Fast calcium and voltage-sensitive dye imaging in enteric neurones reveal calcium peaks associated with single action potential discharge.

PubMed

Michel, K; Michaelis, M; Mazzuoli, G; Mueller, K; Vanden Berghe, P; Schemann, M

2011-12-15

Slow changes in [Ca(2+)](i) reflect increased neuronal activity. Our study demonstrates that single-trial fast [Ca(2+)](i) imaging (≥200 Hz sampling rate) revealed peaks each of which are associated with single spike discharge recorded by consecutive voltage-sensitive dye (VSD) imaging in enteric neurones and nerve fibres. Fast [Ca(2+)](i) imaging also revealed subthreshold fast excitatory postsynaptic potentials. Nicotine-evoked [Ca(2+)](i) peaks were reduced by -conotoxin and blocked by ruthenium red or tetrodotoxin. Fast [Ca(2+)](i) imaging can be used to directly record single action potentials in enteric neurones. [Ca(2+)](i) peaks required opening of voltage-gated sodium and calcium channels as well as Ca(2+) release from intracellular stores.

Competition between calcium-activated K+ channels determines cholinergic action on firing properties of basolateral amygdala projection neurons.

PubMed

Power, John M; Sah, Pankaj

2008-03-19

Acetylcholine (ACh) is an important modulator of learning, memory, and synaptic plasticity in the basolateral amygdala (BLA) and other brain regions. Activation of muscarinic acetylcholine receptors (mAChRs) suppresses a variety of potassium currents, including sI(AHP), the calcium-activated potassium conductance primarily responsible for the slow afterhyperpolarization (AHP) that follows a train of action potentials. Muscarinic stimulation also produces inositol 1,4,5-trisphosphate (IP(3)), releasing calcium from intracellular stores. Here, we show using whole-cell patch-clamp recordings and high-speed fluorescence imaging that focal application of mAChR agonists evokes large rises in cytosolic calcium in the soma and proximal dendrites in rat BLA projection neurons that are often associated with activation of an outward current that hyperpolarizes the cell. This hyperpolarization results from activation of small conductance calcium-activated potassium (SK) channels, secondary to the release of calcium from intracellular stores. Unlike bath application of cholinergic agonists, which always suppressed the AHP, focal application of ACh often evoked a paradoxical enhancement of the AHP and spike-frequency adaptation. This enhancement was correlated with amplification of the action potential-evoked calcium response and resulted from the activation of SK channels. When SK channels were blocked, cholinergic stimulation always reduced the AHP and spike-frequency adaptation. Conversely, suppression of the sI(AHP) by the beta-adrenoreceptor agonist, isoprenaline, potentiated the cholinergic enhancement of the AHP. These results suggest that competition between cholinergic suppression of the sI(AHP) and cholinergic activation of the SK channels shapes the AHP and spike-frequency adaptation.

Action potentials drive body wall muscle contractions in Caenorhabditis elegans

PubMed Central

Gao, Shangbang; Zhen, Mei

2011-01-01

The sinusoidal locomotion exhibited by Caenorhabditis elegans predicts a tight regulation of contractions and relaxations of its body wall muscles. Vertebrate skeletal muscle contractions are driven by voltage-gated sodium channel–dependent action potentials. How coordinated motor outputs are regulated in C. elegans, which does not have voltage-gated sodium channels, remains unknown. Here, we show that C. elegans body wall muscles fire all-or-none, calcium-dependent action potentials that are driven by the L-type voltage-gated calcium and Kv1 voltage-dependent potassium channels. We further demonstrate that the excitatory and inhibitory motoneuron activities regulate the frequency of action potentials to coordinate muscle contraction and relaxation, respectively. This study provides direct evidence for the dual-modulatory model of the C. elegans motor circuit; moreover, it reveals a mode of motor control in which muscle cells integrate graded inputs of the nervous system and respond with all-or-none electrical signals. PMID:21248227

Na+/H+ exchanger 3 inhibitor diminishes hepcidin-enhanced duodenal calcium transport in hemizygous β-globin knockout thalassemic mice.

PubMed

Charoenphandhu, Narattaphol; Kraidith, Kamonshanok; Lertsuwan, Kornkamon; Sripong, Chanakarn; Suntornsaratoon, Panan; Svasti, Saovaros; Krishnamra, Nateetip; Wongdee, Kannikar

2017-03-01

Recent investigation has shown that the liver-derived iron-regulating hormone, hepcidin, can potentiate intestinal calcium absorption in hemizygous β-globin knockout thalassemic (BKO) mice. Since the upregulation of Fe 2+ and H + cotransporter, divalent metal transporter (DMT)-1, has been shown to correlate with thalassemia-induced intestinal calcium absorption impairment, the inhibition of the apical Na + /H + exchanger (NHE)-3 that is essential for cytoplasmic pH regulation and transepithelial sodium absorption was hypothesized to negatively affect hepcidin action. Herein, the positive effect of hepcidin on the duodenal calcium transport was evaluated using Ussing chamber technique. The results showed that BKO mice had lower absorptive surface area and duodenal calcium transport than wild-type mice. Besides, paracellular transport of zinc in BKO mice was compromised. Hepcidin administration completely restored calcium transport. Since this hepcidin action was totally abolished by inhibitors of the basolateral calcium transporters, Na + /Ca 2+ exchanger (NCX1) and plasma membrane Ca 2+ -ATPase (PMCA 1b ), the enhanced calcium flux potentially occurred through the transcellular pathway rather than paracellular pathway. Interestingly, the selective NHE3 inhibitor, 100 nM tenapanor, markedly inhibited hepcidin-enhanced calcium transport. Accordingly, hepcidin is one of the promising therapeutic agents for calcium malabsorption in β-thalassemia. It mainly stimulates the transcellular calcium transport across the duodenal epithelium in an NHE3-dependent manner.

Spine Calcium Transients Induced by Synaptically-Evoked Action Potentials Can Predict Synapse Location and Establish Synaptic Democracy

PubMed Central

Meredith, Rhiannon M.; van Ooyen, Arjen

2012-01-01

CA1 pyramidal neurons receive hundreds of synaptic inputs at different distances from the soma. Distance-dependent synaptic scaling enables distal and proximal synapses to influence the somatic membrane equally, a phenomenon called “synaptic democracy”. How this is established is unclear. The backpropagating action potential (BAP) is hypothesised to provide distance-dependent information to synapses, allowing synaptic strengths to scale accordingly. Experimental measurements show that a BAP evoked by current injection at the soma causes calcium currents in the apical shaft whose amplitudes decay with distance from the soma. However, in vivo action potentials are not induced by somatic current injection but by synaptic inputs along the dendrites, which creates a different excitable state of the dendrites. Due to technical limitations, it is not possible to study experimentally whether distance information can also be provided by synaptically-evoked BAPs. Therefore we adapted a realistic morphological and electrophysiological model to measure BAP-induced voltage and calcium signals in spines after Schaffer collateral synapse stimulation. We show that peak calcium concentration is highly correlated with soma-synapse distance under a number of physiologically-realistic suprathreshold stimulation regimes and for a range of dendritic morphologies. Peak calcium levels also predicted the attenuation of the EPSP across the dendritic tree. Furthermore, we show that peak calcium can be used to set up a synaptic democracy in a homeostatic manner, whereby synapses regulate their synaptic strength on the basis of the difference between peak calcium and a uniform target value. We conclude that information derived from synaptically-generated BAPs can indicate synapse location and can subsequently be utilised to implement a synaptic democracy. PMID:22719238

Calcium dynamics in cardiac excitatory and non-excitatory cells and the role of gap junction.

PubMed

Das, Phonindra Nath; Mehrotra, Parul; Mishra, Aseem; Bairagi, Nandadulal; Chatterjee, Samrat

2017-07-01

Calcium ions aid in the generation of action potential in myocytes and are responsible for the excitation-contraction coupling of heart. The heart muscle has specialized patches of cells, called excitatory cells (EC) such as the Sino-atrial node cells capable of auto-generation of action potential and cells which receive signals from the excitatory cells, called non-excitatory cells (NEC) such as cells of the ventricular and auricular walls. In order to understand cardiac calcium homeostasis, it is, therefore, important to study the calcium dynamics taking into account both types of cardiac cells. Here we have developed a model to capture the calcium dynamics in excitatory and non-excitatory cells taking into consideration the gap junction mediated calcium ion transfer from excitatory cell to non-excitatory cell. Our study revealed that the gap junctional coupling between excitatory and non-excitatory cells plays important role in the calcium dynamics. It is observed that any reduction in the functioning of gap junction may result in abnormal calcium oscillations in NEC, even when the calcium dynamics is normal in EC cell. Sensitivity of gap junction is observed to be independent of the pacing rate and hence a careful monitoring is required to maintain normal cardiomyocyte condition. It also highlights that sarcoplasmic reticulum may not be always able to control the amount of cytoplasmic calcium under the condition of calcium overload. Copyright © 2017 Elsevier Inc. All rights reserved.

Active action potential propagation but not initiation in thalamic interneuron dendrites

PubMed Central

Casale, Amanda E.; McCormick, David A.

2012-01-01

Inhibitory interneurons of the dorsal lateral geniculate nucleus of the thalamus modulate the activity of thalamocortical cells in response to excitatory input through the release of inhibitory neurotransmitter from both axons and dendrites. The exact mechanisms by which release can occur from dendrites are, however, not well understood. Recent experiments using calcium imaging have suggested that Na/K based action potentials can evoke calcium transients in dendrites via local active conductances, making the back-propagating action potential a candidate for dendritic neurotransmitter release. In this study, we employed high temporal and spatial resolution voltage-sensitive dye imaging to assess the characteristics of dendritic voltage deflections in response to Na/K action potentials in interneurons of the mouse dorsal lateral geniculate nucleus. We found that trains or single action potentials elicited by somatic current injection or local synaptic stimulation led to action potentials that rapidly and actively back-propagated throughout the entire dendritic arbor and into the fine filiform dendritic appendages known to release GABAergic vesicles. Action potentials always appeared first in the soma or proximal dendrite in response to somatic current injection or local synaptic stimulation, and the rapid back-propagation into the dendritic arbor depended upon voltage-gated sodium and TEA-sensitive potassium channels. Our results indicate that thalamic interneuron dendrites integrate synaptic inputs that initiate action potentials, most likely in the axon initial segment, that then back-propagate with high-fidelity into the dendrites, resulting in a nearly synchronous release of GABA from both axonal and dendritic compartments. PMID:22171033

Voltage-gated currents in identified rat olfactory receptor neurons.

PubMed

Trombley, P Q; Westbrook, G L

1991-02-01

Whole-cell recording techniques were used to characterize voltage-gated membrane currents in neonatal rat olfactory receptor neurons (ORNs) in cell culture. Mature ORNs were identified in culture by their characteristic bipolar morphology, by retrograde labeling techniques, and by olfactory marker protein (OMP) immunoreactivity. ORNs did not have spontaneous activity, but fired action potentials to depolarizing current pulses. Action potentials were blocked by tetrodotoxin (TTX), which contrasts with the TTX-resistant action potentials in salamander olfactory receptor cells (e.g., Firestein and Werblin, 1987). Prolonged, suprathreshold current pulses evoked only a single action potential; however, repetitive firing up to 35 Hz could be elicited by a series of brief depolarizing pulses. Under voltage clamp, the TTX-sensitive sodium current had activation and inactivation properties similar to other excitable cells. In TTX and 20 mM barium, sustained inward current were evoked by voltage steps positive to -30 mV. This current was blocked by Cd (100 microM) and by nifedipine (IC50 = 368 nM) consistent with L-type calcium channels in other neurons. No T-type calcium current was observed. Voltage steps positive to -20 mV also evoked an outward current that did not inactivate during 100-msec depolarizations. Tail current analysis of this current was consistent with a selective potassium conductance. The outward current was blocked by external tetraethylammonium but was unaffected by Cd or 4-aminopyridine (4-AP) or by removal of external calcium. A transient outward current was not observed. The 3 voltage-dependent conductances in cultured rat ORNs appear to be sufficient for 2 essential functions: action potential generation and transmitter release. As a single odorant-activated channel can trigger an action potential (e.g., Lynch and Barry, 1989), the repetitive firing seen with brief depolarizing pulses suggests that ORNs do not integrate sensory input, but rather act as high-fidelity relays such that each opening of an odorant-activated channel reaches the olfactory bulb glomeruli as an action potential.

Back-Propagation of Physiological Action Potential Output in Dendrites of Slender-Tufted L5A Pyramidal Neurons

PubMed Central

Grewe, Benjamin F.; Bonnan, Audrey; Frick, Andreas

2009-01-01

Pyramidal neurons of layer 5A are a major neocortical output type and clearly distinguished from layer 5B pyramidal neurons with respect to morphology, in vivo firing patterns, and connectivity; yet knowledge of their dendritic properties is scant. We used a combination of whole-cell recordings and Ca2+ imaging techniques in vitro to explore the specific dendritic signaling role of physiological action potential patterns recorded in vivo in layer 5A pyramidal neurons of the whisker-related ‘barrel cortex’. Our data provide evidence that the temporal structure of physiological action potential patterns is crucial for an effective invasion of the main apical dendrites up to the major branch point. Both the critical frequency enabling action potential trains to invade efficiently and the dendritic calcium profile changed during postnatal development. In contrast to the main apical dendrite, the more passive properties of the short basal and apical tuft dendrites prevented an efficient back-propagation. Various Ca2+ channel types contributed to the enhanced calcium signals during high-frequency firing activity, whereas A-type K+ and BKCa channels strongly suppressed it. Our data support models in which the interaction of synaptic input with action potential output is a function of the timing, rate and pattern of action potentials, and dendritic location. PMID:20508744

One nuclear calcium transient induced by a single burst of action potentials represents the minimum signal strength in activity-dependent transcription in hippocampal neurons.

PubMed

Yu, Yan; Oberlaender, Kristin; Bengtson, C Peter; Bading, Hilmar

2017-07-01

Neurons undergo dramatic changes in their gene expression profiles in response to synaptic stimulation. The coupling of neuronal excitation to gene transcription is well studied and is mediated by signaling pathways activated by cytoplasmic and nuclear calcium transients. Despite this, the minimum synaptic activity required to induce gene expression remains unknown. To address this, we used cultured hippocampal neurons and cellular compartment analysis of temporal activity by fluorescence in situ hybridization (catFISH) that allows detection of nascent transcripts in the cell nucleus. We found that a single burst of action potentials, consisting of 24.4±5.1 action potentials during a 6.7±1.9s depolarization of 19.5±2.0mV causing a 9.3±0.9s somatic calcium transient, is sufficient to activate transcription of the immediate early gene arc (also known as Arg3.1). The total arc mRNA yield produced after a single burst-induced nuclear calcium transient was very small and, compared to unstimulated control neurons, did not lead to a significant increase in arc mRNA levels measured using quantitative reverse transcriptase PCR (qRT-PCR) of cell lysates. Significantly increased arc mRNA levels became detectable in hippocampal neurons that had undergone 5-8 consecutive burst-induced nuclear calcium transients at 0.05-0.15Hz. These results indicate that a single burst-induced nuclear calcium transient can activate gene expression and that transcription is rapidly shut off after synaptic stimulation has ceased. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effects of changing the ionic environment on passive and active membrane properties of pregnant rat uterus

PubMed Central

Abe, Y.

