potential of IK.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1393293

Clinical significance of the summating potential-action potential ratio and the action potential latency difference for condensation and rarefaction clicks in Meniere's disease.

PubMed

Ohashi, Toru; Nishino, Hirohito; Arai, Yoko; Hyodo, Makoto; Takatsu, Mitsuharu

2009-04-01

This study was aimed to elucidate the diagnostic significance of the summating potential (SP)-action potential (AP) ratio and the AP latency difference between condensation and rarefaction clicks (AP con-rar difference) in Meniere's disease. The AP and SP were recorded transtympanically in 67 patients with definite Meniere's disease. The SP/AP ratio and the AP con-rar difference were assessed in terms of 1) their interrelationship, 2) their relationship to hearing level, and 3) the rate of occurrence of abnormal values according to the stages of Meniere's disease. No correlation was found between the SP/AP ratio and the AP con-rar difference. Neither the SP/AP ratio in general nor the AP con-rar difference was correlated with the hearing level. However, enhanced values of the SP/AP ratio (0.35 or higher) were moderately correlated with the hearing level (r = 0.51), and their occurrence rate was 55.2%. An increased AP con-rar difference (0.13 ms or longer) was not correlated with the hearing level, and its occurrence rate was 50.2%; it appeared most frequently at stage 3 (p <0.05). An enhanced SP/AP ratio might not always indicate the presence of endolymphatic hydrops associated with an increase in endolymphatic pressure. An increased AP con-rar difference might reflect the presence of a biased basilar membrane resulting from an increased endolymphatic pressure, and hence it is diagnostically essential to simultaneously evaluate the SP/AP ratio and the AP con-rar difference.

Novel experimental results in human cardiac electrophysiology: measurement of the Purkinje fibre action potential from the undiseased human heart.

PubMed

Nagy, Norbert; Szél, Tamás; Jost, Norbert; Tóth, András; Gy Papp, Julius; Varró, András

2015-09-01

Data obtained from canine cardiac electrophysiology studies are often extrapolated to the human heart. However, it has been previously demonstrated that because of the lower density of its K(+) currents, the human ventricular action potential has a less extensive repolarization reserve. Since the relevance of canine data to the human heart has not yet been fully clarified, the aim of the present study was to determine for the first time the action potentials of undiseased human Purkinje fibres (PFs) and to compare them directly with those of dog PFs. All measurements were performed at 37 °C using the conventional microelectrode technique. At a stimulation rate of 1 Hz, the plateau potential of human PFs is more positive (8.0 ± 1.8 vs 8.6 ± 3.4 mV, n = 7), while the amplitude of the spike is less pronounced. The maximal rate of depolarization is significantly lower in human PKs than in canine PFs (406.7 ± 62 vs 643 ± 36 V/s, respectively, n = 7). We assume that the appreciable difference in the protein expression profiles of the 2 species may underlie these important disparities. Therefore, caution is advised when canine PF data are extrapolated to humans, and further experiments are required to investigate the characteristics of human PF repolarization and its possible role in arrhythmogenesis.

Sprint training shortens prolonged action potential duration in postinfarction rat myocyte: mechanisms.

PubMed

Zhang, X Q; Zhang, L Q; Palmer, B M; Ng, Y C; Musch, T I; Moore, R L; Cheung, J Y

2001-05-01

Two electrophysiological manifestations of myocardial infarction (MI)-induced myocyte hypertrophy are prolongation of action potential duration (APD) and reduction of transient outward current (I(to)) density. Because high-intensity sprint training (HIST) ameliorated myocyte hypertrophy and improved myocyte Ca(2+) homeostasis and contractility after MI, the present study evaluated whether 6-8 wk of HIST would shorten the prolonged APD and improve the depressed I(to) in post-MI myocytes. There were no differences in resting membrane potential and action potential amplitude (APA) measured in myocytes isolated from sham-sedentary (Sed), MI-Sed, and MI-HIST groups. Times required for repolarization to 50 and 90% APA were significantly (P < 0.001) prolonged in MI-Sed myocytes. HIST reduced times required for repolarization to 50 and 90% APA to values observed in Sham-Sed myocytes. The fast and slow components of I(to) were significantly (P < 0.0001) reduced in MI-Sed myocytes. HIST significantly (P < 0.001) enhanced the fast and slow components of I(to) in MI myocytes, although not to levels observed in Sham-Sed myocytes. There were no significant differences in steady-state I(to) inactivation and activation parameters among Sham-Sed, MI-Sed, and MI-HIST myocytes. Likewise, recovery from time-dependent inactivation was also similar among the three groups. We suggest that normalization of APD after MI by HIST may be mediated by restoration of I(to) toward normal levels.

The augmented anticancer potential of AP9-cd loaded solid lipid nanoparticles in human leukemia Molt-4 cells and experimental tumor.

PubMed

Bhushan, Shashi; Kakkar, Vandita; Pal, Harish Chandra; Mondhe, D M; Kaur, Indu Pal

2016-01-25

AP9-cd, a novel lignan composition from Cedrus deodara has significant anticancer potential, and to further enhance its activity, it was lucratively encumbered into solid lipid nanoparticles (SLNs). These nanoparticles were formulated by micro-emulsion technique with 70% drug trap competence. AP9-cd-SLNs were regular, solid, globular particles in the range of 100-200 nm, which were confirmed by electron microscopic studies. Moreover, AP9-cd-SLNs were found to be stable for up to six months in terms of color, particle size, zeta potential, drug content and entrapment. AP9-cd-SLNs have 30-50% higher cytotoxic and apoptotic potential than the AP9-cd alone. The augmented anticancer potential of AP9-cd-SLNs was observed in cytotoxic IC50 value, apoptosis signaling cascade and in Ehrlich ascites tumor (EAT) model. AP9-cd-SLNs induce apoptosis in Molt-4 cells via both intrinsic and extrinsic pathway. Moreover, the dummy nanoparticles (SLNs without AP9-cd) did not have any cytotoxic effect in cancer as well as in normal cells. Consequently, SLNs of AP9-cd significantly augment the apoptotic and antitumor potential of AP9-cd. The present study provides a podium for ornamental the remedial latent via novel delivery systems like solid lipid nanoparticles. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Prolonged Tp-e Interval in Down Syndrome Patients with Congenitally Normal Hearts.

PubMed

Kucuk, Mehmet; Karadeniz, Cem; Ozdemir, Rahmi; Meşe, Timur

2018-03-25

Heterogeneity of ventricular repolarization has been assessed by using the QT dispersion in Down syndrome (DS) patients with congenitally normal hearts. However, novel repolarization indexes, the Tp-e interval and Tp-e/QT ratio, have not previously been evaluated in these patients. The aim of this study was to evaluate the Tp-e interval and Tp-e/QT ratio in DS patients without congenital heart defects. Twelve-lead surface electrocardiograms of 160 DS patients and 110 age- and sex-matched healthy controls were used to evaluate and compare the Tp-e interval, Tp-e dispersion, and Tp-e/QT ratio. Heart rate, Tp-e interval, Tp-e dispersion, Tp-e/QT and Tp-e/QTc ratios were significantly higher in DS group than in the controls. Myocardial repolarization indexes in DS patients with congenitally normal hearts were found to be prolonged compared to those in normal controls. Further evaluation is warranted to reveal a relationship between prolonged repolarization indexes and arrhythmic events in these patients. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Curvature effects on activation speed and repolarization in an ionic model of cardiac myocytes

NASA Astrophysics Data System (ADS)

Comtois, P.; Vinet, A.

1999-10-01

Reentry is a major mechanism underlying the initiation and perpetuation of many cardiac arrhythmias 12345. Stimulated ventricular myocytes give action potential characterized by a fast upstroke, a long-lasting plateau, and a late repolarization phase. The plateau phase determines the action potential duration (APD) during which the system remains refractory, a property essential to the synchronization of the heart cycle. The APD varies much with prematurity and this change has been shown to be the main determinant of the dynamics in models of paced cells and cable, and during reentry in the one-dimensional loop. Curvature has also been shown to be an important factor for propagation in experimental and theoretical cardiac extended tissue. The objective of this paper is to combine both curvature and prematurity effects in a kinematical model of propagation in cardiac tissue. First, an approximation of the ionic model is used to obtain the effects of curvature and prematurity on the speed of propagation, the APD, and the absolute refractory period. Two versions of the ionic model are studied that differ in their rate of excitability recovery. The functions are used in a kinematical model describing the propagation of period-1 solutions around an annulus.

Hyperventilation assists proarrhythmia development during delayed repolarization in clofilium-treated, anaesthetized, mechanically ventilated rabbits.

PubMed

Papp, H; Sarusi, A; Farkas, A S; Takacs, H; Kui, P; Vincze, D; Ivany, E; Varro, A; Papp, J G; Forster, T; Farkas, A

2016-10-01

Hyperventilation reduces partial pressure of CO 2 (PCO 2 ) in the blood, which results in hypokalaemia. Hypokalaemia helps the development of the life-threatening torsades de pointes type ventricular arrhythmia (TdP) evoked by repolarization delaying drugs. This implies that hyperventilation may assist the development of proarrhythmic events. Therefore, this study experimentally investigated the effect of hyperventilation on proarrhythmia development during delayed repolarization. Phenylephrine (an α 1 -adrenoceptor agonist) and clofilium (as a representative repolarization delaying agent inhibiting the rapid component of the delayed rectifier potassium current, I Kr ) were administered intravenously to pentobarbital-anaesthetized, mechanically ventilated, open chest rabbits. ECG was recorded, and the onset times and incidences of the arrhythmias were determined. Serum K + , pH and PCO 2 were measured in arterial blood samples. Clofilium prolonged the rate corrected QT interval. TdP occurred in 15 animals (TdP+ group), and did not occur in 14 animals (TdP- group). We found a strong, positive, linear correlation between serum K + and PCO 2 . There was no relationship between the occurrence of TdP and the baseline K + and PCO 2 values. However, a positive, linear correlation was found between the onset time of the first arrhythmias and the K + and PCO 2 values. The regression lines describing the relationship between PCO 2 and onset time of first arrhythmias were parallel in the TdP+ and TdP- groups, but the same PCO 2 resulted in earlier arrhythmia onset in the TdP+ group than in the TdP- group. We conclude that hyperventilation and hypocapnia with the resultant hypokalaemia assist the multifactorial process of proarrhythmia development during delayed repolarization. This implies that PCO 2 and serum K + should be controlled tightly during mechanical ventilation in experimental investigations and clinical settings when repolarization-delaying drugs are applied.

Sleep-disordered breathing is associated with disturbed cardiac repolarization in patients with a coronary artery bypass graft surgery.

PubMed

Schmidleitner, Christina; Arzt, Michael; Tafelmeier, Maria; Ripfel, Sarah; Fauser, Miriam; Weizenegger, Teresa; Flörchinger, Bernhard; Camboni, Daniele; Wittmann, Sigrid; Zeman, Florian; Schmid, Christof; Maier, Lars S; Wagner, Stefan; Fisser, Christoph

2018-02-01

The development of malignant ventricular arrhythmias due to abnormal cardiac repolarization is a major complication after coronary artery bypass graft surgery (CABG). Sleep-disordered breathing (SDB) is linked to prolonged cardiac repolarization in non-surgical patients. This study evaluates cardiac repolarization in patients with and without SDB who underwent CABG. 100 patients who had received CABG (84% men, age 68 ± 10 years, body-mass-index [BMI] 28.7 ± 4.2 kg/m 2 ) were retrospectively evaluated. Polygraphy was recorded the night before CABG. SDB was defined as an apnea-hypopnea index (AHI) of ≥15/h and differentiated into central (CSA) and obstructive (OSA) sleep apnea. Cardiac repolarization was assessed by means of T-peak-to-end (TpTe) and QTc-intervals and TpTe/QT-ratios derived from 12-lead electrocardiography (ECG). 37% of patients had SDB, 14% CSA and 23% OSA. Before CABG, patients with CSA and OSA had longer TpTe intervals than those without SDB (TpTe: CSA 100 ± 26 vs. OSA 97 ± 19 vs. no SDB 85 ± 14 ms, p = 0.013). QTc intervals and TpTe/QT ratios differed between the two groups (QTc: 444 ± 54 vs. 462 ± 36 vs. 421 ± 32 ms, p < 0.001; TpTe/QT ratio: 0.24 ± 0.04 vs. 0.23 ± 0.05 vs. 0.21 ± 0.03, p = 0.045). SDB was associated with abnormal cardiac repolarization independent of known risk factors for cardiac arrhythmias, such as age, sex, BMI, N-terminal-pro-brain-natriuretic-peptide (NT-proBNP), and heart failure (TpTe: B-coefficient [95%CI]: 16.0, [7.6-24.3], p < 0.001; QTc: 27.2 [9.3-45.1], p = 0.003; TpTe/QT ratio: 2.9 [1.2-4.6], p < 0.001). Independent of known risk factors for cardiac arrhythmias, SDB was significantly associated with abnormal cardiac repolarization before CABG. Data suggest that SDB may contribute to an increased risk of ventricular arrhythmias after CABG. Copyright © 2018 Elsevier B.V. All rights reserved.

The Effects of Phrenic Nerve Degeneration by Axotomy and Crush on the Electrical Activities of Diaphragm Muscles of Rats.

PubMed

Alkiş, Mehmet Eşref; Kavak, Servet; Sayır, Fuat; Him, Aydin

2016-03-01

The aim of this study was to investigate the effect of axotomy and crush-related degeneration on the electrical activities of diaphragm muscle strips of experimental rats. In the present study, twenty-one male Wistar-albino rats were used and divided into three groups. The animals in the first group were not crushed or axotomized and served as controls. Phrenic nerves of the rats in the second and third groups were crushed or axotomized in the diaphragm muscle. Resting membrane potential (RMP) was decreased significantly in both crush and axotomy of diaphragm muscle strips of experimental rats (p < 0.05). Depolarization time (T DEP) and half-repolarization (1/2 RT) time were significantly prolonged in crush and axotomy rats (p < 0.05). Crushing or axotomizing the phrenic nerves may produce electrical activities in the diaphragm muscle of the rat by depolarization time and half-repolarization time prolonged in crush and axotomy rats.

Connexin 43 and ATP-sensitive potassium channels crosstalk: a missing link in hypoxia/ischemia stress.

PubMed

Ahmad Waza, Ajaz; Ahmad Bhat, Shabir; Ul Hussain, Mahboob; Ganai, Bashir A

2018-02-01

Connexin 43 (Cx43) is a gap junction protein expressed in various tissues and organs of vertebrates. Besides functioning as a gap junction, Cx43 also regulates diverse cellular processes like cell growth and differentiation, cell migration, cell survival, etc. Cx43 is critical for normal cardiac functioning and is therefore abundantly expressed in cardiomyocytes. On the other hand, ATP-sensitive potassium (K ATP ) channels are metabolic sensors converting metabolic changes into electrical activity. These channels are important in maintaining the neurotransmitter release, smooth muscle relaxation, cardiac action potential repolarization, normal physiology of cellular repolarization, insulin secretion and immune function. Cx43 and K ATP channels are part of the same signaling pathway, regulating cell survival during stress conditions and ischemia/hypoxia preconditioning. However, the underlying molecular mechanism for their combined role in ischemia/hypoxia preconditioning is largely unknown. The current review focuses on understanding the molecular mechanism responsible for the coordinated role of Cx43 and K ATP channel protein in protecting cardiomyocytes against ischemia/hypoxia stress.

Complex expression and localization of inactivating Kv channels in cultured hippocampal astrocytes.

PubMed

Bekar, Lane K; Loewen, Matthew E; Cao, Kun; Sun, Xianfeng; Leis, Jerome; Wang, Rui; Forsyth, George W; Walz, Wolfgang

2005-03-01

Voltage-gated potassium channels are well established as critical for setting action potential frequency, membrane potential, and neurotransmitter release in neurons. However, their role in the "nonexcitable" glial cell type is yet to be fully understood. We used whole cell current kinetics, pharmacology, immunocytochemistry, and RT-PCR to characterize A-type current in hippocampal astrocyte cultures to better understand its function. Pharmacological analysis suggests that approximately 70, 10, and <5% of total A current is associated with Kv4, Kv3, and Kv1 channels, respectively. In addition, pharmacology and kinetics provide evidence for a significant contribution of KChIP accessory proteins to astrocytic A-channel composition. Localization of the Shaw Kv3.4 channel to astrocytic processes and the Shal Kv4.3 channel to soma suggest that these channels serve a specific function. Given this complex A-type channel expression pattern, we assessed the role of A currents in membrane voltage oscillations in response to current injections. Although TEA-sensitive delayed-rectifying currents are involved in the extent of repolarization, 4-AP-sensitive A currents serve to increase the rate. As in neurons, this effect may enable astrocytes to respond rapidly to high-frequency synaptic events. Our results indicate that hippocampal astrocytes in vitro express multiple A-type Kv channel alpha-subunits with accessory, possibly Ca(2+)-sensitive, cytoplasmic subunits that appear to be specifically localized to subcellular membrane compartments. Function of these channels remains to be determined in a physiological setting. However, this study suggests that they enable astrocytes to respond rapidly with membrane voltage oscillations to high-frequency incoming signals, possibly synchronizing astrocyte function to neuronal activity.

Ionic channels underlying the ventricular action potential in zebrafish embryo.

PubMed

Alday, Aintzane; Alonso, Hiart; Gallego, Monica; Urrutia, Janire; Letamendia, Ainhoa; Callol, Carles; Casis, Oscar

2014-06-01

Over the last years zebrafish has become a popular model in the study of cardiac physiology, pathology and pharmacology. Recently, the application of the 3Rs regulation and the characteristics of the embryo have reduced the use of adult zebrafish use in many studies. However, the zebrafish embryo cardiac physiology is poorly characterized since most works have used indirect techniques and direct recordings of cardiac action potential and ionic currents are scarce. In order to optimize the zebrafish embryo model, we used electrophysiological, pharmacological and immunofluorescence tools to identify the characteristics and the ionic channels involved in the ventricular action potentials of zebrafish embryos. The application of Na(+) or T-type Ca(+2) channel blockers eliminated the cardiac electrical activity, indicating that the action potential upstroke depends on Na(+) and T-type Ca(+2) currents. The plateau phase depends on L-type Ca(+2) channels since it is abolished by specific blockade. The direct channel blockade indicates that the action potential repolarization and diastolic potential depends on ERG K(+) channels. The presence in the embryonic heart of the Nav1.5, Cav1.2, Cav3.2 and ERG channels was also confirmed by immunofluorescence, while the absence of effect of specific blockers and immunostaining indicate that two K(+) repolarizing currents present in human heart, Ito and IKs, are absent in the embryonic zebrafish heart. Our results describe the ionic channels present and its role in the zebrafish embryo heart and support the use of zebrafish embryos to study human diseases and their use for drug testing. Copyright © 2014 Elsevier Ltd. All rights reserved.

PubMed Central

Russo, Vincenzo; Papa, Andrea Antonio; Rago, Anna; D'Ambrosio, Paola; Cimmino, Giovanni; Palladino, Alberto; Nigro, Gerardo

2016-01-01

Sudden cardiac death in myotonic dystrophy type I (DM1) patients can be attributed to atrioventricular blocks as far as to the development of life-threatening arrhythmias which occur even in hearts with normal left ventricular systolic and diastolic function. Heterogeneity of ventricular repolarization is considered to provide an electrophysiological substrate for malignant arrhythmias. QTc dispersion (QTc-D), JTc dispersion (JTc-D) and transmural dispersion of repolarization (TDR) could reflect the physiological variability of regional and transmural ventricular repolarization. Aim of the present study was to investigate the heterogeneity of ventricular repolarization in patients with DM1 and preserved diastolic and systolic cardiac function. The study enrolled 50 DM1 patients (mean age 44 ± 5 years; M:F: 29:21) with preserved systolic and diastolic function of left ventricle among 247 DM1 patients followed at Cardiomyology and Medical Genetics of Second University of Naples, and 50 sexand age-matched healthy controls. The electrocardiographic parameters investigated were the following: Heart Rate, QRS duration, maximum and minimum QT and JT intervals, QTc- D, JTc-D and TDR. Compared to the controls, the DM1 group presented increased values of QTc-D (86.7 ± 40.1 vs 52.3 ± 11.9 ms; p = 0.03), JTc-D (78.6 ± 31.3 vs 61.3 ± 10.2 ms; p = 0.001) and TDR (101.6 ± 18.06 vs 90.1 ± 14.3 ms; p = 0.004) suggesting a significant increase in regional and transmural heterogeneity of the ventricular repolarization in these patients, despite a preserved systolic and diastolic cardiac function. PMID:28344440

Targeting RAW 264.7 macrophages (M1 type) with Withaferin-A decorated mannosylated liposomes induces repolarization via downregulation of NF-κB and controlled elevation of STAT-3.

PubMed

Neog, Manoj Kumar; Sultana, Farhath; Rasool, Mahaboobkhan

2018-05-25

In the present study, we intend to gain an insight into the mechanism of Withaferin-A (WA), a steroidal lactone with reference to repolarization of RAW 264.7 macrophages (M1 to M2 type). We found that successful internalization of WA via mannosylated liposomal delivery system (ML-WA) reduced the RAW 264.7 macrophage (M1) mediated pro-inflammatory cytokines (IL-1β, IL-6, IL-23, and TNF-α) through the attenuation of transcription factor NF-κB-p65 expression. Whereas, ML-WA treatment induced a controlled upregulation of p-STAT3, and ablated the key oxidative stress markers (NO, iNOS, and ROS) in M1 → M2 RAW 264.7 macrophage repolarization, which suggested the recalibration of M1 macrophage metabolic function. Further, the elevated expression of M2 macrophage associated CD163 over the M1 macrophage related CD86 concluded that ML-WA induces an anti-inflammatory response by repolarizing the M1 → M2 RAW 264.7 macrophage. Copyright © 2018 Elsevier B.V. All rights reserved.

Modeling and quantification of repolarization feature dependency on heart rate.

PubMed

Minchole, A; Zacur, E; Pueyo, E; Laguna, P

2014-01-01

This article is part of the Focus Theme of Methods of Information in Medicine on "Biosignal Interpretation: Advanced Methods for Studying Cardiovascular and Respiratory Systems". This work aims at providing an efficient method to estimate the parameters of a non linear model including memory, previously proposed to characterize rate adaptation of repolarization indices. The physiological restrictions on the model parameters have been included in the cost function in such a way that unconstrained optimization techniques such as descent optimization methods can be used for parameter estimation. The proposed method has been evaluated on electrocardiogram (ECG) recordings of healthy subjects performing a tilt test, where rate adaptation of QT and Tpeak-to-Tend (Tpe) intervals has been characterized. The proposed strategy results in an efficient methodology to characterize rate adaptation of repolarization features, improving the convergence time with respect to previous strategies. Moreover, Tpe interval adapts faster to changes in heart rate than the QT interval. In this work an efficient estimation of the parameters of a model aimed at characterizing rate adaptation of repolarization features has been proposed. The Tpe interval has been shown to be rate related and with a shorter memory lag than the QT interval.

β-Adrenergic receptor stimulation inhibits proarrhythmic alternans in postinfarction border zone cardiomyocytes: a computational analysis.

PubMed

Tomek, Jakub; Rodriguez, Blanca; Bub, Gil; Heijman, Jordi

2017-08-01

The border zone (BZ) of the viable myocardium adjacent to an infarct undergoes extensive autonomic and electrical remodeling and is prone to repolarization alternans-induced cardiac arrhythmias. BZ remodeling processes may promote or inhibit Ca 2+ and/or repolarization alternans and may differentially affect ventricular arrhythmogenesis. Here, we used a detailed computational model of the canine ventricular cardiomyocyte to study the determinants of alternans in the BZ and their regulation by β-adrenergic receptor (β-AR) stimulation. The BZ model developed Ca 2+ transient alternans at slower pacing cycle lengths than the control model, suggesting that the BZ may promote spatially heterogeneous alternans formation in an infarcted heart. β-AR stimulation abolished alternans. By evaluating all combinations of downstream β-AR stimulation targets, we identified both direct (via ryanodine receptor channels) and indirect [via sarcoplasmic reticulum (SR) Ca 2+ load] modulation of SR Ca 2+ release as critical determinants of Ca 2+ transient alternans. These findings were confirmed in a human ventricular cardiomyocyte model. Cell-to-cell coupling indirectly modulated the likelihood of alternans by affecting the action potential upstroke, reducing the trigger for SR Ca 2+ release in one-dimensional strand simulations. However, β-AR stimulation inhibited alternans in both single and multicellular simulations. Taken together, these data highlight a potential antiarrhythmic role of sympathetic hyperinnervation in the BZ by reducing the likelihood of alternans and provide new insights into the underlying mechanisms controlling Ca 2+ transient and repolarization alternans. NEW & NOTEWORTHY We integrated, for the first time, postmyocardial infarction electrical and autonomic remodeling in a detailed, validated computer model of β-adrenergic stimulation in ventricular cardiomyocytes. Here, we show that β-adrenergic stimulation inhibits alternans and provide novel insights into underlying mechanisms, adding to a recent controversy about pro-/antiarrhythmic effects of postmyocardial infarction hyperinnervation.Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/%CE%B2-ar-stimulation-and-alternans-in-border-zone-cardiomyocytes/. Copyright © 2017 the American Physiological Society.

Delayed Repolarization Underlies Ventricular Arrhythmias in Rats With Heart Failure and Preserved Ejection Fraction.

PubMed

Cho, Jae Hyung; Zhang, Rui; Kilfoil, Peter J; Gallet, Romain; de Couto, Geoffrey; Bresee, Catherine; Goldhaber, Joshua I; Marbán, Eduardo; Cingolani, Eugenio

2017-11-21

Heart failure with preserved ejection fraction (HFpEF) represents approximately half of heart failure, and its incidence continues to increase. The leading cause of mortality in HFpEF is sudden death, but little is known about the underlying mechanisms. Dahl salt-sensitive rats were fed a high-salt diet (8% NaCl) from 7 weeks of age to induce HFpEF (n=38). Rats fed a normal-salt diet (0.3% NaCl) served as controls (n=13). Echocardiograms were performed to assess systolic and diastolic function from 14 weeks of age. HFpEF-verified and control rats underwent programmed electrical stimulation. Corrected QT interval was measured by surface ECG. The mechanisms of ventricular arrhythmias (VA) were probed by optical mapping, whole-cell patch clamp to measure action potential duration and ionic currents, and quantitative polymerase chain reaction and Western blotting to investigate changes in ion channel expression. After 7 weeks of a high-salt diet, 31 of 38 rats showed diastolic dysfunction and preserved ejection fraction along with signs of heart failure and hence were diagnosed with HFpEF. Programmed electric stimulation demonstrated increased susceptibility to VA in HFpEF rats ( P <0.001 versus controls). The arrhythmogenicity index was increased ( P <0.001) and the corrected QT interval on ECG was prolonged ( P <0.001) in HFpEF rats. Optical mapping of HFpEF hearts demonstrated prolonged action potentials ( P <0.05) and multiple reentry circuits during induced VA. Single-cell recordings of cardiomyocytes isolated from HFpEF rats confirmed a delay of repolarization ( P =0.001) and revealed downregulation of transient outward potassium current ( I to ; P <0.05). The rapid components of the delayed rectifier potassium current ( I Kr ) and the inward rectifier potassium current ( I K1 ) were also downregulated ( P <0.05), but the current densities were much lower than for I to . In accordance with the reduction of I to , both Kcnd3 transcript and Kv4.3 protein levels were decreased in HFpEF rat hearts. Susceptibility to VA was markedly increased in rats with HFpEF. Underlying abnormalities include QT prolongation, delayed repolarization from downregulation of potassium currents, and multiple reentry circuits during VA. Our findings are consistent with the hypothesis that potassium current downregulation leads to abnormal repolarization in HFpEF, which in turn predisposes to VA and sudden cardiac death. © 2017 American Heart Association, Inc.

Impact of Ancillary Subunits on Ventricular Repolarization

PubMed Central

Abbott, Geoffrey W.; Xu, Xianghua; Roepke, Torsten K.

2007-01-01

Voltage-gated potassium (Kv) channels generate the outward K+ ion currents that constitute the primary force in ventricular repolarization. Kv channels comprise tetramers of pore-forming α subunits and, in probably the majority of cases in vivo, ancillary or β subunits that help define the properties of the Kv current generated. Ancillary subunits can be broadly categorized as cytoplasmic or transmembrane, and can modify Kv channel trafficking, conductance, gating, ion selectivity, regulation and pharmacology. Because of their often profound effects on Kv channel function, studies of the molecular correlates of ventricular repolarization must take into account ancillary subunits as well as α subunits. Cytoplasmic ancillary subunits include the Kvβ subunits, which regulate a range of Kv channels and may link channel gating to redox potential; and the KChIPs, which appear most often associated with Kv4 subfamily channels that generate the ventricular Ito current. Transmembrane ancillary subunits include the MinK-related proteins (MiRPs) encoded by KCNE genes, which modulate members of most Kv α subunit subfamilies; and the putative 12-transmembrane domain KCR1 protein which modulates hERG. In some cases, such as the ventricular IKs channel complex, it is well-established that the KCNQ1 α subunit must co-assemble with the MinK (KCNE1) single transmembrane domain ancillary subunit for recapitulation of the characteristic, unusually slowly-activating IKs current. In other cases it is not so clear-cut, and in particular the roles of the other MinK-related proteins (MiRPs 1–4) in regulating cardiac Kv channels such as KCNQ1 and hERG in vivo are under debate. MiRP1 alters hERG function and pharmacology, and inherited MiRP1 mutations are associated with inherited and acquired arrhythmias, but controversy exists over the native role of MiRP1 in regulating hERG (and therefore ventricular IKr) in vivo. Some ancillary subunits may exhibit varied expression to shape spatial Kv current variation, e.g. KChIP2 and the epicardial-endocardial Ito current density gradient. Indeed, it is likely that most native ventricular Kv channels exhibit temporal and spatial heterogeneity of subunit composition, complicating both modeling of their functional impact on the ventricular action potential and design of specific current-targeted compounds. Here, we discuss current thinking and lines of experimentation aimed at resolving the complexities of the Kv channel complexes that repolarize the human ventricular myocardium. PMID:17993327

Estrogen Contributes to Gender Differences in Mouse Ventricular Repolarization

PubMed Central

Saito, Tomoaki; Ciobotaru, Andrea; Bopassa, Jean Chrisostome; Toro, Ligia; Stefani, Enrico; Eghbali, Mansoureh

2010-01-01

Rationale Fast-transient outward K+ (Ito,f) and ultra-rapid delayed rectifier K+ currents (IKur or IK,slow) contribute to mouse cardiac repolarization. Gender studies on these currents have reported conflicting results. Objective One key missing piece information in these studies is the animals’ estral stage. We decided to revisit gender-related differences in K+ currents, taking into consideration the females’ estral stage. Methods and Results We hypothesized that changes in estrogen levels during the estral cycle could play a role in determining the densities of K+ currents underlying ventricular repolarization. Peak total K+ current (IK,total) densities (pA/pF, at +40 mV) were much higher in males (48.6±3.0) than in females at estrus (27.2±2.3) but not at diestrus-2 (39.1±3.4). Underlying this change, Ito,f and IK,slow were lower in females at estrus vs males and diestrus-2 (IK,slow: male 21.9±1.8, estrus 14.6±0.6, diestrus-2 20.3±1.4; Ito,f: male 26.8±1.9, estrus 14.9±1.6, diestrus-2 22.1±2.1). The lower IK,slow in estrus was only due to IK,slow1 reduction without changes of IK,slow2. Estrogen treatment of ovariectomized mice decreased IK,total (46.4±3.0 to 28.4±1.6), Ito,f (26.6±1.6 to 12.8±1.0) and IK,slow (22.2±1.6 to 17.2±1.4). Transcript levels of Kv4.3 and Kv1.5 (underlying Ito,f and IK,slow, respectively) were lower in estrus vs. diestrus-2 and male. In ovariectomized mice, estrogen treatment resulted in downregulation of Kv4.3 and Kv1.5, but not Kv4.2, KChIP2 and Kv2.1 transcripts. K+ current reduction in high estrogenic conditions were associated with prolongation of the action potential duration and corrected QT interval. Conclusion Downregulation of Kv4.3 and Kv1.5 transcripts by estrogen are one mechanism defining gender-related differences in mouse ventricular repolarization. PMID:19608983

The tetravalent organic cation spermine causes the gating of the IRK1 channel expressed in murine fibroblast cells.

PubMed Central

Ishihara, K; Hiraoka, M; Ochi, R

1996-01-01

1. The activation kinetics of the IRK1 channel stably expressed in L cells (a murine fibroblast cell line) were studied under the whole-cell voltage clamp. Without polyamines or Mg2+ in the pipettes, inward currents showed an exponential activation on hyperpolarization. The steep inward rectification of the currents around the reversal potential (Erev) could be described by the open-close transition of the channel with first-order kinetics. 2. When the tetravalent organic cation spermine (Spm) was added in the pipettes, the activation kinetics changed; this was explicable by the increase in the closing rate constant. The activation of the currents observed without Spm or Mg2+ in the pipettes was ascribed to the unblocking of the 'endogenous-Spm block'. 3. In the presence of the divalent cation putrescine (Put) or of Mg2+ in the pipettes, a different non-conductive state suppressed the outward currents on depolarization; the channels instantaneously changed to the open state on repolarization. As the depolarization was prolonged, this non-conductive state was replaced by the non-conductive state that shows an exponential activation on repolarization. This phenomenon was attributed to the redistribution of the channels from the Put- or Mg(2+)-blocked state to the 'endogenous Spm-blocked state' during depolarization. 4. In the presence of the trivalent cation spermidine (Spd) in the pipettes, two different non-conductive states occurred, showing a faster and a slower activation on repolarization. The rectification around Erev was mainly due to the non-conductive state showing a faster activation, which appeared to be the Spd-blocked state. During depolarization, redistribution of the channels to the 'endogenous Spm-blocked state' also occurred. 5. In the presence of Spd, Put or Mg2+ in the pipettes, the voltage dependence of the activation time constant reflecting the unblocking of the 'endogenous Spm' was shifted in the hyperpolarizing direction. 6. Our results suggest that the 'intrinsic gating' that shows the time-dependent activation on repolarization, and that is responsible for the inward rectification around Erev, reflects the blocking kinetics of the tetravalent Spm. PMID:8866861

Single cell wound generates electric current circuit and cell membrane potential variations that requires calcium influx.

PubMed

Luxardi, Guillaume; Reid, Brian; Maillard, Pauline; Zhao, Min

2014-07-24

Breaching of the cell membrane is one of the earliest and most common causes of cell injury, tissue damage, and disease. If the compromise in cell membrane is not repaired quickly, irreversible cell damage, cell death and defective organ functions will result. It is therefore fundamentally important to efficiently repair damage to the cell membrane. While the molecular aspects of single cell wound healing are starting to be deciphered, its bio-physical counterpart has been poorly investigated. Using Xenopus laevis oocytes as a model for single cell wound healing, we describe the temporal and spatial dynamics of the wound electric current circuitry and the temporal dynamics of cell membrane potential variation. In addition, we show the role of calcium influx in controlling electric current circuitry and cell membrane potential variations. (i) Upon wounding a single cell: an inward electric current appears at the wound center while an outward electric current is observed at its sides, illustrating the wound electric current circuitry; the cell membrane is depolarized; calcium flows into the cell. (ii) During cell membrane re-sealing: the wound center current density is maintained for a few minutes before decreasing; the cell membrane gradually re-polarizes; calcium flow into the cell drops. (iii) In conclusion, calcium influx is required for the formation and maintenance of the wound electric current circuitry, for cell membrane re-polarization and for wound healing.

Basis for the Induction of Tissue-Level Phase-2 Reentry as a Repolarization Disorder in the Brugada Syndrome

PubMed Central

Bueno-Orovio, Alfonso; Cherry, Elizabeth M.; Evans, Steven J.; Fenton, Flavio H.

2015-01-01

Aims. Human action potentials in the Brugada syndrome have been characterized by delayed or even complete loss of dome formation, especially in the right ventricular epicardial layers. Such a repolarization pattern is believed to trigger phase-2 reentry (P2R); however, little is known about the conditions necessary for its initiation. This study aims to determine the specific mechanisms that facilitate P2R induction in Brugada-affected cardiac tissue in humans. Methods. Ionic models for Brugada syndrome in human epicardial cells were developed and used to study the induction of P2R in cables, sheets, and a three-dimensional model of the right ventricular free wall. Results. In one-dimensional cables, P2R can be induced by adjoining lost-dome and delayed-dome regions, as mediated by tissue excitability and transmembrane voltage profiles, and reduced coupling facilitates its induction. In two and three dimensions, sustained reentry can arise when three regions (delayed-dome, lost-dome, and normal epicardium) are present. Conclusions. Not only does P2R induction by Brugada syndrome require regions of action potential with delayed-dome and lost-dome, but in order to generate a sustained reentry from a triggered waveback multiple factors are necessary, including heterogeneity in action potential distribution, tissue coupling, direction of stimulation, the shape of the late plateau, the duration of lost-dome action potentials, and recovery of tissue excitability, which is predominantly modulated by tissue coupling. PMID:26583094

Effects of nerve growth factor on the action potential duration and repolarizing currents in a rabbit model of myocardial infarction

PubMed Central

Lan, Yun-Feng; Zhang, Jian-Cheng; Gao, Jin-Lao; Wang, Xue-Ping; Fang, Zhou; Fu, Yi-Cheng; Chen, Mei-Yan; Lin, Min; Xue, Qiao; Li, Yang

2013-01-01

Objectives To investigate the effect of nerve growth factor (NGF) on the action potential and potassium currents of non-infarcted myocardium in the myocardial infarcted rabbit model. Methods Rabbits with occlusion of the left anterior descending coronary artery were prepared and allowed to recover for eight weeks (healed myocardial infarction, HMI). During ligation surgery of the left coronary artery, a polyethylene tube was placed near the left stellate ganglion in the subcutis of the neck for the purpose of administering NGF 400 U/d for eight weeks (HMI + NGF group). Cardiomyocytes were isolated from regions of the non-infarcted left ventricular wall and the action potentials and ion currents in these cells were recorded using whole-cell patch clamps. Results Compared with HMI and control cardiomyocytes, significant prolongation of APD50 or APD90 (Action potential duration (APD) measured at 50% and 90% of repolarization) in HMI + NGF cardiomyocytes was found. The results showed that the 4-aminopyridine sensitive transient outward potassium current (Ito), the rapidly activated omponent of delayed rectifier potassium current (IKr), the slowly activated component of delayed rectifier potassium current (IKs), and the L-type calcium current (ICaL) were significantly altered in NGF + HMI cardiomyocytes compared with HMI and control cells. Conclusions Our results suggest that NGF treatment significantly prolongs APD in HMI cardiomyocytes and that a decrease in outward potassium currents and an increase of inward Ca2+ current are likely the underlying mechanism of action. PMID:23610573

Effects of nerve growth factor on the action potential duration and repolarizing currents in a rabbit model of myocardial infarction.

PubMed

Lan, Yun-Feng; Zhang, Jian-Cheng; Gao, Jin-Lao; Wang, Xue-Ping; Fang, Zhou; Fu, Yi-Cheng; Chen, Mei-Yan; Lin, Min; Xue, Qiao; Li, Yang

2013-03-01

To investigate the effect of nerve growth factor (NGF) on the action potential and potassium currents of non-infarcted myocardium in the myocardial infarcted rabbit model. Rabbits with occlusion of the left anterior descending coronary artery were prepared and allowed to recover for eight weeks (healed myocardial infarction, HMI). During ligation surgery of the left coronary artery, a polyethylene tube was placed near the left stellate ganglion in the subcutis of the neck for the purpose of administering NGF 400 U/d for eight weeks (HMI + NGF group). Cardiomyocytes were isolated from regions of the non-infarcted left ventricular wall and the action potentials and ion currents in these cells were recorded using whole-cell patch clamps. Compared with HMI and control cardiomyocytes, significant prolongation of APD50 or APD90 (Action potential duration (APD) measured at 50% and 90% of repolarization) in HMI + NGF cardiomyocytes was found. The results showed that the 4-aminopyridine sensitive transient outward potassium current (I to), the rapidly activated omponent of delayed rectifier potassium current (I Kr), the slowly activated component of delayed rectifier potassium current (I Ks), and the L-type calcium current (I CaL) were significantly altered in NGF + HMI cardiomyocytes compared with HMI and control cells. Our results suggest that NGF treatment significantly prolongs APD in HMI cardiomyocytes and that a decrease in outward potassium currents and an increase of inward Ca(2+) current are likely the underlying mechanism of action.

Effects of allocryptopine on outward potassium current and slow delayed rectifier potassium current in rabbit myocardium.

PubMed

Fu, Yi-Cheng; Zhang, Yu; Tian, Liu-Yang; Li, Nan; Chen, Xi; Cai, Zhong-Qi; Zhu, Chao; Li, Yang

2016-05-01

Allocryptopine (ALL) is an effective alkaloid of Corydalis decumbens (Thunb.) Pers. Papaveraceae and has proved to be anti-arrhythmic. The purpose of our study is to investigate the effects of ALL on transmural repolarizing ionic ingredients of outward potassium current (I to) and slow delayed rectifier potassium current (I Ks). The monophasic action potential (MAP) technique was used to record the MAP duration of the epicardium (Epi), myocardium (M) and endocardium (Endo) of the rabbit heart and the whole cell patch clamp was used to record I to and I Ks in cardiomyocytes of Epi, M and Endo layers that were isolated from rabbit ventricles. The effects of ALL on MAP of Epi, M and Endo layers were disequilibrium. ALL could effectively reduce the transmural dispersion of repolarization (TDR) in rabbit transmural ventricular wall. ALL decreased the current densities of I to and I Ks in a voltage and concentration dependent way and narrowed the repolarizing differences among three layers. The analysis of gating kinetics showed ALL accelerated the channel activation of I to in M layers and partly inhibit the channel openings of I to in Epi, M and Endo cells. On the other hand, ALL mainly slowed channel deactivation of I Ks channel in Epi and Endo layers without affecting its activation. Our study gives partially explanation about the mechanisms of transmural inhibition of I to and I Ks channels by ALL in rabbit myocardium. These findings provide novel perspective regarding the anti-arrhythmogenesis application of ALL in clinical settings.

Differential Regulation of Action Potential Shape and Burst-Frequency Firing by BK and Kv2 Channels in Substantia Nigra Dopaminergic Neurons

PubMed Central

Kimm, Tilia; Khaliq, Zayd M.

2015-01-01

Little is known about the voltage-dependent potassium currents underlying spike repolarization in midbrain dopaminergic neurons. Studying mouse substantia nigra pars compacta dopaminergic neurons both in brain slice and after acute dissociation, we found that BK calcium-activated potassium channels and Kv2 channels both make major contributions to the depolarization-activated potassium current. Inhibiting Kv2 or BK channels had very different effects on spike shape and evoked firing. Inhibiting Kv2 channels increased spike width and decreased the afterhyperpolarization, as expected for loss of an action potential-activated potassium conductance. BK inhibition also increased spike width but paradoxically increased the afterhyperpolarization. Kv2 channel inhibition steeply increased the slope of the frequency–current (f–I) relationship, whereas BK channel inhibition had little effect on the f–I slope or decreased it, sometimes resulting in slowed firing. Action potential clamp experiments showed that both BK and Kv2 current flow during spike repolarization but with very different kinetics, with Kv2 current activating later and deactivating more slowly. Further experiments revealed that inhibiting either BK or Kv2 alone leads to recruitment of additional current through the other channel type during the action potential as a consequence of changes in spike shape. Enhancement of slowly deactivating Kv2 current can account for the increased afterhyperpolarization produced by BK inhibition and likely underlies the very different effects on the f–I relationship. The cross-regulation of BK and Kv2 activation illustrates that the functional role of a channel cannot be defined in isolation but depends critically on the context of the other conductances in the cell. SIGNIFICANCE STATEMENT This work shows that BK calcium-activated potassium channels and Kv2 voltage-activated potassium channels both regulate action potentials in dopamine neurons of the substantia nigra pars compacta. Although both channel types participate in action potential repolarization about equally, they have contrasting and partially opposite effects in regulating neuronal firing at frequencies typical of bursting. Our analysis shows that this results from their different kinetic properties, with fast-activating BK channels serving to short-circuit activation of Kv2 channels, which tend to slow firing by producing a deep afterhyperpolarization. The cross-regulation of BK and Kv2 activation illustrates that the functional role of a channel cannot be defined in isolation but depends critically on the context of the other conductances in the cell. PMID:26674866

Differential Regulation of Action Potential Shape and Burst-Frequency Firing by BK and Kv2 Channels in Substantia Nigra Dopaminergic Neurons.

PubMed

Kimm, Tilia; Khaliq, Zayd M; Bean, Bruce P

2015-12-16

Little is known about the voltage-dependent potassium currents underlying spike repolarization in midbrain dopaminergic neurons. Studying mouse substantia nigra pars compacta dopaminergic neurons both in brain slice and after acute dissociation, we found that BK calcium-activated potassium channels and Kv2 channels both make major contributions to the depolarization-activated potassium current. Inhibiting Kv2 or BK channels had very different effects on spike shape and evoked firing. Inhibiting Kv2 channels increased spike width and decreased the afterhyperpolarization, as expected for loss of an action potential-activated potassium conductance. BK inhibition also increased spike width but paradoxically increased the afterhyperpolarization. Kv2 channel inhibition steeply increased the slope of the frequency-current (f-I) relationship, whereas BK channel inhibition had little effect on the f-I slope or decreased it, sometimes resulting in slowed firing. Action potential clamp experiments showed that both BK and Kv2 current flow during spike repolarization but with very different kinetics, with Kv2 current activating later and deactivating more slowly. Further experiments revealed that inhibiting either BK or Kv2 alone leads to recruitment of additional current through the other channel type during the action potential as a consequence of changes in spike shape. Enhancement of slowly deactivating Kv2 current can account for the increased afterhyperpolarization produced by BK inhibition and likely underlies the very different effects on the f-I relationship. The cross-regulation of BK and Kv2 activation illustrates that the functional role of a channel cannot be defined in isolation but depends critically on the context of the other conductances in the cell. This work shows that BK calcium-activated potassium channels and Kv2 voltage-activated potassium channels both regulate action potentials in dopamine neurons of the substantia nigra pars compacta. Although both channel types participate in action potential repolarization about equally, they have contrasting and partially opposite effects in regulating neuronal firing at frequencies typical of bursting. Our analysis shows that this results from their different kinetic properties, with fast-activating BK channels serving to short-circuit activation of Kv2 channels, which tend to slow firing by producing a deep afterhyperpolarization. The cross-regulation of BK and Kv2 activation illustrates that the functional role of a channel cannot be defined in isolation but depends critically on the context of the other conductances in the cell. Copyright © 2015 the authors 0270-6474/15/3516404-14$15.00/0.

Transient voltage-dependent potassium currents are reduced in NTS neurons isolated from renal wrap hypertensive rats.

PubMed

Belugin, Sergei; Mifflin, Steve

2005-12-01

Whole cell patch-clamp measurements were made in neurons enzymatically dispersed from the nucleus of the solitary tract (NTS) to determine if alterations occur in voltage-dependent potassium channels from rats made hypertensive (HT) by unilateral nephrectomy/renal wrap for 4 wk. Some rats had the fluorescent tracer DiA applied to the aortic nerve before the experiment to identify NTS neurons receiving monosynaptic baroreceptor afferent inputs. Mean arterial pressure (MAP) was greater in 4-wk HT (165 +/- 5 mmHg, n = 26, P < 0.001) rats compared with normotensive (NT) rats (109 +/- 3 mmHg measured in 10 of 69 rats). Transient outward currents (TOCs) were observed in 67-82% of NTS neurons from NT and HT rats. At activation voltages from -10 to +10 mV, TOCs were significantly less in HT neurons compared with those observed in NT neurons (P < 0.001). There were no differences in the voltage-dependent activation kinetics, the voltage dependence of steady-state inactivation, and the rise and decay time constants of the TOCs comparing neurons isolated from NT and HT rats. The 4-aminopyridine-sensitive component of the TOC was significantly less in neurons from HT compared with NT rats (P < 0.001), whereas steady-state outward currents, whether or not sensitive to 4-aminopyridine or tetraethylammonium, were not different. Delayed excitation, studied under current clamp, was observed in 60-80% of NTS neurons from NT and HT rats and was not different comparing neurons from NT and HT rats. However, examination of the subset of NTS neurons exhibiting somatic DiA fluorescence revealed that DiA-labeled neurons from HT rats had a significantly shorter duration delayed excitation (n = 8 cells, P = 0.022) than DiA-labeled neurons from NT rats (n = 7 cells). Neurons with delayed excitation from HT rats had a significantly broader first action potential (AP) and a slower maximal downstroke velocity of repolarization compared with NT neurons with delayed excitation (P = 0.016 and P = 0.014, respectively). The number of APs in the first 200 ms of a sustained depolarization was greater in HT than NT neurons (P = 0.012). These results suggest that HT of 4-wk duration reduces TOCs in NTS neurons, and this contributes to reduced delayed excitation and increased AP responses to depolarizing inputs. Such changes could alter baroreflex function in hypertension.

[The influence of occupational lead exposure on transmural repolarization dispersion].

PubMed

Zyśko, Dorota; Gajek, Jacek; Chlebda, Ewa; Mazurek, Walentyna

2005-02-01

The parts of QT interval: time from Q wave to the peak of T wave (QTp) representing the de- and repolarization of subepicardial layer and the time from the peak of T wave to its end (QTp-e) building the transmural dispersion of repolarization enable more exact assessment of repolarization period of the heart muscle. Occupational exposure to lead influences the electrophysiologic properties of the heart. The aim of our study was to assess the QTp and QTp-e interval in workers occupationally exposed to lead. The study was carried out in 22 copper smelters aged 41.8 +/- 8.7 years, occupationally exposed to lead. The control group consisted of 14 healthy men. In all studied subjects blood lead concentration (Pb) and the concentration of free protoporphyrins in erytrocytes were assessed. 24-hour ECG holter monitoring was done to study rhythm disturbances and the duration in lead CM5 of QT interval, QTp interval, RR interval preceding the assessed QT interval (pRR) during sleep, rest during the awake state and moderate daily activity. The QTp-e interval is the difference between the duration of QT and QTp interval. The duration of QTp and QTp-e in occupationally exposed workers and healthy persons did not differ significantly. These parameters were significantly lower in both groups during moderately physical activity comparing to the values during sleep. The QTp-e/ QTp ratio in occupationally exposed workers during night hours was significantly lower than during daily activity what was not the case in control persons. Occupational exposure to lead do not change significantly the transmural dispersion of repolarization. Occupational exposure to lead diminishes the QTp-e/QTp ratio during the night.

A Novel Lead Configuration for Optimal Spatio-Temporal Detection of Intracardiac Repolarization Alternans

PubMed Central

Weiss, Eric H.; Merchant, Faisal M.; d’Avila, Andre; Foley, Lori; Reddy, Vivek Y.; Singh, Jagmeet P.; Mela, Theofanie; Ruskin, Jeremy N.; Armoundas, Antonis A.

2011-01-01

Background Electrical alternans is a pattern of variation in the shape of electrocardiographic waveform that occurs every other beat. In humans, alternation in ventricular repolarization, known as repolarization alternans (RA), has been associated with increased vulnerability to ventricular tachycardia/fibrillation and sudden cardiac death. Methods and Results This study investigates the spatio-temporal variability of intracardiac RA and its relationship to body surface RA in an acute myocardial ischemia model in swine. We developed a real-time multi-channel repolarization signal acquisition, display and analysis system to record electrocardiographic signals from catheters in the right ventricle, coronary sinus, left ventricle, and epicardial surface prior to and following circumflex coronary artery balloon occlusion. We found that RA is detectable within 4 minutes following the onset ischemia, and is most prominently seen during the first half of the repolarization interval. Ischemia-induced RA was detectable on unipolar and bipolar leads (both in near- and far-field configurations) and on body surface leads. Far-field bipolar intracardiac leads were more sensitive for RA detection than body surface leads, with the probability of body surface RA detection increasing as the number of intracardiac leads detecting RA increased, approaching 100% when at least three intracardiac leads detected RA. We developed a novel, clinically-applicable intracardiac lead system based on a triangular arrangement of leads spanning the right ventricular (RV) and coronary sinus (CS) catheters which provided the highest sensitivity for intracardiac RA detection when compared to any other far-field bipolar sensing configurations (p < 0.0001). Conclusions In conclusion, intracardiac alternans, a complex spatio-temporal phenomenon associated with arrhythmia susceptibility and sudden cardiac death, can be reliably detected through a novel triangular RV-CS lead configuration. PMID:21430127

Memory-induced nonlinear dynamics of excitation in cardiac diseases.

PubMed

Landaw, Julian; Qu, Zhilin

2018-04-01

Excitable cells, such as cardiac myocytes, exhibit short-term memory, i.e., the state of the cell depends on its history of excitation. Memory can originate from slow recovery of membrane ion channels or from accumulation of intracellular ion concentrations, such as calcium ion or sodium ion concentration accumulation. Here we examine the effects of memory on excitation dynamics in cardiac myocytes under two diseased conditions, early repolarization and reduced repolarization reserve, each with memory from two different sources: slow recovery of a potassium ion channel and slow accumulation of the intracellular calcium ion concentration. We first carry out computer simulations of action potential models described by differential equations to demonstrate complex excitation dynamics, such as chaos. We then develop iterated map models that incorporate memory, which accurately capture the complex excitation dynamics and bifurcations of the action potential models. Finally, we carry out theoretical analyses of the iterated map models to reveal the underlying mechanisms of memory-induced nonlinear dynamics. Our study demonstrates that the memory effect can be unmasked or greatly exacerbated under certain diseased conditions, which promotes complex excitation dynamics, such as chaos. The iterated map models reveal that memory converts a monotonic iterated map function into a nonmonotonic one to promote the bifurcations leading to high periodicity and chaos.

Memory-induced nonlinear dynamics of excitation in cardiac diseases

NASA Astrophysics Data System (ADS)

Landaw, Julian; Qu, Zhilin

2018-04-01

Excitable cells, such as cardiac myocytes, exhibit short-term memory, i.e., the state of the cell depends on its history of excitation. Memory can originate from slow recovery of membrane ion channels or from accumulation of intracellular ion concentrations, such as calcium ion or sodium ion concentration accumulation. Here we examine the effects of memory on excitation dynamics in cardiac myocytes under two diseased conditions, early repolarization and reduced repolarization reserve, each with memory from two different sources: slow recovery of a potassium ion channel and slow accumulation of the intracellular calcium ion concentration. We first carry out computer simulations of action potential models described by differential equations to demonstrate complex excitation dynamics, such as chaos. We then develop iterated map models that incorporate memory, which accurately capture the complex excitation dynamics and bifurcations of the action potential models. Finally, we carry out theoretical analyses of the iterated map models to reveal the underlying mechanisms of memory-induced nonlinear dynamics. Our study demonstrates that the memory effect can be unmasked or greatly exacerbated under certain diseased conditions, which promotes complex excitation dynamics, such as chaos. The iterated map models reveal that memory converts a monotonic iterated map function into a nonmonotonic one to promote the bifurcations leading to high periodicity and chaos.

Nonlinear Dynamic Modeling of Neuron Action Potential Threshold During Synaptically Driven Broadband Intracellular Activity

PubMed Central

Roach, Shane M.; Song, Dong; Berger, Theodore W.

2012-01-01

Activity-dependent variation of neuronal thresholds for action potential (AP) generation is one of the key determinants of spike-train temporal-pattern transformations from presynaptic to postsynaptic spike trains. In this study, we model the nonlinear dynamics of the threshold variation during synaptically driven broadband intracellular activity. First, membrane potentials of single CA1 pyramidal cells were recorded under physiologically plausible broadband stimulation conditions. Second, a method was developed to measure AP thresholds from the continuous recordings of membrane potentials. It involves measuring the turning points of APs by analyzing the third-order derivatives of the membrane potentials. Four stimulation paradigms with different temporal patterns were applied to validate this method by comparing the measured AP turning points and the actual AP thresholds estimated with varying stimulation intensities. Results show that the AP turning points provide consistent measurement of the AP thresholds, except for a constant offset. It indicates that 1) the variation of AP turning points represents the nonlinearities of threshold dynamics; and 2) an optimization of the constant offset is required to achieve accurate spike prediction. Third, a nonlinear dynamical third-order Volterra model was built to describe the relations between the threshold dynamics and the AP activities. Results show that the model can predict threshold accurately based on the preceding APs. Finally, the dynamic threshold model was integrated into a previously developed single neuron model and resulted in a 33% improvement in spike prediction. PMID:22156947

Heart Electrical Actions as Biometric Indicia

NASA Technical Reports Server (NTRS)

Schipper, John F. (Inventor); Dusan, Sorin V. (Inventor); Jorgensen, Charles C. (Inventor); Belousof, Eugene (Inventor)

2013-01-01

A method and associated system for use of statistical parameters based on peak amplitudes and/or time interval lengths and/or depolarization-repolarization vector angles and/or depolarization-repolarization vector lengths for PQRST electrical signals associated with heart waves, to identify a person. The statistical parameters, estimated to be at least 192, serve as biometric indicia, to authenticate, or to decline to authenticate, an asserted identity of a candidate person.

Effects of premature stimulation on HERG K+ channels

PubMed Central

Lu, Yu; Mahaut-Smith, Martyn P; Varghese, Anthony; Huang, Christopher L-H; Kemp, Paul R; Vandenberg, Jamie I

2001-01-01

The unusual kinetics of human ether-à-go-go-related gene (HERG) K+ channels are consistent with a role in the suppression of arrhythmias initiated by premature beats. Action potential clamp protocols were used to investigate the effect of premature stimulation on HERG K+ channels, transfected in Chinese hamster ovary cells, at 37 °C. HERG K+ channel currents peaked during the terminal repolarization phase of normally paced action potential waveforms. However, the magnitude of the current and the time point at which conductance was maximal depended on the type of action potential waveform used (epicardial, endocardial, Purkinje fibre or atrial). HERG K+ channel currents recorded during premature action potentials consisted of an early transient outward current followed by a sustained outward current. The magnitude of the transient current component showed a biphasic dependence on the coupling interval between the normally paced and premature action potentials and was maximal at a coupling interval equivalent to 90% repolarization (APD90) for ventricular action potentials. The largest transient current response occurred at shorter coupling intervals for Purkinje fibre (APD90– 20 ms) and atrial (APD90– 30 ms) action potentials. The magnitude of the sustained current response following premature stimulation was similar to that recorded during the first action potential for ventricular action potential waveforms. However, for Purkinje and atrial action potentials the sustained current response was significantly larger during the premature action potential than during the normally paced action potential. A Markov model that included three closed states, one open and one inactivated state with transitions permitted between the pre-open closed state and the inactivated state, successfully reproduced our results for the effects of premature stimuli, both during square pulse and action potential clamp waveforms. These properties of HERG K+ channels may help to suppress arrhythmias initiated by early afterdepolarizations and premature beats in the ventricles, Purkinje fibres or atria. PMID:11744759

Differential responses of rabbit ventricular and atrial transient outward current (Ito) to the Ito modulator NS5806.

PubMed

Cheng, Hongwei; Cannell, Mark B; Hancox, Jules C

2017-03-01

Transient outward potassium current (I to ) in the heart underlies phase 1 repolarization of cardiac action potentials and thereby affects excitation-contraction coupling. Small molecule activators of I to may therefore offer novel treatments for cardiac dysfunction, including heart failure and atrial fibrillation. NS5806 has been identified as a prototypic activator of canine I to This study investigated, for the first time, actions of NS5806 on rabbit atrial and ventricular I to Whole cell patch-clamp recordings of I to and action potentials were made at physiological temperature from rabbit ventricular and atrial myocytes. 10  μ mol/L NS5806 increased ventricular I to with a leftward shift in I to activation and accelerated restitution. At higher concentrations, stimulation of I to was followed by inhibition. The EC 50 for stimulation was 1.6  μ mol/L and inhibition had an IC 50 of 40.7  μ mol/L. NS5806 only inhibited atrial I to (IC 50 of 18  μ mol/L) and produced a modest leftward shifts in I to activation and inactivation, without an effect on restitution. 10  μ mol/L NS5806 shortened ventricular action potential duration (APD) at APD 20 -APD 90 but prolonged atrial APD NS5806 also reduced atrial AP upstroke and amplitude, consistent with an additional atrio-selective effect on Na + channels. In contrast to NS5806, flecainide, which discriminates between Kv1.4 and 4.x channels, produced similar levels of inhibition of ventricular and atrial I to NS5806 discriminates between rabbit ventricular and atrial I to, with mixed activator and inhibitor actions on the former and inhibitor actions against the later. NS5806 may be of significant value for pharmacological interrogation of regional differences in native cardiac I to . © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

Factor Xa Mediates Calcium Flux in Endothelial Cells and is Potentiated by Igg From Patients With Lupus and/or Antiphospholipid Syndrome.

PubMed

Artim-Esen, Bahar; Smoktunowicz, Natalia; McDonnell, Thomas; Ripoll, Vera M; Pericleous, Charis; Mackie, Ian; Robinson, Eifion; Isenberg, David; Rahman, Anisur; Ioannou, Yiannis; Chambers, Rachel C; Giles, Ian

2017-09-07

Factor (F) Xa reactive IgG isolated from patients with antiphospholipid syndrome (APS) display higher avidity binding to FXa with greater coagulant effects compared to systemic lupus erythematosus (SLE) non APS IgG. FXa signalling via activation of protease-activated receptors (PAR) leads to increased intracellular calcium (Ca 2+ ). Therefore, we measured alterations in Ca 2+ levels in human umbilical vein endothelial cells (HUVEC) following FXa-mediated PAR activation and investigated whether FXa reactive IgG from patients with APS or SLE/APS- alter these responses. We observed concentration-dependent induction of Ca 2+ release by FXa that was potentiated by APS-IgG and SLE/APS- IgG compared to healthy control subjects' IgG, and FXa alone. APS-IgG and SLE/APS- IgG increased FXa mediated NFκB signalling and this effect was fully-retained in the affinity purified anti-FXa IgG sub-fraction. Antagonism of PAR-1 and PAR-2 reduced FXa-induced Ca 2+ release. Treatment with a specific FXa inhibitor, hydroxychloroquine or fluvastatin significantly reduced FXa-induced and IgG-potentiated Ca 2+ release. In conclusion, PAR-1 and PAR-2 are involved in FXa-mediated intracellular Ca 2+ release in HUVEC and FXa reactive IgG from patients with APS and/or SLE potentiate this effect. Further work is required to explore the potential use of IgG FXa reactivity as a novel biomarker to stratify treatment with FXa inhibitors in these patients.

Choline-modulated arsenic trioxide-induced prolongation of cardiac repolarization in Guinea pig.

PubMed

Sun, Hong-Li; Chu, Wen-Feng; Dong, De-Li; Liu, Yan; Bai, Yun-Long; Wang, Xiao-Hui; Zhou, Jin; Yang, Bao-Feng

2006-04-01

Arsenic trioxide (As(2)O(3)) has been found to be effective for relapsed or refractory acute promyelocytic leukaemia, but its clinical use is burdened by QT prolongation, Torsade de pointes tachycardias, and sudden cardiac death. The aim of the present study was to elucidate the ionic mechanisms of As(2)O(3)-induced abnormalities of cardiac electrophysiology and the therapeutic action of choline on As(2)O(3)-caused QT prolongation in guinea pig. Intravenous administration of As(2)O(3) prolonged the QT interval in a dose- and time-dependent manner in guinea pig hearts, and the QT prolongation could be modulated by choline. By using whole-cell patch clamp technique and confocal laser scanning microscopy, we found that As(2)O(3) significantly lengthened action potential duration measured at 50 and 90% of repolarization, enhanced L-type calcium currents (I(Ca-L)), inhibited delayed rectifier potassium currents (I(K)), and increased intracellular calcium concentration ([Ca(2+)](i)) in guinea pig ventricular myocytes. Choline corrected As(2)O(3)-mediated alterations of action potential duration, I(Ca-L) and [Ca(2+)](i), but had no effect on the I(K) inhibition. As(2)O(3) markedly disturbed the normal equilibrium of transmembrane currents (increasing I(Ca-L) and suppressing I(K)) in guinea pig cardiomyocyte, and induced prolongation of action potential duration, further degenerated into QT prolongation. Choline normalized QT interval abnormality and corrected lengthened action potential duration by inhibiting the elevated I(Ca-L) and [Ca(2+)](i) in ventricular myocytes during As(2)O(3) application.

Vitamin K modulates cardiac action potential by blocking sodium and potassium ion channels.

PubMed

Drolet, B; Emond, A; Fortin, V; Daleau, P; Rousseau, G; Cardinal, R; Turgeon, J

2000-10-01

Cardiovascular collapses, syncopes, and sudden deaths have been observed following the rapid administration of intravenous vitamin K. Our objectives were to characterize the effects of vitamin K on cardiac action potentials and to evaluate effects of vitamin K on sodium and potassium currents, namely I(Na), I(Kr), and I(Ks). Guinea pig hearts (n = 21) were paced at a cycle length of 250 msec and exposed to vitamin K at 1.15-4.6 micromol/L (2.5-10 mg/L). Monophasic action potential duration measured at 90% repolarization (MAPD(90)) was not significantly reduced (-1.6 +/- 0.3 msec; P >.05; N.S.) at 1.15 micromol/L, but increased by 6.5 +/- 0.4 msec (P <.05) at 2.3 micromol/L. MAPD(90) was not measurable at 4.6 micromol/L, as a result of inexcitability. Patch-clamp experiments in ventricular myocytes demonstrated a approximately 50% reduction in I(Na) by 10 micromol/L vitamin K and a concentration-dependent reduction of the K(+) current elicited by short depolarizations (250 msec; I(K250)). Estimated IC(50) for I(K250), mostly representing I(Kr), was 2.3 micromol/L. Vitamin K was less potent to block the K(+) current elicited by long depolarizations (5,000 msec; I(K5000)), mostly representing I(Ks), with an estimated IC(50) over 100 micromol/L. Therapeutic concentrations ( approximately 1.5 micromol/L) of intravenous vitamin K modulate cardiac action potential by blocking ionic currents involved in cardiac depolarization and repolarization.

Changes in left ventricular repolarization and ion channel currents following a transient rate increase superimposed on bradycardia in anesthetized dogs.

PubMed

Rubart, M; Lopshire, J C; Fineberg, N S; Zipes, D P

2000-06-01

We previously demonstrated in dogs that a transient rate increase superimposed on bradycardia causes prolongation of ventricular refractoriness that persists for hours after resumption of bradycardia. In this study, we examined changes in membrane currents that are associated with this phenomenon. The whole cell, patch clamp technique was used to record transmembrane voltages and currents, respectively, in single mid-myocardial left ventricular myocytes from dogs with 1 week of complete AV block; dogs either underwent 1 hour of left ventricular pacing at 120 beats/min or did not undergo pacing. Pacing significantly heightened mean phase 1 and peak plateau amplitudes by approximately 6 and approximately 3 mV, respectively (P < 0.02), and prolonged action potential duration at 90% repolarization from 235+/-8 msec to 278+/-8 msec (1 Hz; P = 0.02). Rapid pacing-induced changes in transmembrane ionic currents included (1) a more pronounced cumulative inactivation of the 4-aminopyridine-sensitive transient outward K+ current, Ito, over the range of physiologic frequencies, resulting from a approximately 30% decrease in the population of quickly reactivating channels; (2) increases in peak density of L-type Ca2+ currents, I(Ca.L), by 15% to 35 % between +10 and +60 mV; and (3) increases in peak density of the Ca2+-activated chloride current, I(Cl.Ca), by 30% to 120% between +30 and +50 mV. Frequency-dependent reduction in Ito combined with enhanced I(Ca.L) causes an increase in net inward current that may be responsible for the observed changes in ventricular repolarization. This augmentation of net cation influx is partially antagonized by an increase in outward I(Ca.Cl).

Ventricular stimulus site influences dynamic dispersion of repolarization in the intact human heart

PubMed Central

Orini, Michele; Simon, Ron B.; Providência, Rui; Khan, Fakhar Z.; Segal, Oliver R.; Babu, Girish G.; Bradley, Richard; Rowland, Edward; Ahsan, Syed; Chow, Anthony W.; Lowe, Martin D.; Taggart, Peter

2016-01-01

The spatial variation in restitution properties in relation to varying stimulus site is poorly defined. This study aimed to investigate the effect of varying stimulus site on apicobasal and transmural activation time (AT), action potential duration (APD) and repolarization time (RT) during restitution studies in the intact human heart. Ten patients with structurally normal hearts, undergoing clinical electrophysiology studies, were enrolled. Decapolar catheters were placed apex to base in the endocardial right ventricle (RVendo) and left ventricle (LVendo), and an LV branch of the coronary sinus (LVepi) for transmural recording. S1–S2 restitution protocols were performed pacing RVendo apex, LVendo base, and LVepi base. Overall, 725 restitution curves were analyzed, 74% of slopes had a maximum slope of activation recovery interval (ARI) restitution (Smax) > 1 (P < 0.001); mean Smax = 1.76. APD was shorter in the LVepi compared with LVendo, regardless of pacing site (30-ms difference during RVendo pacing, 25-ms during LVendo, and 48-ms during LVepi; 50th quantile, P < 0.01). Basal LVepi pacing resulted in a significant transmural gradient of RT (77 ms, 50th quantile: P < 0.01), due to loss of negative transmural AT-APD coupling (mean slope 0.63 ± 0.3). No significant transmural gradient in RT was demonstrated during endocardial RV or LV pacing, with preserved negative transmural AT-APD coupling (mean slope −1.36 ± 1.9 and −0.71 ± 0.4, respectively). Steep ARI restitution slopes predominate in the normal ventricle and dynamic ARI; RT gradients exist that are modulated by the site of activation. Epicardial stimulation to initiate ventricular activation promotes significant transmural gradients of repolarization that could be proarrhythmic. PMID:27371682

QT Adaptation and Intrinsic QT Variability in Congenital Long QT Syndrome.

PubMed

Seethala, Srikanth; Singh, Prabhpreet; Shusterman, Vladimir; Ribe, Margareth; Haugaa, Kristina H; Němec, Jan

2015-12-16

Increased variability of QT interval (QTV) has been linked to arrhythmias in animal experiments and multiple clinical situations. Congenital long QT syndrome (LQTS), a pure repolarization disease, may provide important information on the relationship between delayed repolarization and QTV. Twenty-four-hour Holter monitor tracings from 78 genotyped congenital LQTS patients (52 females; 51 LQT1, 23 LQT2, 2 LQT5, 2 JLN, 27 symptomatic; age, 35.2±12.3 years) were evaluated with computer-assisted annotation of RR and QT intervals. Several models of RR-QT relationship were tested in all patients. A model assuming exponential decrease of past RR interval contributions to QT duration with 60-second time constant provided the best data fit. This model was used to calculate QTc and residual "intrinsic" QTV, which cannot be explained by heart rate change. The intrinsic QTV was higher in patients with long QTc (r=0.68; P<10(-4)), and in LQT2 than in LQT1/5 patients (5.65±1.28 vs 4.46±0.82; P<0.0002). Both QTc and intrinsic QTV were similar in symptomatic and asymptomatic patients (467±52 vs 459±53 ms and 5.10±1.19 vs 4.74±1.09, respectively). In LQTS patients, QT interval adaptation to heart rate changes occurs with time constant ≈60 seconds, similar to results reported in control subjects. Intrinsic QTV correlates with the degree of repolarization delay and might reflect action potential instability observed in animal models of LQTS. © 2015 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.