1971-01-01

1. In pregnant rat myometrium electrotonic potentials, produced by externally applied current, were recorded intracellularly. 2. The space constant, λ, was 1·8 mm, the time constant, τm, 120 msec. The values obtained on the 7th day and on the 20th day of pregnancy were the same. 3. The magnitude of the electrotonic potential and the time constant of the membrane were increased in the absence of potassium from the external solution and decreased by excess potassium. 4. The magnitude of the electrotonic potential and the time constant of the membrane were increased by the replacement of chloride with C6H5SO3- or SO42-, and decreased with NO3- or I- replacement. 5. When the sodium chloride was replaced with sucrose (16·7 mM sodium remaining in the buffers) the spontaneous spikes deteriorated and activity stopped within 30 min. However, for periods up to 4 hr, a spike of larger amplitude and faster rate of rise than in normal solution could be evoked when a depolarizing current was applied. 6. When the external calcium concentration was raised (5 and 10 mM) the amplitude and the rate of rise of the evoked spike were increased. They were decreased by reducing calcium. In zero calcium spontaneous activity stopped within 15 min. 7. The effects of calcium deficiency were much less marked and slower in onset when, simultaneously, the sodium concentration was reduced to 16·7 mM. 8. When calcium was replaced with strontium (2·5 mM), the membrane was depolarized and the duration of the spontaneous and evoked action potential was prolonged, mainly due to a slowed rate of repolarization. When the concentration of strontium was raised to 7·5 or 12·5 mM the membrane was hyperpolarized, the duration of the action potential became short and the amplitude of the spike was increased. 9. Addition of barium or the replacement of calcium with barium caused depolarization and oscillatory membrane activity. However, a spike could be evoked by applying conditioning hyperpolarization. 10. Manganese abolished the spontaneous and evoked spike. Tetrodotoxin had no effect. 11. The results show that rat uterus has cable-like properties. The action potential may be due to calcium entry, while sodium, by influencing the membrane potential in competition with calcium, may be involved in the spontaneous spike generation and the spread of excitation. PMID:5103422

Nanopore formation in neuroblastoma cells following ultrashort electric pulse exposure

NASA Astrophysics Data System (ADS)

Roth, Caleb C.; Payne, Jason A.; Wilmink, Gerald J.; Ibey, Bennett L.

2011-03-01

Ultrashort or nanosecond electrical pulses (USEP) cause repairable damage to the plasma membranes of cells through formation of nanopores. These nanopores are able to pass small ions such as sodium, calcium, and potassium, but remain impermeable to larger molecules like trypan blue and propidium iodide. What remains uncertain is whether generation of nanopores by ultrashort electrical pulses can inhibit action potentials in excitable cells. In this paper, we explored the sensitivity of excitable cells to USEP using Calcium Green AM 1 ester fluorescence to measure calcium uptake indicative of nanopore formation in the plasma membrane. We determined the threshold for nanopore formation in neuroblastoma cells for three pulse parameters (amplitude, pulse width, and pulse number). Measurement of such thresholds will guide future studies to determine if USEP can inhibit action potentials without causing irreversible membrane damage.

Ionotropic glutamate receptor GluA4 and T-type calcium channel Cav 3.1 subunits control key aspects of synaptic transmission at the mouse L5B-POm giant synapse.

PubMed

Seol, Min; Kuner, Thomas

2015-12-01

The properties and molecular determinants of synaptic transmission at giant synapses connecting layer 5B (L5B) neurons of the somatosensory cortex (S1) with relay neurons of the posteriomedial nucleus (POm) of the thalamus have not been investigated in mice. We addressed this by using direct electrical stimulation of fluorescently labelled single corticothalamic terminals combined with molecular perturbations and whole-cell recordings from POm relay neurons. Consistent with their function as drivers, we found large-amplitude excitatory postsynaptic currents (EPSCs) and multiple postsynaptic action potentials triggered by a single presynaptic action potential. To study the molecular basis of these two features, ionotropic glutamate receptors and low voltage-gated T-type calcium channels were probed by virus-mediated genetic perturbation. Loss of GluA4 almost abolished the EPSC amplitude, strongly delaying the onset of action potential generation, but maintaining the number of action potentials generated per presynaptic action potential. In contrast, knockdown of the Cav 3.1 subunit abrogated the driver function of the synapse at a typical resting membrane potential of -70 mV. However, when depolarizing the membrane potential to -60 mV, the synapse relayed single action potentials. Hence, GluA4 subunits are required to produce an EPSC sufficiently large to trigger postsynaptic action potentials within a defined time window after the presynaptic action potential, while Cav 3.1 expression is essential to establish the driver function of L5B-POm synapses at hyperpolarized membrane potentials. © 2015 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Memristive Model of the Barnacle Giant Muscle Fibers

NASA Astrophysics Data System (ADS)

Sah, Maheshwar Pd.; Kim, Hyongsuk; Eroglu, Abdullah; Chua, Leon

The generation of action potentials (oscillations) in biological systems is a complex, yet poorly understood nonlinear dynamical phenomenon involving ions. This paper reveals that the time-varying calcium ion and the time-varying potassium ion, which are essential for generating action potentials in Barnacle giant muscle fibers are in fact generic memristors in the perspective of electrical circuit theory. We will show that these two ions exhibit all the fingerprints of memristors from the equations of the Morris-Lecar model of the Barnacle giant muscle fibers. This paper also gives a textbook reference to understand the difference between memristor and nonlinear resistor via analysis of the potassium ion-channel memristor and calcium ion-channel nonlinear resistor. We will also present a comprehensive in-depth analysis of the generation of action potentials (oscillations) in memristive Morris-Lecar model using small-signal circuit model and the Hopf bifurcation theorem.

Characterization of postsynaptic calcium signals in the pyramidal neurons of anterior cingulate cortex

PubMed Central

Li, Xu-Hui; Song, Qian; Chen, Tao; Zhuo, Min

2017-01-01

Calcium signaling is critical for synaptic transmission and plasticity. N-methyl-D-aspartic acid (NMDA) receptors play a key role in synaptic potentiation in the anterior cingulate cortex. Most previous studies of calcium signaling focus on hippocampal neurons, little is known about the activity-induced calcium signals in the anterior cingulate cortex. In the present study, we show that NMDA receptor-mediated postsynaptic calcium signals induced by different synaptic stimulation in anterior cingulate cortex pyramidal neurons. Single and multi-action potentials evoked significant suprathreshold Ca2+ increases in somas and spines. Both NMDA receptors and voltage-gated calcium channels contributed to this increase. Postsynaptic Ca2+signals were induced by puff-application of glutamate, and a NMDA receptor antagonist AP5 blocked these signals in both somas and spines. Finally, long-term potentiation inducing protocols triggered postsynaptic Ca2+ influx, and these influx were NMDA receptor dependent. Our results provide the first study of calcium signals in the anterior cingulate cortex and demonstrate that NMDA receptors play important roles in postsynaptic calcium signals in anterior cingulate cortex pyramidal neurons. PMID:28726541

Differential calcium sensitivity in NaV 1.5 mixed syndrome mutants.

PubMed

Abdelsayed, Mena; Baruteau, Alban-Elouen; Gibbs, Karen; Sanatani, Shubhayan; Krahn, Andrew D; Probst, Vincent; Ruben, Peter C

2017-09-15

SCN5a mutations may express gain-of-function (Long QT Syndrome-3), loss-of-function (Brugada Syndrome 1) or both (mixed syndromes), depending on the mutation and environmental triggers. One such trigger may be an increase in cytosolic calcium, accompanying exercise. Many mixed syndromes mutants, including ∆KPQ, E1784K, 1795insD and Q1909R, are found in calcium-sensitive regions. Elevated cytosolic calcium attenuates gain-of-function properties in ∆KPQ, 1795insD and Q1909R, but not in E1784K. By contrast, elevated cytosolic calcium further exacerbates gain-of-function in E1784K by destabilizing slow inactivation. Action potential modelling, using a modified O'Hara Rudy model, suggests that elevated heart rate rescues action potential duration in ∆KPQ, 1795insD and Q1909R, but not in E1784K. Action potential simulations suggest that E1784K carriers have an increased intracellular sodium-to-calcium ratio under bradycardia and tachycardia conditions. Elevated cytosolic calcium, which is common during high heart rates, ameliorates or exacerbates the mixed syndrome phenotype depending on the genetic signature. Inherited arrhythmias may arise from mutations in the gene for SCN5a, which encodes the cardiac voltage-gated sodium channel, Na V 1.5. Mutants in Na V 1.5 result in Brugada Syndrome (BrS1), Long-QT Syndrome (LQT3) or mixed syndromes (an overlap of BrS1/LQT3). Exercise is a potential arrhythmogenic trigger in mixed syndromes. We aimed to determine the effects of elevated cytosolic calcium, which is common during exercise, in mixed syndrome Na V 1.5 mutants. We used whole-cell patch clamp to assess the biophysical properties of Na V 1.5 wild-type (WT), ∆KPQ, E1784K, 1795insD and Q1909R mutants in human embryonic kidney 293 cells transiently transfected with the Na V 1.5 α subunit (WT or mutants), β1 subunit and enhanced green fluorescent protein. Voltage-dependence and kinetics were measured at cytosolic calcium levels of approximately 0, 500 and 2500 nm. In silico, action potential (AP) model simulations were performed using a modified O'Hara Rudy model. Elevated cytosolic calcium attenuates the late sodium current in ∆KPQ, 1795insD and Q1909R, but not in E1784K. Elevated cytosolic calcium restores steady-state slow inactivation (SSSI) to the WT-form in Q1909R, but depolarized SSSI in E1784K. Our AP simulations showed a frequency-dependent reduction of AP duration in ∆KPQ, 1795insD and Q1909R carriers. In E1784K, AP duration is relatively prolonged at both low and high heart rates, resulting in a sodium overload. Cellular perturbations during exercise may affect BrS1/LQT3 patients differently depending on their individual genetic signature. Thus, exercise may be therapeutic or may be an arrhythmogenic trigger in some SCN5a patients. © 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.

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.

Atorvastatin affects negatively respiratory function of isolated endothelial mitochondria.

PubMed

Broniarek, Izabela; Jarmuszkiewicz, Wieslawa

2018-01-01

The purpose of this research was to elucidate the direct effects of two popular blood cholesterol-lowering drugs used to treat cardiovascular diseases, atorvastatin and pravastatin, on respiratory function, membrane potential, and reactive oxygen species formation in mitochondria isolated from human umbilical vein endothelial cells (EA.hy926 cell line). Hydrophilic pravastatin did not significantly affect endothelial mitochondria function. In contrast, hydrophobic calcium-containing atorvastatin induced a loss of outer mitochondrial membrane integrity, an increase in hydrogen peroxide formation, and reductions in maximal (phosphorylating or uncoupled) respiratory rate, membrane potential and oxidative phosphorylation efficiency. The atorvastatin-induced changes indicate an impairment of mitochondrial function at the level of ATP synthesis and at the level of the respiratory chain, likely at complex I and complex III. The atorvastatin action on endothelial mitochondria was highly dependent on calcium ions and led to a disturbance in mitochondrial calcium homeostasis. Uptake of calcium ions included in atorvastatin molecule induced mitochondrial uncoupling that enhanced the inhibition of the mitochondrial respiratory chain by atorvastatin. Our results indicate that hydrophobic calcium-containing atorvastatin, widely used as anti-atherosclerotic agent, has a direct negative action on isolated endothelial mitochondria. Copyright © 2017. Published by Elsevier Inc.

Cellular Mechanisms of Myocardial Depression in Porcine Septic Shock.

PubMed

Jarkovska, Dagmar; Markova, Michaela; Horak, Jan; Nalos, Lukas; Benes, Jan; Al-Obeidallah, Mahmoud; Tuma, Zdenek; Sviglerova, Jitka; Kuncova, Jitka; Matejovic, Martin; Stengl, Milan

2018-01-01

The complex pathogenesis of sepsis and septic shock involves myocardial depression, the pathophysiology of which, however, remains unclear. In this study, cellular mechanisms of myocardial depression were addressed in a clinically relevant, large animal (porcine) model of sepsis and septic shock. Sepsis was induced by fecal peritonitis in eight anesthetized, mechanically ventilated, and instrumented pigs of both sexes and continued for 24 h. In eight control pigs, an identical experiment but without sepsis induction was performed. In vitro analysis of cardiac function included measurements of action potentials and contractions in the right ventricle trabeculae, measurements of sarcomeric contractions, calcium transients and calcium current in isolated cardiac myocytes, and analysis of mitochondrial respiration by ultrasensitive oxygraphy. Increased values of modified sequential organ failure assessment score and serum lactate levels documented the development of sepsis/septic shock, accompanied by hyperdynamic circulation with high heart rate, increased cardiac output, peripheral vasodilation, and decreased stroke volume. In septic trabeculae, action potential duration was shortened and contraction force reduced. In septic cardiac myocytes, sarcomeric contractions, calcium transients, and L-type calcium current were all suppressed. Similar relaxation trajectory of the intracellular calcium-cell length phase-plane diagram indicated unchanged calcium responsiveness of myofilaments. Mitochondrial respiration was diminished through inhibition of Complex II and Complex IV. Defective calcium handling with reduced calcium current and transients, together with inhibition of mitochondrial respiration, appears to represent the dominant cellular mechanisms of myocardial depression in porcine septic shock.

Remodelling of action potential and intracellular calcium cycling dynamics during subacute myocardial infarction promotes ventricular arrhythmias in Langendorff-perfused rabbit hearts

PubMed Central

Chou, Chung-Chuan; Zhou, Shengmei; Hayashi, Hideki; Nihei, Motoki; Liu, Yen-Bin; Wen, Ming-Shien; Yeh, San-Jou; Fishbein, Michael C; Weiss, James N; Lin, Shien-Fong; Wu, Delon; Chen, Peng-Sheng

2007-01-01

We hypothesize that remodelling of action potential and intracellular calcium (Cai) dynamics in the peri-infarct zone contributes to ventricular arrhythmogenesis in the postmyocardial infarction setting. To test this hypothesis, we performed simultaneous optical mapping of Cai and membrane potential (Vm) in the left ventricle in 15 rabbit hearts with myocardial infarction for 1 week. Ventricular premature beats frequently originated from the peri-infarct zone, and 37% showed elevation of Cai prior to Vm depolarization, suggesting reverse excitation–contraction coupling as their aetiology. During electrically induced ventricular fibrillation, the highest dominant frequency was in the peri-infarct zone in 61 of 70 episodes. The site of highest dominant frequency had steeper action potential duration restitution and was more susceptible to pacing-induced Cai alternans than sites remote from infarct. Wavebreaks during ventricular fibrillation tended to occur at sites of persistently elevated Cai. Infusion of propranolol flattened action potential duration restitution, reduced wavebreaks and converted ventricular fibrillation to ventricular tachycardia. We conclude that in the subacute phase of myocardial infarction, the peri-infarct zone exhibits regions with steep action potential duration restitution slope and unstable Cai dynamics. These changes may promote ventricular extrasystoles and increase the incidence of wavebreaks during ventricular fibrillation. Whereas increased tissue heterogeneity after subacute myocardial infarction creates a highly arrhythmogenic substrate, dynamic action potential and Cai cycling remodelling also contribute to the initiation and maintenance of ventricular fibrillation in this setting. PMID:17272354

Optical cell stimulation for neuronal excitation (Conference Presentation)

NASA Astrophysics Data System (ADS)

Johannsmeier, Sonja; Heeger, Patrick; Terakawa, Mitsuhiro; Heisterkamp, Alexander; Ripken, Tammo; Heinemann, Dag

2017-02-01

Optical manipulation of cellular functions represents a growing field in biomedical sciences. The possibility to modulate specific targets with high spatial and temporal precision in a contactless manner allows a broad range of applications. Here, we present a study on stimulation of neuronal cells by optical means. As a long-term objective, we seek to improve the performance of current electric neurostimulation, especially in the context of cochlear implants. Firstly, we tested a gold nanoparticle mediated approach to modulate transmembrane conductivity by irradiation using a picosecond pulsed Nd:YAG laser at 532 nm for 40 ms in a neuroblastoma cell line (N2A) and primary murine neurons. The light absorption leads to a rapid temperature increase of the gold nanoparticles, which can induce an increased permeabilisation of the cellular membrane. Calcium transients were recorded as an indicator of neuronal activity. Although calcium signals were reliably detected upon laser irradiation, the temporal behavior did not resemble action potentials. The origin of these signals was investigated by an inhibitor study. These results indicate calcium induced calcium release (CICR) as the major source of the calcium transients. Consecutively, we tested alternative approaches for cell stimulation, such as glutamate release and optogenetics, and evaluated the potential of these methods for the application in a cochlear implant. Compared to the gold nanoparticle approach, both techniques induce less cellular stress and reliably produce action potentials.

Simultaneous Quantification of Spatially Discordant Alternans in Voltage and Intracellular Calcium in Langendorff-Perfused Rabbit Hearts and Inconsistencies with Models of Cardiac Action Potentials and Ca Transients

PubMed Central

Uzelac, Ilija; Ji, Yanyan C.; Hornung, Daniel; Schröder-Scheteling, Johannes; Luther, Stefan; Gray, Richard A.; Cherry, Elizabeth M.; Fenton, Flavio H.

2017-01-01

Rationale: Discordant alternans, a phenomenon in which the action potential duration (APDs) and/or intracellular calcium transient durations (CaDs) in different spatial regions of cardiac tissue are out of phase, present a dynamical instability for complex spatial dispersion that can be associated with long-QT syndrome (LQTS) and the initiation of reentrant arrhythmias. Because the use of numerical simulations to investigate arrhythmic effects, such as acquired LQTS by drugs is beginning to be studied by the FDA, it is crucial to validate mathematical models that may be used during this process. Objective: In this study, we characterized with high spatio-temporal resolution the development of discordant alternans patterns in transmembrane voltage (Vm) and intracellular calcium concentration ([Cai]+2) as a function of pacing period in rabbit hearts. Then we compared the dynamics to that of the latest state-of-the-art model for ventricular action potentials and calcium transients to better understand the underlying mechanisms of discordant alternans and compared the experimental data to the mathematical models representing Vm and [Cai]+2 dynamics. Methods and Results: We performed simultaneous dual optical mapping imaging of Vm and [Cai]+2 in Langendorff-perfused rabbit hearts with higher spatial resolutions compared with previous studies. The rabbit hearts developed discordant alternans through decreased pacing period protocols and we quantified the presence of multiple nodal points along the direction of wave propagation, both in APD and CaD, and compared these findings with results from theoretical models. In experiments, the nodal lines of CaD alternans have a steeper slope than those of APD alternans, but not as steep as predicted by numerical simulations in rabbit models. We further quantified several additional discrepancies between models and experiments. Conclusions: Alternans in CaD have nodal lines that are about an order of magnitude steeper compared to those of APD alternans. Current action potential models lack the necessary coupling between voltage and calcium compared to experiments and fail to reproduce some key dynamics such as, voltage amplitude alternans, smooth development of calcium alternans in time, conduction velocity and the steepness of the nodal lines of APD and CaD. PMID:29104543

Altered calcium handling and increased contraction force in human embryonic stem cell derived cardiomyocytes following short term dexamethasone exposure

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

Kosmidis, Georgios; Bellin, Milena; Ribeiro, Marcelo C.

One limitation in using human pluripotent stem cell derived cardiomyocytes (hPSC-CMs) for disease modeling and cardiac safety pharmacology is their immature functional phenotype compared with adult cardiomyocytes. Here, we report that treatment of human embryonic stem cell derived cardiomyocytes (hESC-CMs) with dexamethasone, a synthetic glucocorticoid, activated glucocorticoid signaling which in turn improved their calcium handling properties and contractility. L-type calcium current and action potential properties were not affected by dexamethasone but significantly faster calcium decay, increased forces of contraction and sarcomeric lengths, were observed in hESC-CMs after dexamethasone exposure. Activating the glucocorticoid pathway can thus contribute to mediating hPSC-CMs maturation.more » - Highlights: • Dexamethasone accelerates Ca{sup 2+} transient decay in hESC-CMs. • Dexamethasone enhances SERCA and NCX function in hESC-CMs. • Dexamethasone increases force of contraction and sarcomere length in hESC-CMs. • Dexamethasone does not alter I{sub Ca,L} and action potential characteristics in hESC-CMs.« less

From damage response to action potentials: early evolution of neural and contractile modules in stem eukaryotes.

PubMed

Brunet, Thibaut; Arendt, Detlev

2016-01-05

Eukaryotic cells convert external stimuli into membrane depolarization, which in turn triggers effector responses such as secretion and contraction. Here, we put forward an evolutionary hypothesis for the origin of the depolarization-contraction-secretion (DCS) coupling, the functional core of animal neuromuscular circuits. We propose that DCS coupling evolved in unicellular stem eukaryotes as part of an 'emergency response' to calcium influx upon membrane rupture. We detail how this initial response was subsequently modified into an ancient mechanosensory-effector arc, present in the last eukaryotic common ancestor, which enabled contractile amoeboid movement that is widespread in extant eukaryotes. Elaborating on calcium-triggered membrane depolarization, we reason that the first action potentials evolved alongside the membrane of sensory-motile cilia, with the first voltage-sensitive sodium/calcium channels (Nav/Cav) enabling a fast and coordinated response of the entire cilium to mechanosensory stimuli. From the cilium, action potentials then spread across the entire cell, enabling global cellular responses such as concerted contraction in several independent eukaryote lineages. In animals, this process led to the invention of mechanosensory contractile cells. These gave rise to mechanosensory receptor cells, neurons and muscle cells by division of labour and can be regarded as the founder cell type of the nervous system. © 2015 The Authors.

From damage response to action potentials: early evolution of neural and contractile modules in stem eukaryotes

PubMed Central

Brunet, Thibaut; Arendt, Detlev

2016-01-01

Eukaryotic cells convert external stimuli into membrane depolarization, which in turn triggers effector responses such as secretion and contraction. Here, we put forward an evolutionary hypothesis for the origin of the depolarization–contraction–secretion (DCS) coupling, the functional core of animal neuromuscular circuits. We propose that DCS coupling evolved in unicellular stem eukaryotes as part of an ‘emergency response’ to calcium influx upon membrane rupture. We detail how this initial response was subsequently modified into an ancient mechanosensory–effector arc, present in the last eukaryotic common ancestor, which enabled contractile amoeboid movement that is widespread in extant eukaryotes. Elaborating on calcium-triggered membrane depolarization, we reason that the first action potentials evolved alongside the membrane of sensory-motile cilia, with the first voltage-sensitive sodium/calcium channels (Nav/Cav) enabling a fast and coordinated response of the entire cilium to mechanosensory stimuli. From the cilium, action potentials then spread across the entire cell, enabling global cellular responses such as concerted contraction in several independent eukaryote lineages. In animals, this process led to the invention of mechanosensory contractile cells. These gave rise to mechanosensory receptor cells, neurons and muscle cells by division of labour and can be regarded as the founder cell type of the nervous system. PMID:26598726

Effects of temperature and calcium availability on ventricular myocardium from rainbow trout.

PubMed

Coyne, M D; Kim, C S; Cameron, J S; Gwathmey, J K

2000-06-01

We studied the mechanical and electrophysiological properties of ventricular myocardium from rainbow trout (Oncorhynchus mykiss) in vitro at 4, 10, and 18 degrees C from fish acclimated at 10 degrees C. Temperature alone did not significantly alter the contractile force of the myocardium, but the time to peak tension and time to 80% relaxation were prolonged at 4 degrees C and shortened at 18 degrees C. The duration of the action potential was also prolonged at 4 degrees C and progressively shortened at higher temperatures. An alteration of the stimulation frequency did not affect contraction amplitude at any temperature. Calcium influx via L-type calcium channels was increased by raising extracellular calcium concentration (¿Ca(2+)(o)) or including Bay K 8644 (Bay K) and isoproterenol in the bathing medium. These treatments significantly enhanced the contractile force at all temperatures. Calcium channel blockers had a reverse-negative inotropic effect. Unexpectedly, the duration of the action potential at 10 degrees C was shortened as ¿Ca(2+)(o) increased. However, Bay K prolonged the plateau phase at 4 degrees C. Caffeine, which promotes the release of sarcoplasmic reticulum (SR) calcium, increased contractile force eightfold at all three temperatures, but the SR blocker ryanodine was only inhibitory at 4 degrees C. Our results suggest that contractile force in ventricular myocardium from Oncorhynchus mykiss is primarily regulated by sarcolemmal calcium influx and that ventricular contractility is maintained during exposure to a wide range of temperatures.

Single-Pixel Optical Fluctuation Analysis of Calcium Channel Function in Active Zones of Motor Nerve Terminals

PubMed Central

Luo, Fujun; Dittrich, Markus; Stiles, Joel R.; Meriney, Stephen D.

2011-01-01

We used high-resolution fluorescence imaging and single-pixel optical fluctuation analysis to estimate the opening probability of individual voltage-gated calcium (Ca2+) channels during an action potential and the number of such Ca2+ channels within active zones of frog neuromuscular junctions. Analysis revealed ~36 Ca2+ channels within each active zone, similar to the number of docked synaptic vesicles but far less than the total number of transmembrane particles reported based on freeze-fracture analysis (~200–250). The probability that each channel opened during an action potential was only ~0.2. These results suggest why each active zone averages only one quantal release event during every other action potential, despite a substantial number of docked vesicles. With sparse Ca2+ channels and low opening probability, triggering of fusion for each vesicle is primarily controlled by Ca2+ influx through individual Ca2+ channels. In contrast, the entire synapse is highly reliable because it contains hundreds of active zones. PMID:21813687

Progress in the structural understanding of voltage-gated calcium channel (CaV) function and modulation

PubMed Central

Findeisen, Felix

2010-01-01

Voltage-gated calcium channels (CaVs) are large, transmembrane multiprotein complexes that couple membrane depolarization to cellular calcium entry. These channels are central to cardiac action potential propagation, neurotransmitter and hormone release, muscle contraction and calcium-dependent gene transcription. Over the past six years, the advent of high-resolution structural studies of CaV components from different isoforms and CaV modulators has begun to reveal the architecture that underlies the exceptionally rich feedback modulation that controls CaV action. These descriptions of CaV molecular anatomy have provided new, structure-based insights into the mechanisms by which particular channel elements affect voltage-dependent inactivation (VDI), calcium-dependent inactivation (CDI) and calcium-dependent facilitation (CDF). The initial successes have been achieved through structural studies of soluble channel domains and modulator proteins and have proven most powerful when paired with biochemical and functional studies that validate ideas inspired by the structures. Here, we review the progress in this growing area and highlight some key open challenges for future efforts. PMID:21139419

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.

Developmental axon stretch stimulates neuron growth while maintaining normal electrical activity, intracellular calcium flux, and somatic morphology

PubMed Central

Loverde, Joseph R.; Pfister, Bryan J.

2015-01-01

Elongation of nerve fibers intuitively occurs throughout mammalian development, and is synchronized with expansion of the growing body. While most tissue systems enlarge through mitosis and differentiation, elongation of nerve fibers is remarkably unique. The emerging paradigm suggests that axons undergo stretch as contiguous tissues enlarge between the proximal and distal segments of spanning nerve fibers. While stretch is distinct from growth, tension is a known stimulus which regulates the growth of axons. Here, we hypothesized that the axon stretch-growth process may be a natural form of injury, whereby regenerative processes fortify elongating axons in order to prevent disconnection. Harnessing the live imaging capability of our axon stretch-growth bioreactors, we assessed neurons both during and following stretch for biomarkers associated with injury. Utilizing whole-cell patch clamp recording, we found no evidence of changes in spontaneous action potential activity or degradation of elicited action potentials during real-time axon stretch at strains of up to 18% applied over 5 min. Unlike traumatic axonal injury, functional calcium imaging of the soma revealed no shifts in free intracellular calcium during axon stretch. Finally, the cross-sectional areas of nuclei and cytoplasms were normal, with no evidence of chromatolysis following week-long stretch-growth limited to the lower of 25% strain or 3 mm total daily stretch. The neuronal growth cascade coupled to stretch was concluded to be independent of the changes in membrane potential, action potential generation, or calcium flux associated with traumatic injury. While axon stretch-growth is likely to share overlap with regenerative processes, we conclude that developmental stretch is a distinct stimulus from traumatic axon injury. PMID:26379492

Protective effects of isorhynchophylline on cardiac arrhythmias in rats and guinea pigs.

PubMed

Gan, Runtao; Dong, Guo; Yu, Jiangbo; Wang, Xu; Fu, Songbin; Yang, Shusen

2011-09-01

As one important constituent extracted from a traditional Chinese medicine, Uncaria Rhynchophylla Miq Jacks, isorhynchophylline has been used to treat hypertension, epilepsy, headache, and other illnesses. Whether isorhynchophylline protects hearts against cardiac arrhythmias is still incompletely investigated. This study was therefore aimed to examine the preventive effects of isorhynchophylline on heart arrhythmias in guinea pigs and rats and then explore their electrophysiological mechanisms. In vivo, ouabain and calcium chloride were used to establish experimental arrhythmic models in guinea pigs and rats. In vitro, the whole-cell patch-lamp technique was used to study the effect of isorhynchophylline on action potential duration and calcium channels in acutely isolated guinea pig and rat cardiomyocytes. The dose of ouabain required to induce cardiac arrhythmias was much larger in guinea pigs administered with isorhynchophylline. Additionally, the onset time of cardiac arrhythmias induced by calcium chloride was prolonged, and the duration was shortened in rats pretreated with isorhynchophylline. The further study showed that isorhynchophylline could significantly decrease action potential duration and inhibit calcium currents in isolated guinea pig and rat cardiomyocytes in a dose-dependent manner. In summary, isorhynchophylline played a remarkably preventive role in cardiac arrhythmias through the inhibition of calcium currents in rats and guinea pigs. © Georg Thieme Verlag KG Stuttgart · New York.

Fast calcium transients translate the distribution and conduction of neural activity in different regions of a single sensory neuron.

PubMed

Purali, Nuhan

2017-09-01

In the present study, cytosolic calcium concentration changes were recorded in response to various forms of excitations, using the fluorescent calcium indicator dye OG-BAPTA1 together with the current or voltage clamp methods in stretch receptor neurons of crayfish. A single action potential evoked a rise in the resting calcium level in the axon and axonal hillock, whereas an impulse train or a large saturating current injection would be required to evoke an equivalent response in the dendrite region. Under voltage clamp conditions, amplitude differences between axon and dendrite responses vanished completely. The fast activation time and the modulation of the response by extracellular calcium concentration changes indicated that the evoked calcium transients might be mediated by calcium entry into the cytosol through a voltage-gated calcium channel. The decay of the responses was slow and sensitive to extracellular sodium and calcium concentrations as well as exposure to 1-10 mM NiCl 2 and 10-500 µM lanthanum. Thus, a sodium calcium exchanger and a calcium ATPase might be responsible for calcium extrusion from the cytosol. Present results indicate that the calcium indicator OG-BAPTA1 might be an efficient but indirect way of monitoring regional membrane potential differences in a single neuron.

Effects of the new imidazopyridine CL 86-02-01 on isolated papillary muscle of guinea-pig hearts.

PubMed

Studenik, C; Lemmens-Gruber, R; Heistracher, P

1998-06-01

Inotropic activity and the effect of CL 86-02-01 (2-(3-methoxy-5-methylsulfinyl-2-thienyl)-1H-imidazo[4,5-c]pyridine hydrochloride, CAS 109 792-24-7) on membrane resting and action potentials were studied in isolated guinea-pig papillary muscles. Membrane resting potential and action potential parameters were not significantly changed, while CL 86-02-01 exerted a concentration-dependent inotropic effect by increasing the maximum rate of force development and maximum rate of force relaxation. Time to peak force, relaxation time and total contraction time were reduced. These effects are similar to those of beta-adrenergic drugs and phosphodiesterase inhibitors, but markedly differ from those described for other positive inotropic agents like cardiac glycosides, calcium agonists, alpha-adrenergic drugs or increased extracellular calcium concentration.

Crataegus extract blocks potassium currents in guinea pig ventricular cardiac myocytes.