Electrophysiological determinants of arrhythmic susceptibility upon endocardial and epicardial pacing in guinea-pig heart.

PubMed

Osadchii, O E

2012-08-01

Endocardial pacing instituted to treat symptomatic bradycardia may nevertheless promote tachyarrhythmia in some pacemaker-implanted patients. We sought to determine the contributing electrophysiological mechanisms. Left ventricular (LV) monophasic action potential duration (APD(90)) and effective refractory periods were determined in perfused guinea-pig hearts along with volume-conducted ECG recordings during epicardial and endocardial stimulations. Consistent with electrotonic modulation of repolarization, APD(90) at a given (either epicardial or endocardial) recording site tended to be longer while pacing from the ipsilateral LV site as compared to stimulations applied at the opposite side of ventricular wall. As a result, the intrinsic transmural repolarization gradient was amplified during endocardial pacing while being significantly reduced upon epicardial stimulations. The maximum slope of APD(90) restitution was greater upon endocardial than epicardial pacing. The excitability was found to recur at earlier repolarization time point at endocardium than epicardium, thereby contributing to increased endocardial critical intervals for re-excitation. Premature extrasystolic beats could have been elicited at shorter coupling stimulation intervals and propagated with greater transmural conduction delay upon endocardial than epicardial stimulations. Endocardial site exhibited lower ventricular fibrillation thresholds and greater inducibility of tachyarrhythmia upon extrasystolic stimulations as compared to epicardium. Arrhythmic susceptibility in guinea-pig heart is greater during endocardial than epicardial pacing because of greater transmural APD(90) dispersion, steeper electrical restitution slopes, greater critical intervals for LV re-excitation and slower transmural conduction of the earliest premature ectopic beats. Further studies are warranted to determine whether these effects may contribute to proarrhythmia in paced human patients. © 2012 The Author Acta Physiologica © 2012 Scandinavian Physiological Society.

Electrophysiological changes of autonomic cells in left ventricular outflow tract in guinea pigs with iron deficiency anemia complicated with chronic heart failure.

PubMed

Fan, Ling; Chen, Li-Feng; Fan, Jing

2017-12-01

To investigate the electrophysiological changes of autonomic cells in left ventricular outflow tract in guinea pigs with iron deficiency anemia complicated with chronic heart failure. Guinea pigs model of iron deficiency anemia complicated with chronic heart failure in 10 guinea pigs of the experimental group was made by feeding a low iron diet, pure water and subcutaneous injection of isoproterenol. The control group consisting of 11 guinea pigs was given normal food, normal water and injected with normal saline. The left ventricular outflow tract model specimen was also prepared. The standard microelectrode technique was used to observe electrophysiological changes of autonomic cells in the outflow tract of left ventricular heart failure complicated with iron deficiency anemia in guinea pig model. The indicators of observation were maximal diastolic potential, action potential amplitude, 0 phase maximal depolarization velocity, 4 phase automatic depolarization velocity, repolarization 50% and 90%, and spontaneous discharge frequency. Compared with the control group, 4 phase automatic depolarization velocity, spontaneous discharge frequency and 0 phase maximal depolarization velocity decreased significantly (P < 0.01) and action potential amplitude reduced (P < 0.01) in model group. Moreover, repolarization 50% and 90% increased (P < 0.01). There are electrophysiological abnormalities of the left ventricular outflow tract in guinea pigs with iron deficiency anemia complicated with heart failure. Copyright © 2017 Hainan Medical University. Production and hosting by Elsevier B.V. All rights reserved.

Changes in extracellular pH and myocardial ischaemia alter the cardiac effects of diadenosine tetraphosphate and pentaphosphate

PubMed Central

Stavrou, Brigitte M; Beck, Caroline; Flores, Nicholas A

2001-01-01

The structural conformation of diadenosine tetraphosphate (Ap4A) and pentaphosphate (Ap5A) has been reported to alter as pH is reduced. As such, it is possible that the cardiac effects of Ap4A and Ap5A vary during acidosis and myocardial ischaemia due to changes in ligand structure, receptor proteins or intracellular signalling. We investigated whether the cardiac electrophysiological and coronary vasomotor effects of Ap4A and Ap5A are preserved under conditions of extracellular acidosis (pH 6.5) and alkalosis (pH 8.5) and whether Ap4A has any electrophysiological or antiarrhythmic effects during ischaemia. Transmembrane right ventricular action potentials, refractory periods and coronary perfusion pressure were recorded from isolated, Langendorff-perfused guinea-pig hearts under constant flow conditions. The effects of 1 nM and 1 μM Ap4A and Ap5A were studied at pH 7.4, 6.5 and 8.5. The effects of 1 μM Ap4A were studied during global low-flow ischaemia and reperfusion. At pH 7.4, Ap4A and Ap5A increased action potential duration (APD95) and refractory period (RP) and reduced coronary perfusion pressure. The electrophysiological effects were absent at pH 6.5 while the reductions in perfusion pressure were attenuated. At pH 8.5, Ap4A increased RP but the effects of Ap4A and Ap5A on perfusion pressure were attenuated. During ischaemia, Ap4A had no antiarrhythmic or electrophysiological effects. These data demonstrate the importance of extracellular pH in influencing the effects of Ap4A and Ap5A on the heart and indicate that any potentially cardioprotective effects of these compounds during normal perfusion at physiological pH are absent during ischaemia. PMID:11588119

Effects of early afterdepolarizations on excitation patterns in an accurate model of the human ventricles

PubMed Central

Seemann, Gunnar; Panfilov, Alexander V.; Vandersickel, Nele

2017-01-01

Early Afterdepolarizations, EADs, are defined as the reversal of the action potential before completion of the repolarization phase, which can result in ectopic beats. However, the series of mechanisms of EADs leading to these ectopic beats and related cardiac arrhythmias are not well understood. Therefore, we aimed to investigate the influence of this single cell behavior on the whole heart level. For this study we used a modified version of the Ten Tusscher-Panfilov model of human ventricular cells (TP06) which we implemented in a 3D ventricle model including realistic fiber orientations. To increase the likelihood of EAD formation at the single cell level, we reduced the repolarization reserve (RR) by reducing the rapid delayed rectifier Potassium current and raising the L-type Calcium current. Varying these parameters defined a 2D parametric space where different excitation patterns could be classified. Depending on the initial conditions, by either exciting the ventricles with a spiral formation or burst pacing protocol, we found multiple different spatio-temporal excitation patterns. The spiral formation protocol resulted in the categorization of a stable spiral (S), a meandering spiral (MS), a spiral break-up regime (SB), spiral fibrillation type B (B), spiral fibrillation type A (A) and an oscillatory excitation type (O). The last three patterns are a 3D generalization of previously found patterns in 2D. First, the spiral fibrillation type B showed waves determined by a chaotic bi-excitable regime, i.e. mediated by both Sodium and Calcium waves at the same time and in same tissue settings. In the parameter region governed by the B pattern, single cells were able to repolarize completely and different (spiral) waves chaotically burst into each other without finishing a 360 degree rotation. Second, spiral fibrillation type A patterns consisted of multiple small rotating spirals. Single cells failed to repolarize to the resting membrane potential hence prohibiting the Sodium channel gates to recover. Accordingly, we found that Calcium waves mediated these patterns. Third, a further reduction of the RR resulted in a more exotic parameter regime whereby the individual cells behaved independently as oscillators. The patterns arose due to a phase-shift of different oscillators as disconnection of the cells resulted in continuation of the patterns. For all patterns, we computed realistic 9 lead ECGs by including a torso model. The B and A type pattern exposed the behavior of Ventricular Tachycardia (VT). We conclude that EADs at the single cell level can result in different types of cardiac fibrillation at the tissue and 3D ventricle level. PMID:29216239

A four-component model of the action potential in mouse detrusor smooth muscle cell

PubMed Central

Brain, Keith L.; Young, John S.; Manchanda, Rohit

2018-01-01

Background and hypothesis Detrusor smooth muscle cells (DSMCs) of the urinary bladder are electrically connected to one another via gap junctions and form a three dimensional syncytium. DSMCs exhibit spontaneous electrical activity, including passive depolarizations and action potentials. The shapes of spontaneous action potentials (sAPs) observed from a single DSM cell can vary widely. The biophysical origins of this variability, and the precise components which contribute to the complex shapes observed are not known. To address these questions, the basic components which constitute the sAPs were investigated. We hypothesized that linear combinations of scaled versions of these basic components can produce sAP shapes observed in the syncytium. Methods and results The basic components were identified as spontaneous evoked junction potentials (sEJP), native AP (nAP), slow after hyperpolarization (sAHP) and very slow after hyperpolarization (vsAHP). The experimental recordings were grouped into two sets: a training data set and a testing data set. A training set was used to estimate the components, and a test set to evaluate the efficiency of the estimated components. We found that a linear combination of the identified components when appropriately amplified and time shifted replicated various AP shapes to a high degree of similarity, as quantified by the root mean square error (RMSE) measure. Conclusions We conclude that the four basic components—sEJP, nAP, sAHP, and vsAHP—identified and isolated in this work are necessary and sufficient to replicate all varieties of the sAPs recorded experimentally in DSMCs. This model has the potential to generate testable hypotheses that can help identify the physiological processes underlying various features of the sAPs. Further, this model also provides a means to classify the sAPs into various shape classes. PMID:29351282

A four-component model of the action potential in mouse detrusor smooth muscle cell.

PubMed

Padmakumar, Mithun; Brain, Keith L; Young, John S; Manchanda, Rohit

2018-01-01

Detrusor smooth muscle cells (DSMCs) of the urinary bladder are electrically connected to one another via gap junctions and form a three dimensional syncytium. DSMCs exhibit spontaneous electrical activity, including passive depolarizations and action potentials. The shapes of spontaneous action potentials (sAPs) observed from a single DSM cell can vary widely. The biophysical origins of this variability, and the precise components which contribute to the complex shapes observed are not known. To address these questions, the basic components which constitute the sAPs were investigated. We hypothesized that linear combinations of scaled versions of these basic components can produce sAP shapes observed in the syncytium. The basic components were identified as spontaneous evoked junction potentials (sEJP), native AP (nAP), slow after hyperpolarization (sAHP) and very slow after hyperpolarization (vsAHP). The experimental recordings were grouped into two sets: a training data set and a testing data set. A training set was used to estimate the components, and a test set to evaluate the efficiency of the estimated components. We found that a linear combination of the identified components when appropriately amplified and time shifted replicated various AP shapes to a high degree of similarity, as quantified by the root mean square error (RMSE) measure. We conclude that the four basic components-sEJP, nAP, sAHP, and vsAHP-identified and isolated in this work are necessary and sufficient to replicate all varieties of the sAPs recorded experimentally in DSMCs. This model has the potential to generate testable hypotheses that can help identify the physiological processes underlying various features of the sAPs. Further, this model also provides a means to classify the sAPs into various shape classes.

Cardiac Autonomic Regulation and Repolarization During Acute Experimental Hypoglycemia in Type 2 Diabetes

PubMed Central

Chow, Elaine; Bernjak, Alan; Walkinshaw, Emma; Lubina-Solomon, Alexandra; Freeman, Jenny; Macdonald, Ian A.; Sheridan, Paul J.

2017-01-01

Hypoglycemia is associated with increased cardiovascular mortality in trials of intensive therapy in type 2 diabetes mellitus (T2DM). We previously observed an increase in arrhythmias during spontaneous prolonged hypoglycemia in patients with T2DM. We examined changes in cardiac autonomic function and repolarization during sustained experimental hypoglycemia. Twelve adults with T2DM and 11 age- and BMI-matched control participants without diabetes underwent paired hyperinsulinemic clamps separated by 4 weeks. Glucose was maintained at euglycemia (6.0 mmol/L) or hypoglycemia (2.5 mmol/L) for 1 h. Heart rate, blood pressure, and heart rate variability were assessed every 30 min and corrected QT intervals and T-wave morphology every 60 min. Heart rate initially increased in participants with T2DM but then fell toward baseline despite maintained hypoglycemia at 1 h accompanied by reactivation of vagal tone. In control participants, vagal tone remained depressed during sustained hypoglycemia. Participants with T2DM exhibited greater heterogeneity of repolarization during hypoglycemia as demonstrated by T-wave symmetry and principal component analysis ratio compared with control participants. Epinephrine levels during hypoglycemia were similar between groups. Cardiac autonomic regulation during hypoglycemia appears to be time dependent. Individuals with T2DM demonstrate greater repolarization abnormalities for a given hypoglycemic stimulus despite comparable sympathoadrenal responses. These mechanisms could contribute to arrhythmias during clinical hypoglycemic episodes. PMID:28137792

AP® Potential Predicted by PSAT/NMSQT® Scores Using Logistic Regression. Statistical Report 2014-1

ERIC Educational Resources Information Center

Zhang, Xiuyuan; Patel, Priyank; Ewing, Maureen

2014-01-01

AP Potential™ is an educational guidance tool that uses PSAT/NMSQT® scores to identify students who have the potential to do well on one or more Advanced Placement® (AP®) Exams. Students identified as having AP potential, perhaps students who would not have been otherwise identified, should consider enrolling in the corresponding AP course if they…

Characteristics of action potentials and their underlying outward currents in rat taste receptor cells.

PubMed

Chen, Y; Sun, X D; Herness, S

1996-02-01

1. Taste receptor cells produce action potentials as a result of transduction mechanisms that occur when these cells are stimulated with tastants. These action potentials are thought to be key signaling events in relaying information to the central nervous system. We explored the ionic basis of action potentials from dissociated posterior rat taste cells using the patch-clamp recording technique in both voltage-clamp and current-clamp modes. 2. Action potentials were evoked by intracellular injection of depolarizing current pulses from a holding potential of -80 mV. The threshold potential for firing of action potentials was approximately -35 mV; the input resistance of these cells averaged 6.9 G omega. With long depolarizing pulses, two or three action potentials could be elicited with successive attenuation of the spike height. Afterhyperpolarizations were observed often. 3. Both sodium and calcium currents contribute to depolarizing phases of the action potential. Action potentials were blocked completely in the presence of the sodium channel blocker tetrodotoxin. Calcium contributions could be visualized as prolonged calcium plateaus when repolarizing potassium currents were blocked and barium was used as a charge carrier. 4. Outward currents were composed of sustained delayed rectifier current, transient potassium current, and calcium-activated potassium current. Transient and sustained potassium currents activated close to -30 mV and increased monotonically with further depolarization. Up to half the outward current inactivated with decay constants on the order of seconds. Sustained and transient currents displayed steep voltage dependence in conductance and inactivation curves. Half inactivation occurred at -20 +/- 3.1 mV (mean +/- SE) with a decrease of 11.2 +/- 0.5 mV per e-fold. Half maximal conductance occurred at 3.6 +/- 1.8 mV and increased 12.2 +/- 0.6 mV per e-fold. Calcium-activated potassium current was evidenced by application of apamin and the use of calcium-free bathing solution. It was most obvious at more depolarized holding potentials that inactivated much of the transient and sustained outward currents. 5. Potassium currents contribute to both the repolarization and afterhyperpolarization phases of the action potential. These currents were blocked by bath application of tetraethylammonium, which also substantially broadened the action potential. Application of 4-aminopyridine was able to selectively block transient potassium currents without affecting sustained currents. This also broadened the action potential as well as eliminated the afterhyperpolarization. 6. A second type of action potential was observed that differed in duration. These slow action potentials had t1/2 durations of 9.6 ms compared with 1.4 ms for fast action potentials. Input resistances of the two groups were indistinguishable. Approximately one-fourth of the cells eliciting action potentials were of the slow type. 7. Cells eliciting fast action potentials had large outward currents capable of producing a quick repolarization, whereas cells with slow action potentials had small outward currents by comparison. The average values of fast cells were 2,563 pA and 1.4 ms compared with 373 pA and 9.6 ms for slow cells. Current and duration values were related exponentially. No significant difference was noted for inward currents. 8. These results suggest that many taste receptor cells conduct action potentials, which may be classified broadly into two groups on the basis of action potential duration and potassium current magnitude. These groups may be related to cell turnover. The physiological role of action potentials remains to be elucidated but may be important for communication within the taste bud as well as to the afferent nerve.

A non-inactivating high-voltage-activated two-pore Na+ channel that supports ultra-long action potentials and membrane bistability

NASA Astrophysics Data System (ADS)

Cang, Chunlei; Aranda, Kimberly; Ren, Dejian

2014-09-01

Action potentials (APs) are fundamental cellular electrical signals. The genesis of short APs lasting milliseconds is well understood. Ultra-long APs (ulAPs) lasting seconds to minutes also occur in eukaryotic organisms, but their biological functions and mechanisms of generation are largely unknown. Here, we identify TPC3, a previously uncharacterized member of the two-pore channel protein family, as a new voltage-gated Na+ channel (NaV) that generates ulAPs, and that establishes membrane potential bistability. Unlike the rapidly inactivating NaVs that generate short APs in neurons, TPC3 has a high activation threshold, activates slowly and does not inactivate—three properties that help generate long-lasting APs and guard the membrane against unintended perturbation. In amphibian oocytes, TPC3 forms a channel similar to channels induced by depolarization and sperm entry into eggs. TPC3 homologues are present in plants and animals, and they may be important for cellular processes and behaviours associated with prolonged membrane depolarization.

Dendritic mechanisms underlying the coupling of the dendritic with the axonal action potential initiation zone of adult rat layer 5 pyramidal neurons

PubMed Central

Larkum, M E; Zhu, J J; Sakmann, B

2001-01-01

Double, triple and quadruple whole-cell voltage recordings were made simultaneously from different parts of the apical dendritic arbor and the soma of adult layer 5 (L5) pyramidal neurons. We investigated the membrane mechanisms that support the conduction of dendritic action potentials (APs) between the dendritic and axonal AP initiation zones and their influence on the subsequent AP pattern. The duration of the current injection to the distal dendritic initiation zone controlled the degree of coupling with the axonal initiation zone and the AP pattern. Two components of the distally evoked regenerative potential were pharmacologically distinguished: a rapidly rising peak potential that was TTX sensitive and a slowly rising plateau-like potential that was Cd2+ and Ni2+ sensitive and present only with longer-duration current injection. The amplitude of the faster forward-propagating Na+-dependent component and the amplitude of the back-propagating AP fell into two classes (more distinctly in the forward-propagating case). Current injection into the dendrite altered propagation in both directions. Somatic current injections that elicited single Na+ APs evoked bursts of Na+ APs when current was injected simultaneously into the proximal apical dendrite. The mechanism did not depend on dendritic Na+–Ca2+ APs. A three-compartment model of a L5 pyramidal neuron is proposed. It comprises the distal dendritic and axonal AP initiation zones and the proximal apical dendrite. Each compartment contributes to the initiation and to the pattern of AP discharge in a distinct manner. Input to the three main dendritic arbors (tuft dendrites, apical oblique dendrites and basal dendrites) has a dominant influence on only one of these compartments. Thus, the AP pattern of L5 pyramids reflects the laminar distribution of synaptic activity in a cortical column. PMID:11389204

Unique Cardiac Purkinje Fiber Transient Outward Current β-Subunit Composition

PubMed Central

Xiao, Ling; Koopmann, Tamara T.; Ördög, Balázs; Postema, Pieter G.; Verkerk, Arie O.; Iyer, Vivek; Sampson, Kevin J.; Boink, Gerard J.J.; Mamarbachi, Maya A.; Varro, Andras; Jordaens, Luc; Res, Jan; Kass, Robert S.; Wilde, Arthur A.; Bezzina, C.R.; Nattel, Stanley

2015-01-01

Rationale A chromosomal haplotype producing cardiac overexpression of dipeptidyl peptidase-like protein-6 (DPP6) causes familial idiopathic ventricular fibrillation. The molecular basis of transient outward current (Ito) in Purkinje fibers (PFs) is poorly understood. We hypothesized that DPP6 contributes to PF Ito and that its overexpression might specifically alter PF Ito properties and repolarization. Objective To assess the potential role of DPP6 in PF Ito. Methods and Results Clinical data in 5 idiopathic ventricular fibrillation patients suggested arrhythmia origin in the PF-conducting system. PF and ventricular muscle Ito had similar density, but PF Ito differed from ventricular muscle in having tetraethylammonium sensitivity and slower recovery. DPP6 overexpression significantly increased, whereas DPP6 knockdown reduced, Ito density and tetraethylammonium sensitivity in canine PF but not in ventricular muscle cells. The K+-channel interacting β-subunit K+-channel interacting protein type-2, essential for normal expression of Ito in ventricular muscle, was weakly expressed in human PFs, whereas DPP6 and frequenin (neuronal calcium sensor-1) were enriched. Heterologous expression of Kv4.3 in Chinese hamster ovary cells produced small Ito; Ito amplitude was greatly enhanced by coexpression with K+-channel interacting protein type-2 or DPP6. Coexpression of DPP6 with Kv4.3 and K+-channel interacting protein type-2 failed to alter Ito compared with Kv4.3/K+-channel interacting protein type-2 alone, but DPP6 expression with Kv4.3 and neuronal calcium sensor-1 (to mimic PF Ito composition) greatly enhanced Ito compared with Kv4.3/neuronal calcium sensor-1 and recapitulated characteristic PF kinetic/pharmacological properties. A mathematical model of cardiac PF action potentials showed that Ito enhancement can greatly accelerate PF repolarization. Conclusions These results point to a previously unknown central role of DPP6 in PF Ito, with DPP6 gain of function selectively enhancing PF current, and suggest that a DPP6-mediated PF early-repolarization syndrome might be a novel molecular paradigm for some forms of idiopathic ventricular fibrillation. PMID:23532596

Can optical recordings of membrane potential be used to screen for drug-induced action potential prolongation in single cardiac myocytes?

PubMed

Hardy, M E L; Lawrence, C L; Standen, N B; Rodrigo, G C

2006-01-01

Potential-sensitive dyes have primarily been used to optically record action potentials (APs) in whole heart tissue. Using these dyes to record drug-induced changes in AP morphology of isolated cardiac myocytes could provide an opportunity to develop medium throughout assays for the pharmaceutical industry. Ideally, this requires that the dye has a consistent and rapid response to membrane potential, is insensitive to movement, and does not itself affect AP morphology. We recorded the AP from isolated adult guinea-pig ventricular myocytes optically using di-8-ANEPPS in a single-excitation dual-emission ratiometric system, either separately in electrically field stimulated myocytes, or simultaneously with an electrical AP recorded with a patch electrode in the whole-cell bridge mode. The ratio of di-8-ANEPPS fluorescence signal was calibrated against membrane potential using a switch-clamp to voltage clamp the myocyte. Our data show that the ratio of the optical signals emitted at 560/620 nm is linearly related to voltage over the voltage range of an AP, producing a change in ratio of 7.5% per 100 mV, is unaffected by cell movement and is identical to the AP recorded simultaneously with a patch electrode. However, the APD90 recorded optically in myocytes loaded with di-8-ANEPPS was significantly longer than in unloaded myocytes recorded with a patch electrode (355.6+/-13.5 vs. 296.2+/-16.2 ms; p<0.01). Despite this effect, the apparent IC50 for cisapride, which prolongs the AP by blocking IKr, was not significantly different whether determined optically or with a patch electrode (91+/-46 vs. 81+/-20 nM). These data show that the optical AP recorded ratiometrically using di-8-ANEPPS from a single ventricular myocyte accurately follows the action potential morphology. This technique can be used to estimate the AP prolonging effects of a compound, although di-8-ANEPPS itself prolongs APD90. Optical dyes require less technical skills and are less invasive than conventional electrophysiological techniques and, when coupled to ventricular myocytes, decreases animal usage and facilitates higher throughput assays.

Contribution of the Axon Initial Segment to Action Potentials Recorded Extracellularly.

PubMed

Teleńczuk, Maria; Brette, Romain; Destexhe, Alain; Teleńczuk, Bartosz

2018-01-01

Action potentials (APs) are electric phenomena that are recorded both intracellularly and extracellularly. APs are usually initiated in the short segment of the axon called the axon initial segment (AIS). It was recently proposed that at the onset of an AP the soma and the AIS form a dipole. We study the extracellular signature [the extracellular AP (EAP)] generated by such a dipole. First, we demonstrate the formation of the dipole and its extracellular signature in detailed morphological models of a reconstructed pyramidal neuron. Then, we study the EAP waveform and its spatial dependence in models with axonal AP initiation and contrast it with the EAP obtained in models with somatic AP initiation. We show that in the models with axonal AP initiation the dipole forms between somatodendritic compartments and the AIS, and not between soma and dendrites as in the classical models. The soma-dendrites dipole is present only in models with somatic AP initiation. Our study has consequences for interpreting extracellular recordings of single-neuron activity and determining electrophysiological neuron types, but also for better understanding the origins of the high-frequency macroscopic extracellular potentials recorded in the brain.

Superresolution imaging reveals activity-dependent plasticity of axon morphology linked to changes in action potential conduction velocity.

PubMed

Chéreau, Ronan; Saraceno, G Ezequiel; Angibaud, Julie; Cattaert, Daniel; Nägerl, U Valentin

2017-02-07

Axons convey information to nearby and distant cells, and the time it takes for action potentials (APs) to reach their targets governs the timing of information transfer in neural circuits. In the unmyelinated axons of hippocampus, the conduction speed of APs depends crucially on axon diameters, which vary widely. However, it is not known whether axon diameters are dynamic and regulated by activity-dependent mechanisms. Using time-lapse superresolution microscopy in brain slices, we report that axons grow wider after high-frequency AP firing: synaptic boutons undergo a rapid enlargement, which is mostly transient, whereas axon shafts show a more delayed and progressive increase in diameter. Simulations of AP propagation incorporating these morphological dynamics predicted bidirectional effects on AP conduction speed. The predictions were confirmed by electrophysiological experiments, revealing a phase of slowed down AP conduction, which is linked to the transient enlargement of the synaptic boutons, followed by a sustained increase in conduction speed that accompanies the axon shaft widening induced by high-frequency AP firing. Taken together, our study outlines a morphological plasticity mechanism for dynamically fine-tuning AP conduction velocity, which potentially has wide implications for the temporal transfer of information in the brain.

Measurement and regulation of cardiac ventricular repolarization: from the QT interval to repolarization morphology

PubMed Central

Couderc, Jean-Philippe

2009-01-01

Ventricular repolarization (VR) is a crucial step in cardiac electrical activity because it corresponds to a recovery period setting the stage for the next heart contraction. Small perturbations of the VR process can predispose an individual to lethal arrhythmias. In this review, I aim to provide an overview of the methods developed to analyse static and dynamic aspects of the VR process when recorded from a surface electrocardiogram (ECG). The first section describes the list of physiological and clinical factors that can affect the VR. Technical aspects important to consider when digitally processing ECGs are provided as well. Special attention is given to the analysis of the effect of heart rate on the VR and its regulation by the autonomic nervous system. The final section provides the rationale for extending the analysis of the VR from its duration to its morphology. Several modelling techniques and measurement methods will be presented and their role within the arena of cardiac safety will be discussed. PMID:19324709

Shock wave compression and self-generated electric field repolarization in ferroelectric ceramics Pb0.99[(Zr0.90Sn0.10)0.96Ti0.04]0.98Nb0.02O3

NASA Astrophysics Data System (ADS)

Jiang, Dongdong; Du, Jinmei; Gu, Yan; Feng, Yujun

2012-03-01

The shock wave induced depoling current of Pb0.99[(Zr0.90Sn0.10)0.96Ti0.04]0.98Nb0.02O3 ceramics was investigated with a system composed of a resistive load and an unpoled ceramic. Disparity in the depoling current was explained by considering the drawing charge effect of unpoled ceramic. The drawing effect for poled ceramics was analysed by developing a model incorporating a time- and electric-field-dependent repolarization. This model predicts that the high-impedance current eventually becomes higher than the short-circuit current, which is consistent with the experimental results in the literature. This work indicates that both the repolarization of uncompressed ceramics caused by the self-generated electric field and depolarization of compressed ceramics caused by the shock wave govern the output current.

High level of oxygen treatment causes cardiotoxicity with arrhythmias and redox modulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chapalamadugu, Kalyan C.; Panguluri, Siva K.; Bennett, Eric S.

2015-01-01

Hyperoxia exposure in mice leads to cardiac hypertrophy and voltage-gated potassium (Kv) channel remodeling. Because redox balance of pyridine nucleotides affects Kv function and hyperoxia alters cellular redox potential, we hypothesized that hyperoxia exposure leads to cardiac ion channel disturbances and redox changes resulting in arrhythmias. In the present study, we investigated the electrical changes and redox abnormalities caused by 72 h hyperoxia treatment in mice. Cardiac repolarization changes were assessed by acquiring electrocardiogram (ECG) and cardiac action potentials (AP). Biochemical assays were employed to identify the pyridine nucleotide changes, Kv1.5 expression and myocardial injury. Hyperoxia treatment caused marked bradycardia,more » arrhythmia and significantly prolonged (ms) the, RR (186.2 ± 10.7 vs. 146.4 ± 6.2), PR (46.8 ± 3.1 vs. 39.3 ± 1.6), QRS (10.8 ± 0.6 vs. 8.5 ± 0.2), QTc (57.1 ± 3.5 vs. 40 ± 1.4) and JT (13.4 ± 2.1 vs. 7.0 ± 0.5) intervals, when compared with normoxia group. Hyperoxia treatment also induced significant increase in cardiac action potential duration (APD) (ex-APD{sub 90}; 73.8 ± 9.5 vs. 50.9 ± 3.1 ms) and elevated levels of serum markers of myocardial injury; cardiac troponin I (TnI) and lactate dehydrogenase (LDH). Hyperoxia exposure altered cardiac levels of mRNA/protein expression of; Kv1.5, Kvβ subunits and SiRT1, and increased ratios of reduced pyridine nucleotides (NADH/NAD and NADPH/NADP). Inhibition of SiRT1 in H9C2 cells using Splitomicin resulted in decreased SiRT1 and Kv1.5 expression, suggesting that SiRT1 may mediate Kv1.5 downregulation. In conclusion, the cardiotoxic effects of hyperoxia exposure involve ion channel disturbances and redox changes resulting in arrhythmias. - Highlights: • Hyperoxia treatment leads to arrhythmia with prolonged QTc and action potential duration. • Hyperoxia treatment alters cardiac pyridine nucleotide [NAD(P)H/NAD(P)] levels. • SiRT1 and Kv1.5 are co-regulated in hyperoxic heart injury. • Hyperoxia may lead to cardiotoxicity.« less

Action potential propagation recorded from single axonal arbors using multi-electrode arrays.

PubMed

Tovar, Kenneth R; Bridges, Daniel C; Wu, Bian; Randall, Connor; Audouard, Morgane; Jang, Jiwon; Hansma, Paul K; Kosik, Kenneth S

2018-04-11

We report the presence of co-occurring extracellular action potentials (eAPs) from cultured mouse hippocampal neurons among groups of planar electrodes on multi-electrode arrays (MEAs). The invariant sequences of eAPs among co-active electrode groups, repeated co-occurrences and short inter-electrode latencies are consistent with action potential propagation in unmyelinated axons. Repeated eAP co-detection by multiple electrodes was widespread in all our data records. Co-detection of eAPs confirms they result from the same neuron and allows these eAPs to be isolated from all other spikes independently of spike sorting algorithms. We averaged co-occurring events and revealed additional electrodes with eAPs that would otherwise be below detection threshold. We used these eAP cohorts to explore the temperature sensitivity of action potential propagation and the relationship between voltage-gated sodium channel density and propagation velocity. The sequence of eAPs among co-active electrodes 'fingerprints' neurons giving rise to these events and identifies them within neuronal ensembles. We used this property and the non-invasive nature of extracellular recording to monitor changes in excitability at multiple points in single axonal arbors simultaneously over several hours, demonstrating independence of axonal segments. Over several weeks, we recorded changes in inter-electrode propagation latencies and ongoing changes in excitability in different regions of single axonal arbors. Our work illustrates how repeated eAP co-occurrences can be used to extract physiological data from single axons with low electrode density MEAs. However, repeated eAP co-occurrences leads to over-sampling spikes from single neurons and thus can confound traditional spike-train analysis.

Acute effects of Red Bull energy drink on ventricular repolarization in healthy young volunteers: a prospective study

PubMed Central

Elitok, Ali; Öz, Fahrettin; Panc, Cafer; Sarıkaya, Remzi; Sezikli, Selim; Pala, Yasin; Bugan, Övgü Sinem; Ateş, Müge; Parıldar, Hilal; Ayaz, Mustafa Buğra; Atıcı, Adem; Oflaz, Hüseyin

2016-01-01

Objective: Energy drinks (EDs) are widely consumed products of the beverage industry and are often chosen by teenagers and young adults. Several adverse cardiovascular events and malignant cardiac arrhythmias following consumption of EDs have been reported in the literature. Several studies have suggested that the interval from the peak to the end of the electrocardiographic T wave (Tp-e) may correspond to the dispersion of repolarization and that an increased Tp-e interval and Tp-e/QT ratio are associated with malignant ventricular arrhythmias. This study investigated the acute effects of Red Bull ED on ventricular repolarization as assessed by the Tp-e interval and Tp-e/QT ratio. Methods: A prospective, open-label study design was used. After an 8-h fast, 50 young, healthy subjects consumed 355 mL of Red Bull ED. The Tp-e interval, Tp-e/QTc ratio, and several other electrocardiographic parameters were measured at baseline and 2 h after ingestion of Red Bull ED. Results: No significant changes in the Tp-e interval or Tp-e/QTc ratio were observed with Red Bull ED consumption. Red Bull ED consumption led to increases in both systolic and diastolic blood pressures, which were associated with an increased heart rate. Conclusion: Although ingestion of Red Bull ED increases the heart rate and diastolic and systolic blood pressures, it does not cause alterations in ventricular repolarization as assessed by the Tp-e interval and Tp-e/QTc ratio. PMID:25868042

The Role of Serotonin in Ventricular Repolarization in Pregnant Mice

PubMed Central

Park, Hyelim; Mun, Dasom; Lee, Seung-Hyun; Kim, Hyoeun; Yun, Nuri; Kim, Hail; Kim, Michael; Pak, Hui-Nam; Lee, Moon-Hyoung

2018-01-01

Purpose The mechanisms underlying repolarization abnormalities during pregnancy are not fully understood. Although maternal serotonin (5-hydroxytryptamine, 5-HT) production is an important determinant for normal fetal development in mice, its role in mothers remains unclear. We evaluated the role of serotonin in ventricular repolarization in mice hearts via 5Htr3 receptor (Htr3a) and investigated the mechanism of QT-prolongation during pregnancy. Materials and Methods We measured current amplitudes and the expression levels of voltage-gated K+ (Kv) channels in freshly-isolated left ventricular myocytes from wild-type non-pregnant (WT-NP), late-pregnant (WT-LP), and non-pregnant Htr3a homozygous knockout mice (Htr3a−/−-NP). Results During pregnancy, serotonin and tryptophan hydroxylase 1, a rate-limiting enzyme for the synthesis of serotonin, were markedly increased in hearts and serum. Serotonin increased Kv current densities concomitant with the shortening of the QT interval in WT-NP mice, but not in WT-LP and Htr3a−/−-NP mice. Ondansetron, an Htr3 antagonist, decreased Kv currents in WT-LP mice, but not in WT-NP mice. Kv4.3 directly interacted with Htr3a, and this binding was facilitated by serotonin. Serotonin increased the trafficking of Kv4.3 channels to the cellular membrane in WT-NP. Conclusion Serotonin increases repolarizing currents by augmenting Kv currents. Elevated serotonin levels during pregnancy counterbalance pregnancy-related QT prolongation by facilitating Htr3-mediated Kv currents. PMID:29436197

The Role of Serotonin in Ventricular Repolarization in Pregnant Mice.

PubMed

Cui, Shanyu; Park, Hyewon; Park, Hyelim; Mun, Dasom; Lee, Seung Hyun; Kim, Hyoeun; Yun, Nuri; Kim, Hail; Kim, Michael; Pak, Hui Nam; Lee, Moon Hyoung; Joung, Boyoung

2018-03-01

The mechanisms underlying repolarization abnormalities during pregnancy are not fully understood. Although maternal serotonin (5-hydroxytryptamine, 5-HT) production is an important determinant for normal fetal development in mice, its role in mothers remains unclear. We evaluated the role of serotonin in ventricular repolarization in mice hearts via 5Htr3 receptor (Htr3a) and investigated the mechanism of QT-prolongation during pregnancy. We measured current amplitudes and the expression levels of voltage-gated K⁺ (Kv) channels in freshly-isolated left ventricular myocytes from wild-type non-pregnant (WT-NP), late-pregnant (WT-LP), and non-pregnant Htr3a homozygous knockout mice (Htr3a(-/-)-NP). During pregnancy, serotonin and tryptophan hydroxylase 1, a rate-limiting enzyme for the synthesis of serotonin, were markedly increased in hearts and serum. Serotonin increased Kv current densities concomitant with the shortening of the QT interval in WT-NP mice, but not in WT-LP and Htr3a(-/-)-NP mice. Ondansetron, an Htr3 antagonist, decreased Kv currents in WT-LP mice, but not in WT-NP mice. Kv4.3 directly interacted with Htr3a, and this binding was facilitated by serotonin. Serotonin increased the trafficking of Kv4.3 channels to the cellular membrane in WT-NP. Serotonin increases repolarizing currents by augmenting Kv currents. Elevated serotonin levels during pregnancy counterbalance pregnancy-related QT prolongation by facilitating Htr3-mediated Kv currents. © Copyright: Yonsei University College of Medicine 2018

Acute effects of Red Bull energy drink on ventricular repolarization in healthy young volunteers: a prospective study.

PubMed

Elitok, Ali; Öz, Fahrettin; Panc, Cafer; Sarıkaya, Remzi; Sezikli, Selim; Pala, Yasin; Bugan, Övgü Sinem; Ateş, Müge; Parıldar, Hilal; Ayaz, Mustafa Buğra; Atıcı, Adem; Oflaz, Hüseyin

2015-11-01

Energy drinks (EDs) are widely consumed products of the beverage industry and are often chosen by teenagers and young adults. Several adverse cardiovascular events and malignant cardiac arrhythmias following consumption of EDs have been reported in the literature. Several studies have suggested that the interval from the peak to the end of the electrocardiographic T wave (Tp-e) may correspond to the dispersion of repolarization and that an increased Tp-e interval and Tp-e/QT ratio are associated with malignant ventricular arrhythmias. This study investigated the acute effects of Red Bull ED on ventricular repolarization as assessed by the Tp-e interval and Tp-e/QT ratio. A prospective, open-label study design was used. After an 8-h fast, 50 young, healthy subjects consumed 355 mL of Red Bull ED. The Tp-e interval, Tp-e/QTc ratio, and several other electrocardiographic parameters were measured at baseline and 2 h after ingestion of Red Bull ED. No significant changes in the Tp-e interval or Tp-e/QTc ratio were observed with Red Bull ED consumption. Red Bull ED consumption led to increases in both systolic and diastolic blood pressures, which were associated with an increased heart rate. Although ingestion of Red Bull ED increases the heart rate and diastolic and systolic blood pressures, it does not cause alterations in ventricular repolarization as assessed by the Tp-e interval and Tp-e/QTc ratio.

Ivabradine prolongs phase 3 of cardiac repolarization and blocks the hERG1 (KCNH2) current over a concentration-range overlapping with that required to block HCN4.

PubMed

Lees-Miller, James P; Guo, Jiqing; Wang, Yibo; Perissinotti, Laura L; Noskov, Sergei Y; Duff, Henry J

2015-08-01

In Europe, ivabradine has recently been approved to treat patients with angina who have intolerance to beta blockers and/or heart failure. Ivabradine is considered to act specifically on the sinoatrial node by inhibiting the If current (the funny current) to slow automaticity. However, in vitro studies show that ivabradine prolongs phase 3 repolarization in ventricular tissue. No episodes of Torsades de Pointes have been reported in randomized clinical studies. The objective of this study is to assess whether ivabradine blocked the hERG1 current. In the present study we discovered that ivabradine prolongs action potential and blocks the hERG current over a range of concentrations overlapping with those required to block HCN4. Ivabradine produced tonic, rather than use-dependent block. The mutation Y652A significantly suppressed pharmacologic block of hERG by ivabradine. Disruption of C-type inactivation also suppressed block of hERG1 by ivabradine. Molecular docking and molecular dynamics simulations indicate that ivabradine may access the inner cavity of the hERG1 via a lipophilic route and has a well-defined binding site in the closed state of the channel. Structural organization of the binding pockets for ivabradine is discussed. Ivabradine blocks hERG and prolongs action potential duration. Our study is potentially important because it indicates the need for active post marketing surveillance of ivabradine. Importantly, proarrhythmia of a number of other drugs has only been discovered during post marketing surveillance. Copyright © 2015 Elsevier Ltd. All rights reserved.

β1-Adrenoceptor autoantibodies affect action potential duration and delayed rectifier potassium currents in guinea pigs.

PubMed

Zhao, Yuhui; Huang, Haixia; Du, Yunhui; Li, Xiao; Lv, Tingting; Zhang, Suli; Wei, Hua; Shang, Jianyu; Liu, Ping; Liu, Huirong

2015-01-01

β1-Adrenoceptor autoantibodies (β1-AAs) affect the action potential duration (APD) in cardiomyocytes and are related to ventricular arrhythmias. The delayed rectifier potassium current (I K) plays a crucial role in APD, but the effects of β1-AAs on I K have not been completely illuminated. This work aimed to observe the effects of β1-AAs on I K and APD and further explore the mechanisms of β1-AA-mediated ventricular arrhythmias. β1-AAs were obtained from sera of patients with coronary heart disease (CHD) and nonsustained ventricular tachycardia. With whole-cell patch clamp technique, action potentials and I K were recorded. The results illustrated 0.1 μmol/L β1-AAs shortened APD at 50 % (APD50) and 90 % (APD90) of the repolarization. However, at 0.01 μmol/L, β1-AAs had no effects on either APD90 or APD50 (P > 0.05). At 0.001 μmol/L, β1-AAs significantly prolonged APD90 and APD50. Moreover, β1-AAs (0.001, 0.01, 0.1 μmol/L) dose-dependently increased the rapidly activating delayed rectifier potassium current (I Kr), but similarly decreased the slowly activating delayed rectifier potassium current (I Ks) and increased L-type calcium currents at the different concentrations. Taken together, the IKr increase induced by high β1-AA concentrations is responsible for a significant APD reduction which would contribute to repolarization changes and trigger the malignant ventricular arrhythmias in CHD patients.

Thrombopoietin as Early Biomarker of Disease Severity in Patients With Acute Pancreatitis.

PubMed

Lupia, Enrico; Pigozzi, Luca; Pivetta, Emanuele; Bosco, Ornella; Vizio, Barbara; Loiacono, Maria; Lucchiari, Manuela; Battista, Stefania; Morello, Fulvio; Moiraghi, Corrado; Mengozzi, Giulio; Montrucchio, Giuseppe

2017-02-01

To study the concentrations of thrombopoietin (TPO), a growth factor recently involved in the pathogenesis of experimental acute pancreatitis (AP), and its potential role as an early diagnostic and prognostic biomarker in patients with AP. Thrombopoietin was measured in 44 AP patients, 18 patients with nonpancreatic acute abdominal pain, and 18 healthy volunteers. Acute pancreatitis severity was classified on the basis of the 2012 International Atlanta Symposium on Acute Pancreatitis criteria. Thrombopoietin levels did not differ between AP patients and control subjects, whereas these were higher in patients with moderately severe or severe AP compared with those with mild AP. Receiver operating characteristic curve analysis of TPO for severe AP diagnosis showed an area under the curve of 0.80. A cutoff value of 31.48 pg/mL showed the highest sensitivity, allowing to rule out severe AP when TPO was lower, whereas TPO higher than 98.23 pg/mL was associated with severe AP with high specificity (93.5%). Furthermore, TPO levels were greater in AP patients developing organ dysfunction or sepsis and in nonsurvivors compared with survivors. Our data provide the first evidence for TPO as potential early prognostic biomarker in AP patients. High TPO levels at hospital admission may predict organ dysfunction, sepsis, and fatal outcome in AP patients.

Relationships between resting conductances, excitability, and t-system ionic homeostasis in skeletal muscle.

PubMed

Fraser, James A; Huang, Christopher L-H; Pedersen, Thomas H

2011-07-01

Activation of skeletal muscle fibers requires rapid sarcolemmal action potential (AP) conduction to ensure uniform excitation along the fiber length, as well as successful tubular excitation to initiate excitation-contraction coupling. In our companion paper in this issue, Pedersen et al. (2011. J. Gen. Physiol. doi:10.1085/jgp.201010510) quantify, for subthreshold stimuli, the influence upon both surface conduction velocity and tubular (t)-system excitation of the large changes in resting membrane conductance (G(M)) that occur during repetitive AP firing. The present work extends the analysis by developing a multi-compartment modification of the charge-difference model of Fraser and Huang to provide a quantitative description of the conduction velocity of actively propagated APs; the influence of voltage-gated ion channels within the t-system; the influence of t-system APs on ionic homeostasis within the t-system; the influence of t-system ion concentration changes on membrane potentials; and the influence of Phase I and Phase II G(M) changes on these relationships. Passive conduction properties of the novel model agreed with established linear circuit analysis and previous experimental results, while key simulations of AP firing were tested against focused experimental microelectrode measurements of membrane potential. This study thereby first quantified the effects of the t-system luminal resistance and voltage-gated Na(+) channel density on surface AP propagation and the resultant electrical response of the t-system. Second, it demonstrated the influence of G(M) changes during repetitive AP firing upon surface and t-system excitability. Third, it showed that significant K(+) accumulation occurs within the t-system during repetitive AP firing and produces a baseline depolarization of the surface membrane potential. Finally, it indicated that G(M) changes during repetitive AP firing significantly influence both t-system K(+) accumulation and its influence on the resting membrane potential. Thus, the present study emerges with a quantitative description of the changes in membrane potential, excitability, and t-system ionic homeostasis that occur during repetitive AP firing in skeletal muscle.

Theoretical studies on the electronic and optoelectronic properties of [A.2AP(w)/A*.2AP(WC)/C.2AP(w)/C*.2AP(WC)/C.A(w)/C*.A(WC)]-Au8 mismatch nucleobase complexes

NASA Astrophysics Data System (ADS)

Srivastava, Ruby

2018-01-01

The electronic and optoelectronic properties of [A.2AP(w)/A*.2AP(WC)/C.2AP(w)/C*.2AP(WC)/C.A(w)/ C*.A(WC)]-Au8 metal-mismatch nucleobase complexes are investigated by means of density functional theory and time-dependent methods. We selected these mispairs as 2-aminopurine (2AP) produces incorporation errors when binding with cytosine (C) into the wobble (w) C.2AP(w) mispair, and is tautomerised into Watson-Crick (WC)-like base mispair C*.2AP(WC) and less effectively produces A.2AP(w)/A*.2AP(WC) mispairs. The vertical ionisation potential, vertical electron affinity, hardness and electrophilicity index of these complexes have also been discussed. The modifications of energy levels and charge density distributions of the frontier orbitals are also analysed. The absorption spectra of these complexes lie in the visible region, which suggests their application in fluorescent-bio imaging. The mechanism of cooperativity effect is studied by molecular orbital potential (MEP), atoms-in-molecules (AIM) and natural bond orbital analyses. Most metalated pairs have smaller HOMO-LUMO band gaps than the isolated mismatch nucleobases which suggest interesting consequences for electron transfer through DNA duplexes.

Diadenosine tetra- and pentaphosphates affect contractility and bioelectrical activity in the rat heart via P2 purinergic receptors.

PubMed

Pustovit, Ksenia B; Kuzmin, Vladislav S; Abramochkin, Denis V

2016-03-01

Diadenosine polyphosphates (Ap(n)As) are endogenously produced molecules which have been identified in various tissues of mammalian organism, including myocardium. Ap(n)As contribute to the blood clotting and are also widely accepted as regulators of blood vascular tone. Physiological role of Ap(n)As in cardiac muscle has not been completely elucidated. The present study aimed to investigate the effects of diadenosine tetra- (Ap4A) and penta- (Ap5A) polyphosphates on contractile function and action potential (AP) waveform in rat supraventricular and ventricular myocardium. We have also demonstrated the effects of A4pA and Ap5A in myocardial sleeves of pulmonary veins (PVs), which play a crucial role in genesis of atrial fibrillation. APs were recorded with glass microelectrodes in multicellular myocardial preparations. Contractile activity was measured in isolated Langendorff-perfused rat hearts. Both Ap4A and Ap5A significantly reduced contractility of isolated Langendorff-perfused heart and produced significant reduction of AP duration in left and right auricle, interatrial septum, and especially in right ventricular wall myocardium. Ap(n)As also shortened APs in rat pulmonary veins and therefore may be considered as potential proarrhythmic factors. Cardiotropic effects of Ap4A and Ap5A were strongly antagonized by selective blockers of P2 purine receptors suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), while P1 blocker DPCPX was not effective. We conclude that Ap(n)As may be considered as new class of endogenous cardioinhibitory compounds. P2 purine receptors play the central role in mediation of Ap4A and Ap5A inhibitory effects on electrical and contractile activity in different regions of the rat heart.

Action potential properties are gravity dependent

NASA Astrophysics Data System (ADS)

Meissner, Klaus; Hanke, Wolfgang

2005-06-01

The functional properties of neuronal tissue critically depend on cellular composition and intercellular comunication. A basic principle of such communication found in various types of neurons is the generation of action potentials (APs). These APs depend on the presence of voltage gated ion channels and propagate along cellular processes (e.g. axons) towards target neurons or other cells. It has already been shown that the properties of ion channels depend on gravity. To discover whether the properties of APs also depend on gravity, we examined the propagation of APs in earthworms (invertebrates) and isolated nerve fibres (i.e. bundles of axons) from earthworms under conditions of micro- and macro-gravity. In a second set of experiments we could verify our results on rat axons (vertebrates). Our experiments carried out during two parabolic flight campaigns revealed that microgravity slows AP propagation velocity and macrogravity accelerates the transmission of action potentials. The relevance for live-science related questions is considerable, taking into account that altered gravity conditions might affect AP velocity in man during space flight missions.

Tracking individual action potentials throughout mammalian axonal arbors.

PubMed

Radivojevic, Milos; Franke, Felix; Altermatt, Michael; Müller, Jan; Hierlemann, Andreas; Bakkum, Douglas J

2017-10-09

Axons are neuronal processes specialized for conduction of action potentials (APs). The timing and temporal precision of APs when they reach each of the synapses are fundamentally important for information processing in the brain. Due to small diameters of axons, direct recording of single AP transmission is challenging. Consequently, most knowledge about axonal conductance derives from modeling studies or indirect measurements. We demonstrate a method to noninvasively and directly record individual APs propagating along millimeter-length axonal arbors in cortical cultures with hundreds of microelectrodes at microsecond temporal resolution. We find that cortical axons conduct single APs with high temporal precision (~100 µs arrival time jitter per mm length) and reliability: in more than 8,000,000 recorded APs, we did not observe any conduction or branch-point failures. Upon high-frequency stimulation at 100 Hz, successive became slower, and their arrival time precision decreased by 20% and 12% for the 100th AP, respectively.

TRPM4 non-selective cation channels influence action potentials in rabbit Purkinje fibres.

PubMed

Hof, Thomas; Sallé, Laurent; Coulbault, Laurent; Richer, Romain; Alexandre, Joachim; Rouet, René; Manrique, Alain; Guinamard, Romain

2016-01-15

The transient receptor potential melastatin 4 (TRPM4) inhibitor 9-phenanthrol reduces action potential duration in rabbit Purkinje fibres but not in ventricle. TRPM4-like single channel activity is observed in isolated rabbit Purkinje cells but not in ventricular cells. The TRPM4-like current develops during the notch and early repolarization phases of the action potential in Purkinje cells. Transient receptor potential melastatin 4 (TRPM4) Ca(2+)-activated non-selective cation channel activity has been recorded in cardiomyocytes and sinus node cells from mammals. In addition, TRPM4 gene mutations are associated with human diseases of cardiac conduction, suggesting that TRPM4 plays a role in this aspect of cardiac function. Here we evaluate the TRPM4 contribution to cardiac electrophysiology of Purkinje fibres. Ventricular strips with Purkinje fibres were isolated from rabbit hearts. Intracellular microelectrodes recorded Purkinje fibre activity and the TRPM4 inhibitor 9-phenanthrol was applied to unmask potential TRPM4 contributions to the action potential. 9-Phenanthrol reduced action potential duration measured at the point of 50 and 90% repolarization with an EC50 of 32.8 and 36.1×10(-6) mol l(-1), respectively, but did not modulate ventricular action potentials. Inside-out patch-clamp recordings were used to monitor TRPM4 activity in isolated Purkinje cells. TRPM4-like single channel activity (conductance = 23.8 pS; equal permeability for Na(+) and K(+); sensitivity to voltage, Ca(2+) and 9-phenanthrol) was observed in 43% of patches from Purkinje cells but not from ventricular cells (0/16). Action potential clamp experiments performed in the whole-cell configuration revealed a transient inward 9-phenanthrol-sensitive current (peak density = -0.65 ± 0.15 pA pF(-1); n = 5) during the plateau phases of the Purkinje fibre action potential. These results show that TRPM4 influences action potential characteristics in rabbit Purkinje fibres and thus could modulate cardiac conduction and be involved in triggering arrhythmias. © 2015 The Authors. The Journal of Physiology © 2015 The Physiological Society.

An Excel‐based implementation of the spectral method of action potential alternans analysis

PubMed Central

Pearman, Charles M.

2014-01-01

Abstract Action potential (AP) alternans has been well established as a mechanism of arrhythmogenesis and sudden cardiac death. Proper interpretation of AP alternans requires a robust method of alternans quantification. Traditional methods of alternans analysis neglect higher order periodicities that may have greater pro‐arrhythmic potential than classical 2:1 alternans. The spectral method of alternans analysis, already widely used in the related study of microvolt T‐wave alternans, has also been used to study AP alternans. Software to meet the specific needs of AP alternans analysis is not currently available in the public domain. An AP analysis tool is implemented here, written in Visual Basic for Applications and using Microsoft Excel as a shell. This performs a sophisticated analysis of alternans behavior allowing reliable distinction of alternans from random fluctuations, quantification of alternans magnitude, and identification of which phases of the AP are most affected. In addition, the spectral method has been adapted to allow detection and quantification of higher order regular oscillations. Analysis of action potential morphology is also performed. A simple user interface enables easy import, analysis, and export of collated results. PMID:25501439

The Effects of Different Purifying Methods on the Chemical Properties, in Vitro Anti-Tumor and Immunomodulatory Activities of Abrus cantoniensis Polysaccharide Fractions

PubMed Central

Wu, Shaowei; Fu, Xiong; Brennan, Margaret A.; Brennan, Charles S.; Chun, Chen

2016-01-01

Abrus cantoniensis (Hance) is a popular Chinese vegetable consumed as a beverage, soup or folk medicine. To fully exploit the potential of the polysaccharide in Abrus cantoniensis, nine polysaccharide fractions of Abrus cantoniensis were isolated and purified (AP-AOH30-1, AP-AOH30-2, AP-AOH80-1, AP-AOH80-2, AP-ACl-1, AP-ACl-2, AP-ACl-3, AP-H and AP-L). Fourier-transform infrared spectroscopy (FT-IR) and gas chromatography (GC) were used to characterize these Abrus polysaccharides fractions (APF). In vitro anti-tumor and immunomodulatory activities were also investigated and compared using the rank-sum ratio (RSR) method. Results demonstrated significant differences in the structure and bioactivities among APF, which were associated to the process used for their purification. Among the APF, AP-ACl-3 yield was 613.5 mg/kg of product and consisted of rhamnose (9.8%), arabinose (8.9%), fructose (3.0%), galactose (9.9%), glucose (4.3%), galacturonic acid (3.0%) and glucuronic acid (61.1%) with a molecular weight of 4.4 × 104 Da. Furthermore, AP-ACl-3 exhibited considerable bioactivities significantly preventing the migration of MCF-7 cells and stimulating lymphocyte proliferation along with nitric oxide (NO) production of peritoneal macrophages. AP-ACl-3 could be explored as a novel potential anti-tumor and immunomodulatory agent. PMID:27058538

Onset dynamics of action potentials in rat neocortical neurons and identified snail neurons: quantification of the difference.

PubMed

Volgushev, Maxim; Malyshev, Aleksey; Balaban, Pavel; Chistiakova, Marina; Volgushev, Stanislav; Wolf, Fred

2008-04-09

The generation of action potentials (APs) is a key process in the operation of nerve cells and the communication between neurons. Action potentials in mammalian central neurons are characterized by an exceptionally fast onset dynamics, which differs from the typically slow and gradual onset dynamics seen in identified snail neurons. Here we describe a novel method of analysis which provides a quantitative measure of the onset dynamics of action potentials. This method captures the difference between the fast, step-like onset of APs in rat neocortical neurons and the gradual, exponential-like AP onset in identified snail neurons. The quantitative measure of the AP onset dynamics, provided by the method, allows us to perform quantitative analyses of factors influencing the dynamics.

Onset Dynamics of Action Potentials in Rat Neocortical Neurons and Identified Snail Neurons: Quantification of the Difference

PubMed Central

Volgushev, Maxim; Malyshev, Aleksey; Balaban, Pavel; Chistiakova, Marina; Volgushev, Stanislav; Wolf, Fred

2008-01-01

The generation of action potentials (APs) is a key process in the operation of nerve cells and the communication between neurons. Action potentials in mammalian central neurons are characterized by an exceptionally fast onset dynamics, which differs from the typically slow and gradual onset dynamics seen in identified snail neurons. Here we describe a novel method of analysis which provides a quantitative measure of the onset dynamics of action potentials. This method captures the difference between the fast, step-like onset of APs in rat neocortical neurons and the gradual, exponential-like AP onset in identified snail neurons. The quantitative measure of the AP onset dynamics, provided by the method, allows us to perform quantitative analyses of factors influencing the dynamics. PMID:18398478

Action Potential Energy Efficiency Varies Among Neuron Types in Vertebrates and Invertebrates

PubMed Central

Sengupta, Biswa; Stemmler, Martin; Laughlin, Simon B.; Niven, Jeremy E.

2010-01-01

The initiation and propagation of action potentials (APs) places high demands on the energetic resources of neural tissue. Each AP forces ATP-driven ion pumps to work harder to restore the ionic concentration gradients, thus consuming more energy. Here, we ask whether the ionic currents underlying the AP can be predicted theoretically from the principle of minimum energy consumption. A long-held supposition that APs are energetically wasteful, based on theoretical analysis of the squid giant axon AP, has recently been overturned by studies that measured the currents contributing to the AP in several mammalian neurons. In the single compartment models studied here, AP energy consumption varies greatly among vertebrate and invertebrate neurons, with several mammalian neuron models using close to the capacitive minimum of energy needed. Strikingly, energy consumption can increase by more than ten-fold simply by changing the overlap of the Na+ and K+ currents during the AP without changing the APs shape. As a consequence, the height and width of the AP are poor predictors of energy consumption. In the Hodgkin–Huxley model of the squid axon, optimizing the kinetics or number of Na+ and K+ channels can whittle down the number of ATP molecules needed for each AP by a factor of four. In contrast to the squid AP, the temporal profile of the currents underlying APs of some mammalian neurons are nearly perfectly matched to the optimized properties of ionic conductances so as to minimize the ATP cost. PMID:20617202

Action potential energy efficiency varies among neuron types in vertebrates and invertebrates.

PubMed

Sengupta, Biswa; Stemmler, Martin; Laughlin, Simon B; Niven, Jeremy E

2010-07-01

The initiation and propagation of action potentials (APs) places high demands on the energetic resources of neural tissue. Each AP forces ATP-driven ion pumps to work harder to restore the ionic concentration gradients, thus consuming more energy. Here, we ask whether the ionic currents underlying the AP can be predicted theoretically from the principle of minimum energy consumption. A long-held supposition that APs are energetically wasteful, based on theoretical analysis of the squid giant axon AP, has recently been overturned by studies that measured the currents contributing to the AP in several mammalian neurons. In the single compartment models studied here, AP energy consumption varies greatly among vertebrate and invertebrate neurons, with several mammalian neuron models using close to the capacitive minimum of energy needed. Strikingly, energy consumption can increase by more than ten-fold simply by changing the overlap of the Na(+) and K(+) currents during the AP without changing the APs shape. As a consequence, the height and width of the AP are poor predictors of energy consumption. In the Hodgkin-Huxley model of the squid axon, optimizing the kinetics or number of Na(+) and K(+) channels can whittle down the number of ATP molecules needed for each AP by a factor of four. In contrast to the squid AP, the temporal profile of the currents underlying APs of some mammalian neurons are nearly perfectly matched to the optimized properties of ionic conductances so as to minimize the ATP cost.

Stereoselective Inhibition of the hERG1 Potassium Channel

PubMed Central

Grilo, Liliana Sintra; Carrupt, Pierre-Alain; Abriel, Hugues

2010-01-01

A growing number of drugs have been shown to prolong cardiac repolarization, predisposing individuals to life-threatening ventricular arrhythmias known as Torsades de Pointes. Most of these drugs are known to interfere with the human ether à-gogo related gene 1 (hERG1) channel, whose current is one of the main determinants of action potential duration. Prolonged repolarization is reflected by lengthening of the QT interval of the electrocardiogram, as seen in the suitably named drug-induced long QT syndrome. Chirality (presence of an asymmetric atom) is a common feature of marketed drugs, which can therefore exist in at least two enantiomers with distinct three-dimensional structures and possibly distinct biological fates. Both the pharmacokinetic and pharmacodynamic properties can differ between enantiomers, as well as also between individuals who take the drug due to metabolic polymorphisms. Despite the large number of reports about drugs reducing the hERG1 current, potential stereoselective contributions have only been scarcely investigated. In this review, we present a non-exhaustive list of clinically important molecules which display chiral toxicity that may be related to hERG1-blocking properties. We particularly focus on methadone cardiotoxicity, which illustrates the importance of the stereoselective effect of drug chirality as well as individual variations resulting from pharmacogenetics. Furthermore, it seems likely that, during drug development, consideration of chirality in lead optimization and systematic assessment of the hERG1 current block with all enantiomers could contribute to the reduction of the risk of drug-induced LQTS. PMID:21833176

Sildenafil (Viagra) prolongs cardiac repolarization by blocking the rapid component of the delayed rectifier potassium current.

PubMed

Geelen, P; Drolet, B; Rail, J; Bérubé, J; Daleau, P; Rousseau, G; Cardinal, R; O'Hara, G E; Turgeon, J

2000-07-18

BACKGROUND-Several cases of unexpected death have been reported with sildenafil in patients predisposed to ischemic cardiac events. Although acute episodes of ischemia could account for some of these deaths, we hypothesized that sildenafil may have unsuspected electrophysiological effects predisposing some patients to proarrhythmia. METHODS AND RESULTS-Studies were undertaken in 10 isolated guinea pig hearts that demonstrated prolongation of cardiac repolarization in a reverse use-dependent manner by sildenafil 30 mcmol/L. Action potential duration increased 15% from baseline 117+/-3 to 134+/-2 ms with sildenafil during pacing at 250 ms cycle length, whereas a 6% increase from 99+/-2 to 105+/-2 ms was seen with pacing at 150 ms cycle length. Experiments in human ether-a-go-go-related gene (HERG)-transfected HEK293 cells (n=30) demonstrated concentration-dependent block of the rapid component (I(Kr)) of the delayed rectifier potassium current: activating current was 50% decreased at 100 mcmol/L. This effect was confirmed using HERG-transfected Chinese hamster ovary (CHO) cells, which exhibit no endogenous I(K)-like current. CONCLUSIONS-Sildenafil possesses direct cardiac electrophysiological effects similar to class III antiarrhythmic drugs. These effects are observed at concentrations that may be found in conditions of impaired drug elimination such as renal or hepatic insufficiency, during coadministration of another CYP3A substrate/inhibitor, or after drug overdose and offer a new potential explanation for sudden death during sildenafil treatment.

Spatially divergent cardiac responses to nicotinic stimulation of ganglionated plexus neurons in the canine heart.

PubMed

Cardinal, René; Pagé, Pierre; Vermeulen, Michel; Ardell, Jeffrey L; Armour, J Andrew

2009-01-28

Ganglionated plexuses (GPs) are major constituents of the intrinsic cardiac nervous system, the final common integrator of regional cardiac control. We hypothesized that nicotinic stimulation of individual GPs exerts divergent regional influences, affecting atrial as well as ventricular functions. In 22 anesthetized canines, unipolar electrograms were recorded from 127 atrial and 127 ventricular epicardial loci during nicotine injection (100 mcg in 0.1 ml) into either the 1) right atrial (RA), 2) dorsal atrial, 3) left atrial, 4) inferior vena cava-inferior left atrial, 5) right ventricular, 6) ventral septal ventricular or 7) cranial medial ventricular (CMV) GP. In addition to sinus and AV nodal function, neural effects on atrial and ventricular repolarization were identified as changes in the area subtended by unipolar recordings under basal conditions and at maximum neurally-induced effects. Animals were studied with intact AV node or following ablation to achieve ventricular rate control. Atrial rate was affected in response to stimulation of all 7 GPs with an incidence of 50-95% of the animals among the different GPs. AV conduction was affected following stimulation of 6/7 GP with an incidence of 22-75% among GPs. Atrial and ventricular repolarization properties were affected by atrial as well as ventricular GP stimulation. Distinct regional patterns of repolarization changes were identified in response to stimulation of individual GPs. RAGP predominantly affected the RA and posterior right ventricular walls whereas CMVGP elicited biatrial and biventricular repolarization changes. Spatially divergent and overlapping cardiac regions are affected in response to nicotinic stimulation of neurons in individual GPs.

Characterization of ventricular depolarization and repolarization changes in a porcine model of myocardial infarction.

PubMed

Romero, Daniel; Ringborn, Michael; Demidova, Marina; Koul, Sasha; Laguna, Pablo; Platonov, Pyotr G; Pueyo, Esther

2012-12-01

In this study, several electrocardiogram (ECG)-derived indices corresponding to both ventricular depolarization and repolarization were evaluated during acute myocardial ischemia in an experimental model of myocardial infarction produced by 40 min coronary balloon inflation in 13 pigs. Significant changes were rapidly observed from minute 4 after the start of coronary occlusion, achieving their maximum values between 11 and 22 min for depolarization and between 9 and 12 min for repolarization indices, respectively. Subsequently, these maximum changes started to decrease during the latter part of the occlusion. Depolarization changes associated with the second half of the QRS complex showed a significant but inverse correlation with the myocardium at risk (MaR) estimated by scintigraphic images. The correlation between MaR and changes of the downward slope of the QRS complex, [Formula: see text], evaluated at the two more relevant peaks observed during the occlusion, was r = -0.75, p < 0.01 and r = -0.79, p < 0.01 for the positive and negative deflections observed in [Formula: see text], temporal evolution, respectively. Repolarization changes, analyzed by evaluation of ST segment elevation at the main observed positive peak, also showed negative, however non-significant correlation with MaR: r = -0.34, p = 0.28. Our results suggest that changes evaluated in the latter part of the depolarization, such as those described by [Formula: see text], which are influenced by R-wave amplitude, QRS width and ST level variations simultaneously, correlate better with the amount of ischemia than other indices evaluated in the earlier part of depolarization or during the ST segment.

Kinetics of cycle length dependence of ventricular repolarization: effect of autonomic blockade

NASA Technical Reports Server (NTRS)

Raeder, E. A.; Albrecht, P.; Perrott, M.; Cohen, R. J.

1995-01-01

INTRODUCTION: Beat-to-beat adaptation of ventricular repolarization duration to cardiac cycle length and autonomic activity has not been previously characterized in the spontaneously beating human heart. METHODS AND RESULTS: The ECG of 14 healthy subjects was recorded from the supine and upright positions. Autonomic blockade was accomplished by atropine and propranolol. RR and RT intervals were measured by a computer algorithm, and the impulse response (h) from RR to RT computed. In the supine position the maximal adjustment of the RT interval occurred in the first beat following a change in cycle length (hpeak = 17.8 +/- 1.6 msec/sec), but continued to be detectable for 3.8 seconds (2.9-4.7 sec). Propranolol attenuated the peak impulse response to 15.8 +/- 4.0 msec/sec (P = NS). In the standing position the peak impulse response was increased to 25.2 +/- 5.0 msec/sec (P = 0.004 vs supine), and the impulse response duration (hdur) shortened to 1.4 seconds (1.3-1.6). This was reversed by beta blockade (hpeak = 10.7 +/- 3.6 [P = 0.005 vs standing]; hdur = 5.5 sec [4.8-6.1]). Parasympathetic and combined autonomic blockade resulted in too little residual heart rate variability to estimate the impulse response accurately. The slope of the regression of delta RT and delta RR in the supine position was 0.0177 +/- 0.0016, which was closely correlated with the peak impulse response (r = 0.91). CONCLUSIONS: System identification techniques can assist in characterizing the cycle dependence of ventricular repolarization and may provide new insights into conditions associated with abnormal repolarization.

Microvolt T-wave alternans and beat-to-beat variability of repolarization during early postischemic remodeling in a pig heart.

PubMed

Floré, Vincent; Claus, Piet; Antoons, Gudrun; Oosterhoff, Peter; Holemans, Patricia; Vos, Marc A; Sipido, Karin R; Willems, Rik

2011-07-01

Repolarization variability is considered to predict sudden cardiac death. T-wave alternans (TWA) has been the subject of exhaustive research, whereas beat-to-beat variability of repolarization (BVR) is a new parameter that possibly predicts proarrhythmia. How these parameters interact has not been tested. The purpose of this study was to compare TWA and BVR as predictors of proarrhythmic substrate early after myocardial infarction (MI). In nine pigs, MI was induced by 1-hour occlusion of the left anterior descending coronary artery. Cardiac magnetic resonance imaging was performed at day 21. Six sham pigs served as control. Spectral TWA was tested during right atrial pacing before induction of MI and after 21 days. BVR was calculated from 60 consecutive QT intervals. Magnetic resonance imaging showed transmural MI. TWA was negative in all pigs at clinical threshold rate and equally present in MI versus sham pigs at higher rates (170 bpm: 55% vs 50% positive TWA). In MI pigs, BVR of QT intervals increased significantly during acute ischemia (2.44 ± 0.43 ms vs 3.55 ± 0.41 ms, P <.01) and even more on day 21 (5.80 ± 1.12 ms), but it differed significantly from sham (2.14 ± 0.54 ms, P <.01). A clinical ventricular tachycardia induction protocol was positive in 2 of 8 MI pigs and in none of 6 shams. In early remodeling after MI, BVR at intrinsic heart rate was a consistent phenomenon, whereas TWA during atrial pacing or baseline QT-interval changes were not. TWA and BVR could reflect different post-MI remodeling processes. BVR may be a new technique for predicting a potentially proarrhythmic substrate in the early postinfarction period. Copyright © 2011 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

Rationale, objectives, and design of the EUTrigTreat clinical study: a prospective observational study for arrhythmia risk stratification and assessment of interrelationships among repolarization markers and genotype

PubMed Central

Seegers, Joachim; Vos, Marc A.; Flevari, Panagiota; Willems, Rik; Sohns, Christian; Vollmann, Dirk; Lüthje, Lars; Kremastinos, Dimitrios T.; Floré, Vincent; Meine, Mathias; Tuinenburg, Anton; Myles, Rachel C.; Simon, Dirk; Brockmöller, Jürgen; Friede, Tim; Hasenfuß, Gerd; Lehnart, Stephan E.; Zabel, Markus

2012-01-01

Aims The EUTrigTreat clinical study has been designed as a prospective multicentre observational study and aims to (i) risk stratify patients with an implantable cardioverter defibrillator (ICD) for mortality and shock risk using multiple novel and established risk markers, (ii) explore a link between repolarization biomarkers and genetics of ion (Ca2+, Na+, K+) metabolism, (iii) compare the results of invasive and non-invasive electrophysiological (EP) testing, (iv) assess changes of non-invasive risk stratification tests over time, and (v) associate arrythmogenomic risk through 19 candidate genes. Methods and results Patients with clinical ICD indication are eligible for the trial. Upon inclusion, patients will undergo non-invasive risk stratification, including beat-to-beat variability of repolarization (BVR), T-wave alternans, T-wave morphology variables, ambient arrhythmias from Holter, heart rate variability, and heart rate turbulence. Non-invasive or invasive programmed electrical stimulation will assess inducibility of ventricular arrhythmias, with the latter including recordings of monophasic action potentials and assessment of restitution properties. Established candidate genes are screened for variants. The primary endpoint is all-cause mortality, while one of the secondary endpoints is ICD shock risk. A mean follow-up of 3.3 years is anticipated. Non-invasive testing will be repeated annually during follow-up. It has been calculated that 700 patients are required to identify risk predictors of the primary endpoint, with a possible increase to 1000 patients based on interim risk analysis. Conclusion The EUTrigTreat clinical study aims to overcome current shortcomings in sudden cardiac death risk stratification and to answer several related research questions. The initial patient recruitment is expected to be completed in July 2012, and follow-up is expected to end in September 2014. Clinicaltrials.gov identifier: NCT01209494. PMID:22117037

Protection against severe hypokalemia but impaired cardiac repolarization after intense rowing exercise in healthy humans receiving salbutamol.