PubMed

Müller, A; Linke, W; Klaus, W

1999-05-01

Crataegus extract is used in cardiology for the treatment of mild to moderate heart failure (NYHA II) in Germany. However, little is known about the electrophysiological actions of Crataegus extract in the heart. Recently, it was shown that Crataegus extract prolongs the refractory period in isolated perfused hearts and increases action potential duration in guinea pig papillary muscle. It was the aim of this study to find out the mechanism of the increase in action potential duration caused by Crataegus extract. Using the patch-clamp technique, we measured the effects of Crataegus extract (10 mg/l; flavonoid content: 2.25%, total procyanidin content: 11.3 +/- 0.4%) on the inward rectifier and the delayed rectifier potassium current in isolated guinea pig ventricular myocytes. To get some insight into the mechanism underlying the positive inotropic effect of Crataegus extract, we also looked for effects on the L-type calcium current. Crataegus extract slightly blocked both the delayed and the inward rectifier potassium current. The inhibition amounted to 25% and about 15%, respectively. This amount of inhibition of these repolarising currents is sufficient to explain the prolongation of action potential duration caused by Crataegus extract. To our surprise we could not detect any influence of Crataegus extract on the L-type calcium current. In summary, our results show that Crataegus extract blocks repolarising potassium currents in ventricular myocytes. This effect is similar to the action of class III antiarrhythmic drugs and might be the basis of the antiarrhythmic effects described for Crataegus extract. Our measurements of the L-type calcium current indicate that Crataegus extract's positive inotropic effect is not caused by phosphodiesterase inhibition or a beta-sympathomimetic effect.

Calcium channel blockers: spectrum of side effects and drug interactions.

PubMed

Hedner, T

1986-01-01

Calcium antagonists are a chemically heterogenous group of agents with potent cardiovascular effects which are beneficial in the treatment of angina pectoris, arterial hypertension and cardiac arrhythmias. The main side effects for the group are dose-dependent and the result of the main action or actions of the calcium antagonists, i.e. vasodilatation, negative inotropic effects and antiarrhythmic effects. Pronounced hypotension is reported for the main calcium antagonist drugs; verapamil, diltiazem and nifedipine. While conduction disturbances and bradycardia are seen more often after verapamil and diltiazem, tachycardia, headache and flush are more frequent after nifedipine. Constipation is relatively frequent after verapamil while nifedipine is reported to induce diarrhea in som patients. Idiosyncratic side effects are rare but have been reported from the skin, mouth, musculoskeletal system, the liver and the central nervous system. These side effects include urticarial rashes, gingival hyperplasia, arthralgia, hepathotoxicity and transistory mental confusion or akathisia. Verapamil, diltiazem and possibly also nifedipine have been reported to increase serum digoxin concentrations but the clinical relevance of these drug interactions are not clear. Furthermore, verapamil and diltiazem may potentiate the effects of beta-adrenergic blocking drugs and verapamil may also potentiate the effects of neuromuscular blocking drugs. It is concluded that side effects after calcium antagonist drugs are mostly trivial and transient although they may sometimes be relatively common. Clinically relevant drug interactions are few. Judged from the point of efficacy and safety, calcium antagonists will have a major place in the future pharmacotherapy of several cardiovascular disorders.

Calcium signaling properties of a thyrotroph cell line, mouse TαT1 cells.

PubMed

Tomić, Melanija; Bargi-Souza, Paula; Leiva-Salcedo, Elias; Nunes, Maria Tereza; Stojilkovic, Stanko S

2015-12-01

TαT1 cells are mouse thyrotroph cell line frequently used for studies on thyroid-stimulating hormone beta subunit gene expression and other cellular functions. Here we have characterized calcium-signaling pathways in TαT1 cells, an issue not previously addressed in these cells and incompletely described in native thyrotrophs. TαT1 cells are excitable and fire action potentials spontaneously and in response to application of thyrotropin-releasing hormone (TRH), the native hypothalamic agonist for thyrotrophs. Spontaneous electrical activity is coupled to small amplitude fluctuations in intracellular calcium, whereas TRH stimulates both calcium mobilization from intracellular pools and calcium influx. Non-receptor-mediated depletion of intracellular pool also leads to a prominent facilitation of calcium influx. Both receptor and non-receptor stimulated calcium influx is substantially attenuated but not completely abolished by inhibition of voltage-gated calcium channels, suggesting that depletion of intracellular calcium pool in these cells provides a signal for both voltage-independent and -dependent calcium influx, the latter by facilitating the pacemaking activity. These cells also express purinergic P2Y1 receptors and their activation by extracellular ATP mimics TRH action on calcium mobilization and influx. The thyroid hormone triiodothyronine prolongs duration of TRH-induced calcium spikes during 30-min exposure. These data indicate that TαT1 cells are capable of responding to natively feed-forward TRH signaling and intrapituitary ATP signaling with acute calcium mobilization and sustained calcium influx. Amplification of TRH-induced calcium signaling by triiodothyronine further suggests the existence of a pathway for positive feedback effects of thyroid hormones probably in a non-genomic manner. Published by Elsevier Ltd.

Differential calcium dependence in basal and forskolin-potentiated spontaneous transmitter release in basolateral amygdala neurons.

PubMed

Miura, Yuki; Naka, Masamitsu; Matsuki, Norio; Nomura, Hiroshi

2012-10-31

Action potential-independent transmitter release, or spontaneous release, is postulated to produce multiple postsynaptic effects (e.g., maintenance of dendritic spines and suppression of local dendritic protein synthesis). Potentiation of spontaneous release may contribute to the precise modulation of synaptic function. However, the expression mechanism underlying potentiated spontaneous release remains unclear. In this study, we investigated the involvement of extracellular and intracellular calcium in basal and potentiated spontaneous release. Miniature excitatory postsynaptic currents (mEPSCs) of the basolateral amygdala neurons in acute brain slices were recorded. Forskolin, an adenylate cyclase activator, increased mEPSC frequency, and the increase lasted at least 25 min after washout. Removal of the extracellular calcium decreased mEPSC frequency in both naïve and forskolin-treated slices. On the other hand, chelation of intracellular calcium by BAPTA-AM decreased mEPSC frequency in naïve, but not in forskolin-treated slices. A blockade of the calcium-sensing receptor (CaSR) resulted in an increase in mEPSC frequency in forskolin-treated, but not in naïve slices. These findings indicate that forskolin-induced potentiation is accompanied by changes in the mechanisms underlying Ca(2+)-dependent spontaneous release. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Mechanisms contributing to cluster formation in the inferior olivary nucleus in brainstem slices from postnatal mice

PubMed Central

Kølvraa, Mathias; Müller, Felix C; Jahnsen, Henrik; Rekling, Jens C

2014-01-01

Abstract The inferior olivary nucleus (IO) in in vitro slices from postnatal mice (P5.5–P15.5) spontaneously generates clusters of neurons with synchronous calcium transients, and intracellular recordings from IO neurons suggest that electrical coupling between neighbouring IO neurons may serve as a synchronizing mechanism. Here, we studied the cluster-forming mechanism and find that clusters overlap extensively with an overlap distribution that resembles the distribution for a random overlap model. The average somatodendritic field size of single curly IO neurons was ∼6400 μm2, which is slightly smaller than the average IO cluster size. Eighty-seven neurons with overlapping dendrites were estimated to be contained in the principal olive mean cluster size, and about six non-overlapping curly IO neurons could be contained within the largest clusters. Clusters could also be induced by iontophoresis with glutamate. Induced clusters were inhibited by tetrodotoxin, carbenoxelone and 18β-glycyrrhetinic acid, suggesting that sodium action potentials and electrical coupling are involved in glutamate-induced cluster formation, which could also be induced by activation of N-methyl-d-aspartate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. Spikelets and a small transient depolarizing response were observed during glutamate-induced cluster formation. Calcium transients spread with decreasing velocity during cluster formation, and somatic action potentials and cluster formation are accompanied by large dendritic calcium transients. In conclusion, cluster formation depends on gap junctions, sodium action potentials and spontaneous clusters occur randomly throughout the IO. The relative slow signal spread during cluster formation, combined with a strong dendritic influx of calcium, may signify that active dendritic properties contribute to cluster formation. PMID:24042500

Calcium dependence of rapid auxin action in maize roots

NASA Technical Reports Server (NTRS)

Hasenstein, K. H.; Evans, M. L.

1986-01-01

We investigated the interaction of Ca2+ and auxin on root elongation in seedlings of Zea mays L. The seedlings were raised either in the presence of Ca2+ (high calcium; HC = imbibed and raised in 10 millimolar CaCl2), in the absence of additional Ca2+ (intermediate calcium; IC = imbibed and raised in distilled H2O, calcium supply from seed only), or without additional Ca2+ and subsequently depleting them of Ca2+ (low calcium; LC = imbibed and raised in distilled H2O and subsequently treated with 1 millimolar ethyleneglycol-bis-[beta-aminoethylether]-N,N,N',N'-tetraacetic acid [EGTA]). Exposure of roots of either HC or IC seedlings to auxin concentrations from 0.1 to 10 micromolar resulted in strong inhibition of elongation. In roots of LC seedlings, on the other hand, auxin concentrations as high as 10 micromolar caused only slight inhibition of elongation. Adding 0.5 millimolar Ca2+ to LC roots in the presence of IAA allowed normal expression of the inhibitory action of the hormone. Inhibition of elongation in IC roots by indoleacetic acid was reversible upon treatment of the roots with 1 millimolar EGTA. The inhibitory action of auxin could then be re-established by supplying 0.5 millimolar Ca2+. The data indicate that Ca2+ may be necessary to the growth-regulating action of auxin. The significance of this finding is discussed with respect to the potential role of Ca2+ as a second messenger of auxin action and the relevance of this model to recent evidence for gravi-induced redistribution of Ca2+ and its role in establishing gravitropic curvature.

Calcium glycerophosphate and caries: a review of the literature.

PubMed

Lynch, R J M

2004-01-01

To review studies in the dental literature regarding the anti-caries mode of action of glycerophosphate with special reference to calcium glycerophosphate. The cariostatic properties of calcium glycerophosphate have been demonstrated during numerous in vivo and in vitro studies. Several mechanisms have been suggested and these include plaque-pH buffering, elevation of plaque calcium and phosphate levels and direct interaction with dental mineral. There is credible evidence that calcium glycerophosphate has the potential to reduce the progression of caries via all of these mechanisms if it is applied frequently and at a sufficiently high concentration. Reduction of plaque mass has also been proposed as a cariostatic mechanism but this seems less likely. Animal studies have shown that the calcium glycerophosphate/sodium monofluorophosphate system can have a greater anti-caries effect than sodium monofluorophosphate alone and this was subsequently confirmed in a caries clinical trial. We conclude that elevation of calcium levels in plaque is the most likely explanation and that any means of enhancing this effect has significant promise as a means to further increase in anti-caries potential of the calcium glycerophosphate/sodium monofluorophosphate system compared to sodium monofluorophosphate alone.

Carbachol induces burst firing of dopamine cells in the ventral tegmental area by promoting calcium entry through L-type channels in the rat

PubMed Central

Zhang, Lei; Liu, Yudan; Chen, Xihua

2005-01-01

Enhanced activity of the central dopamine system has been implicated in many psychiatric disorders including schizophrenia and addiction. Besides terminal mechanisms that boost dopamine levels at the synapse, the cell body of dopamine cells enhances terminal dopamine concentration through encoding action potentials in bursts. This paper presents evidence that burst firing of dopamine cells in the ventral tegmental area was under cholinergic control using nystatin-perforated patch clamp recording from slice preparations. The non-selective cholinergic agonist carbachol excited the majority of recorded neurones, an action that was not affected by blocking glutamate and GABA ionotropic receptors. Twenty per cent of dopamine cells responded to carbachol with robust bursting, an effect mediated by both muscarinic and nicotinic cholinoceptors postsynaptically. Burst firing induced as such was completely dependent on calcium entry as it could be blocked by cadmium and more specifically the L-type blocker nifedipine. In the presence of the sodium channel blocker tetrodotoxin, carbachol induced membrane potential oscillation that had similar kinetics and frequency as burst firing cycles and could also be blocked by cadmium and nifedipine. Direct activation of the L-type channel with Bay K8644 induced strong bursting which could be blocked by nifedipine but not by depleting internal calcium stores. These results indicate that carbachol increases calcium entry into the postsynaptic cell through L-type channels to generate calcium-dependent membrane potential oscillation and burst firing. This could establish the L-type channel as a target for modulating the function of the central dopamine system in disease conditions. PMID:16081481

Progress in the structural understanding of voltage-gated calcium channel (CaV) function and modulation.

PubMed

Minor, Daniel L; Findeisen, Felix

2010-01-01

Voltage-gated calcium channels (CaVs) are large, transmembrane multiprotein complexes that couple membrane depolarization to cellular calcium entry. These channels are central to cardiac action potential propagation, neurotransmitter and hormone release, muscle contraction, and calcium-dependent gene transcription. Over the past six years, the advent of high-resolution structural studies of CaV components from different isoforms and CaV modulators has begun to reveal the architecture that underlies the exceptionally rich feedback modulation that controls CaV action. These descriptions of CaV molecular anatomy have provided new, structure-based insights into the mechanisms by which particular channel elements affect voltage-dependent inactivation (VDI), calcium‑dependent inactivation (CDI), and calcium‑dependent facilitation (CDF). The initial successes have been achieved through structural studies of soluble channel domains and modulator proteins and have proven most powerful when paired with biochemical and functional studies that validate ideas inspired by the structures. Here, we review the progress in this growing area and highlight some key open challenges for future efforts.

Regulation of ATP production: dependence on calcium concentration and respiratory state.

PubMed

Fink, Brian D; Bai, Fan; Yu, Liping; Sivitz, William I

2017-08-01

Nanomolar free calcium enhances oxidative phosphorylation. However, the effects over a broad concentration range, at different respiratory states, or on specific energy substrates are less clear. We examined the action of varying [Ca 2+ ] over respiratory states ranging 4 to 3 on skeletal muscle mitochondrial respiration, potential, ATP production, and H 2 O 2 production using ADP recycling to clamp external [ADP]. Calcium at 450 nM enhanced respiration in mitochondria energized by the complex I substrates, glutamate/malate (but not succinate), at [ADP] of 4-256 µM, but more substantially at intermediate respiratory states and not at all at state 4. Using varied [Ca 2+ ], we found that the stimulatory effects on respiration and ATP production were most prominent at nanomolar concentrations, but inhibitory at 10 µM or higher. ATP production decreased more than respiration at 10 µM calcium. However, potential continued to increase up to 10 µM; suggesting a calcium-induced inability to utilize potential for phosphorylation independent of opening of the mitochondrial permeability transition pore (MTP). This effect of 10 µM calcium was confirmed by direct determination of ATP production over a range of potential created by differing substrate concentrations. Consistent with past reports, nanomolar [Ca 2+ ] had a stimulatory effect on utilization of potential for phosphorylation. Increasing [Ca 2+ ] was positively and continuously associated with H 2 O 2 production. In summary, the stimulatory effect of calcium on mitochondrial function is substrate dependent and most prominent over intermediate respiratory states. Calcium stimulates or inhibits utilization of potential for phosphorylation dependent on concentration with inhibition at higher concentration independent of MTP opening.

Voltage-gated calcium flux mediates Escherichia coli mechanosensation.

PubMed

Bruni, Giancarlo N; Weekley, R Andrew; Dodd, Benjamin J T; Kralj, Joel M

2017-08-29

Electrically excitable cells harness voltage-coupled calcium influx to transmit intracellular signals, typically studied in neurons and cardiomyocytes. Despite intense study in higher organisms, investigations of voltage and calcium signaling in bacteria have lagged due to their small size and a lack of sensitive tools. Only recently were bacteria shown to modulate their membrane potential on the timescale of seconds, and little is known about the downstream effects from this modulation. In this paper, we report on the effects of electrophysiology in individual bacteria. A genetically encoded calcium sensor expressed in Escherichia coli revealed calcium transients in single cells. A fusion sensor that simultaneously reports voltage and calcium indicated that calcium influx is induced by voltage depolarizations, similar to metazoan action potentials. Cytoplasmic calcium levels and transients increased upon mechanical stimulation with a hydrogel, and single cells altered protein concentrations dependent on the mechanical environment. Blocking voltage and calcium flux altered mechanically induced changes in protein concentration, while inducing calcium flux reproduced these changes. Thus, voltage and calcium relay a bacterial sense of touch and alter cellular lifestyle. Although the calcium effectors remain unknown, these data open a host of new questions about E. coli , including the identity of the underlying molecular players, as well as other signals conveyed by voltage and calcium. These data also provide evidence that dynamic voltage and calcium exists as a signaling modality in the oldest domain of life, and therefore studying electrophysiology beyond canonical electrically excitable cells could yield exciting new findings.

Voltage-gated calcium flux mediates Escherichia coli mechanosensation

PubMed Central

Weekley, R. Andrew; Dodd, Benjamin J. T.

2017-01-01

Electrically excitable cells harness voltage-coupled calcium influx to transmit intracellular signals, typically studied in neurons and cardiomyocytes. Despite intense study in higher organisms, investigations of voltage and calcium signaling in bacteria have lagged due to their small size and a lack of sensitive tools. Only recently were bacteria shown to modulate their membrane potential on the timescale of seconds, and little is known about the downstream effects from this modulation. In this paper, we report on the effects of electrophysiology in individual bacteria. A genetically encoded calcium sensor expressed in Escherichia coli revealed calcium transients in single cells. A fusion sensor that simultaneously reports voltage and calcium indicated that calcium influx is induced by voltage depolarizations, similar to metazoan action potentials. Cytoplasmic calcium levels and transients increased upon mechanical stimulation with a hydrogel, and single cells altered protein concentrations dependent on the mechanical environment. Blocking voltage and calcium flux altered mechanically induced changes in protein concentration, while inducing calcium flux reproduced these changes. Thus, voltage and calcium relay a bacterial sense of touch and alter cellular lifestyle. Although the calcium effectors remain unknown, these data open a host of new questions about E. coli, including the identity of the underlying molecular players, as well as other signals conveyed by voltage and calcium. These data also provide evidence that dynamic voltage and calcium exists as a signaling modality in the oldest domain of life, and therefore studying electrophysiology beyond canonical electrically excitable cells could yield exciting new findings. PMID:28808010

[G-protein potentiates the activation of TNF-alpha on calcium-activated potassium channel in ECV304].

PubMed

Lin, L; Zheng, Y; Qu, J; Bao, G

2000-06-01

Observe the effect of tumor necrosis factor-alpha (TNF-alpha) on calcium-activated potassium channel in ECV304 and the possible involvement of G-protein mediation in the action of TNF-alpha. Using the cell-attached configuration of patch clamp technique. (1) the activity of high-conductance calcium-activated potassium channel (BKca) was recorded. Its conductance is (202.54 +/- 16.62) pS; (2) the activity of BKca was potentiated by 200 U/ml TNF-alpha; (3) G-protein would intensify this TNF-alpha activation. TNF-alpha acted on vascular endothelial cell ECV304 could rapidly activate the activity of BKca. Opening of BKca resulted in membrane hyper-polarization which could increase electro-chemical gradient for the resting Ca2+ influx and open leakage calcium channel, thus resting cytoplasmic free Ca2+ concentration could be elevated. G-protein may exert an important regulation in this process.

Directionality in drug action on sodium-calcium exchange.

PubMed

Noble, D; Blaustein, M P

2007-03-01

In pathological conditions, the exchanger may generate deleterious calcium entry. A drug that inhibited calcium entry, while still allowing transport of calcium out of the cell would then seem attractive. In fact, this is impossible for thermodynamic reasons. Inhibitors may appear to be more effective when the exchanger is operating in net calcium entry mode than in calcium exit mode. This is, however, always attributable to differences in conditions because there is strong internal sodium dependence of drug action on the exchanger. When the exchanger is operating near equilibrium, drug action is found to be equally effective in both directions.

Contributions of two types of calcium channels to synaptic transmission and plasticity.

PubMed

Edmonds, B; Klein, M; Dale, N; Kandel, E R

1990-11-23

In Aplysia sensory and motor neurons in culture, the contributions of the major classes of calcium current can be selectively examined while transmitter release and its modulation are examined. A slowly inactivating, dihydropyridine-sensitive calcium current does not contribute either to normal synaptic transmission or to any of three different forms of plasticity: presynaptic inhibition, homosynaptic depression, and presynaptic facilitation. This current does contribute, however, to a fourth form of plasticity--modulation of transmitter release by tonic depolarization of the sensory neuron. By contrast, a second calcium current, which is rapidly inactivating and dihydropyridine-insensitive, contributes to release elicited by the transient depolarization of an action potential and to the other three forms of plasticity.

Photolysis of caged calcium in femtoliter volumes using two-photon excitation.

PubMed Central

Brown, E B; Shear, J B; Adams, S R; Tsien, R Y; Webb, W W

1999-01-01

A new technique for the determination of the two-photon uncaging action cross section (deltau) of photolyzable calcium cages is described. This technique is potentially applicable to other caged species that can be chelated by a fluorescent indicator dye, as well as caged fluorescent compounds. The two-photon action cross sections of three calcium cages, DM-nitrophen, NP-EGTA, and azid-1, are studied in the range of excitation wavelengths between 700 and 800 nm. Azid-1 has a maximum deltau of approximately 1.4 GM at 700 nm, DM-nitrophen has a maximum deltau of approximately 0.013 GM at 730 nm, and NP-EGTA has no measurable uncaging yield. The equations necessary to predict the amount of cage photolyzed and the temporal behavior of the liberated calcium distribution under a variety of conditions are derived. These equations predict that by using 700-nm light from a Ti:sapphire laser focused with a 1.3-NA objective, essentially all of the azid-1 within the two-photon focal volume would be photolyzed with a 10-micros pulse train of approximately 7 mW average power. The initially localized distributions of free calcium will dissipate rapidly because of diffusion of free calcium and uptake by buffers. In buffer-free cytoplasm, the elevation of the calcium concentration at the center of the focal volume is expected to last for approximately 165 micros. PMID:9876162

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

Calmodulin Activation by Calcium Transients in the Postsynaptic Density of Dendritic Spines

PubMed Central

Keller, Daniel X.; Franks, Kevin M.; Bartol, Thomas M.; Sejnowski, Terrence J.

2008-01-01

The entry of calcium into dendritic spines can trigger a sequence of biochemical reactions that begins with the activation of calmodulin (CaM) and ends with long-term changes to synaptic strengths. The degree of activation of CaM can depend on highly local elevations in the concentration of calcium and the duration of transient increases in calcium concentration. Accurate measurement of these local changes in calcium is difficult because the spaces are so small and the numbers of molecules are so low. We have therefore developed a Monte Carlo model of intracellular calcium dynamics within the spine that included calcium binding proteins, calcium transporters and ion channels activated by voltage and glutamate binding. The model reproduced optical recordings using calcium indicator dyes and showed that without the dye the free intracellular calcium concentration transient was much higher than predicted from the fluorescent signal. Excitatory postsynaptic potentials induced large, long-lasting calcium gradients across the postsynaptic density, which activated CaM. When glutamate was released at the synapse 10 ms before an action potential occurred, simulating activity patterns that strengthen hippocampal synapses, the calcium gradient and activation of CaM in the postsynaptic density were much greater than when the order was reversed, a condition that decreases synaptic strengths, suggesting a possible mechanism underlying the induction of long-term changes in synaptic strength. The spatial and temporal mechanisms for selectivity in CaM activation demonstrated here could be used in other signaling pathways. PMID:18446197

Assessing potential targets of calcium action in light-modulated gravitropism

NASA Technical Reports Server (NTRS)

Roux, S. J.

1995-01-01

Light, through the mediation of the pigment phytochrome, modulates the gravitropic response of the shoots and roots of many plants. The transduction of both light and gravity stimuli appears to involve Ca(2+)-regulated steps, one or more of which may represent points of intersection between the two transduction chains. To be confident that Ca2+ plays a critical role in stimulus-response coupling for gravitropism, it will be important to identify specific targets of Ca2+ action whose function can be clearly linked to the regulation of growth. Calcium typically exerts its influence on cell metabolism through binding to and activating key regulatory proteins. The three best characterized of these proteins in plants are the calmodulins, calcium-dependent protein kinases, and annexins. In this review we summarize what is known about the structure and function of these proteins and speculate on how their activation by Ca2+ could influence the differential growth response of gravitropism.

Opposing Roles of Calcium and Intracellular ATP on Gating of the Purinergic P2X2 Receptor Channel.

PubMed

Rokic, Milos B; Castro, Patricio; Leiva-Salcedo, Elias; Tomic, Melanija; Stojilkovic, Stanko S; Coddou, Claudio

2018-04-11

P2X2 receptors (P2X2R) exhibit a slow desensitization during the initial ATP application and a progressive, calcium-dependent increase in rates of desensitization during repetitive stimulation. This pattern is observed in whole-cell recordings from cells expressing recombinant and native P2X2R. However, desensitization is not observed in perforated-patched cells and in two-electrode voltage clamped oocytes. Addition of ATP, but not ATPγS or GTP, in the pipette solution also abolishes progressive desensitization, whereas intracellular injection of apyrase facilitates receptor desensitization. Experiments with injection of alkaline phosphatase or addition of staurosporine and ATP in the intracellular solution suggest a role for a phosphorylation-dephosphorylation in receptor desensitization. Mutation of residues that are potential phosphorylation sites identified a critical role of the S363 residue in the intracellular ATP action. These findings indicate that intracellular calcium and ATP have opposing effects on P2X2R gating: calcium allosterically facilitates receptor desensitization and ATP covalently prevents the action of calcium. Single cell measurements further revealed that intracellular calcium stays elevated after washout in P2X2R-expressing cells and the blockade of mitochondrial sodium/calcium exchanger lowers calcium concentrations during washout periods to basal levels, suggesting a role of mitochondria in this process. Therefore, the metabolic state of the cell can influence P2X2R gating.

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

Optical mapping of optogenetically shaped cardiac action potentials.

PubMed

Park, Sarah A; Lee, Shin-Rong; Tung, Leslie; Yue, David T

2014-08-19

Light-mediated silencing and stimulation of cardiac excitability, an important complement to electrical stimulation, promises important discoveries and therapies. To date, cardiac optogenetics has been studied with patch-clamp, multielectrode arrays, video microscopy, and an all-optical system measuring calcium transients. The future lies in achieving simultaneous optical acquisition of excitability signals and optogenetic control, both with high spatio-temporal resolution. Here, we make progress by combining optical mapping of action potentials with concurrent activation of channelrhodopsin-2 (ChR2) or halorhodopsin (eNpHR3.0), via an all-optical system applied to monolayers of neonatal rat ventricular myocytes (NRVM). Additionally, we explore the capability of ChR2 and eNpHR3.0 to shape action-potential waveforms, potentially aiding the study of short/long QT syndromes that result from abnormal changes in action potential duration (APD). These results show the promise of an all-optical system to acquire action potentials with precise temporal optogenetics control, achieving a long-sought flexibility beyond the means of conventional electrical stimulation.

Optical mapping of optogenetically shaped cardiac action potentials

PubMed Central

Park, Sarah A.; Lee, Shin-Rong; Tung, Leslie; Yue, David T.

2014-01-01

Light-mediated silencing and stimulation of cardiac excitability, an important complement to electrical stimulation, promises important discoveries and therapies. To date, cardiac optogenetics has been studied with patch-clamp, multielectrode arrays, video microscopy, and an all-optical system measuring calcium transients. The future lies in achieving simultaneous optical acquisition of excitability signals and optogenetic control, both with high spatio-temporal resolution. Here, we make progress by combining optical mapping of action potentials with concurrent activation of channelrhodopsin-2 (ChR2) or halorhodopsin (eNpHR3.0), via an all-optical system applied to monolayers of neonatal rat ventricular myocytes (NRVM). Additionally, we explore the capability of ChR2 and eNpHR3.0 to shape action-potential waveforms, potentially aiding the study of short/long QT syndromes that result from abnormal changes in action potential duration (APD). These results show the promise of an all-optical system to acquire action potentials with precise temporal optogenetics control, achieving a long-sought flexibility beyond the means of conventional electrical stimulation. PMID:25135113

Effects of procaine on a central neuron of the snail, Achatina fulica Ferussac.

PubMed

Lin, Chia-Hsien; Tsai, Ming-Cheng

2005-02-18

Effects of procaine on a central neuron (RP1) of the giant African snail (Achatina fulica Ferussac) were studied pharmacologically. The RP1 neuron showed spontaneous firing of action potential. Extra-cellular application of procaine (10 mM) reversibly elicited bursts of potential. The bursts of potential elicited by procaine were not blocked after administration of (1) prazosin, propranolol, atropine, d-tubocurarine, (2) calcium-free solution, (3) ryanodine (4) pretreatment with KT-5720 or chelerythrine. The bursts of potential elicited by procaine were blocked by adding U73122 (10 microM) and the bursts of potential were decreased if physiological sodium ion was replaced with lithium ion or incubated with either neomycin (3.5 mM) or high magnesium solution (30 mM). Preatment with U73122 (10 microM) blocked the initiation of bursts of potential. Ruthenium red (100 microM) or caffeine (10 mM) facilitated the procaine-elicited bursts of potential. It is concluded that procaine reversibly elicits bursts of potential in the central snail neuron. This effect was not directly related to (1) the extra-cellular calcium ion fluxes, (2) the ryanodine sensitive calcium channels in the neuron, or (3) the PKC or PKA related messenger systems. The procaine-elicited bursts of potential were associated with the phospholipase activity and the calcium mobilization in the neuron.

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.

Homeostatic synaptic depression is achieved through a regulated decrease in presynaptic calcium channel abundance

PubMed Central

Gaviño, Michael A; Ford, Kevin J; Archila, Santiago; Davis, Graeme W

2015-01-01

Homeostatic signaling stabilizes synaptic transmission at the neuromuscular junction (NMJ) of Drosophila, mice, and human. It is believed that homeostatic signaling at the NMJ is bi-directional and considerable progress has been made identifying mechanisms underlying the homeostatic potentiation of neurotransmitter release. However, very little is understood mechanistically about the opposing process, homeostatic depression, and how bi-directional plasticity is achieved. Here, we show that homeostatic potentiation and depression can be simultaneously induced, demonstrating true bi-directional plasticity. Next, we show that mutations that block homeostatic potentiation do not alter homeostatic depression, demonstrating that these are genetically separable processes. Finally, we show that homeostatic depression is achieved by decreased presynaptic calcium channel abundance and calcium influx, changes that are independent of the presynaptic action potential waveform. Thus, we identify a novel mechanism of homeostatic synaptic plasticity and propose a model that can account for the observed bi-directional, homeostatic control of presynaptic neurotransmitter release. DOI: http://dx.doi.org/10.7554/eLife.05473.001 PMID:25884248

Activity-Dependent Gating of Calcium Spikes by A-type K+ Channels Controls Climbing Fiber Signaling in Purkinje Cell Dendrites

PubMed Central

Otsu, Yo; Marcaggi, Païkan; Feltz, Anne; Isope, Philippe; Kollo, Mihaly; Nusser, Zoltan; Mathieu, Benjamin; Kano, Masanobu; Tsujita, Mika; Sakimura, Kenji; Dieudonné, Stéphane

2014-01-01

Summary In cerebellar Purkinje cell dendrites, heterosynaptic calcium signaling induced by the proximal climbing fiber (CF) input controls plasticity at distal parallel fiber (PF) synapses. The substrate and regulation of this long-range dendritic calcium signaling are poorly understood. Using high-speed calcium imaging, we examine the role of active dendritic conductances. Under basal conditions, CF stimulation evokes T-type calcium signaling displaying sharp proximodistal decrement. Combined mGluR1 receptor activation and depolarization, two activity-dependent signals, unlock P/Q calcium spikes initiation and propagation, mediating efficient CF signaling at distal sites. These spikes are initiated in proximal smooth dendrites, independently from somatic sodium action potentials, and evoke high-frequency bursts of all-or-none fast-rising calcium transients in PF spines. Gradual calcium spike burst unlocking arises from increasing inactivation of mGluR1-modulated low-threshold A-type potassium channels located in distal dendrites. Evidence for graded activity-dependent CF calcium signaling at PF synapses refines current views on cerebellar supervised learning rules. PMID:25220810

Activity-dependent gating of calcium spikes by A-type K+ channels controls climbing fiber signaling in Purkinje cell dendrites.