PubMed

Atanasovska, Tania; Smith, Robert; Graff, Claus; Tran, Cao Thach; Melgaard, Jacob; Kanters, Jørgen K; Petersen, Aaron C; Tobin, Antony; Kjeldsen, Keld P; McKenna, Michael John

2018-05-10

Intense exercise induces pronounced hyperkalemia, followed by transient hypokalemia in recovery. We investigated whether the β 2 -agonist salbutamol attenuated the exercise-hyperkalemia, and exacerbated the post-exercise hypokalemia, and whether hypokalemia was associated with impaired cardiac repolarization (QT hysteresis). Eleven healthy adults participated in a randomized, counterbalanced, double-blind trial receiving either 1000 µg salbutamol (SAL) or placebo (PLAC) by inhalation. Arterial plasma potassium concentration ([K + ] a ) was measured at rest, during 3 min intense rowing exercise and 60 min recovery. QT hysteresis was calculated from ECG (n=8). [K + ] a increased above baseline during exercise (rest, 3.72{plus minus}0.7 vs end-exercise, 6.81{plus minus}1.4 mM, P<0.001, mean{plus minus}SD) and decreased rapidly during early recovery to below baseline; restoration was incomplete at 60 min post-exercise (P<0.05). [K + ] a was less during SAL than PLAC (4.39{plus minus}0.13 vs. 4.73{plus minus}0.19 mM, pooled across all times, P=0.001, treatment main effect). [K + ] a was lower after SAL than PLAC, from 2 min pre-exercise until 2.5 min during exercise, and at 50 and 60 min post-exercise (P<0.05). The post-exercise decline in [K + ] a was correlated with QT hysteresis (r=0.343, n=112, pooled data, P=0.001). Thus the decrease in [K + ] a from end-exercise by ~4 mM was associated with reduced QT hysteresis by ~75 ms. Whilst salbutamol lowered [K + ] a during exercise, no additive hypokalemic effects occurred in early recovery, suggesting there may be a protective mechanism against severe or prolonged hypokalemia after exercise when treated by salbutamol. This is important since post-exercise hypokalemia impaired cardiac repolarization, which could potentially trigger arrhythmias and sudden cardiac death in susceptible individuals with pre-existing hypokalemia and/or heart disease.

Aging modulates dispersion of ventricular repolarization in the very old of the geriatric population.

PubMed

Huang, Jen-Hung; Lin, Ying-Qin; Pan, Nan-Hung; Chen, Yi-Jen

2010-11-01

Aging plays an essential role in cardiac pathophysiology. Knowledge on the ventricular repolarization in very old individuals is limited. An increase of QT dispersion is associated with higher cardiovascular mortality. The purpose of this study is to investigate whether aging changes the QT dispersion in the very old. Heart rate, P wave duration, PR interval, QRS axis, QRS duration, QT interval, and QTc interval were measured from 12-lead resting ECG. QT dispersion (46 ± 21, 47 ± 17, 69 ± 31 ms, p < 0.005) was significantly increased in the age group ≧85 years (n = 29, 89 ± 4 years) than in the age group 75-84 years (n = 33, 79 ± 3 years) and the age group 65-74 years (n = 32, 68 ± 3 years). Aging modulates dispersion of ventricular repolarization, which may contribute to the cardiac mortality in the very old Asian population.

Realising their potential? Exploring interprofessional perceptions and potential of the advanced practitioner role: a qualitative analysis

PubMed Central

Powell, Tom; Watkins, Dianne; Kelly, Daniel

2015-01-01

Objectives To explore perceptions of the current practice and future potential of advanced practitioners (APs) from the perspectives of different professional groups in Wales UK. Design A qualitative study consisting of nine focus group interviews. Methods Initially verbatim transcriptions of each focus group interviews were analysed thematically before themes were merged to represent perceptions for the whole data set. Participants Data were gathered from a total of 67 stakeholders—including APs from a variety of professional groups (eg, nursing, physiotherapy, paramedics) as well as managers, workforce developers, educators and medical staff who have a role developing and supporting APs in practice. Results The results are presented in four themes: (1) demand, policy context and future priorities, (2) role clarity and standardisation, (3) agreement and understanding of the role and (4) interprofessional working. The context within which current and future AP roles were considered was influenced by inexorable demands for healthcare and the requirements to meet health policy priorities. Developing AP roles were hampered currently by a lack of shared understanding and ‘joined-up’ working between different groups such as medical practitioners, managers, commissioners and educators. Conclusions For the AP role to flourish more ‘joined-up’ thinking, support and development opportunities are required between APs, managers, senior clinicians, commissioners and educators. Working together to plan and deliver education, innovation and service delivery is of prime importance to meeting ever increasing complex health needs. This will ensure that future APs are adequately prepared and supported to reach their full potential and help deliver necessary innovations in current models of care delivery. PMID:26656024

Alkaline Phosphatase, an Unconventional Immune Protein.

PubMed

Rader, Bethany A

2017-01-01

Recent years have seen an increase in the number of studies focusing on alkaline phosphatases (APs), revealing an expanding complexity of function of these enzymes. Of the four human AP (hAP) proteins, most is known about tissue non-specific AP (TNAP) and intestinal AP (IAP). This review highlights current understanding of TNAP and IAP in relation to human health and disease. TNAP plays a role in multiple processes, including bone mineralization, vitamin B6 metabolism, and neurogenesis, is the genetic cause of hypophosphatasia, influences inflammation through regulation of purinergic signaling, and has been implicated in Alzheimer's disease. IAP regulates fatty acid absorption and has been implicated in the regulation of diet-induced obesity and metabolic syndrome. IAP and TNAP can dephosphorylate bacterial-derived lipopolysaccharide, and IAP has been identified as a potential regulator of the composition of the intestinal microbiome, an evolutionarily conserved function. Endogenous and recombinant bovine APs and recombinant hAPs are currently being explored for their potential as pharmacological agents to treat AP-associated diseases and mitigate multiple sources of inflammation. Continued research on these versatile proteins will undoubtedly provide insight into human pathophysiology, biochemistry, and the human holobiont.

Contribution of two-pore K+ channels to cardiac ventricular action potential revealed using human iPSC-derived cardiomyocytes.

PubMed

Chai, Sam; Wan, Xiaoping; Nassal, Drew M; Liu, Haiyan; Moravec, Christine S; Ramirez-Navarro, Angelina; Deschênes, Isabelle

2017-06-01

Two-pore K + (K 2p ) channels have been described in modulating background conductance as leak channels in different physiological systems. In the heart, the expression of K 2p channels is heterogeneous with equivocation regarding their functional role. Our objective was to determine the K 2p expression profile and their physiological and pathophysiological contribution to cardiac electrophysiology. Induced pluripotent stem cells (iPSCs) generated from humans were differentiated into cardiomyocytes (iPSC-CMs). mRNA was isolated from these cells, commercial iPSC-CM (iCells), control human heart ventricular tissue (cHVT), and ischemic (iHF) and nonischemic heart failure tissues (niHF). We detected 10 K 2p channels in the heart. Comparing quantitative PCR expression of K 2p channels between human heart tissue and iPSC-CMs revealed K 2p 1.1, K 2p 2.1, K 2p 5.1, and K 2p 17.1 to be higher expressed in cHVT, whereas K 2p 3.1 and K 2p 13.1 were higher in iPSC-CMs. Notably, K 2p 17.1 was significantly lower in niHF tissues compared with cHVT. Action potential recordings in iCells after K 2p small interfering RNA knockdown revealed prolongations in action potential depolarization at 90% repolarization for K 2p 2.1, K 2p 3.1, K 2p 6.1, and K 2p 17.1. Here, we report the expression level of 10 human K 2p channels in iPSC-CMs and how they compared with cHVT. Importantly, our functional electrophysiological data in human iPSC-CMs revealed a prominent role in cardiac ventricular repolarization for four of these channels. Finally, we also identified K 2p 17.1 as significantly reduced in niHF tissues and K 2p 4.1 as reduced in niHF compared with iHF. Thus, we advance the notion that K 2p channels are emerging as novel players in cardiac ventricular electrophysiology that could also be remodeled in cardiac pathology and therefore contribute to arrhythmias. NEW & NOTEWORTHY Two-pore K + (K 2p ) channels are traditionally regarded as merely background leak channels in myriad physiological systems. Here, we describe the expression profile of K 2p channels in human-induced pluripotent stem cell-derived cardiomyocytes and outline a salient role in cardiac repolarization and pathology for multiple K 2p channels. Copyright © 2017 the American Physiological Society.

Functional conversion between A-type and delayed rectifier K+ channels by membrane lipids.

PubMed

Oliver, Dominik; Lien, Cheng-Chang; Soom, Malle; Baukrowitz, Thomas; Jonas, Peter; Fakler, Bernd

2004-04-09

Voltage-gated potassium (Kv) channels control action potential repolarization, interspike membrane potential, and action potential frequency in excitable cells. It is thought that the combinatorial association between distinct alpha and beta subunits determines whether Kv channels function as non-inactivating delayed rectifiers or as rapidly inactivating A-type channels. We show that membrane lipids can convert A-type channels into delayed rectifiers and vice versa. Phosphoinositides remove N-type inactivation from A-type channels by immobilizing the inactivation domains. Conversely, arachidonic acid and its amide anandamide endow delayed rectifiers with rapid voltage-dependent inactivation. The bidirectional control of Kv channel gating by lipids may provide a mechanism for the dynamic regulation of electrical signaling in the nervous system.

Sodium Channel β2 Subunits Prevent Action Potential Propagation Failures at Axonal Branch Points.

PubMed

Cho, In Ha; Panzera, Lauren C; Chin, Morven; Hoppa, Michael B

2017-09-27

Neurotransmitter release depends on voltage-gated Na + channels (Na v s) to propagate an action potential (AP) successfully from the axon hillock to a synaptic terminal. Unmyelinated sections of axon are very diverse structures encompassing branch points and numerous presynaptic terminals with undefined molecular partners of Na + channels. Using optical recordings of Ca 2+ and membrane voltage, we demonstrate here that Na + channel β2 subunits (Na v β2s) are required to prevent AP propagation failures across the axonal arborization of cultured rat hippocampal neurons (mixed male and female). When Na v β2 expression was reduced, we identified two specific phenotypes: (1) membrane excitability and AP-evoked Ca 2+ entry were impaired at synapses and (2) AP propagation was severely compromised with >40% of axonal branches no longer responding to AP-stimulation. We went on to show that a great deal of electrical signaling heterogeneity exists in AP waveforms across the axonal arborization independent of axon morphology. Therefore, Na v β2 is a critical regulator of axonal excitability and synaptic function in unmyelinated axons. SIGNIFICANCE STATEMENT Voltage-gated Ca 2+ channels are fulcrums of neurotransmission that convert electrical inputs into chemical outputs in the form of vesicle fusion at synaptic terminals. However, the role of the electrical signal, the presynaptic action potential (AP), in modulating synaptic transmission is less clear. What is the fidelity of a propagating AP waveform in the axon and what molecules shape it throughout the axonal arborization? Our work identifies several new features of AP propagation in unmyelinated axons: (1) branches of a single axonal arborization have variable AP waveforms independent of morphology, (2) Na + channel β2 subunits modulate AP-evoked Ca 2+ -influx, and (3) β2 subunits maintain successful AP propagation across the axonal arbor. These findings are relevant to understanding the flow of excitation in the brain. Copyright © 2017 the authors 0270-6474/17/379519-15$15.00/0.

BDNF mRNA abundance regulated by antidromic action potentials and AP-LTD in hippocampus.

PubMed

Bukalo, Olena; Lee, Philip R; Fields, R Douglas

2016-12-02

Action-potential-induced LTD (AP-LTD) is a form of synaptic plasticity that reduces synaptic strength in CA1 hippocampal neurons firing antidromically during sharp-wave ripples. This firing occurs during slow-wave sleep and quiet moments of wakefulness, which are periods of offline replay of neural sequences learned during encoding sensory information. Here we report that rapid and persistent down-regulation of different mRNA transcripts of the BDNF gene accompanies AP-LTD, and that AP-LTD is abolished in mice with the BDNF gene knocked out in CA1 hippocampal neurons. These findings increase understanding of the mechanism of AP-LTD and the cellular mechanisms of memory consolidation. Published by Elsevier Ireland Ltd.

Ventricular fibrillation associated with early repolarization in a patient with thyroid storm.

PubMed

Ueno, Akira; Yamamoto, Takeshi; Sato, Naoki; Tanaka, Keiji

2010-11-01

We present a case of a 69-year-old male who was hospitalized for the treatment of thyroid storm due to Grave's disease, who presented with unexpected ventricular fibrillation (VF). The possible etiology was early repolarization (ER), characterized by J-point elevation in inferior and posterolateral leads, unmasked by the attenuation of beta-adrenergic effect with normalization of thyroid hormones and following the administration of a beta-blocker. Our case focuses attention on the occurrence of VF in a patient with ER during the treatment of hyperthyroidism, which to our knowledge is the first such report.

Restitution slope is principally determined by steady-state action potential duration.

PubMed

Shattock, Michael J; Park, Kyung Chan; Yang, Hsiang-Yu; Lee, Angela W C; Niederer, Steven; MacLeod, Kenneth T; Winter, James

2017-06-01

The steepness of the action potential duration (APD) restitution curve and local tissue refractoriness are both thought to play important roles in arrhythmogenesis. Despite this, there has been little recognition of the apparent association between steady-state APD and the slope of the restitution curve. The objective of this study was to test the hypothesis that restitution slope is determined by APD and to examine the relationship between restitution slope, refractoriness and susceptibility to VF. Experiments were conducted in isolated hearts and ventricular myocytes from adult guinea pigs and rabbits. Restitution curves were measured under control conditions and following intervention to prolong (clofilium, veratridine, bretylium, low [Ca]e, chronic transverse aortic constriction) or shorten (catecholamines, rapid pacing) ventricular APD. Despite markedly differing mechanisms of action, all interventions that prolonged the action potential led to a steepening of the restitution curve (and vice versa). Normalizing the restitution curve as a % of steady-state APD abolished the difference in restitution curves with all interventions. Effects on restitution were preserved when APD was modulated by current injection in myocytes pre-treated with the calcium chelator BAPTA-AM - to abolish the intracellular calcium transient. The non-linear relation between APD and the rate of repolarization of the action potential is shown to underpin the common influence of APD on the slope of the restitution curve. Susceptibility to VF was found to parallel changes in APD/refractoriness, rather than restitution slope. Steady-state APD is the principal determinant of the slope of the ventricular electrical restitution curve. In the absence of post-repolarization refractoriness, factors that prolong the action potential would be expected to steepen the restitution curve. However, concomitant changes in tissue refractoriness act to reduce susceptibility to sustained VF. Dependence on steady-state APD may contribute to the failure of restitution slope to predict sudden cardiac death. © The Author 2017. Published by Oxford University Press on behalf of the European Society of Cardiology

Restitution slope is principally determined by steady-state action potential duration

PubMed Central

Shattock, Michael J.; Park, Kyung Chan; Yang, Hsiang-Yu; Lee, Angela W. C.; Niederer, Steven; MacLeod, Kenneth T.

2017-01-01

Aims The steepness of the action potential duration (APD) restitution curve and local tissue refractoriness are both thought to play important roles in arrhythmogenesis. Despite this, there has been little recognition of the apparent association between steady-state APD and the slope of the restitution curve. The objective of this study was to test the hypothesis that restitution slope is determined by APD and to examine the relationship between restitution slope, refractoriness and susceptibility to VF. Methods and results Experiments were conducted in isolated hearts and ventricular myocytes from adult guinea pigs and rabbits. Restitution curves were measured under control conditions and following intervention to prolong (clofilium, veratridine, bretylium, low [Ca]e, chronic transverse aortic constriction) or shorten (catecholamines, rapid pacing) ventricular APD. Despite markedly differing mechanisms of action, all interventions that prolonged the action potential led to a steepening of the restitution curve (and vice versa). Normalizing the restitution curve as a % of steady-state APD abolished the difference in restitution curves with all interventions. Effects on restitution were preserved when APD was modulated by current injection in myocytes pre-treated with the calcium chelator BAPTA-AM – to abolish the intracellular calcium transient. The non-linear relation between APD and the rate of repolarization of the action potential is shown to underpin the common influence of APD on the slope of the restitution curve. Susceptibility to VF was found to parallel changes in APD/refractoriness, rather than restitution slope. Conclusion(s) Steady-state APD is the principal determinant of the slope of the ventricular electrical restitution curve. In the absence of post-repolarization refractoriness, factors that prolong the action potential would be expected to steepen the restitution curve. However, concomitant changes in tissue refractoriness act to reduce susceptibility to sustained VF. Dependence on steady-state APD may contribute to the failure of restitution slope to predict sudden cardiac death. PMID:28371805

QT prolongation and proarrhythmia by moxifloxacin: concordance of preclinical models in relation to clinical outcome

PubMed Central

Chen, Xian; Cass, Jessica D; Bradley, Jenifer A; Dahm, Corinn M; Sun, Zhuoqian; Kadyszewski, Edmund; Engwall, Michael J; Zhou, Jun

2005-01-01

Moxifloxacin, a fluoroquinolone antibiotic associated with QT prolongation, has been recommended as a positive control by regulatory authorities to evaluate the sensitivity of both clinical and preclinical studies to detect small but significant increases in QT interval measurements. In this study, we investigated effects of moxifloxacin on the hERG current in HEK-293 cells, electrocardiograms in conscious telemetered dogs, and repolarization parameters and arrhythmogenic potentials in the arterially perfused rabbit ventricular wedge model. Moxifloxacin inhibited the hERG current with an IC50 of 35.7 μM. In conscious telemetered dogs, moxifloxacin significantly prolonged QTc at 30 and 90 mg kg−1, with mean serum Cmax of 8.52 and 22.3 μg ml−1, respectively. In the wedge preparation, moxifloxacin produced a concentration-dependent prolongation of the action potential duration, QT interval, and the time between peak and end of the T wave, an indicator for transmural dispersion of repolarization. Phase 2 early after-depolarizations were observed in one of five experiments at 30 μM and five of five experiments at 100 μM. The arrhythmogenic potential was also concentration-dependent, and 100 μM (∼18-fold above the typical unbound Cmax exposure in clinical usage) appeared to have a high risk of inducing torsade de pointes (TdP). Our data indicated a good correlation among the concentration–response relationships in the three preclinical models and with the available clinical data. The lack of TdP report by moxifloxacin in patients without other risk factors might be attributable to its well-behaved pharmacokinetic profile and other dose-limiting effects. PMID:16158069

Low proarrhythmic potential of citalopram and escitalopram in contrast to haloperidol in an experimental whole-heart model.

PubMed

Frommeyer, Gerrit; Brücher, Benedict; von der Ahe, Henning; Kaese, Sven; Dechering, Dirk G; Kochhäuser, Simon; Bogossian, Harilaos; Milberg, Peter; Eckardt, Lars

2016-10-05

In several case reports proarrhythmic effects of citalopram and escitalopram have been reported. Systematic analyses on prorarrhythmic effects of these drugs are not yet available. The aim of the present study was to investigate if application of citalopram, escitalopram or haloperidol provokes polymorphic ventricular tachycardia in a sensitive model of proarrhythmia. In isolated rabbit hearts monophasic action potentials and ECG showed a significant QT-prolongation after application of citalopram (2µM: +47ms, 4µM: +56ms, P<0.05) accompanied by an increase of action potential duration (APD) but not dispersion of repolarization. Reduced potassium concentration in bradycardic AV-blocked hearts provoked early afterdepolarizations (EAD) in 2 of 12 hearts but no polymorphic ventricular tachycardia (pVT). Application of escitalopram also increased QT-interval (2µM: +3ms, 4µM: +30ms, P<0.05) and APD without effects on dispersion. 3 of 10 hearts showed EAD and pVT in 2 of 10 hearts (32 episodes). The results were compared to 12 rabbits treated with haloperidol which led to an increase in QT-interval (1µM:+62ms; 2µM:+96ms; P<0.01), APD and dispersion (1µM:+15ms, 2µM:+40ms; P<0.01) and induced EAD in all 12 and pVT in 10 of 12 hearts (152 episodes). Citalopram and escitalopram demonstrated a rather safe electrophysiologic profile despite significant QT prolongation. In contrast, haloperidol led to significant increase of dispersion of repolarization while this parameter remained stable under the influence of citalopram or escitalopram. These results imply that application of citalopram or escitalopram is not as proarrhythmic as some case reports might suggest while haloperidol is torsadogenic. Copyright © 2016 Elsevier B.V. All rights reserved.

M3 cholinoreceptors alter electrical activity of rat left atrium via suppression of L-type Ca2+ current without affecting K+ conductance.

PubMed

Filatova, Tatiana S; Naumenko, Nikolay; Galenko-Yaroshevsky, Pavel A; Abramochkin, Denis V

2017-05-01

Electrophysiological effects produced by selective activation of M3 cholinoreceptors were studied in isolated left atrium preparations from rat using the standard sharp glass microelectrode technique. The stimulation of M3 receptors was obtained by application of muscarinic agonist pilocarpine (10 -5  M) in the presence of selective M2 antagonist methoctramine (10 -7  M). Stimulation of M3 receptors induced marked reduction of action potential duration by 14.4 ± 2.4% and 16.1 ± 2.5% of control duration measured at 50 and 90% of repolarization, respectively. This effect was completely abolished by selective M3 blocker 4-DAMP (10 -8  M). In isolated myocytes obtained from the rat left atrium, similar pharmacological stimulation of M3 receptors led to suppression of peak L-type calcium current by 13.9 ± 2.6% of control amplitude (measured at +10 mV), but failed to affect K + currents I to , I Kur , and I Kir . In the absence of M2 blocker methoctramine, pilocarpine (10 -5  M) produced stronger attenuation of I CaL and induced an increase in I Kir . This additive inward rectifier current could be abolished by highly selective blocker of K ir 3.1/3.4 channels tertiapin-Q (10 -6  M) and therefore was identified as I KACh . Thus, in the rat atrial myocardium activation of M3 receptors leads to shortening of action potentials via suppression of I CaL , but does not enhance the major potassium currents involved in repolarization. Joint stimulation of M2 and M3 receptors produces stronger action potential shortening due to M2-mediated activation of I KACh.

Fitting membrane resistance along with action potential shape in cardiac myocytes improves convergence: application of a multi-objective parallel genetic algorithm.

PubMed

Kaur, Jaspreet; Nygren, Anders; Vigmond, Edward J

2014-01-01

Fitting parameter sets of non-linear equations in cardiac single cell ionic models to reproduce experimental behavior is a time consuming process. The standard procedure is to adjust maximum channel conductances in ionic models to reproduce action potentials (APs) recorded in isolated cells. However, vastly different sets of parameters can produce similar APs. Furthermore, even with an excellent AP match in case of single cell, tissue behaviour may be very different. We hypothesize that this uncertainty can be reduced by additionally fitting membrane resistance (Rm). To investigate the importance of Rm, we developed a genetic algorithm approach which incorporated Rm data calculated at a few points in the cycle, in addition to AP morphology. Performance was compared to a genetic algorithm using only AP morphology data. The optimal parameter sets and goodness of fit as computed by the different methods were compared. First, we fit an ionic model to itself, starting from a random parameter set. Next, we fit the AP of one ionic model to that of another. Finally, we fit an ionic model to experimentally recorded rabbit action potentials. Adding the extra objective (Rm, at a few voltages) to the AP fit, lead to much better convergence. Typically, a smaller MSE (mean square error, defined as the average of the squared error between the target AP and AP that is to be fitted) was achieved in one fifth of the number of generations compared to using only AP data. Importantly, the variability in fit parameters was also greatly reduced, with many parameters showing an order of magnitude decrease in variability. Adding Rm to the objective function improves the robustness of fitting, better preserving tissue level behavior, and should be incorporated.

Dynamics of action potential backpropagation in basal dendrites of prefrontal cortical pyramidal neurons.

PubMed

Zhou, Wen-Liang; Yan, Ping; Wuskell, Joseph P; Loew, Leslie M; Antic, Srdjan D

2008-02-01

Basal dendrites of neocortical pyramidal neurons are relatively short and directly attached to the cell body. This allows electrical signals arising in basal dendrites to strongly influence the neuronal output. Likewise, somatic action potentials (APs) should readily propagate back into the basilar dendritic tree to influence synaptic plasticity. Two recent studies, however, determined that sodium APs are severely attenuated in basal dendrites of cortical pyramidal cells, so that they completely fail in distal dendritic segments. Here we used the latest improvements in the voltage-sensitive dye imaging technique (Zhou et al., 2007) to study AP backpropagation in basal dendrites of layer 5 pyramidal neurons of the rat prefrontal cortex. With a signal-to-noise ratio of > 15 and minimal temporal averaging (only four sweeps) we were able to sample AP waveforms from the very last segments of individual dendritic branches (dendritic tips). We found that in short- (< 150 microm) and medium (150-200 microm in length)-range basal dendrites APs backpropagated with modest changes in AP half-width or AP rise-time. The lack of substantial changes in AP shape and dynamics of rise is inconsistent with the AP-failure model. The lack of substantial amplitude boosting of the third AP in the high-frequency burst also suggests that in short- and medium-range basal dendrites backpropagating APs were not severely attenuated. Our results show that the AP-failure concept does not apply in all basal dendrites of the rat prefrontal cortex. The majority of synaptic contacts in the basilar dendritic tree actually received significant AP-associated electrical and calcium transients.

An Excel-based implementation of the spectral method of action potential alternans analysis.

PubMed

Pearman, Charles M

2014-12-01

Action potential (AP) alternans has been well established as a mechanism of arrhythmogenesis and sudden cardiac death. Proper interpretation of AP alternans requires a robust method of alternans quantification. Traditional methods of alternans analysis neglect higher order periodicities that may have greater pro-arrhythmic potential than classical 2:1 alternans. The spectral method of alternans analysis, already widely used in the related study of microvolt T-wave alternans, has also been used to study AP alternans. Software to meet the specific needs of AP alternans analysis is not currently available in the public domain. An AP analysis tool is implemented here, written in Visual Basic for Applications and using Microsoft Excel as a shell. This performs a sophisticated analysis of alternans behavior allowing reliable distinction of alternans from random fluctuations, quantification of alternans magnitude, and identification of which phases of the AP are most affected. In addition, the spectral method has been adapted to allow detection and quantification of higher order regular oscillations. Analysis of action potential morphology is also performed. A simple user interface enables easy import, analysis, and export of collated results. © 2014 The Author. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

Beat-to-Beat Variability of Ventricular Action Potential Duration Oscillates at Low Frequency During Sympathetic Provocation in Humans

PubMed Central

Porter, Bradley; van Duijvenboden, Stefan; Bishop, Martin J.; Orini, Michele; Claridge, Simon; Gould, Justin; Sieniewicz, Benjamin J.; Sidhu, Baldeep; Razavi, Reza; Rinaldi, Christopher A.; Gill, Jaswinder S.; Taggart, Peter

2018-01-01

Background: The temporal pattern of ventricular repolarization is of critical importance in arrhythmogenesis. Enhanced beat-to-beat variability (BBV) of ventricular action potential duration (APD) is pro-arrhythmic and is increased during sympathetic provocation. Since sympathetic nerve activity characteristically exhibits burst patterning in the low frequency range, we hypothesized that physiologically enhanced sympathetic activity may not only increase BBV of left ventricular APD but also impose a low frequency oscillation which further increases repolarization instability in humans. Methods and Results: Heart failure patients with cardiac resynchronization therapy defibrillator devices (n = 11) had activation recovery intervals (ARI, surrogate for APD) recorded from left ventricular epicardial electrodes alongside simultaneous non-invasive blood pressure and respiratory recordings. Fixed cycle length was achieved by right ventricular pacing. Recordings took place during resting conditions and following an autonomic stimulus (Valsalva). The variability of ARI and the normalized variability of ARI showed significant increases post Valsalva when compared to control (p = 0.019 and p = 0.032, respectively). The oscillatory behavior was quantified by spectral analysis. Significant increases in low frequency (LF) power (p = 0.002) and normalized LF power (p = 0.019) of ARI were seen following Valsalva. The Valsalva did not induce changes in conduction variability nor the LF oscillatory behavior of conduction. However, increases in the LF power of ARI were accompanied by increases in the LF power of systolic blood pressure (SBP) and the rate of systolic pressure increase (dP/dtmax). Positive correlations were found between LF-SBP and LF-dP/dtmax (rs = 0.933, p < 0.001), LF-ARI and LF-SBP (rs = 0.681, p = 0.001) and between LF-ARI and LF-dP/dtmax (rs = 0.623, p = 0.004). There was a strong positive correlation between the variability of ARI and LF power of ARI (rs = 0.679, p < 0.001). Conclusions: In heart failure patients, physiological sympathetic provocation induced low frequency oscillation (~0.1 Hz) of left ventricular APD with a strong positive correlation between the LF power of APD and the BBV of APD. These findings may be of importance in mechanisms underlying stability/instability of repolarization and arrhythmogenesis in humans. PMID:29670531

The effects of anticonvulsants on 4-aminopyridine-induced bursting: in vitro studies on rat peripheral nerve and dorsal roots.

PubMed Central

Lees, G.

1996-01-01

1. Aminopyridines have been used as beneficial symptomatic treatments in a variety of neurological conditions including multiple sclerosis but have been associated with considerable toxicity in the form of abdominal pain, paraesthesias and (rarely) convulsions. 2. Extracellular and intracellular recording was used to characterize action potentials in rat sciatic nerves and dorsal roots and the effects of 4-aminopyridine (4-AP). 3. In sciatic nerve trunks, 1 mM 4-AP produced pronounced after potentials at room temperature secondary to regenerative firing in affected axons (5-10 spikes per stimulus). At physiological temperatures, after potentials (2-3 spikes) were greatly attenuated in peripheral axons. 4. 4-AP evoked more pronounced and prolonged after discharges in isolated dorsal roots at 37 degrees C (3-5.5 mV and 80-100 ms succeeded by a smaller inhibitory/depolarizing voltage shift) which were used to assess the effects of anticonvulsants. 5. Phenytoin, carbamazepine and lamotrigine dose-dependently reduced the area of 4-AP-induced after potentials at 100 and 320 microM but the amplitude of compound action potentials (evoked at 0.5 Hz) was depressed in parallel. 6. The tonic block of sensory action potentials by all three drugs (at 320 microM) was enhanced by high frequency stimulation (5-500 Hz). 7. The lack of selectivity of these frequency-dependent Na+ channel blockers for burst firing compared to low-frequency spikes, is discussed in contrast to their effects on 4-AP-induced seizures and paroxysmal activity in CNS tissue (which is associated with large and sustained depolarizing plateau potentials). 8. In conclusion, these in vitro results confirm the marked sensitivity of sensory axons to 4-AP (the presumptive basis for paraesthesias). Burst firing was not preferentially impaired at relatively high concentrations suggesting that anticonvulsants will not overcome the toxic peripheral actions of 4-AP in neurological patients. PMID:8821551

Pharmacokinetics and repolarization effects of intravenous and transdermal granisetron.

PubMed

Mason, Jay W; Selness, Daniel S; Moon, Thomas E; O'Mahony, Bridget; Donachie, Peter; Howell, Julian

2012-05-15

The need for greater clarity about the effects of 5-HT(3) receptor antagonists on cardiac repolarization is apparent in the changing product labeling across this therapeutic class. This study assessed the repolarization effects of granisetron, a 5-HT(3) receptor antagonist antiemetic, administered intravenously and by a granisetron transdermal system (GTDS). In a parallel four-arm study, healthy subjects were randomized to receive intravenous granisetron, GTDS, placebo, or oral moxifloxacin (active control). The primary endpoint was difference in change from baseline in mean Fridericia-corrected QT interval (QTcF) between GTDS and placebo (ddQTcF) on days 3 and 5. A total of 240 subjects were enrolled, 60 in each group. Adequate sensitivity for detection of QTc change was shown by a 5.75 ms lower bound of the 90% confidence interval (CI) for moxifloxacin versus placebo at 2 hours postdose on day 3. Day 3 ddQTcF values varied between 0.2 and 1.9 ms for GTDS (maximum upper bound of 90% CI, 6.88 ms), between -1.2 and 1.6 ms for i.v. granisetron (maximum upper bound of 90% CI, 5.86 ms), and between -3.4 and 4.7 ms for moxifloxacin (maximum upper bound of 90% CI, 13.45 ms). Day 5 findings were similar. Pharmacokinetic-ddQTcF modeling showed a minimally positive slope of 0.157 ms/(ng/mL), but a very low correlation (r = 0.090). GTDS was not associated with statistically or clinically significant effects on QTcF or other electrocardiographic variables. This study provides useful clarification on the effect of granisetron delivered by GTDS on cardiac repolarization. ©2012 AACR.

Indexes of temporal myocardial repolarization dispersion and sudden cardiac death in heart failure: any difference?

PubMed

Piccirillo, Gianfranco; Rossi, Pietro; Mitra, Marilena; Quaglione, Raffaele; Dell'Armi, Annalaura; Di Barba, Daniele; Maisto, Damiana; Lizio, Andrea; Barillà, Francesco; Magrì, Damiano

2013-03-01

The QT variability index, calculated between Q- and the T-wave end (QTend VI), is an index of temporal myocardial repolarization lability associated with sudden cardiac death (SCD) in chronic heart failure (CHF). Little is known about temporal variability in the other two temporal myocardial repolarization descriptors obtained from Q-Tpeak and Tpeak -Tend intervals. We therefore investigated differences between these indexes in patients with CHF who died suddenly and in those who survived with a left ventricular ejection fraction (LVEF) ≤35% or >35%. We selected 127 ECG and systolic blood pressure (SPB) recordings from outpatients with CHF all of whom had been followed up for 30 months. We calculated RR and SPB variability by power spectral analysis and QTend VI, QTpeak VI, Tpeak Tend VI. We then subdivided data patients into three groups SCD, LVEF ≤ 35%, and LVEF > 35%. The LVEF was higher in the SCD than in the LVEF ≤ 35% group, whereas no difference was found between the SCD and LVEF > 35% groups. QTend VI, QTpeak VI, and Tpeak Tend VI were higher in the SCD and LVEF ≤ 35% groups than in the LVEF > 35% group. Multivariate analysis detected a negative relationship between all repolarization variability indexes, low frequency obtained from RR intervals and LVEF. Our data show that variability in the first (QTpeak VI) and second halves of the QT interval (Tpeak -Tend VI) significantly contributes to the QTend VI in patients with CHF. Further studies should investigate whether these indexes might help stratify the risk of SCD in patients with a moderately depressed LVEF. ©2012, Wiley Periodicals, Inc.

Early repolarization in Wolff-Parkinson-White syndrome: prevalence and clinical significance.

PubMed

Mizumaki, Koichi; Nishida, Kunihiro; Iwamoto, Jotaro; Nakatani, Yosuke; Yamaguchi, Yoshiaki; Sakamoto, Tamotsu; Tsuneda, Takayuki; Inoue, Hiroshi; Sakabe, Masao; Fujiki, Akira

2011-08-01

Idiopathic ventricular fibrillation (IVF) with early repolarization (ER) has recently been reported; however, ER is a common finding in healthy subjects and is also found sporadically in patients with Wolff-Parkinson-White (WPW) syndrome. The present study was designed to evaluate the prevalence and clinical significance of ER in patients with WPW syndrome. One hundred and eleven patients with WPW syndrome were studied retrospectively. Early repolarization was defined as QRS slurring or notching with J-point elevation ≥ 1 mm. The prevalence of ER was determined before and after successful catheter ablation. Before ablation, ER was found in 35 of 75 patients with a left free wall, 6 of 23 with a right free wall, and 7 of 13 with a septal accessory pathway (48 of 111, 43% as a whole). Early repolarization was always observed in leads with positive deflection of the initial part of the delta wave. After successful ablation of accessory pathways, ER was preserved in 28 (25%), disappeared in 20 (18%), and newly developed in 8 (7%) patients. In the remaining 55 (50%) patients, ER was not observed either before or after ablation. In patients with persistent ER, the amplitude and width of ER were significantly decreased 3-7 days after the ablation (1.7 ± 0.7 vs. 1.4 ± 0.6 mm, P < 0.005 and 42 ± 11 vs. 34 ± 9 ms, P < 0.001, respectively). In patients with WPW syndrome, ER could be partly related to early depolarization through the accessory pathway. However, persistent ER and new ER appearing after the ablation were frequently found. Therefore, in these patients, mechanisms other than early depolarization may be involved in the genesis of ER.

The mechanism of excitation by acetylcholine in the cerebral cortex

PubMed Central

Krnjević, K.; Pumain, R.; Renaud, L.

1971-01-01

1. The muscarinic depolarizing action of ACh on cortical neurones is associated with an increase in membrane resistance (mean ΔV/ΔR = 3·16 mV/MΩ). 2. ACh also promotes repetitive firing by slowing repolarization after spikes. 3. The depolarizing effect has a mean reversal level of -86·7 mV (with mean resting potential -56 mV). 4. It is concluded that as a muscarinic excitatory agent, ACh probably acts by reducing the resting K+ conductance of cortical neurones, and also the delayed K+ current of the action potential. 5. These results are discussed in relation to the possible role of ACh in cortical function. PMID:5579661

Na+ current in presynaptic terminals of the crayfish opener cannot initiate action potentials.

PubMed

Lin, Jen-Wei

2016-01-01

Action potential (AP) propagation in presynaptic axons of the crayfish opener neuromuscular junction (NMJ) was investigated by simultaneously recording from a terminal varicosity and a proximal branch. Although orthodromically conducting APs could be recorded in terminals with amplitudes up to 70 mV, depolarizing steps in terminals to -20 mV or higher failed to fire APs. Patch-clamp recordings did detect Na(+) current (INa) in most terminals. The INa exhibited a high threshold and fast activation rate. Local perfusion of Na(+)-free saline showed that terminal INa contributed to AP waveform by slightly accelerating the rising phase and increasing the peak amplitude. These findings suggest that terminal INa functions to "touch up" but not to generate APs. Copyright © 2016 the American Physiological Society.

Heart rate variability alters cardiac repolarization and electromechanical dynamics.

PubMed

Phadumdeo, Vrishti M; Weinberg, Seth H

2018-04-07

Heart rate continuously varies due to autonomic regulation, stochasticity in pacemaking, and circadian rhythm, collectively termed heart rate variability (HRV), during normal physiological conditions. Low HRV is clinically associated with an elevated risk of cardiac arrhythmias. Alternans, a beat-to-beat alternation in action potential duration (APD) and/or intracellular calcium (Ca) transient, is a well-known risk factor associated with cardiac arrhythmias that is typically studied under conditions of a constant pacing rate, i.e., the absence of HRV. In this study, we investigate the effects of HRV on the interplay between APD, Ca, and electromechanical properties, employing a nonlinear discrete-time map model that governs APD and intracellular Ca cycling with a stochastic pacing period. We find that HRV can decrease variation in APD and peak Ca at fast pacing rates for which alternans is present. Further, increased HRV typically disrupts the alternating pattern for both APD and peak Ca and weakens the correlation between APD and peak Ca, thus decoupling Ca-mediated instabilities from repolarization alternation. We find that the efficacy of these effects is regulated by the sarcoplasmic reticulum Ca uptake rate. Overall, these results demonstrate that HRV disrupts arrhythmogenic alternans and suggests that HRV may be a significant factor in preventing life-threatening arrhythmias. Copyright © 2018 Elsevier Ltd. All rights reserved.

Risperidone prolongs cardiac repolarization by blocking the rapid component of the delayed rectifier potassium current.

PubMed

Drolet, Benoit; Yang, Tao; Daleau, Pascal; Roden, Dan M; Turgeon, Jacques

2003-06-01

Cases of QT prolongation and sudden death have been reported with risperidone, a neuroleptic agent increasingly prescribed worldwide. Although hypokalemia was present in some of these events, we hypothesized that risperidone may have unsuspected electrophysiologic effects predisposing patients to proarrhythmia. In six isolated guinea pig hearts, risperidone elicited prolongation of cardiac repolarization: action potential duration increased from a baseline value of 128 ms +/- 5 to 147 ms +/- 5 (15%) with risperidone 1 microM during pacing at 250-ms cycle length, whereas the increase was only 10%, from 101 ms +/- 2 to 111 ms +/- 4, with pacing at a cycle length of 150 ms. In human ether-a-go-go (HERG)-transfected Chinese hamster ovary cells (n = 16), risperidone caused concentration-dependent block of the rapid component (I(Kr)) of the delayed rectifier potassium current with an IC(50) for tail block of 261 nM. Risperidone did not block I(Ks). Risperidone exerts cardiac electrophysiologic effects similar to those of Class III antiarrhythmic drugs. These effects are observed at clinically relevant concentrations. Because risperidone is metabolized primarily by CYP2D6, these actions likely enhance risk for risperidone-related QT prolongation and proarrhythmia in specific patient subsets (e.g., poor metabolizers and those taking interacting drugs).

Computational modeling of inhibition of voltage-gated Ca channels: identification of different effects on uterine and cardiac action potentials.

PubMed

Tong, Wing-Chiu; Ghouri, Iffath; Taggart, Michael J

2014-01-01

The uterus and heart share the important physiological feature whereby contractile activation of the muscle tissue is regulated by the generation of periodic, spontaneous electrical action potentials (APs). Preterm birth arising from premature uterine contractions is a major complication of pregnancy and there remains a need to pursue avenues of research that facilitate the use of drugs, tocolytics, to limit these inappropriate contractions without deleterious actions on cardiac electrical excitation. A novel approach is to make use of mathematical models of uterine and cardiac APs, which incorporate many ionic currents contributing to the AP forms, and test the cell-specific responses to interventions. We have used three such models-of uterine smooth muscle cells (USMC), cardiac sinoatrial node cells (SAN), and ventricular cells-to investigate the relative effects of reducing two important voltage-gated Ca currents-the L-type (ICaL) and T-type (ICaT) Ca currents. Reduction of ICaL (10%) alone, or ICaT (40%) alone, blunted USMC APs with little effect on ventricular APs and only mild effects on SAN activity. Larger reductions in either current further attenuated the USMC APs but with also greater effects on SAN APs. Encouragingly, a combination of ICaL and ICaT reduction did blunt USMC APs as intended with little detriment to APs of either cardiac cell type. Subsequent overlapping maps of ICaL and ICaT inhibition profiles from each model revealed a range of combined reductions of ICaL and ICaT over which an appreciable diminution of USMC APs could be achieved with no deleterious action on cardiac SAN or ventricular APs. This novel approach illustrates the potential for computational biology to inform us of possible uterine and cardiac cell-specific mechanisms. Incorporating such computational approaches in future studies directed at designing new, or repurposing existing, tocolytics will be beneficial for establishing a desired uterine specificity of action.

Computational modeling of inhibition of voltage-gated Ca channels: identification of different effects on uterine and cardiac action potentials

PubMed Central

Tong, Wing-Chiu; Ghouri, Iffath; Taggart, Michael J.

2014-01-01

The uterus and heart share the important physiological feature whereby contractile activation of the muscle tissue is regulated by the generation of periodic, spontaneous electrical action potentials (APs). Preterm birth arising from premature uterine contractions is a major complication of pregnancy and there remains a need to pursue avenues of research that facilitate the use of drugs, tocolytics, to limit these inappropriate contractions without deleterious actions on cardiac electrical excitation. A novel approach is to make use of mathematical models of uterine and cardiac APs, which incorporate many ionic currents contributing to the AP forms, and test the cell-specific responses to interventions. We have used three such models—of uterine smooth muscle cells (USMC), cardiac sinoatrial node cells (SAN), and ventricular cells—to investigate the relative effects of reducing two important voltage-gated Ca currents—the L-type (ICaL) and T-type (ICaT) Ca currents. Reduction of ICaL (10%) alone, or ICaT (40%) alone, blunted USMC APs with little effect on ventricular APs and only mild effects on SAN activity. Larger reductions in either current further attenuated the USMC APs but with also greater effects on SAN APs. Encouragingly, a combination of ICaL and ICaT reduction did blunt USMC APs as intended with little detriment to APs of either cardiac cell type. Subsequent overlapping maps of ICaL and ICaT inhibition profiles from each model revealed a range of combined reductions of ICaL and ICaT over which an appreciable diminution of USMC APs could be achieved with no deleterious action on cardiac SAN or ventricular APs. This novel approach illustrates the potential for computational biology to inform us of possible uterine and cardiac cell-specific mechanisms. Incorporating such computational approaches in future studies directed at designing new, or repurposing existing, tocolytics will be beneficial for establishing a desired uterine specificity of action. PMID:25360118

In vitro and in vivo antioxidant potential of milks, yoghurts, fermented milks and cheeses: a narrative review of evidence.

PubMed

Fardet, Anthony; Rock, Edmond

2018-06-01

The antioxidant potential (AP) is an important nutritional property of foods, as increased oxidative stress is involved in most diet-related chronic diseases. In dairy products, the protein fraction contains antioxidant activity, especially casein. Other antioxidants include: antioxidant enzymes; lactoferrin; conjugated linoleic acid; coenzyme Q10; vitamins C, E, A and D3; equol; uric acid; carotenoids; and mineral activators of antioxidant enzymes. The AP of dairy products has been extensively studied in vitro, with few studies in animals and human subjects. Available in vivo studies greatly differ in their design and objectives. Overall, on a 100 g fresh weight-basis, AP of dairy products is close to that of grain-based foods and vegetable or fruit juices. Among dairy products, cheeses present the highest AP due to their higher protein content. AP of milk increases during digestion by up to 2·5 times because of released antioxidant peptides. AP of casein is linked to specific amino acids, whereas β-lactoglobulin thiol groups play a major role in the AP of whey. Thermal treatments such as ultra-high temperature processing have no clear effect on the AP of milk. Raw fat-rich milks have higher AP than less fat-rich milk, because of lipophilic antioxidants. Probiotic yoghurts and fermented milks have higher AP than conventional yoghurt and milk because proteolysis by probiotics releases antioxidant peptides. Among the probiotics, Lactobacillus casei/acidophilus leads to the highest AP. The data are insufficient for cheese, but fermentation-based changes appear to make a positive impact on AP. In conclusion, AP might participate in the reported dairy product-protective effects against some chronic diseases.

Computational Modeling Reveals Key Contributions of KCNQ and hERG Currents to the Malleability of Uterine Action Potentials Underpinning Labor

PubMed Central

Tong, Wing-Chiu; Tribe, Rachel M.; Smith, Roger; Taggart, Michael J.

2014-01-01

The electrical excitability of uterine smooth muscle cells is a key determinant of the contraction of the organ during labor and is manifested by spontaneous, periodic action potentials (APs). Near the end of term, APs vary in shape and size reflecting an ability to change the frequency, duration and amplitude of uterine contractions. A recent mathematical model quantified several ionic features of the electrical excitability in uterine smooth muscle cells. It replicated many of the experimentally recorded uterine AP configurations but its limitations were evident when trying to simulate the long-duration bursting APs characteristic of labor. A computational parameter search suggested that delayed rectifying K+ currents could be a key model component requiring improvement to produce the longer-lasting bursting APs. Of the delayed rectifying K+ currents family it is of interest that KCNQ and hERG channels have been reported to be gestationally regulated in the uterus. These currents exhibit features similar to the broadly defined uterine I K1 of the original mathematical model. We thus formulated new quantitative descriptions for several I KCNQ and I hERG. Incorporation of these currents into the uterine cell model enabled simulations of the long-lasting bursting APs. Moreover, we used this modified model to simulate the effects of different contributions of I KCNQ and I hERG on AP form. Our findings suggest that the alterations in expression of hERG and KCNQ channels can potentially provide a mechanism for fine tuning of AP forms that lends a malleability for changing between plateau-like and long-lasting bursting-type APs as uterine cells prepare for parturition. PMID:25474527

Cardiac Repolarization Changes in the Children with Breath-Holding Spells

PubMed Central

Amoozgar, Hamid; Saleh, Fazl; Farhani, Nahal; Rafiei, Mohammad; Inaloo, Soroor; Asadipooya, Ali-Akbar

2013-01-01

Objective Breath-holding spells are known as benign attacks, frequencies of which decrease by the development of the autonomic nervous system. The present study aims to compare the electrocardiographic repolarization in children with breath-holding spells. Methods In this study, QT dispersion, QTc dispersion, T peak to T end dispersion, and P wave dispersion of the twelve-lead surface electrocardiography of fifty children who had breath-holding spells were measured and compared with normal children from April 2011 to August 2012. Findings Forty-four (88%) patients had cyanotic spells, while 6 (12%) had pallid spells. QTc dispersion was increased in the patients with breath-holding spells (148.2±33.1) compared to the healthy children (132±27.3) and the difference was statically significant (P = 0.01). Meanwhile, no statistically significant differences were observed between the patients and the control subjects regarding the other parameters (P > 0.05). Conclusion QTc dispersion was significantly increased in the patients with breath-holding spells compared to normal children and this is a sign of cardiac repolarization abnormality as well as the increased risk of cardiac arrhythmia in patients with breath-holding spells. PMID:24910749

Changes in autonomic regulation and ventricular repolarization induced by subclinical hyperthyroidism.

PubMed

Galetta, F; Franzoni, F; Fallahi, P; Tocchini, L; Graci, F; Gaddeo, C; Rossi, M; Cini, G; Carpi, A; Santoro, G; Antonelli, A

2010-10-01

The aim of the present study was to evaluate the effect of subclinical hyperthyroidism (SHT) on cardiovascular autonomic function and ventricular repolarization. Thirty subjects (25 females; mean age 49.6 ± 9.8 years) with SHT, as judged by reduced TSH serum levels and normal free T4 and T3 serum levels, and 30 age and sex-matched control subjects underwent standard 12-lead ECG, and 24h ambulatory ECG monitoring. The dispersion of the QT interval, an index of inhomogeneity of repolarization, and the heart rate variability (HRV), a measure of cardiac autonomic modulation, were studied. Patients with SHT showed higher QT dispersion (p<0.001) and lower HRV measures (0.01>p<0.001) than controls. In SHT patients, QT dispersion was inversely related to HRV (r=-0.47, p<0.01). The results of the present study demonstrated that SHT is associated with a sympathovagal imbalance, characterized by increased sympathetic activity in the presence of diminished vagal tone, and with an increased inhomogeneity of ventricular recovery times. The assessment of HRV and QT dispersion in patients with SHT may represent a useful tool in monitoring the cardiovascular risk of this condition. Copyright © 2009 Elsevier Masson SAS. All rights reserved.

Decreased inward rectifier potassium current IK1 in dystrophin-deficient ventricular cardiomyocytes.

PubMed

Rubi, Lena; Koenig, Xaver; Kubista, Helmut; Todt, Hannes; Hilber, Karlheinz

2017-03-04

Kir2.x channels in ventricular cardiomyocytes (most prominently Kir2.1) account for the inward rectifier potassium current I K1 , which controls the resting membrane potential and the final phase of action potential repolarization. Recently it was hypothesized that the dystrophin-associated protein complex (DAPC) is important in the regulation of Kir2.x channels. To test this hypothesis, we investigated potential I K1 abnormalities in dystrophin-deficient ventricular cardiomyocytes derived from the hearts of Duchenne muscular dystrophy mouse models. We found that I K1 was substantially diminished in dystrophin-deficient cardiomyocytes when compared to wild type myocytes. This finding represents the first functional evidence for a significant role of the DAPC in the regulation of Kir2.x channels.

Electrical and Structural Substrate of Arrhythmogenic Right Ventricular Cardiomyopathy Determined Using Noninvasive Electrocardiographic Imaging and Late Gadolinium Magnetic Resonance Imaging.

PubMed

Andrews, Christopher M; Srinivasan, Neil T; Rosmini, Stefania; Bulluck, Heerajnarain; Orini, Michele; Jenkins, Sharon; Pantazis, Antonis; McKenna, William J; Moon, James C; Lambiase, Pier D; Rudy, Yoram

2017-07-01

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a significant cause of sudden cardiac death in the young. Improved noninvasive assessment of ARVC and better understanding of the disease substrate are important for improving patient outcomes. We studied 20 genotyped ARVC patients with a broad spectrum of disease using electrocardiographic imaging (a method for noninvasive cardiac electrophysiology mapping) and advanced late gadolinium enhancement cardiac magnetic resonance scar imaging. Compared with 20 healthy controls, ARVC patients had longer ventricular activation duration (median, 52 versus 42 ms; P =0.007) and prolonged mean epicardial activation-recovery intervals (a surrogate for local action potential duration; median, 275 versus 241 ms; P =0.014). In these patients, we observed abnormal and varied epicardial activation breakthrough locations and regions of nonuniform conduction and fractionated electrograms. Nonuniform conduction and fractionated electrograms were present in the early concealed phase of ARVC. Electrophysiological abnormalities colocalized with late gadolinium enhancement scar, indicating a relationship with structural disease. Premature ventricular contractions were common in ARVC patients with variable initiation sites in both ventricles. Premature ventricular contraction rate increased with exercise, and within anatomic segments, it correlated with prolonged repolarization, electric markers of scar, and late gadolinium enhancement (all P <0.001). Electrocardiographic imaging reveals electrophysiological substrate properties that differ in ARVC patients compared with healthy controls. A novel mechanistic finding is the presence of repolarization abnormalities in regions where ventricular ectopy originates. The results suggest a potential role for electrocardiographic imaging and late gadolinium enhancement in early diagnosis and noninvasive follow-up of ARVC patients. © 2017 American Heart Association, Inc.

Slow adaptation of ventricular repolarization as a cause of arrhythmia?

PubMed

Bueno-Orovio, A; Hanson, B M; Gill, J S; Taggart, P; Rodriguez, B

2014-01-01

This article is part of the Focus Theme of Methods of Information in Medicine on "Biosignal Interpretation: Advanced Methods for Studying Cardiovascular and Respiratory Systems". Adaptation of the QT-interval to changes in heart rate reflects on the body-surface electrocardiogram the adaptation of action potential duration (APD) at the cellular level. The initial fast phase of APD adaptation has been shown to modulate the arrhythmia substrate. Whether the slow phase is potentially proarrhythmic remains unclear. To analyze in-vivo human data and use computer simulations to examine effects of the slow APD adaptation phase on dispersion of repolarization and reentry in the human ventricle. Electrograms were acquired from 10 left and 10 right ventricle (LV/RV) endocardial sites in 15 patients with normal ventricles during RV pacing. Activation-recovery intervals, as a surrogate for APD, were measured during a sustained increase in heart rate. Observed dynamics were studied using computer simulations of human tissue electrophysiology. Spatial heterogeneity of rate adaptation was observed in all patients. Inhomogeneity in slow APD adaptation time constants (Δτ(s)) was greater in LV than RV (Δτ(s)(LV) = 31.8 ± 13.2, Δτ(s)(RV) = 19.0 ± 12.8 s , P< 0.01). Simulations showed that altering local slow time constants of adaptation was sufficient to convert partial wavefront block to block with successful reentry. Using electrophysiological data acquired in-vivo in human and computer simulations, we identify heterogeneity in the slow phase of APD adaptation as an important component of arrhythmogenesis.

Reduction of atrial fibrillation by Tanshinone IIA in chronic heart failure.

PubMed

He, Zhifeng; Sun, Changzheng; Xu, Yi; Cheng, Dezhi

2016-12-01

The aim of the present study was to confirm the effect of Tanshinone IIA (TAN) on the prevention of AF in chronic heart failure (CHF), and to elucidate the underlying electrophysiological mechanisms for the antiarrhythmic effects of TAN at the level of the atrium in an experimental model of CHF. In 10 female rabbits, CHF was induced by rapid ventricular pacing, leading to a significant decrease in ejection fraction in the presence of a dilated left ventricle and atrial enlargement. Twelve rabbits were sham-operated and served as controls. Isolated hearts were perfused using the Langendorff method. Burst pacing was used to induce AF. Monophasic action potential recordings showed an increase of atrial action potential duration (aAPD) and effective refractory period (aERP) in CHF hearts compared with sham hearts. Infusion of acetylcholine (1μm) and isoproterenol (1μm) led to AF in all failing hearts and in 11 sham hearts. Simultaneous infusion of TAN (10μm) remarkably reduced inducibility of AF in 50% of sham and 50% of failing hearts. TAN had no effect on aAPD but significantly increased aERP, leading to a marked increase in atrial post-repolarization refractoriness. Moreover, TAN application moderately increased interatrial conduction time. TAN has been shown to be effective in reducing the inducibility of AF in an experimental model of AF. The antiarrhythmic effect is mainly due to prolongations of atrial post-repolarization refractoriness and a moderate increase in interatrial conduction time. Copyright © 2016. Published by Elsevier Masson SAS.

Variable Action Potential Backpropagation during Tonic Firing and Low-Threshold Spike Bursts in Thalamocortical But Not Thalamic Reticular Nucleus Neurons.

PubMed

Connelly, William M; Crunelli, Vincenzo; Errington, Adam C

2017-05-24

Backpropagating action potentials (bAPs) are indispensable in dendritic signaling. Conflicting Ca 2+ -imaging data and an absence of dendritic recording data means that the extent of backpropagation in thalamocortical (TC) and thalamic reticular nucleus (TRN) neurons remains unknown. Because TRN neurons signal electrically through dendrodendritic gap junctions and possibly via chemical dendritic GABAergic synapses, as well as classical axonal GABA release, this lack of knowledge is problematic. To address this issue, we made two-photon targeted patch-clamp recordings from rat TC and TRN neuron dendrites to measure bAPs directly. These recordings reveal that "tonic"' and low-threshold-spike (LTS) "burst" APs in both cell types are always recorded first at the soma before backpropagating into the dendrites while undergoing substantial distance-dependent dendritic amplitude attenuation. In TC neurons, bAP attenuation strength varies according to firing mode. During LTS bursts, somatic AP half-width increases progressively with increasing spike number, allowing late-burst spikes to propagate more efficiently into the dendritic tree compared with spikes occurring at burst onset. Tonic spikes have similar somatic half-widths to late burst spikes and undergo similar dendritic attenuation. In contrast, in TRN neurons, AP properties are unchanged between LTS bursts and tonic firing and, as a result, distance-dependent dendritic attenuation remains consistent across different firing modes. Therefore, unlike LTS-associated global electrical and calcium signals, the spatial influence of bAP signaling in TC and TRN neurons is more restricted, with potentially important behavioral-state-dependent consequences for synaptic integration and plasticity in thalamic neurons. SIGNIFICANCE STATEMENT In most neurons, action potentials (APs) initiate in the axosomatic region and propagate into the dendritic tree to provide a retrograde signal that conveys information about the level of cellular output to the locations that receive most input: the dendrites. In thalamocortical and thalamic reticular nucleus neurons, the site of AP generation and the true extent of backpropagation remain unknown. Using patch-clamp recordings, this study measures dendritic propagation of APs directly in these neurons. In either cell type, high-frequency low-threshold spike burst or lower-frequency tonic APs undergo substantial voltage attenuation as they spread into the dendritic tree. Therefore, backpropagating spikes in these cells can only influence signaling in the proximal part of the dendritic tree. Copyright © 2017 Connelly et al.

Dendritic small conductance calcium-activated potassium channels activated by action potentials suppress EPSPs and gate spike-timing dependent synaptic plasticity.

PubMed

Jones, Scott L; To, Minh-Son; Stuart, Greg J

2017-10-23

Small conductance calcium-activated potassium channels (SK channels) are present in spines and can be activated by backpropagating action potentials (APs). This suggests they may play a critical role in spike-timing dependent synaptic plasticity (STDP). Consistent with this idea, EPSPs in both cortical and hippocampal pyramidal neurons were suppressed by preceding APs in an SK-dependent manner. In cortical pyramidal neurons EPSP suppression by preceding APs depended on their precise timing as well as the distance of activated synapses from the soma, was dendritic in origin, and involved SK-dependent suppression of NMDA receptor activation. As a result SK channel activation by backpropagating APs gated STDP induction during low-frequency AP-EPSP pairing, with both LTP and LTD absent under control conditions but present after SK channel block. These findings indicate that activation of SK channels in spines by backpropagating APs plays a key role in regulating both EPSP amplitude and STDP induction.

Diadenosine tetraphosphate (Ap4A) and triphosphate (Ap3A) signaling of human sperm motility.

PubMed

Chan, P J; Su, B C; Tredway, D R

1991-01-01

The ubiquitous dinucleotide polyphosphate, diadenosine tetraphosphate (Ap4A), has been shown to be a signal molecule for DNA replication in mammalian cells. In this study, Ap4A and a related compound, diadenosine triphosphate (Ap3A), were tested for possible signaling functions in human spermatozoa. A computerized automated semen analyzer was used to detect changes in spermatozoa motility parameters. Cryopreserved-thawed donor spermatozoa were washed and incubated in 0.1 mM Ap4A, 0.1 mM Ap3A, or control medium. The data indicated that both Ap4A and Ap3A decreased the percentage of motile spermatozoa after 4 or more hours of incubation in vitro. The two dinucleotide polyphosphates caused an increase in the amplitude of lateral spermatozoa head displacement parameter only at the start of incubation. The other spermatozoa kinematic parameters were unaffected. No opposing ying-yang dual actions of Ap4A to Ap3A were seen. From the results, Ap4A and Ap3A were observed to be potential inhibitory signals of spermatozoa motility after prolonged exposure.

Electrophysiological mechanisms of sophocarpine as a potential antiarrhythmic agent.

PubMed

Yang, Zhi-fang; Li, Ci-zhen; Wang, Wei; Chen, Ying-min; Zhang, Ying; Liu, Yuan-mou; Wang, Hong-wei

2011-03-01

To examine the electrophysiological effects of sophocarpine on action potentials (AP) and ionic currents of cardiac myocytes and to compare some of these effects with those of amiodarone. Langendorff perfusion set-up was used in isolated guinea pig heart, and responses to sophocarpine were monitored using electrocardiograph. Conventional microelectrode, voltage clamp technique and perforated patch were employed to record fast response AP (fAP), slow response AP (sAP) and ionic currents in guinea pig papillary muscle or rabbit sinus node cells. Tachyarrhythmia produced by isoprenaline (15 μmol/L) could be reversed by sophocarpine (300 μmol/L). Sophocarpine (10 μmol/L) decreased the amplitude by 4.0%, maximal depolarization velocity (V(max)) of the fAP by 24.4%, and Na(+) current (I(Na)) by 18.0%, while it prolonged the effective refractory period (ERP) by 21.1%. The same concentration of sophocarpine could also decrease the amplitude and V(max) of the sAP, by 26.8% and 25.7%, respectively, and attenuated the Ca(2+) current (I(CaL)) and the K(+) tail current substantially. Comparison of sophocarpine with amiodarone demonstrated that both prolonged the duration and the ERP of fAP and sAP, both decreased the amplitude and V(max) of the fAP and sAP, and both slowed the automatic heart rate. Sophocarpine could reverse isoprenaline-induced arrhythmia and inhibit I(Na), I(CaL), and I(Kr) currents. The electrophysiological effects of sophocarpine are similar to those of amiodarone, which might be regarded as a prospective antiarrhythmic agent.

Patent foramen ovale and atrial septal aneurysm can cause ischemic stroke in patients with antiphospholipid syndrome.

PubMed

Tanaka, Yasutaka; Ueno, Yuji; Miyamoto, Nobukazu; Shimada, Yoshiaki; Tanaka, Ryota; Hattori, Nobutaka; Urabe, Takao

2013-01-01

The purpose of the present study was to evaluate the contributions of embolic etiologies, patent foramen ovale (PFO) and atrial septal aneurysm (ASA) to the pathogenesis of ischemic stroke in patients with antiphospholipid syndrome (APS). We performed transesophageal echocardiography (TEE) examination for consecutive stroke patients who had been diagnosed with APS (APS group) to detect potential embolic sources. APS was diagnosed based on the modified Sapporo criteria. The control stroke group comprised age- and sex-matched cryptogenic stroke patients undergoing TEE. We assessed and compared the clinical characteristics and TEE findings between stroke patients with APS and control stroke groups. Among 582 patients, nine patients (nine women; mean age, 50 ± 18 years) were classified into the APS group. In 137 patients undergoing TEE, 41 age-matched female stroke patients were recruited to the control stroke group. Prevalences of PFO and ASA were significantly higher in the APS group than in the control stroke group (89 vs. 41 %, p = 0.027; 67 vs. 20 %, p = 0.015, respectively). Multiple logistic regression analysis showed that PFO (odds ratio (OR), 13.71; 95 % confidence interval (CI), 1.01-185.62; p = 0.049) and ASA (OR, 8.06; 95 % CI, 1.17-55.59; p = 0.034) were independently associated with the APS group. PFO and ASA were strongly associated with the APS group, and could thus represent potential embolic sources in ischemic stroke patients with APS.

Arrhythmogenic drugs can amplify spatial heterogeneities in the electrical restitution in perfused guinea-pig heart: An evidence from assessments of monophasic action potential durations and JT intervals

PubMed Central

2018-01-01

Non-uniform shortening of the action potential duration (APD90) in different myocardial regions upon heart rate acceleration can set abnormal repolarization gradients and promote arrhythmia. This study examined whether spatial heterogeneities in APD90 restitution can be amplified by drugs with clinically proved proarrhythmic potential (dofetilide, quinidine, procainamide, and flecainide) and, if so, whether these effects can translate to the appropriate changes of the ECG metrics of ventricular repolarization, such as JT intervals. In isolated, perfused guinea-pig heart preparations, monophasic action potentials and volume-conducted ECG were recorded at progressively increased pacing rates. The APD90 measured at distinct ventricular sites, as well as the JTpeak and JTend values were plotted as a function of preceding diastolic interval, and the maximum slopes of the restitution curves were determined at baseline and upon drug administration. Dofetilide, quinidine, and procainamide reverse rate-dependently prolonged APD90 and steepened the restitution curve, with effects being greater at the endocardium than epicardium, and in the right ventricular (RV) vs. the left ventricular (LV) chamber. The restitution slope was increased to a greater extent for the JTend vs. the JTpeak interval. In contrast, flecainide reduced the APD90 restitution slope at LV epicardium without producing effect at LV endocardium and RV epicardium, and reduced the JTpeak restitution slope without changing the JTend restitution. Nevertheless, with all agents, these effects translated to the amplified epicardial-to-endocardial and the LV-to-RV non-uniformities in APD90 restitution, paralleled by the increased JTend vs. JTpeak difference in the restitution slope. In summary, these findings suggest that arrhythmic drug profiles are partly attributable to the accentuated regional heterogeneities in APD90 restitution, which can be indirectly determined through ECG assessments of the JTend vs. JTpeak dynamics at variable pacing rates. PMID:29352276

Arrhythmogenic drugs can amplify spatial heterogeneities in the electrical restitution in perfused guinea-pig heart: An evidence from assessments of monophasic action potential durations and JT intervals.

PubMed

Osadchii, Oleg E

2018-01-01

Non-uniform shortening of the action potential duration (APD90) in different myocardial regions upon heart rate acceleration can set abnormal repolarization gradients and promote arrhythmia. This study examined whether spatial heterogeneities in APD90 restitution can be amplified by drugs with clinically proved proarrhythmic potential (dofetilide, quinidine, procainamide, and flecainide) and, if so, whether these effects can translate to the appropriate changes of the ECG metrics of ventricular repolarization, such as JT intervals. In isolated, perfused guinea-pig heart preparations, monophasic action potentials and volume-conducted ECG were recorded at progressively increased pacing rates. The APD90 measured at distinct ventricular sites, as well as the JTpeak and JTend values were plotted as a function of preceding diastolic interval, and the maximum slopes of the restitution curves were determined at baseline and upon drug administration. Dofetilide, quinidine, and procainamide reverse rate-dependently prolonged APD90 and steepened the restitution curve, with effects being greater at the endocardium than epicardium, and in the right ventricular (RV) vs. the left ventricular (LV) chamber. The restitution slope was increased to a greater extent for the JTend vs. the JTpeak interval. In contrast, flecainide reduced the APD90 restitution slope at LV epicardium without producing effect at LV endocardium and RV epicardium, and reduced the JTpeak restitution slope without changing the JTend restitution. Nevertheless, with all agents, these effects translated to the amplified epicardial-to-endocardial and the LV-to-RV non-uniformities in APD90 restitution, paralleled by the increased JTend vs. JTpeak difference in the restitution slope. In summary, these findings suggest that arrhythmic drug profiles are partly attributable to the accentuated regional heterogeneities in APD90 restitution, which can be indirectly determined through ECG assessments of the JTend vs. JTpeak dynamics at variable pacing rates.

Acute Pancreatitis and Use of Pancreatitis-Associated Drugs: A 10-Year Population-Based Cohort Study.

PubMed

Bertilsson, Sara; Kalaitzakis, Evangelos

2015-10-01

To assess the use of acute pancreatitis (AP)-associated drugs in patients with AP, the relation between sales of these drugs and the incidence of AP, and the potential impact on AP severity and recurrence. All patients with incident AP between 2003 and 2012, in a well-defined area, were retrospectively identified. Data regarding AP etiology, severity, and recurrence and use of AP-associated drugs were extracted from medical records. Drugs were classified according to an evidence-based classification system. Annual drug sales data were obtained from the Swedish drug administration service. Overall, 1457 cases of incident AP were identified. Acute pancreatitis-associated drug users increased from 32% in 2003 to 51% in 2012, reflecting increasing user rates in the general population. The incidence of AP increased during the study period but was not related to AP-associated drug user rates (P > 0.05). Recurrent AP occurred in 23% but was unrelated to AP-associated drug use (P > 0.05). In logistic regression analysis, after adjustment for comorbidity, AP-associated drug use was not related to AP severity (P > 0.05). Use of AP-associated drugs is increasingly frequent in patients with AP. However, it does not have any major impact on the observed epidemiological changes in occurrence, severity, or recurrence of AP.