PubMed

Otsu, Yo; Marcaggi, Païkan; Feltz, Anne; Isope, Philippe; Kollo, Mihaly; Nusser, Zoltan; Mathieu, Benjamin; Kano, Masanobu; Tsujita, Mika; Sakimura, Kenji; Dieudonné, Stéphane

2014-10-01

In cerebellar Purkinje cell dendrites, heterosynaptic calcium signaling induced by the proximal climbing fiber (CF) input controls plasticity at distal parallel fiber (PF) synapses. The substrate and regulation of this long-range dendritic calcium signaling are poorly understood. Using high-speed calcium imaging, we examine the role of active dendritic conductances. Under basal conditions, CF stimulation evokes T-type calcium signaling displaying sharp proximodistal decrement. Combined mGluR1 receptor activation and depolarization, two activity-dependent signals, unlock P/Q calcium spikes initiation and propagation, mediating efficient CF signaling at distal sites. These spikes are initiated in proximal smooth dendrites, independently from somatic sodium action potentials, and evoke high-frequency bursts of all-or-none fast-rising calcium transients in PF spines. Gradual calcium spike burst unlocking arises from increasing inactivation of mGluR1-modulated low-threshold A-type potassium channels located in distal dendrites. Evidence for graded activity-dependent CF calcium signaling at PF synapses refines current views on cerebellar supervised learning rules. Copyright © 2014 Elsevier Inc. All rights reserved.

A Quantitative Comparison of the Behavior of Human Ventricular Cardiac Electrophysiology Models in Tissue

PubMed Central

Elshrif, Mohamed M.; Cherry, Elizabeth M.

2014-01-01

Numerical integration of mathematical models of heart cell electrophysiology provides an important computational tool for studying cardiac arrhythmias, but the abundance of available models complicates selecting an appropriate model. We study the behavior of two recently published models of human ventricular action potentials, the Grandi-Pasqualini-Bers (GPB) and the O'Hara-Virág-Varró-Rudy (OVVR) models, and compare the results with four previously published models and with available experimental and clinical data. We find the shapes and durations of action potentials and calcium transients differ between the GPB and OVVR models, as do the magnitudes and rate-dependent properties of transmembrane currents and the calcium transient. Differences also occur in the steady-state and S1–S2 action potential duration and conduction velocity restitution curves, including a maximum conduction velocity for the OVVR model roughly half that of the GPB model and well below clinical values. Between single cells and tissue, both models exhibit differences in properties, including maximum upstroke velocity, action potential amplitude, and minimum diastolic interval. Compared to experimental data, action potential durations for the GPB and OVVR models agree fairly well (although OVVR epicardial action potentials are shorter), but maximum slopes of steady-state restitution curves are smaller. Although studies show alternans in normal hearts, it occurs only in the OVVR model, and only for a narrow range of cycle lengths. We find initiated spiral waves do not progress to sustained breakup for either model. The dominant spiral wave period of the GPB model falls within clinically relevant values for ventricular tachycardia (VT), but for the OVVR model, the dominant period is longer than periods associated with VT. Our results should facilitate choosing a model to match properties of interest in human cardiac tissue and to replicate arrhythmia behavior more closely. Furthermore, by indicating areas where existing models disagree, our findings suggest avenues for further experimental work. PMID:24416228

Asymmetrical electrically induced injury of rabbit ventricular myocytes.

PubMed

Knisley, S B; Grant, A O

1995-05-01

Strong defibrillation-type electric field stimulation may injure myocytes when transmembrane potentials during the pulse exceed the threshold for membrane permeabilization. The location of injury may depend on intrinsic transmembrane potential or influx of calcium by "electro-osmosis" during the stimulation pulse in addition to the transmembrane potential changes induced by the pulse. We have studied injury by examining contracture and changes in transmembrane potential-sensitive dye fluorescence induced by electric field stimulation (St) with a duration of 20 ms and strength of 16-400 V/cm in isolated rabbit ventricular myocytes. St of 100-150 V/cm produced injury in myocytes oriented parallel to the St field frequently without injuring myocytes oriented perpendicular to the field. Injury required calcium in the solution and was asymmetric, occurring first at the myocyte and facing the St anode in 100% of injured myocytes in normal Tyrode's solution. Injury depended significantly on whether the product of the electric field strength and myocyte length exceeded a threshold of 1.1 V (P < 0.05). Asymmetric injury at the end facing the anode was still present in 96% of injured myocytes for stimulation after depolarization by an action potential or 20 mM or 125 mM potassium, suggesting that intrinsic transmembrane potential is not responsible for asymmetry. In 125 mM potassium, eliminating calcium from the bathing solution during the St pulse and introducing calcium after the pulse decreased the fraction of injured myocytes in which injury occurred at the end facing the anode to 62%, suggesting that calcium influx by "electro-osmosis" at the myocyte end facing the anode contributes to asymmetry. Asymmetric injury at the end facing the anode was still present in 100% of injured myocytes after adding 1 mM tetraethylammonium chloride, indicating that asymmetry is not sensitive to the potassium channel blockade. For stimulation pulses stronger than 50 V/cm given after depolarization by an action potential, transmembrane potentials at both myocyte ends decayed after the initial deflection indicating that permeabilization occurred at both ends. In conclusion, injury depends on myocyte orientation and is asymmetric occurring first at the myocyte end facing the anode. Asymmetric injury is not explained by asymmetric permeabilization, is independent of the intrinsic transmembrane potential and may result from "electro-osmosis" during the stimulation pulse.

Mechanism of cytotoxic action of perfluorinated acids. III. Disturbance in Ca{sup 2+} homeostasis

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

Kleszczynski, Konrad; Skladanowski, Andrzej C., E-mail: acskla@gumed.edu.pl

The global distribution of perfluorinated acids (PFAs) in industry and in household is well known. Their increasing environmental occurrence and biomagnification in the living organisms have drawn growing interests in efforts to describe precisely the mechanisms of action in vitro and in vivo. Our previous investigations widely described lipophilicity-dependent cytotoxicity of PFAs as well as the effect of perfluorination of carbon chain on depolarization of plasma membrane potential, acidification or mitochondrial dysfunctions. In this study we presented in dose- and time-dependent manner the impact of PFAs on calcium homeostasis in HCT116 cells. Comparative analysis of cytosolic [Ca{sup 2+}]{sub c} andmore » mitochondrial calcium [Ca{sup 2+}]{sub m} carried out by flow cytometry revealed distinct uptake of calcium into mitochondria in correlation to increasing lipophilicity of PFAs. Massive accumulation of [Ca{sup 2+}]{sub m} was not accompanied by equivalent loss of [Ca{sup 2+}]{sub c}. Indeed, moderate changes of [Ca{sup 2+}]{sub c} were observed after incubation with 400 {mu}M PFDoDA reaching 29.83% and 49.17% decrease at 4th and 72nd hour, respectively. At the same time, mitochondrial calcium uptake increased from 2- to more than 4-fold comparing with non-treated cells. Incubation with non-fluorinated decanoic acid (DA) did not cause any changes in calcium homeostasis. Presented data show that PFAs-induced perturbations in calcium distribution seem to be a missing link related to mitochondria dysfunction playing a crucial role in determination of apoptotic cell death. Complete scheme for the mechanism of cytotoxic action of PFAs has been included.« less

Antibacterial action of calcium hydroxide vehicles and calcium hydroxide pastes.

PubMed

Pacios, María Gabriela; Silva, Clara; López, María Elena; Cecilia, Marta

2012-11-01

To evaluate the in vitro action of vehicles alone and with calcium hydroxide against different bacterial species. Agar plates were inoculated with the microbial suspensions, and wells were made and filled with the calcium hydroxide pastes and the vehicles used to prepare the pastes. The zones of inhibited bacterial growth were recorded, and the resulting measurements were statistically analyzed. Enterococcus faecalis was the most resistant microorganism to all medicaments. Calcium hydroxide + p-monochlorophenol; calcium hydroxide + p-monochlorophenol-propylene glycol pastes; and p-monochlorophenol, p-monochlorophenol-propylene glycol, and chlorhexidine gluconate gel alone showed the largest zones of inhibition against all the tested microorganisms. The vehicle used to prepare the calcium hydroxide paste might contribute to its antibacterial action. Chlorhexidine gluconate gel used alone, and camphorated p-monochlorophenol and camphorated p-monochlorophenol-propylene glycol as vehicles of calcium hydroxide, could be recommended, in an antimicrobial sense. © 2012 Wiley Publishing Asia Pty Ltd.

Calcium and ROS: A mutual interplay

PubMed Central

Görlach, Agnes; Bertram, Katharina; Hudecova, Sona; Krizanova, Olga

2015-01-01

Calcium is an important second messenger involved in intra- and extracellular signaling cascades and plays an essential role in cell life and death decisions. The Ca2+ signaling network works in many different ways to regulate cellular processes that function over a wide dynamic range due to the action of buffers, pumps and exchangers on the plasma membrane as well as in internal stores. Calcium signaling pathways interact with other cellular signaling systems such as reactive oxygen species (ROS). Although initially considered to be potentially detrimental byproducts of aerobic metabolism, it is now clear that ROS generated in sub-toxic levels by different intracellular systems act as signaling molecules involved in various cellular processes including growth and cell death. Increasing evidence suggests a mutual interplay between calcium and ROS signaling systems which seems to have important implications for fine tuning cellular signaling networks. However, dysfunction in either of the systems might affect the other system thus potentiating harmful effects which might contribute to the pathogenesis of various disorders. PMID:26296072

Intracellular calcium movements during excitation–contraction coupling in mammalian slow-twitch and fast-twitch muscle fibers

PubMed Central

Hollingworth, Stephen

2012-01-01

In skeletal muscle fibers, action potentials elicit contractions by releasing calcium ions (Ca2+) from the sarcoplasmic reticulum. Experiments on individual mouse muscle fibers micro-injected with a rapidly responding fluorescent Ca2+ indicator dye reveal that the amount of Ca2+ released is three- to fourfold larger in fast-twitch fibers than in slow-twitch fibers, and the proportion of the released Ca2+ that binds to troponin to activate contraction is substantially smaller. PMID:22450485

A highly sensitive fluorescent indicator dye for calcium imaging of neural activity in vitro and in vivo

PubMed Central

Tada, Mayumi; Takeuchi, Atsuya; Hashizume, Miki; Kitamura, Kazuo; Kano, Masanobu

2014-01-01

Calcium imaging of individual neurons is widely used for monitoring their activity in vitro and in vivo. Synthetic fluorescent calcium indicator dyes are commonly used, but the resulting calcium signals sometimes suffer from a low signal-to-noise ratio (SNR). Therefore, it is difficult to detect signals caused by single action potentials (APs) particularly from neurons in vivo. Here we showed that a recently developed calcium indicator dye, Cal-520, is sufficiently sensitive to reliably detect single APs both in vitro and in vivo. In neocortical neurons, calcium signals were linearly correlated with the number of APs, and the SNR was > 6 for in vitro slice preparations and > 1.6 for in vivo anesthetised mice. In cerebellar Purkinje cells, dendritic calcium transients evoked by climbing fiber inputs were clearly observed in anesthetised mice with a high SNR and fast decay time. These characteristics of Cal-520 are a great advantage over those of Oregon Green BAPTA-1, the most commonly used calcium indicator dye, for monitoring the activity of individual neurons both in vitro and in vivo. PMID:24405482

Calcium channel blockers and transmitter release at the normal human neuromuscular junction.

PubMed

Protti, D A; Reisin, R; Mackinley, T A; Uchitel, O D

1996-05-01

Transmitter release evoked by nerve stimulation is highly dependent on Ca2+ entry through voltage-activated plasma membrane channels. Calcium influx may be modified in some neuromuscular diseases like Lambert-Eaton syndrome and amyotrophic lateral sclerosis. We studied the pharmacologic sensitivity of the transmitter release process to different calcium channel blockers in normal human muscles and found that funnel web toxin and omega-Agatoxin-IVA, both P-type calcium channel blockers, blocked nerve-elicited muscle action potentials and inhibited evoked synaptic transmission. The transmitter release was not affected either by nitrendipine, an L-type channel blocker, or omega-Conotoxin-GVIA, an N-type channel blocker. The pharmacologic profile of neuromuscular transmission observed in normal human muscles indicates that P-like channels mediate transmitter release at the motor nerve terminals.

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

Enhanced effect of VEGF165 on L-type calcium currents in guinea-pig cardiac ventricular myocytes.

PubMed

Xing, Wenlu; Gao, Chuanyu; Qi, Datun; Zhang, You; Hao, Peiyuan; Dai, Guoyou; Yan, Ganxin

2017-01-01

The mechanisms of vascular endothelial growth factor 165 (VEGF165) on electrical properties of cardiomyocytes have not been fully elucidated. The aim of this study is to test the hypothesis that VEGF165, an angiogenesis-initiating factor, affects L-type calcium currents (I Ca,L ) and cell membrane potential in cardiac myocytes by acting on VEGF type-2 receptors (VEGFR2). I Ca,L and action potentials (AP) were recorded by the whole-cell patch clamp method in isolated guinea-pig ventricular myocytes treated with different concentrations of VEGF165 proteins. Using a VEGFR2 inhibitor, we also tested the receptor of VEGF165 in cardiomyocytes. We found that VEGF165 increased I Ca,L in a concentration-dependent manner. SU5416, a VEGFR2 inhibitor, almost completely eliminated VEGF165-induced I Ca,L increase. VEGF165 had no significant influence on action potential 90 (APD90) and other properties of AP. We conclude that in guinea-pig ventricular myocytes, I Ca,L can be increased by VEGF165 in a concentration-dependent manner through binding to VEGFR2 without causing any significant alteration to action potential duration. Results of this study may further expound the safety of VEGF165 when used in the intervention of heart diseases. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

Functional role of ambient GABA in refining neuronal circuits early in postnatal development

PubMed Central

Cellot, Giada; Cherubini, Enrico

2013-01-01

Early in development, γ-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the mature brain, depolarizes and excites targeted neurons by an outwardly directed flux of chloride, resulting from the peculiar balance between the cation-chloride importer NKCC1 and the extruder KCC2. The low expression of KCC2 at birth leads to accumulation of chloride inside the cell and to the equilibrium potential for chloride positive respect to the resting membrane potential. GABA exerts its action via synaptic and extrasynaptic GABAA receptors mediating phasic and tonic inhibition, respectively. Here, recent data on the contribution of “ambient” GABA to the refinement of neuronal circuits in the immature brain have been reviewed. In particular, we focus on the hippocampus, where, prior to the formation of conventional synapses, GABA released from growth cones and astrocytes in a calcium- and SNARE (soluble N-ethylmaleimide-sensitive-factor attachment protein receptor)-independent way, diffuses away to activate in a paracrine fashion extrasynaptic receptors localized on distal neurons. The transient increase in intracellular calcium following the depolarizing action of GABA leads to inhibition of DNA synthesis and cell proliferation. Tonic GABA exerts also a chemotropic action on cell migration. Later on, when synapses are formed, GABA spilled out from neighboring synapses, acting mainly on extrasynaptic α5, β2, β3, and γ containing GABAA receptor subunits, provides the membrane depolarization necessary for principal cells to reach the window where intrinsic bursts are generated. These are instrumental in triggering calcium transients associated with network-driven giant depolarizing potentials which act as coincident detector signals to enhance synaptic efficacy at emerging GABAergic and glutamatergic synapses. PMID:23964205

Calcium waves.