Activation of the Arabidopsis B class homeotic genes by APETALA1.

PubMed

Ng, M; Yanofsky, M F

2001-04-01

Proper development of petals and stamens in Arabidopsis flowers requires the activities of APETALA3 (AP3) and PISTILLATA (PI), whose transcripts can be detected in the petal and stamen primordia. Localized expression of AP3 and PI requires the activities of at least three genes: APETALA1 (AP1), LEAFY (LFY), and UNUSUAL FLORAL ORGANS (UFO). It has been proposed that UFO provides spatial cues and that LFY specifies competence for AP3 and PI expression in the developing flower. To understand the epistatic relationship among AP1, LFY, and UFO in regulating AP3 and PI expression, we generated two versions of AP1 that have strong transcriptional activation potential. Genetic and molecular analyses of transgenic plants expressing these activated AP1 proteins show that the endogenous AP1 protein acts largely as a transcriptional activator in vivo and that AP1 specifies petals by regulating the spatial domains of AP3 and PI expression through UFO.

Advances in Bacterial Methionine Aminopeptidase Inhibition

PubMed Central

Helgren, Travis R.; Wangtrakuldee, Phumvadee; Staker, Bart L.; Hagen, Timothy J.

2016-01-01

Methionine aminopeptidases (MetAPs) are metalloenzymes that cleave the N-terminal methionine from newly synthesized peptides and proteins. These MetAP enzymes are present in bacteria, and knockout experiments have shown that MetAP activity is essential for cell life, suggesting that MetAPs are good antibacterial drug targets. MetAP enzymes are also present in the human host and selectivity is essential. There have been significant structural biology efforts and over 65 protein crystal structures of bacterial MetAPs are deposited into the PDB. This review highlights the available crystallographic data for bacterial MetAPs. Structural comparison of bacterial MetAPs with human MetAPs highlights differences that can lead to selectivity. In addition, this review includes the chemical diversity of molecules that bind and inhibit the bacterial MetAP enzymes. Analysis of the structural biology and chemical space of known bacterial MetAP inhibitors leads to a greater understanding of this antibacterial target and the likely development of potential antibacterial agents. PMID:26268344

The non-competitive acetylcholinesterase inhibitor APS12-2 is a potent antagonist of skeletal muscle nicotinic acetylcholine receptors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grandič, Marjana; Aráoz, Romulo; Molgó, Jordi

APS12-2, a non-competitive acetylcholinesterase inhibitor, is one of the synthetic analogs of polymeric alkylpyridinium salts (poly-APS) isolated from the marine sponge Reniera sarai. In the present work the effects of APS12-2 were studied on isolated mouse phrenic nerve–hemidiaphragm muscle preparations, using twitch tension measurements and electrophysiological recordings. APS12-2 in a concentration-dependent manner blocked nerve-evoked isometric muscle contraction (IC{sub 50} = 0.74 μM), without affecting directly-elicited twitch tension up to 2.72 μM. The compound (0.007–3.40 μM) decreased the amplitude of miniature endplate potentials until a complete block by concentrations higher than 0.68 μM, without affecting their frequency. Full size endplate potentials,more » recorded after blocking voltage-gated muscle sodium channels, were inhibited by APS12-2 in a concentration-dependent manner (IC{sub 50} = 0.36 μM) without significant change in the resting membrane potential of the muscle fibers up to 3.40 μM. The compound also blocked acetylcholine-evoked inward currents in Xenopus oocytes in which Torpedo (α1{sub 2}β1γδ) muscle-type nicotinic acetylcholine receptors (nAChRs) have been incorporated (IC{sub 50} = 0.0005 μM), indicating a higher affinity of the compound for Torpedo (α1{sub 2}β1γδ) than for the mouse (α1{sub 2}β1γε) nAChR. Our data show for the first time that APS12-2 blocks neuromuscular transmission by a non-depolarizing mechanism through an action on postsynaptic nAChRs of the skeletal neuromuscular junction. -- Highlights: ► APS12-2 produces concentration-dependent inhibition of nerve-evoked muscle contraction in vitro. ► APS12-2 blocks MEPPs and EPPs at the neuromuscular junction. APS12-2 blocks ACh-activated current in Xenopus oocytes incorporated with Torpedo nAChRs.« less

Tumor-targeting peptide conjugated pH-responsive micelles as a potential drug carrier for cancer therapy.

PubMed

Wu, Xiang Lan; Kim, Jong Ho; Koo, Heebeom; Bae, Sang Mun; Shin, Hyeri; Kim, Min Sang; Lee, Byung-Heon; Park, Rang-Woon; Kim, In-San; Choi, Kuiwon; Kwon, Ick Chan; Kim, Kwangmeyung; Lee, Doo Sung

2010-02-17

Herein, we prepared tumor-targeting peptide (AP peptide; CRKRLDRN) conjugated pH-responsive polymeric micelles (pH-PMs) in cancer therapy by active and pH-responsive tumor targeting delivery systems, simultaneously. The active tumor targeting and tumoral pH-responsive polymeric micelles were prepared by mixing AP peptide conjugated PEG-poly(d,l-lactic acid) block copolymer (AP-PEG-PLA) into the pH-responsive micelles of methyl ether poly(ethylene glycol) (MPEG)-poly(beta-amino ester) (PAE) block copolymer (MPEG-PAE). These mixed amphiphilic block copolymers were self-assembled to form stable AP peptide-conjugated and pH-responsive AP-PEG-PLA/MPEG-PAE micelles (AP-pH-PMs) with an average size of 150 nm. The AP-pH-PMs containing 10 wt % of AP-PEG-PLA showed a sharp pH-dependent micellization/demicellization transition at the tumoral acid pH. Also, they presented the pH-dependent drug release profile at the acidic pH of 6.4. The fluorescence dye, TRITC, encapsulated AP-pH-PMs (TRITC-AP-pH-PMs) presented the higher tumor-specific targeting ability in vitro cancer cell culture system and in vivo tumor-bearing mice, compared to control pH-responsive micelles of MPEG-PAE. For the cancer therapy, the anticancer drug, doxorubicin (DOX), was efficiently encapsulated into the AP-pH-PMs (DOX-AP-pH-PMs) with a higher loading efficiency. DOX-AP-pH-PMs efficiently deliver anticancer drugs in MDA-MB231 human breast tumor-bearing mice, resulted in excellent anticancer therapeutic efficacy, compared to free DOX and DOX encapsulated MEG-PAE micelles, indicating the excellent tumor targeting ability of AP-pH-PMs. Therefore, these tumor-targeting peptide-conjugated and pH-responsive polymeric micelles have great potential application in cancer therapy.

AP Potential Expectancy Tables Based on PSAT/NMSQT and SAT Scores on the 2015-16 Redesigned Scales Using Final Concordance Tables. Statistical Report

ERIC Educational Resources Information Center

Ewing, Maureen; Wyatt, Jeff

2017-01-01

Historically, AP Potential™ has used PSAT/NMSQT® scores to identify students who are likely to earn a 3 or higher on a specific AP Exam based on research showing moderate to strong relationships between PSAT/NMSQT scores and AP Exam scores (Camara & Millsap, 1998; Ewing, Camara, & Millsap, 2006; Zhang, Patel, & Ewing, 2014a). For most…

The Role of Potassium Channels in Arabidopsis thaliana Long Distance Electrical Signalling: AKT2 Modulates Tissue Excitability While GORK Shapes Action Potentials.

PubMed

Cuin, Tracey Ann; Dreyer, Ingo; Michard, Erwan

2018-03-21

Fast responses to an external threat depend on the rapid transmission of signals through a plant. Action potentials (APs) are proposed as such signals. Plant APs share similarities with their animal counterparts; they are proposed to depend on the activity of voltage-gated ion channels. Nonetheless, despite their demonstrated role in (a)biotic stress responses, the identities of the associated voltage-gated channels and transporters remain undefined in higher plants. By demonstrating the role of two potassium-selective channels in Arabidopsis thaliana in AP generation and shaping, we show that the plant AP does depend on similar Kv -like transport systems to those of the animal signal. We demonstrate that the outward-rectifying potassium-selective channel GORK limits the AP amplitude and duration, while the weakly-rectifying channel AKT2 affects membrane excitability. By computational modelling of plant APs, we reveal that the GORK activity not only determines the length of an AP but also the steepness of its rise and the maximal amplitude. Thus, outward-rectifying potassium channels contribute to both the repolarisation phase and the initial depolarisation phase of the signal. Additionally, from modelling considerations we provide indications that plant APs might be accompanied by potassium waves, which prime the excitability of the green cable.

Combined soft and hard X-ray ambient pressure photoelectron spectroscopy studies of semiconductor/electrolyte interfaces

DOE PAGES

Starr, David E.; Favaro, Marco; Abdi, Fatwa F.; ...

2017-05-18

The development of solar fuel generating materials would greatly benefit from a molecular level understanding of the semiconductor/electrolyte interface and changes in the interface induced by an applied potential and illumination by solar light. Ambient pressure photoelectron spectroscopy techniques with both soft and hard X-rays, AP-XPS and AP-HAXPES respectively, have the potential to markedly contribute to this understanding. In this paper we initially provide two examples of current challenges in solar fuels material development that AP-XPS and AP-HAXPES can directly a ddress. This will be followed by a brief description of the distinguishing and complementary characteristics of soft and hardmore » X-ray AP-XPS and AP-HAXPES and best approaches to achieving monolayer sensitivity in solid/aqueous electrolyte studies. In particular we focus on the detection of surface adsorbed hydroxyl groups in the presence of aqueous hydroxide anions in the electrolyte, a common situation when investigating photoanodes for solar fuel generating applications. Finally, the article concludes by providing an example of a combined AP-XPS and AP-HAXPES study of a semiconductor/aqueous electrolyte interface currently used in water splitting devices specifically the BiVO 4/aqueous potassium phosphate electrolyte interface.« less

Dendritic Properties Control Energy Efficiency of Action Potentials in Cortical Pyramidal Cells

PubMed Central

Yi, Guosheng; Wang, Jiang; Wei, Xile; Deng, Bin

2017-01-01

Neural computation is performed by transforming input signals into sequences of action potentials (APs), which is metabolically expensive and limited by the energy available to the brain. The metabolic efficiency of single AP has important consequences for the computational power of the cell, which is determined by its biophysical properties and morphologies. Here we adopt biophysically-based two-compartment models to investigate how dendrites affect energy efficiency of APs in cortical pyramidal neurons. We measure the Na+ entry during the spike and examine how it is efficiently used for generating AP depolarization. We show that increasing the proportion of dendritic area or coupling conductance between two chambers decreases Na+ entry efficiency of somatic AP. Activating inward Ca2+ current in dendrites results in dendritic spike, which increases AP efficiency. Activating Ca2+-activated outward K+ current in dendrites, however, decreases Na+ entry efficiency. We demonstrate that the active and passive dendrites take effects by altering the overlap between Na+ influx and internal current flowing from soma to dendrite. We explain a fundamental link between dendritic properties and AP efficiency, which is essential to interpret how neural computation consumes metabolic energy and how biophysics and morphologies contribute to such consumption. PMID:28919852

Dendritic Properties Control Energy Efficiency of Action Potentials in Cortical Pyramidal Cells.

PubMed

Yi, Guosheng; Wang, Jiang; Wei, Xile; Deng, Bin

2017-01-01

Neural computation is performed by transforming input signals into sequences of action potentials (APs), which is metabolically expensive and limited by the energy available to the brain. The metabolic efficiency of single AP has important consequences for the computational power of the cell, which is determined by its biophysical properties and morphologies. Here we adopt biophysically-based two-compartment models to investigate how dendrites affect energy efficiency of APs in cortical pyramidal neurons. We measure the Na + entry during the spike and examine how it is efficiently used for generating AP depolarization. We show that increasing the proportion of dendritic area or coupling conductance between two chambers decreases Na + entry efficiency of somatic AP. Activating inward Ca 2+ current in dendrites results in dendritic spike, which increases AP efficiency. Activating Ca 2+ -activated outward K + current in dendrites, however, decreases Na + entry efficiency. We demonstrate that the active and passive dendrites take effects by altering the overlap between Na + influx and internal current flowing from soma to dendrite. We explain a fundamental link between dendritic properties and AP efficiency, which is essential to interpret how neural computation consumes metabolic energy and how biophysics and morphologies contribute to such consumption.

Comment on "Penetration of Action Potentials During Collision in the Median and Lateral Giant Axons of Invertebrates"

NASA Astrophysics Data System (ADS)

Berg, Rune W.; Stauning, Marius Tving; Sørensen, Jakob Balslev; Jahnsen, Henrik

2017-04-01

The action potential (AP) is an electrical impulse elicited by depolarization of the neuronal membrane from the resting membrane potential (around -70 mV ). It propagates along the axon, allowing for rapid and distant communication. Recently, it was claimed that two APs traveling in opposite direction will pass unhindered through each other (penetrate) upon collision [Gonzalez-Perez et al.Phys. Rev. X 4, 031047 (2014), 10.1103/PhysRevX.4.031047]. We tested this claim under carefully controlled conditions and found that we cannot reproduce penetration. Instead, APs consistently annihilated upon collision. This is consistent with a vast body of literature.

Three-dimensional mapping and regulation of action potential propagation in nanoelectronics-innervated tissues.

PubMed

Dai, Xiaochuan; Zhou, Wei; Gao, Teng; Liu, Jia; Lieber, Charles M

2016-09-01

Real-time mapping and manipulation of electrophysiology in three-dimensional (3D) tissues could have important impacts on fundamental scientific and clinical studies, yet realization is hampered by a lack of effective methods. Here we introduce tissue-scaffold-mimicking 3D nanoelectronic arrays consisting of 64 addressable devices with subcellular dimensions and a submillisecond temporal resolution. Real-time extracellular action potential (AP) recordings reveal quantitative maps of AP propagation in 3D cardiac tissues, enable in situ tracing of the evolving topology of 3D conducting pathways in developing cardiac tissues and probe the dynamics of AP conduction characteristics in a transient arrhythmia disease model and subsequent tissue self-adaptation. We further demonstrate simultaneous multisite stimulation and mapping to actively manipulate the frequency and direction of AP propagation. These results establish new methodologies for 3D spatiotemporal tissue recording and control, and demonstrate the potential to impact regenerative medicine, pharmacology and electronic therapeutics.

Three-dimensional mapping and regulation of action potential propagation in nanoelectronics innervated tissues

PubMed Central

Dai, Xiaochuan; Zhou, Wei; Gao, Teng; Liu, Jia; Lieber, Charles M.

2016-01-01

Real-time mapping and manipulation of electrophysiology in three-dimensional (3D) tissues could impact broadly fundamental scientific and clinical studies, yet realization lacks effective methods. Here we introduce tissue-scaffold-mimicking 3D nanoelectronic arrays consisting of 64 addressable devices with subcellular dimensions and sub-millisecond time-resolution. Real-time extracellular action potential (AP) recordings reveal quantitative maps of AP propagation in 3D cardiac tissues, enable in situ tracing of the evolving topology of 3D conducting pathways in developing cardiac tissues, and probe the dynamics of AP conduction characteristics in a transient arrhythmia disease model and subsequent tissue self-adaptation. We further demonstrate simultaneous multi-site stimulation and mapping to manipulate actively the frequency and direction of AP propagation. These results establish new methodologies for 3D spatiotemporal tissue recording and control, and demonstrate the potential to impact regenerative medicine, pharmacology and electronic therapeutics. PMID:27347837

Reconstruction of electrocardiogram using ionic current models for heart muscles.

PubMed

Yamanaka, A; Okazaki, K; Urushibara, S; Kawato, M; Suzuki, R

1986-11-01

A digital computer model is presented for the simulation of the electrocardiogram during ventricular activation and repolarization (QRS-T waves). The part of the ventricular septum and the left ventricular free wall of the heart are represented by a two dimensional array of 730 homogeneous functional units. Ionic currents models are used to determine the spatial distribution of the electrical activities of these units at each instant of time during simulated cardiac cycle. In order to reconstruct the electrocardiogram, the model is expanded three-dimensionally with equipotential assumption along the third axis and then the surface potentials are calculated using solid angle method. Our digital computer model can be used to improve the understanding of the relationship between body surface potentials and intracellular electrical events.

Use and Characteristics of Antipsychotic/Methylphenidate Combination Therapy in Children and Adolescents with a Diagnosis of Attention-Deficit/Hyperactivity Disorder.

PubMed

Scholle, Oliver; Banaschewski, Tobias; Enders, Dirk; Garbe, Edeltraut; Riedel, Oliver

2018-05-16

Children and adolescents with attention-deficit/hyperactivity disorder (ADHD) frequently have comorbidities that are potential indications for antipsychotics (APs). Some studies have suggested that the combined use of methylphenidate (MPH) and APs is increasing in this population group. Longitudinal analyses and in-depth investigations on the substance level are lacking. This study aimed to estimate the cumulative proportion of concomitant AP/MPH use in children and adolescents with ADHD over a follow-up of up to 9 years and to describe patient characteristics stratified by specific AP drug. Based on claims data, concomitant AP/MPH use was identified among 67,595 children and adolescents with ADHD starting MPH treatment between 2005 and 2013. Characteristics and diagnoses-including those indicating appropriateness of AP use according to approved indications and/or guidelines-were examined at the time of first AP/MPH combination therapy. In addition, subsequent use of AP/MPH combination therapy was evaluated. The cumulative proportion of individuals with any AP/MPH combination therapy rose to over 6% within 9 years after initiating MPH. The most frequent APs first used in combination with MPH were risperidone (72%), pipamperone (15%), and tiapride (8%). Percentages of psychiatric hospitalization in the year preceding the first combination therapy with MPH were 33%, 43%, and 19%, respectively. The proportion of individuals with potentially appropriate use was high (>72%) in risperidone/MPH and tiapride/MPH and low (15%) in pipamperone/MPH combination users. Conduct disorders and tic disorders were frequent in users who were prescribed MPH with risperidone and tiapride, respectively. One-quarter of patients with AP/MPH combination therapy were one-time-only combination users. Our study suggests that a considerable proportion of children and adolescents with ADHD receive MPH in combination with APs and that this is a factor not only during the first years of MPH treatment. ADHD guidelines should specify algorithms concerning the use of AP medication.

Some properties of the action potentials conducted in the spines of the sea urchin Diadema antillarum.

PubMed

Berrios, A; Brink, D; del Castillo, J; Smith, D S

1985-01-01

Brief (2-5 msec) electrical pulses applied to the primary spines of the sea urchin Diadema antillarum elicit graded action potentials (ap's). These ap's can be attributed to the electrical activity of a set of 14-21 bundles of neurites, each comprising 1000 processes near the spine base and tapering towards the spine tip. The shape of the ap's varies from a simple diphasic deflection to a complex waveform with 6 or more components. Peak-to-peak amplitude is less than 1mV. The ap's are conducted at a uniform speed of ca. 27 cm/sec. The ap's are not affected by tetrodotoxin (1 microgram/ml) and continue to be produced in Na-free artificial sea water (ASW). The amplitude of the ap's is greatly reduced or totally abolished in Ca-free ASW. However, some electrical activity may continue in the absence of external Ca, due to release of Ca2+ ions from the calcium carbonate crystals of the spine shaft. Replacing the Ca content of ASW by barium ions causes an irreversible blockade of the ap's. Spines equilibrated with ASW containing Sr2+ ions instead of Ca2+ produce ap's of increased amplitude (up to X 2). The ap's are blocked by La3+, Co2+, Cd2+ (2-5 mM) and by the organic Ca channel blocker Bepridil (2 mM). We conclude that the spinal ap's are due to the summation of Ca spikes produced by the activation of Ca channels which are blocked by barium and have a high affinity for, or permeability to Sr vs Ca.

Biological substantiation of antipsychotic-associated pneumonia: Systematic literature review and computational analyses

PubMed Central

2017-01-01

Introduction Antipsychotic (AP) safety has been widely investigated. However, mechanisms underlying AP-associated pneumonia are not well-defined. Aim The aim of this study was to investigate the known mechanisms of AP-associated pneumonia through a systematic literature review, confirm these mechanisms using an independent data source on drug targets and attempt to identify novel AP drug targets potentially linked to pneumonia. Methods A search was conducted in Medline and Web of Science to identify studies exploring the association between pneumonia and antipsychotic use, from which information on hypothesized mechanism of action was extracted. All studies had to be in English and had to concern AP use as an intervention in persons of any age and for any indication, provided that the outcome was pneumonia. Information on the study design, population, exposure, outcome, risk estimate and mechanism of action was tabulated. Public repositories of pharmacology and drug safety data were used to identify the receptor binding profile and AP safety events. Cytoscape was then used to map biological pathways that could link AP targets and off-targets to pneumonia. Results The literature search yielded 200 articles; 41 were included in the review. Thirty studies reported a hypothesized mechanism of action, most commonly activation/inhibition of cholinergic, histaminergic and dopaminergic receptors. In vitro pharmacology data confirmed receptor affinities identified in the literature review. Two targets, thromboxane A2 receptor (TBXA2R) and platelet activating factor receptor (PTAFR) were found to be novel AP target receptors potentially associated with pneumonia. Biological pathways constructed using Cytoscape identified plausible biological links potentially leading to pneumonia downstream of TBXA2R and PTAFR. Conclusion Innovative approaches for biological substantiation of drug-adverse event associations may strengthen evidence on drug safety profiles and help to tailor pharmacological therapies to patient risk factors. PMID:29077727

Biological substantiation of antipsychotic-associated pneumonia: Systematic literature review and computational analyses.

PubMed

Sultana, Janet; Calabró, Marco; Garcia-Serna, Ricard; Ferrajolo, Carmen; Crisafulli, Concetta; Mestres, Jordi; Trifirò', Gianluca

2017-01-01

Antipsychotic (AP) safety has been widely investigated. However, mechanisms underlying AP-associated pneumonia are not well-defined. The aim of this study was to investigate the known mechanisms of AP-associated pneumonia through a systematic literature review, confirm these mechanisms using an independent data source on drug targets and attempt to identify novel AP drug targets potentially linked to pneumonia. A search was conducted in Medline and Web of Science to identify studies exploring the association between pneumonia and antipsychotic use, from which information on hypothesized mechanism of action was extracted. All studies had to be in English and had to concern AP use as an intervention in persons of any age and for any indication, provided that the outcome was pneumonia. Information on the study design, population, exposure, outcome, risk estimate and mechanism of action was tabulated. Public repositories of pharmacology and drug safety data were used to identify the receptor binding profile and AP safety events. Cytoscape was then used to map biological pathways that could link AP targets and off-targets to pneumonia. The literature search yielded 200 articles; 41 were included in the review. Thirty studies reported a hypothesized mechanism of action, most commonly activation/inhibition of cholinergic, histaminergic and dopaminergic receptors. In vitro pharmacology data confirmed receptor affinities identified in the literature review. Two targets, thromboxane A2 receptor (TBXA2R) and platelet activating factor receptor (PTAFR) were found to be novel AP target receptors potentially associated with pneumonia. Biological pathways constructed using Cytoscape identified plausible biological links potentially leading to pneumonia downstream of TBXA2R and PTAFR. Innovative approaches for biological substantiation of drug-adverse event associations may strengthen evidence on drug safety profiles and help to tailor pharmacological therapies to patient risk factors.

Effects of exogenous nicotinamide adenine dinucleotide (NAD+) in the rat heart are mediated by P2 purine receptors.

PubMed

Kuzmin, Vladislav S; Pustovit, Ksenia B; Abramochkin, Denis V

2016-06-27

Recently, NAD+ has been considered as an essential factor, participating in nerve control of physiological functions and intercellular communication. NAD+ also has been supposed as endogenous activator of P1 and P2 purinoreceptors. Effects of extracellular NAD+ remain poorly investigated in cardiac tissue. This study aims to investigate the effects of extracellular NAD+ in different types of supraventricular and ventricular working myocardium from rat and their potential mechanisms. The standard technique of sharp microelectrode action potential recording in cardiac multicellular preparations was used to study the effects of NAD+. Extracellular NAD+ induced significant changes in bioelectrical activity of left auricle (LA), right auricle (RA), pulmonary veins (PV) and right ventricular wall (RV) myocardial preparations. 10-100 μM NAD+ produced two opposite effects in LA and RA - quickly developing and transient prolongation of action potentials (AP) and delayed sustained AP shortening, which follows the initial positive effect. In PV and RV only AP shortening was observed in response to NAD+ application. In PV preparations AP shortening induced by NAD+ may be considered as a potential proarrhythmic effect. Revealed cardiotropic effects of NAD+ are likely to be mediated by P2 purine receptors, since P1 blocker DPCPX failed to affect them and P2 antagonist suramin abolished NAD + -induced alterations of electrical activity. P2X receptors may be responsible for NAD + -induced short-lasting AP prolongation, while P2Y receptors mediate persistent AP shortening. The latter effect is partially removed by PLC inhibitor U73122 showing the potential involvement of phosphoinositide signaling pathway in mediation of NAD+ cardiotropic effects. Extracellular NAD+ is supposed to be a novel regulator of cardiac electrical activity. P2 receptors represent the main target of NAD+ at least in the rat heart.

DiAs User Interface: A Patient-Centric Interface for Mobile Artificial Pancreas Systems

PubMed Central

Keith-Hynes, Patrick; Guerlain, Stephanie; Mize, Benton; Hughes-Karvetski, Colleen; Khan, Momin; McElwee-Malloy, Molly; Kovatchev, Boris P.

2013-01-01

Background Recent in-hospital studies of artificial pancreas (AP) systems have shown promising results in improving glycemic control in patients with type 1 diabetes mellitus. The next logical step in AP development is to conduct transitional outpatient clinical trials with a mobile system that is controlled by the patient. In this article, we present the user interface (UI) of the Diabetes Assistant (DiAs), an experimental smartphone-based mobile AP system, and describe the reactions of a round of focus groups to the UI. This work is an initial inquiry involving a relatively small number of potential users, many of whom had never seen an AP system before, and the results should be understood in that light. Methods We began by considering how the UI of an AP system could be designed to make use of the familiar touch-based graphical UI of a consumer smartphone. After developing a working prototype UI, we enlisted a human factors specialist to perform a heuristic expert analysis. Next we conducted a formative evaluation of the UI through a series of three focus groups with N = 13 potential end users as participants. The UI was modified based upon the results of these studies, and the resulting DiAs system was used in transitional outpatient AP studies of adults in the United States and Europe. Results The DiAs UI was modified based on focus group feedback from potential users. The DiAs was subsequently used in JDRF- and AP@Home-sponsored transitional outpatient AP studies in the United States and Europe by 40 subjects for 2400 h with no adverse events. Conclusions Adult patients with type 1 diabetes mellitus are able to control an AP system successfully using a patient-centric UI on a commercial smartphone in a transitional outpatient environment. PMID:24351168

Epicardial distribution of ST segment and T wave changes produced by stimulation of intrathoracic ganglia or cardiopulmonary nerves in dogs.

PubMed

Savard, P; Cardinal, R; Nadeau, R A; Armour, J A

1991-06-01

Sixty-three ventricular epicardial electrograms were recorded simultaneously in 8 atropinized dogs during stimulation of acutely decentralized intrathoracic autonomic ganglia or cardiopulmonary nerves. Three variables were measured: (1) isochronal maps representing the epicardial activation sequence, (2) maps depicting changes in areas under the QRS complex and T wave (regional inhomogeneity of repolarization), and (3) local and total QT intervals. Neural stimulations did not alter the activation sequence but induced changes in the magnitude and polarity of the ST segments and T waves as well as in QRST areas. Stimulation of the same neural structure in different dogs induced electrical changes with different amplitudes and in different regions of the ventricles, except for the ventral lateral cardiopulmonary nerve which usually affected the dorsal wall of the left ventricle. Greatest changes occurred when the right recurrent, left intermediate medial, left caudal pole, left ventral lateral cardiopulmonary nerves and stellate ganglia were stimulated. Local QT durations either decreased or did not change, whereas total QT duration as measured using a root-mean-square signal did not change, indicating the regional nature of repolarization changes. Taken together, these data indicate that intrathoracic efferent sympathetic neurons can induce regional inhomogeneity of repolarization without prolonging the total QT interval.

Localization and functional consequences of a direct interaction between TRIOBP-1 and hERG proteins in the heart.

PubMed

Jones, David K; Johnson, Ashley C; Roti Roti, Elon C; Liu, Fang; Uelmen, Rebecca; Ayers, Rebecca A; Baczko, Istvan; Tester, David J; Ackerman, Michael J; Trudeau, Matthew C; Robertson, Gail A

2018-03-22

Reduced levels of the cardiac human (h)ERG ion channel protein and the corresponding repolarizing current I Kr can cause arrhythmia and sudden cardiac death, but the underlying cellular mechanisms controlling hERG surface expression are not well understood. Here, we identified TRIOBP-1, an F-actin-binding protein previously associated with actin polymerization, as a putative hERG-interacting protein in a yeast-two hybrid screen of a cardiac library. We corroborated this interaction by performing Förster resonance energy transfer (FRET) in HEK293 cells and co-immunoprecipitation in HEK293 cells and native cardiac tissue. TRIOBP-1 overexpression reduced hERG surface expression and current density, whereas reducing TRIOBP-1 expression via shRNA knockdown resulted in increased hERG protein levels. Immunolabeling in rat cardiomyocytes showed that native TRIOBP-1 colocalized predominantly with myosin-binding protein C and secondarily with rat ERG. In human stem cell-derived cardiomyocytes, TRIOBP-1 overexpression caused intracellular co-sequestration of hERG signal, reduced native I Kr and disrupted action potential repolarization. Ca 2+ currents were also somewhat reduced and cell capacitance was increased. These findings establish that TRIOBP-1 interacts directly with hERG and can affect protein levels, I Kr magnitude and cardiac membrane excitability. © 2018. Published by The Company of Biologists Ltd.

Role of the sodium pump in pacemaker generation in dog colonic smooth muscle.

PubMed Central

Barajas-López, C; Chow, E; Den Hertog, A; Huizinga, J D

1989-01-01

1. The role of the Na+ pump in the generation of slow wave activity in circular muscle of the dog colon was investigated using a partitioned 'Abe-Tomita' type chamber for voltage control. 2. Blockade of the Na+ pump by omission of extracellular K+, by ouabain, or the combination of 0 mM-Na+ and ouabain, depolarized the membrane up to approximately -40 mV and abolished the slow wave activity. Repolarization back to the control membrane potential by hyperpolarizing current restored the slow wave activity. 3. Slow waves continued to be present in 0 Na+, Li+ HEPES solution. 4. The depolarization induced by the procedures to block Na+ pump activity was associated with an increase in input membrane resistance. 5. Voltage-current relationships show the presence of an inward rectification. 6. Reduction of temperature depolarized the membrane, and decreased the slow wave frequency and amplitude. The slow wave amplitude was restored by repolarization of the membrane. 7. Brief depolarizing pulses evoked premature slow waves. Brief hyperpolarizing pulses terminated the slow waves. 8. We conclude that abolition of slow wave activity by Na+ pump blockade is a direct effect of membrane depolarization and that the Na+ pump is not responsible for the generation of the slow wave. 9. Our results are consistent with the hypothesis that pacemaker activity in smooth muscle is a consequence of membrane conductance changes which are metabolically dependent. PMID:2607455

Regulation of rat mesangial cell growth by diadenosine phosphates.

PubMed Central

Heidenreich, S; Tepel, M; Schlüter, H; Harrach, B; Zidek, W

1995-01-01

The newly recognized human endogenous vasoconstrictive dinucleotides, diadenosine pentaphosphate (AP5A) and diadenosine hexaphosphate (AP6A), were tested for growth stimulatory effects in rat mesangial cells (MC). Both AP5A and AP6A stimulated growth in micromolar concentrations. The growth stimulatory effect exceeded that of ATP, alpha,beta-methylene ATP, adenosine 5'-O-(3-thio)triphosphate and UTP. Both diadenosine phosphates potentiated the growth response to platelet-derived growth factor, but not to insulin-like growth factor-1. To further elucidate the site of action in the cell cycle, RNA and protein synthesis were assessed. AP5 and AP6A stimulated protein synthesis, but not RNA formation. Furthermore, both agents increased cytosolic free Ca2+ concentration. It is concluded that AP5A and AP6A may play a regulatory role in MC growth as progression factors and possibly modify MC proliferation in glomerular disease. PMID:7769127

Calcineurin Dysregulation Underlies Spinal Cord Injury-Induced K+ Channel Dysfunction in DRG Neurons

PubMed Central

Zemel, Benjamin M.; Brown, Eric V.; Urban, Mark W.; Tymanskyj, Stephen R.; Lepore, Angelo C.

2017-01-01

Dysfunction of the fast-inactivating Kv3.4 potassium current in dorsal root ganglion (DRG) neurons contributes to the hyperexcitability associated with persistent pain induced by spinal cord injury (SCI). However, the underlying mechanism is not known. In light of our previous work demonstrating modulation of the Kv3.4 channel by phosphorylation, we investigated the role of the phosphatase calcineurin (CaN) using electrophysiological, molecular, and imaging approaches in adult female Sprague Dawley rats. Pharmacological inhibition of CaN in small-diameter DRG neurons slowed repolarization of the somatic action potential (AP) and attenuated the Kv3.4 current. Attenuated Kv3.4 currents also exhibited slowed inactivation. We observed similar effects on the recombinant Kv3.4 channel heterologously expressed in Chinese hamster ovary cells, supporting our findings in DRG neurons. Elucidating the molecular basis of these effects, mutation of four previously characterized serines within the Kv3.4 N-terminal inactivation domain eliminated the effects of CaN inhibition on the Kv3.4 current. SCI similarly induced concurrent Kv3.4 current attenuation and slowing of inactivation. Although there was little change in CaN expression and localization after injury, SCI induced upregulation of the native regulator of CaN 1 (RCAN1) in the DRG at the transcript and protein levels. Consistent with CaN inhibition resulting from RCAN1 upregulation, overexpression of RCAN1 in naive DRG neurons recapitulated the effects of pharmacological CaN inhibition on the Kv3.4 current and the AP. Overall, these results demonstrate a novel regulatory pathway that links CaN, RCAN1, and Kv3.4 in DRG neurons. Dysregulation of this pathway might underlie a peripheral mechanism of pain sensitization induced by SCI. SIGNIFICANCE STATEMENT Pain sensitization associated with spinal cord injury (SCI) involves poorly understood maladaptive modulation of neuronal excitability. Although central mechanisms have received significant attention, recent studies have identified peripheral nerve hyperexcitability as a driver of persistent pain signaling after SCI. However, the ion channels and signaling molecules responsible for this change in primary sensory neuron excitability are still not well defined. To address this problem, this study used complementary electrophysiological and molecular methods to determine how Kv3.4, a voltage-gated K+ channel robustly expressed in dorsal root ganglion neurons, becomes dysfunctional upon calcineurin (CaN) inhibition. The results strongly suggest that CaN inhibition underlies SCI-induced dysfunction of Kv3.4 and the associated excitability changes through upregulation of the native regulator of CaN 1 (RCAN1). PMID:28751455

Evaluation of Tp-e interval and Tp-e/QT ratio in patients with rheumatoid arthritis.

PubMed

Acar, Gu Rkan; Akkoyun, Murat; Nacar, Alper Bugra; Dirnak, Imran; Yıldırım Çetin, Gözde; Nur Yıldırım, Makbule; Zencir, Cemil; Karaman, Kayıhan; Cetin, Mustafa; Sayarlıoğlu, Mehmet

2014-01-01

Several studies have suggested that the interval from the peak to the end of the electrocardiographic T wave (Tp-e) may correspond to the transmural dispersion of repolarization and that increased Tp-e interval and Tp-e/QT ratio are associated with malignant ventricular arrhythmias. The aim of this study was to evaluate ventricular repolarization by using the Tp-e interval and Tp-e/QT ratio in patients with rheumatoid arthritis (RA), and to assess the relation with inflammation. Ninety-six patients (72 females, 24 males; mean age 43.8±11.8 years) with RA and 50 controls (35 females, 15 males; mean age 44.2±11.1 years) were included. From the 12-lead electrocardiogram, Tp-e interval and Tp-e/QT ratio were measured. Blood samples were taken for erythrocyte sedimentation rate (ESR) and plasma levels of C-reactive protein (CRP). These parameters were compared between groups. The relationship between ventricular repolarization and inflammation was assessed by Pearson correlation coefficients. Tp-e interval and Tp-e/QT ratio were increased in RA patients compared to the controls (72.6±8.2 vs 66.4±8.5 ms, 0.20±0.02 vs 0.18±0.02; p<0.001 and p<0.001, respectively). The Tp-e interval was significantly correlated with CRP, ESR, and disease activity score (DAS-28) (r=0.56, p<0.001, r=0.57, p<0.001, and r=0.29, p=0.02, respectively). The Tp-e/QT ratio was also correlated with CRP, ESR, and DAS-28 score (r=0.43, p<0.001, r=0.53, p<0.001, and r=0.25, p=0.03, respectively). In RA patients, the increased frequency of ventricular arrhythmias may be explained by increased indexes of ventricular repolarization and their relationship with inflammation.

Cardiac Repolarization Instability during Psychological Stress in Patients with Ventricular Arrhythmias

PubMed Central

Abisse, Saddam S.; Lampert, Rachel; Burg, Mattew; Soufer, Robert; Shusterman, Vladimir

2011-01-01

Introduction Changes in the autonomic nervous system activity (ANS) are a major trigger of life-threatening ventricular tachyarrhythmias (VTA). Mental arithmetic, a condition administered in a laboratory setting, can provide insight into the ANS effects on cardiac physiology. We examined the responses of cardiac repolarization to laboratory-induced psychological stressors in patients with implantable cardioverter defibrillators (ICDs) with the objective of identifying the indices that differentiate patients with and without subsequent VTA in follow-up. Methods Continuous ECG signals were recorded using 3 standard bipolar (Holter) leads in 56 patients (age: 63.6±11.9, female: 12%, LVEF: 32.3±11) with ICDs during mental arithmetic. The patients were separated into those with subsequent VTA during 3–4 years of follow-up (Group 1: N=9 pts) and those without VTA (Group 2: N=47 pts). Changes in repolarization (QT-interval, mean T-wave amplitude (Tamp), and T-wave area (Tarea) were analyzed during 5min of baseline, stress and recovery. The temporal instability of Tamp and Tarea was examined using the range (Δ) and variance (σ2) of beat-to-beat variations of the corresponding parameters. Results There were no significant differences in HR between the two groups at baseline (61 vs. 63 bpm, p=0.97), during stress (64 vs. 65 bpm, p=0.40), and recovery (62 vs. 61 bpm, p= 0.88). However, during mental stress and post-stress recovery ΔTamp was almost 2-fold greater in Group 1 compared with Group 2 (111 (57–203)) vs. 68 (44–94) μV p=0.04, respectively). Changes in QT-intervals were also greater in Group 1 compared with Group 2 (p=0.02). Conclusion Among patients with ICDs, changes of T-wave amplitude after psychological stress were greater in those with subsequent arrhythmic events. This might signal proarrhythmic repolarization response and help identify patients who would benefit the most from ICD implantation and proactive management. PMID:21920534

Effects of bilastine on T-wave morphology and the QTc interval: a randomized, double-blind, placebo-controlled, thorough QTc study.

PubMed

Graff, Claus; Struijk, Johannes J; Kanters, Jørgen K; Andersen, Mads P; Toft, Egon; Tyl, Benoît

2012-05-01

The International Conference of Harmonisation (ICH) E14 guideline for thorough QT studies requires assessing the propensity of new non-antiarrhythmic drugs to affect cardiac repolarization. The present study investigates whether a composite ECG measure of T-wave morphology (Morphology Combination Score [MCS]) can be used together with the heart rate corrected QT interval (QTc) in a fully ICH E14-compliant thorough QT study to exclude clinically relevant repolarization effects of bilastine, a novel antihistamine. Thirty participants in this crossover study were randomly assigned to receive placebo, moxifloxacin 400 mg, bilastine at therapeutic and supratherapeutic doses (20 and 100 mg) and bilastine 20 mg co-administered with ketoconazole 400 mg. Resting ECGs recorded at 12 nominal time points before and after treatments were used to determine Fridericia corrected QTc (QTcF) and MCS from the T-wave characteristics: asymmetry, flatness and notching. There were no effects of bilastine monotherapy (20 and 100 mg) on MCS or QTcF at those study times where the bilastine plasma concentrations were highest. MCS changes for bilastine monotherapy did not exceed the normal intrasubject variance of T-wave shapes for triplicate ECG recordings. Maximum QTcF prolongation for bilastine monotherapy was 5 ms or less: 3.8 ms (90% CI 0.3, 7.3 ms) for bilastine 20 mg and 5.0 ms (90% CI 2.0, 8.0 ms) for bilastine 100 mg. There were no indications of bilastine inducing larger repolarization effects on T-wave morphology as compared with the QTcF interval, as evidenced by the similarity of z-score equivalents for placebo-corrected changes in MCS and QTcF values. This study shows that bilastine, at therapeutic and supratherapeutic dosages, does not induce any effects on T-wave morphology or QTcF. These results confirm the absence of an effect for bilastine on cardiac repolarization.

Cardiac repolarization during fingolimod treatment in patients with relapsing-remitting multiple sclerosis.

PubMed

Laiho, Aapo; Laitinen, Tiina M; Hartikainen, Päivi; Hartikainen, Juha E K; Laitinen, Tomi P; Simula, Sakari

2018-02-01

Fingolimod is a sphingosine-1-phosphate receptor modulator for the treatment of relapsing-remitting multiple sclerosis (RRMS). Despite an established effect on heart rate, the effect of fingolimod on cardiac repolarization is not completely known. Twenty-seven patients with RRMS underwent 24-hr ambulatory ECG before fingolimod (baseline), at the day of fingolimod initiation (1D) and after three-month treatment (3M). The mean values of RR-interval as well as QT-interval corrected by Bazzet's (QTcBaz) and Fridericia's (QTcFri) formula were compared between baseline, 1D, and 3M over 24-hr period as well as at daytime and nighttime. QTcBaz over 24-hr was shorter at 1D (414 ± 20 ms, p  < .001) and at 3M (414 ± 20 ms, p  < .001) than at baseline (418 ± 20 ms). In contrast, QTcFri over 24-hr was longer at 1D (410 ± 19 ms, p  < .001) but similar at 3M (406 ± 19 ms, p  = .355) compared to baseline (407 ± 19 ms). Daytime QTcBaz was shorter at 1D ( p  < .001) and at 3M ( p  = .007), whereas daytime QTcFri was longer at 1D ( p  < .05) but similar at 3M ( p  = ns) compared to baseline. During the night, changes were observed neither in QTcBaz nor in QTcFri between baseline, 1D, and 3M. Changes in cardiac repolarization after fingolimod initiation were mild and occurred at daytime. Ambiguously, QTcBaz demonstrated shortening, whereas QTcFri showed prolongation in cardiac repolarization after fingolimod initiation. The formula applied for QT-interval correction needs to be taken carefully into account as evaluating pharmacovigilance issues related to fingolimod.

Effect of Loss of Heart Rate Variability on T-Wave Heterogeneity and QT Variability in Heart Failure Patients: Implications in Ventricular Arrhythmogenesis.

PubMed

Nayyar, Sachin; Hasan, Muhammad A; Roberts-Thomson, Kurt C; Sullivan, Thomas; Baumert, Mathias

2017-06-01

Heart rate variability (HRV) modulates dynamics of ventricular repolarization. A diminishing value of HRV is associated with increased vulnerability to life-threatening ventricular arrhythmias, however the causal relationship is not well-defined. We evaluated if fixed-rate atrial pacing that abolishes the effect of physiological HRV, will alter ventricular repolarization wavefronts and is relevant to ventricular arrhythmogenesis. The study was performed in 16 subjects: 8 heart failure patients with spontaneous ventricular tachycardia [HFVT], and 8 subjects with structurally normal hearts (H Norm ). The T-wave heterogeneity descriptors [total cosine angle between QRS and T-wave loop vectors (TCRT, negative value corresponds to large difference in the 2 loops), T-wave morphology dispersion, T-wave loop dispersion] and QT intervals were analyzed in a beat-to-beat manner on 3-min records of 12-lead surface ECG at baseline and during atrial pacing at 80 and 100 bpm. The global T-wave heterogeneity was expressed as mean values of each of the T-wave morphology descriptors and variability in QT intervals (QTV) as standard deviation of QT intervals. Baseline T-wave morphology dispersion and QTV were higher in HFVT compared to H Norm subjects (p ≤ 0.02). While group differences in T-wave morphology dispersion and T-wave loop dispersion remained unaltered with atrial pacing, TCRT tended to fall more in HFVT patients compared to H Norm subjects (interaction p value = 0.086). Atrial pacing failed to reduce QTV in both groups, however group differences were augmented (p < 0.0001). Atrial pacing and consequent loss of HRV appears to introduce unfavorable changes in ventricular repolarization in HFVT subjects. It widens the spatial relationship between wavefronts of ventricular depolarization and repolarization. This may partly explain the concerning relation between poorer HRV and the risk of ventricular arrhythmias.

Characterization of Myocardial Repolarization Reserve in Adolescent Females With Anorexia Nervosa.

PubMed

Padfield, Gareth J; Escudero, Carolina A; DeSouza, Astrid M; Steinberg, Christian; Gibbs, Karen; Puyat, Joseph H; Lam, Pei Yoong; Sanatani, Shubhayan; Sherwin, Elizabeth; Potts, James E; Sandor, George; Krahn, Andrew D

2016-02-09

Patients with anorexia nervosa exhibit abnormal myocardial repolarization and are susceptible to sudden cardiac death. Exercise testing is useful in unmasking QT prolongation in disorders associated with abnormal repolarization. We characterized QT adaptation during exercise in anorexia. Sixty-one adolescent female patients with anorexia nervosa and 45 age- and sex-matched healthy volunteers performed symptom-limited cycle ergometry during 12-lead ECG monitoring. Changes in the QT interval during exercise were measured, and QT/RR-interval slopes were determined by using mixed-effects regression modeling. Patients had significantly lower body mass index than controls; however, resting heart rates and QT/QTc intervals were similar at baseline. Patients had shorter exercise times (13.7±4.5 versus 20.6±4.5 minutes; P<0.001) and lower peak heart rates (159±20 versus 184±9 beats/min; P<0.001). The mean QTc intervals were longer at peak exercise in patients (442±29 versus 422±19 ms; P<0.001). During submaximal exertion at comparable heart rates (114±6 versus 115±11 beats/min; P=0.54), the QTc interval had prolonged significantly more in patients than controls (37±28 versus 24±25 ms; P<0.016). The RR/QT slope, best described by a curvilinear relationship, was more gradual in patients than in controls (13.4; 95% confidence interval, 12.8-13.9 versus 15.8; 95% confidence interval, 15.3-16.4 ms QT change per 10% change in RR interval; P<0.001) and steepest in patients within the highest body mass index tertile versus the lowest (13.9; 95% confidence interval, 12.9-14.9 versus 12.3; 95% confidence interval, 11.3-13.3; P=0.026). Despite the absence of manifest QT prolongation, adolescent anorexic females have impaired repolarization reserve in comparison with healthy controls. Further study may identify impaired QT dynamics as a risk factor for arrhythmias in anorexia nervosa. © 2016 American Heart Association, Inc.

GM2-activator protein: a new biomarker for lung cancer.

PubMed

Potprommanee, Laddawan; Ma, Haou-Tzong; Shank, Lalida; Juan, Yi-Hsiu; Liao, Wei-Yu; Chen, Shui-Tein; Yu, Chong-Jen

2015-01-01

Effective biomarkers for early diagnosis of lung cancer are needed. A recent study demonstrated that urinary GM2-activator protein (GM2AP) level was increased in lung cancer patients. This study aims to validate the potential application of GM2AP as a biomarker for diagnosis of lung cancer. Serum and urine samples were obtained from 189 participants (133 patients for treatment naive lung cancer, 26 healthy volunteers for urine, and 30 healthy volunteers for serum). GM2AP level was detected by Western blotting and quantified using enzyme-linked immunosorbent assay (ELISA). The GM2AP expression in tumors and nontumor parts of lung tissues from 143 nonsmall cell lung cancers was detected by immunohistochemical stains. There was an 8.11 ± 1.36 folds increase in urine and a 5.41 ± 0.73 folds increase in serum level of GM2AP in lung cancer patients compared with healthy volunteers (p < 0.0001), achieving a 0.89 AUC value in urine and 0.90 AUC value in serum for the receiver-operating characteristic curves. Both serum and urine levels of GM2AP correlated significantly with pathology stages (urine, p = 0.009; serum, p < 0.0001). Using immunohistochemical, positive expression of GM2AP was found at 83.9% of nonsmall cell lung cancers patients and none in normal tissue. The GM2AP expression was significantly correlated with pathology stage (p = 0.0001). Patients with higher GM2AP expression had shorter overall survival (p = 0.045) and disease-free survival (p = 0.049) than lower GM2AP expression. Moreover, the multivariate analysis suggested GM2AP as an independent predictors of disease-free survival and overall survival. Our study demonstrates that GM2AP might serve as potential diagnostic and prognostic biomarkers in patients with lung cancer.

Nutrient and Trace Metal Controls on Alkaline Phosphatase in the Subtropical Ocean: Insights from Bioassays and Gene Expression

NASA Astrophysics Data System (ADS)

Mahaffey, C.; Reynolds, S.; Davis, C. E.; Lohan, M. C.

2016-02-01

Phosphorus is an essential nutrient for all life on earth. In the ocean, the most bioavailable form of phosphorus is inorganic phosphate, but in the extensive subtropical gyres, phosphate concentrations can be chronically low in the surface ocean and limit biological activity. In response to phosphate limitation, organisms produce phosphohydrolytic enzymes, such as alkaline phosphatases (AP), that enable them to utilize the more replete dissolved organic phosphorus (DOP) pool to meet their cellular phosphorus demands. Synthesis of data from the surface ocean from 14 open ocean studies reveals an inverse hyperbolic relationship between phosphate and AP, where AP is significantly induced at phosphate concentrations below 50 nM and DOP concentrations decrease as AP increases. AP activity was significantly higher in the subtropical Atlantic compared to the subtropical Pacific Ocean, even over the same low phosphate concentration range (0 to 50 nM). While the phosphate concentration may have a first order control on the rates of AP, we demonstrate that other factors influence AP activity. AP are metalloenzymes and zinc and iron are co-factors of the AP proteins PhoA and PhoX, respectively. Using bioassay experiments, we show that the addition of Saharan dust and zinc significantly increases the rate of AP. To our knowledge, our results are the first direct field-based evidence that AP activity is limited by zinc in the subtropical ocean. In colonies of nitrogen fixer, Trichodesmium, we found enhanced expression of the phoA gene in a region of elevated zinc concentrations and enhanced expression of the phoX gene in a region of elevated iron concentrations around the intertropical convergence zone. Our study highlights the potential link between the phosphorus cycle and trace metals, specifically zinc and iron, and implies that there is potential for zinc-phosphorus and iron-phosphorus co-limitation in the ocean via AP.

Patch-Clamp Recording from Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes: Improving Action Potential Characteristics through Dynamic Clamp

PubMed Central

Veerman, Christiaan C.; Zegers, Jan G.; Mengarelli, Isabella; Bezzina, Connie R.

2017-01-01

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) hold great promise for studying inherited cardiac arrhythmias and developing drug therapies to treat such arrhythmias. Unfortunately, until now, action potential (AP) measurements in hiPSC-CMs have been hampered by the virtual absence of the inward rectifier potassium current (IK1) in hiPSC-CMs, resulting in spontaneous activity and altered function of various depolarising and repolarising membrane currents. We assessed whether AP measurements in “ventricular-like” and “atrial-like” hiPSC-CMs could be improved through a simple, highly reproducible dynamic clamp approach to provide these cells with a substantial IK1 (computed in real time according to the actual membrane potential and injected through the patch-clamp pipette). APs were measured at 1 Hz using perforated patch-clamp methodology, both in control cells and in cells treated with all-trans retinoic acid (RA) during the differentiation process to increase the number of cells with atrial-like APs. RA-treated hiPSC-CMs displayed shorter APs than control hiPSC-CMs and this phenotype became more prominent upon addition of synthetic IK1 through dynamic clamp. Furthermore, the variability of several AP parameters decreased upon IK1 injection. Computer simulations with models of ventricular-like and atrial-like hiPSC-CMs demonstrated the importance of selecting an appropriate synthetic IK1. In conclusion, the dynamic clamp-based approach of IK1 injection has broad applicability for detailed AP measurements in hiPSC-CMs. PMID:28867785

The stochastic nature of action potential backpropagation in apical tuft dendrites.

PubMed

Short, Shaina M; Oikonomou, Katerina D; Zhou, Wen-Liang; Acker, Corey D; Popovic, Marko A; Zecevic, Dejan; Antic, Srdjan D

2017-08-01

In cortical pyramidal neurons, backpropagating action potentials (bAPs) supply Ca 2+ to synaptic contacts on dendrites. To determine whether the efficacy of AP backpropagation into apical tuft dendrites is stable over time, we performed dendritic Ca 2+ and voltage imaging in rat brain slices. We found that the amplitude of bAP-Ca 2+ in apical tuft branches was unstable, given that it varied from trial to trial (termed "bAP-Ca 2+ flickering"). Small perturbations in dendritic physiology, such as spontaneous synaptic inputs, channel inactivation, or temperature-induced changes in channel kinetics, can cause bAP flickering. In the tuft branches, the density of Na + and K + channels was sufficient to support local initiation of fast spikelets by glutamate iontophoresis. We quantified the time delay between the somatic AP burst and the peak of dendritic Ca 2+ transient in the apical tuft, because this delay is important for induction of spike-timing dependent plasticity. Depending on the frequency of the somatic AP triplets, Ca 2+ signals peaked in the apical tuft 20-50 ms after the 1st AP in the soma. Interestingly, at low frequency (<20 Hz), the Ca 2+ peaked sooner than at high frequency, because only the 1st AP invaded tuft. Activation of dendritic voltage-gated Ca 2+ channels is sensitive to the duration of the dendritic voltage transient. In apical tuft branches, small changes in the duration of bAP voltage waveforms cause disproportionately large increases in dendritic Ca 2+ influx (bAP-Ca 2+ flickering). The stochastic nature of bAP-Ca 2+ adds a new perspective on the mechanisms by which pyramidal neurons combine inputs arriving at different cortical layers. NEW & NOTEWORTHY The bAP-Ca 2+ signal amplitudes in some apical tuft branches randomly vary from moment to moment. In repetitive measurements, successful AP invasions are followed by complete failures. Passive spread of voltage from the apical trunk into the tuft occasionally reaches the threshold for local Na + spike, resulting in stronger Ca 2+ influx. During a burst of three somatic APs, the peak of dendritic Ca 2+ in the apical tuft occurs with a delay of 20-50 ms depending on AP frequency. Copyright © 2017 the American Physiological Society.

The roles of mid-myocardial and epicardial cells in T-wave alternans development: a simulation study.

PubMed

Janusek, D; Svehlikova, J; Zelinka, J; Weigl, W; Zaczek, R; Opolski, G; Tysler, M; Maniewski, R

2018-05-08

The occurrence of T-wave alternans in electrocardiographic signals was recently linked to susceptibility to ventricular arrhythmias and sudden cardiac death. Thus, by detecting and comprehending the origins of T-wave alternans, it might be possible to prevent such events. Here, we simulated T-wave alternans in a computer-generated human heart model by modulating the action potential duration and amplitude during the first part of the repolarization phase. We hypothesized that changes in the intracardiac alternans patterns of action potential properties would differentially influence T-wave alternans measurements at the body surface. Specifically, changes were simulated globally in the whole left and right ventricles to simulate concordant T-wave alternans, and locally in selected regions to simulate discordant and regional discordant, hereinafter referred to as "regional", T-wave alternans. Body surface potential maps and 12-lead electrocardiographic signals were then computed. In depth discrimination, the influence of epicardial layers on T-wave alternans development was significantly higher than that of mid-myocardial cells. Meanwhile, spatial discrimination revealed that discordant and regional action potential property changes had a higher influence on T-wave alternans amplitude than concordant changes. Notably, varying T-wave alternans sources yielded distinct body surface potential map patterns for T-wave alternans amplitude, which can be used for location of regions within hearts exhibiting impaired repolarization. The highest ability for T-wave alternans detection was achieved in lead V1. Ultimately, we proposed new parameters Vector Magnitude Alternans and Vector Angle Alternans, with higher ability for T-wave alternans detection when using multi-lead electrocardiographic signals processing than for single leads. Finally, QT alternans was found to be associated with the process of T-wave alternans generation. The distributions of the body surface T-wave alternans amplitude have been shown to have unique patterns depending on the type of alternans (concordant, discordant or regional) and the location of the disturbance in the heart. The influence of epicardial cells on T-wave alternans development is significantly higher than that of mid-myocardial cells, among which the sub-endocardial layer exerted the highest influence. QT interval alternans is identified as a phenomenon that correlate with T-wave alternans.

PSAT Component Scores as a Predictor of Success on AP Exam Performance for Diverse Students

ERIC Educational Resources Information Center

Richardson, Cristianne C.; Gonzalez, Alejandro; Leal, Lonnie; Castillo, Mary Z.; Carman, Carol A.

2016-01-01

While studies have shown the positive effect of the Advanced Placement (AP) program on college readiness, there are still barriers preventing minority and low socioeconomic status (SES) students who possess high academic potential from participating in the opportunity that AP courses offer. One tool that could help identify students for…

Increased Late Sodium Current Contributes to the Electrophysiological Effects of Chronic, but Not Acute, Dofetilide Administration.

PubMed

Qiu, Xiaoliang S; Chauveau, Samuel; Anyukhovsky, Evgeny P; Rahim, Tania; Jiang, Ya-Ping; Harleton, Erin; Feinmark, Steven J; Lin, Richard Z; Coronel, Ruben; Janse, Michiel J; Opthof, Tobias; Rosen, Tove S; Cohen, Ira S; Rosen, Michael R

2016-04-01

Drugs are screened for delayed rectifier potassium current (IKr) blockade to predict long QT syndrome prolongation and arrhythmogenesis. However, single-cell studies have shown that chronic (hours) exposure to some IKr blockers (eg, dofetilide) prolongs repolarization additionally by increasing late sodium current (INa-L) via inhibition of phosphoinositide 3-kinase. We hypothesized that chronic dofetilide administration to intact dogs prolongs repolarization by blocking IKr and increasing INa-L. We continuously infused dofetilide (6-9 μg/kg bolus+6-9 μg/kg per hour IV infusion) into anesthetized dogs for 7 hours, maintaining plasma levels within the therapeutic range. In separate experiments, myocardial biopsies were taken before and during 6-hour intravenous dofetide infusion, and the level of phospho-Akt was determined. Acute and chronic dofetilide effects on action potential duration (APD) were studied in canine left ventricular subendocardial slabs using microelectrode techniques. Dofetilide monotonically increased QTc and APD throughout 6.5-hour exposure. Dofetilide infusion during ≥210 minutes inhibited Akt phosphorylation. INa-L block with lidocaine shortened QTc and APD more at 6.5 hours than at 50 minutes (QTc) or 30 minutes (APD) dofetilide administration. In comparison, moxifloxacin, an IKr blocker with no effects on phosphoinositide 3-kinase and INa-L prolonged APD acutely but no additional prolongation occurred on chronic superfusion. Lidocaine shortened APD equally during acute and chronic moxifloxacin superfusion. Increased INa-L contributes to chronic dofetilide effects in vivo. These data emphasize the need to include time and INa-L in evaluating the phosphoinositide 3-kinase inhibition-derived proarrhythmic potential of drugs and provide a mechanism for benefit from lidocaine administration in clinical acquired long QT syndrome. © 2016 American Heart Association, Inc.

Mechanistic Insight into Human ether-à-go-go-related Gene (hERG) K+ Channel Deactivation Gating from the Solution Structure of the EAG Domain

PubMed Central

Muskett, Frederick W.; Thouta, Samrat; Thomson, Steven J.; Bowen, Alexander; Stansfeld, Phillip J.; Mitcheson, John S.

2011-01-01

Human ether-à-go-go-related gene (hERG) K+ channels have a critical role in cardiac repolarization. hERG channels close (deactivate) very slowly, and this is vital for regulating the time course and amplitude of repolarizing current during the cardiac action potential. Accelerated deactivation is one mechanism by which inherited mutations cause long QT syndrome and potentially lethal arrhythmias. hERG deactivation is highly dependent upon an intact EAG domain (the first 135 amino acids of the N terminus). Importantly, deletion of residues 2–26 accelerates deactivation to a similar extent as removing the entire EAG domain. These and other experiments suggest the first 26 residues (NT1–26) contain structural elements required to slow deactivation by stabilizing the open conformation of the pore. Residues 26–135 form a Per-Arnt-Sim domain, but a structure for NT1–26 has not been forthcoming, and little is known about its site of interaction on the channel. In this study, we present an NMR structure for the entire EAG domain, which reveals that NT1–26 is structurally independent from the Per-Arnt-Sim domain and contains a stable amphipathic helix with one face being positively charged. Mutagenesis and electrophysiological studies indicate that neutralizing basic residues and breaking the amphipathic helix dramatically accelerate deactivation. Furthermore, scanning mutagenesis and molecular modeling studies of the cyclic nucleotide binding domain suggest that negatively charged patches on its cytoplasmic surface form an interface with the NT1–26 domain. We propose a model in which NT1–26 obstructs gating motions of the cyclic nucleotide binding domain to allosterically stabilize the open conformation of the pore. PMID:21135103

Ca2+ removal mechanisms in rat cerebral resistance size arteries.

PubMed Central

Kamishima, T; McCarron, J G

1998-01-01

Tissue blood flow and blood pressure are each regulated by the contractile behavior of resistance artery smooth muscle. Vascular diseases such as hypertension have also been attributed to changes in vascular smooth muscle function as a consequence of altered Ca2+ removal. In the present study of Ca2+ removal mechanisms, in dissociated single cells from resistance arteries using fura-2 microfluorimetry and voltage clamp, Ca2+ uptake by the sarcoplasmic reticulum and extrusion by the Ca2+ pump in the cell membrane were demonstrably important in regulating Ca2+. In contrast, the Na+-Ca2+ exchanger played no detectable role in clearing Ca2+. Thus a voltage pulse to 0 mV, from a holding potential of -70 mV, triggered a Ca2+ influx and increased intracellular Ca2+ concentration ([Ca2+]i). On repolarization, [Ca2+]i returned to the resting level. The decline in [Ca2+]i consisted of three phases. Ca2+ removal was fast immediately after repolarization (first phase), then plateaued (second phase), and finally accelerated just before [Ca2+]i returned to resting levels (third phase). Thapsigargin or ryanodine, which each inhibit Ca2+ uptake into stores, did not affect the first but significantly inhibited the third phase. On the other hand, Na+ replacement with choline+ did not affect either the phasic features of Ca2+ removal or the absolute rate of its decline. Ca2+ removal was voltage-independent; holding the membrane potential at 120 mV, rather than at -70 mV, after the voltage pulse to 0 mV, did not attenuate Ca2+ removal rate. These results suggest that Ca2+ pumps in the sarcoplasmic reticulum and the plasma membrane, but not the Na+-Ca2+ exchanger, are important in Ca2+ removal in cerebral resistance artery cells. PMID:9746518

Stimulus waveform determines the characteristics of sensory nerve action potentials.

PubMed

Pereira, Pedro; Leote, João; Cabib, Christopher; Casanova-Molla, Jordi; Valls-Sole, Josep

2016-03-01

In routine nerve conduction studies supramaximal electrical stimuli generate sensory nerve action potentials by depolarization of nerve fibers under the cathode. However, stimuli of submaximal intensity may give rise to action potentials generated under the anode. We tested if this phenomenon depends on the characteristics of stimulus ending. We added a circuit to our stimulation device that allowed us to modify the end of the stimulus by increasing the time constant of the decay phase. Increasing the fall time caused a reduction of anode action potential (anAP) amplitude, and eventually abolished it, in all tested subjects. We subsequently examined the stimulus waveform in a series of available electromyographs stimulators and found that the anAP could only be obtained with stimulators that issued stimuli ending sharply. Our results prove that the anAP is generated at stimulus end, and depends on the sharpness of current shut down. Electromyographs produce stimuli of varying characteristics, which limits the reproducibility of anAP results by interested researchers. The study of anodal action potentials might be a useful tool to have a quick appraisal of distal human sensory nerve excitability. Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

The influence of type 2 diabetes and gender on ventricular repolarization dispersion in patients with sub-clinic left ventricular diastolic dysfunction

PubMed Central

Jani, Ylber; Kamberi, Ahmet; Xhunga, Sotir; Pocesta, Bekim; Ferati, Fatmir; Lala, Dali; Zeqiri, Agim; Rexhepi, Atila

2015-01-01

Objective: To assess the influence of type 2 DM and gender, on the QT dispersion, Tpeak-Tend dispersion of ventricular repolarization, in patients with sub-clinic left ventricular diastolic dysfunction of the heart. Background: QT dispersion, that reflects spatial inhomogeneity in ventricular repolarization, Tpeak-Tend dispersion, this on the other hand reflects transmural inhomogeneity in ventricular repolarization, that is increased in an early stage of cardiomyopathy, and in patients with left ventricular diastolic dysfunction, as well. The left ventricular diastolic dysfunction, a basic characteristic of diabetic heart disease (diabetic cardiomyopathy), that developes earlier than systolic dysfunction, suggests that diastolic markers might be sensitive for early cardiac injury. It is also demonstrated that gender has complex influence on indices of myocardial repolarization abnormalities such as QT interval and QT dispersion. Material and methods: We performed an observational study including 300 diabetic patients with similar epidemiological-demographic characteristics recruited in our institution from May 2009 to July 2014, divided into two groups. Demographic and laboratory echocardiographic data were obtained, twelve lead resting electrocardiography, QT, QTc, Tpeak-Tend-intervals and dispersion, were determined manually, and were compared between various groups. For statistical analysis a t-test, X2 test, and logistic regression are used according to the type of variables. A p value <0.05 was considered statistically significant for a confidence interval of 95%. Results: QTc max. interval, QTc dispersion and Tpeak-Tend dispersion, were significantly higher in diabetic group with subclinical LV (left ventricular) diastolic dysfunction, than in diabetic group with normal left ventricular diastolic function (445.24±14.7 ms vs. 433.55±14.4 ms, P<0.000; 44.98±18.78 ms vs. 32.05±17.9 ms, P<0.000; 32.60±1.6 ms vs. 17.46±2.0 ms, P<0.02. Prolonged QTc max. interval was found in 33% of patients, indiabetic group with subclinical left ventricular diastolic dysfunction vs. 13.3% of patients in diabetic group with normal left ventricular diastolic function, (Chi-square: 16.77, P<0.0001). A prolonged QTc dispersion, was found in 40.6% of patients, in diabetic group with subclinical left ventricular diastolic dysfunction vs. 20% of patients in diabetic group with normal left ventricular diastolic function Chi-square: 14.11, P<0.0002). A prolonged dispersion of Tpeak-Tend interval was found in 24% of patients in diabetic group with subclinical left ventricular diastolic dysfunction vs. 13.3% of patients in diabetic group with normal left ventricular diastolic function (Chi-square: 12.00, P<0.005). Females in diabetic group with subclinical left ventricular diastolic dysfunction in comparison with males in diabetic group with subclinical left ventricular diastolic dysfunction, have a significantly prolonged: mean QTc max. interval (23.3% vs. 10%, Chisquare: 12.0, P<0.005), mean QTc dispersion (27.3% vs. 13.3%, Chi-square: 10.24, P<0.001), mean Tpeak-Tend interval (10% vs. 3.3%, Chi-square: 5.77, P<0.01), mean Tpek-Tend dispersion (16.6% vs. 6.6%, Chi-square: 8.39, P<0.003). Conclusion: The present study has shown that influences of type 2 diabetes and gender in diabetics with sub-clinical left-ventricular diastolic dysfunction are reflected in a set of electrophysiological parameters that indicate a prolonged and more heterogeneous repolarization than in diabetic patients with normal diastolic function. In addition, it demonstrates that there exist differences between diabetic females with sub-clinic LV dysfunction and those with diabetes and normal LV function in the prevalence of increased set of electrophysiological parameters that indicate a prolonged and more heterogeneous repolarization. PMID:26550530

The influence of type 2 diabetes and gender on ventricular repolarization dispersion in patients with sub-clinic left ventricular diastolic dysfunction.

PubMed

Jani, Ylber; Kamberi, Ahmet; Xhunga, Sotir; Pocesta, Bekim; Ferati, Fatmir; Lala, Dali; Zeqiri, Agim; Rexhepi, Atila

2015-01-01

To assess the influence of type 2 DM and gender, on the QT dispersion, Tpeak-Tend dispersion of ventricular repolarization, in patients with sub-clinic left ventricular diastolic dysfunction of the heart. QT dispersion, that reflects spatial inhomogeneity in ventricular repolarization, Tpeak-Tend dispersion, this on the other hand reflects transmural inhomogeneity in ventricular repolarization, that is increased in an early stage of cardiomyopathy, and in patients with left ventricular diastolic dysfunction, as well. The left ventricular diastolic dysfunction, a basic characteristic of diabetic heart disease (diabetic cardiomyopathy), that developes earlier than systolic dysfunction, suggests that diastolic markers might be sensitive for early cardiac injury. It is also demonstrated that gender has complex influence on indices of myocardial repolarization abnormalities such as QT interval and QT dispersion. We performed an observational study including 300 diabetic patients with similar epidemiological-demographic characteristics recruited in our institution from May 2009 to July 2014, divided into two groups. Demographic and laboratory echocardiographic data were obtained, twelve lead resting electrocardiography, QT, QTc, Tpeak-Tend-intervals and dispersion, were determined manually, and were compared between various groups. For statistical analysis a t-test, X(2) test, and logistic regression are used according to the type of variables. A p value <0.05 was considered statistically significant for a confidence interval of 95%. QTc max. interval, QTc dispersion and Tpeak-Tend dispersion, were significantly higher in diabetic group with subclinical LV (left ventricular) diastolic dysfunction, than in diabetic group with normal left ventricular diastolic function (445.24±14.7 ms vs. 433.55±14.4 ms, P<0.000; 44.98±18.78 ms vs. 32.05±17.9 ms, P<0.000; 32.60±1.6 ms vs. 17.46±2.0 ms, P<0.02. Prolonged QTc max. interval was found in 33% of patients, indiabetic group with subclinical left ventricular diastolic dysfunction vs. 13.3% of patients in diabetic group with normal left ventricular diastolic function, (Chi-square: 16.77, P<0.0001). A prolonged QTc dispersion, was found in 40.6% of patients, in diabetic group with subclinical left ventricular diastolic dysfunction vs. 20% of patients in diabetic group with normal left ventricular diastolic function Chi-square: 14.11, P<0.0002). A prolonged dispersion of Tpeak-Tend interval was found in 24% of patients in diabetic group with subclinical left ventricular diastolic dysfunction vs. 13.3% of patients in diabetic group with normal left ventricular diastolic function (Chi-square: 12.00, P<0.005). Females in diabetic group with subclinical left ventricular diastolic dysfunction in comparison with males in diabetic group with subclinical left ventricular diastolic dysfunction, have a significantly prolonged: mean QTc max. interval (23.3% vs. 10%, Chisquare: 12.0, P<0.005), mean QTc dispersion (27.3% vs. 13.3%, Chi-square: 10.24, P<0.001), mean Tpeak-Tend interval (10% vs. 3.3%, Chi-square: 5.77, P<0.01), mean Tpek-Tend dispersion (16.6% vs. 6.6%, Chi-square: 8.39, P<0.003). The present study has shown that influences of type 2 diabetes and gender in diabetics with sub-clinical left-ventricular diastolic dysfunction are reflected in a set of electrophysiological parameters that indicate a prolonged and more heterogeneous repolarization than in diabetic patients with normal diastolic function. In addition, it demonstrates that there exist differences between diabetic females with sub-clinic LV dysfunction and those with diabetes and normal LV function in the prevalence of increased set of electrophysiological parameters that indicate a prolonged and more heterogeneous repolarization.

Collision of two action potentials in a single excitable cell.

PubMed

Fillafer, Christian; Paeger, Anne; Schneider, Matthias F

2017-12-01

It is a common incident in nature, that two waves or pulses run into each other head-on. The outcome of such an event is of special interest, because it allows conclusions about the underlying physical nature of the pulses. The present experimental study dealt with the head-on meeting of two action potentials (AP) in a single excitable plant cell (Chara braunii internode). The membrane potential was monitored with multiple sensors along a single excitable cell. In control experiments, an AP was excited electrically at either end of the cell cylinder. Subsequently, stimuli were applied simultaneously at both ends of the cell in order to generate two APs that met each other head-on. When two action potentials propagated into each other, the pulses did not penetrate but annihilated (N=26 experiments in n=10 cells). APs in excitable plant cells did not penetrate upon meeting head-on. In the classical electrical model, this behavior is specifically attributed to relaxation of ion channel proteins. From an acoustic point of view, annihilation can be viewed as a result of nonlinear material properties (e.g. a phase change). The present results suggest that APs in excitable animal and plant cells belong to a similar class of nonlinear phenomena. Intriguingly, other excitation waves in biology (intracellular waves, cortical spreading depression, etc.) also annihilate upon collision and are thus expected to follow the same underlying principles as the observed action potentials. Copyright © 2017 Elsevier B.V. All rights reserved.

CT-1-CP-induced ventricular electrical remodeling in mice.

PubMed

Chen, Shu-fen; Wei, Tao-zhi; Rao, Li-ya; Xu, Ming-guang; Dong, Zhan-ling

2015-02-01

The chronic effects of carboxyl-terminal polypeptide of Cardiotrophin-1 (CT-1-CP) on ventricular electrical remodeling were investigated. CT-1-CP, which contains 16 amino acids in sequence of the C-terminal of Cardiotrophin-1, was selected and synthesized, and then administered to Kunming mice (aged 5 weeks) by intraperitoneal injection (500 ng·g⁻¹·day⁻¹) (4 groups, n=10 and female: male=1:1 in each group) for 1, 2, 3 and 4 weeks, respectively. The control group (n=10, female: male=1:1) was injected by physiological saline for 4 weeks. The epicardial monophasic action potential (MAP) was recorded by using a contact-type MAP electrode placed vertically on the left ventricular (LV) epicardium surface, and the electrocardiogram (ECG) signal in lead II was monitored synchronously. ECG intervals (RR, PR, QRS and QT) and the amplitude of MAP (Am), the maximum upstroke velocity (Vmax), as well as action potential durations (APDs) at different repolarization levels (APD30, APD50, APD70, and APD90) of MAP were determined and analyzed in detail. There were no significant differences in RR and P intervals between CT-1-CP-treated groups and control group, but the PR segment and the QRS complex were greater in the former than in the latter (F=2.681 and 5.462 respectively, P<0.05). Though QT interval and the corrected QT interval (QTc) were shorter in CT-1-CP-treated groups than in control group, the QT dispersion (QTd) of them was greater in the latter than in the former (F=3.090, P<0.05) and increased with the time. The ECG monitoring synchronously with the MAP showed that the compression of MAP electrode on the left ventricular epicardium induced performance similar to myocardium ischemia. As compared with those before chest-opening, the PR segment and QT intervals remained basically unchanged in control group, but prolonged significantly in all CT-1-CP-treated groups and the prolongation of QT intervals increased gradually along with the time of exposure to CT-1-CP. The QRS complex had no significant change in control group, one-week and three-week CT-1-CP-treated groups, but prolonged significantly in two-week and four-week CT-1-CP-treated groups. Interestingly, the QTd after chest-opening was significantly greater than that before chest-opening in control group (t=5.242, P<0.01), but decreased along with the time in CT-1-CP-treated groups. The mean MAP amplitude, Vmax and APD were greater in CT-1-CP-treated groups than those in control group, and became more obvious along with the time. The APD in four CT-1-CP-treat groups was prolonged mainly in middle to final repolarization phase. The difference among these groups became significant in middle phase (APD50) (F=6.076, P<0.01) and increased furthermore in late and final phases (APD70: F=10.054; APD90: F=18.691, P<0.01) along with the time of injection of CT-1-CP. The chronic action of CT-1-CP might induce the adapting alteration in cardiac conductivity and ventricular repolarization. The amplitude and the Vmax of the anterior LV epicardial MAP increased obviously, and the APD prolonged mainly in late and final phase of repolarization.

Dendritic Na+ spikes enable cortical input to drive action potential output from hippocampal CA2 pyramidal neurons

PubMed Central

Sun, Qian; Srinivas, Kalyan V; Sotayo, Alaba; Siegelbaum, Steven A

2014-01-01

Synaptic inputs from different brain areas are often targeted to distinct regions of neuronal dendritic arbors. Inputs to proximal dendrites usually produce large somatic EPSPs that efficiently trigger action potential (AP) output, whereas inputs to distal dendrites are greatly attenuated and may largely modulate AP output. In contrast to most other cortical and hippocampal neurons, hippocampal CA2 pyramidal neurons show unusually strong excitation by their distal dendritic inputs from entorhinal cortex (EC). In this study, we demonstrate that the ability of these EC inputs to drive CA2 AP output requires the firing of local dendritic Na+ spikes. Furthermore, we find that CA2 dendritic geometry contributes to the efficient coupling of dendritic Na+ spikes to AP output. These results provide a striking example of how dendritic spikes enable direct cortical inputs to overcome unfavorable distal synaptic locale to trigger axonal AP output and thereby enable efficient cortico-hippocampal information flow. DOI: http://dx.doi.org/10.7554/eLife.04551.001 PMID:25390033

Electrophysiological characteristics of hamster dorsal root ganglion cells and their response to axotomy.

PubMed

Gurtu, S; Smith, P A

1988-02-01

1. The active and passive membrane properties of neurons in the lower lumbar (L6, L7) or sacral (S1) dorsal root ganglia from golden hamsters were examined in vitro by means of conventional intracellular recording techniques. Data were collected from neurons exhibiting action potentials (AP) of 70 mV or more in amplitude. 2. Cells with axonal conduction velocities (CV) greater than 20 m/s were termed fast-A-cells, those with CVs between 2.5 and 20 m/s were termed A-delta-cells, and those with CVs less than 1 m/s were termed C-cells. 3. Fast-A-cells usually exhibited short-duration APs (2.51 +/- 0.41 ms, n = 19) followed by short (less than 50 ms) afterhyperpolarizations (AHPs). C-cells usually exhibited long-duration APs (10.5 +/- 0.69 ms, n = 18) followed by long-duration AHPs (much greater than 50 ms). The characteristics of APs in A-delta-cells (AP mean duration 3.34 +/- 0.42 ms, n = 32) were intermediate between those of fast-A- and C-cells. Long AHPs (duration much greater than 50 ms) were manifest in 43.8% of A-delta-cells. 4. A time-dependent sag in hyperpolarizing electrotonic potentials (rectification) was found in 68.8% of fast-A-cells, 45.5% of A-delta-cells, and 62.5% of C-cells. 5. To examine neuronal properties 1-6 wk after transection of the sciatic nerve (axotomy), cells were reclassified as SAP (short action potential) cells and LAP (long action potential) cells. Cells in the SAP category had AP durations less than 5 ms and included all fast-A-cells and the majority of A-delta-cells. The LAP category included cells with AP durations greater than 8 ms contained only C-cells. 6. Axotomy failed to decrease the CV of LAP cells or A-delta-cells in the SAP group. The CV of LAP cells may have increased (P less than 0.05), whereas that of SAP cells was unchanged. 7. The duration of the AP and AHP of SAP cells were slightly increased (0.1 greater than P greater than 0.05), whereas AP and AHP duration of LAP cells were unchanged after axotomy. AHP amplitudes of all cell types tended to be smaller (0.1 greater than P greater than 0.05). Axotomy did not alter the resting membrane potential or reduce the incidence of rectification in any cell type. 8. Invasion of the soma by axonally evoked APs was impeded in all cell types after axotomy even though a decrease (P less than 0.05) in rheobase of SAP cells occurred.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular dynamics simulation for the test of calibrated OPLS-AA force field for binary liquid mixture of tri-iso-amyl phosphate and n-dodecane.

PubMed

Das, Arya; Ali, Sk Musharaf

2018-02-21

Tri-isoamyl phosphate (TiAP) has been proposed to be an alternative for tri-butyl phosphate (TBP) in the Plutonium Uranium Extraction (PUREX) process. Recently, we have successfully calibrated and tested all-atom optimized potentials for liquid simulations using Mulliken partial charges for pure TiAP, TBP, and dodecane by performing molecular dynamics (MD) simulation. It is of immense importance to extend this potential for the various molecular properties of TiAP and TiAP/n-dodecane binary mixtures using MD simulation. Earlier, efforts were devoted to find out a suitable force field which can explain both structural and dynamical properties by empirical parameterization. Therefore, the present MD study reports the structural, dynamical, and thermodynamical properties with different mole fractions of TiAP-dodecane mixtures at the entire range of mole fraction of 0-1 employing our calibrated Mulliken embedded optimized potentials for liquid simulation (OPLS) force field. The calculated electric dipole moment of TiAP was seen to be almost unaffected by the TiAP concentration in the dodecane diluent. The calculated liquid densities of the TiAP-dodecane mixture are in good agreement with the experimental data. The mixture densities at different temperatures are also studied which was found to be reduced with temperature as expected. The plot of diffusivities for TiAP and dodecane against mole fraction in the binary mixture intersects at a composition in the range of 25%-30% of TiAP in dodecane, which is very much closer to the TBP/n-dodecane composition used in the PUREX process. The excess volume of mixing was found to be positive for the entire range of mole fraction and the excess enthalpy of mixing was shown to be endothermic for the TBP/n-dodecane mixture as well as TiAP/n-dodecane mixture as reported experimentally. The spatial pair correlation functions are evaluated between TiAP-TiAP and TiAP-dodecane molecules. Further, shear viscosity has been computed by performing the non-equilibrium molecular dynamics employing the periodic perturbation method. The calculated shear viscosity of the binary mixture is found to be in excellent agreement with the experimental values. The use of the newly calibrated OPLS force field embedding Mulliken charges is shown to be equally reliable in predicting the structural and dynamical properties for the mixture without incorporating any arbitrary scaling in the force field or Lennard-Jones parameters. Further, the present MD simulation results demonstrate that the Stokes-Einstein relation breaks down at the molecular level. The present methodology might be adopted to evaluate the liquid state properties of an aqueous-organic biphasic system, which is of great significance in the interfacial science and technology.

Molecular dynamics simulation for the test of calibrated OPLS-AA force field for binary liquid mixture of tri-iso-amyl phosphate and n-dodecane

NASA Astrophysics Data System (ADS)

Das, Arya; Ali, Sk. Musharaf

2018-02-01

Tri-isoamyl phosphate (TiAP) has been proposed to be an alternative for tri-butyl phosphate (TBP) in the Plutonium Uranium Extraction (PUREX) process. Recently, we have successfully calibrated and tested all-atom optimized potentials for liquid simulations using Mulliken partial charges for pure TiAP, TBP, and dodecane by performing molecular dynamics (MD) simulation. It is of immense importance to extend this potential for the various molecular properties of TiAP and TiAP/n-dodecane binary mixtures using MD simulation. Earlier, efforts were devoted to find out a suitable force field which can explain both structural and dynamical properties by empirical parameterization. Therefore, the present MD study reports the structural, dynamical, and thermodynamical properties with different mole fractions of TiAP-dodecane mixtures at the entire range of mole fraction of 0-1 employing our calibrated Mulliken embedded optimized potentials for liquid simulation (OPLS) force field. The calculated electric dipole moment of TiAP was seen to be almost unaffected by the TiAP concentration in the dodecane diluent. The calculated liquid densities of the TiAP-dodecane mixture are in good agreement with the experimental data. The mixture densities at different temperatures are also studied which was found to be reduced with temperature as expected. The plot of diffusivities for TiAP and dodecane against mole fraction in the binary mixture intersects at a composition in the range of 25%-30% of TiAP in dodecane, which is very much closer to the TBP/n-dodecane composition used in the PUREX process. The excess volume of mixing was found to be positive for the entire range of mole fraction and the excess enthalpy of mixing was shown to be endothermic for the TBP/n-dodecane mixture as well as TiAP/n-dodecane mixture as reported experimentally. The spatial pair correlation functions are evaluated between TiAP-TiAP and TiAP-dodecane molecules. Further, shear viscosity has been computed by performing the non-equilibrium molecular dynamics employing the periodic perturbation method. The calculated shear viscosity of the binary mixture is found to be in excellent agreement with the experimental values. The use of the newly calibrated OPLS force field embedding Mulliken charges is shown to be equally reliable in predicting the structural and dynamical properties for the mixture without incorporating any arbitrary scaling in the force field or Lennard-Jones parameters. Further, the present MD simulation results demonstrate that the Stokes-Einstein relation breaks down at the molecular level. The present methodology might be adopted to evaluate the liquid state properties of an aqueous-organic biphasic system, which is of great significance in the interfacial science and technology.

Melatonin potentiates tear secretion induced by diadenosine tetraphosphate in the rabbit.

PubMed

Hoyle, Charles H V; Peral, Assumpta; Pintor, Jesús

2006-12-15

Diadenosine tetraphosphate (Ap(4)A, 0.03 nmol) applied topically to the cornea of New Zealand white rabbits, evoked an increase in tear secretion of 9.7 +/- 2.60% (N=7). Melatonin (1 nmol) had no significant effect. Application of Ap(4)A in combination with melatonin, evoked a significantly greater increase in tear secretion of 34.2 +/- 5.8% (N=11). This potentiating effect of melatonin was blocked by pretreating the cornea with a topical application of the melatonin receptor antagonist, luzindole (240 nmol). Melatonin combined with Ap(4)A may be useful for treating dry eye conditions.

A model for studying the energetics of sustained high frequency firing

PubMed Central

Morris, Catherine E.

2018-01-01

Regulating membrane potential and synaptic function contributes significantly to the energetic costs of brain signaling, but the relative costs of action potentials (APs) and synaptic transmission during high-frequency firing are unknown. The continuous high-frequency (200-600Hz) electric organ discharge (EOD) of Eigenmannia, a weakly electric fish, underlies its electrosensing and communication. EODs reflect APs fired by the muscle-derived electrocytes of the electric organ (EO). Cholinergic synapses at the excitable posterior membranes of the elongated electrocytes control AP frequency. Based on whole-fish O2 consumption, ATP demand per EOD-linked AP increases exponentially with AP frequency. Continual EOD-AP generation implies first, that ion homeostatic processes reliably counteract any dissipation of posterior membrane ENa and EK and second that high frequency synaptic activation is reliably supported. Both of these processes require energy. To facilitate an exploration of the expected energy demands of each, we modify a previous excitability model and include synaptic currents able to drive APs at frequencies as high as 600 Hz. Synaptic stimuli are modeled as pulsatile cation conductance changes, with or without a small (sustained) background conductance. Over the full species range of EOD frequencies (200–600 Hz) we calculate frequency-dependent “Na+-entry budgets” for an electrocyte AP as a surrogate for required 3Na+/2K+-ATPase activity. We find that the cost per AP of maintaining constant-amplitude APs increases nonlinearly with frequency, whereas the cost per AP for synaptic input current is essentially constant. This predicts that Na+ channel density should correlate positively with EOD frequency, whereas AChR density should be the same across fish. Importantly, calculated costs (inferred from Na+-entry through Nav and ACh channels) for electrocyte APs as frequencies rise are much less than expected from published whole-fish EOD-linked O2 consumption. For APs at increasingly high frequencies, we suggest that EOD-related costs external to electrocytes (including packaging of synaptic transmitter) substantially exceed the direct cost of electrocyte ion homeostasis. PMID:29708986

A novel framework for feature extraction in multi-sensor action potential sorting.

PubMed

Wu, Shun-Chi; Swindlehurst, A Lee; Nenadic, Zoran

2015-09-30

Extracellular recordings of multi-unit neural activity have become indispensable in neuroscience research. The analysis of the recordings begins with the detection of the action potentials (APs), followed by a classification step where each AP is associated with a given neural source. A feature extraction step is required prior to classification in order to reduce the dimensionality of the data and the impact of noise, allowing source clustering algorithms to work more efficiently. In this paper, we propose a novel framework for multi-sensor AP feature extraction based on the so-called Matched Subspace Detector (MSD), which is shown to be a natural generalization of standard single-sensor algorithms. Clustering using both simulated data and real AP recordings taken in the locust antennal lobe demonstrates that the proposed approach yields features that are discriminatory and lead to promising results. Unlike existing methods, the proposed algorithm finds joint spatio-temporal feature vectors that match the dominant subspace observed in the two-dimensional data without needs for a forward propagation model and AP templates. The proposed MSD approach provides more discriminatory features for unsupervised AP sorting applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Catecholamine exocytosis during low frequency stimulation in mouse adrenal chromaffin cells is primarily asynchronous and controlled by the novel mechanism of Ca2+ syntilla suppression

PubMed Central

Lefkowitz, Jason J; DeCrescenzo, Valerie; Duan, Kailai; Bellve, Karl D; Fogarty, Kevin E; Walsh, John V; ZhuGe, Ronghua

2014-01-01

Adrenal chromaffin cells (ACCs), stimulated by the splanchnic nerve, generate action potentials (APs) at a frequency near 0.5 Hz in the resting physiological state, at times described as ‘rest and digest’. How such low frequency stimulation in turn elicits sufficient catecholamine exocytosis to set basal sympathetic tone is not readily explained by the classical mechanism of stimulus–secretion coupling, where exocytosis is synchronized to AP-induced Ca2+ influx. By using simulated action potentials (sAPs) at 0.5 Hz in isolated patch-clamped mouse ACCs, we show here that less than 10% of all catecholaminergic exocytosis, measured by carbon fibre amperometry, is synchronized to an AP. The asynchronous phase, the dominant phase, of exocytosis does not require Ca2+ influx. Furthermore, increased asynchronous exocytosis is accompanied by an AP-dependent decrease in frequency of Ca2+ syntillas (i.e. transient, focal Ca2+ release from internal stores) and is ryanodine sensitive. We propose a mechanism of disinhibition, wherein APs suppress Ca2+ syntillas, which themselves inhibit exocytosis as they do in the case of spontaneous catecholaminergic exocytosis. PMID:25128575

Stimulatory effect of exogenous diadenosine tetraphosphate on insulin and glucagon secretion in the perfused rat pancreas

PubMed Central

Silvestre, Ramona A; Rodríguez-Gallardo, Jovita; Egido, Eva M; Marco, José

1999-01-01

Diadenosine triphosphate (AP3A) and diadenosine tetraphosphate (AP4A) are released by various cells (e.g. platelets and chromaffin cells), and may act as extracellular messengers. In pancreatic B-cells, AP3A and AP4A are inhibitors of the ATP-regulated K+ channels, and glucose increases intracellular levels of both substances.We have studied the effect of exogenous AP3A and AP4A on insulin and glucagon secretion by the perfused rat pancreas.AP3A did not significantly modify insulin or glucagon release, whereas AP4A induced a prompt, short-lived insulin response (≈4 fold higher than basal value; P<0.05) in pancreases perfused at different glucose concentrations (3.2, 5.5 or 9 mM). AP4A-induced insulin release was abolished by somatostatin and by diazoxide. These two substances share the capacity to activate ATP-dependent K+ channels, suggesting that these channels are a potential target for AP4A in the B-cell.AP4A stimulated glucagon release at both 3.2 and 5.5 mM glucose. This effect was abolished by somatostatin.The results suggest that extracellular AP4A may play a physiological role in the control of insulin and glucagon secretion. PMID:10516664

Stimulatory effect of exogenous diadenosine tetraphosphate on insulin and glucagon secretion in the perfused rat pancreas.

PubMed

Silvestre, R A; Rodríguez-Gallardo, J; Egido, E M; Marco, J

1999-10-01

1. Diadenosine triphosphate (AP3A) and diadenosine tetraphosphate (AP4A) are released by various cells (e.g. platelets and chromaffin cells), and may act as extracellular messengers. In pancreatic B-cells, AP3A and AP4A are inhibitors of the ATP-regulated K+ channels, and glucose increases intracellular levels of both substances. 2. We have studied the effect of exogenous AP3A and AP4A on insulin and glucagon secretion by the perfused rat pancreas. 3. AP3A did not significantly modify insulin or glucagon release, whereas AP4A induced a prompt, short-lived insulin response ( approximately 4 fold higher than basal value; P<0.05) in pancreases perfused at different glucose concentrations (3.2, 5.5 or 9 mM). AP4A-induced insulin release was abolished by somatostatin and by diazoxide. These two substances share the capacity to activate ATP-dependent K+ channels, suggesting that these channels are a potential target for AP4A in the B-cell. 4. AP4A stimulated glucagon release at both 3.2 and 5.5 mM glucose. This effect was abolished by somatostatin. 5. The results suggest that extracellular AP4A may play a physiological role in the control of insulin and glucagon secretion.

Polysorbate 80-coated PLGA nanoparticles improve the permeability of acetylpuerarin and enhance its brain-protective effects in rats.

PubMed

Sun, Deqing; Xue, Aiying; Zhang, Bin; Lou, Haiyan; Shi, Huanying; Zhang, Xiumei

2015-12-01

Acetylpuerarin (AP) is an acetylated derivative of puerarin (PUE). The study aimed to prepare polysorbate 80-coated poly(lactic-co-glycolic acid) (PLGA) nanoparticles to improve the permeability of AP across the blood-brain barrier (BBB) and enhance its brain-protective effects. AP-loaded PLGA nanoparticles (AP-PLGA-NPs) were prepared using a solvent diffusion methodology. The NPs were characterized. The pharmacokinetics, tissue distributions and brain-protective effects of AP-PLGA-NPs were evaluated in animals. AP-PLGA-NPs were successfully prepared with a mean particle size of 145.0 nm and a zeta potential of -14.81 mV. The in-vitro release of AP from the PLGA-NPs showed a biphasic release profile. AP was metabolized into PUE in rats. The AUC0-∞ values of AP and PUE for AP-PLGA-NPs were 2.90- and 2.29-fold as great as those for AP solution, respectively. The values of the relative targeting efficiency in the brain were 2.40 and 2.58 for AP and PUE, and the ratios of peak concentration were 1.91 and 1.89 for AP and PUE, respectively. Compared with the crude drug, AP-PLGA-NPs showed better brain-protective effects in rats. Polysorbate 80-coated PLGA-NPs can improve the permeability of AP cross the BBB and enhance its brain-protective effects in rats. © 2015 Royal Pharmaceutical Society.

Developing an undue influence screening tool for Adult Protective Services.

PubMed

Quinn, Mary Joy; Nerenberg, Lisa; Navarro, Adria E; Wilber, Kathleen H

2017-03-01

The study purpose was to develop and pilot an undue influence screening tool for California's Adult Protective Services (APS) personnel based on the definition of undue influence enacted into California law January 1, 2014. Methods included four focus groups with APS providers (n = 33), piloting the preliminary tool by APS personnel (n = 15), and interviews with four elder abuse experts and two APS administrators. Social service literature-including existing undue influence models-was reviewed, as were existing screening and assessment tools. Using the information from these various sources, the California Undue Influence Screening Tool (CUIST) was developed. It can be applied to APS cases and potentially adapted for use by other professionals and for use in other states. Implementation of the tool into APS practice, policy, procedures, and training of personnel will depend on the initiative of APS management. Future work will need to address the reliability and validity of CUIST.

New method for estimating clustering of DNA lesions induced by physical/chemical mutagens using fluorescence anisotropy.

PubMed

Akamatsu, Ken; Shikazono, Naoya; Saito, Takeshi

2017-11-01

We have developed a new method for estimating the localization of DNA damage such as apurinic/apyrimidinic sites (APs) on DNA using fluorescence anisotropy. This method is aimed at characterizing clustered DNA damage produced by DNA-damaging agents such as ionizing radiation and genotoxic chemicals. A fluorescent probe with an aminooxy group (AlexaFluor488) was used to label APs. We prepared a pUC19 plasmid with APs by heating under acidic conditions as a model for damaged DNA, and subsequently labeled the APs. We found that the observed fluorescence anisotropy (r obs ) decreases as averaged AP density (λ AP : number of APs per base pair) increases due to homo-FRET, and that the APs were randomly distributed. We applied this method to three DNA-damaging agents, 60 Co γ-rays, methyl methanesulfonate (MMS), and neocarzinostatin (NCS). We found that r obs -λ AP relationships differed significantly between MMS and NCS. At low AP density (λ AP  < 0.001), the APs induced by MMS seemed to not be closely distributed, whereas those induced by NCS were remarkably clustered. In contrast, the AP clustering induced by 60 Co γ-rays was similar to, but potentially more likely to occur than, random distribution. This simple method can be used to estimate mutagenicity of ionizing radiation and genotoxic chemicals. Copyright © 2017 Elsevier Inc. All rights reserved.

MRP2 mediated drug-drug interaction: indomethacin increases sulfasalazine absorption in the small intestine, potentially decreasing its colonic targeting.

PubMed

Dahan, Arik; Amidon, Gordon L

2010-02-15

We have recently shown that efflux transport, mediated by multidrug resistance-associated protein 2 (MRP2) and breast cancer resistance protein (BCRP), is responsible for sulfasalazine low-permeability in the small intestine, thereby enabling its colonic targeting and therapeutic action. The purpose of the present study was to evaluate the potential pharmacokinetic interaction between indomethacin and sulfasalazine, in the mechanism of efflux transporter competition. The concentration-dependent effects of indomethacin on sulfasalazine intestinal epithelial transport were investigated across Caco-2 cell monolayers, in both apical to basolateral (AP-BL) and BL-AP directions. The interaction was then investigated in the in situ single-pass rat jejunal perfusion model. Sulfasalazine displayed 30-fold higher BL-AP than AP-BL Caco-2 permeability, indicative of net mucosal secretion. Indomethacin significantly increased AP-BL and decreased BL-AP sulfasalazine Caco-2 transport, in a concentration-dependent manner, with IC(50) values of 75 and 196 microM respectively. In the rat model, higher sulfasalazine concentrations resulted in higher intestinal permeability, consistent with saturation of efflux transporter. Without indomethacin, sulfasalazine demonstrated low rat jejunal permeability (vs. metoprolol). Indomethacin significantly increased sulfasalazine P(eff), effectively shifting it from BCS (biopharmaceutics classification system) Class IV to II. In conclusion, the data indicate that concomitant intake of indomethacin and sulfasalazine may lead to increased absorption of sulfasalazine in the small intestine, thereby reducing its colonic concentration and potentially altering its therapeutic effect. Copyright 2009 Elsevier B.V. All rights reserved.

Induction of temporally dissociated morphological and physiological differentiation of N1E-115 cells.

PubMed

Cosgrove, C; Cobbett, P

1991-07-01

Clonal cells derived from neural tumors have been widely used to study the processes of neuronal differentiation in vitro. The murine neuroblastoma clone N1E-115 has recently been shown to differentiate morphologically in response to removal of serum from the culture medium. In the present study, the nature and time course of electrophysiological differentiation of N1E-115 cells maintained in serum-free medium was examined. Differentiated cells had a higher resting potential and lower input conductance than nondifferentiated cells. Differentiated but not nondifferentiated cells generated current evoked action potentials, and differentiated cells fired spontaneous, repetitive action potentials after 13 days in serum-free medium. The rate of potential change during the depolarizing and repolarizing phases of the action potential became faster as the duration of maintenance of cells in serum-free medium increased. Remarkably, morphological differentiation appeared to be complete after exposure to serum-free medium for 5 days but electrophysiological differentiation was not complete until 13 days in this medium.

Optical magnetic detection of single-neuron action potentials using quantum defects in diamond

PubMed Central

Barry, John F.; Turner, Matthew J.; Schloss, Jennifer M.; Glenn, David R.; Song, Yuyu; Lukin, Mikhail D.; Park, Hongkun; Walsworth, Ronald L.

2016-01-01

Magnetic fields from neuronal action potentials (APs) pass largely unperturbed through biological tissue, allowing magnetic measurements of AP dynamics to be performed extracellularly or even outside intact organisms. To date, however, magnetic techniques for sensing neuronal activity have either operated at the macroscale with coarse spatial and/or temporal resolution—e.g., magnetic resonance imaging methods and magnetoencephalography—or been restricted to biophysics studies of excised neurons probed with cryogenic or bulky detectors that do not provide single-neuron spatial resolution and are not scalable to functional networks or intact organisms. Here, we show that AP magnetic sensing can be realized with both single-neuron sensitivity and intact organism applicability using optically probed nitrogen-vacancy (NV) quantum defects in diamond, operated under ambient conditions and with the NV diamond sensor in close proximity (∼10 µm) to the biological sample. We demonstrate this method for excised single neurons from marine worm and squid, and then exterior to intact, optically opaque marine worms for extended periods and with no observed adverse effect on the animal. NV diamond magnetometry is noninvasive and label-free and does not cause photodamage. The method provides precise measurement of AP waveforms from individual neurons, as well as magnetic field correlates of the AP conduction velocity, and directly determines the AP propagation direction through the inherent sensitivity of NVs to the associated AP magnetic field vector. PMID:27911765

Optical magnetic detection of single-neuron action potentials using quantum defects in diamond.

PubMed

Barry, John F; Turner, Matthew J; Schloss, Jennifer M; Glenn, David R; Song, Yuyu; Lukin, Mikhail D; Park, Hongkun; Walsworth, Ronald L

2016-12-06

Magnetic fields from neuronal action potentials (APs) pass largely unperturbed through biological tissue, allowing magnetic measurements of AP dynamics to be performed extracellularly or even outside intact organisms. To date, however, magnetic techniques for sensing neuronal activity have either operated at the macroscale with coarse spatial and/or temporal resolution-e.g., magnetic resonance imaging methods and magnetoencephalography-or been restricted to biophysics studies of excised neurons probed with cryogenic or bulky detectors that do not provide single-neuron spatial resolution and are not scalable to functional networks or intact organisms. Here, we show that AP magnetic sensing can be realized with both single-neuron sensitivity and intact organism applicability using optically probed nitrogen-vacancy (NV) quantum defects in diamond, operated under ambient conditions and with the NV diamond sensor in close proximity (∼10 µm) to the biological sample. We demonstrate this method for excised single neurons from marine worm and squid, and then exterior to intact, optically opaque marine worms for extended periods and with no observed adverse effect on the animal. NV diamond magnetometry is noninvasive and label-free and does not cause photodamage. The method provides precise measurement of AP waveforms from individual neurons, as well as magnetic field correlates of the AP conduction velocity, and directly determines the AP propagation direction through the inherent sensitivity of NVs to the associated AP magnetic field vector.

Seasonal acclimatization of the cardiac action potential in the Arctic navaga cod (Eleginus navaga, Gadidae).

PubMed

Hassinen, Minna; Abramochkin, Denis V; Vornanen, Matti

2014-04-01

Freshwater fishes of north-temperate latitudes adjust electrical excitability of the heart to seasonal temperature changes by changing expression levels of ion channel isoforms. However, little is known about thermal responses of action potential (AP) in the hearts of marine polar fishes. To this end, we examined cardiac AP in the atrial myocardium of the Arctic navaga cod (Eleginus navaga) from the White Sea (Russia) acclimatized to winter (March) and summer (September) seasons. Acute increases in temperature from 4 to 10 °C were associated with increases in heart rate, maximum velocity of AP upstroke and negative resting membrane potential, while duration of AP was shortened in both winter-acclimatized and summer-acclimatized navaga hearts. In winter, there was a compensatory shortening (41.1%) of atrial AP duration and this was associated with a strong increase in transcript expression of Erg K(+) channels, known to produce the rapid component of the delayed rectifier K(+) current, I(Kr). Smaller increases were found in the expression of Kir2.1 channels that produce the inward rectifier K(+) current, I(K1). These findings indicate that the heart of navaga cod has a good acclimatory capacity in electrical excitation of cardiac myocytes, which enables cardiac function in the cold-eurythermal waters of the subarctic White Sea.

Simultaneous epicardial and noncontact endocardial mapping of the canine right atrium: simulation and experiment.

PubMed

Sabouri, Sepideh; Matene, Elhacene; Vinet, Alain; Richer, Louis-Philippe; Cardinal, René; Armour, J Andrew; Pagé, Pierre; Kus, Teresa; Jacquemet, Vincent

2014-01-01

Epicardial high-density electrical mapping is a well-established experimental instrument to monitor in vivo the activity of the atria in response to modulations of the autonomic nervous system in sinus rhythm. In regions that are not accessible by epicardial mapping, noncontact endocardial mapping performed through a balloon catheter may provide a more comprehensive description of atrial activity. We developed a computer model of the canine right atrium to compare epicardial and noncontact endocardial mapping. The model was derived from an experiment in which electroanatomical reconstruction, epicardial mapping (103 electrodes), noncontact endocardial mapping (2048 virtual electrodes computed from a 64-channel balloon catheter), and direct-contact endocardial catheter recordings were simultaneously performed in a dog. The recording system was simulated in the computer model. For simulations and experiments (after atrio-ventricular node suppression), activation maps were computed during sinus rhythm. Repolarization was assessed by measuring the area under the atrial T wave (ATa), a marker of repolarization gradients. Results showed an epicardial-endocardial correlation coefficients of 0.80 and 0.63 (two dog experiments) and 0.96 (simulation) between activation times, and a correlation coefficients of 0.57 and 0.46 (two dog experiments) and 0.92 (simulation) between ATa values. Despite distance (balloon-atrial wall) and dimension reduction (64 electrodes), some information about atrial repolarization remained present in noncontact signals.

Simultaneous Epicardial and Noncontact Endocardial Mapping of the Canine Right Atrium: Simulation and Experiment

PubMed Central

Sabouri, Sepideh; Matene, Elhacene; Vinet, Alain; Richer, Louis-Philippe; Cardinal, René; Armour, J. Andrew; Pagé, Pierre; Kus, Teresa; Jacquemet, Vincent

2014-01-01

Epicardial high-density electrical mapping is a well-established experimental instrument to monitor in vivo the activity of the atria in response to modulations of the autonomic nervous system in sinus rhythm. In regions that are not accessible by epicardial mapping, noncontact endocardial mapping performed through a balloon catheter may provide a more comprehensive description of atrial activity. We developed a computer model of the canine right atrium to compare epicardial and noncontact endocardial mapping. The model was derived from an experiment in which electroanatomical reconstruction, epicardial mapping (103 electrodes), noncontact endocardial mapping (2048 virtual electrodes computed from a 64-channel balloon catheter), and direct-contact endocardial catheter recordings were simultaneously performed in a dog. The recording system was simulated in the computer model. For simulations and experiments (after atrio-ventricular node suppression), activation maps were computed during sinus rhythm. Repolarization was assessed by measuring the area under the atrial T wave (ATa), a marker of repolarization gradients. Results showed an epicardial-endocardial correlation coefficients of 0.80 and 0.63 (two dog experiments) and 0.96 (simulation) between activation times, and a correlation coefficients of 0.57 and 0.46 (two dog experiments) and 0.92 (simulation) between ATa values. Despite distance (balloon-atrial wall) and dimension reduction (64 electrodes), some information about atrial repolarization remained present in noncontact signals. PMID:24598778

Army and Marine Corps Active Protection System (APS) Efforts

DTIC Science & Technology

2016-08-30

safe enough for operational use, the benefits of MAPS relative to non-developmental efforts, MAPS’ impacts on NDI APS performance and costs, the Army’s...APSs Effective and Safe Enough for Operational Use? .............................. 24 What are the Benefits of MAPS Relative to Non-Developmental...corrosion—which will also factor into their eventual APS plans. Potential issues for Congress include whether current NDI APSs are effective and

Selectivity and activity of adenine dinucleotides at recombinant P2X2 and P2Y1 purinoceptors.

PubMed Central

Pintor, J.; King, B. F.; Miras-Portugal, M. T.; Burnstock, G.

1996-01-01

1. Adenine dinucleotides (Ap3A, x = 2-6) are naturally-occurring polyphosphated nucleotidic substances which are found in the CNS and are known to be released in a calcium-dependent manner from storage vesicles in brain synaptosomes. The selectivity and activity of adenine dinucleotides for neuronally-derived recombinant P2 purinoceptors were studied using P2X2 and P2Y1 subtypes expressed in Xenopus oocytes. 2. For the P2Y1 subtype derived from chick brain, Ap3A was equipotent and as active as ATP (EC50 values: 375 +/- 86 nM and 334 +/- 25 nM, respectively). Ap4A was a weak partial agonist and other dinucleotides were inactive as agonists. None of the inactive dinucleotides were antagonists nor modulated the activity of Ap3A and ATP. 3. For the P2X2 subtype derived from rat PC12 cells, Ap4A was as active as ATP but less potent (EC50 values: 15.2 +/- 1 microM and 3.7 +/- 0.7 microM, respectively). Other adenosine dinucleotides were inactive as either agonists or antagonists. 4. Ap5A (1-100 nM) potentiated ATP-responses at the P2X2 subtype, showing an EC50 of 2.95 +/- 0.7 nM for this modulatory effect. Ap5A (10 nM) shifted the concentration-response curves for ATP to the left by one-half log10 unit but did not alter the Hill co-efficient for ATP (nH = 2.1 +/- 0.1). Ap5A (10 nM) failed to potentiate Ap4A-responses but did enhance the efficacy of the P2 purinoceptor antagonist, suramin, by 12 fold at the P2X2 subtype. 5. In conclusion, the results show that ionotropic (P2X2) and metabotropic (P2Y1) ATP receptors which occur in the CNS are activated selectively by naturally-occurring adenine dinucleotides which are known to be released with nucleotides from storage vesicles. The observed potentiation of P2X2-responses by Ap5A, where co-released with ATP by brain synaptosomes, may have a functional bearing in purinergic signalling in the CNS. PMID:8922753

A novel hypothesis for an alkaline phosphatase 'rescue' mechanism in the hepatic acute phase immune response.

PubMed

Pike, Adrianne F; Kramer, Nynke I; Blaauboer, Bas J; Seinen, Willem; Brands, Ruud

2013-12-01

The liver isoform of the enzyme alkaline phosphatase (AP) has been used classically as a serum biomarker for hepatic disease states such as hepatitis, steatosis, cirrhosis, drug-induced liver injury, and hepatocellular carcinoma. Recent studies have demonstrated a more general anti-inflammatory role for AP, as it is capable of dephosphorylating potentially deleterious molecules such as nucleotide phosphates, the pathogenic endotoxin lipopolysaccharide (LPS), and the contact clotting pathway activator polyphosphate (polyP), thereby reducing inflammation and coagulopathy systemically. Yet the mechanism underlying the observed increase in liver AP levels in circulation during inflammatory insults is largely unknown. This paper hypothesizes an immunological role for AP in the liver and the potential of this system for damping generalized inflammation along with a wide range of ancillary pathologies. Based on the provided framework, a mechanism is proposed in which AP undergoes transcytosis in hepatocytes from the canalicular membrane to the sinusoidal membrane during inflammation and the enzyme's expression is upregulated as a result. Through a tightly controlled, nucleotide-stimulated negative feedback process, AP is transported in this model as an immune complex with immunoglobulin G by the asialoglycoprotein receptor through the cell and secreted into the serum, likely using the receptor's State 1 pathway. The subsequent dephosphorylation of inflammatory stimuli by AP and uptake of the circulating immune complex by endothelial cells and macrophages may lead to decreased inflammation and coagulopathy while providing an early upstream signal for the induction of a number of anti-inflammatory gene products, including AP itself. © 2013.

Calcium Dynamics in Basal Dendrites of Layer 5A and 5B Pyramidal Neurons Is Tuned to the Cell-Type Specific Physiological Action Potential Discharge

PubMed Central

Krieger, Patrik; de Kock, Christiaan P. J.; Frick, Andreas

2017-01-01

Layer 5 (L5) is a major neocortical output layer containing L5A slender-tufted (L5A-st) and L5B thick-tufted (L5B-tt) pyramidal neurons. These neuron types differ in their in vivo firing patterns, connectivity and dendritic morphology amongst other features, reflecting their specific functional role within the neocortical circuits. Here, we asked whether the active properties of the basal dendrites that receive the great majority of synaptic inputs within L5 differ between these two pyramidal neuron classes. To quantify their active properties, we measured the efficacy with which action potential (AP) firing patterns backpropagate along the basal dendrites by measuring the accompanying calcium transients using two-photon laser scanning microscopy in rat somatosensory cortex slices. For these measurements we used both “artificial” three-AP patterns and more complex physiological AP patterns that were previously recorded in anesthetized rats in L5A-st and L5B-tt neurons in response to whisker stimulation. We show that AP patterns with relatively few APs (3APs) evoke a calcium response in L5B-tt, but not L5A-st, that is dependent on the temporal pattern of the three APs. With more complex in vivo recorded AP patterns, the average calcium response was similar in the proximal dendrites but with a decay along dendrites (measured up to 100 μm) of L5B-tt but not L5A-st neurons. Interestingly however, the whisker evoked AP patterns—although very different for the two cell types—evoke similar calcium responses. In conclusion, although the effectiveness with which different AP patterns evoke calcium transients vary between L5A-st and L5B-tt cell, the calcium influx appears to be tuned such that whisker-evoked calcium transients are within the same dynamic range for both cell types. PMID:28744201

Characterization of Canna yellow mottle virus in a New Host, Alpinia purpurata, in Hawaii.

PubMed

Zhang, Jingxin; Dey, Kishore K; Lin, Birun; Borth, Wayne B; Melzer, Michael J; Sether, Diane; Wang, Yanan; Wang, I-Chin; Shen, Huifang; Pu, Xiaoming; Sun, Dayuan; Hu, John S

2017-06-01

Canna yellow mottle virus (CaYMV) is an important badnavirus infecting Canna spp. worldwide. This is the first report of CaYMV in flowering ginger (Alpinia purpurata) in Hawaii, where it is associated with yellow mottling and necrosis of leaves, vein streaking, and stunted plants. We have sequenced CaYMV in A. purpurata (CaYMV-Ap) using a combination of next-generation sequencing and traditional Sanger sequencing techniques. The complete genome of CaYMV-Ap was 7,120 bp with an organization typical of other Badnavirus species. Our results indicated that CaYMV-Ap was present in the episomal form in infected flowering ginger. We determined that this virus disease is prevalent in Hawaii and could potentially have significant economic impact on the marketing of A. purpurata as cut flowers. There is a potential concern that the host range of CaYMV-Ap may expand to include other important tropical plants.

Liposomal TriCurin, A Synergistic Combination of Curcumin, Epicatechin Gallate and Resveratrol, Repolarizes Tumor-Associated Microglia/Macrophages, and Eliminates Glioblastoma (GBM) and GBM Stem Cells.

PubMed

Mukherjee, Sumit; Baidoo, Juliet N E; Sampat, Samay; Mancuso, Andrew; David, Lovena; Cohen, Leah S; Zhou, Shuiqin; Banerjee, Probal

2018-01-18

Glioblastoma (GBM) is a deadly brain tumor with a current mean survival of 12-15 months. Despite being a potent anti-cancer agent, the turmeric ingredient curcumin (C) has limited anti-tumor efficacy in vivo due to its low bioavailability. We have reported earlier a strategy involving the use two other polyphenols, epicatechin gallate (E) from green tea and resveratrol (R) from red grapes at a unique, synergistic molar ratio with C (C:E:R: 4:1:12.5, termed TriCurin) to achieve superior potency against HPV+ tumors than C alone at C:E:R (μM): 32:8:100 (termed 32 μM+ TriCurin). We have now prepared liposomal TriCurin (TrLp) and demonstrated that TrLp boosts activated p53 in cultured GL261 mouse GBM cells to trigger apoptosis of GBM and GBM stem cells in vitro. TrLp administration into mice yielded a stable plasma concentration of 210 nM C for 60 min, which, though sub-lethal for cultured GL261 cells, was able to cause repolarization of M2-like tumor (GBM)-associated microglia/macrophages to the tumoricidal M1-like phenotype and intra-GBM recruitment of activated natural killer cells. The intratumor presence of such tumoricidal immune cells was associated with concomitant suppression of tumor-load, and apoptosis of GBM and GBM stem cells. Thus, TrLp is a potential onco-immunotherapeutic agent against GBM tumors.

Electrophysiological safety of DW-286a, a novel fluoroquinolone antibiotic agent.

PubMed

Kim, Eun-Joo; Kim, Ki-Suk; Shin, Won-Ho

2005-01-01

Inhibition of the potassium current I(Kr) and QT prolongation has been known to be associated with drug-induced torsades de pointes arrhythmias (TdP) and sudden cardiac death. We investigated the cardiac electrophysiological effects of DW-286a, a new class of fluoroquinolone antibiotics reported to prolong the QT interval. To investigate the electrophysiological safety of DW-286a, we used conventional microelectrode recording techniques in isolated guinea pig papillary muscles, whole-cell patch clamp techniques in human ether-à-go-go related gene (hERG)-transient transfected Chinese hamster ovary cells, and in vivo electrocardiogram (ECG) measurements in Sprague-Dawley (SD) rats by the use of a telemetry system. DW-286a at 300 microM significantly (P<0.01) prolonged action potentials at 50% repolarization (APD50) and 90% repolarization (APD90). For IHERG, the IC50 value was 89.00+/-37.85 microM with a Hill coefficient (nH) of -0.97+/-0.49. However, when DW-286a was orally administered to conscious SD rats at a high dose (1000 mg/kg), no significant effect on ECG in vivo was detected. From a previous study, we know that concentration at 19.8 microM is the antimicrobial end-point of DW-286a. Therefore, our data suggest that in the electrophysiological aspect, it can be thought that the effective concentrations of DW-286a are between 19.8 and 100 microM (concentration in serum).

Catecholamines release mediators in the opossum oesophageal circular smooth muscle.

PubMed Central

Daniel, E E; Jager, L P; Jury, J

1987-01-01

1. Effects of catecholamines applied exogenously to the circular smooth muscle layer of the body of the oesophagus of the opossum (Didelphis marsupialis) were studied, simultaneously measuring changes in the membrane potential, the membrane conductance and the contractility of the muscle, using the double sucrose-gap technique. 2. Superfusion of the smooth muscle with Krebs solution at 27 degrees C containing dopamine (10(-6)-10(-4) M) dose-dependently caused a hyperpolarization of the smooth muscle cells and an increased membrane resistance followed after gradual repolarization by oscillations of the membrane potential, often accompanied by muscle action potentials. During the hyperpolarization, the tendency for the membrane potential to sag during prolonged application of hyperpolarizing currents was reduced and the 'off' depolarization following such currents was increased. This muscle did not develop active tension prior to treatment; it therefore did not relax during the hyperpolarizations, but contracted following the depolarized phase of oscillations. 3. The non-adrenergic, non-cholinergic nerve-mediated inhibitory junction potential (i.j.p.) showed a small reduction in amplitude during superfusion with dopamine, explicable as a result of the drug-induced hyperpolarization. The 'off' response following the i.j.p., decreased transiently when the membrane potential was hyperpolarized to its maximum value. Then it increased to values larger than control as the membrane repolarized. Vasoactive intestinal polypeptide (VIP, 10(-6) M) produced a similar response but hyperpolarizations were smaller. 4. Of the tested catecholamines, isoprenaline, phenylephrine, butylated hydroxytoluene-920 (BHT-920) and clonidine were ineffective whereas the potency order for other catecholamines was dopamine greater than noradrenaline greater than or equal to adrenaline greater than DOPA. The catecholamine-induced responses were not affected by alpha- or beta-adrenoreceptor antagonists given alone or in combination. Of the dopamine receptor antagonists tested domperidone was without effect, whereas haloperidol reduced and bulbocapnine blocked the response. The findings suggested that a receptor resembling DA1-type peripheral receptor mediated the effects of dopamine on opossum oesophagus. 5. The catecholamine-induced responses and those to VIP disappeared completely in Cl-(-)free medium (isethionate replacement). 6. Conditioning depolarization of the smooth muscle cells decreased but hyperpolarization increased the amplitude of the hyperpolarization (up to 20 mV). With larger hyperpolarizations the responses decreased and disappeared at around 50 mV hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:3625558

Hepatoprotective effects of Auricularia cornea var. Li. polysaccharides against the alcoholic liver diseases through different metabolic pathways.

PubMed

Wang, Xiuxiu; Lan, Yufei; Zhu, Yongfa; Li, Shangshang; Liu, Min; Song, Xinling; Zhao, Huajie; Liu, Weiru; Zhang, Jianjun; Wang, Shouxian; Jia, Le

2018-05-15

The present work was designed to evaluate the antioxidation and hepatoprotective effects of Auricularia cornea var. Li. polysaccharides (APS) and enzymatic-extractable APS (EAPS) on the acute alcohol-induced alcoholic liver diseases (ALD). The in vitro antioxidant activities demonstrated that both APS and EAPS had strong reducing power and potential effects on scavenging reactive oxygen species. The in vivo mice experiments showed that the pretreatment with APS or EAPS showed potential hepatoprotective effects on the ALD possibly by increasing the antioxidant activities, reducing the lipid peroxidation, improving the alcohol metabolism, inhibiting the expression levels of inflammatory mediators and preventing the alcohol-induced histopathological alterations. In addition, the fourier-transform infrared (FT-IR), 1 H and 13 C nuclear magnetic resonance spectroscopy (NMR) and gas chromatography (GC) had been analyzed to obtained the primarily characteristics. The results indicated that abundant xylose and glucose contents probably had potential effects on possessing the bioactivities. The findings suggested that the A. cornea var. Li. might be considered as promising natural resource on exploring clinical drugs for the prevention and treatment with ALD and its complications.

Changes in intrinsic excitability of ganglion cells in degenerated retinas of RCS rats.

PubMed

Ren, Yi-Ming; Weng, Chuan-Huang; Zhao, Cong-Jian; Yin, Zheng-Qin

2018-01-01

To evaluate the intrinsic excitability of retinal ganglion cells (RGCs) in degenerated retinas. The intrinsic excitability of various morphologically defined RGC types using a combination of patch-clamp recording and the Lucifer yellow tracer in retinal whole-mount preparations harvested from Royal College of Surgeons (RCS) rats, a common retinitis pigmentosa (RP) model, in a relatively late stage of retinal degeneration (P90) were investigated. Several parameters of RGC morphologies and action potentials (APs) were measured and compared to those of non-dystrophic control rats, including dendritic stratification, dendritic field diameter, peak amplitude, half width, resting membrane potential, AP threshold, depolarization to threshold, and firing rates. Compared with non-dystrophic control RGCs, more depolarizations were required to reach the AP threshold in RCS RGCs with low spontaneous spike rates and in RCS OFF cells (especially A2o cells), and RCS RGCs maintained their dendritic morphologies, resting membrane potentials and capabilities to generate APs. RGCs are relatively well preserved morphologically and functionally, and some cells are more susceptible to decreased excitability during retinal degeneration. These findings provide valuable considerations for optimizing RP therapeutic strategies.

Hydrogen-Rich Saline Inhibits NLRP3 Inflammasome Activation and Attenuates Experimental Acute Pancreatitis in Mice

PubMed Central

Ma, Jie; Jin, Wei-Hua; Wu, Juan; Fan, Kai-Hua

2014-01-01

Increasing evidence has demonstrated that reactive oxygen species (ROS) induces oxidative stress and plays a crucial role in the pathogenesis of acute pancreatitis (AP). Hydrogen-rich saline (HRS), a well-known ROS scavenger, has been shown to possess therapeutic benefit on AP in many animal experiments. Recent findings have indicated that the NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome, an intracellular multiprotein complex required for the maturation of interleukin- (IL-) 1β, may probably be a potential target of HRS in the treatment of AP. Therefore, in this study, we evaluated the activation of NLRP3 inflammasome and meanwhile assessed the degree of oxidative stress and inflammatory cascades, as well as the histological alterations in mice suffering from cerulein-induced AP after the treatment of HRS. The results showed that the activation of NLRP3 inflammasome in AP mice was substantially inhibited following the administration of HRS, which was paralleled with the decreased NF-κB activity and cytokines production, attenuated oxidative stress and the amelioration of pancreatic tissue damage. In conclusion, our study has, for the first time, revealed that inhibition of the activation of NLRP3 inflammasome probably contributed to the therapeutic potential of HRS in AP. PMID:25214720

Patients With Long-QT Syndrome Caused by Impaired hERG-Encoded Kv11.1 Potassium Channel Have Exaggerated Endocrine Pancreatic and Incretin Function Associated With Reactive Hypoglycemia

PubMed Central

Hyltén-Cavallius, Louise; Iepsen, Eva W.; Wewer Albrechtsen, Nicolai J.; Svendstrup, Mathilde; Lubberding, Anniek F.; Hartmann, Bolette; Jespersen, Thomas; Linneberg, Allan; Christiansen, Michael; Vestergaard, Henrik; Pedersen, Oluf; Holst, Jens J.; Kanters, Jørgen K.

2017-01-01

Background: Loss-of-function mutations in hERG (encoding the Kv11.1 voltage-gated potassium channel) cause long-QT syndrome type 2 (LQT2) because of prolonged cardiac repolarization. However, Kv11.1 is also present in pancreatic α and β cells and intestinal L and K cells, secreting glucagon, insulin, and the incretins glucagon-like peptide-1 (GLP-1) and GIP (glucose-dependent insulinotropic polypeptide), respectively. These hormones are crucial for glucose regulation, and long-QT syndrome may cause disturbed glucose regulation. We measured secretion of these hormones and cardiac repolarization in response to glucose ingestion in LQT2 patients with functional mutations in hERG and matched healthy participants, testing the hypothesis that LQT2 patients have increased incretin and β-cell function and decreased α-cell function, and thus lower glucose levels. Methods: Eleven patients with LQT2 and 22 sex-, age-, and body mass index–matched control participants underwent a 6-hour 75-g oral glucose tolerance test with ECG recording and blood sampling for measurements of glucose, insulin, C-peptide, glucagon, GLP-1, and GIP. Results: In comparison with matched control participants, LQT2 patients had 56% to 78% increased serum insulin, serum C-peptide, plasma GLP-1, and plasma GIP responses (P=0.03–0.001) and decreased plasma glucose levels after glucose ingestion (P=0.02) with more symptoms of hypoglycemia (P=0.04). Sixty-three percent of LQT2 patients developed hypoglycemic plasma glucose levels (<70 mg/dL) versus 36% control participants (P=0.16), and 18% patients developed serious hypoglycemia (<50 mg/dL) versus none of the controls. LQT2 patients had defective glucagon responses to low glucose, P=0.008. β-Cell function (Insulin Secretion Sensitivity Index-2) was 2-fold higher in LQT2 patients than in controls (4398 [95% confidence interval, 2259–8562] versus 2156 [1961–3201], P=0.03). Pharmacological Kv11.1 blockade (dofetilide) in rats had similar effect, and small interfering RNA inhibition of hERG in β and L cells increased insulin and GLP-1 secretion up to 50%. Glucose ingestion caused cardiac repolarization disturbances with increased QTc intervals in both patients and controls, but with a 122% greater increase in QTcF interval in LQT2 patients (P=0.004). Conclusions: Besides a prolonged cardiac repolarization phase, LQT2 patients display increased GLP-1, GIP, and insulin secretion and defective glucagon secretion, causing decreased plasma glucose and thus increased risk of hypoglycemia. Furthermore, glucose ingestion increased QT interval and aggravated the cardiac repolarization disturbances in LQT2 patients. Clinical Trial Registration: URL: http://clinicaltrials.gov. Unique identifier: NCT02775513. PMID:28235848

Mannose-coated gadolinium liposomes for improved magnetic resonance imaging in acute pancreatitis.

PubMed

Tian, Bing; Liu, Ri; Chen, Shiyue; Chen, Luguang; Liu, Fang; Jia, Guorong; Dong, Yinmei; Li, Jing; Chen, Huaiwen; Lu, Jianping

2017-01-01

Acute pancreatitis (AP) is an acute inflammatory condition of the pancreas. The symptoms, treatment, and prognosis of mild and severe AP are different, and severe AP is a potentially life-threatening disease with a high incidence of complications and high mortality rate. Thus, it is urgent to develop an effective approach to reliably discriminate between mild and severe AP. We have developed novel gadolinium-diethylenetriaminepentaacetic (Gd-DTPA)-loaded mannosylated liposomes (named thereafter M-Gd-NL) that preferably target macrophages in AP. The targeting ability of M-Gd-NL toward macrophages in AP and its ability to discriminate between mild and severe AP were evaluated. The liposomes were of desired particle size (~100 nm), Gd-DTPA encapsulation efficiency (~85%), and stability. M-Gd-NL and non-targeted Gd-DTPA-loaded liposomes (Gd-NL) exhibited increased relaxivity compared with Gd-DTPA. Compared with Gd-NL and Gd-DTPA, M-Gd-NL showed increased uptake in macrophages, resulting in increased T 1 imaging ability both in vitro (macrophage cell line) and in vivo (severe AP model). Importantly, M-Gd-NL had the ability to discriminate between mild and severe AP, as reflected by a significantly higher T 1 magnetic resonance imaging signal in severe AP than in mild AP. M-Gd-NL did not show severe organ toxicity in rats. Our data suggest that M-Gd-NL had enhanced magnetic resonance imaging ability by targeting macrophages in AP and good ability to discriminate between mild and severe AP. We believe that M-Gd-NL could shed new light on the diagnosis of AP in the near future.

Thermal and photo-stability of the antioxidant potential of Spirulina platensis powder.

PubMed

Colla, L M; Bertol, C D; Ferreira, D J; Bavaresco, J; Costa, J A V; Bertolin, T E

2017-01-01

This work aimed to evaluate the thermal and photo stability of the antioxidant potential (AP) of the Spirulina platensis biomass. Thermal stability was established at 25ºC, 40ºC and 50ºC for 60 days, in the dark, protected from light. Photo stability was evaluated using UV (15 W, λ = 265 nm) and fluorescent (20 W, 0.16 A, power factor FP > 0.5, 50/60 Hz, 60 lm/w, 1200 lm) light for 90 days in capsules, glass and Petri dishes, at room temperature. The AP of the biomass in these conditions was determined at intervals (every 7 and 30 days in the studies of thermal and photo stability, respectively) using the induction of the oxidation of a lipid system by heat and aeration. In this lipid system, the biomass submitted to degradation was used as an antioxidant. The kinetics of the reaction was determined by the Arrhenius method. Thermal degradation was found to follow zero order kinetics, whereas photo degradation followed first order kinetics. The AP decreased 50% after 50 days at 25°C. At 40°C and 50°C, the AP decreased more than 50% after 35 and 21 days of exposition, respectively. The decrease of the AP of Spirulina was more sensible to UV and fluorescence light. After 30 days of exposition, the AP decreased more than 50% in all storage conditions tested. The antioxidant potential of Spirulina platensis is easily degraded when the biomass is exposed to heat and light, indicating the need for care to be taken in its storage.

Diadenosine pentaphosphate affects electrical activity in guinea pig atrium via activation of potassium acetylcholine-dependent inward rectifier.

PubMed

Abramochkin, Denis V; Karimova, Viktoria M; Filatova, Tatiana S; Kamkin, Andre

2017-07-01

Diadenosine pentaphosphate (Ap5A) belongs to the family of diadenosine polyphosphates, endogenously produced compounds that affect vascular tone and cardiac performance when released from platelets. The previous findings indicate that Ap5A shortens action potentials (APs) in rat myocardium via activation of purine P2 receptors. The present study demonstrates alternative mechanism of Ap5A electrophysiological effects found in guinea pig myocardium. Ap5A (10 -4  M) shortens APs in guinea pig working atrial myocardium and slows down pacemaker activity in the sinoatrial node. P1 receptors antagonist DPCPX (10 -7  M) or selective GIRK channels blocker tertiapin (10 -6  M) completely abolished all Ap5A effects, while P2 blocker PPADS (10 -4  M) was ineffective. Patch-clamp experiments revealed potassium inward rectifier current activated by Ap5A in guinea pig atrial myocytes. The current was abolished by DPCPX or tertiapin and therefore was considered as potassium acetylcholine-dependent inward rectifier (I KACh ). Thus, unlike rat, in guinea pig atrium Ap5A produces activation of P1 receptors and subsequent opening of KACh channels leading to negative effects on cardiac electrical activity.

AP1S3 Mutations Are Associated with Pustular Psoriasis and Impaired Toll-like Receptor 3 Trafficking

PubMed Central

Setta-Kaffetzi, Niovi; Simpson, Michael A.; Navarini, Alexander A.; Patel, Varsha M.; Lu, Hui-Chun; Allen, Michael H.; Duckworth, Michael; Bachelez, Hervé; Burden, A. David; Choon, Siew-Eng; Griffiths, Christopher E.M.; Kirby, Brian; Kolios, Antonios; Seyger, Marieke M.B.; Prins, Christa; Smahi, Asma; Trembath, Richard C.; Fraternali, Franca; Smith, Catherine H.; Barker, Jonathan N.; Capon, Francesca

2014-01-01

Adaptor protein complex 1 (AP-1) is an evolutionary conserved heterotetramer that promotes vesicular trafficking between the trans-Golgi network and the endosomes. The knockout of most murine AP-1 complex subunits is embryonically lethal, so the identification of human disease-associated alleles has the unique potential to deliver insights into gene function. Here, we report two founder mutations (c.11T>G [p.Phe4Cys] and c.97C>T [p.Arg33Trp]) in AP1S3, the gene encoding AP-1 complex subunit σ1C, in 15 unrelated individuals with a severe autoinflammatory skin disorder known as pustular psoriasis. Because the variants are predicted to destabilize the 3D structure of the AP-1 complex, we generated AP1S3-knockdown cell lines to investigate the consequences of AP-1 deficiency in skin keratinocytes. We found that AP1S3 silencing disrupted the endosomal translocation of the innate pattern-recognition receptor TLR-3 (Toll-like receptor 3) and resulted in a marked inhibition of downstream signaling. These findings identify pustular psoriasis as an autoinflammatory phenotype caused by defects in vesicular trafficking and demonstrate a requirement of AP-1 for Toll-like receptor homeostasis. PMID:24791904

Acquired pellicle as a modulator for dental erosion.

PubMed

Vukosavljevic, Dusa; Custodio, William; Buzalaf, Marilia A R; Hara, Anderson T; Siqueira, Walter L

2014-06-01

Dental erosion is a multifactorial condition that can result in the loss of tooth structure and function, potentially increasing tooth sensitivity. The exposure of enamel to acids from non-bacterial sources is responsible for the progression of erosion. These erosive challenges are counteracted by the anti-erosive properties of the acquired pellicle (AP), an integument formed in vivo as a result of selective adsorption of salivary proteins on the tooth surface, containing also lipids and glycoproteins. This review provides an in-depth discussion regarding how the physical structure of the AP, along with its composition, contributes to AP anti-erosive properties. The physical properties that contribute to AP protective nature include pellicle thickness, maturation time, and site of development. The pellicle contains salivary proteins embedded within its structure that demonstrate anti-erosive properties; however, rather than individual proteins, protein-protein interactions play a fundamental role in the protective nature of the AP. In addition, dietary and synthetic proteins can modify the pellicle, enhancing its protective efficiency against dental erosion. The salivary composition of the AP and its corresponding protein-profile may be employed as a diagnostic tool, since it likely contains salivary biomarkers for oral diseases that initiate at the enamel surface, including dental erosion. Finally, by modifying the composition and structure of the AP, this protein integument has the potential to be used as a target-specific treatment option for oral diseases related to tooth demineralization. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

Lipopolysaccharide potentiates the effect of hepatocyte growth factor on hepatocyte replication in rats by augmenting AP-1 activity.

PubMed

Gao, C; Jokerst, R; Gondipalli, P; Cai, S R; Kennedy, S; Flye, M W; Ponder, K P

1999-12-01

The liver regenerates by replication of differentiated hepatocytes after damage or removal of part of the liver. Although several growth factors and signaling pathways are activated during regeneration, it is unclear as to which of these are essential for hepatocyte replication. We show here that low- (1 mg/kg) and high- (10 mg/kg) dose hepatocyte growth factor (HGF) induced replication of 2.1% and 11.1% of hepatocytes in rats, respectively. Lipopolysaccharide (LPS), an inducer of the acute phase response, augmented hepatocyte replication in response to low- and high-dose HGF by 4- and 2-fold, respectively. HGF alone induced moderate levels of c-Jun-N-terminal kinase (JNK) and p44/p42 mitogen-activated protein kinase (MAPK), resulting in moderate levels of AP-1-DNA binding activity. The combination of LPS + HGF increased JNK and AP-1-DNA binding activity more than levels seen with LPS or HGF alone. The activation of Stat3 that was observed after administration of LPS + HGF, but not HGF alone, could contribute to increased transcription of AP-1 components. Because phosphorylation of the c-Jun component of AP-1 by JNK increases its ability to activate transcription, the AP-1 in hepatocytes from animals treated with LPS + HGF may be more active than in rats treated with LPS or HGF alone. LPS may contribute to hepatocyte replication by potentiating the effect of HGF on the activation of both AP-1-DNA binding and transcriptional activity.

Physiological time-series analysis: what does regularity quantify?

NASA Technical Reports Server (NTRS)

Pincus, S. M.; Goldberger, A. L.

1994-01-01

Approximate entropy (ApEn) is a recently developed statistic quantifying regularity and complexity that appears to have potential application to a wide variety of physiological and clinical time-series data. The focus here is to provide a better understanding of ApEn to facilitate its proper utilization, application, and interpretation. After giving the formal mathematical description of ApEn, we provide a multistep description of the algorithm as applied to two contrasting clinical heart rate data sets. We discuss algorithm implementation and interpretation and introduce a general mathematical hypothesis of the dynamics of a wide class of diseases, indicating the utility of ApEn to test this hypothesis. We indicate the relationship of ApEn to variability measures, the Fourier spectrum, and algorithms motivated by study of chaotic dynamics. We discuss further mathematical properties of ApEn, including the choice of input parameters, statistical issues, and modeling considerations, and we conclude with a section on caveats to ensure correct ApEn utilization.

Mechanism for Amplitude Alternans in Electrocardiograms and the Initiation of Spatiotemporal Chaos

NASA Astrophysics Data System (ADS)

Chen, Diandian Diana; Gray, Richard A.; Uzelac, Ilija; Herndon, Conner; Fenton, Flavio H.

2017-04-01

It is widely believed that one major life-threatening transition to chaotic fibrillation occurs via spiral-wave breakup that is preceded by spatiotemporal dispersion of refractoriness due to alternations in the duration of the cardiac action potential (AP). However, recent clinical and experimental evidence suggests that other characteristics of the AP may contribute to, and perhaps drive, this dangerous dynamical instability. To identify the relative roles of AP characteristics, we performed experiments in rabbit hearts under conditions to minimize AP duration dynamics which unmasked pronounced AP amplitude alternans just before the onset of fibrillation. We used a simplified ionic cell model to derive a return map and a stability condition that elucidates a novel underlying mechanism for AP alternans and spiral breakup. We found that inactivation of the sodium current is key to developing amplitude alternans and is directly connected to conduction block and initiation of arrhythmias. Simulations in 2D where AP amplitude alternation led to turbulence confirm our hypothesis.

Cytokine Autoantibody Screening in the Swedish Addison Registry Identifies Patients With Undiagnosed APS1.

PubMed

Eriksson, Daniel; Dalin, Frida; Eriksson, Gabriel Nordling; Landegren, Nils; Bianchi, Matteo; Hallgren, Åsa; Dahlqvist, Per; Wahlberg, Jeanette; Ekwall, Olov; Winqvist, Ola; Catrina, Sergiu-Bogdan; Rönnelid, Johan; Hulting, Anna-Lena; Lindblad-Toh, Kerstin; Alimohammadi, Mohammad; Husebye, Eystein S; Knappskog, Per Morten; Rosengren Pielberg, Gerli; Bensing, Sophie; Kämpe, Olle

2018-01-01

Autoimmune polyendocrine syndrome type 1 (APS1) is a monogenic disorder that features autoimmune Addison disease as a major component. Although APS1 accounts for only a small fraction of all patients with Addison disease, early identification of these individuals is vital to prevent the potentially lethal complications of APS1. To determine whether available serological and genetic markers are valuable screening tools for the identification of APS1 among patients diagnosed with Addison disease. We systematically screened 677 patients with Addison disease enrolled in the Swedish Addison Registry for autoantibodies against interleukin-22 and interferon-α4. Autoantibody-positive patients were investigated for clinical manifestations of APS1, additional APS1-specific autoantibodies, and DNA sequence and copy number variations of AIRE. In total, 17 patients (2.5%) displayed autoantibodies against interleukin-22 and/or interferon-α4, of which nine were known APS1 cases. Four patients previously undiagnosed with APS1 fulfilled clinical, genetic, and serological criteria. Hence, we identified four patients with undiagnosed APS1 with this screening procedure. We propose that patients with Addison disease should be routinely screened for cytokine autoantibodies. Clinical or serological support for APS1 should warrant DNA sequencing and copy number analysis of AIRE to enable early diagnosis and prevention of lethal complications. Copyright © 2017 Endocrine Society

Aptamer-functionalized PEG-PLGA nanoparticles for enhanced anti-glioma drug delivery.

PubMed

Guo, Jianwei; Gao, Xiaoling; Su, Lina; Xia, Huimin; Gu, Guangzhi; Pang, Zhiqing; Jiang, Xinguo; Yao, Lei; Chen, Jun; Chen, Hongzhuan

2011-11-01

Targeted delivery of therapeutic nanoparticles in a disease-specific manner represents a potentially powerful technology especially when treating infiltrative brain tumors such as gliomas. We developed a nanoparticulate drug delivery system decorated with AS1411 (Ap), a DNA aptamer specifically binding to nucleolin which was highly expressed in the plasma membrane of both cancer cells and endothelial cells in angiogenic blood vessels, as the targeting ligand to facilitate anti-glioma delivery of paclitaxel (PTX). Ap was conjugated to the surface of PEG-PLGA nanoparticles (NP) via an EDC/NHS technique. With the conjugation confirmed by Urea PAGE and XPS, the resulting Ap-PTX-NP was uniformly round with particle size at 156.0 ± 54.8 nm and zeta potential at -32.93 ± 3.1 mV. Ap-nucleolin interaction significantly enhanced cellular association of nanoparticles in C6 glioma cells, and increased the cytotoxicity of its payload. Prolonged circulation and enhanced PTX accumulation at the tumor site was achieved for Ap-PTX-NP, which eventually obtained significantly higher tumor inhibition on mice bearing C6 glioma xenografts and prolonged animal survival on rats bearing intracranial C6 gliomas when compared with PTX-NP and Taxol(®). The results of this contribution demonstrated the potential utility of AS1411-functionalized nanoparticles for a therapeutic application in the treatment of gliomas. Copyright © 2011 Elsevier Ltd. All rights reserved.