PubMed

Jaffe, Lionel F

2008-04-12

Waves through living systems are best characterized by their speeds at 20 degrees C. These speeds vary from those of calcium action potentials to those of ultraslow ones which move at 1-10 and/or 10-20 nm s(-1). All such waves are known or inferred to be calcium waves. The two classes of calcium waves which include ones with important morphogenetic effects are slow waves that move at 0.2-2 microm s(-1) and ultraslow ones. Both may be propagated by cycles in which the entry of calcium through the plasma membrane induces subsurface contraction. This contraction opens nearby stretch-sensitive calcium channels. Calcium entry through these channels propagates the calcium wave. Many slow waves are seen as waves of indentation. Some are considered to act via cellular peristalsis; for example, those which seem to drive the germ plasm to the vegetal pole of the Xenopus egg. Other good examples of morphogenetic slow waves are ones through fertilizing maize eggs, through developing barnacle eggs and through axolotl embryos during neural induction. Good examples of ultraslow morphogenetic waves are ones during inversion in developing Volvox embryos and across developing Drosophila eye discs. Morphogenetic waves may be best pursued by imaging their calcium with aequorins.

Wide-field in vivo neocortical calcium dye imaging using a convection-enhanced loading technique combined with simultaneous multiwavelength imaging of voltage-sensitive dyes and hemodynamic signals

PubMed Central

Ma, Hongtao; Harris, Samuel; Rahmani, Redi; Lacefield, Clay O.; Zhao, Mingrui; Daniel, Andy G. S.; Zhou, Zhiping; Bruno, Randy M.; Berwick, Jason; Schwartz, Theodore H.

2014-01-01

Abstract. In vivo calcium imaging is an incredibly powerful technique that provides simultaneous information on fast neuronal events, such as action potentials and subthreshold synaptic activity, as well as slower events that occur in the glia and surrounding neuropil. Bulk-loading methods that involve multiple injections can be used for single-cell as well as wide-field imaging studies. However, multiple injections result in inhomogeneous loading as well as multiple sites of potential cortical injury. We used convection-enhanced delivery to create smooth, continuous loading of a large area of the cortical surface through a solitary injection site and demonstrated the efficacy of the technique using confocal microscopy imaging of single cells and physiological responses to single-trial events of spontaneous activity, somatosensory-evoked potentials, and epileptiform events. Combinations of calcium imaging with voltage-sensitive dye and intrinsic signal imaging demonstrate the utility of this technique in neurovascular coupling investigations. Convection-enhanced loading of calcium dyes may be a useful technique to advance the study of cortical processing when widespread loading of a wide-field imaging is required. PMID:25525611

Wide-field in vivo neocortical calcium dye imaging using a convection-enhanced loading technique combined with simultaneous multiwavelength imaging of voltage-sensitive dyes and hemodynamic signals.

PubMed

Ma, Hongtao; Harris, Samuel; Rahmani, Redi; Lacefield, Clay O; Zhao, Mingrui; Daniel, Andy G S; Zhou, Zhiping; Bruno, Randy M; Berwick, Jason; Schwartz, Theodore H

2014-07-24

In vivo calcium imaging is an incredibly powerful technique that provides simultaneous information on fast neuronal events, such as action potentials and subthreshold synaptic activity, as well as slower events that occur in the glia and surrounding neuropil. Bulk-loading methods that involve multiple injections can be used for single-cell as well as wide-field imaging studies. However, multiple injections result in inhomogeneous loading as well as multiple sites of potential cortical injury. We used convection-enhanced delivery to create smooth, continuous loading of a large area of the cortical surface through a solitary injection site and demonstrated the efficacy of the technique using confocal microscopy imaging of single cells and physiological responses to single-trial events of spontaneous activity, somatosensory-evoked potentials, and epileptiform events. Combinations of calcium imaging with voltage-sensitive dye and intrinsic signal imaging demonstrate the utility of this technique in neurovascular coupling investigations. Convection-enhanced loading of calcium dyes may be a useful technique to advance the study of cortical processing when widespread loading of a wide-field imaging is required.

(2R,3S,2”R,3”R)-manniflavanone, a new gastrointestinal smooth muscle L-type calcium channel inhibitor, which underlies the spasmolytic properties of Garcinia buchananii stem bark extract

PubMed Central

Balemba, Onesmo B.; Stark, Timo D.; Lösch, Sofie; Patterson, Savannah; McMillan, John S.; Mawe, Gary M.; Hofmann, Thomas

2014-01-01

Garcinia buchananii Baker stem bark extract (GBB) is a traditional medication of diarrhea and dysentery in sub-Saharan Africa. It is believed that GBB causes gastrointestinal smooth muscle relaxation. The aim of this study was to determine whether GBB has spasmolytic actions and identify compounds underlying these actions. Calcium (Ca2+) imaging was used to analyze the effect of GBB on Ca2+ flashes and Ca2+ waves in guinea pig gallbladder and distal colon smooth muscle. Intracellular microelectrode recording was used to determine the effect of GBB, six fractions of GBB, M1–5 and M7, and (2R,3S,2”R,3”R)-manniflavanone, a compound isolated from M3 on action potentials in gallbladder smooth muscle. The technique was also used to analyze the effect of GBB, M3, and (2R,3S,2”R,3”R)-manniflavanone on action potentials in the circular muscle of mouse and guinea pig distal colons, and the effect of GBB and (2R,3S,2”R,3”R)-manniflavanone on slow waves in porcine ileum. GBB inhibited Ca2+ flashes and Ca2+ waves. GBB, M3 and (2R,3S,2”R,3”R)-manniflavanone inhibited action potentials. L-type Ca2+ channel activator Bay K 8644 increased the discharge of action potentials in mouse colon but did not trigger or increase action potentials in the presence of GBB and (2R,3S,2”R,3”R)-manniflavanone. GBB and (2R,3S,2”R,3”R)-manniflavanone inhibited action potentials in the presence of Bay K 8644. GBB and (2R,3S,2”R,3”R)-manniflavanone reduced the amplitude but did not alter the frequency of slow waves in the porcine ileum. In conclusion, GBB and (2R,3S,2”R,3”R)-manniflavanone relax smooth muscle by inhibiting L-type Ca2+ channels, thus have potential for use as therapies of gastrointestinal smooth muscle spasms, and arrhythmias. PMID:26081368

Direct Inhibitory Effect of Hypercalcemia on Renal Actions of Parathyroid Hormone

PubMed Central

Beck, Nama; Singh, Harbans; Reed, Sarah W.; Davis, Bernard B.

1974-01-01

The effects of calcium on the renal actions of parathyroid hormone (PTH) were studied in vivo and in vitro. In parathyroidectomized rats, variable levels of blood calcium concentration were induced by intravenous infusion of calcium. The renal responses to the injected PTH, i.e. phosphate and cyclic AMP excretion, were compared in these animals. After PTH injection, the increases of both phosphate and cyclic AMP excretion were less in the calcium-infused animals than in the control group without calcium infusion. There was an inverse correlation between the renal responses to PTH and plasma calcium concentration of 4.2-13.5 mg/100 ml. But calcium had no effect on phosphate excretion induced by infusion of dibutyryl cyclic AMP. In the in vitro experiments, the increase of cyclic AMP concentration in response to PTH was less in renal cortical slices taken from the calcium-infused animals than in ones from the control group without calcium infusion. Calcium also inhibited the activation of renal cortical adenylate cyclase in response to PTH, but calcium had no effect on phosphodiesterase. The data indicate that calcium directly inhibits renal actions of PTH both in vivo and in vitro. Such inhibitory mechanism is probably at or before the step of PTH-dependent cyclic AMP generation in the kidney. PMID:4359938

Off Label Antiviral Therapeutics for Henipaviruses: New Light Through Old Windows

PubMed Central

Aljofan, Mohamad; Lo, Michael K.; Rota, Paul A.; Michalski, Wojtek P.; Mungall, Bruce A.

2010-01-01

Hendra and Nipah viruses are recently emerged zoonotic paramyxoviruses for which there is no vaccine or protective therapy available. While a number of experimental therapeutics and vaccines have recently been reported, all of these will require lengthy approval processes, limiting their usefulness in the short term. To address the urgent need for henipavirus therapeutics, a number of currently licensed pharmaceuticals have been evaluated for off label efficacy against henipavirus replication in vitro. Initially it was observed that compounds which released intracellular calcium stores induced a potent inhibition of henipaviruses replication, prompting the evaluation of known drugs with a similar effect on calcium mobilisation. Of the eight compounds randomly selected based on existing literature, seven inhibited virus replication in the micromolar range while the remaining compound also inhibited virus replication but only at millimolar concentrations. Pretreatment experiments with various calcium chelators, channel antagonists or endoplasmic reticulum release inhibitors supported a calcium mediated mechanism of action for five of these compounds. The mechanism of antiviral action for the remaining three compounds is currently unknown. Additionally, a number of other modulators of calcium flux, including calcium channel and calmodulin antagonists also exhibited potent antiviral activity in vitro providing a broad range of potential therapeutic options for the treatment of henipavirus infections. Importantly, as many of these compounds are currently licensed drugs, regulatory approval should be a much more streamlined process, with the caveat that appropriate in vivo efficacy can be demonstrated in animal models. PMID:20668647

Gene expression profiles following exposure to a developmental neurotoxicant, Aroclor 1254: Pathway analysis for possible mode(s) of action.

EPA Science Inventory

Epidemiological studies indicate that low levels of polychlorinated biphenyl (PCB) exposure can adversely affect neurocognitive development. In animal models, perturbations in calcium signaling, neurotransmitters, and thyroid hormones have been postulated as potential mechanisms...

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.

Effects of S(+)-efonidipine on the rabbit sinus node action potential and calcium channel subunits Ca(V)1.2, Ca(V)1.3 and Ca(V)3.1.

PubMed

Tanaka, Hikaru; Namekata, Iyuki; Ogawa, Toru; Tsuneoka, Yayoi; Komikado, Chisa; Takahara, Akira; Iida-Tanaka, Naoko; Izumi-Nakaseko, Hiroko; Tsuru, Hiromichi; Adachi-Akahane, Satomi

2010-12-15

The effect of S(+)-efonidipine on sinus node action potential and calcium channel α-subunits was examined. The slope of the phase 4 depolarization of isolated rabbit sinus node tissue was significantly reduced by S(+)-efonidipine (1 μM), slightly reduced by nifedipine (1 μM), but was not affected by R(-)-efonidipine. S(+)-efonidipine (1 μM), inhibited the expressed Ca(V)1.2, Ca(V)1.3 and Ca(V)3.1 channel currents by 75.7%, 75.3% and 94.0%, nifedipine 84.0%, 43.2% and 14.9%, and R(-)-efonidipine 30.0%, 19.6% and 92.8%, respectively. Thus, the prolongation of the phase 4 depolarization of the rabbit sinus node by S(+)-efonidipine may be explained by blockade of the Ca(V)1.3 channel current. Copyright © 2010 Elsevier B.V. All rights reserved.

Calcium antagonism: aldosterone and vascular responses to catecholamines and angiotensin II in man.

PubMed

Elliott, H L

1993-12-01

Effects of calcium antagonists on pressor mechanisms: A number of differences have been reported in the variable extent to which calcium antagonists interfere with various pressor mechanisms. In theory, high lipid solubility, membrane-binding characteristics and a prolonged duration of action appear to be requirements for a calcium antagonist to affect mechanisms such as vasodilation, endogenous vasoconstrictor responses, hormone release and natriuretic activity. Reduction in peripheral vascular resistance: A reduction in peripheral vascular resistance is fundamental to the antihypertensive effect not only of calcium antagonists but also of angiotensin converting enzyme inhibitors and alpha 1-adrenoceptor antagonists. However, only the calcium antagonists interfere directly with the pressor responses mediated by both the adrenergic nervous system and the renin-angiotensin system. Mechanism of lacidipine effects: Preliminary results with the new dihydropyridine calcium antagonist lacidipine indicate that it not only has vasodilator activity but that it also interferes with both adrenergic and non-adrenergic endogenous vasoconstrictor mechanisms. This may provide additional potentially beneficial cardiovascular effects, particularly in relation to left ventricular hypertrophy and dysfunction.

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

THE CRITICAL ROLE OF VOLTAGE-DEPENDENT CALCIUM CHANNEL IN AXONAL REPAIR FOLLOWING MECHANICAL TRAUMA

PubMed Central

Nehrt, Ashley; Rodgers, Richard; Shapiro, Scott; Borgens, Richard; Shi, Riyi

2009-01-01

Membrane disruption following mechanical injury likely plays a critical role in the pathology of spinal cord trauma. It is known that intracellular calcium is a key factor that is essential to membrane resealing. However, the differential role of calcium influx through the injury site and through voltage dependent calcium channels (VDCC) has not been examined in detail. Using a well established ex vivo guinea pig spinal cord white matter preparation, we have found that axonal membrane resealing was significantly inhibited following transection or compression in the presence of cadmiun, a non-specific calcium channel blocker, or nimodipine, a specific L-type calcium channel blocker. Membrane resealing was assessed by the changes of membrane potential and compound action potential (CAP), and exclusion of horseradish peroxidase 60 minutes following trauma. Furthermore, 1 μM BayK 8644, a VDCC agonist, significantly enhanced membrane resealing. Interestingly, this effect was completely abolished when the concentration of BayK 8644 was increased to 30 μM. These data suggest that VDCC play a critical role in membrane resealing. Further, there is likely an appropriate range of calcium influx through VDCC which ensures effective axonal membrane resealing. Since elevated intracellular calcium has also been linked to axonal deterioration, blockage of VDCC is proposed to be a clinical treatment for various injuries. The knowledge gained in this study will likely help us better understand the role of calcium in various CNS trauma, which is critical for designing new approaches or perhaps optimizing the effectiveness of existing methods in the treatment of CNS trauma. PMID:17448606

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.

Zolpidem Reduces Hippocampal Neuronal Activity in Freely Behaving Mice: A Large Scale Calcium Imaging Study with Miniaturized Fluorescence Microscope

PubMed Central

Berdyyeva, Tamara; Otte, Stephani; Aluisio, Leah; Ziv, Yaniv; Burns, Laurie D.; Dugovic, Christine; Yun, Sujin; Ghosh, Kunal K.; Schnitzer, Mark J.; Lovenberg, Timothy; Bonaventure, Pascal

2014-01-01

Therapeutic drugs for cognitive and psychiatric disorders are often characterized by their molecular mechanism of action. Here we demonstrate a new approach to elucidate drug action on large-scale neuronal activity by tracking somatic calcium dynamics in hundreds of CA1 hippocampal neurons of pharmacologically manipulated behaving mice. We used an adeno-associated viral vector to express the calcium sensor GCaMP3 in CA1 pyramidal cells under control of the CaMKII promoter and a miniaturized microscope to observe cellular dynamics. We visualized these dynamics with and without a systemic administration of Zolpidem, a GABAA agonist that is the most commonly prescribed drug for the treatment of insomnia in the United States. Despite growing concerns about the potential adverse effects of Zolpidem on memory and cognition, it remained unclear whether Zolpidem alters neuronal activity in the hippocampus, a brain area critical for cognition and memory. Zolpidem, when delivered at a dose known to induce and prolong sleep, strongly suppressed CA1 calcium signaling. The rate of calcium transients after Zolpidem administration was significantly lower compared to vehicle treatment. To factor out the contribution of changes in locomotor or physiological conditions following Zolpidem treatment, we compared the cellular activity across comparable epochs matched by locomotor and physiological assessments. This analysis revealed significantly depressive effects of Zolpidem regardless of the animal’s state. Individual hippocampal CA1 pyramidal cells differed in their responses to Zolpidem with the majority (∼65%) significantly decreasing the rate of calcium transients, and a small subset (3%) showing an unexpected and significant increase. By linking molecular mechanisms with the dynamics of neural circuitry and behavioral states, this approach has the potential to contribute substantially to the development of new therapeutics for the treatment of CNS disorders. PMID:25372144

Update on the mechanism of action of antiepileptic drugs.