Preparation, crystallization and preliminary X-ray crystallographic studies of diadenosine tetraphosphate hydrolase from Shigella flexneri 2a.

PubMed

Hu, Wenxin; Wang, Qihai; Bi, Ruchang

2005-12-01

Diadenosine tetraphosphate (Ap4A) hydrolase (EC 3.6.1.41) hydrolyzes Ap4A symmetrically in prokaryotes. It plays a potential role in organisms by regulating the concentration of Ap4A in vivo. To date, no three-dimensional structures of proteins with significant sequence homology to this protein have been determined. The 31.3 kDa Ap4A hydrolase from Shigella flexneri 2a has been cloned, expressed and purified using an Escherichia coli expression system. Crystals of Ap4A hydrolase have been obtained by the hanging-drop technique at 291 K using PEG 550 MME as precipitant. Ap4A hydrolase crystals diffract X-rays to 3.26 A and belong to space group P2(1), with unit-cell parameters a = 118.9, b = 54.6, c = 128.5 A, beta = 95.7 degrees.

Glucose hydrogen breath test for small intestinal bacterial overgrowth in children with abdominal pain-related functional gastrointestinal disorders.

PubMed

Korterink, Judith J; Benninga, Marc A; van Wering, Herbert M; Deckers-Kocken, Judith M

2015-04-01

A potential link between small intestinal bacterial overgrowth (SIBO) and abdominal pain-related functional gastrointestinal disorders (AP-FGID) has been suggested by symptom similarities and by the reported prevalence of SIBO in children with irritable bowel syndrome (IBS) and functional AP. The aim of this study is to evaluate the prevalence of SIBO using the glucose hydrogen breath test (GHBT), in a cohort of Dutch children with AP-FGID fulfilling the Rome III criteria, and to identify potential predictors. Children ages 6 to 18 years with AP-FGID fulfilling the Rome III criteria were included. All of the children underwent a GHBT. SIBO was diagnosed if the fasting breath hydrogen concentration was ≥20 ppm or an increase in H2 levels of ≥12 ppm above the baseline value was measured after ingestion of glucose. Gastrointestinal symptoms were collected using a standardised AP questionnaire. A total of 161 Dutch children with AP-FGID were enrolled. Twenty-three patients (14.3%) were diagnosed as having SIBO, as assessed by GHBT; 78% of the children diagnosed as having SIBO had fasting hydrogen levels ≥20 ppm. IBS was significantly more found in children with SIBO compared with children without SIBO (P = 0.001). An altered defecation pattern (ie, change in frequency or form of stool) (P = 0.013), loss of appetite (P = 0.007), and belching (P = 0.023) were significantly more found in children with SIBO compared with those without SIBO. SIBO is present in 14.3% of children presenting with AP-FGID. IBS, altered defecation pattern, loss of appetite, and belching were predictors for SIBO in children with AP-FGID.

Different role of TTX-sensitive voltage-gated sodium channel (NaV 1) subtypes in action potential initiation and conduction in vagal airway nociceptors.

PubMed

Kollarik, M; Sun, H; Herbstsomer, R A; Ru, F; Kocmalova, M; Meeker, S N; Undem, B J

2018-04-15

The action potential initiation in the nerve terminals and its subsequent conduction along the axons of afferent nerves are not necessarily dependent on the same voltage-gated sodium channel (Na V 1) subunits. The action potential initiation in jugular C-fibres within airway tissues is not blocked by TTX; nonetheless, conduction of action potentials along the vagal axons of these nerves is often dependent on TTX-sensitive channels. This is not the case for nodose airway Aδ-fibres and C-fibres, where both action potential initiation and conduction is abolished by TTX or selective Na V 1.7 blockers. The difference between the initiation of action potentials within the airways vs. conduction along the axons should be considered when developing Na V 1 blocking drugs for topical application to the respiratory tract. The action potential (AP) initiation in the nerve terminals and its subsequent AP conduction along the axons do not necessarily depend on the same subtypes of voltage-gated sodium channels (Na V 1s). We evaluated the role of TTX-sensitive and TTX-resistant Na V 1s in vagal afferent nociceptor nerves derived from jugular and nodose ganglia innervating the respiratory system. Single cell RT-PCR was performed on vagal afferent neurons retrogradely labelled from the guinea pig trachea. Almost all of the jugular neurons expressed the TTX-sensitive channel Na V 1.7 along with TTX-resistant Na V 1.8 and Na V 1.9. Tracheal nodose neurons also expressed Na V 1.7 but, less frequently, Na V 1.8 and Na V 1.9. Na V 1.6 were expressed in ∼40% of the jugular and 25% of nodose tracheal neurons. Other Na V 1 α subunits were only rarely expressed. Single fibre recordings were made from the vagal nodose and jugular nerve fibres innervating the trachea or lung in the isolated perfused vagally-innervated preparations that allowed for selective drug delivery to the nerve terminal compartment (AP initiation) or to the desheathed vagus nerve (AP conduction). AP initiation in jugular C-fibres was unaffected by TTX, although it was inhibited by Na V 1.8 blocker (PF-01247324) and abolished by combination of TTX and PF-01247324. However, AP conduction in the majority of jugular C-fibres was abolished by TTX. By contrast, both AP initiation and conduction in nodose nociceptors was abolished by TTX or selective Na V 1.7 blockers. Distinction between the effect of a drug with respect to inhibiting AP in the nerve terminals within the airways vs. at conduction sites along the vagus nerve is relevant to therapeutic strategies involving inhaled Na V 1 blocking drugs. © 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.

Risk Factor Differences in Calcified and Non-Calcified Aortic Plaque: The Framingham Heart Study

PubMed Central

Chuang, Michael L.; Gona, Philimon; Oyama-Manabe, Noriko; Manders, Emily S.; Salton, Carol J.; Hoffmann, Udo; Manning, Warren J.; O'Donnell, Christopher J.

2014-01-01

Objective Determine the prevalence and risk factor (RF) correlates of aortic plaque (AP) detected by cardiovascular magnetic resonance (CMR), which mainly shows noncalcified plaques, and by noncontrast computed tomography (CT), which best depicts calcified plaques, in community-dwelling adults. Approach and Results 1016 Framingham Offspring cohort members (64±9y, 474 men) underwent CMR and CT of the aorta. Potential RFs for AP (age; sex; BMI; blood pressure; LDL and HDL cholesterol; fasting glucose; C-reactive protein; prevalent hypertension, diabetes, smoking; use of antihypertensive, diabetes or lipid-lowering drugs) were compared between participants with zero versus nonzero AP by CMR and by CT. Candidate RFs attaining p<0.05 for difference with either imaging modality were entered into multivariable logistic regression models adjusting for age, sex and other RFs. Odds ratios were calculated for modality-specific prevalence of AP. Associations between RFs and continuous measures of AP were assessed using Tobit regression. Prevalences of CMR and CT AP were 49% and 82% respectively. AP burdens by CMR and CT were correlated, r=0.28, p<0.0001. Increasing age and smoking were associated with prevalent AP by both CMR and CT. Additionally, prevalent AP by CMR was associated with female sex and fasting glucose, prevalent AP by CT with hypertension treatment and with adverse lipid profile. Conclusions AP by CMR and CT are both associated with smoking and increasing age, but other risk factors differ between calcified and noncalcified AP. The relative predictive value of AP detected by CMR versus by CT for incident cardiovascular events remains to be determined. PMID:24833796

Charge movement in a fast twitch skeletal muscle from rat.

PubMed

Simon, B J; Beam, K G

1983-02-01

Voltage-dependent charge movement in the rat omohyoid muscle was investigated using the three microelectrode voltage clamp technique. The charge that moved during a depolarization from the holding potential (-90 mV) to the test potential, V, increased with increasing V, saturating around 0 mV. The charge vs. voltage relationship was well fitted by Q = Q(max)/{1 + exp[-(V - V)/k]}, with Q(max) = 28.5 nC/muF, V = -34.2 mV, and k = 8.7 mV. Repolarization of the fiber from the test potential back to the holding potential caused an equal but opposite amount of charge to move. The kinetics of ON charge movement could be well described by a model developed for frog muscle by Horowicz and Schneider (1981b), which suggests that rat and frog charge movements are similar. This model failed to describe the kinetics of OFF charge movement for steps in potential from 0 mV to test potentials of -10 to -90 mV. OFF-charge movement rose to a peak more slowly and decayed more slowly than predicted by the theory.

LaAP2L1, a heterosis-associated AP2/EREBP transcription factor of Larix, increases organ size and final biomass by affecting cell proliferation in Arabidopsis.

PubMed

Li, Ai; Zhou, Yanan; Jin, Chuan; Song, Wenqin; Chen, Chengbin; Wang, Chunguo

2013-11-01

In Larix and in some crops, heterosis is prevalent and has been widely used in breeding to produce excellent varieties. However, the molecular basis of heterosis in Larix remains ambiguous. LaAP2L1, a member of the AP2/EREBP transcription factor family, has been suggested to be involved in heterosis in Larix hybrids. Here, the function and regulation of LaAP2L1 were further explored. Overexpression of LaAP2L1 led to markedly enlarged organs and heterosis-like traits in Arabidopsis. Fresh weight of leaves was almost twice as great as in vector controls. Likewise, seed yield of 35S::LaAP2L1 individual plants was >200% greater than that of control plants. The enlarged organs and heterosis-like traits displayed by 35S::LaAP2L1 plants were mainly due to enhanced cell proliferation and prolonged growth duration. At the molecular level, LaAP2L1 upregulated the expression of ANT, EBP1, and CycD3;1 and inhibited the expression of ARGOS in 35S::LaAP2L1 plants, suggesting an important molecular role of LaAP2L1 in regulating plant organ development. These findings provide new insights into the formation of heterosis in woody plants and suggest that LaAP2L1 has potential applications in breeding high-yielding crops and energy plants. In addition, 50 AP2/EREBP transcription factors, including LaAP2L1, in Larix were identified by transcriptome sequencing, and phylogenetic analysis was conducted. This provided information that will be important in further revealing the functions of these transcription factors.

P alpha-chiral phosphorothioate analogues of bis(5'-adenosyl)tetraphosphate (Ap4A); their enzymatic synthesis and degradation.

PubMed Central

Lazewska, D; Guranowski, A

1990-01-01

Synthesis of Sp and Rp diastereomers of Ap4A alpha S has been characterized in two enzymatic systems, the lysyl-tRNA synthetase from Escherichia coli and the Ap4A alpha, beta-phosphorylase from Saccharomyces cerevisiae. The synthetase was able to use both (Sp)ATP alpha S and (Rp)ATP alpha S as acceptors of adenylate thus yielding corresponding monothioanalogues of Ap4A,(Sp) Ap4A alpha S and (Rp)Ap4A alpha S. No dithiophosphate analogue was formed. Relative synthetase velocities of the formation of Ap4A,(Sp) Ap4A alpha S and (Rp)Ap4A alpha S were 1:0.38:0.15, and the computed Km values for (Sp)ATP alpha S and (Rp)ATP alpha S were 0.48 and 1.34 mM, respectively. The yeast Ap4A phosphorylase synthesized (Sp)Ap4A alpha S and (Rp)Ap4A alpha S using adenosine 5'-phosphosulfate (APS) as source of adenylate. The adenylate was accepted by corresponding thioanalogues of ATP. In that system, relative velocities of Ap4A, (Sp)Ap4A alpha S and (Rp)Ap4A alpha S formation were 1:0.15:0.60. The two isomeric phosphorothioate analogues of Ap4A were tested as substrates for the following specific Ap4A-degrading enzymes: (asymmetrical) Ap4A hydrolase (EC 3.6.1.17) from yellow lupin (Lupinus luteus) seeds hydrolyzed each of the analogues to AMP and the corresponding isomer of ATP alpha S; (symmetrical) Ap4A hydrolase (EC 3.6.1.41) from E. coli produced ADP and the corresponding diastereomer of ADP alpha S; and Ap4A phosphorylase (EC 2.7.7.53) from S. cerevisiae cleaved the Rp isomer only at the unmodified end yielding ADP and (Rp)ATP alpha S whereas the Sp isomer was degraded non-specifically yielding a mixture of ADP, (Sp)ADP alpha S, ATP and (Sp)ATP alpha S. For all the Ap4A-degrading enzymes, the Rp isomer of Ap4A alpha S appeared to be a better substrate than its Sp counterpart; stereoselectivity of the three enzymes for the Ap4A alpha S diastereomers is 51, 6 and 2.5, respectively. Basic kinetic parameters of the degradation reactions are presented and structural requirements of the Ap4A-metabolizing enzymes with respect to the potential substrates modified at the Ap4A-P alpha are discussed. PMID:2172926

Macrophage Repolarization with Targeted Alginate Nanoparticles Containing IL-10 Plasmid DNA for the Treatment of Experimental Arthritis

PubMed Central

Jain, Shardool; Tran, Thanh-Huyen; Amiji, Mansoor

2015-01-01

In this study, we have shown for the first time the effectiveness of a non-viral gene transfection strategy to re-polarize macrophages from M1 to M2 functional sub-type for the treatment of rheumatoid arthritis (RA). An anti-inflammatory (IL-10) cytokine encoding plasmid DNA was successfully encapsulated into non-condensing alginate based nanoparticles and the surface of the nano-carriers was modified with tuftsin peptide to achieve active macrophage targeting. Enhanced localization of tuftsin-modified alginate nanoparticles was observed in the inflamed paws of arthritic rats upon intraperitoneal administration. Importantly, targeted nanoparticle treatment was successful in reprogramming macrophage phenotype balance as ~66% of total synovial macrophages from arthritic rats treated with the IL-10 plasmid DNA loaded tuftsin/alginate nanoparticles were in the M2 state compared to ~9% of macrophages in the M2 state from untreated arthritic rats. Treatment significantly reduced systemic and joint tissue pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) expression and prevented the progression of inflammation and joint damage as revealed by magnetic resonance imaging and histology. Treatment enabled animals to retain their mobility throughout the course of study, whereas untreated animals suffered from impaired mobility. Overall, this study demonstrates that targeted alginate nanoparticles loaded with IL-10 plasmid DNA can efficiently re-polarize macrophages from an M1 to an M2 state, offering a novel treatment paradigm for treatment of chronic inflammatory diseases. PMID:26004232

Single therapeutic and supratherapeutic doses of sacubitril/valsartan (LCZ696) do not affect cardiac repolarization.

PubMed

Langenickel, Thomas H; Jordaan, Pierre; Petruck, Jesika; Kode, Kiran; Pal, Parasar; Vaidya, Soniya; Chandra, Priya; Rajman, Iris

2016-08-01

Sacubitril/valsartan (LCZ696) is a first-in-class angiotensin receptor neprilysin inhibitor (ARNI) indicated to reduce the risk of cardiovascular death and hospitalization for heart failure in patients with chronic heart failure (NYHA class II-IV) and reduced ejection fraction. This study was aimed to evaluate the effect of single oral therapeutic (400 mg) and supratherapeutic (1200 mg) doses of LCZ696 on cardiac repolarization. This randomized double-blind crossover study in healthy male subjects compared the effect of therapeutic and supratherapeutic doses of LCZ696 with placebo and moxifloxacin 400 mg (open-label treatment) as positive control. The primary assessment was mean baseline- and placebo-corrected QTcF (∆∆QTcF; Fridericia correction). Additional assessments included the ∆∆QTcB (Bazett's correction), PR interval, QRS duration, heart rate (HR), LCZ696 pharmacokinetics, pharmacokinetic/pharmacodynamic relationships, and safety. Of the 84 subjects enrolled, 81 completed the study. The maximum upper bound of the two-sided 90 % confidence interval for ∆∆QTcF for LCZ696 400 mg and 1200 mg were <10 ms, and assay sensitivity was confirmed with moxifloxacin. No relevant treatment-emergent changes were observed in any of the ECG-derived parameters with LCZ696 or placebo, and the incidence of adverse events was comparable among the treatment groups. Single therapeutic and supratherapeutic doses of LCZ696 did not affect cardiac repolarization as defined by the E14 ICH guidelines.

Accession-dependent action potentials in Arabidopsis.

PubMed

Favre, Patrick; Greppin, Hubert; Degli Agosti, Robert

2011-05-01

Plant excitability, as measured by the appearance and circulation of action potentials (APs) after biotic and abiotic stress treatments, is a far lesser and more versatile phenomenon than in animals. To examine the genetic basis of plant excitability we used different Arabidopsis thaliana accessions. APs were induced by wounding (W) with a subsequent deposition (D) of 5μL of 1M KCl onto adult leaves. This treatment elicited transient voltage responses (APs) that were detected by 2 extracellular electrodes placed at a distance from the wounding location over an experimental time of 150min. The first electrode (e1) was placed at the end of the petiole and the beginning of the leaf, and the second (e2) electrode was placed on the petiole near the center of the rosette. All accessions (Columbia (Col), Wassilewskija (Ws) and Landsberg erecta (Ler)) responded to the W & D treatment. After W & D treatment was performed on 100 plants for each accession, the number of APs ranged from 0 to 37 (median 8, total 940), 0 to 16 (median 5, total 528) and 0 to 18 (median 2, total 296) in Col, Ws and Ler, respectively. Responding plants (>0 APs) showed significantly different behaviors depending on their accessions of origin (i.e., Col 91, Ws 83 and Ler 76%). Some AP characteristics, such as amplitude and speed of propagation from e1 to e2 (1.28mms(-1)), were the same for all accessions, whereas the average duration of APs was similar in Col and Ws, but different in Ler. Self-sustained oscillations were observed more frequently in Col than Ws and least often in Ler, and the mean oscillation frequency was more rapid in Col, followed by Ws, and was slowest in Ler. In general, Col was the most excitable accession, followed by Ws, and Ler was the least excitable; this corresponded well with voltage elicited action potentials. In conclusion, part of Arabidopsis excitability in AP responses is genetically pre-determined. Copyright © 2010 Elsevier GmbH. All rights reserved.

The Role of Complement in Cnidarian-Dinoflagellate Symbiosis and Immune Challenge in the Sea Anemone Aiptasia pallida

PubMed Central

Poole, Angela Z.; Kitchen, Sheila A.; Weis, Virginia M.

2016-01-01

The complement system is an innate immune pathway that in vertebrates, is responsible for initial recognition and ultimately phagocytosis and destruction of microbes. Several complement molecules including C3, Factor B, and mannose binding lectin associated serine proteases (MASP) have been characterized in invertebrates and while most studies have focused on their conserved role in defense against pathogens, little is known about their role in managing beneficial microbes. The purpose of this study was to (1) characterize complement pathway genes in the symbiotic sea anemone Aiptasia pallida, (2) investigate the evolution of complement genes in invertebrates, and (3) examine the potential dual role of complement genes Factor B and MASP in the onset and maintenance of cnidarian-dinoflagellate symbiosis and immune challenge using qPCR based studies. The results demonstrate that A. pallida has multiple Factor B genes (Ap_Bf-1, Ap_Bf-2a, and Ap_Bf-2b) and one MASP gene (Ap_MASP). Phylogenetic analysis indicates that the evolutionary history of complement genes is complex, and there have been many gene duplications or gene loss events, even within members of the same phylum. Gene expression analyses revealed a potential role for complement in both onset and maintenance of cnidarian-dinoflagellate symbiosis and immune challenge. Specifically, Ap_Bf-1 and Ap_MASP are significantly upregulated in the light at the onset of symbiosis and in response to challenge with the pathogen Serratia marcescens suggesting that they play a role in the initial recognition of both beneficial and harmful microbes. Ap_Bf-2b in contrast, was generally downregulated during the onset and maintenance of symbiosis and in response to challenge with S. marcescens. Therefore, the exact role of Ap_Bf-2b in response to microbes remains unclear, but the results suggest that the presence of microbes leads to repressed expression. Together, these results indicate functional divergence between Ap_Bf-1 and Ap_Bf-2b, and that Ap_Bf-1 and Ap_MASP may be functioning together in an ancestral hybrid of the lectin and alternative complement pathways. Overall, this study provides information on the role of the complement system in a basal metazoan and its role in host-microbe interactions. PMID:27148208

The Role of Complement in Cnidarian-Dinoflagellate Symbiosis and Immune Challenge in the Sea Anemone Aiptasia pallida.

PubMed

Poole, Angela Z; Kitchen, Sheila A; Weis, Virginia M

2016-01-01

The complement system is an innate immune pathway that in vertebrates, is responsible for initial recognition and ultimately phagocytosis and destruction of microbes. Several complement molecules including C3, Factor B, and mannose binding lectin associated serine proteases (MASP) have been characterized in invertebrates and while most studies have focused on their conserved role in defense against pathogens, little is known about their role in managing beneficial microbes. The purpose of this study was to (1) characterize complement pathway genes in the symbiotic sea anemone Aiptasia pallida, (2) investigate the evolution of complement genes in invertebrates, and (3) examine the potential dual role of complement genes Factor B and MASP in the onset and maintenance of cnidarian-dinoflagellate symbiosis and immune challenge using qPCR based studies. The results demonstrate that A. pallida has multiple Factor B genes (Ap_Bf-1, Ap_Bf-2a, and Ap_Bf-2b) and one MASP gene (Ap_MASP). Phylogenetic analysis indicates that the evolutionary history of complement genes is complex, and there have been many gene duplications or gene loss events, even within members of the same phylum. Gene expression analyses revealed a potential role for complement in both onset and maintenance of cnidarian-dinoflagellate symbiosis and immune challenge. Specifically, Ap_Bf-1 and Ap_MASP are significantly upregulated in the light at the onset of symbiosis and in response to challenge with the pathogen Serratia marcescens suggesting that they play a role in the initial recognition of both beneficial and harmful microbes. Ap_Bf-2b in contrast, was generally downregulated during the onset and maintenance of symbiosis and in response to challenge with S. marcescens. Therefore, the exact role of Ap_Bf-2b in response to microbes remains unclear, but the results suggest that the presence of microbes leads to repressed expression. Together, these results indicate functional divergence between Ap_Bf-1 and Ap_Bf-2b, and that Ap_Bf-1 and Ap_MASP may be functioning together in an ancestral hybrid of the lectin and alternative complement pathways. Overall, this study provides information on the role of the complement system in a basal metazoan and its role in host-microbe interactions.

Osmotic and Salt Stresses Modulate Spontaneous and Glutamate-Induced Action Potentials and Distinguish between Growth and Circumnutation in Helianthus annuus Seedlings

PubMed Central

Stolarz, Maria; Dziubinska, Halina

2017-01-01

Action potentials (APs), i.e., long-distance electrical signals, and circumnutations (CN), i.e., endogenous plant organ movements, are shaped by ion fluxes and content in excitable and motor tissues. The appearance of APs and CN as well as growth parameters in seedlings and 3-week old plants of Helianthus annuus treated with osmotic and salt stress (0–500 mOsm) were studied. Time-lapse photography and extracellular measurements of electrical potential changes were performed. The hypocotyl length was strongly reduced by the osmotic and salt stress. CN intensity declined due to the osmotic but not salt stress. The period of CN in mild salt stress was similar to the control (~164 min) and increased to more than 200 min in osmotic stress. In sunflower seedlings growing in a hydroponic medium, spontaneous APs (SAPs) propagating basipetally and acropetally with a velocity of 12–20 cm min−1 were observed. The number of SAPs increased 2–3 times (7–10 SAPs 24 h−1plant−1) in the mild salt stress (160 mOsm NaCl and KCl), compared to the control and strong salt stress (3–4 SAPs 24 h−1 plant−1 in the control and 300 mOsm KCl and NaCl). Glutamate-induced series of APs were inhibited in the strong salt stress-treated seedlings but not at the mild salt stress and osmotic stress. Additionally, in 3-week old plants, the injection of the hypo- or hyperosmotic solution at the base of the sunflower stem evoked series of APs (3–24 APs) transmitted along the stem. It has been shown that osmotic and salt stresses modulate differently hypocotyl growth and CN and have an effect on spontaneous and evoked APs in sunflower seedlings. We suggested that potassium, sodium, and chloride ions at stress concentrations in the nutrient medium modulate sunflower excitability and CN. PMID:29093722

Surfactant protein A (SP-A) inhibits agglomeration and macrophage uptake of toxic amine modified nanoparticles.

PubMed

McKenzie, Zofi; Kendall, Michaela; Mackay, Rose-Marie; Whitwell, Harry; Elgy, Christine; Ding, Ping; Mahajan, Sumeet; Morgan, Cliff; Griffiths, Mark; Clark, Howard; Madsen, Jens

2015-01-01

The lung provides the main route for nanomaterial exposure. Surfactant protein A (SP-A) is an important respiratory innate immune molecule with the ability to bind or opsonise pathogens to enhance phagocytic removal from the airways. We hypothesised that SP-A, like surfactant protein D, may interact with inhaled nanoparticulates, and that this interaction will be affected by nanoparticle (NP) surface characteristics. In this study, we characterise the interaction of SP-A with unmodified (U-PS) and amine-modified (A-PS) polystyrene particles of varying size and zeta potential using dynamic light scatter analysis. SP-A associated with both 100 nm U-PS and A-PS in a calcium-independent manner. SP-A induced significant calcium-dependent agglomeration of 100 nm U-PS NPs but resulted in calcium-independent inhibition of A-PS self agglomeration. SP-A enhanced uptake of 100 nm U-PS into macrophage-like RAW264.7 cells in a dose-dependent manner but in contrast inhibited A-PS uptake. Reduced association of A-PS particles in RAW264.7 cells following pre-incubation of SP-A was also observed with coherent anti-Stokes Raman spectroscopy. Consistent with these findings, alveolar macrophages (AMs) from SP-A(-/-) mice were more efficient at uptake of 100 nm A-PS compared with wild type C57Bl/6 macrophages. No difference in uptake was observed with 500 nm U-PS or A-PS particles. Pre-incubation with SP-A resulted in a significant decrease in uptake of 100 nm A-PS in macrophages isolated from both groups of mice. In contrast, increased uptake by AMs of U-PS was observed after pre-incubation with SP-A. Thus we have demonstrated that SP-A promotes uptake of non-toxic U-PS particles but inhibits the clearance of potentially toxic A-PS particles by blocking uptake into macrophages.

Interaction between the plant ApDef1 defensin and Saccharomyces cerevisiae results in yeast death through a cell cycle- and caspase-dependent process occurring via uncontrolled oxidative stress.

PubMed

Soares, Júlia Ribeiro; José Tenório de Melo, Edésio; da Cunha, Maura; Fernandes, Kátia Valevski Sales; Taveira, Gabriel Bonan; da Silva Pereira, Lidia; Pimenta, Samy; Trindade, Fernanda Gomes; Regente, Mariana; Pinedo, Marcela; de la Canal, Laura; Gomes, Valdirene Moreira; de Oliveira Carvalho, André

2017-01-01

Plant defensins were discovered at beginning of the 90s'; however, their precise mechanism of action is still unknown. Herein, we studied ApDef 1 -Saccharomyces cerevisiae interaction. ApDef 1 -S. cerevisiae interaction was studied by determining the MIC, viability and death kinetic assays. Viability assay was repeated with hydroxyurea synchronized-yeast and pretreated with CCCP. Plasma membrane permeabilization, ROS induction, chromatin condensation, and caspase activation analyses were assessed through Sytox green, DAB, DAPI and FITC-VAD-FMK, respectively. Viability assay was done in presence of ascorbic acid and Z-VAD-FMK. Ultrastructural analysis was done by electron microscopy. ApDef 1 caused S. cerevisiae cell death and MIC was 7.8μM. Whole cell population died after 18h of ApDef 1 interaction. After 3h, 98.76% of synchronized cell population died. Pretreatment with CCCP protected yeast from ApDef 1 induced death. ApDef 1 -S. cerevisiae interaction resulted in membrane permeabilization, H 2 O 2 increased production, chromatin condensation and caspase activation. Ascorbic acid prevented yeast cell death and membrane permeabilization. Z-VAD-FMK prevented yeast cell death. ApDef 1 -S. cerevisiae interaction caused cell death through cell cycle dependentprocess which requires preserved membrane potential. After interaction, yeast went through uncontrolled ROS production and accumulation, which led to plasma membrane permeabilization, chromatin condensation and, ultimately, cell death by activation of caspase-dependent apoptosis via. We show novel requirements for the interaction between plant defensin and fungi cells, i.e. cell cycle phase and membrane potential, and we indicate that membrane permeabilization is probably caused by ROS and therefore, it would be an indirect event of the ApDef 1 -S. cerevisiae interaction. Copyright © 2016 Elsevier B.V. All rights reserved.

Necroptosis: a potential, promising target and switch in acute pancreatitis.

PubMed

Wang, Gang; Qu, Feng-Zhi; Li, Le; Lv, Jia-Chen; Sun, Bei

2016-02-01

Pancreatic acinar cell death is the major pathophysiological change in early acute pancreatitis (AP), and the death modalities are important factors determining its progression and prognosis. During AP, acinar cells undergo two major modes of death, including necrosis and apoptosis. Acinar necrosis can lead to intensely local and systemic inflammatory responses, which both induce and aggravate the lesion. Necrosis has long been considered an unregulated, and passive cell death process. Since the effective interventions of necrosis are difficult to perform, its relevant studies have not received adequate attention. Necroptosis is a newly discovered cell death modality characterized by both necrosis and apoptosis, i.e., it is actively regulated by special genes, while has the typical morphological features of necrosis. Currently, necroptosis is gradually becoming an important topic in the fields of inflammatory diseases. The preliminary results from necroptosis in AP have confirmed the existence of acinar cell necroptosis, which may be a potential target for effectively regulating inflammatory injuries and improving its outcomes; however, the functional changes and mechanisms of necroptosis still require further investigation. This article reviewed the progress of necroptosis in AP to provide a reference for deeply understanding the pathogenic mechanisms of AP and identifying new therapeutic targets.

AP1S3 mutations are associated with pustular psoriasis and impaired Toll-like receptor 3 trafficking.

PubMed

Setta-Kaffetzi, Niovi; Simpson, Michael A; Navarini, Alexander A; Patel, Varsha M; Lu, Hui-Chun; Allen, Michael H; Duckworth, Michael; Bachelez, Hervé; Burden, A David; Choon, Siew-Eng; Griffiths, Christopher E M; Kirby, Brian; Kolios, Antonios; Seyger, Marieke M B; Prins, Christa; Smahi, Asma; Trembath, Richard C; Fraternali, Franca; Smith, Catherine H; Barker, Jonathan N; Capon, Francesca

2014-05-01

Adaptor protein complex 1 (AP-1) is an evolutionary conserved heterotetramer that promotes vesicular trafficking between the trans-Golgi network and the endosomes. The knockout of most murine AP-1 complex subunits is embryonically lethal, so the identification of human disease-associated alleles has the unique potential to deliver insights into gene function. Here, we report two founder mutations (c.11T>G [p.Phe4Cys] and c.97C>T [p.Arg33Trp]) in AP1S3, the gene encoding AP-1 complex subunit σ1C, in 15 unrelated individuals with a severe autoinflammatory skin disorder known as pustular psoriasis. Because the variants are predicted to destabilize the 3D structure of the AP-1 complex, we generated AP1S3-knockdown cell lines to investigate the consequences of AP-1 deficiency in skin keratinocytes. We found that AP1S3 silencing disrupted the endosomal translocation of the innate pattern-recognition receptor TLR-3 (Toll-like receptor 3) and resulted in a marked inhibition of downstream signaling. These findings identify pustular psoriasis as an autoinflammatory phenotype caused by defects in vesicular trafficking and demonstrate a requirement of AP-1 for Toll-like receptor homeostasis. Copyright © 2014 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.

Intestinal Fatty Acid Binding Protein as a Marker of Necrosis and Severity in Acute Pancreatitis.

PubMed

Kupčinskas, Juozas; Gedgaudas, Rolandas; Hartman, Hannes; Sippola, Tomi; Lindström, Outi; Johnson, Colin D; Regnér, Sara

2018-07-01

The aim of this study was to study intestinal fatty acid binding protein (i-FABP) as a potential biomarker in predicting severity of acute pancreatitis (AP). In a prospective multicenter cohort study, plasma levels of i-FABP were measured in 402 patients with AP. Severity of AP was determined based on the 1992 Atlanta Classification. Admission levels of plasma i-FABP were significantly higher in patients with pancreatic necrosis, in patients having systemic complications, in patients treated invasively, in patients treated in the intensive care unit, in patients with severe AP, and in deceased patients. Plasma i-FABP levels on admission yielded an area under curve (AUC) of 0.732 in discriminating patients with or without pancreatic necrosis and AUC of 0.669 in predicting severe AP. Combination of levels of i-FABP and venous lactate on the day of admission showed higher discriminative power in severe AP-AUC of 0.808. Higher i-FABP levels on admission were associated with pancreatic necrosis, systemic complications, and severe AP. Low levels of i-FABP had a high negative predictive value for pancreatic necrosis and severe AP. Combination of levels of i-FABP and venous lactates on admission were superior to either of markers used alone in predicting severe AP.

Amphioxus and lamprey AP-2 genes: implications for neural crest evolution and migration patterns

NASA Technical Reports Server (NTRS)

Meulemans, Daniel; Bronner-Fraser, Marianne

2002-01-01

The neural crest is a uniquely vertebrate cell type present in the most basal vertebrates, but not in cephalochordates. We have studied differences in regulation of the neural crest marker AP-2 across two evolutionary transitions: invertebrate to vertebrate, and agnathan to gnathostome. Isolation and comparison of amphioxus, lamprey and axolotl AP-2 reveals its extensive expansion in the vertebrate dorsal neural tube and pharyngeal arches, implying co-option of AP-2 genes by neural crest cells early in vertebrate evolution. Expression in non-neural ectoderm is a conserved feature in amphioxus and vertebrates, suggesting an ancient role for AP-2 genes in this tissue. There is also common expression in subsets of ventrolateral neurons in the anterior neural tube, consistent with a primitive role in brain development. Comparison of AP-2 expression in axolotl and lamprey suggests an elaboration of cranial neural crest patterning in gnathostomes. However, migration of AP-2-expressing neural crest cells medial to the pharyngeal arch mesoderm appears to be a primitive feature retained in all vertebrates. Because AP-2 has essential roles in cranial neural crest differentiation and proliferation, the co-option of AP-2 by neural crest cells in the vertebrate lineage was a potentially crucial event in vertebrate evolution.

A retrospective, longitudinal study of factors associated with new antipsychotic medication use among recently admitted long-term care residents.

PubMed

Foebel, Andrea; Ballokova, Anna; Wellens, Nathalie I H; Fialova, Daniela; Milisen, Koen; Liperoti, Rosa; Hirdes, John P

2015-10-19

Use of antipsychotic (AP) medications is high and often inappropriate among institutionalized populations. Little is known about the correlates of new AP drug use following admission to long-term care (LTC) settings. This study investigated the frequency and correlates of new AP drug use among newly admitted LTC residents. This longitudinal, retrospective study used data from the interRAI - Nursing Home Minimum Data Set version 2.0 (MDS 2.0) instrument. Data about demographic, clinical and social characteristics, and medication use, were collected in Ontario, Canada, from 2003-2011 by trained nurses. Residents with complete admission and 3-6 month follow-up data were included (N = 47,768). Multivariate logistic regression analyses, stratified by gender, explored correlates of new AP drug use upon admission to LTC. New AP drug users comprised 7 % of the final cohort. Severe cognitive impairment, dementia, and motor agitation were significantly associated with new AP drug use among both sexes. Additionally, behavioural problems, conflicts with staff and reduced social engagement were strong correlates of new AP drug use. Social factors were as strongly associated with new AP drug use after LTC admission as clinical factors. Strategies to prevent the potential misuse of AP drugs upon LTC admission should consider the social determinants of such prescribing.

Shape-selective recognition of DNA abasic sites by metallohelices: inhibition of human AP endonuclease 1

PubMed Central

Malina, Jaroslav; Scott, Peter; Brabec, Viktor

2015-01-01

Loss of a base in DNA leading to creation of an abasic (AP) site leaving a deoxyribose residue in the strand, is a frequent lesion that may occur spontaneously or under the action of various physical and chemical agents. Progress in the understanding of the chemistry and enzymology of abasic DNA largely relies upon the study of AP sites in synthetic duplexes. We report here on interactions of diastereomerically pure metallo–helical ‘flexicate’ complexes, bimetallic triple-stranded ferro-helicates [Fe2(NN-NN)3]4+ incorporating the common NN–NN bis(bidentate) helicand, with short DNA duplexes containing AP sites in different sequence contexts. The results show that the flexicates bind to AP sites in DNA duplexes in a shape-selective manner. They preferentially bind to AP sites flanked by purines on both sides and their binding is enhanced when a pyrimidine is placed in opposite orientation to the lesion. Notably, the Λ-enantiomer binds to all tested AP sites with higher affinity than the Δ-enantiomer. In addition, the binding of the flexicates to AP sites inhibits the activity of human AP endonuclease 1, which is as a valid anticancer drug target. Hence, this finding indicates the potential of utilizing well-defined metallo–helical complexes for cancer chemotherapy. PMID:25940617

Grapefruit juice and its constituents augment colchicine intestinal absorption: potential hazardous interaction and the role of p-glycoprotein.

PubMed

Dahan, Arik; Amidon, Gordon L

2009-04-01

To investigate the potential interaction between grapefruit juice (GFJ) and the oral microtubule polymerization inhibitor colchicine, a P-gp and CYP3A4 substrate. Colchicine intestinal epithelial transport was investigated across Caco-2 cell monolayers in both AP-BL and BL-AP directions, in the absence/presence of known P-gp inhibitors (verapamil and quinidine). The concentration-dependent effects of GFJ and its major constituents (6'-7'-dihydroxybergamottin, naringin and naringenin) on colchicine Caco-2 mucosal secretion were examined. The effect of GFJ on colchicine intestinal-permeability was then investigated in-situ in the rat perfusion model, in both jejunum and ileum. Colchicine exhibited 20-fold higher BL-AP than AP-BL Caco-2 permeability, indicative of net mucosal secretion, which was reduced by verapamil/quinidine. Colchicine AP-BL permeability was increased and BL-AP was decreased by GFJ in a concentration-dependent manner (IC(50) values of 0.75% and 0.46% respectively), suggesting inhibition of efflux transport, rather than metabolizing enzyme. Similar effects obtained following pre-experiment incubation with GFJ, even though the juice was not present throughout the transepithelial study. 6'-7'-Dihydroxybergamottin, naringin and naringenin displayed concentration-dependent inhibition on colchicine BL-AP secretion (IC(50) values of 90, 592 and 11.6 microM respectively). Ten percent GFJ doubled colchicine rat in-situ ileal permeability, and increased 1.5-fold jejunal permeability. The data suggest that GFJ may augment colchicine oral bioavailability. Due to colchicine narrow therapeutic-index and severely toxic side-effects, awareness of this interaction is prudent.

Characteristics of the isomeric flavonoids apigenin and genistein binding to hemoglobin by spectroscopic methods

NASA Astrophysics Data System (ADS)

Yuan, Jiang-Lan; Liu, Hui; Kang, Xu; Lv, Zhong; Zou, Guo-Lin

2008-11-01

Apigenin (Ap) and genistein (Ge), a couple of isomeric flavonoids with extensive bioactivities, are the most common dietary ingredients. They have been widely investigated due to their potential therapeutic actions for some diseases. In our work, binding characteristics of Ap and Ge to hemoglobin (Hb) were analyzed with fluorescence spectroscopy, circular dichroism (CD) and UV-vis absorption spectroscopy. The results indicated that Ap and Ge caused strong fluorescence quenching of Hb by static quenching mechanism, but their quenching efficiency and mechanisms were different. The binding site n suggested that there was a single binding site in Hb for Ap and Ge. The results of synchronous fluorescence showed that the microenvironment around Tyr residues of Hb had a slight trend of polarity decreasing, but the polarity around Trp residues increased by adding Ap. Results of CD indicated that the Ap and Ge did not changed the secondary structure of Hb. According to the theory of Förster resonance energy transfer, the binding distance r between Trp 37 and Ap/Ge was predicted to be 3.4 nm and 3.32 nm, respectively. The affinity of Ge toward Hb was higher than that of Ap.

Evaluation of 99mTc labeled diadenosine tetraphosphate as an atherosclerotic plaque imaging agent in experimental models.

PubMed

Cao, Wei; Zhang, Yongxue; An, Rui

2006-01-01

The potential of 99mTc labeled P1, P4-di (adenosine-5')-tetraphosphate (Ap4A) for imaging experimental atherosclerotic plaques was evaluated in New Zealand white (NZW) rabbits. To label the 99mTc to Ap4A, stannous tartrate solution was used. 99mTc-Ap4A was purified on a Sephadex G-25 column. The radiochemistry purities of 99mTc-Ap4A were 85% to 91%. Biodistribution study revealed 99mTc-Ap4A cleared from blood rapidly. Thirty min after 99mTc-Ap4A administrated on NZW atherosclerotic rabbits, lesion to blood (target/blood, T/B) ratio was 3.17 +/- 1.27, and lesions to normal (target/non-target, T/NT) ratio was 5.23 +/- 1.87. Shadows of atherosclerotic plaques were clearly visible on radioautographic film. Aortas with atherosclerotic plaques also could be seen on ex vivo gamma camera images. Atherosclerotic abdominal aortas were clearly visible on in vivo images 15 min to 3 h after 99mTc-Ap4A administration. 99mTc-labeled Ap4A can be used for rapid noninvasive detection of experimental atherosclerotic plaque.

Changes in intrinsic excitability of ganglion cells in degenerated retinas of RCS rats

PubMed Central

Ren, Yi-Ming; Weng, Chuan-Huang; Zhao, Cong-Jian; Yin, Zheng-Qin

2018-01-01

AIM To evaluate the intrinsic excitability of retinal ganglion cells (RGCs) in degenerated retinas. METHODS The intrinsic excitability of various morphologically defined RGC types using a combination of patch-clamp recording and the Lucifer yellow tracer in retinal whole-mount preparations harvested from Royal College of Surgeons (RCS) rats, a common retinitis pigmentosa (RP) model, in a relatively late stage of retinal degeneration (P90) were investigated. Several parameters of RGC morphologies and action potentials (APs) were measured and compared to those of non-dystrophic control rats, including dendritic stratification, dendritic field diameter, peak amplitude, half width, resting membrane potential, AP threshold, depolarization to threshold, and firing rates. RESULTS Compared with non-dystrophic control RGCs, more depolarizations were required to reach the AP threshold in RCS RGCs with low spontaneous spike rates and in RCS OFF cells (especially A2o cells), and RCS RGCs maintained their dendritic morphologies, resting membrane potentials and capabilities to generate APs. CONCLUSION RGCs are relatively well preserved morphologically and functionally, and some cells are more susceptible to decreased excitability during retinal degeneration. These findings provide valuable considerations for optimizing RP therapeutic strategies. PMID:29862172

Antifouling Activity of Synthetic Alkylpyridinium Polymers Using the Barnacle Model

PubMed Central

Piazza, Veronica; Dragić, Ivanka; Sepčić, Kristina; Faimali, Marco; Garaventa, Francesca; Turk, Tom; Berne, Sabina

2014-01-01

Polymeric alkylpyridinium salts (poly-APS) isolated from the Mediterranean marine sponge, Haliclona (Rhizoniera) sarai, effectively inhibit barnacle larva settlement and natural marine biofilm formation through a non-toxic and reversible mechanism. Potential use of poly-APS-like compounds as antifouling agents led to the chemical synthesis of monomeric and oligomeric 3-alkylpyridinium analogues. However, these are less efficient in settlement assays and have greater toxicity than the natural polymers. Recently, a new chemical synthesis method enabled the production of poly-APS analogues with antibacterial, antifungal and anti-acetylcholinesterase activities. The present study examines the antifouling properties and toxicity of six of these synthetic poly-APS using the barnacle (Amphibalanus amphitrite) as a model (cyprids and II stage nauplii larvae) in settlement, acute and sub-acute toxicity assays. Two compounds, APS8 and APS12-3, show antifouling effects very similar to natural poly-APS, with an anti-settlement effective concentration that inhibits 50% of the cyprid population settlement (EC50) after 24 h of 0.32 mg/L and 0.89 mg/L, respectively. The toxicity of APS8 is negligible, while APS12-3 is three-fold more toxic (24-h LC50: nauplii, 11.60 mg/L; cyprids, 61.13 mg/L) than natural poly-APS. This toxicity of APS12-3 towards nauplii is, however, 60-fold and 1200-fold lower than that of the common co-biocides, Zn- and Cu-pyrithione, respectively. Additionally, exposure to APS12-3 for 24 and 48 h inhibits the naupliar swimming ability with respective IC50 of 4.83 and 1.86 mg/L. PMID:24699112

Acute pancreatitis with gradient echo T2*-weighted magnetic resonance imaging

PubMed Central

Tang, Meng Yue; Chen, Tian Wu; Huang, Xiao Hua; Li, Xing Hui; Wang, Si Yue; Liu, Nian

2016-01-01

Background To study gradient recalled echo (GRE) T2*-weighted imaging (T2*WI) for normal pancreas and acute pancreatitis (AP). Methods Fifty-one patients without any pancreatic disorders (control group) and 117 patients with AP were recruited. T2* values derived from T2*WI of the pancreas were measured for the two groups. The severity of AP was graded by the magnetic resonance severity index (MRSI) and the Acute Physiology and Chronic Healthy Evaluation II (APACHE II) scoring system. Logistic regression was used to analyze the relationship between the T2* values and AP severity. The usefulness of the T2* value for diagnosing AP and the relationship between the T2* values and the severity of AP were analyzed. Results On GRE-T2*WI, the normal pancreas showed a well-marinated and consistently homogeneous isointensity. Edematous AP, as well as the non-necrotic area in necrotizing AP, showed ill-defined but homogeneous signal intensity. AP with pancreatic hemorrhage showed a decreased T2* value and a signal loss on the signal decay curve. The T2* value of pancreas in the AP group was higher than that of the control group (t=−8.20, P<0.05). The T2* value tended to increase along with the increase in MRSI scores but not with the APACHE II scores (P>0.05). AP was associated with a one standard deviation increment in the T2* value (OR =1.37; 95% CI: 1.216–1.532). Conclusions T2*WI demonstrates a few characteristics of the normal pancreas and AP, which could potentially be helpful for detecting hemorrhage, and contributes to diagnosing AP and its severity. PMID:27190768

Risk factor differences in calcified and noncalcified aortic plaque: the Framingham Heart Study.

PubMed

Chuang, Michael L; Gona, Philimon; Oyama-Manabe, Noriko; Manders, Emily S; Salton, Carol J; Hoffmann, Udo; Manning, Warren J; O'Donnell, Christopher J

2014-07-01

The objective of this study was to determine the prevalence and risk factor (RF) correlates of aortic plaque (AP) detected by cardiovascular magnetic resonance (CMR), which mainly shows noncalcified plaques, and by noncontrast computed tomography (CT), which best depicts calcified plaques, in community-dwelling adults. A total of 1016 Framingham Heart Study Offspring cohort members (64 ± 9 years; 474 men) underwent CMR and CT of the aorta. Potential RFs for AP (age; sex; body mass index; blood pressure; low-density lipoprotein and high-density lipoprotein cholesterol; fasting glucose; C-reactive protein; prevalent hypertension, diabetes mellitus, smoking; use of antihypertensive, diabetes mellitus, or lipid-lowering drugs) were compared between participants, with zero versus nonzero AP by CMR and by CT. Candidate RFs attaining P<0.05 for difference with either imaging modality were entered into multivariable logistic regression models adjusting for age, sex, and other RFs. Odds ratios were calculated for modality-specific prevalence of AP. Associations between RFs and continuous measures of AP were assessed using Tobit regression. Prevalence of CMR and CT AP was 49% and 82%, respectively. AP burdens by CMR and CT were correlated, r=0.28, P<0.0001. Increasing age and smoking were associated with prevalent AP by both CMR and CT. Additionally, prevalent AP by CMR was associated with female sex and fasting glucose and prevalent AP by CT with hypertension treatment and adverse lipid profile. AP by CMR and CT are both associated with smoking and increasing age, but other RFs differ between calcified and noncalcified AP. The relative predictive value of AP detected by CMR versus by CT for incident cardiovascular events remains to be determined. © 2014 American Heart Association, Inc.

On the Perceptual Subprocess of Absolute Pitch.

PubMed

Kim, Seung-Goo; Knösche, Thomas R

2017-01-01

Absolute pitch (AP) is the rare ability of musicians to identify the pitch of tonal sound without external reference. While there have been behavioral and neuroimaging studies on the characteristics of AP, how the AP is implemented in human brains remains largely unknown. AP can be viewed as comprising of two subprocesses: perceptual (processing auditory input to extract a pitch chroma) and associative (linking an auditory representation of pitch chroma with a verbal/non-verbal label). In this review, we focus on the nature of the perceptual subprocess of AP. Two different models on how the perceptual subprocess works have been proposed: either via absolute pitch categorization (APC) or based on absolute pitch memory (APM). A major distinction between the two views is that whether the AP uses unique auditory processing (i.e., APC) that exists only in musicians with AP or it is rooted in a common phenomenon (i.e., APM), only with heightened efficiency. We review relevant behavioral and neuroimaging evidence that supports each notion. Lastly, we list open questions and potential ideas to address them.

On the Perceptual Subprocess of Absolute Pitch

PubMed Central

Kim, Seung-Goo; Knösche, Thomas R.

2017-01-01

Absolute pitch (AP) is the rare ability of musicians to identify the pitch of tonal sound without external reference. While there have been behavioral and neuroimaging studies on the characteristics of AP, how the AP is implemented in human brains remains largely unknown. AP can be viewed as comprising of two subprocesses: perceptual (processing auditory input to extract a pitch chroma) and associative (linking an auditory representation of pitch chroma with a verbal/non-verbal label). In this review, we focus on the nature of the perceptual subprocess of AP. Two different models on how the perceptual subprocess works have been proposed: either via absolute pitch categorization (APC) or based on absolute pitch memory (APM). A major distinction between the two views is that whether the AP uses unique auditory processing (i.e., APC) that exists only in musicians with AP or it is rooted in a common phenomenon (i.e., APM), only with heightened efficiency. We review relevant behavioral and neuroimaging evidence that supports each notion. Lastly, we list open questions and potential ideas to address them. PMID:29085275

Contribution of delayed rectifier potassium currents to the electrical activity of murine colonic smooth muscle

PubMed Central

Koh, S D; Ward, S M; Dick, G M; Epperson, A; Bonner, H P; Sanders, K M; Horowitz, B; Kenyon, J L

1999-01-01

We used intracellular microelectrodes to record the membrane potential (Vm) of intact murine colonic smooth muscle. Electrical activity consisted of spike complexes separated by quiescent periods (Vm≈−60 mV). The spike complexes consisted of about a dozen action potentials of approximately 30 mV amplitude. Tetraethylammonium (TEA, 1–10 mM) had little effect on the quiescent periods but increased the amplitude of the action potential spikes. 4-Aminopyridine (4-AP, ⋧ 5 mM) caused continuous spiking.Voltage clamp of isolated myocytes identified delayed rectifier K+ currents that activated rapidly (time to half-maximum current, 11.5 ms at 0 mV) and inactivated in two phases (τf = 96 ms, τs = 1.5 s at 0 mV). The half-activation voltage of the permeability was −27 mV, with significant activation at −50 mV.TEA (10 mM) reduced the outward current at potentials positive to 0 mV. 4-AP (5 mM) reduced the early current but increased outward current at later times (100–500 ms) consistent with block of resting channels relieved by depolarization. 4-AP inhibited outward current at potentials negative to −20 mV, potentials where TEA had no effect.Qualitative PCR amplification of mRNA identified transcripts encoding delayed rectifier K+ channel subunits Kv1.6, Kv4.1, Kv4.2, Kv4.3 and the Kvβ1.1 subunit in murine colon myocytes. mRNA encoding Kv 1.4 was not detected.We find that TEA-sensitive delayed rectifier currents are important determinants of action potential amplitude but not rhythmicity. Delayed rectifier currents sensitive to 4-AP are important determinants of rhythmicity but not action potential amplitude. PMID:10050014

Calcineurin Dysregulation Underlies Spinal Cord Injury-Induced K+ Channel Dysfunction in DRG Neurons.

PubMed

Zemel, Benjamin M; Muqeem, Tanziyah; Brown, Eric V; Goulão, Miguel; Urban, Mark W; Tymanskyj, Stephen R; Lepore, Angelo C; Covarrubias, Manuel

2017-08-23

Dysfunction of the fast-inactivating Kv3.4 potassium current in dorsal root ganglion (DRG) neurons contributes to the hyperexcitability associated with persistent pain induced by spinal cord injury (SCI). However, the underlying mechanism is not known. In light of our previous work demonstrating modulation of the Kv3.4 channel by phosphorylation, we investigated the role of the phosphatase calcineurin (CaN) using electrophysiological, molecular, and imaging approaches in adult female Sprague Dawley rats. Pharmacological inhibition of CaN in small-diameter DRG neurons slowed repolarization of the somatic action potential (AP) and attenuated the Kv3.4 current. Attenuated Kv3.4 currents also exhibited slowed inactivation. We observed similar effects on the recombinant Kv3.4 channel heterologously expressed in Chinese hamster ovary cells, supporting our findings in DRG neurons. Elucidating the molecular basis of these effects, mutation of four previously characterized serines within the Kv3.4 N-terminal inactivation domain eliminated the effects of CaN inhibition on the Kv3.4 current. SCI similarly induced concurrent Kv3.4 current attenuation and slowing of inactivation. Although there was little change in CaN expression and localization after injury, SCI induced upregulation of the native regulator of CaN 1 (RCAN1) in the DRG at the transcript and protein levels. Consistent with CaN inhibition resulting from RCAN1 upregulation, overexpression of RCAN1 in naive DRG neurons recapitulated the effects of pharmacological CaN inhibition on the Kv3.4 current and the AP. Overall, these results demonstrate a novel regulatory pathway that links CaN, RCAN1, and Kv3.4 in DRG neurons. Dysregulation of this pathway might underlie a peripheral mechanism of pain sensitization induced by SCI. SIGNIFICANCE STATEMENT Pain sensitization associated with spinal cord injury (SCI) involves poorly understood maladaptive modulation of neuronal excitability. Although central mechanisms have received significant attention, recent studies have identified peripheral nerve hyperexcitability as a driver of persistent pain signaling after SCI. However, the ion channels and signaling molecules responsible for this change in primary sensory neuron excitability are still not well defined. To address this problem, this study used complementary electrophysiological and molecular methods to determine how Kv3.4, a voltage-gated K + channel robustly expressed in dorsal root ganglion neurons, becomes dysfunctional upon calcineurin (CaN) inhibition. The results strongly suggest that CaN inhibition underlies SCI-induced dysfunction of Kv3.4 and the associated excitability changes through upregulation of the native regulator of CaN 1 (RCAN1). Copyright © 2017 the authors 0270-6474/17/378257-17$15.00/0.

Assessment of cardiac autonomic regulation and ventricular repolarization after off-pump coronary artery bypass grafting.

PubMed

Kalisnik, Jurij M; Avbelj, Viktor; Trobec, Roman; Ivaskovic, Daroslav; Vidmar, Gaj; Troise, Giovanni; Gersak, Borut

2006-01-01

Altered autonomic regulation precipitates cardiac arrhythmias and increases the risk of sudden cardiac death. This risk is further increased by changes in ventricular repolarization. Autonomic regulation is deranged in patients after myocardial on-pump revascularization. We aimed to clarify how off-pump coronary artery bypass grafting (CABG) affects postoperative cardiac autonomic regulation and ventricular repolarization within 4 weeks after CABG. Forty-two patients (mean age, 61.9 +/- 9.3 years; mean EURO score 2.6 +/- 1.9) were electively admitted for off-pump CABG. The electrocardiographic and respiratory waveform recordings were performed in the afternoon in the supine position for 10 minutes. Autonomic modulation was assessed using heart rate variability analysis. Power spectra were computed from 5-minute stable RR intervals using Fourier Transform analysis. Total power of spectra was defined in the range of 0.01 to 0.40 Hz, high-frequency power within 0.15 to 0.40 Hz, and low-frequency power within 0.04 to 0.15 Hz. Normalized power was defined as a ratio of power in each band/total power. The high- and low-frequency power as well as their normalized values indicated cardiac vagal and sympathetic modulation, respectively. Ventricular repolarization was assessed using QT interval, QT interval variability, and QT-RR interdependence analysis. QT intervals were determined from the beginning of the 5-minute segments. QT interval variability was evaluated by a T-wave template-matching algorithm. Pearson correlation between length of RR and QT interval was applied to study QT-RR characteristics. The results were tested for significance using the Fisher exact test, nonpaired t test, and analysis of variance; a P <.05 was considered significant. The frequency of arrhythmic events and heart rate increased from the fourth to the seventh postoperative day and returned to preoperative levels 4 weeks after CABG. Heart rate variability measures indicating autonomic modulation remained depressed even 4 weeks after the procedure. QT variability index increased from -1.2 +/- 0.5 to -0.8 +/- 0.4 on the fourth day after the operation (P <.05) and returned to -1.0 +/- 0.5 4 weeks after CABG (P = not significant). QT-RR correlation decreased from 0.41 to 0.23 (P <.05) and remained significantly impaired as long as 4 weeks after CABG. Observed faster heart rates until 1 week after off-pump CABG imply excessive adrenergic activation, which is comparable to on-pump CABG procedure rates. The results indicate profound autonomic derangement and loss of rate-dependent regulation after off-pump CABG even 4 weeks after operation. Restituted repolarization as assessed by QT variability index 4 weeks postoperatively corresponded with decreased frequency of rhythm disturbances 4 weeks after CABG. The loss of coupling between QT and RR intervals shows increased electrical instability postoperatively, which may serve as an additional promoter for postoperative arrhythmias, especially at higher heart rates.

Istaroxime, a positive inotropic agent devoid of proarrhythmic properties in sensitive chronic atrioventricular block dogs.

PubMed

Bossu, Alexandre; Kostense, Amée; Beekman, Henriette D M; Houtman, Marien J C; van der Heyden, Marcel A G; Vos, Marc A

2018-05-16

Current inotropic agents in heart failure therapy associate with low benefit and significant adverse effects, including ventricular arrhythmias. Istaroxime, a novel Na + /K + -transporting ATPase inhibitor, also stimulates SERCA2a activity, which would confer improved inotropic and lusitropic properties with less proarrhythmic effects. We investigated hemodynamic, electrophysiological and potential proarrhythmic and antiarrhythmic effects of istaroxime in control and chronic atrioventricular block (CAVB) dogs sensitive to drug-induced Torsades de Pointes arrhythmias (TdP). In isolated normal canine ventricular cardiomyocytes, istaroxime (0.3-10 μM) evoked no afterdepolarizations and significantly shortened action potential duration (APD) at 3 and 10 μM. Istaroxime at 3 μg/kg/min significantly increased left ventricular (LV) contractility (dP/dt+) and relaxation (dP/dt-) respectively by 81 and 94% in anesthetized control dogs (n = 6) and by 61 and 49% in anesthetized CAVB dogs (n = 7) sensitive to dofetilide-induced TdP. While istaroxime induced no ventricular arrhythmias in control conditions, only single ectopic beats occurred in 2/7 CAVB dogs, which were preceded by increase of short-term variability of repolarization (STV) and T wave alternans in LV unipolar electrograms. Istaroxime pre-treatment (3 μg/kg/min for 60 min) did not alleviate dofetilide-induced increase in repolarization and STV, and mildly reduced incidence of TdP from 6/6 to 4/6 CAVB dogs. In six CAVB dogs with dofetilide-induced TdP, administration of istaroxime (90 μg/kg/5 min) suppressed arrhythmic episodes in two animals. Taken together, inotropic and lusitropic properties of istaroxime in CAVB dogs were devoid of significant proarrhythmic effects in sensitive CAVB dogs, and istaroxime provides a moderate antiarrhythmic efficacy in prevention and suppression of dofetilide-induced TdP. Copyright © 2018. Published by Elsevier Ltd.

Mitochondrial ROS Drive Sudden Cardiac Death and Chronic Proteome Remodeling in Heart Failure.

PubMed

Dey, Swati; DeMazumder, Deeptankar; Sidor, Agnieszka; Foster, D B; O'Rourke, Brian

2018-06-13

Rationale: Despite increasing prevalence and incidence of heart failure (HF), therapeutic options remain limited. In early stages of HF, sudden cardiac death (SCD) from ventricular arrhythmias claims many lives. Reactive oxygen species (ROS) have been implicated in both arrhythmias and contractile dysfunction. However, little is known about how ROS in specific subcellular compartments contribute to HF or SCD pathophysiology. The role of ROS in chronic proteome remodeling has not been explored. Objective: We will test the hypothesis that elevated mitochondrial ROS (mROS) is a principal source of oxidative stress in HF and in vivo reduction of mROS mitigates SCD. Methods and Results: Using a unique guinea pig model of non-ischemic HF that recapitulates important features of human HF, including prolonged QT interval and high incidence of spontaneous arrhythmic SCD. Compartment-specific ROS sensors revealed increased mROS in resting and contracting left ventricular (LV) myocytes in failing hearts. Importantly, mitochondrially-targeted antioxidant (MitoTEMPO) normalized global cellular ROS. Further, in vivo MitoTEMPO treatment of HF animals prevented and reversed HF; eliminated SCD by decreasing dispersion of repolarization and ventricular arrhythmias; suppressed chronic HF-induced remodeling of the expression proteome; and prevented specific phosphoproteome alterations. Pathway analysis of mROS-sensitive networks indicated that increased mROS in HF disrupts the normal coupling between cytosolic signals and nuclear gene programs driving mitochondrial function, antioxidant enzymes, Ca2+ handling and action potential repolarization, suggesting new targets for therapeutic intervention. Conclusions: mROS drive both acute emergent events, such as electrical instability responsibly for SCD, and those that mediate chronic HF remodeling, characterized by suppression or altered phosphorylation of metabolic, antioxidant and ion transport protein networks. In vivo reduction of mROS prevents and reverses electrical instability, SCD and HF. Our findings support the feasibility of targeting the mitochondria as a potential new therapy for HF and SCD while identifying new mROS-sensitive protein modifications.

Gene-environment interaction between SCN5A-1103Y and hypokalemia influences QT interval prolongation in African Americans: the Jackson Heart Study.

PubMed

Akylbekova, Ermeg L; Payne, John P; Newton-Cheh, Christopher; May, Warren L; Fox, Ervin R; Wilson, James G; Sarpong, Daniel F; Taylor, Herman A; Maher, Joseph F

2014-01-01

African-American ancestry, hypokalemia, and QT interval prolongation on the electrocardiogram are all risk factors for sudden cardiac death (SCD), but their interactions remain to be characterized. SCN5A-1103Y is a common missense variant, of African ancestry, of the cardiac sodium channel gene. SCN5A-1103Y is known to interact with QT-prolonging factors to promote ventricular arrhythmias in persons at high risk for SCD, but its clinical impact in the general African-American population has not been established. We genotyped SCN5A-S1103Y in 4,476 participants of the Jackson Heart Study, a population-based cohort of African Americans. We investigated the effect of SCN5A-1103Y, including interaction with hypokalemia, on QT interval prolongation, a widely-used indicator of prolonged myocardial repolarization and predisposition to SCD. We then evaluated the two sub-components of the QT interval: QRS duration and JT interval. The carrier frequency for SCN5A-1103Y was 15.4%. SCN5A-1103Y was associated with QT interval prolongation (2.7 milliseconds; P < .001) and potentiated the effect of hypokalemia on QT interval prolongation (14.6 milliseconds; P = .02). SCN5A-1103Y had opposing effects on the two sub-components of the QT interval, with shortening of QRS duration (-1.5 milliseconds; P = .001) and prolongation of the JT interval (3.4 milliseconds; P < .001). Hypokalemia was associated with diuretic use (78%; P < .001). SCN5A-1103Y potentiates the effect of hypokalemia on prolonging myocardial repolarization in the general African-American population. These findings have clinical implications for modification of QT prolonging factors, such as hypokalemia, in the 15% of African Americans who are carriers of SCN5A-1103Y. © 2014.

Duration differences of corticostriatal responses in striatal projection neurons depend on calcium activated potassium currents

PubMed Central

Arias-García, Mario A.; Tapia, Dagoberto; Flores-Barrera, Edén; Pérez-Ortega, Jesús E.; Bargas, José; Galarraga, Elvira

2013-01-01

The firing of striatal projection neurons (SPNs) exhibits afterhyperpolarizing potentials (AHPs) that determine discharge frequency. They are in part generated by Ca2+-activated K+-currents involving BK and SK components. It has previously been shown that suprathreshold corticostriatal responses are more prolonged and evoke more action potentials in direct pathway SPNs (dSPNs) than in indirect pathway SPNs (iSPNs). In contrast, iSPNs generate dendritic autoregenerative responses. Using whole cell recordings in brain slices, we asked whether the participation of Ca2+-activated K+-currents plays a role in these responses. Secondly, we asked if these currents may explain some differences in synaptic integration between dSPNs and iSPNs. Neurons obtained from BAC D1 and D2 GFP mice were recorded. We used charybdotoxin and apamin to block BK and SK channels, respectively. Both antagonists increased the depolarization and delayed the repolarization of suprathreshold corticostriatal responses in both neuron classes. We also used NS 1619 and NS 309 (CyPPA), to enhance BK and SK channels, respectively. Current enhancers hyperpolarized and accelerated the repolarization of corticostriatal responses in both neuron classes. Nevertheless, these drugs made evident that the contribution of Ca2+-activated K+-currents was different in dSPNs as compared to iSPNs: in dSPNs their activation was slower as though calcium took a diffusion delay to activate them. In contrast, their activation was fast and then sustained in iSPNs as though calcium flux activates them at the moment of entry. The blockade of Ca2+-activated K+-currents made iSPNs to look as dSPNs. Conversely, their enhancement made dSPNs to look as iSPNs. It is concluded that Ca2+-activated K+-currents are a main intrinsic determinant causing the differences in synaptic integration between corticostriatal polysynaptic responses between dSPNs and iSPNs. PMID:24109439

Andrographis Paniculata shows anti-nociceptive effects in an animal model of sensory hypersensitivity associated with migraine

PubMed Central

Greco, Rosaria; Siani, Francesca; Demartini, Chiara; Zanaboni, Annamaria; Nappi, Giuseppe; Davinelli, Sergio; Scapagnini, Giovanni; Tassorelli, Cristina

2016-01-01

Administration of nitroglycerin (NTG) to rats induces a hyperalgesic condition and neuronal activation of central structures involved in migraine pain. In order to identify therapeutic strategies for migraine pain, we evaluated the anti-nociceptive activity of Andrographis Paniculata (AP), a herbaceous plant, in the hyperalgesia induced by NTG administration in the formalin test. We also analyzed mRNA expression of cytokines in specific brain areas after AP treatment. Male Sprague-Dawley rats were pre-treated with AP extract 30 minutes before NTG or vehicle injection. The data show that AP extract significantly reduced NTG-induced hyperalgesia in phase II of the test, 4 hours after NTG injection. In addition, AP extract reduced IL-6 mRNA expression in the medulla and mesencephalon and also mRNA levels of TNF-alpha in the mesencephalic region. These findings suggest that AP extract may be a potential therapeutic approach in the treatment of general pain, and possibly of migraine. PMID:27027895

Andrographis Paniculata shows anti-nociceptive effects in an animal model of sensory hypersensitivity associated with migraine.

PubMed

Greco, Rosaria; Siani, Francesca; Demartini, Chiara; Zanaboni, Annamaria; Nappi, Giuseppe; Davinelli, Sergio; Scapagnini, Giovanni; Tassorelli, Cristina

2016-01-01

Administration of nitroglycerin (NTG) to rats induces a hyperalgesic condition and neuronal activation of central structures involved in migraine pain. In order to identify therapeutic strategies for migraine pain, we evaluated the anti-nociceptive activity of Andrographis Paniculata (AP), a herbaceous plant, in the hyperalgesia induced by NTG administration in the formalin test. We also analyzed mRNA expression of cytokines in specific brain areas after AP treatment. Male Sprague-Dawley rats were pre-treated with AP extract 30 minutes before NTG or vehicle injection. The data show that AP extract significantly reduced NTG-induced hyperalgesia in phase II of the test, 4 hours after NTG injection. In addition, AP extract reduced IL-6 mRNA expression in the medulla and mesencephalon and also mRNA levels of TNFalpha in the mesencephalic region. These findings suggest that AP extract may be a potential therapeutic approach in the treatment of general pain, and possibly of migraine.

Fabrication and Physical Evaluation of Gelatin-Coated Carbonate Apatite Foam.

PubMed

Hara, Kanae; Fujisawa, Kenji; Nagai, Hirokazu; Takamaru, Natsumi; Ohe, Go; Tsuru, Kanji; Ishikawa, Kunio; Miyamoto, Youji

2016-08-23

Carbonate apatite (CO₃Ap) foam has gained much attention in recent years because of its ability to rapidly replace bone. However, its mechanical strength is extremely low for clinical use. In this study, to understand the potential of gelatin-reinforced CO₃Ap foam for bone replacement, CO₃Ap foam was reinforced with gelatin and the resulting physical characteristics were evaluated. The mechanical strength increased significantly with the gelatin reinforcement. The compressive strength of gelatin-free CO₃Ap foam was 74 kPa whereas that of the gelatin-reinforced CO₃Ap foam, fabricated using 30 mass % gelatin solution, was approximately 3 MPa. Heat treatment for crosslinking gelatin had little effect on the mechanical strength of the foam. The gelatin-reinforced foam did not maintain its shape when immersed in a saline solution as this promoted swelling of the gelatin; however, in the same conditions, the heat-treated gelatin-reinforced foam proved to be stable. It is concluded, therefore, that heat treatment is the key to the fabrication of stable gelatin-reinforced CO₃Ap foam.

Kcne3 deletion initiates extracardiac arrhythmogenesis in mice

PubMed Central

Hu, Zhaoyang; Crump, Shawn M.; Anand, Marie; Kant, Ritu; Levi, Roberto; Abbott, Geoffrey W.

2014-01-01

Mutations in the human KCNE3 potassium channel ancillary subunit gene are associated with life-threatening ventricular arrhythmias. Most genes underlying inherited cardiac arrhythmias, including KCNE3, are not exclusively expressed in the heart, suggesting potentially complex disease etiologies. Here we investigated mechanisms of KCNE3-linked arrhythmogenesis in Kcne3−/− mice using real-time qPCR, echo- and electrocardiography, ventricular myocyte patch-clamp, coronary artery ligation/reperfusion, blood analysis, cardiac synaptosome exocytosis, microarray and pathway analysis, and multitissue histology. Kcne3 transcript was undetectable in adult mouse atria, ventricles, and adrenal glands, but Kcne3−/− mice exhibited 2.3-fold elevated serum aldosterone (P=0.003) and differentially expressed gene networks consistent with an adrenal-targeted autoimmune response. Furthermore, 8/8 Kcne3−/− mice vs. 0/8 Kcne3+/+ mice exhibited an activated-lymphocyte adrenal infiltration (P=0.0002). Kcne3 deletion also caused aldosterone-dependent ventricular repolarization delay (19.6% mean QTc prolongation in females; P<0.05) and aldosterone-dependent predisposition to postischemia arrhythmogenesis. Thus, 5/11 Kcne3−/− mice vs. 0/10 Kcne3+/+ mice exhibited sustained ventricular tachycardia during reperfusion (P<0.05). Kcne3 deletion is therefore arrhythmogenic by a novel mechanism in which secondary hyperaldosteronism, associated with an adrenal-specific lymphocyte infiltration, impairs ventricular repolarization. The findings highlight the importance of considering extracardiac pathogenesis when investigating arrhythmogenic mechanisms, even in inherited, monogenic channelopathies.—Hu, Z., Crump, S. M., Anand, M., Kant, R., Levi, R., Abbott, G. W. Kcne3 deletion initiates extracardiac arrhythmogenesis in mice. PMID:24225147

Leptin decreases heart rate associated with increased ventricular repolarization via its receptor.

PubMed

Lin, Yen-Chang; Huang, Jianying; Hileman, Stan; Martin, Karen H; Hull, Robert; Davis, Mary; Yu, Han-Gang

2015-11-15

Leptin has been proposed to modulate cardiac electrical properties via β-adrenergic receptor activation. The presence of leptin receptors and adipocytes in myocardium raised a question as to whether leptin can directly modulate cardiac electrical properties such as heart rate and QT interval via its receptor. In this work, the role of local direct actions of leptin on heart rate and ventricular repolarization was investigated. We identified the protein expression of leptin receptors at cell surface of sinus node, atrial, and ventricular myocytes isolated from rat heart. Leptin at low doses (0.1-30 μg/kg) decreased resting heart rate; at high doses (150-300 μg/kg), leptin induced a biphasic effect (decrease and then increase) on heart rate. In the presence of high-dose propranolol (30 mg/kg), high-dose leptin only reduced heart rate and sometimes caused sinus pauses and ventricular tachycardia. The leptin-induced inhibition of resting heart rate was fully reversed by leptin antagonist. Leptin also increased heart rate-corrected QT interval (QTc), and leptin antagonist did not. In isolated ventricular myocytes, leptin (0.03-0.3 μg/ml) reversibly increased the action potential duration. These results supported our hypothesis that in addition to indirect pathway via sympathetic tone, leptin can directly decrease heart rate and increase QT interval via its receptor independent of β-adrenergic receptor stimulation. During inhibition of β-adrenergic receptor activity, high concentration of leptin in myocardium can cause deep bradycardia, prolonged QT interval, and ventricular arrhythmias. Copyright © 2015 the American Physiological Society.

Leptin decreases heart rate associated with increased ventricular repolarization via its receptor

PubMed Central

Lin, Yen-Chang; Huang, Jianying; Hileman, Stan; Martin, Karen H.; Hull, Robert; Davis, Mary

2015-01-01

Leptin has been proposed to modulate cardiac electrical properties via β-adrenergic receptor activation. The presence of leptin receptors and adipocytes in myocardium raised a question as to whether leptin can directly modulate cardiac electrical properties such as heart rate and QT interval via its receptor. In this work, the role of local direct actions of leptin on heart rate and ventricular repolarization was investigated. We identified the protein expression of leptin receptors at cell surface of sinus node, atrial, and ventricular myocytes isolated from rat heart. Leptin at low doses (0.1–30 μg/kg) decreased resting heart rate; at high doses (150–300 μg/kg), leptin induced a biphasic effect (decrease and then increase) on heart rate. In the presence of high-dose propranolol (30 mg/kg), high-dose leptin only reduced heart rate and sometimes caused sinus pauses and ventricular tachycardia. The leptin-induced inhibition of resting heart rate was fully reversed by leptin antagonist. Leptin also increased heart rate-corrected QT interval (QTc), and leptin antagonist did not. In isolated ventricular myocytes, leptin (0.03–0.3 μg/ml) reversibly increased the action potential duration. These results supported our hypothesis that in addition to indirect pathway via sympathetic tone, leptin can directly decrease heart rate and increase QT interval via its receptor independent of β-adrenergic receptor stimulation. During inhibition of β-adrenergic receptor activity, high concentration of leptin in myocardium can cause deep bradycardia, prolonged QT interval, and ventricular arrhythmias. PMID:26408544

Bradycardia as a Marker of Chronic Cocaine Use: A Novel Cardiovascular Finding.

PubMed

Sharma, Jyoti; Rathnayaka, Nuvan; Green, Charles; Moeller, F Gerard; Schmitz, Joy M; Shoham, Daniel; Dougherty, Anne Hamilton

2016-01-01

Few studies have examined the effects of chronic cocaine use on the resting surface electrocardiogram (ECG) between exposures to cocaine. Researchers compared 12-lead ECGs from 97 treatment-seeking cocaine-dependent patients, with ECG parameters from 8,513 non-cocaine-using control patients from the Atherosclerosis Risk in Communities study. After matching and adjusting for relevant covariates, cocaine use demonstrated large and statistically reliable effects on early repolarization, bradycardia, severe bradycardia, and heart rate. Current cocaine dependence corresponds to an increased odds of demonstrating early repolarization by a factor of 4.92 and increased odds of bradycardia and severe bradycardia by factors 3.02 and 5.11, respectively. This study demonstrates the novel finding that long-lasting effects of cocaine use on both the cardiac conduction and the autonomic nervous system pose a risk of adverse cardiovascular events between episodes of cocaine use, and that bradycardia is a marker of chronic cocaine use.

Repolarization of hepatocytes in culture.

PubMed

Talamini, M A; Kappus, B; Hubbard, A

1997-01-01

We have evaluated the biochemical, morphological, and functional redevelopment of polarity in freshly isolated hepatocytes cultured using a double layer collagen gel sandwich technique. Western blot analysis showed increased cellular levels of the cell adhesion protein uvomorulin as cultured hepatocytes repolarized. Immunofluorescence studies using antibodies against domain-specific membrane proteins showed polarity as early as 48 hours, although the pattern of the polymeric Immunoglobulin-A receptor (pIgA-R) differed from in vivo liver. Electron microscopy showed developing bile canaliculi at 1 day. However, the functional presence of tight junctions was absent at 1 day, but present at 5 days. We further showed functional polarity to be present at 4 days by documenting the ability of cultured hepatocytes to metabolize and excrete fluorescein diacetate into visible bile canaliculi. We conclude that hepatocytes cultured appropriately develop morphological and functional polarity. Hepatocyte culture is therefore a useful tool for the study of mechanisms responsible for the development of polarized function.

Acute physiology and chronic health evaluation (APACHE II) and Medicare reimbursement

PubMed Central

Wagner, Douglas P.; Draper, Elizabeth A.

1984-01-01

This article describes the potential for the acute physiology score (APS) of acute physiology and chronic health evaluation (APACHE) II, to be used as a severity adjustment to diagnosis-related groups (DRG's) or other diagnostic classifications. The APS is defined by a relative value scale applied to 12 objective physiologic variables routinely measured on most hospitalized patients shortly after hospital admission. For intensive care patients, APS at admission is strongly related to subsequent resource costs of intensive care for 5,790 consecutive admissions to 13 large hospitals, across and within diagnoses. The APS could also be used to evaluate quality of care, medical technology, and the response to changing financial incentives. PMID:10311080

Extracellular NAD+ Suppresses Adrenergic Effects in the Atrial Myocardium of Rats during the Early Postnatal Ontogeny.

PubMed

Pustovit, K B; Ivanova, A D; Kuz'min, V S

2018-05-01

The effects of sympathetic cotransmitter NAD+ (10 μM) on bioelectric activity of the heart under conditions of adrenergic stimulation were studied on isolated spontaneously contracting preparations (without stimulation) of the right atrium from 2-7-day-old rats. Action potentials were recorded in the working myocardium using standard microelectrode technique. Perfusion of the right atrium with norepinephrine solution (1 μM) altered the configuration and significantly lengthened the action potentials. NAD + against the background of norepinephrine stimulation significantly decreased the duration of action potentials, in particular, at 25% repolarization. The effect of purine compounds NAD + , ATP, and adenosine on bioelectrical activity of the heart of newborn rats was studied under basal conditions (without norepinephrine stimulation). The effect of NAD + against the background of adrenergic stimulation was more pronounced than under basal conditions and was probably determined by suppression of I CaL , which can be the main mechanism of NAD + action on rat heart.

Loss of AP-5 results in accumulation of aberrant endolysosomes: defining a new type of lysosomal storage disease

PubMed Central

Hirst, Jennifer; Edgar, James R.; Esteves, Typhaine; Darios, Frédéric; Madeo, Marianna; Chang, Jaerak; Roda, Ricardo H.; Dürr, Alexandra; Anheim, Mathieu; Gellera, Cinzia; Li, Jun; Züchner, Stephan; Mariotti, Caterina; Stevanin, Giovanni; Blackstone, Craig; Kruer, Michael C.; Robinson, Margaret S.

2015-01-01

Adaptor proteins (AP 1–5) are heterotetrameric complexes that facilitate specialized cargo sorting in vesicular-mediated trafficking. Mutations in AP5Z1, encoding a subunit of the AP-5 complex, have been reported to cause hereditary spastic paraplegia (HSP), although their impact at the cellular level has not been assessed. Here we characterize three independent fibroblast lines derived from skin biopsies of patients harbouring nonsense mutations in AP5Z1 and presenting with spastic paraplegia accompanied by neuropathy, parkinsonism and/or cognitive impairment. In all three patient-derived lines, we show that there is complete loss of AP-5 ζ protein and a reduction in the associated AP-5 µ5 protein. Using ultrastructural analysis, we show that these patient-derived lines consistently exhibit abundant multilamellar structures that are positive for markers of endolysosomes and are filled with aberrant storage material organized as exaggerated multilamellar whorls, striated belts and ‘fingerprint bodies’. This phenotype can be replicated in a HeLa cell culture model by siRNA knockdown of AP-5 ζ. The cellular phenotype bears striking resemblance to features described in a number of lysosomal storage diseases (LSDs). Collectively, these findings reveal an emerging picture of the role of AP-5 in endosomal and lysosomal homeostasis, illuminates a potential pathomechanism that is relevant to the role of AP-5 in neurons and expands the understanding of recessive HSPs. Moreover, the resulting accumulation of storage material in endolysosomes leads us to propose that AP-5 deficiency represents a new type of LSDs. PMID:26085577

Endotoxin- and ATP-neutralizing activity of alkaline phosphatase as a strategy to limit neuroinflammation

PubMed Central

2012-01-01

Background Alkaline phosphatase (AP) is a ubiquitously expressed enzyme which can neutralize endotoxin as well as adenosine triphosphate (ATP), an endogenous danger signal released during brain injury. In this study we assessed a potential therapeutic role for AP in inhibiting neuroinflammation using three complementary approaches. Methods Mice were immunized to induce experimental autoimmune encephalomyelitis (EAE) and treated with AP for seven days during different phases of disease. In addition, serological assays to determine AP activity, endotoxin levels and endotoxin-reactive antibodies were performed in a cohort of multiple sclerosis (MS) patients and controls. Finally, the expression of AP and related enzymes CD39 and CD73 was investigated in brain tissue from MS patients and control subjects. Results AP administration during the priming phase, but not during later stages, of EAE significantly reduced neurological signs. This was accompanied by reduced proliferation of splenocytes to the immunogen, myelin oligodendrocyte glycoprotein peptide. In MS patients, AP activity and isoenzyme distribution were similar to controls. Although endotoxin-reactive IgM was reduced in primary-progressive MS patients, plasma endotoxin levels were not different between groups. Finally, unlike AP and CD73, CD39 was highly upregulated on microglia in white matter lesions of patients with MS. Conclusions Our findings demonstrate that: 1) pre-symptomatic AP treatment reduces neurological signs of EAE; 2) MS patients do not have altered circulating levels of AP or endotoxin; and 3) the expression of the AP-like enzyme CD39 is increased on microglia in white matter lesions of MS patients. PMID:23231745

P4-ATPase Requirement for AP-1/Clathrin Function in Protein Transport from the trans-Golgi Network and Early Endosomes

PubMed Central

Liu, Ke; Surendhran, Kavitha; Nothwehr, Steven F.

2008-01-01

Drs2p is a resident type 4 P-type ATPase (P4-ATPase) and potential phospholipid translocase of the trans-Golgi network (TGN) where it has been implicated in clathrin function. However, precise protein transport pathways requiring Drs2p and how it contributes to clathrin-coated vesicle budding remain unclear. Here we show a functional codependence between Drs2p and the AP-1 clathrin adaptor in protein sorting at the TGN and early endosomes of Saccharomyces cerevisiae. Genetic criteria indicate that Drs2p and AP-1 operate in the same pathway and that AP-1 requires Drs2p for function. In addition, we show that loss of AP-1 markedly increases Drs2p trafficking to the plasma membrane, but does not perturb retrieval of Drs2p from the early endosome back to the TGN. Thus AP-1 is required at the TGN to sort Drs2p out of the exocytic pathway, presumably for delivery to the early endosome. Moreover, a conditional allele that inactivates Drs2p phospholipid translocase (flippase) activity disrupts its own transport in this AP-1 pathway. Drs2p physically interacts with AP-1; however, AP-1 and clathrin are both recruited normally to the TGN in drs2Δ cells. These results imply that Drs2p acts independently of coat recruitment to facilitate AP-1/clathrin-coated vesicle budding from the TGN. PMID:18508916

Health in All Policies in South Australia: what has supported early implementation?

PubMed

Delany, Toni; Lawless, Angela; Baum, Frances; Popay, Jennie; Jones, Laura; McDermott, Dennis; Harris, Elizabeth; Broderick, Danny; Marmot, Michael

2016-12-01

Health in All Policies (HiAP) is a policy development approach that facilitates intersectoral responses to addressing the social determinants of health and health equity whilst, at the same time, contributing to policy priorities across the various sectors of government. Given that different models of HiAP have been implemented in at least 16 countries, there is increasing interest in how its effectiveness can be optimized. Much of the existing literature on HiAP remains descriptive, however, and lacks critical, empirically informed analyses of the elements that support implementation. Furthermore, literature on HiAP, and intersectoral action more generally, provides little detail on the practical workings of policy collaborations. This paper contributes empirical findings from a multi-method study of HiAP implementation in South Australia (SA) between 2007 and 2013. It considers the views of public servants and presents analysis of elements that have supported, and impeded, implementation of HiAP in SA. We found that HiAP has been implemented in SA using a combination of interrelated elements. The operation of these elements has provided a strong foundation, which suggests the potential for HiAP to extend beyond being an isolated strategy, to form a more integrated and systemic mechanism of policy-making. We conclude with learnings from the SA experience of HiAP implementation to inform the ongoing development and implementation of HiAP in SA and internationally. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

The soil sulphate effect and maize plant (Zea mays L.) growth of sulphate reducing bacteria (SRB) inoculation in acid sulfate soils with the different soil water condition

NASA Astrophysics Data System (ADS)

Asmarlaili, S.; Rauf, A.; Hanafiah, D. S.; Sudarno, Y.; Abdi, P.

2018-02-01

The objective of the study was to determine the potential application of sulphate reducing bacteria on acid sulfate soil with different water content in the green house. The research was carried out in the Laboratory and Green House, Faculty of Agriculture, Universitas Sumatera Utara. This research used Randomized Block Design with two treatments factors, ie sulphate reducing bacteria (SRB) isolate (control, LK4, LK6, TSM4, TSM3, AP4, AP3, LK4 + TSM3, LK4 + AP4, LK4 + AP3, LK6 + TSM3, LK6 + AP4, LK6 + AP3, TSM4 + TSM3, TSM4 + AP4, TSM4 + AP3) and water condition (100% field capacity and 110% field capacity). The results showed that application of isolate LK4 + AP4 with water condition 110% field capacity decreased the soil sulphate content (27.38 ppm) significantly after 6 weeks. Application of isolate LK4 + AP3 with water condition 110% field capacity increased soil pH (5.58) after-week efficacy 6. Application of isolate LK4 with water condition 110% field capacity increased plant growth (140 cm; 25.74 g) significantly after week 6. The best treatment was application isolate LK4 with water condition 110% field Capacity (SRB population 2.5x108; soil sulphate content 29.10ppm; soil acidity 4.78; plant height 140cm; plant weight 25.74g).

Human stem cell-derived cardiomyocytes detect drug-mediated changes in action potentials and ion currents.

PubMed

Gibson, John K; Yue, Yimei; Bronson, Jared; Palmer, Cassie; Numann, Randy

2014-01-01

It has been proposed that proarrhythmia assessment for safety pharmacology testing includes the use of human pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) to detect drug-induced changes in cardiac electrophysiology. This study measured the actions of diverse agents on action potentials (AP) and ion currents recorded from hiPSC-CM. During AP experiments, the hiPSC-CM were paced at 1Hz during a baseline period, and when increasing concentrations of test compound were administered at 4-minute intervals. AP parameters, including duration (APD60 and APD90), resting membrane potential, rate of rise, and amplitude, were measured throughout the entire experiment. Voltage clamp experiments with E-4031 and nifedipine were similarly conducted. E-4031 produced a dose-dependent prolongation of cardiac action potential and blocked the hERG/IKr current with an IC50 of 17nM. At 3nM, dofetilide significantly increased APD90. Astemizole significantly increased APD60 and APD90 at 30nM. Terfenadine significantly increased APD90 at concentrations greater than 10nM. Fexofenadine, a metabolite of terfenadine, did not produce any electrophysiologic changes in cardiac action potentials. Flecainide produced a dose-dependent prolongation of the cardiac action potential at 1 and 3μM. Acute exposure to nifedipine significantly decreased APD60 and APD90 and produced a dose-dependent block of calcium current with an IC50 of 0.039μM. Verapamil first shortened APD60 and APD90 in a dose-dependent manner, until a compensating increase in APD90, presumably via hERG blockade, was observed at 1 and 3μM. Following a chronic exposure (20-24h) to clinically relevant levels of pentamidine, a significant increase in action potential duration was accompanied by early afterdepolarizations (EADs). These experiments show the ability of AP measured from hiPSC-CM to record the interactions of various ion channels via AP recording and avoid the limitations of using several single ion channel assays in a noncardiac tissue. Copyright © 2014 Elsevier Inc. All rights reserved.

Adenanthera pavonina trypsin inhibitor retard growth of Anagasta kuehniella (Lepidoptera: Pyralidae).

PubMed

Macedo, Maria Lígia Rodrigues; Durigan, Roberta Aparecida; da Silva, Desiree Soares; Marangoni, Sérgio; Freire, Maria das Graças Machado; Parra, José Roberto Postali

2010-04-01

Anagasta kuehniella is a polyphagous pest that feeds on a wide variety of stored products. The possible roles suggested for seed proteinase inhibitors include the function as a part of the plant defensive system against pest via inhibition of their proteolytic enzymes. In this study, a trypsin inhibitor (ApTI) was purified from Adenanthera pavonina seed and was tested for insect growth regulatory effect. The chronic ingestion of ApTI did result in a significant reduction in larval survival and weight. Larval and pupal developmental time of larvae fed on ApTI diet at 1% was significantly longer; the larval period was extended by 5 days and pupal period was 10 days longer, therefore delaying by up to 20 days and resulting in a prolonged period of development from larva to adult. As a result, the ApTI diet emergence rate was only 28% while the emergence rate of control larvae was 80%. The percentage of surviving adults (%S) decreased to 62%. The fourth instar larvae reared on a diet containing 1% ApTI showed a decrease in tryptic activity of gut and that no novel proteolytic form resistant to ApTI was induced. In addition, the tryptic activity in ApTI -fed larvae was sensitive to ApTI. These results suggest that ApTI have a potential antimetabolic effect when ingested by A. kuehniella. (c) 2010 Wiley Periodicals, Inc.

Chinese Herbal Medicines Attenuate Acute Pancreatitis: Pharmacological Activities and Mechanisms

PubMed Central

Xiang, Hong; Zhang, Qingkai; Qi, Bing; Tao, Xufeng; Xia, Shilin; Song, Huiyi; Qu, Jialin; Shang, Dong

2017-01-01

Acute pancreatitis (AP) is a commonly occurring gastrointestinal disorder. An increase in the annual incidence of AP has been observed, and it causes acute hospitalization and high mortality. The diagnosis and treatment guidelines for AP recommend conservative medical treatments focused on reducing pancreatic secretion and secondary injury, as a primary therapeutic approach. Unfortunately, the existing treatment options have limited impact on the incidence and severity of AP due to the complex and multifaceted pathological process of this disease. In recent decades, Chinese herbal medicines (CHMs) have been used as efficient therapeutic agents to attenuate AP in Asian countries. Despite early cell culture, animal models, and clinical trials, CHMs are capable of interacting with numerous molecular targets participating in the pathogenesis of AP; however, comprehensive, up-to-date communication in this field is not yet available. This review focuses on the pharmacological activities of CHMs against AP in vitro and in vivo and the underlying mechanisms. A computational prediction of few selected and promising plant-derived molecules (emodin, baicalin, resveratrol, curcumin, ligustrazine, and honokiol) to target numerous proteins or networks involved in AP was initially established based on a network pharmacology simulation. Moreover, we also summarized some potential toxic natural products for pancreas in order to more safe and reasonable medication. These breakthrough findings may have important implications for innovative drug research and the future development of treatments for AP. PMID:28487653

Kinase activation through dimerization by human SH2-B.

PubMed

Nishi, Masahiro; Werner, Eric D; Oh, Byung-Chul; Frantz, J Daniel; Dhe-Paganon, Sirano; Hansen, Lone; Lee, Jongsoon; Shoelson, Steven E

2005-04-01

The isoforms of SH2-B, APS, and Lnk form a family of signaling proteins that have been described as activators, mediators, or inhibitors of cytokine and growth factor signaling. We now show that the three alternatively spliced isoforms of human SH2-B readily homodimerize in yeast two-hybrid and cellular transfections assays, and this is mediated specifically by a unique domain in its amino terminus. Consistent with previous reports, we further show that the SH2 domains of SH2-B and APS bind JAK2 at Tyr813. These findings suggested a model in which two molecules of SH2-B or APS homodimerize with their SH2 domains bound to two JAK2 molecules, creating heterotetrameric JAK2-(SH2-B)2-JAK2 or JAK2-(APS)2-JAK2 complexes. We further show that APS and SH2-B isoforms heterodimerize. At lower levels of SH2-B or APS expression, dimerization approximates two JAK2 molecules to induce transactivation. At higher relative concentrations of SH2-B or APS, kinase activation is blocked. SH2-B or APS homodimerization and SH2-B/APS heterodimerization thus provide direct mechanisms for activating and inhibiting JAK2 and other kinases from the inside of the cell and for potentiating or attenuating cytokine and growth factor receptor signaling when ligands are present.

Shape-selective recognition of DNA abasic sites by metallohelices: inhibition of human AP endonuclease 1.

PubMed

Malina, Jaroslav; Scott, Peter; Brabec, Viktor

2015-06-23

Loss of a base in DNA leading to creation of an abasic (AP) site leaving a deoxyribose residue in the strand, is a frequent lesion that may occur spontaneously or under the action of various physical and chemical agents. Progress in the understanding of the chemistry and enzymology of abasic DNA largely relies upon the study of AP sites in synthetic duplexes. We report here on interactions of diastereomerically pure metallo-helical 'flexicate' complexes, bimetallic triple-stranded ferro-helicates [Fe2(NN-NN)3](4+) incorporating the common NN-NN bis(bidentate) helicand, with short DNA duplexes containing AP sites in different sequence contexts. The results show that the flexicates bind to AP sites in DNA duplexes in a shape-selective manner. They preferentially bind to AP sites flanked by purines on both sides and their binding is enhanced when a pyrimidine is placed in opposite orientation to the lesion. Notably, the Λ-enantiomer binds to all tested AP sites with higher affinity than the Δ-enantiomer. In addition, the binding of the flexicates to AP sites inhibits the activity of human AP endonuclease 1, which is as a valid anticancer drug target. Hence, this finding indicates the potential of utilizing well-defined metallo-helical complexes for cancer chemotherapy. © The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.

Dynamic modulation of spike timing-dependent calcium influx during corticostriatal upstates

PubMed Central

Evans, R. C.; Maniar, Y. M.

2013-01-01

The striatum of the basal ganglia demonstrates distinctive upstate and downstate membrane potential oscillations during slow-wave sleep and under anesthetic. The upstates generate calcium transients in the dendrites, and the amplitude of these calcium transients depends strongly on the timing of the action potential (AP) within the upstate. Calcium is essential for synaptic plasticity in the striatum, and these large calcium transients during the upstates may control which synapses undergo plastic changes. To investigate the mechanisms that underlie the relationship between calcium and AP timing, we have developed a realistic biophysical model of a medium spiny neuron (MSN). We have implemented sophisticated calcium dynamics including calcium diffusion, buffering, and pump extrusion, which accurately replicate published data. Using this model, we found that either the slow inactivation of dendritic sodium channels (NaSI) or the calcium inactivation of voltage-gated calcium channels (CDI) can cause high calcium corresponding to early APs and lower calcium corresponding to later APs. We found that only CDI can account for the experimental observation that sensitivity to AP timing is dependent on NMDA receptors. Additional simulations demonstrated a mechanism by which MSNs can dynamically modulate their sensitivity to AP timing and show that sensitivity to specifically timed pre- and postsynaptic pairings (as in spike timing-dependent plasticity protocols) is altered by the timing of the pairing within the upstate. These findings have implications for synaptic plasticity in vivo during sleep when the upstate-downstate pattern is prominent in the striatum. PMID:23843436

Alkaline Phosphatases in the Complex Chronic Kidney Disease-Mineral and Bone Disorders.

PubMed

Bover, Jordi; Ureña, Pablo; Aguilar, Armando; Mazzaferro, Sandro; Benito, Silvia; López-Báez, Víctor; Ramos, Alejandra; daSilva, Iara; Cozzolino, Mario

2018-02-14

Alkaline phosphatases (APs) remove the phosphate (dephosphorylation) needed in multiple metabolic processes (from many molecules such as proteins, nucleotides, or pyrophosphate). Therefore, APs are important for bone mineralization but paradoxically they can also be deleterious for other processes, such as vascular calcification and the increasingly known cross-talk between bone and vessels. A proper balance between beneficial and harmful activities is further complicated in the context of chronic kidney disease (CKD). In this narrative review, we will briefly update the complexity of the enzyme, including its different isoforms such as the bone-specific alkaline phosphatase or the most recently discovered B1x. We will also analyze the correlations and potential discrepancies with parathyroid hormone and bone turnover and, most importantly, the valuable recent associations of AP's with cardiovascular disease and/or vascular calcification, and survival. Finally, a basic knowledge of the synthetic and degradation pathways of APs promises to open new therapeutic strategies for the treatment of the CKD-Mineral and Bone Disorder (CKD-MBD) in the near future, as well as for other processes such as sepsis, acute kidney injury, inflammation, endothelial dysfunction, metabolic syndrome or, in diabetes, cardiovascular complications. However, no studies have been done using APs as a primary therapeutic target for clinical outcomes, and therefore, AP's levels cannot yet be used alone as an isolated primary target in the treatment of CKD-MBD. Nonetheless, its diagnostic and prognostic potential should be underlined.

Conditional depletion of intellectual disability and Parkinsonism candidate gene ATP6AP2 in fly and mouse induces cognitive impairment and neurodegeneration

PubMed Central

Dubos, Aline; Castells-Nobau, Anna; Meziane, Hamid; Oortveld, Merel A.W.; Houbaert, Xander; Iacono, Giovanni; Martin, Christelle; Mittelhaeuser, Christophe; Lalanne, Valérie; Kramer, Jamie M.; Bhukel, Anuradha; Quentin, Christine; Slabbert, Jan; Verstreken, Patrik; Sigrist, Stefan J.; Messaddeq, Nadia; Birling, Marie-Christine; Selloum, Mohammed; Stunnenberg, Henk G.; Humeau, Yann; Schenck, Annette; Herault, Yann

2015-01-01

ATP6AP2, an essential accessory component of the vacuolar H+ ATPase (V-ATPase), has been associated with intellectual disability (ID) and Parkinsonism. ATP6AP2 has been implicated in several signalling pathways; however, little is known regarding its role in the nervous system. To decipher its function in behaviour and cognition, we generated and characterized conditional knockdowns of ATP6AP2 in the nervous system of Drosophila and mouse models. In Drosophila, ATP6AP2 knockdown induced defective phototaxis and vacuolated photoreceptor neurons and pigment cells when depleted in eyes and altered short- and long-term memory when depleted in the mushroom body. In mouse, conditional Atp6ap2 deletion in glutamatergic neurons (Atp6ap2Camk2aCre/0 mice) caused increased spontaneous locomotor activity and altered fear memory. Both Drosophila ATP6AP2 knockdown and Atp6ap2Camk2aCre/0 mice presented with presynaptic transmission defects, and with an abnormal number and morphology of synapses. In addition, Atp6ap2Camk2aCre/0 mice showed autophagy defects that led to axonal and neuronal degeneration in the cortex and hippocampus. Surprisingly, axon myelination was affected in our mutant mice, and axonal transport alterations were observed in Drosophila. In accordance with the identified phenotypes across species, genome-wide transcriptome profiling of Atp6ap2Camk2aCre/0 mouse hippocampi revealed dysregulation of genes involved in myelination, action potential, membrane-bound vesicles and motor behaviour. In summary, ATP6AP2 disruption in mouse and fly leads to cognitive impairment and neurodegeneration, mimicking aspects of the neuropathology associated with ATP6AP2 mutations in humans. Our results identify ATP6AP2 as an essential gene for the nervous system. PMID:26376863

Conditional depletion of intellectual disability and Parkinsonism candidate gene ATP6AP2 in fly and mouse induces cognitive impairment and neurodegeneration.

PubMed

Dubos, Aline; Castells-Nobau, Anna; Meziane, Hamid; Oortveld, Merel A W; Houbaert, Xander; Iacono, Giovanni; Martin, Christelle; Mittelhaeuser, Christophe; Lalanne, Valérie; Kramer, Jamie M; Bhukel, Anuradha; Quentin, Christine; Slabbert, Jan; Verstreken, Patrik; Sigrist, Stefan J; Messaddeq, Nadia; Birling, Marie-Christine; Selloum, Mohammed; Stunnenberg, Henk G; Humeau, Yann; Schenck, Annette; Herault, Yann

2015-12-01

ATP6AP2, an essential accessory component of the vacuolar H+ ATPase (V-ATPase), has been associated with intellectual disability (ID) and Parkinsonism. ATP6AP2 has been implicated in several signalling pathways; however, little is known regarding its role in the nervous system. To decipher its function in behaviour and cognition, we generated and characterized conditional knockdowns of ATP6AP2 in the nervous system of Drosophila and mouse models. In Drosophila, ATP6AP2 knockdown induced defective phototaxis and vacuolated photoreceptor neurons and pigment cells when depleted in eyes and altered short- and long-term memory when depleted in the mushroom body. In mouse, conditional Atp6ap2 deletion in glutamatergic neurons (Atp6ap2(Camk2aCre/0) mice) caused increased spontaneous locomotor activity and altered fear memory. Both Drosophila ATP6AP2 knockdown and Atp6ap2(Camk2aCre/0) mice presented with presynaptic transmission defects, and with an abnormal number and morphology of synapses. In addition, Atp6ap2(Camk2aCre/0) mice showed autophagy defects that led to axonal and neuronal degeneration in the cortex and hippocampus. Surprisingly, axon myelination was affected in our mutant mice, and axonal transport alterations were observed in Drosophila. In accordance with the identified phenotypes across species, genome-wide transcriptome profiling of Atp6ap2(Camk2aCre/0) mouse hippocampi revealed dysregulation of genes involved in myelination, action potential, membrane-bound vesicles and motor behaviour. In summary, ATP6AP2 disruption in mouse and fly leads to cognitive impairment and neurodegeneration, mimicking aspects of the neuropathology associated with ATP6AP2 mutations in humans. Our results identify ATP6AP2 as an essential gene for the nervous system. © The Author 2015. Published by Oxford University Press.

Glutathione-S-transferase profiles in the emerald ash borer, Agrilus planipennis.

PubMed

Rajarapu, Swapna Priya; Mittapalli, Omprakash

2013-05-01

The emerald ash borer, Agrilus planipennis Fairmaire is a recently discovered invasive insect pest of ash, Fraxinus spp. in North America. Glutathione-S-transferases (GST) are a multifunctional superfamily of enzymes which function in conjugating toxic compounds to less toxic and excretable forms. In this study, we report the molecular characterization and expression patterns of different classes of GST genes in different tissues and developmental stages plus their specific activity. Multiple sequence alignment of all six A. planipennis GSTs (ApGST-E1, ApGST-E2, ApGST-E3, ApGST-O1, ApGST-S1 and ApGST-μ1) revealed conserved features of insect GSTs and a phylogenetic analysis grouped the GSTs within the epsilon, sigma, omega and microsomal classes of GSTs. Real time quantitative PCR was used to study field collected samples. In larval tissues high mRNA levels for ApGST-E1, ApGST-E3 and ApGST-O1 were obtained in the midgut and Malpighian tubules. On the other hand, ApGST-E2 and ApGST-S1 showed high mRNA levels in fat body and ApGST-μ1 showed constitutive levels in all the tissues assayed. During development, mRNA levels for ApGST-E2 were observed to be the highest in feeding instars, ApGST-S1 in prepupal instars; while the others showed constitutive patterns in all the developmental stages examined. At the enzyme level, total GST activity was similar in all the tissues and developmental stages assayed. Results obtained suggest that A. planipennis is potentially primed with GST-driven detoxification to metabolize ash allelochemicals. To our knowledge this study represents the first report of GSTs in A. planipennis and also in the family of wood boring beetles. Copyright © 2013 Elsevier Inc. All rights reserved.

Mitochondrial Protection and Anti-aging Activity of Astragalus Polysaccharides and Their Potential Mechanism

PubMed Central

Li, Xing-Tai; Zhang, Ya-Kui; Kuang, Hai-Xue; Jin, Feng-Xin; Liu, De-Wen; Gao, Ming-Bo; Liu, Ze; Xin, Xiao-Juan

2012-01-01

The current study was performed to investigate mitochondrial protection and anti-aging activity of Astragalus polysaccharides (APS) and the potential underlying mechanism. Lipid peroxidation of liver and brain mitochondria was induced by Fe2+–Vit C in vitro. Thiobarbituric acid (TBA) colorimetry was used to measure the content of thiobarbituric acid reactive substances (TBARS). Mouse liver mitochondrial permeability transition (PT) was induced by calcium overload in vitro and spectrophotometry was used to measure it. The scavenging activities of APS on superoxide anion (O2•−) and hydroxyl radical (•OH), which were produced by reduced nicotinamide adenine dinucleotide (NADH)—N-Methylphenazonium methyl sulfate (PMS) and hydrogen peroxide (H2O2)–Fe2+ system respectively, were measured by 4-nitrobluetetrazolium chloride (NBT) reduction and Fenton reaction colorimetry respectively. The Na2S2O3 titration method was used to measure the scavenging activities of APS on H2O2. APS could inhibit TBARS production, protect mitochondria from PT, and scavenge O2•−, •OH and H2O2 significantly in a concentration-dependent manner respectively. The back of the neck of mice was injected subcutaneously with D-galactose to induce aging at a dose of 100 mg/kg/d for seven weeks. Moreover, the activities of catalase (CAT), surperoxide dismutase (SOD) and glutathione peroxidase (GPx) and anti-hydroxyl radical which were assayed by using commercial monitoring kits were increased significantly in vivo by APS. According to this research, APS protects mitochondria by scavenging reactive oxygen species (ROS), inhibiting mitochondrial PT and increasing the activities of antioxidases. Therefore, APS has the effect of promoting health. PMID:22408421

The ionic bases of the action potential in isolated mouse cardiac Purkinje cell.

PubMed

Vaidyanathan, Ravi; O'Connell, Ryan P; Deo, Makarand; Milstein, Michelle L; Furspan, Philip; Herron, Todd J; Pandit, Sandeep V; Musa, Hassan; Berenfeld, Omer; Jalife, José; Anumonwo, Justus M B

2013-01-01

Collecting electrophysiological and molecular data from the murine conduction system presents technical challenges. Thus, only little advantage has been taken of numerous genetically engineered murine models to study excitation through the cardiac conduction system of the mouse. To develop an approach for isolating murine cardiac Purkinje cells (PCs), to characterize major ionic currents and to use the data to simulate action potentials (APs) recorded from PCs. Light microscopy was used to isolate and identify PCs from apical and septal cells. Current and voltage clamp techniques were used to record APs and whole cell currents. We then simulated a PC AP on the basis of our experimental data. APs recorded from PCs were significantly longer than those recorded from ventricular cells. The prominent plateau phase of the PC AP was very negative (≈-40 mV). Spontaneous activity was observed only in PCs. The inward rectifier current demonstrated no significant differences compared to ventricular myocytes (VMs). However, sodium current density was larger, and the voltage-gated potassium current density was significantly less in PCs compared with myocytes. T-type Ca(2+) currents (I(Ca,T)) were present in PCs but not VMs. Computer simulations suggest that I(Ca,T) and cytosolic calcium diffusion significantly modulate AP profile recorded in PCs, as compared to VMs. Our study provides the first comprehensive ionic profile of murine PCs. The data show unique features of PC ionic mechanisms that govern its excitation process. Experimental data and numerical modeling results suggest that a smaller voltage-gated potassium current and the presence of I(Ca,T) are important determinants of the longer and relatively negative plateau phase of the APs. Copyright © 2013 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

Electrocardiographic abnormalities and arrhythmic risk markers in adult patients with beta thalassemia major.

PubMed

Kolios, Marios; Korantzopoulos, Panagiotis; Vlahos, Antonios P; Kapsali, Eleni; Briasoulis, Evangelos; Goudevenos, John A

2016-10-15

There seems to be a significant arrhythmia burden in β-thalassemia major (TM) patients without overt cardiomyopathy. Apart from conventional electrocardiographic (ECG) and arrhythmic risk markers we studied novel markers of ventricular repolarization and autonomic imbalance both at rest and after exercise testing. We studied 47 adult TM patients without systolic heart failure and 47 age and sex-matched healthy control subjects. The median age of the studied population was 36 [32-43] years, 57% men. Baseline demographic and clinical characteristics were recorded while 12-lead electrocardiograms, 24-hour ECG Holter recordings, and treadmill exercise stress tests were analyzed. TM patients exhibited increased QTc intervals in both 12-lead ECG recordings and in 24-hour Holter recordings. In addition, they had increased indexes of ventricular repolarization heterogeneity such as QT dispersion, and T peak-to-end/QT ratios. Furthermore, TM patients had decreased indexes of heart rate variability while the heart rate recovery after exercise was significantly attenuated compared to controls. Also, they had increased P wave and QRS duration while the QRS fragmentation was very prevalent. Finally, premature atrial extrasystoles and paroxysmal atrial fibrillation episodes were more frequent in TM patients. TM patients with preserved left ventricular systolic function have several ECG abnormalities including alterations in ventricular depolarization and repolarization. Also, cardiac autonomic dysfunction is evident in 24-hour ECG monitoring as well as in the recovery phase after exercise testing. The prognostic value of specific arrhythmic risk indexes in this setting remains to be elucidated. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Potassium channel KCNH2 K897T polymorphism and cardiac repolarization during exercise test: The Finnish Cardiovascular Study.

PubMed

Koskela, J; Laiho, J; KäHönen, M; Rontu, R; Lehtinen, R; Viik, J; Niemi, M; Niemelä, K; Kööbi, T; Turjanmaa, V; Pörsti, I; Lehtimäki, T; Nieminen, T

2008-01-01

Cardiac repolarization is regulated, in part, by the KCNH2 gene, which encodes a rapidly activating component of the delayed rectifier potassium channel. The gene expresses a functional single nucleotide polymorphism, K897T, which changes the biophysical properties of the channel. The objective of this study was to evaluate whether this polymorphism influences two indices of repolarization--the QT interval and T-wave alternans (TWA)--during different phases of a physical exercise test. The cohort consisted of 1,975 patients undergoing an exercise test during which on-line electrocardiographic data were registered. Information on coronary risk factors and medication was recorded. The 2690A>C nucleotide variation in the KCNH2 gene corresponding to the K897T amino acid change was analysed after polymerase chain reaction with allele-specific TaqMan probes. Among all subjects, the QTc intervals did not differ between the three genotype groups (p> or =0.31, RANOVA). Women with the CC genotype tended to have longer QT intervals during the exercise test, but the difference was statistically significant only at rest (p = 0.011, ANOVA). This difference was also detected when the analysis was adjusted for several factors influencing the QT interval. No statistically significant effects of the K897T polymorphism on TWA were observed among all subjects (p = 0.16, RANOVA), nor in men and women separately. The K897T polymorphism of the KCNH2 gene may not be a major genetic determinant for the TWA, but the influence of the CC genotype on QT interval deserves further research among women.

The analysis of QT interval and repolarization morphology of the heart in chronic exposure to lead.

PubMed

Kiełtucki, J; Dobrakowski, M; Pawlas, N; Średniawa, B; Boroń, M; Kasperczyk, S

2017-10-01

There are no common recommendations regarding electrocardiographic monitoring in occupationally exposed workers. Therefore, the present study was designed to investigate whether exposure to lead results in an increase of selected electrocardiography (ECG) pathologies, such as QT interval prolongation and repolarization disorders, in occupationally exposed workers. The study group included 180 workers occupationally exposed to lead compounds. The exposed group was divided according to the median of the mean blood lead level (PbB mean ) calculated based on a series of measurements performed during 5-year observation period (35 µg/dl) into two subgroups: low exposure (LE, PbB mean = 20.0-35.0 µg/dl) and high exposure (HE, PbB mean = 35.1-46.4 µg/dl). The control group consisted of 69 healthy workers without occupational exposure to lead. ECG evaluation included the analysis of heart rate (HR), QT interval and repolarization abnormalities. Mean QT interval was significantly greater in the exposed population than in the control group by 2%. In the HE group, mean QT interval was significantly greater than in the control group by 4% and significantly different from those noted in the LE group. Positive correlations between QT interval and lead exposure indices were also reported. Besides, there was a negative correlation between HR and blood lead level. Increased concentration of lead in the blood above 35 μg/dl is associated with the QT interval prolongation, which may trigger arrhythmias when combined with other abnormalities, such as long QT syndrome. Therefore, electrocardiographic evaluation should be a part of a routine monitoring of occupationally exposed populations.

Recent advances in understanding sex differences in cardiac repolarization.

PubMed

James, Andrew F; Choisy, Stéphanie C M; Hancox, Jules C

2007-07-01

A number of gender differences exist in the human electrocardiogram (ECG): the P-wave and P-R intervals are slightly longer in men than in women, whilst women have higher resting heart rates than do men, but a longer rate-corrected QT (QT(C)) interval. Women with the LQT1 and LQT2 variants of congenital long-QT syndrome (LQTS) are at greater risk of adverse cardiac events. Similarly, many drugs associated with acquired LQTS have a greater risk of inducing torsades de pointes (TdP) arrhythmia in women than in men. There are also male:female differences in Brugada syndrome, early repolarisation syndrome and sudden cardiac death. The differences in the ECG between men and women, and in particular those relating to the QT interval, have been explored experimentally and provide evidence of differences in the processes underlying ventricular repolarization. The data available from rabbit, canine, rat, mouse and guinea pig models are reviewed and highlight involvement of male:female differences in Ca and K currents, although the possible involvement of rapid and persistent Na current and Na-Ca exchange currents cannot yet be excluded. The mechanisms underlying observed differences remain to be elucidated fully, but are likely to involve the influence of gonadal steroids. With respect to the QT interval and risk of TdP, a range of evidence implicates a protective role of testosterone in male hearts, possibly by both genomic and non-genomic pathways. Evidence regarding oestrogen and progesterone is less unequivocal, although the interplay between these two hormones may influence both repolarization and pro-arrhythmic risk.

Understanding and treating amotivation in people with psychosis: An experimental study of the role of guided imagery.

PubMed

Cox, Charlotte; Jolley, Suzanne; Johns, Louise

2016-12-30

Psychological models propose that the amotivational negative symptoms (ANS) of psychosis are influenced by expectations of future events; both anticipatory success (believing one can achieve something, AS) and anticipatory pleasure (mentally pre-creating potential future experiences of enjoyment, AP). Mental imagery manipulations have been shown to change expectations across a range of settings, and may therefore enhance psychological interventions for ANS in people with psychosis. We set out to investigate the impact of a guided imagery manipulation on AS and AP in this group. Forty-two participants with psychosis and ANS completed measures of ANS severity, before random allocation to either a positive or neutral imagery manipulation. AS and AP towards a dart-throwing task were measured before and after the manipulation. Greater ANS severity was associated with lower levels of AS, but not of AP, irrespective of task performance. AS, but not AP, improved during both positive and neutral imagery manipulations, with no effect of imagery type. Anticipatory success is a candidate psychological factor influencing the severity of ANS in psychosis that may be changed by guided imagery manipulation. Imagery interventions are feasible and acceptable for this group: further investigation is needed of their mechanism of action and potential to improve functioning. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

AP-1-mediated chromatin looping regulates ZEB2 transcription: new insights into TNFα-induced epithelial-mesenchymal transition in triple-negative breast cancer.

PubMed

Qiao, Yichun; Shiue, Chiou-Nan; Zhu, Jian; Zhuang, Ting; Jonsson, Philip; Wright, Anthony P H; Zhao, Chunyan; Dahlman-Wright, Karin

2015-04-10

The molecular determinants of malignant cell behaviour in triple-negative breast cancer (TNBC) are poorly understood. Recent studies have shown that regulators of epithelial-mesenchymal transition (EMT) are potential therapeutic targets for TNBC. In this study, we demonstrate that the inflammatory cytokine TNFα induces EMT in TNBC cells via activation of AP-1 signaling and subsequently induces expression of the EMT regulator ZEB2. We also show that TNFα activates both the PI3K/Akt and MAPK/ERK pathways, which act upstream of AP-1. We further investigated in detail AP-1 regulation of ZEB2 expression. We show that two ZEB2 transcripts derived from distinct promoters are both expressed in breast cancer cell lines and breast tumor samples. Using the chromosome conformation capture assay, we demonstrate that AP-1, when activated by TNFα, binds to a site in promoter 1b of the ZEB2 gene where it regulates the expression of both promoter 1b and 1a, the latter via mediating long range chromatin interactions. Overall, this work provides a plausible mechanism for inflammation-induced metastatic potential in TNBC, involving a novel regulatory mechanism governing ZEB2 isoform expression.

AP-1-mediated chromatin looping regulates ZEB2 transcription: new insights into TNFα-induced epithelial–mesenchymal transition in triple-negative breast cancer

PubMed Central

Qiao, Yichun; Shiue, Chiou-Nan; Zhu, Jian; Zhuang, Ting; Jonsson, Philip; Wright, Anthony P.H.; Zhao, Chunyan; Dahlman-Wright, Karin

2015-01-01

The molecular determinants of malignant cell behaviour in triple-negative breast cancer (TNBC) are poorly understood. Recent studies have shown that regulators of epithelial-mesenchymal transition (EMT) are potential therapeutic targets for TNBC. In this study, we demonstrate that the inflammatory cytokine TNFα induces EMT in TNBC cells via activation of AP-1 signaling and subsequently induces expression of the EMT regulator ZEB2. We also show that TNFα activates both the PI3K/Akt and MAPK/ERK pathways, which act upstream of AP-1. We further investigated in detail AP-1 regulation of ZEB2 expression. We show that two ZEB2 transcripts derived from distinct promoters are both expressed in breast cancer cell lines and breast tumor samples. Using the chromosome conformation capture assay, we demonstrate that AP-1, when activated by TNFα, binds to a site in promoter 1b of the ZEB2 gene where it regulates the expression of both promoter 1b and 1a, the latter via mediating long range chromatin interactions. Overall, this work provides a plausible mechanism for inflammation-induced metastatic potential in TNBC, involving a novel regulatory mechanism governing ZEB2 isoform expression. PMID:25762639

Covariation of axon initial segment location and dendritic tree normalizes the somatic action potential

PubMed Central

Hamada, Mustafa S.; Goethals, Sarah; de Vries, Sharon I.; Brette, Romain

2016-01-01

In mammalian neurons, the axon initial segment (AIS) electrically connects the somatodendritic compartment with the axon and converts the incoming synaptic voltage changes into a temporally precise action potential (AP) output code. Although axons often emanate directly from the soma, they may also originate more distally from a dendrite, the implications of which are not well-understood. Here, we show that one-third of the thick-tufted layer 5 pyramidal neurons have an axon originating from a dendrite and are characterized by a reduced dendritic complexity and thinner main apical dendrite. Unexpectedly, the rising phase of somatic APs is electrically indistinguishable between neurons with a somatic or a dendritic axon origin. Cable analysis of the neurons indicated that the axonal axial current is inversely proportional to the AIS distance, denoting the path length between the soma and the start of the AIS, and to produce invariant somatic APs, it must scale with the local somatodendritic capacitance. In agreement, AIS distance inversely correlates with the apical dendrite diameter, and model simulations confirmed that the covariation suffices to normalize the somatic AP waveform. Therefore, in pyramidal neurons, the AIS location is finely tuned with the somatodendritic capacitive load, serving as a homeostatic regulation of the somatic AP in the face of diverse neuronal morphologies. PMID:27930291

Lecithin-based microemulsions for targeted delivery of ceramide AP into the stratum corneum: formulation, characterizations, and in vitro release and penetration studies.

PubMed

Sahle, Fitsum F; Metz, Hendrik; Wohlrab, Johannes; Neubert, Reinhard H H

2013-02-01

To improve the solubility and penetration of Ceramide AP (CER [AP]) into the stratum corneum that potentially restores the barrier function of aged and affected skin. CER [AP] microemulsions (MEs) were formulated using lecithin, Miglyol® 812 (miglyol) and water-1,2 pentandiol (PeG) mixture as amphiphilic, oily and hydrophilic components, respectively. The nanostructure of the MEs was revealed using electrical conductivity, differential scanning calorimeter (DSC) and electron paramagnetic resonance (EPR) techniques. Photon correlation spectroscopy (PCS) was used to measure the sizes and shape of ME droplets. The release and penetration of the CER into the stratum corneum was investigated in vitro using a multi-layer membrane model. The MEs exhibited excellent thermodynamic stability (>2 years) and loading capacity (0.5% CER [AP]). The pseudo-ternary phase diagrams of the MEs were obtained and PCS results showed that the droplets are spherical in shape and bigger in size. In vitro investigations showed that the MEs exhibited excellent rate and extent of release and penetration. Stable lecithin-based CER [AP] MEs that significantly enhance the solubility and penetration of CER [AP] into the stratum corneum were developed. The MEs also have better properties than the previously reported polyglycerol fatty acid surfactant-based CER [AP] MEs.

Effect of knockout of α2δ-1 on action potentials in mouse sensory neurons.

PubMed

Margas, Wojciech; Ferron, Laurent; Nieto-Rostro, Manuela; Schwartz, Arnold; Dolphin, Annette C

2016-08-05

Gene deletion of the voltage-gated calcium channel auxiliary subunit α2δ-1 has been shown previously to have a cardiovascular phenotype, and a reduction in mechano- and cold sensitivity, coupled with delayed development of neuropathic allodynia. We have also previously shown that dorsal root ganglion (DRG) neuron calcium channel currents were significantly reduced in α2δ-1 knockout mice. To extend our findings in these sensory neurons, we have examined here the properties of action potentials (APs) in DRG neurons from α2δ-1 knockout mice in comparison to their wild-type (WT) littermates, in order to dissect how the calcium channels that are affected by α2δ-1 knockout are involved in setting the duration of individual APs and their firing frequency. Our main findings are that there is reduced Ca(2+) entry on single AP stimulation, particularly in the axon proximal segment, reduced AP duration and reduced firing frequency to a 400 ms stimulation in α2δ-1 knockout neurons, consistent with the expected role of voltage-gated calcium channels in these events. Furthermore, lower intracellular Ca(2+) buffering also resulted in reduced AP duration, and a lower frequency of AP firing in WT neurons, mimicking the effect of α2δ-1 knockout. By contrast, we did not obtain any consistent evidence for the involvement of Ca(2+)-activation of large conductance calcium-activated potassium (BK) and small conductance calcium-activated potassium (SK) channels in these events. In conclusion, the reduced Ca(2+) elevation as a result of single AP stimulation is likely to result from the reduced duration of the AP in α2δ-1 knockout sensory neurons.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'. © 2016 The Authors.

New descriptors of homogeneity of the propagation of ventricular repolarization.

PubMed

Batchvarov, V; Dilaveris, P; Färbom, P; Ghuran, A; Acar, B; Hnatkova, K; Camm, A J; Malik, M

2000-11-01

Available descriptors of irregularities of ventricular repolarization are of limited clinical value. We studied the effect of autonomic variations on several new descriptors of the three-dimensional T loop. Twelve-lead digital ECGs were recorded continuously in 40 healthy subjects at baseline in the supine position, during postural changes (supine-->sitting-->standing-->supine-->standing), and during Valsalva maneuver performed three times in the supine and three times in the standing positions. A minimum dimensional space was constructed from the 12-lead ECG, using singular value decomposition, on the basis of median ECG beats constructed from 10-second consecutive ECG recordings. Temporal variations (TLA and PL, which measure the T loop area, and LD, the interlead relationship during repolarization) and wavefront direction descriptors (TCRT, the deviation between the QRS and T vectors) were calculated and expressed as normalized values. Values of TLA, PL, and TCRT were significantly lower in the sitting than in the supine position (-38,139 +/- 9099 vs 47,133 +/- 7511, -0.017 +/- 0.005 vs 0.033 +/- 0.005 and -0.032 +/- 0.019 vs 0.071 +/- 0.015, respectively, P < 0.001 for all) and decreased further in the standing position (-88,288 +/- 14,468, -0.067 +/- 0.013, -0.198 +/- 0.025, respectively, P < 0.001 for all). LD increased from supine to sitting (98.7 +/- 29.4 vs -87.5 +/- 15.2, P < 0.001) and increased further, though nonsignificantly in the standing position (118.3 +/- 35.2). TLA, PL, and TCRT decreased from baseline during Valsalva in the supine (-34,118 +/- 11,424 vs 62,234 +/- 12,215, -0.038 +/- 0.014 vs 0.065 +/- 0.010, -0.08 +/- 0.03 vs 0.10 +/- 0.02, respectively, P < 0.001 for all) and standing positions (-108,263 +/- 21,051 vs -68,909 +/- 10,271, -0.109 +/- 0.014 vs -0.048 +/- 0.009, -0.30 +/- 0.035 vs -015 +/- 0.016, respectively, P < 0.05 for all). LD was significantly increased by Valsalva in the supine position (13 +/- 46 vs -153 +/- 30, P < 0.001) and nonsignificantly in the standing position (99 +/- 50 vs 86 +/- 30, P = NS). There were significant correlations among TLA, PL, and LD, and no significant correlation between TCRT and any of the temporal variation descriptors. These new temporal and wavefront direction descriptors are sensitive and rapid detectors of autonomic effects on ventricular repolarization.

QUEST: Qualifying Environmentally Sustainable Technologies

NASA Technical Reports Server (NTRS)

2006-01-01

Over the years, pollution prevention has proven to be a means to comply with environmental regulations, improve product performance and reduce costs. The NASA Acquisition Pollution Prevention (AP2) Program was created to help individual NASA Centers and programs work together to evaluate and adopt environmentally preferable technologies and practices. The AP2 Program accomplishes its mission using a variety of tools such as networking, information/technology exchange and partnering. Due to its extensive network of contacts, the AP2 Program is an excellent resource for finding existing solutions to problems. If no solution is readily known, the AP2 Program works to identify potential solutions and partners for demonstration/ validation projects. Partnering to prevent pollution is a cornerstone of NASA's prime mission and the One NASA Initiative. This annual newsletter highlights some of our program's collaborative efforts. I believe you will discover how the AP2 Program is responsive in meeting the Agency's environmental management strategic plans.

Diversity of layer 5 projection neurons in the mouse motor cortex

PubMed Central

Oswald, Manfred J.; Tantirigama, Malinda L. S.; Sonntag, Ivo; Hughes, Stephanie M.; Empson, Ruth M.

2013-01-01

In the primary motor cortex (M1), layer 5 projection neurons signal directly to distant motor structures to drive movement. Despite their pivotal position and acknowledged diversity these neurons are traditionally separated into broad commissural and corticofugal types, and until now no attempt has been made at resolving the basis for their diversity. We therefore probed the electrophysiological and morphological properties of retrogradely labeled M1 corticospinal (CSp), corticothalamic (CTh), and commissural projecting corticostriatal (CStr) and corticocortical (CC) neurons. An unsupervised cluster analysis established at least four phenotypes with additional differences between lumbar and cervical projecting CSp neurons. Distinguishing parameters included the action potential (AP) waveform, firing behavior, the hyperpolarisation-activated sag potential, sublayer position, and soma and dendrite size. CTh neurons differed from CSp neurons in showing spike frequency acceleration and a greater sag potential. CStr neurons had the lowest AP amplitude and maximum rise rate of all neurons. Temperature influenced spike train behavior in corticofugal neurons. At 26°C CTh neurons fired bursts of APs more often than CSp neurons, but at 36°C both groups fired regular APs. Our findings provide reliable phenotypic fingerprints to identify distinct M1 projection neuron classes as a tool to understand their unique contributions to motor function. PMID:24137110

The interaction of diadenosine polyphosphates with P2x-receptors in the guinea-pig isolated vas deferens.

PubMed

Westfall, T D; McIntyre, C A; Obeid, S; Bowes, J; Kennedy, C; Sneddon, P

1997-05-01

1. The site(s) at which diadenosine 5',5"'-P1,P4-tetraphosphate (AP4A) and diadenosine 5', 5"'-P1,P5-pentaphosphate (AP5A) act to evoke contraction of the guinea-pig isolated vas deferens was studied by use of a series of P2-receptor antagonists and the ecto-ATPase inhibitor 6-N,N-diethyl-D-beta,gamma-dibromomethyleneATP (ARL 67156). 2. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (300 nM - 30 microM), suramin (3-100 microM) and pyridoxal-5'-phosphate (P-5-P) (3-1000 microM) inhibited contractions evoked by equi-effective concentrations of AP5A (3 microM), AP4A (30 microM) and alpha,beta-methyleneATP (alpha,beta-meATP) (1 microM), in a concentration-dependent manner and abolished them at the highest concentrations used. 3. PPADS was more potent than suramin, which in turn was more potent than P-5-P. PPADS inhibited AP5A, AP4A and alpha,beta-meATP with similar IC50 values. No significant difference was found between IC50 values for suramin against alpha,beta-meATP and AP5A or alpha,beta-meATP and AP4A, but suramin was more than 2.5 times more potent against AP4A than AP5A. P-5-P showed the same pattern of antagonism. 4. Desensitization of the P2xi-receptor by alpha,beta-meATP abolished contractions evoked by AP5A (3 microM) and AP4A (30 microM), but had no effect on those elicited by noradrenaline (100 microM). 5. ARL 67156 (100 microM) reversibly potentiated contractions evoked by AP4A (30 microM) by 61%, but caused a small, significant decrease in the mean response to AP5A (3 microM). 6. It is concluded that AP4A and AP5A act at the P2xi-receptor, or a site similar to the P2xi-receptor, to evoke contraction of the guinea-pig isolated vas deferens. Furthermore, the potency of AP4A, but not AP5A, appears to be inhibited by an ecto-enzyme which is sensitive to ARL 67156.

Molecular characterization and specific detection of Anaplasma species (AP-sd) in sika deer and its first detection in wild brown bears and rodents in Hokkaido, Japan.

PubMed

Moustafa, Mohamed Abdallah Mohamed; Lee, Kyunglee; Taylor, Kyle; Nakao, Ryo; Sashika, Mariko; Shimozuru, Michito; Tsubota, Toshio

2015-12-01

A previously undescribed Anaplasma species (herein referred to as AP-sd) has been detected in sika deer, cattle and ticks in Japan. Despite being highly similar to some strains of A. phagocytophilum, AP-sd has never been detected in humans. Its ambiguous epidemiology and the lack of tools for its specific detection make it difficult to understand and interpret the prevalence of this Anaplasma species. We developed a method for specific detection, and examined AP-sd prevalence in Hokkaido wildlife. Our study included 250 sika deer (Cervus nippon yesoensis), 13 brown bears (Ursus arctos yesoensis) and 252 rodents including 138 (Apodemus speciosus), 45 (Apodemus argenteus), 42 (Myodes rufocanus) and 27 (Myodes rutilus) were collected from Hokkaido island, northern Japan, collected during 2010 to 2015. A 770 bp and 382 bp segment of the 16S rRNA and gltA genes, respectively, were amplified by nested PCR. Results were confirmed by cloning and sequencing of the positive PCR products. A reverse line blot hybridization (RLB) based on the 16S rRNA gene was then developed for the specific detection of AP-sd. The prevalence of AP-sd by nested PCR in sika deer was 51% (128/250). We detected this Anaplasma sp. for the first time in wild brown bears and rodents with a prevalence of 15% (2/13) and 2.4% (6/252), respectively. The sequencing results of the 16S rRNA and gltA gene amplicons were divergent from the selected A. phagocytophilum sequences in GenBank. Using a newly designed AP-sd specific probe for RLB has enabled us to specifically detect this Anaplasma species. Besides sika deer and cattle, wild brown bears and rodents were identified as potential reservoir hosts for AP-sd. This study provided a high throughput molecular method that specifically detects AP-sd, and which can be used to investigate its ecology and its potential as a threat to humans in Japan. Copyright © 2015 Elsevier B.V. All rights reserved.

Experimental and clinical evidence of antioxidant therapy in acute pancreatitis

PubMed Central

Esrefoglu, Mukaddes

2012-01-01

Oxidative stress has been shown to play an important role in the pathogenesis of acute pancreatitis (AP). Antioxidants, alone or in combination with conventional therapy, should improve oxidative-stress-induced organ damage and therefore accelerate the rate of recovery. In recent years, substantial amounts of data about the efficiency of antioxidants against oxidative damage have been obtained from experiments with rodents. Some of these antioxidants have been found beneficial in the treatment of AP in humans; however, at present there is insufficient clinical data to support the benefits of antioxidants, alone or in combination with conventional therapy, in the management of AP in humans. Conflicting results obtained from experimental animals and humans may represent distinct pathophysiological mechanisms mediating tissue injury in different species. Further detailed studies should be done to clarify the exact mechanisms of tissue injury in human AP. Herein I tried to review the existing experimental and clinical studies on AP in order to determine the efficiency of antioxidants. The use of antioxidant enriched nutrition is a potential direction of clinical research in AP given the lack of clues about the efficiency and safety of antioxidant usage in patients with AP. PMID:23112545

Biotransformation of potentially persistent alkylphenols in natural seawater.

PubMed

Lofthus, Synnøve; Almås, Inger K; Evans, Peter; Pelz, Oliver; Brakstad, Odd Gunnar

2016-08-01

Produced water (PW) discharged to the marine environment may contain both natural substances and industrial chemicals that are potentially persistent, bioaccumulating and toxic (PBT). Identification of substances as PBT is dependent upon accurate assessment of biodegradation rates, but these measurements can be impeded where substances exhibit inherently low solubility in water. Examples of substances of this kind include some alkylated phenols (APs). Biotransformation of three APs, suspected to be PBT compounds in PW, was investigated by adopting a new methodology in which they were immobilized to hydrophobic adsorbents submerged in natural seawater. These compounds were not ready biodegradable by conventional screening biochemical oxygen demand (BOD) methods at high concentrations (2 mg/L). However, potential biodegradability for two of the three APs were demonstrated by the immobilization method at low concentrations (appr. 100 μg/L), with biotransformation half-lives <50 days. Thus, standard screening tests should be supplemented by biodegradation methods suited for testing of poorly soluble substances before the persistence of potential PBT substances are defined. Copyright © 2016 Elsevier Ltd. All rights reserved.

High-performance space shuttle auxiliary propellant valve system

NASA Technical Reports Server (NTRS)

Smith, G. M.

1973-01-01

Several potential valve closures for the space shuttle auxiliary propulsion system (SS/APS) were investigated analytically and experimentally in a modeling program. The most promising of these were analyzed and experimentally evaluated in a full-size functional valve test fixture of novel design. The engineering investigations conducted for both model and scale evaluations of the SS/APS valve closures and functional valve fixture are described. Preliminary designs, laboratory tests, and overall valve test fixture designs are presented, and a final recommended flightweight SS/APS valve design is presented.

Circulating microRNAs as biomarkers of disease and typification of the atherothrombotic status in antiphospholipid syndrome

PubMed Central

Pérez-Sánchez, Carlos; Arias-de la Rosa, Iván; Aguirre, María Ángeles; Luque-Tévar, María; Ruiz-Limón, Patricia; Barbarroja, Nuria; Jiménez-Gómez, Yolanda; Ábalos-Aguilera, María Carmen; Collantes-Estévez, Eduardo; Segui, Pedro; Velasco, Francisco; Herranz, María Teresa; Lozano-Herrero, Jesús; Hernandez-Vidal, María Julia; Martínez, Constantino; González-Conejero, Rocío; Radin, Massimo; Sciascia, Savino; Cecchi, Irene; Cuadrado, María José; López-Pedrera, Chary

2018-01-01

We aimed to identify the plasma miRNA profile of antiphospholipid syndrome (APS) patients and to investigate the potential role of specific circulating miRNAs as non-invasive disease biomarkers. Ninety APS patients and 42 healthy donors were recruited. Profiling of miRNAs by PCR-array in plasma of APS patients identified a set of miRNAs differentially expressed and collectively involved in clinical features. Logistic regression and ROC analysis identified a signature of 10 miRNA ratios as biomarkers of disease. In addition, miRNA signature was related to fetal loss, atherosclerosis, and type of thrombosis, and correlated with parameters linked to inflammation, thrombosis, and autoimmunity. Hard clustering analysis differentiated 3 clusters representing different thrombotic risk profile groups. Significant differences between groups for several miRNA ratios were found. Moreover, miRNA signature remained stable over time, demonstrated by their analysis three months after the first sample collection. Parallel analysis in two additional cohorts of patients, including thrombosis without autoimmune disease, and systemic lupus erythematosus without antiphospholipid antibodies, each displayed specific miRNA profiles that were distinct from those of APS patients. In vitro, antiphospholipid antibodies of IgG isotype promoted deregulation in selected miRNAs and their potential atherothrombotic protein targets in monocytes and endothelial cells. Taken together, differentially expressed circulating miRNAs in APS patients, modulated at least partially by antiphospholipid antibodies of IgG isotype, might have the potential to serve as novel biomarkers of disease features and to typify patients’ atherothrombotic status, thus constituting a useful tool in the management of the disease. PMID:29545345

A novel bradykinin potentiating peptide isolated from Bothrops jararacussu venom using catallytically inactive oligopeptidase EP24.15.

PubMed

Rioli, Vanessa; Prezoto, Benedito C; Konno, Katsuhiro; Melo, Robson L; Klitzke, Clécio F; Ferro, Emer S; Ferreira-Lopes, Mônica; Camargo, Antonio C M; Portaro, Fernanda C V

2008-05-01

Characterization of the peptide content of venoms has a number of potential benefits for basic research, clinical diagnosis, development of new therapeutic agents, and production of antiserum. Here, we use a substrate-capture assay that employs a catalytically inactive mutant of thimet oligopeptidase (EC 3.4.24.15; EP24.15) to identify novel bioactive peptides in Bothrops jararacussu venom. Of the peptides captured with inactive EP24.15 and identified by mass spectrometry, three were previously identified bradykinin-potentiating peptides (BPP),

Learning rules for spike timing-dependent plasticity depend on dendritic synapse location.

PubMed

Letzkus, Johannes J; Kampa, Björn M; Stuart, Greg J

2006-10-11

Previous studies focusing on the temporal rules governing changes in synaptic strength during spike timing-dependent synaptic plasticity (STDP) have paid little attention to the fact that synaptic inputs are distributed across complex dendritic trees. During STDP, propagation of action potentials (APs) back to the site of synaptic input is thought to trigger plasticity. However, in pyramidal neurons, backpropagation of single APs is decremental, whereas high-frequency bursts lead to generation of distal dendritic calcium spikes. This raises the question whether STDP learning rules depend on synapse location and firing mode. Here, we investigate this issue at synapses between layer 2/3 and layer 5 pyramidal neurons in somatosensory cortex. We find that low-frequency pairing of single APs at positive times leads to a distance-dependent shift to long-term depression (LTD) at distal inputs. At proximal sites, this LTD could be converted to long-term potentiation (LTP) by dendritic depolarizations suprathreshold for BAC-firing or by high-frequency AP bursts. During AP bursts, we observed a progressive, distance-dependent shift in the timing requirements for induction of LTP and LTD, such that distal synapses display novel timing rules: they potentiate when inputs are activated after burst onset (negative timing) but depress when activated before burst onset (positive timing). These findings could be explained by distance-dependent differences in the underlying dendritic voltage waveforms driving NMDA receptor activation during STDP induction. Our results suggest that synapse location within the dendritic tree is a crucial determinant of STDP, and that synapses undergo plasticity according to local rather than global learning rules.

Complementing the Mainstream: An Exploration of Partnership Work between Complementary Alternative Provisions and Mainstream Schools

ERIC Educational Resources Information Center

Pennacchia, Jodie; Thomson, Pat

2016-01-01

In the English context, complementary alternative provisions (APs) can make specific positive contributions for young people at risk of exclusion from mainstream school. Whilst recognising the potential value of all complementary AP that is carefully selected and of high quality, we problematise the "repair and return" rationale that…

[Role of CD2-associated protein in podocyte differentiation.].

PubMed

Jiang, Hua-Jun; Chang, Ying; Zhu, Zhong-Hua; Liu, Jian-She; Deng, An-Guo; Zhang, Chun

2008-02-25

To study the cellular changes and the potential role of CD2-associated protein (CD2AP) in podocyte differentiation, conditionally immortalized murine podocyte cell line was cultured in RPMI 1640 medium under permissive condition at 33 °C. After transfection with CD2AP small interfering RNA (siRNA) the cells were shifted to non-permissive condition at 37 °C. Simultaneously, untransfected cells were taken as differentiation control. The podocyte proliferation rate was determined by MTT method. The expressions of CD2AP, WT1, synaptopodin and nephrin mRNAs were examined by RT-PCR. CD2AP, WT1 and nephrin protein expressions were examined by Western blot. The distribution of CD2AP, nephrin, F-actin and tubulin in differentiated and undifferentiated podocytes was detected by laser scanning confocal microscopy. The results showed: (1) CD2AP, WT1 and nephrin were stably expressed in differentiated and undifferentiated podocytes while synaptopodin was only expressed in differentiated podocytes. (2) CD2AP and nephrin mRNA and protein expressions were up-regulated during podocyte differentiation (P<0.05). (3) CD2AP and tubulin were distributed in the cytoplasm and perinulcear region in undifferentiated podocytes, and F-actin was predominantly localized to a cortical belt and paralleled to the cell axis. Under differentiation condition, CD2AP distribution profile was presented as peripheral accumulation, tubulin took on fascicular style and F-actin extended into foot processes in podocytes. CD2AP colocalized with nephrin and F-actin in undifferentiated podocytes. (4) After transfection with CD2AP siRNA, the expression of CD2AP was partially inhibited and cell growth was arrested; Synaptopodin, the differentiation podocyte marker, was apparently down-regulated; The differentiation of podocytes was delayed. The results demonstrate that podocyte differentiation is accompanied by cytoskeleton rearrangement and cell morphology change. CD2AP might play an essential role in podocyte differentiation.

Adiponectin attenuates kidney injury and fibrosis in deoxycorticosterone acetate-salt and angiotensin II induced CKD mice.

PubMed

Tian, Mi; Tang, Li; Wu, Yuanyuan; Beddhu, Srinivasan; Huang, Yufeng

2018-06-06

Adiponectin (ApN) is a multifunctional adipokine. However high, rather than low, concentrations of ApN are unexpectedly found in patients with chronic kidney disease (CKD) via an as yet unknown mechanism and the role of ApN in CKD is unclear. We, herein, investigated the effect of ApN overexpression on the progressive renal injury resulted from deoxycorticosterone acetate-salt (DOCA) and angiotensin II (Ang-II) infusion using a transgenic, inducible ApN-overexpressing mouse model. Three groups of mice (wild type receiving no infusion (WT), WT and cyp1a1 ApN transgenic mice (ApN-Tg) receiving DOCA+Ang-II infusion (WT/DOCA+Ang-II and ApN-Tg/DOCA+Ang-II)) were assigned to receive a normal food containing 0.15% of the transgene inducer indol-3-carbinol (I3C) for 3 weeks. The I3C-induced ApN-Tg/DOCA+Ang-II mice, not the WT or WT/DOCA+Ang-II mice, overexpressing ApN in liver resulted in 3.15-fold increases in circulating ApN than non-transgenic controls. Of note, these transgenic mice receiving DOCA+Ang-II infusion were still hypertensive but had much less albuminuria and glomerular and tubulointerstitial fibrosis, which were associated with ameliorated podocyte injury determined by ameliorated podocyte loss and foot process effacement; and alleviated tubular injury determined by ameliorated mRNA overexpression of KIM-1 and NGAL and mRNA decreases of cubilin and megalin in tubular cells, compared with WT/DOCA+Ang-II mice. In addition, renal production of NF-kB-p65, NAPDH oxidase-2 and p47phox, and MAPK-related cellular proliferation, which were induced in WT/DOCA+Ang-II mice, were markedly reduced in ApN-Tg/DOCA+Ang-II mice. These results indicate that elevated ApN in CKD mouse model is renal protective. Enhancing adiponectin production or signaling may have therapeutic potential for CKD.

Genome-wide investigation and expression analysis of AP2-ERF gene family in salt tolerant common bean

PubMed Central

Kavas, Musa; Kizildogan, Aslihan; Gökdemir, Gökhan; Baloglu, Mehmet Cengiz

2015-01-01

Apetala2-ethylene-responsive element binding factor (AP2-ERF) superfamily with common AP2-DNA binding domain have developmentally and physiologically important roles in plants. Since common bean genome project has been completed recently, it is possible to identify all of the AP2-ERF genes in the common bean genome. In this study, a comprehensive genome-wide in silico analysis identified 180 AP2-ERF superfamily genes in common bean (Phaseolus vulgaris). Based on the amino acid alignment and phylogenetic analyses, superfamily members were classified into four subfamilies: DREB (54), ERF (95), AP2 (27) and RAV (3), as well as one soloist. The physical and chemical characteristics of amino acids, interaction between AP2-ERF proteins, cis elements of promoter region of AP2-ERF genes and phylogenetic trees were predicted and analyzed. Additionally, expression levels of AP2-ERF genes were evaluated by in silico and qRT-PCR analyses. In silico micro-RNA target transcript analyses identified nearly all PvAP2-ERF genes as targets of by 44 different plant species' miRNAs were identified in this study. The most abundant target genes were PvAP2/ERF-20-25-62-78-113-173. miR156, miR172 and miR838 were the most important miRNAs found in targeting and BLAST analyses. Interactome analysis revealed that the transcription factor PvAP2-ERF78, an ortholog of Arabidopsis At2G28550, was potentially interacted with at least 15 proteins, indicating that it was very important in transcriptional regulation. Here we present the first study to identify and characterize the AP2-ERF transcription factors in common bean using whole-genome analysis, and the findings may serve as a references for future functional research on the transcription factors in common bean. PMID:27152109

Angelica polysaccharides inhibit the growth and promote the apoptosis of U251 glioma cells in vitro and in vivo.

PubMed

Zhang, Wen-Feng; Yang, Yan; Li, Xin; Xu, Da-Yan; Yan, Yu-Li; Gao, Qiao; Jia, Ai-Ling; Duan, Ming-Hua

2017-09-15

Angelica sinensis (Oliv) Diels (Apiaceae) is a traditional medicine that has been used for more than 2000 years in China. It exhibits various therapeutic effects including neuroprotective, anti-oxidant, anti-inflammatory, and immunomodulatory activities. Angelica polysaccharides (APs), bioactive constituents of Angelica have been shown to be responsible for these effects; however, the utility of APs for the treatment of glioma and their mechanism of action remain to be elucidated. In this study, we investigated the inhibitory effects of APs on a glioma cell line and their molecular mechanism of action. U251 cells were utilized to confirm the effects of APs on glioma. The human glioblastoma cell line U251 was utilized for both in vitro and in vivo models, in which we tested the effects of APs. Flow cytometry, gene expression analysis, western blotting, and MTT assays were used to elucidate the effects of APs on cell proliferation, cell cycle, and apoptosis. The results demonstrated that APs significantly inhibited the growth and proliferation of U251 cells and induced their apoptosis. Furthermore, APs effectively reduced the expression of several cell cycle regulators: cyclins D1, B, and E. The apoptosis suppressor protein Bcl-2 was also downregulated, and the expression of pro-apoptotic proteins Bax and cleaved-caspase-3 increased. Additionally, APs inhibited the transforming growth factor (TGF)-β signaling pathway and stimulated the expression of E-cadherin, thus prohibiting cell growth. In conclusion, the results indicate that APs attenuate the tumorigenicity of glioma cells and promote their apoptosis by suppressing the TGF-β signaling pathway. The present study therefore provides evidence of the inhibitory effects of APs against glioma progression, and proposes their potential application as alternative therapeutic agents for glioma. Copyright © 2017 Elsevier GmbH. All rights reserved.

4-aminopyridine, a Kv channel antagonist, prevents apoptosis of rat cerebellar granule neurons.

PubMed

Hu, Chang-Long; Liu, Zheng; Zeng, Xi-Min; Liu, Zi-Qiang; Chen, Xian-Hua; Zhang, Zhi-Hong; Mei, Yan-Ai

2006-09-01

Compelling evidence indicates that excessive potassium (K+) efflux and intracellular K+ depletion are the key early steps in apoptosis. Previously, we reported that apoptosis of cerebellar granule neurons induced by incubation in low-K+ (5 mM) and serum-free medium was associated with an increase in A-type transient inactivation of K+ channel current (IA) amplitude and modulation of channels' gating properties. Here, we showed that a classic K+ channel blocker, 4-aminopyradine (4-AP), significantly inhibited IA amplitude in a concentration-dependent manner (reduction of current by 10 microM and 10 mM 4-AP was 11.4+/-1.3% and 72.2+/-3.3%, respectively). Moreover, 4-AP modified the steady-state activation and inactivation kinetics of IA channels, such that the activation and inactivation curves were shifted to the right about 20 mV and 17 mV, respectively. Fluorescence staining showed that 4-AP dramatically increased the viability of cells undergoing apoptosis in a dose-dependent manner. That is, while 5 mM 4-AP was present, cell viability was 84.9+/-5.2%. Consistent with the cell viability analysis, internucleosomal DNA fragmentation by gel electrophoresis analysis showed that 5 mM 4-AP also protected against neuronal apoptosis. Furthermore, 4-AP significantly inhibited cytochrome c release and caspase-3 activity induced by low-K+/serum-free incubation. Finally, current-clamp analysis indicated that 5 mM 4-AP did not significantly depolarize the membrane potential. These results suggest that 4-AP has robust neuroprotective effects on apoptotic granule cells. The neuroprotective effect of 4-AP is likely not due to membrane depolarization, but rather that 4-AP may modulate the gating properties of IA channels in an anti-apoptotic manner.

A two-channel action-potential generator for testing neurophysiologic data acquisition/analysis systems.

PubMed

Lisiecki, R S; Voigt, H F

1995-08-01

A 2-channel action-potential generator system was designed for use in testing neurophysiologic data acquisition/analysis systems. The system consists of a personal computer controlling an external hardware unit. This system is capable of generating 2 channels of simulated action potential (AP) waveshapes. The AP waveforms are generated from the linear combination of 2 principal-component template functions. Each channel generates randomly occurring APs with a specified rate ranging from 1 to 200 events per second. The 2 trains may be independent of one another or the second channel may be made to be excited or inhibited by the events from the first channel with user-specified probabilities. A third internal channel may be made to excite or inhibit events in both of the 2 output channels with user-specified rate parameters and probabilities. The system produces voltage waveforms that may be used to test neurophysiologic data acquisition systems for recording from 2 spike trains simultaneously and for testing multispike-train analysis (e.g., cross-correlation) software.

Rethinking the evaluation and measurement of Health in all policies.

PubMed

Bauman, Adrian E; King, Lesley; Nutbeam, Don

2014-06-01

Current international attention to Health in all policies (HiAP) has its origins in a more sophisticated understanding of the impact of public policies on health, and a recognition that policies across government have an impact on the social and environmental determinants of health and related inequalities in health. As an emerging field, there has been limited attention focused on comprehensive approaches to the evaluation of HiAP to date, and the research focus around HiAP has mainly examined the processes of cross-sectoral policy development, rather than their health-related impacts or outcomes. The purpose of this paper is to explore issues in assessing the implementation of HiAP and describe an expanded evaluation framework for assessing the potential intermediate and end-point effects of HiAP actions, using a planning logic model for 'complex programs'. This meets the needs of public sector policy-makers who express an interest in understanding the relationship between HiAP and health-related and social outcomes. The paper proposes applying a contribution analysis method to estimate and model the anticipated impacts of HiAP policies on intermediate and longer term outcomes, in advance of empirical studies of these outcomes, and as an innovative input into HiAP and evaluation planning. A broader long-term evaluation framework will enhance the political saliency of HiAP initiatives, especially from governments considering HiAP approaches in financially constrained environments. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Genome-wide analysis of the emerging infection with Mycobacterium avium subspecies paratuberculosis in the Arabian camels (Camelus dromedarius).

PubMed

Ghosh, Pallab; Hsu, Chungyi; Alyamani, Essam J; Shehata, Maher M; Al-Dubaib, Musaad A; Al-Naeem, Abdulmohsen; Hashad, Mahmoud; Mahmoud, Osama M; Alharbi, Khalid B J; Al-Busadah, Khalid; Al-Swailem, Abdulaziz M; Talaat, Adel M

2012-01-01

Mycobacterium avium subspecies paratuberculosis (M. ap) is the causative agent of paratuberculosis or Johne's disease (JD) in herbivores with potential involvement in cases of Crohn's disease in humans. JD is spread worldwide and is economically important for both beef and dairy industries. Generally, pathogenic ovine strains (M. ap-S) are mainly found in sheep while bovine strains (M. ap-C) infect other ruminants (e.g. cattle, goat, deer), as well as sheep. In an effort to characterize this emerging infection in dromedary/Arabian camels, we successfully cultured M. ap from several samples collected from infected camels suffering from chronic, intermittent diarrhea suggestive of JD. Gene-based typing of isolates indicated that all isolates belong to sheep lineage of strains of M. ap (M. ap-S), suggesting a putative transmission from infected sheep herds. Screening sheep and goat herds associated with camels identified the circulation of this type in sheep but not goats. The current genome-wide analysis recognizes these camel isolates as a sub-lineage of the sheep strain with a significant number of single nucleotide polymorphisms (SNPs) between sheep and camel isolates (∼1000 SNPs). Such polymorphism could represent geographical differences among isolates or host adaptation of M. ap during camel infection. To our knowledge, this is the first attempt to examine the genomic basis of this emerging infection in camels with implications on the evolution of this important pathogen. The sequenced genomes of M. ap isolates from camels will further assist our efforts to understand JD pathogenesis and the dynamic of disease transmission across animal species.

Genome-Wide Analysis of the Emerging Infection with Mycobacterium avium Subspecies paratuberculosis in the Arabian Camels (Camelus dromedarius)

PubMed Central

Ghosh, Pallab; Hsu, Chungyi; Alyamani, Essam J.; Shehata, Maher M.; Al-Dubaib, Musaad A.; Al-Naeem, Abdulmohsen; Hashad, Mahmoud; Mahmoud, Osama M.; Alharbi, Khalid B. J.; Al-Busadah, Khalid; Al-Swailem, Abdulaziz M.; Talaat, Adel M.

2012-01-01

Mycobacterium avium subspecies paratuberculosis (M. ap) is the causative agent of paratuberculosis or Johne's disease (JD) in herbivores with potential involvement in cases of Crohn's disease in humans. JD is spread worldwide and is economically important for both beef and dairy industries. Generally, pathogenic ovine strains (M. ap-S) are mainly found in sheep while bovine strains (M. ap-C) infect other ruminants (e.g. cattle, goat, deer), as well as sheep. In an effort to characterize this emerging infection in dromedary/Arabian camels, we successfully cultured M. ap from several samples collected from infected camels suffering from chronic, intermittent diarrhea suggestive of JD. Gene-based typing of isolates indicated that all isolates belong to sheep lineage of strains of M. ap (M. ap-S), suggesting a putative transmission from infected sheep herds. Screening sheep and goat herds associated with camels identified the circulation of this type in sheep but not goats. The current genome-wide analysis recognizes these camel isolates as a sub-lineage of the sheep strain with a significant number of single nucleotide polymorphisms (SNPs) between sheep and camel isolates (∼1000 SNPs). Such polymorphism could represent geographical differences among isolates or host adaptation of M. ap during camel infection. To our knowledge, this is the first attempt to examine the genomic basis of this emerging infection in camels with implications on the evolution of this important pathogen. The sequenced genomes of M. ap isolates from camels will further assist our efforts to understand JD pathogenesis and the dynamic of disease transmission across animal species. PMID:22393374

Cardiotoxicity screening with simultaneous optogenetic pacing, voltage imaging and calcium imaging.

PubMed

Dempsey, Graham T; Chaudhary, Khuram W; Atwater, Nicholas; Nguyen, Cuong; Brown, Barry S; McNeish, John D; Cohen, Adam E; Kralj, Joel M

2016-01-01

The Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative seeks an in vitro test to accurately predict clinical Torsades de Pointes (TdP). We developed a cardiotoxicity assay incorporating simultaneous measurement of the action potential (AP) waveform and Ca(2+) transient (CT) in human iPSC-derived cardiomyocytes (CMs). Concurrent optogenetic pacing provided a well-controlled electrophysiological background. We used the Optopatch platform for all-optical electrophysiology (Hochbaum et al., 2014). In a monolayer culture, a subset of cells expressed a genetically encoded, calcium and voltage reporter, CaViar (Hou, Kralj, Douglass, Engert, & Cohen, 2014), while others expressed a channelrhodopsin variant, CheRiff. Optical pacing of CheRiff-expressing cells synchronized the syncytium. We screened 12 compounds (11 acute, 1 chronic) to identify electrophysiological (AP rise time, AP50, AP90, beat rate) and CT effects in spontaneously beating and paced cultures (1Hz, 2Hz). CaViar reported spontaneous and paced APs and CTs with high signal-to-noise ratio and low phototoxicity. Quinidine, flecainide, E-4031, digoxin and cisapride prolonged APs, while verapamil and nifedipine shortened APs. Early after depolarizations (EADs) were elicited by quinidine, flecainide and cisapride. All but four compounds (amiodarone, chromanol, nifedipine, verapamil) prolonged AP rise time. Nifedipine and verapamil decreased CT amplitude, while digoxin increased CT amplitude. Pentamidine prolonged APs after chronic exposure. The Optopatch platform provides a robust assay to measure APs and CTs in hiPSC-CMs. This addresses the CiPA mandate and will facilitate comparisons of cell-based assays to human clinical data. Copyright © 2016 Elsevier Inc. All rights reserved.

VANADIUM EXPOSURE ALTERS SPONTANEOUS BEAT RATE AND GENE EXPRESSION OF CULTURED CARDIAC MYOCYTES

EPA Science Inventory

Ambient air pollution particulate matter (PM) exposure is associated with increased morbidity and mortality. Recent toxicological studies report PM-induced changes in a number of cardiac parameters, including heart rate variability, arrhythmias, repolarization, and internal defib...

Comprehensive Analyses of Ventricular Myocyte Models Identify Targets Exhibiting Favorable Rate Dependence

PubMed Central

Bugana, Marco; Severi, Stefano; Sobie, Eric A.

2014-01-01

Reverse rate dependence is a problematic property of antiarrhythmic drugs that prolong the cardiac action potential (AP). The prolongation caused by reverse rate dependent agents is greater at slow heart rates, resulting in both reduced arrhythmia suppression at fast rates and increased arrhythmia risk at slow rates. The opposite property, forward rate dependence, would theoretically overcome these parallel problems, yet forward rate dependent (FRD) antiarrhythmics remain elusive. Moreover, there is evidence that reverse rate dependence is an intrinsic property of perturbations to the AP. We have addressed the possibility of forward rate dependence by performing a comprehensive analysis of 13 ventricular myocyte models. By simulating populations of myocytes with varying properties and analyzing population results statistically, we simultaneously predicted the rate-dependent effects of changes in multiple model parameters. An average of 40 parameters were tested in each model, and effects on AP duration were assessed at slow (0.2 Hz) and fast (2 Hz) rates. The analysis identified a variety of FRD ionic current perturbations and generated specific predictions regarding their mechanisms. For instance, an increase in L-type calcium current is FRD when this is accompanied by indirect, rate-dependent changes in slow delayed rectifier potassium current. A comparison of predictions across models identified inward rectifier potassium current and the sodium-potassium pump as the two targets most likely to produce FRD AP prolongation. Finally, a statistical analysis of results from the 13 models demonstrated that models displaying minimal rate-dependent changes in AP shape have little capacity for FRD perturbations, whereas models with large shape changes have considerable FRD potential. This can explain differences between species and between ventricular cell types. Overall, this study provides new insights, both specific and general, into the determinants of AP duration rate dependence, and illustrates a strategy for the design of potentially beneficial antiarrhythmic drugs. PMID:24675446

Comprehensive analyses of ventricular myocyte models identify targets exhibiting favorable rate dependence.

PubMed

Cummins, Megan A; Dalal, Pavan J; Bugana, Marco; Severi, Stefano; Sobie, Eric A

2014-03-01

Reverse rate dependence is a problematic property of antiarrhythmic drugs that prolong the cardiac action potential (AP). The prolongation caused by reverse rate dependent agents is greater at slow heart rates, resulting in both reduced arrhythmia suppression at fast rates and increased arrhythmia risk at slow rates. The opposite property, forward rate dependence, would theoretically overcome these parallel problems, yet forward rate dependent (FRD) antiarrhythmics remain elusive. Moreover, there is evidence that reverse rate dependence is an intrinsic property of perturbations to the AP. We have addressed the possibility of forward rate dependence by performing a comprehensive analysis of 13 ventricular myocyte models. By simulating populations of myocytes with varying properties and analyzing population results statistically, we simultaneously predicted the rate-dependent effects of changes in multiple model parameters. An average of 40 parameters were tested in each model, and effects on AP duration were assessed at slow (0.2 Hz) and fast (2 Hz) rates. The analysis identified a variety of FRD ionic current perturbations and generated specific predictions regarding their mechanisms. For instance, an increase in L-type calcium current is FRD when this is accompanied by indirect, rate-dependent changes in slow delayed rectifier potassium current. A comparison of predictions across models identified inward rectifier potassium current and the sodium-potassium pump as the two targets most likely to produce FRD AP prolongation. Finally, a statistical analysis of results from the 13 models demonstrated that models displaying minimal rate-dependent changes in AP shape have little capacity for FRD perturbations, whereas models with large shape changes have considerable FRD potential. This can explain differences between species and between ventricular cell types. Overall, this study provides new insights, both specific and general, into the determinants of AP duration rate dependence, and illustrates a strategy for the design of potentially beneficial antiarrhythmic drugs.

Advanced APS impacts on vehicle payloads

NASA Technical Reports Server (NTRS)

Schneider, Steven J.; Reed, Brian D.

1989-01-01

Advanced auxiliary propulsion system (APS) technology has the potential to both, increase the payload capability of earth-to-orbit (ETO) vehicles by reducing APS propellant mass, and simplify ground operations and logistics by reducing the number of fluids on the vehicle and eliminating toxic, corrosive propellants. The impact of integrated cryogenic APS on vehicle payloads is addressed. In this system, launch propulsion system residuals are scavenged from integral launch propulsion tanks for use in the APS. Sufficient propellant is preloaded into the APS to return to earth with margin and noncomplete scavenging assumed. No propellant conditioning is required by the APS, but ambient heat soak is accommodated. High temperature rocket materials enable the use of the unconditioned hydrogen/oxygen in the APS and are estimated to give APS rockets specific impulse of up to about 444 sec. The payload benefits are quantified and compared with an uprated monomethylhydrazine/nitrogen tetroxide system in a conservative fashion, by assuming a 25.5 percent weight growth for the hydrogen/oxygen system and a 0 percent weight growth for the uprated system. The combination of scavenging and high performance gives payload impacts which are highly mission specific. A payload benefit of 861 kg (1898 lbm) was estimated for a Space Station Freedom rendezvous mission and 2099 kg (4626 lbm) for a sortie mission, with payload impacts varying with the amount of launch propulsion residual propellants. Missions without liquid propellant scavenging were estimated to have payload penalties, however, operational benefits were still possible.

Advanced APS Impacts on Vehicle Payloads

NASA Technical Reports Server (NTRS)

Schneider, Steven J.; Reed, Brian D.

1989-01-01

Advanced auxiliary propulsion system (APS) technology has the potential to both, increase the payload capability of earth-to-orbit (ETO) vehicles by reducing APS propellant mass, and simplify ground operations and logistics by reducing the number of fluids on the vehicle and eliminating toxic, corrosive propellants. The impact of integrated cryogenic APS on vehicle payloads is addressed. In this system, launch propulsion system residuals are scavenged from integral launch propulsion tanks for use in the APS. Sufficient propellant is preloaded into the APS to return to earth with margin and noncomplete scavenging assumed. No propellant conditioning is required by the APS, but ambient heat soak is accommodated. High temperature rocket materials enable the use of the unconditioned hydrogen/oxygen in the APS and are estimated to give APS rockets specific impulse of up to about 444 sec. The payload benefits are quantified and compared with an uprated monomethyl hydrazine/nitrogen tetroxide system in a conservative fashion, by assuming a 25.5 percent weight growth for the hydrogen/oxygen system and a 0 percent weight growth for the uprated system. The combination and scavenging and high performance gives payload impacts which are highly mission specific. A payload benefit of 861 kg (1898 lbm) was estimated for a Space Station Freedom rendezvous mission and 2099 kg (4626 lbm) for a sortie mission, with payload impacts varying with the amount of launch propulsion residual propellants. Missions without liquid propellant scavenging were estimated to have payload penalties, however, operational benefits were still possible.

TRO40303 Ameliorates Alcohol-Induced Pancreatitis Through Reduction of Fatty Acid Ethyl Ester–Induced Mitochondrial Injury and Necrotic Cell Death

PubMed Central

Javed, Muhammad Ahsan; Wen, Li; Awais, Muhammad; Latawiec, Diane; Huang, Wei; Chvanov, Michael; Schaller, Sophie; Bordet, Thierry; Michaud, Magali; Pruss, Rebecca; Tepikin, Alexei; Criddle, David; Sutton, Robert

2018-01-01

Objectives Mitochondrial permeability transition pore inhibition is a promising approach to treat acute pancreatitis (AP). We sought to determine (i) the effects of the mitochondrial permeability transition pore inhibitor 3,5-seco-4-nor-cholestan-5-one oxime-3-ol (TRO40303) on murine and human pancreatic acinar cell (PAC) injury induced by fatty acid ethyl esters (FAEEs) or taurolithocholic acid-3-sulfate and (ii) TRO40303 pharmacokinetics and efficacy in experimental alcoholic AP (FAEE-AP). Methods Changes in mitochondrial membrane potential (Δψm), cytosolic Ca2+ ([Ca2+]c), and cell fate were examined in freshly isolated murine or human PACs by confocal microscopy. TRO40303 pharmacokinetics were assessed in cerulein-induced AP and therapeutic efficacy in FAEE-AP induced with palmitoleic acid and ethanol. Severity of AP was assessed by standard biomarkers and blinded histopathology. Results TRO40303 prevented loss of Δψm and necrosis induced by 100 μM palmitoleic acid ethyl ester or 500 μM taurolithocholic acid-3-sulfate in murine and human PACs. Pharmacokinetic analysis found TRO40303 accumulated in the pancreas. A single dose of 3 mg/kg TRO40303 significantly reduced serum amylase (P = 0.043), pancreatic trypsin (P = 0.018), and histopathology scores (P = 0.0058) in FAEE-AP. Conclusions TRO40303 protects mitochondria and prevents necrotic cell death pathway activation in murine and human PACs, ameliorates the severity of FAEE-AP, and is a candidate drug for human AP. PMID:29200128

Electrophysiological characteristics of IB4-negative TRPV1-expressing muscle afferent DRG neurons.

PubMed

Lin, Yi-Wen; Chen, Chih-Cheng

2015-01-01

Muscle afferent neurons that express transient receptor potential vanilloid type I (TRPV1) are responsible for muscle pain associated with tissue acidosis. We have previously found that TRPV1 of isolectin B4 (IB4)-negative muscle nociceptors plays an important role in the acid-induced hyperalgesic priming and the development of chronic hyperalgesia in a mouse model of fibromyalgia. To understand the electrophysiological properties of the TRPV1-expressing muscle afferent neurons, we used whole-cell patch clamp recording to study the acid responsiveness and action potential (AP) configuration of capsaicin-sensitive neurons innervating to gastrocnemius muscle. Here we showed that IB4-negative TRPV1-expressing muscle afferent neurons are heterogeneous in terms of cell size, resting membrane potential, AP configuration, tetrodotoxin (TTX)-resistance, and acid-induced current (I acid), as well as capsaicin-induced current (I cap). TRPV1-expressing neurons were all acid-sensitive and could be divided into two acid-sensitive groups depending on an acid-induced sustained current (type I) or an acid-induced biphasic ASIC3-like current (type II). Type I TRPV1-expressing neurons were distinguishable from type II TRPV1-expressing neurons in AP overshoot, after-hyperpolarization duration, and all I acid parameters, but not in AP threshold, TTX-resistance, resting membrane potential, and I cap parameters. These differential biophysical properties of TRPV1-expressing neurons might partially annotate their different roles involved in the development and maintenance of chronic muscle pain.

Spectrum of cisplatin-induced mutations in Escherichia coli

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burnouf, D.; Duane, M.; Fuchs, R.P.

1987-06-01

Using a forward-mutation assay based on the inactivation of the tetracycline-resistance gene located on plasmid pBR322, we have determined the mutation spectrum induced in Escherichia coli by cisplatin (cis-diamminedichloroplatinum(II)), a widely used antitumor drug. Cisplatin is known to form mainly intrastrand diadducts at ApG and GpG sites. We found that cisplatin efficiently induces mutations in an SOS-dependent way (i.e., dependent upon UV irradiation of the host bacteria). More than 90% of the mutations are single-base-pair substitutions occurring at the potential sites of cisplatin adducts (ApG and GpG). Taking into account the relative proportions of ApG and GpG adducts, we foundmore » that the ApG adducts are at least 5 times more mutagenic than the GpG adducts. Moreover, a strong mutation specificity was seen at the 5' side of the ApG adducts (A X T----T X A transversions). The observation that most mutations occur at the 5' end of the adduct at both ApG and GpG sites is discussed in relation to recent structural data.« less

Fabrication and Physical Evaluation of Gelatin-Coated Carbonate Apatite Foam

PubMed Central

Hara, Kanae; Fujisawa, Kenji; Nagai, Hirokazu; Takamaru, Natsumi; Ohe, Go; Tsuru, Kanji; Ishikawa, Kunio; Miyamoto, Youji

2016-01-01

Carbonate apatite (CO3Ap) foam has gained much attention in recent years because of its ability to rapidly replace bone. However, its mechanical strength is extremely low for clinical use. In this study, to understand the potential of gelatin-reinforced CO3Ap foam for bone replacement, CO3Ap foam was reinforced with gelatin and the resulting physical characteristics were evaluated. The mechanical strength increased significantly with the gelatin reinforcement. The compressive strength of gelatin-free CO3Ap foam was 74 kPa whereas that of the gelatin-reinforced CO3Ap foam, fabricated using 30 mass % gelatin solution, was approximately 3 MPa. Heat treatment for crosslinking gelatin had little effect on the mechanical strength of the foam. The gelatin-reinforced foam did not maintain its shape when immersed in a saline solution as this promoted swelling of the gelatin; however, in the same conditions, the heat-treated gelatin-reinforced foam proved to be stable. It is concluded, therefore, that heat treatment is the key to the fabrication of stable gelatin-reinforced CO3Ap foam. PMID:28773832

Efficacy and safety of novel antipsychotics: a critical review.

PubMed

Balestrieri, Matteo; Vampini, Claudio; Bellantuono, Cesario

2000-10-01

Efficacy and safety of novel antipsychotic (AP) drugs (amisulpride, olanzapine, quetiapine, ziprasidone and zotepine) have been reviewed. Data on their antipsychotic efficacy and side effects profile have been evaluated only on the basis of controlled trials so far published. Overall, all these drugs have shown an antipsychotic efficacy on positive symptoms of schizophrenia similar to that of the conventional AP drugs. On negative symptoms, all novel AP drugs, except quetiapine and ziprasidone, demonstrated a better efficacy than haloperidol. Long-term efficacy of these AP drugs in the maintenance treatment of schizophrenia needs to be explored by further, better-designed, epidemiological studies. The safety profile shows that the novel AP drugs are generally well-tolerated and induce significantly less acute extrapyramidal side effects in comparison with haloperidol. Some methodological flaws in the experimental design of the clinical trials analysed are discussed. Although these novel AP drugs have potential clinical advantages, a number of relevant questions still remain to be addressed, in order to establish the impact of these drugs in the overall treatment of schizophrenia. Copyright 2000 John Wiley & Sons, Ltd.

Quantification of circulating fetal DNA as a tool for potential monitoring of pregnant patients with antiphospholipid antibodies.

PubMed

Korabecna, Marie; Ulcova-Gallova, Zdenka; Horinek, Ales; Pazourková, Eva; Calda, Pavel

2014-11-01

Apoptosis of tissues of fetal origin is thought to be one of the main sources of cell-free fetal DNA (cffDNA) in maternal circulation, impaired apoptosis is also involved in the mechanisms contributing to recurrent spontaneous miscarriages (RSM) associated with antiphospholipid syndrome (APS). The APS increases the risk for preeclampsia nine times. In preeclampsia, the elevated levels of cffDNA were described by different authors. To our knowledge, cffDNA in pregnant patients with APS was never studied. In our pilot study, we focused on the levels of cffDNA in four pregnant patients with treated primary APS and compared them with values obtained in twenty-one healthy subjects of comparable gestation age (the third trimester of pregnancy). We supposed that the increase of cffDNA concentration in our treated patients would signalize the elevated apoptosis of fetal tissues as in other pathological changes of placentation. The aim of our pilot study was to determine cffDNA concentrations in patients with treated APS and to compare them with values detected in healthy pregnant women of comparable gestation age in order to discover potential non-physiological elevations in patients. The elevated values of cffDNA were not observed in our patients (p value = 0.4363, Mann-Whitney test). All patients delivered healthy children. The measurement of concentrations of cffDNA seems to be a promising tool for monitoring of therapy effectiveness in pregnant women with APS but evaluation of randomized controlled trials would be necessary to determine the specificity and the sensitivity of this test.

Shade-Induced Action Potentials in Helianthus annuus L. Originate Primarily from the Epicotyl

PubMed Central

Stephens, Nicholas R; Cleland, Robert E; Van Volkenburgh, Elizabeth

2006-01-01

Repeated observations that shading (a drastic reduction in illumination rate) increased the generation of spikes (rapidly reversed depolarizations) in leaves and stems of many cucumber and sunflower plants suggests a phenomenon widespread among plant organs and species. Although shaded leaves occasionally generate spikes and have been suggested to trigger systemic action potentials (APs) in sunflower stems, we never found leaf-generated spikes to propagate out of the leaf and into the stem. On the contrary, our data consistently implicate the epicotyl as the location where most spikes and APs (propagating spikes) originate. Microelectrode studies of light and shading responses in mesophyll cells of leaf strips and in epidermis/cortex cells of epicotyl segments confirm this conclusion and show that spike induction is not confined to intact plants. 90% of the epicotyl-generated APs undergo basipetal propagation to the lower epicotyl, hypocotyl and root. They propagate with an average rate of 2 ± 0.3 mm s−1 and always undergo a large decrement from the hypocotyl to the root. The few epicotyl-derived APs that can be tracked to leaf blades (< 10%) undergo either a large decrement or fail to be transmitted at all. Occasionally (5% of the observations) spikes were be generated in hypocotyl and lower epicotyl that moved towards the upper epicotyl unaltered, decremented, or amplified. This study confirms that plant APs arise to natural, nontraumatic changes. In simultaneous recordings with epicotyl growth, AP generation was found to parallel the acceleration of stem growth under shade. The possible relatedness of both processes must be further investigated. PMID:19521471

Recording temperature affects the excitability of mouse superficial dorsal horn neurons, in vitro.

PubMed

Graham, B A; Brichta, A M; Callister, R J

2008-05-01

Superficial dorsal horn (SDH) neurons in laminae I-II of the spinal cord play an important role in processing noxious stimuli. These neurons represent a heterogeneous population and are divided into various categories according to their action potential (AP) discharge during depolarizing current injection. We recently developed an in vivo mouse preparation to examine functional aspects of nociceptive processing and AP discharge in SDH neurons and to extend investigation of pain mechanisms to the genetic level of analysis. Not surprisingly, some in vivo data obtained at body temperature (37 degrees C) differed from those generated at room temperature (22 degrees C) in spinal cord slices. In the current study we examine how temperature influences SDH neuron properties by making recordings at 22 and 32 degrees C in transverse spinal cord slices prepared from L3-L5 segments of adult mice (C57Bl/6). Patch-clamp recordings (KCH(3)SO(4) internal) were made from visualized SDH neurons. At elevated temperature all SDH neurons had reduced input resistance and smaller, briefer APs. Resting membrane potential and AP afterhyperpolarization amplitude were temperature sensitive only in subsets of the SDH population. Notably, elevated temperature increased the prevalence of neurons that did not discharge APs during current injection. These reluctant firing neurons expressed a rapid A-type potassium current, which is enhanced at higher temperatures and thus restrains AP discharge. When compared with previously published whole cell recordings obtained in vivo (37 degrees C) our results suggest that, on balance, in vitro data collected at elevated temperature more closely resemble data collected under in vivo conditions.

Experience-dependent increase in spine calcium evoked by backpropagating action potentials in layer 2/3 pyramidal neurons in rat somatosensory cortex.

PubMed

Krieger, Patrik

2009-11-01

In spines on basal dendrites of layer 2/3 pyramidal neurons in somatosensory barrel cortex, calcium transients evoked by back-propagating action potentials (bAPs) were investigated (i) along the length of the basal dendrite, (ii) with postnatal development and (iii) with sensory deprivation during postnatal development. Layer 2/3 pyramidal neurons were investigated at three different ages. At all ages [postnatal day (P)8, P14, P21] the bAP-evoked calcium transient amplitude increased with distance from the soma with a peak at around 50 microm, followed by a gradual decline in amplitude. The effect of sensory deprivation on the bAP-evoked calcium was investigated using two different protocols. When all whiskers on one side of the rat snout were trimmed daily from P8 to P20-24 there was no difference in the bAP-evoked calcium transient between cells in the contralateral hemisphere, lacking sensory input from the whisker, and cells in the ipsilateral barrel cortex, with intact whisker activation. When, however, only the D-row whiskers on one side were trimmed the distribution of bAP-evoked calcium transients in spines was shifted towards larger amplitudes in cells located in the deprived D-column. In conclusion, (i) the bAP-evoked calcium transient gradient along the dendrite length is established at P8, (ii) the calcium transient increases in amplitude with age and (iii) this increase is enhanced in layer 2/3 pyramidal neurons located in a sensory-deprived barrel column that is bordered by non-deprived barrel columns.

Calcium Signaling in Intact Dorsal Root Ganglia

PubMed Central

Gemes, Geza; Rigaud, Marcel; Koopmeiners, Andrew S.; Poroli, Mark J.; Zoga, Vasiliki; Hogan, Quinn H.

2013-01-01

Background Ca2+ is the dominant second messenger in primary sensory neurons. In addition, disrupted Ca2+ signaling is a prominent feature in pain models involving peripheral nerve injury. Standard cytoplasmic Ca2+ recording techniques use high K+ or field stimulation and dissociated neurons. To compare findings in intact dorsal root ganglia, we used a method of simultaneous electrophysiologic and microfluorimetric recording. Methods Dissociated neurons were loaded by bath-applied Fura-2-AM and subjected to field stimulation. Alternatively, we adapted a technique in which neuronal somata of intact ganglia were loaded with Fura-2 through an intracellular microelectrode that provided simultaneous membrane potential recording during activation by action potentials (APs) conducted from attached dorsal roots. Results Field stimulation at levels necessary to activate neurons generated bath pH changes through electrolysis and failed to predictably drive neurons with AP trains. In the intact ganglion technique, single APs produced measurable Ca2+ transients that were fourfold larger in presumed nociceptive C-type neurons than in nonnociceptive Aβ-type neurons. Unitary Ca2+ transients summated during AP trains, forming transients with amplitudes that were highly dependent on stimulation frequency. Each neuron was tuned to a preferred frequency at which transient amplitude was maximal. Transients predominantly exhibited monoexponential recovery and had sustained plateaus during recovery only with trains of more than 100 APs. Nerve injury decreased Ca2+ transients in C-type neurons, but increased transients in Aβ-type neurons. Conclusions Refined observation of Ca2+ signaling is possible through natural activation by conducted APs in undissociated sensory neurons and reveals features distinct to neuronal types and injury state. PMID:20526180

Increased levels of 3-hydroxykynurenine parallel disease severity in human acute pancreatitis.

PubMed

Skouras, Christos; Zheng, Xiaozhong; Binnie, Margaret; Homer, Natalie Z M; Murray, Toby B J; Robertson, Darren; Briody, Lesley; Paterson, Finny; Spence, Heather; Derr, Lisa; Hayes, Alastair J; Tsoumanis, Andreas; Lyster, Dawn; Parks, Rowan W; Garden, O James; Iredale, John P; Uings, Iain J; Liddle, John; Wright, Wayne L; Dukes, George; Webster, Scott P; Mole, Damian J

2016-09-27

Inhibition of kynurenine 3-monooxygenase (KMO) protects against multiple organ dysfunction (MODS) in experimental acute pancreatitis (AP). We aimed to precisely define the kynurenine pathway activation in relation to AP and AP-MODS in humans, by carrying out a prospective observational study of all persons presenting with a potential diagnosis of AP for 90 days. We sampled peripheral venous blood at 0, 3, 6, 12, 24, 48, 72 and 168 hours post-recruitment. We measured tryptophan metabolite concentrations and analysed these in the context of clinical data and disease severity indices, cytokine profiles and C-reactive protein (CRP) concentrations. 79 individuals were recruited (median age: 59.6 years; 47 males, 59.5%). 57 met the revised Atlanta definition of AP: 25 had mild, 23 moderate, and 9 severe AP. Plasma 3-hydroxykynurenine concentrations correlated with contemporaneous APACHE II scores (R 2  = 0.273; Spearman rho = 0.581; P < 0.001) and CRP (R 2  = 0.132; Spearman rho = 0.455, P < 0.001). Temporal profiling showed early tryptophan depletion and contemporaneous 3-hydroxykynurenine elevation. Furthermore, plasma concentrations of 3-hydroxykynurenine paralleled systemic inflammation and AP severity. These findings support the rationale for investigating early intervention with a KMO inhibitor, with the aim of reducing the incidence and severity of AP-associated organ dysfunction.

Increased levels of 3-hydroxykynurenine parallel disease severity in human acute pancreatitis

PubMed Central

Skouras, Christos; Zheng, Xiaozhong; Binnie, Margaret; Homer, Natalie Z. M.; Murray, Toby B. J.; Robertson, Darren; Briody, Lesley; Paterson, Finny; Spence, Heather; Derr, Lisa; Hayes, Alastair J.; Tsoumanis, Andreas; Lyster, Dawn; Parks, Rowan W.; Garden, O. James; Iredale, John P.; Uings, Iain J.; Liddle, John; Wright, Wayne L.; Dukes, George; Webster, Scott P.; Mole, Damian J.

2016-01-01

Inhibition of kynurenine 3-monooxygenase (KMO) protects against multiple organ dysfunction (MODS) in experimental acute pancreatitis (AP). We aimed to precisely define the kynurenine pathway activation in relation to AP and AP-MODS in humans, by carrying out a prospective observational study of all persons presenting with a potential diagnosis of AP for 90 days. We sampled peripheral venous blood at 0, 3, 6, 12, 24, 48, 72 and 168 hours post-recruitment. We measured tryptophan metabolite concentrations and analysed these in the context of clinical data and disease severity indices, cytokine profiles and C-reactive protein (CRP) concentrations. 79 individuals were recruited (median age: 59.6 years; 47 males, 59.5%). 57 met the revised Atlanta definition of AP: 25 had mild, 23 moderate, and 9 severe AP. Plasma 3-hydroxykynurenine concentrations correlated with contemporaneous APACHE II scores (R2 = 0.273; Spearman rho = 0.581; P < 0.001) and CRP (R2 = 0.132; Spearman rho = 0.455, P < 0.001). Temporal profiling showed early tryptophan depletion and contemporaneous 3-hydroxykynurenine elevation. Furthermore, plasma concentrations of 3-hydroxykynurenine paralleled systemic inflammation and AP severity. These findings support the rationale for investigating early intervention with a KMO inhibitor, with the aim of reducing the incidence and severity of AP-associated organ dysfunction. PMID:27669975

Adipocyte fatty acid-binding protein, aP2, alters late atherosclerotic lesion formation in severe hypercholesterolemia.

PubMed

Boord, Jeffrey B; Maeda, Kazuhisa; Makowski, Liza; Babaev, Vladimir R; Fazio, Sergio; Linton, MacRae F; Hotamisligil, Gökhan S

2002-10-01

The adipocyte fatty acid-binding protein, aP2, has important effects on insulin resistance, lipid metabolism, and atherosclerosis. Its expression in macrophages enhances early foam cell formation and atherosclerosis in vivo. This study was designed to determine whether aP2 deficiency has a similar effect in the setting of advanced atherosclerosis and severe hypercholesterolemia. Mice deficient in aP2 and apolipoprotein E (aP2(-/-)apoE(-/-) mice) and apolipoprotein E-deficient control mice (apoE(-/-) mice) were fed a Western diet for 14 weeks. No significant differences in fasting serum levels of cholesterol, triglycerides, or free fatty acids were found between groups for each sex. Compared with apoE(-/-) control mice, male and female aP2(-/-)apoE(-/-) mice had significant reductions in mean atherosclerotic lesion size in the proximal aorta, en face aorta, and innominate/right carotid artery. Feeding the Western diet in the apoE-deficient background did not cause a significant reduction in insulin sensitivity in vivo, as determined by steady-state serum glucose levels and insulin tolerance testing. These data demonstrate an important role for aP2 expression in the advanced stages of atherosclerotic lesion formation. Thus, aP2 provides an important physiological link between different features of the metabolic syndrome and is a potential target for therapy of atherosclerosis.

Antipsychotic Use in Pregnancy and the Risk for Congenital Malformations.

PubMed

Huybrechts, Krista F; Hernández-Díaz, Sonia; Patorno, Elisabetta; Desai, Rishi J; Mogun, Helen; Dejene, Sara Z; Cohen, Jacqueline M; Panchaud, Alice; Cohen, Lee; Bateman, Brian T

2016-09-01

The frequency of antipsychotic (AP) use during pregnancy has approximately doubled during the last decade. However, little is known about their safety for the developing fetus, and concerns have been raised about a potential association with congenital malformations. To examine the risk for congenital malformations overall and cardiac malformations associated with first-trimester exposure to APs. This nationwide sample of 1 360 101 pregnant women enrolled in Medicaid with a live-born infant constituted the pregnancy cohort nested in the Medicaid Analytic Extract database, which included data from January 1, 2000, to December 31, 2010. Participants were enrolled in Medicaid from 3 months before their last menstrual period through at least 1 month after delivery. Relative risks (RRs) were estimated using generalized linear models with fine stratification on the propensity score to control for the underlying psychiatric disorders and other potential confounders. Data were analyzed during 2015. Use of APs during the first trimester, the etiologically relevant period for organogenesis. Major congenital malformations overall and cardiac malformations identified during the first 90 days after delivery. Of the 1 341 715 pregnancies that met inclusion criteria (mean [SD] age of women, 24.02 [5.77] years), 9258 (0.69%) filled at least 1 prescription for an atypical AP and 733 (0.05%) filled at least 1 prescription for a typical AP during the first trimester. Overall, 32.7 (95% CI, 32.4-33.0) per 1000 births not exposed to APs were diagnosed with congenital malformations compared with 44.5 (95% CI, 40.5-48.9) per 1000 births exposed to atypical and 38.2 (95% CI, 26.6-54.7) per 1000 births exposed to typical APs. Unadjusted analyses suggested an increased risk for malformations overall for atypical APs (RR, 1.36; 95% CI, 1.24-1.50) but not for typical APs (RR, 1.17; 95% CI, 0.81-1.68). After confounding adjustment, the RR was reduced to 1.05 (95% CI, 0.96-1.16) for atypical APs and 0.90 (95% CI, 0.62-1.31) for typical APs. The findings for cardiac malformations were similar. For the individual agents examined, a small increased risk in overall malformations (RR, 1.26; 95% CI, 1.02-1.56) and cardiac malformations (RR, 1.26; 95% CI, 0.88-1.81) was found for risperidone that was independent of measured confounders. Evidence from this large study suggests that use of APs early in pregnancy generally does not meaningfully increase the risk for congenital malformations overall or cardiac malformations in particular. The small increase in the risk for malformations observed with risperidone requires additional study.

Genome-Wide Investigation and Expression Profiling of AP2/ERF Transcription Factor Superfamily in Foxtail Millet (Setaria italica L.)

PubMed Central

Lata, Charu; Mishra, Awdhesh Kumar; Muthamilarasan, Mehanathan; Bonthala, Venkata Suresh; Khan, Yusuf; Prasad, Manoj

2014-01-01

The APETALA2/ethylene-responsive element binding factor (AP2/ERF) family is one of the largest transcription factor (TF) families in plants that includes four major sub-families, namely AP2, DREB (dehydration responsive element binding), ERF (ethylene responsive factors) and RAV (Related to ABI3/VP). AP2/ERFs are known to play significant roles in various plant processes including growth and development and biotic and abiotic stress responses. Considering this, a comprehensive genome-wide study was conducted in foxtail millet (Setaria italica L.). A total of 171 AP2/ERF genes were identified by systematic sequence analysis and were physically mapped onto nine chromosomes. Phylogenetic analysis grouped AP2/ERF genes into six classes (I to VI). Duplication analysis revealed that 12 (∼7%) SiAP2/ERF genes were tandem repeated and 22 (∼13%) were segmentally duplicated. Comparative physical mapping between foxtail millet AP2/ERF genes and its orthologs of sorghum (18 genes), maize (14 genes), rice (9 genes) and Brachypodium (6 genes) showed the evolutionary insights of AP2/ERF gene family and also the decrease in orthology with increase in phylogenetic distance. The evolutionary significance in terms of gene-duplication and divergence was analyzed by estimating synonymous and non-synonymous substitution rates. Expression profiling of candidate AP2/ERF genes against drought, salt and phytohormones revealed insights into their precise and/or overlapping expression patterns which could be responsible for their functional divergence in foxtail millet. The study showed that the genes SiAP2/ERF-069, SiAP2/ERF-103 and SiAP2/ERF-120 may be considered as potential candidate genes for further functional validation as well for utilization in crop improvement programs for stress resistance since these genes were up-regulated under drought and salinity stresses in ABA dependent manner. Altogether the present study provides new insights into evolution, divergence and systematic functional analysis of AP2/ERF gene family at genome level in foxtail millet which may be utilized for improving stress adaptation and tolerance in millets, cereals and bioenergy grasses. PMID:25409524

Genome-wide investigation and expression profiling of AP2/ERF transcription factor superfamily in foxtail millet (Setaria italica L.).

PubMed

Lata, Charu; Mishra, Awdhesh Kumar; Muthamilarasan, Mehanathan; Bonthala, Venkata Suresh; Khan, Yusuf; Prasad, Manoj

2014-01-01

The APETALA2/ethylene-responsive element binding factor (AP2/ERF) family is one of the largest transcription factor (TF) families in plants that includes four major sub-families, namely AP2, DREB (dehydration responsive element binding), ERF (ethylene responsive factors) and RAV (Related to ABI3/VP). AP2/ERFs are known to play significant roles in various plant processes including growth and development and biotic and abiotic stress responses. Considering this, a comprehensive genome-wide study was conducted in foxtail millet (Setaria italica L.). A total of 171 AP2/ERF genes were identified by systematic sequence analysis and were physically mapped onto nine chromosomes. Phylogenetic analysis grouped AP2/ERF genes into six classes (I to VI). Duplication analysis revealed that 12 (∼7%) SiAP2/ERF genes were tandem repeated and 22 (∼13%) were segmentally duplicated. Comparative physical mapping between foxtail millet AP2/ERF genes and its orthologs of sorghum (18 genes), maize (14 genes), rice (9 genes) and Brachypodium (6 genes) showed the evolutionary insights of AP2/ERF gene family and also the decrease in orthology with increase in phylogenetic distance. The evolutionary significance in terms of gene-duplication and divergence was analyzed by estimating synonymous and non-synonymous substitution rates. Expression profiling of candidate AP2/ERF genes against drought, salt and phytohormones revealed insights into their precise and/or overlapping expression patterns which could be responsible for their functional divergence in foxtail millet. The study showed that the genes SiAP2/ERF-069, SiAP2/ERF-103 and SiAP2/ERF-120 may be considered as potential candidate genes for further functional validation as well for utilization in crop improvement programs for stress resistance since these genes were up-regulated under drought and salinity stresses in ABA dependent manner. Altogether the present study provides new insights into evolution, divergence and systematic functional analysis of AP2/ERF gene family at genome level in foxtail millet which may be utilized for improving stress adaptation and tolerance in millets, cereals and bioenergy grasses.

Easy Method to Examine Single Nerve Fiber Excitability and Conduction Parameters Using Intact Nonanesthetized Earthworms

ERIC Educational Resources Information Center

Bähring, Robert; Bauer, Christiane K.

2014-01-01

The generation and conduction of neuronal action potentials (APs) were the subjects of a cell physiology exercise for first-year medical students. In this activity, students demonstrated the all-or-none nature of AP generation, measured conduction velocity, and examined the dependence of the threshold stimulus amplitude on stimulus duration. For…

Contributions of adaptation currents to dynamic spike threshold on slow timescales: Biophysical insights from conductance-based models

NASA Astrophysics Data System (ADS)

Yi, Guosheng; Wang, Jiang; Wei, Xile; Deng, Bin; Li, Huiyan; Che, Yanqiu

2017-06-01

Spike-frequency adaptation (SFA) mediated by various adaptation currents, such as voltage-gated K+ current (IM), Ca2+-gated K+ current (IAHP), or Na+-activated K+ current (IKNa), exists in many types of neurons, which has been shown to effectively shape their information transmission properties on slow timescales. Here we use conductance-based models to investigate how the activation of three adaptation currents regulates the threshold voltage for action potential (AP) initiation during the course of SFA. It is observed that the spike threshold gets depolarized and the rate of membrane depolarization (dV/dt) preceding AP is reduced as adaptation currents reduce firing rate. It is indicated that the presence of inhibitory adaptation currents enables the neuron to generate a dynamic threshold inversely correlated with preceding dV/dt on slower timescales than fast dynamics of AP generation. By analyzing the interactions of ionic currents at subthreshold potentials, we find that the activation of adaptation currents increase the outward level of net membrane current prior to AP initiation, which antagonizes inward Na+ to result in a depolarized threshold and lower dV/dt from one AP to the next. Our simulations demonstrate that the threshold dynamics on slow timescales is a secondary effect caused by the activation of adaptation currents. These findings have provided a biophysical interpretation of the relationship between adaptation currents and spike threshold.

Simultaneous mapping of membrane voltage and calcium in zebrafish heart in vivo reveals chamber-specific developmental transitions in ionic currents

PubMed Central

Hou, Jennifer H.; Kralj, Joel M.; Douglass, Adam D.; Engert, Florian; Cohen, Adam E.

2014-01-01

The cardiac action potential (AP) and the consequent cytosolic Ca2+ transient are key indicators of cardiac function. Natural developmental processes, as well as many drugs and pathologies change the waveform, propagation, or variability (between cells or over time) of these parameters. Here we apply a genetically encoded dual-function calcium and voltage reporter (CaViar) to study the development of the zebrafish heart in vivo between 1.5 and 4 days post fertilization (dpf). We developed a high-sensitivity spinning disk confocal microscope and associated software for simultaneous three-dimensional optical mapping of voltage and calcium. We produced a transgenic zebrafish line expressing CaViar under control of the heart-specific cmlc2 promoter, and applied ion channel blockers at a series of developmental stages to map the maturation of the action potential in vivo. Early in development, the AP initiated via a calcium current through L-type calcium channels. Between 90 and 102 h post fertilization (hpf), the ventricular AP switched to a sodium-driven upswing, while the atrial AP remained calcium driven. In the adult zebrafish heart, a sodium current drives the AP in both the atrium and ventricle. Simultaneous voltage and calcium imaging with genetically encoded reporters provides a new approach for monitoring cardiac development, and the effects of drugs on cardiac function. PMID:25309445

Simultaneous mapping of membrane voltage and calcium in zebrafish heart in vivo reveals chamber-specific developmental transitions in ionic currents.

PubMed

Hou, Jennifer H; Kralj, Joel M; Douglass, Adam D; Engert, Florian; Cohen, Adam E

2014-01-01

The cardiac action potential (AP) and the consequent cytosolic Ca(2+) transient are key indicators of cardiac function. Natural developmental processes, as well as many drugs and pathologies change the waveform, propagation, or variability (between cells or over time) of these parameters. Here we apply a genetically encoded dual-function calcium and voltage reporter (CaViar) to study the development of the zebrafish heart in vivo between 1.5 and 4 days post fertilization (dpf). We developed a high-sensitivity spinning disk confocal microscope and associated software for simultaneous three-dimensional optical mapping of voltage and calcium. We produced a transgenic zebrafish line expressing CaViar under control of the heart-specific cmlc2 promoter, and applied ion channel blockers at a series of developmental stages to map the maturation of the action potential in vivo. Early in development, the AP initiated via a calcium current through L-type calcium channels. Between 90 and 102 h post fertilization (hpf), the ventricular AP switched to a sodium-driven upswing, while the atrial AP remained calcium driven. In the adult zebrafish heart, a sodium current drives the AP in both the atrium and ventricle. Simultaneous voltage and calcium imaging with genetically encoded reporters provides a new approach for monitoring cardiac development, and the effects of drugs on cardiac function.

Unexpected Heterodivalent Recruitment of NOS1AP to nNOS Reveals Multiple Sites for Pharmacological Intervention in Neuronal Disease Models.

PubMed

Li, Li-Li; Melero-Fernandez de Mera, Raquel M; Chen, Jia; Ba, Wei; Kasri, Nael Nadif; Zhang, Mingjie; Courtney, Michael J

2015-05-13

The protein NOS1AP/CAPON mediates signaling from a protein complex of NMDA receptor, PSD95 and nNOS. The only stroke trial for neuroprotectants that showed benefit to patients targeted this ternary complex. NOS1AP/nNOS interaction regulates small GTPases, iron transport, p38MAPK-linked excitotoxicity, and anxiety. Moreover, the nos1ap gene is linked to disorders from schizophrenia, post-traumatic stress disorder, and autism to cardiovascular disorders and breast cancer. Understanding protein interactions required for NOS1AP function, therefore, has broad implications for numerous diseases. Here we show that the interaction of NOS1AP with nNOS differs radically from the classical PDZ docking assumed to be responsible. The NOS1AP PDZ motif does not bind nNOS as measured by multiple methods. In contrast, full-length NOS1AP forms an unusually stable interaction with nNOS. We mapped the discrepancy between full-length and C-terminal PDZ motif to a novel internal region we call the ExF motif. The C-terminal PDZ motif, although neither sufficient nor necessary for binding, nevertheless promotes the stability of the complex. It therefore potentially affects signal transduction and suggests that functional interaction of nNOS with NOS1AP might be targetable at two distinct sites. We demonstrate that excitotoxic pathways can be regulated, in cortical neuron and organotypic hippocampal slice cultures from rat, either by the previously described PDZ ligand TAT-GESV or by the ExF motif-bearing region of NOS1AP, even when lacking the critical PDZ residues as long as the ExF motif is intact and not mutated. This previously unrecognized heterodivalent interaction of nNOS with NOS1AP may therefore provide distinct opportunities for pharmacological intervention in NOS1AP-dependent signaling and excitotoxicity. Copyright © 2015 the authors 0270-6474/15/357349-16$15.00/0.

AP39, a mitochondria‐targeting hydrogen sulfide (H2S) donor, protects against myocardial reperfusion injury independently of salvage kinase signalling

PubMed Central

Karwi, Qutuba G; Bornbaum, Julia; Boengler, Kerstin; Torregrossa, Roberta; Whiteman, Matthew; Wood, Mark E; Schulz, Rainer

2017-01-01

Background and Purpose H2S protects myocardium against ischaemia/reperfusion injury. This protection may involve the cytosolic reperfusion injury salvage kinase (RISK) pathway, but direct effects on mitochondrial function are possible. Here, we investigated the potential cardioprotective effect of a mitochondria‐specific H2S donor, AP39, at reperfusion against ischaemia/reperfusion injury. Experimental Approach Anaesthetized rats underwent myocardial ischaemia (30 min)/reperfusion (120 min) with randomization to receive interventions before reperfusion: vehicle, AP39 (0.01, 0.1, 1 μmol·kg−1), or control compounds AP219 and ADT‐OH (1 μmol·kg−1). LY294002, L‐NAME or ODQ were used to investigate the involvement of the RISK pathway. Myocardial samples harvested 5 min after reperfusion were analysed for RISK protein phosphorylation and isolated cardiac mitochondria were used to examine the direct mitochondrial effects of AP39. Key Results AP39, dose‐dependently, reduced infarct size. Inhibition of either PI3K/Akt, eNOS or sGC did not affect this effect of AP39. Western blot analysis confirmed that AP39 did not induce phosphorylation of Akt, eNOS, GSK‐3β or ERK1/2. In isolated subsarcolemmal and interfibrillar mitochondria, AP39 significantly attenuated mitochondrial ROS generation without affecting respiratory complexes I or II. Furthermore, AP39 inhibited mitochondrial permeability transition pore (PTP) opening and co‐incubation of mitochondria with AP39 and cyclosporine A induced an additive inhibitory effect on the PTP. Conclusion and Implications AP39 protects against reperfusion injury independently of the cytosolic RISK pathway. This cardioprotective effect could be mediated by inhibiting PTP via a cyclophilin D‐independent mechanism. Thus, selective delivery of H2S to mitochondria may be therapeutically applicable for employing the cardioprotective utility of H2S. PMID:27930802

Effects of a human recombinant alkaline phosphatase on renal hemodynamics, oxygenation and inflammation in two models of acute kidney injury

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peters, Esther, E-mail: esther.peters@radboudumc.n

Two small clinical trials indicated that administration of bovine intestinal alkaline phosphatase (AP) improves renal function in critically ill patients with sepsis-associated acute kidney injury (AKI), for which the mechanism of action is not completely understood. Here, we investigated the effects of a newly developed human recombinant AP (recAP) on renal oxygenation and hemodynamics and prevention of kidney damage and inflammation in two in vivo AKI models. To induce AKI, male Wistar rats (n = 18) were subjected to renal ischemia (30 min) and reperfusion (I/R), or sham-operated. In a second model, rats (n = 18) received a 30 minmore » infusion of lipopolysaccharide (LPS; 2.5 mg/kg), or saline, and fluid resuscitation. In both models, recAP (1000 U/kg) was administered intravenously (15 min before reperfusion, or 90 min after LPS). Following recAP treatment, I/R-induced changes in renal blood flow, renal vascular resistance and oxygen delivery at early, and cortical microvascular oxygen tension at late reperfusion were no longer significantly affected. RecAP did not influence I/R-induced effects on mean arterial pressure. During endotoxemia, recAP treatment did not modulate the LPS-induced changes in systemic hemodynamics and renal oxygenation. In both models, recAP did exert a clear renal protective anti-inflammatory effect, demonstrated by attenuated immunostaining of inflammatory, tubular injury and pro-apoptosis markers. Whether this renal protective effect is sufficient to improve outcome of patients suffering from sepsis-associated AKI is being investigated in a large clinical trial. - Highlights: • Human recombinant alkaline phosphatase (recAP) is a potential new therapy for sepsis-associated acute kidney injury (AKI). • RecAP can modulate renal oxygenation and hemodynamics immediately following I/R-induced AKI. • RecAP did not modulate endotoxemia-induced changes in systemic hemodynamics and renal oxygenation. • RecAP did exert a clear renal protective anti-inflammatory effect in both models.« less

DL-2-amino-3-phosphonopropionic acid protects primary neurons from oxygen-glucose deprivation induced injury.

PubMed

Cui, Di; Xu, Jun; Xu, Quanyi; Zuo, Guokun

2017-02-21

Cerebral infarction is a type of ischemic stroke and is one of the main causes of irreversible brain damage. Although multiple neuroprotective agents have been investigated recently, the potential of DL-2-amino-3-phosphonopropionic acid (DL-AP3) in treating oxygen-glucose deprivation (OGD)-induced neuronal injury, has not been clarified yet. This study was aimed to explore the role of DL-AP3 in primary neuronal cell cultures. Primary neurons were divided into four groups: (1) a control group that was not treated; (2) DL-AP3 group treated with 10 μM of DL-AP3; (3) OGD group, in which neurons were cultured under OGD conditions; and (4) OGD + DL-AP3 group, in which OGD model was first established and then the cells were treated with 10 μM of DL-AP3. Neuronal viability and apoptosis were measured using Cell Counting Kit-8 and flow cytometry. Expressions of phospho-Akt1 (p-Akt1) and cytochrome c were detected using Western blot. The results showed that DL-AP3 did not affect neuronal viability and apoptosis in DL-AP3 group, nor it changed p-Akt1 and cytochrome c expression (p > 0.05). In OGD + DL-AP3 group, DL-AP3 significantly attenuated the inhibitory effects of OGD on neuronal viability (p < 0.001), and reduced OGD induced apoptosis (p < 0.01). Additionally, the down-regulation of p-Akt1 and up-regulation of cytochrome c, induced by OGD, were recovered to some extent after DL-AP3 treatment (p < 0.05 or p < 0.001). Overall, DL-AP3 could protect primary neurons from OGD-induced injury by affecting the viability and apoptosis of neurons, and by regulating the expressions of p-Akt1 and cytochrome c.

Effect of the 3-halo substitution of the 2'-deoxy aminopyridinyl-pseudocytidine derivatives on the selectivity and stability of antiparallel triplex DNA with a CG inversion site.

PubMed

Wang, Lei; Taniguchi, Yosuke; Okamura, Hidenori; Sasaki, Shigeki

2017-07-15

Triplex formation against a target duplex DNA has the potential to become a tool for the genome research. However, there is an intrinsic restriction on the duplex DNA sequences capable of forming the triplex DNA. Recently, we demonstrated the selective formation of the stable antiparallel triplexes containing the CG inversion sites using the 2'-deoxy-1-methylpseudocytidine derivative (ΨdC), whose amino group was conjugated with the 2-aminopyridine at its 5-position as an additional hydrogen bonding unit (AP-ΨdC). The 1-N of 2-aminopyridine was supposed to be protonated to form the hydrogen bond with the guanine of the CG inversion site. In this study, to test the effect of the 3-substitution of the 2-aminopyridine unit of AP-ΨdC on the triplex stability, we synthesized the 3-halogenated 2-aminopyridine derivatives of AP-ΨdC. The pKa values 1-N of the 2-aminopyridine unit of AP-ΨdC as the monomer nucleoside were determined to be 6.3 for 3-CH 3 ( Me AP-ΨdC), 6.1 for 3-H (AP-ΨdC), 4.3 for 3-Cl ( Cl AP-ΨdC), 4.4 for 3-Br ( Br AP-ΨdC), and 4.7 for 3-I ( I AP-ΨdC), suggesting that all the halogenated AP-ΨdCs are not protonated under neutral conditions. Interestingly, although the recognition selectivity depends on the sequence context, the TFO having the sequence of the 3'-G-( I AP-ΨdC)-A-5' context showed the selective triplex formation with the CG inversion site. These results suggest that the protonation at the 1-N position plays an important role in the stable and selective triplex formation of AP-ΨdC derivatives in any sequences. Copyright © 2017 Elsevier Ltd. All rights reserved.

The interaction of diadenosine polyphosphates with P2X-receptors in the guinea-pig isolated vas deferens

PubMed Central

Westfall, T D; McIntyre, C A; Obeid, S; Bowes, J; Kennedy, C; Sneddon, P

1997-01-01

The site(s) at which diadenosine 5′,5′′′-P1,P4-tetraphosphate (AP4A) and diadenosine 5′, 5′′′-P1,P5-pentaphosphate (AP5A) act to evoke contraction of the guinea-pig isolated vas deferens was studied by use of a series of P2-receptor antagonists and the ecto-ATPase inhibitor 6-N,N-diethyl-D-β,γ-dibromomethyleneATP (ARL 67156). Pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) (300 nM–30 μM), suramin (3–100 μM) and pyridoxal-5′-phosphate (P-5-P) (3–1000 μM) inhibited contractions evoked by equi-effective concentrations of AP5A (3 μM), AP4A (30 μM) and α,β-methyleneATP (α,β-meATP) (1 μM), in a concentration-dependent manner and abolished them at the highest concentrations used. PPADS was more potent than suramin, which in turn was more potent than P-5-P. PPADS inhibited AP5A, AP4A and α,β-meATP with similar IC50 values. No significant difference was found between IC50 values for suramin against α,β-meATP and AP5A or α,β-meATP and AP4A, but suramin was more than 2.5 times more potent against AP4A than AP5A. P-5-P showed the same pattern of antagonism. Desensitization of the P2X1-receptor by α,β-meATP abolished contractions evoked by AP5A (3 μM) and AP4A (30 μM), but had no effect on those elicited by noradrenaline (100 μM). ARL 67156 (100 μM) reversibly potentiated contractions evoked by AP4A (30 μM) by 61%, but caused a small, significant decrease in the mean response to AP5A (3 μM). It is concluded that AP4A and AP5A act at the P2X1-receptor, or a site similar to the P2X1-receptor, to evoke contraction of the guinea-pig isolated vas deferens. Furthermore, the potency of AP4A, but not AP5A, appears to be inhibited by an ecto-enzyme which is sensitive to ARL 67156. PMID:9146887

Electronic neuron within a ganglion of a leech (Hirudo medicinalis).

PubMed

Aliaga, J; Busca, N; Minces, V; Mindlin, G B; Pando, B; Salles, A; Sczcupak, L

2003-06-01

We report the construction of an electronic device that models and replaces a neuron in a midbody ganglion of the leech Hirudo medicinalis. In order to test the behavior of our device, we used a well-characterized synaptic interaction between the mechanosensory, sensitive to pressure, (P) cell and the anteropagoda (because of the action potential shape) (AP) neuron. We alternatively stimulated a P neuron and our device connected to the AP neuron, and studied the response of the latter. The number and timing of the AP spikes were the same when the electronic parameters were properly adjusted. Moreover, after changes in the depolarization of the AP cell, the responses under the stimulation of both the biological neuron and the electronic device vary in a similar manner.

Heterogeneity of ventricular repolarization in newborns with intrauterine growth restriction.

PubMed

Fouzas, Sotirios; Karatza, Ageliki A; Davlouros, Periklis A; Chrysis, Dionisios; Alexopoulos, Dimitrios; Mantagos, Stefanos; Dimitriou, Gabriel

2014-12-01

Intrauterine growth restriction (IUGR) is associated with structural and functional cardiac alterations but the electrophysiological consequences of these disturbances remain unknown. To explore the distribution of ventricular repolarization and its relation to myocardial mechanics in newborns with IUGR. STUDY DESIGN, SUBJECTS AND OUTCOME MEASUREMENTS: Conventional and tissue Doppler echocardiographic data, and electrocardiographic parameters used to describe the distribution of ventricular repolarization (dispersion of QT [QTd] and JT [JTd]), were obtained on the second (D2) and fifth (D5) postnatal day and compared between 25 IUGR newborns and 25 matched-for-gestational age controls. IUGR was associated with relative interventricular septum hypertrophy, increased left ventricular (LV) E/E' ratio and higher LV myocardial performance index (MPI). On both study days, the IUGR infants presented higher QTd and JTd compared to controls (QTd-D2: 66±20 ms vs. 36±12 ms, P<0.001; JTd-D2: 54±13 ms vs. 34±9 ms, P<0.001; QTd-D5: 61±14 ms vs. 27±12 ms, P<0.001; JTd-D5: 54±13 ms vs. 27±9 ms, P<0.001). The association between QTd and LV E/E' (D2: regression coefficient beta 0.747, R(2) 0.585; D5: beta 0.843, R(2) 0.646) and QTd and MPI (D2: beta 0.680, R(2) 0.576; D5: beta 0.698, R(2) 0.650) was also significant (P<0.001 for all analyses). Our findings suggest that IUGR is associated with electrophysiological remodeling of the neonatal heart, a process which is closely related to the underlying alterations in ventricular mechanics and might predispose to adverse electrophysiological events. Copyright © 2014 Elsevier Ltd. All rights reserved.

Charge immobilization of the voltage sensor in domain IV is independent of sodium current inactivation.

PubMed

Sheets, Michael F; Hanck, Dorothy A

2005-02-15

Recovery from fast inactivation in voltage-dependent Na+ channels is associated with a slow component in the time course of gating charge during repolarization (i.e. charge immobilization), which results from the slow movement of the S4 segments in domains III and IV (S4-DIII and S4-DIV). Previous studies have shown that the non-specific removal of fast inactivation by the proteolytic enzyme pronase eliminated charge immobilization, while the specific removal of fast inactivation (by intracellular MTSET modification of a cysteine substituted for the phenylalanine in the IFM motif, ICMMTSET, in the inactivation particle formed by the linker between domains III and IV) only reduced the amount of charge immobilization by nearly one-half. To investigate the molecular origin of the remaining slow component of charge immobilization we studied the human cardiac Na+ channel (hH1a) in which the outermost arginine in the S4-DIV, which contributes approximately 20% to total gating charge (Qmax), was mutated to a cysteine (R1C-DIV). Gating charge could be fully restored in R1C-DIV by exposure to extracellular MTSEA, a positively charged methanethiosulphonate reagent. The RIC-DIV mutation was combined with ICMMTSET to remove fast inactivation, and the gating currents of R1C-DIV-ICM(MTSET) were recorded before and after modification with MTSEAo. Prior to MTSEAo, the time course of the gating charge during repolarization (off-charge) was best described by a single fast time constant. After MTSEA, the off-charge had both fast and slow components, with the slow component accounting for nearly 35% of Qmax. These results demonstrate that the slow movement of the S4-DIV during repolarization is not dependent upon the normal binding of the inactivation particle.