PubMed

Meldrum, B S

1996-01-01

Novel antiepileptic drugs (AEDs) are thought to act on voltage-sensitive ion channels, on inhibitory neurotransmission or on excitatory neurotransmission. Two successful examples of rational AED design that potentiate GABA-mediated inhibition are vigabatrin (VGB) by irreversible inhibition of GABA-transaminase, and tiagabine (TGB) by blocking GABA uptake. Lamotrigine (LTG) prolongs inactivation of voltage-dependent sodium channels. The anticonvulsant action of remacemide (RCM) is probably largely due to blockade of NMDA receptors and prolonged inactivation of sodium channels induced by its desglycinated metabolite. Felbamate (FBM) apparently blocks NMDA receptors, potentiates GABA-mediated responses, blocks L-type calcium channels, and possibly also prolongs sodium channel inactivation. Similarly, topiramate (TPM) has multiple probable sites of action, including sodium channels, GABA receptors, and glutamate (AMPA) receptors. Gabapentin (GBP) apparently has a completely novel type of action, probably involving potentiation of GABA-mediated inhibition and possibly also inactivation of sodium channels. The therapeutic advantages of the novel AEDs are as yet only partially explained by our present understanding of their mechanisms of action.

[Effects of 2-(p-dimethylaminostyryl) pyridine methycholide (DSPM-Ci) on ECG, left atrium contractivity and on papillary muscle action potentials].

PubMed

Jiang, X Y; Zhou, C M; Li, D M; Zhang, K J

1996-01-01

The effects of DSPM-Cl on ECG in rats, on the dose-effect curve in guinea pig left atria and on the fast action potential (AP), high-K+ depolarized slow action potential (SAP) in guinea pigs papillary muscle were examined electrophysiologically. DSPM-Cl (2 mg.kg-1) showed significant nagative frequency, negative conductivity effect, and prolonged the PP and PR interval. DSPM-CI (30-50 mumol.L-1) was shown to inhibit left atria contractility and shift the concentration-response curve of Iso and CaCl2 to the right with PD2' values of 4.60 and 4.13, respectively. In addition, DSPM-Cl was found to prolong the duration of action potential 90 (APD90) and effective refractory period (ERP), and decrease the maximal upstroke velocity (Vmax) in K(+)-depolarized guinea pigs papillary muscles. The results suggest that, like verpamil, DSPM-Cl might be a calcium antagonist.

[How do antiepileptic drugs work?].

PubMed

Nakken, Karl O; Heuser, Kjell; Alfstad, Kristin; Taubøll, Erik

2014-01-14

There are currently around 25 antiepileptic drugs in use in Norway, of which 15 have entered the market in the last 20 years. All have somewhat different effect- and adverse effect profiles and mechanisms of action. Here we present a brief overview of current knowledge regarding the basic mechanisms of action of these drugs. The review is based on a discretionary selection of relevant articles found through a literature search in PubMed and our own clinical and research experience. There are, roughly speaking, four main mechanisms; 1) modulation of ion channels (sodium and calcium channel blockers, potassium channel openers), 2) potentiation of GABAergic inhibition, 3) reduction of glutamatergic excitation and 4) modulation of presynaptic neurotransmitter release. Some of the drugs have several mechanisms of action, and for some of them it is unclear which mechanism is clinically most important. To some extent, the drugs' mechanisms of action predict their effect against different types of epilepsy and seizures. For instance, sodium channel blockers work best against focal seizures, while calcium channel blockers work best against absences, a type of generalised seizure. Optimal treatment of patients with epilepsy requires not only thorough knowledge of seizure- and epilepsy classification, but also insight into the mechanisms of action of antiepileptic drugs.

A Double-Blind Randomized Placebo Controlled Trial of Magnesium Oxide for Alleviation of Chronic Low Back Pain

DTIC Science & Technology

1999-10-01

analgesics has also been extensively researched. Miranda and Paeile (1989) reported a minireview of the interactions between calcium channel blockers and...1990). Interactions between analgesics and calcium channel blockers. General Pharmacology, 21, 171-174. Peikert, A., Wilimzig, C., & Kohne-Volland, R...important actions of magnesium that relates to this study is the regulation of calcium access into the cell and the actions of calcium inside the cell

Mechanisms of action of ligands of potential-dependent sodium channels.

PubMed

Tikhonov, D B

2008-06-01

Potential-dependent sodium channels play a leading role in generating action potentials in excitable cells. Sodium channels are the site of action of a variety of modulator ligands. Despite numerous studies, the mechanisms of action of many modulators remain incompletely understood. The main reason that many important questions cannot be resolved is that there is a lack of precise data on the structures of the channels themselves. Structurally, potential-dependent sodium channels are members of the P-loop channel superfamily, which also include potassium and calcium channels and glutamate receptor channels. Crystallization of a series of potassium channels showed that it was possible to analyze the structures of different members of the superfamily using the "homologous modeling" method. The present study addresses model investigations of the actions of ligands of sodium channels, including tetrodotoxin and batrachotoxin, as well as local anesthetics. Comparison of experimental data on sodium channel ligands with x-ray analysis data allowed us to reach a new level of understanding of the mechanisms of channel modulation and to propose a series of experimentally verifiable hypotheses.

The role of nitrates, beta blockers, and calcium antagonists in stable angina pectoris.

PubMed

Chan, P K; Heo, J Y; Garibian, G; Askenase, A; Segal, B L; Iskandrian, A S

1988-09-01

Numerous controlled studies have shown that nitrates, beta blockers, and calcium antagonists are effective in the treatment of stable angina pectoris. The pharmacokinetics, pharmacodynamics, and hemodynamic effects of these agents are different, and thus combination therapy offers additive improvement and also counterbalancing of the undesirable side effects of each drug. The choice of therapy depends on the severity of symptoms, associated diseases, compliance, side effects, and status of left ventricular function. The main mechanism of improvement is a decrease in myocardial oxygen consumption, though an increase in coronary blood flow is another potential reason for the use of calcium blockers. This review considers the properties of these drugs, their mechanism of action, and the results of randomized studies.

Differential facilitation of N- and P/Q-type calcium channels during trains of action potential-like waveforms

PubMed Central

Currie, Kevin P M; Fox, Aaron P

2002-01-01

Inhibition of presynaptic voltage-gated calcium channels by direct G-protein βγ subunit binding is a widespread mechanism that regulates neurotransmitter release. Voltage-dependent relief of this inhibition (facilitation), most likely to be due to dissociation of the G-protein from the channel, may occur during bursts of action potentials. In this paper we compare the facilitation of N- and P/Q-type Ca2+ channels during short trains of action potential-like waveforms (APWs) using both native channels in adrenal chromaffin cells and heterologously expressed channels in tsA201 cells. While both N- and P/Q-type Ca2+ channels exhibit facilitation that is dependent on the frequency of the APW train, there are important quantitative differences. Approximately 20 % of the voltage-dependent inhibition of N-type ICa was reversed during a train while greater than 40 % of the inhibition of P/Q-type ICa was relieved. Changing the duration or amplitude of the APW dramatically affected the facilitation of N-type channels but had little effect on the facilitation of P/Q-type channels. Since the ratio of N-type to P/Q-type Ca2+ channels varies widely between synapses, differential facilitation may contribute to the fine tuning of synaptic transmission, thereby increasing the computational repertoire of neurons. PMID:11882675

[Propranolol beta-blocker decrease in the concentration of high-affinity binding sites for calcium ions by sarcolemma membranes of the rat heart].

PubMed

Seleznev, Iu M; Martynov, A V; Smirnov, V N

1982-05-01

In vivo administration of propranolol considerably inhibits the isoproterenol-stimulated increase in 45Ca accumulation by the myocardium and completely eliminates the potentiation of isoproterenol effect by hydrocortisone. A significant lowering of the concentration of high affinity binding sites for calcium in the sarcolemmal membranes can be produced by propranolol in vitro. Under these conditions, the glucocorticoids do not change the sarcolemmal Ca2+-binding parameters or modulate the propranolol effect. Therefore, for the manifestation of glucocorticoid action to be brought about, the integrity of the cells is apparently required, while propranolol seems to change calcium binding by direct interaction with the sarcolemmal membranes. It is suggested that in vivo propranolol inhibition of catecholamine effect on calcium ion accumulation by the myocardium depends on the interaction with the beta-receptors and direct modulation of the concentration of high affinity binding sites for calcium ions on the surface of the sarcolemma.

Optimized ratiometric calcium sensors for functional in vivo imaging of neurons and T lymphocytes.

PubMed

Thestrup, Thomas; Litzlbauer, Julia; Bartholomäus, Ingo; Mues, Marsilius; Russo, Luigi; Dana, Hod; Kovalchuk, Yuri; Liang, Yajie; Kalamakis, Georgios; Laukat, Yvonne; Becker, Stefan; Witte, Gregor; Geiger, Anselm; Allen, Taylor; Rome, Lawrence C; Chen, Tsai-Wen; Kim, Douglas S; Garaschuk, Olga; Griesinger, Christian; Griesbeck, Oliver

2014-02-01

The quality of genetically encoded calcium indicators (GECIs) has improved dramatically in recent years, but high-performing ratiometric indicators are still rare. Here we describe a series of fluorescence resonance energy transfer (FRET)-based calcium biosensors with a reduced number of calcium binding sites per sensor. These 'Twitch' sensors are based on the C-terminal domain of Opsanus troponin C. Their FRET responses were optimized by a large-scale functional screen in bacterial colonies, refined by a secondary screen in rat hippocampal neuron cultures. We tested the in vivo performance of the most sensitive variants in the brain and lymph nodes of mice. The sensitivity of the Twitch sensors matched that of synthetic calcium dyes and allowed visualization of tonic action potential firing in neurons and high resolution functional tracking of T lymphocytes. Given their ratiometric readout, their brightness, large dynamic range and linear response properties, Twitch sensors represent versatile tools for neuroscience and immunology.

Inhibition of recombinant Ca(v)3.1 (alpha(1G)) T-type calcium channels by the antipsychotic drug clozapine.

PubMed

Choi, Kee-Hyun; Rhim, Hyewhon

2010-01-25

Low voltage-activated T-type calcium channels are involved in the regulation of the neuronal excitability, and could be subject to many antipsychotic drugs. The effects of clozapine, an atypical antipsychotic drug, on recombinant Ca(v)3.1 T-type calcium channels heterologously expressed in human embryonic kidney 293 cells were examined using whole-cell patch-clamp recordings. At a standard holding potential of -100 mV, clozapine inhibited Ca(v)3.1 currents with an IC(50) value of 23.7+/-1.3 microM in a use-dependent manner. However, 10 microM clozapine inhibited more than 50% of the Ca(v)3.1 currents in recordings at a more physiologically relevant holding potential of -75 mV. Clozapine caused a significant hyperpolarizing shift in the steady-state inactivation curve of the Ca(v)3.1 channels, which is presumably the main mechanism accounting for the inhibition of the Ca(v)3.1 currents. In addition, clozapine slowed Ca(v)3.1 deactivation and inactivation kinetics but not activation kinetics. Clozapine-induced changes in deactivation and inactivation rates of the Ca(v)3.1 channel gating would likely facilitate calcium influx via Ca(v)3.1 T-type calcium channels. Thus, clozapine may exert its therapeutic and/or side effects by altering cell's excitability and firing properties through actions on T-type calcium channels.

Role of calcium in the constriction of isolated cerebral arteries

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

Wendling, W.W.

1987-01-01

Calcium entry blockers (CEB) have been used in the experimental treatment or prevention of many cerebrovascular disorders including stroke, post-ischemic hypoperfusion after cardiac arrest, cerebral vasospasm after subarachnoid hemorrhage, and migraine headache. However, the mechanism of action of these drugs on the cerebral circulation is poorly understood. This study examined the effects of calcium antagonists, Ca/sup 2 +/-deficient solutions, and vasocostrictors on cerebrovascular tone and /sup 45/Ca fluxes, to determine the role of calcium in cerebral arterial constriction. A Scatchard plot of /sup 45/Ca binding to BMCA showed that Ca/sup 2 +/ was bound at either low or high affinitymore » binding sties. The four vasoconstrictors (potassium, serotonin, PGF/sub 2 ..cap alpha../, or SQ-26,655) each increased low affinity /sup 45/Ca uptake into BMCA. The results demonstrate that: (1) Potassium and serotonin constrict BMCA mainly by promoting Ca/sup 2 +/ influx through CEB-sensitive channels; (2) PGF/sub 2 ..cap alpha../ and SQ-26,655 constrict BMCA in part by promoting Ca/sup 2 +/ influx through CEB-sensitive channels, and in part by releasing Ca/sup 2 +/ from depletable internal stores; (3) The major action of CEB on BMCA is to block vasoconstrictor-induced Ca/sup 2 +/ uptake through both potential-operated (K/sup +/-stimulated) and receptor-operated channels.« less

Creation of a genetic calcium channel blocker by targeted gem gene transfer in the heart.

PubMed

Murata, Mitsushige; Cingolani, Eugenio; McDonald, Amy D; Donahue, J Kevin; Marbán, Eduardo

2004-08-20

Calcium channel blockers are among the most commonly used therapeutic drugs. Nevertheless, the utility of calcium channel blockers for heart disease is limited because of the potent vasodilatory effect that causes hypotension, and other side effects attributable to blockade of noncardiac channels. Therefore, focal calcium channel blockade by gene transfer is highly desirable. With a view to creating a focally applicable genetic calcium channel blocker, we overexpressed the ras-related small G-protein Gem in the heart by somatic gene transfer. Adenovirus-mediated delivery of Gem markedly decreased L-type calcium current density in ventricular myocytes, resulting in the abbreviation of action potential duration. Furthermore, transduction of Gem resulted in a significant shortening of the electrocardiographic QTc interval and reduction of left ventricular systolic function. Focal delivery of Gem to the atrioventricular (AV) node significantly slowed AV nodal conduction (prolongation of PR and AH intervals), which was effective in the reduction of heart rate during atrial fibrillation. Thus, these results indicate that gene transfer of Gem functions as a genetic calcium channel blocker, the local application of which can effectively modulate cardiac electrical and contractile function.

The dependence of the action potential of the frog's heart on the external and intracellular sodium concentration

PubMed Central

Niedergerke, R.; Orkand, R. K.

1966-01-01

1. The overshoot of the action potential of the frog's heart was reduced when external sodium chloride was replaced by sucrose. However, the potential decrement was only 17·3 mV for a 10-fold reduction of sodium as compared with 58 mV expected on the basis of the sodium hypothesis of excitation. 2. Replacement of up to 75% of the external sodium by choline did not reduce the overshoot, provided atropine was present in sufficient concentrations to suppress any parasympathomimetic action. 3. The maximum rate of rise of the action potential markedly declined in low sodium fluids whether sucrose or choline chloride was used to replace sodium chloride. 4. The maximum rate of rise was reduced to only a small extent when external sodium was replaced by lithium. 5. Increasing the intracellular sodium concentration in exchange for lost potassium caused overshoots to decline. The effects resembled those obtained in similar experiments with skeletal muscle fibres (Desmedt, 1953). 6. Action potentials occurring under certain conditions even in the presence of very low external sodium concentrations (≤ 5% normal) also declined in height when the intracellular sodium concentration was increased. 7. The behaviour of the action potential in low external sodium concentrations may be explained by an action of calcium on the excitable membrane. PMID:5921833

Growth hormone secretagogues prevent dysregulation of skeletal muscle calcium homeostasis in a rat model of cisplatin-induced cachexia.

PubMed

Conte, Elena; Camerino, Giulia Maria; Mele, Antonietta; De Bellis, Michela; Pierno, Sabata; Rana, Francesco; Fonzino, Adriano; Caloiero, Roberta; Rizzi, Laura; Bresciani, Elena; Ben Haj Salah, Khoubaib; Fehrentz, Jean-Alain; Martinez, Jean; Giustino, Arcangela; Mariggiò, Maria Addolorata; Coluccia, Mauro; Tricarico, Domenico; Lograno, Marcello Diego; De Luca, Annamaria; Torsello, Antonio; Conte, Diana; Liantonio, Antonella

2017-06-01

Cachexia is a wasting condition associated with cancer types and, at the same time, is a serious and dose-limiting side effect of cancer chemotherapy. Skeletal muscle loss is one of the main characteristics of cachexia that significantly contributes to the functional muscle impairment. Calcium-dependent signaling pathways are believed to play an important role in skeletal muscle decline observed in cachexia, but whether intracellular calcium homeostasis is affected in this situation remains uncertain. Growth hormone secretagogues (GHS), a family of synthetic agonists of ghrelin receptor (GHS-R1a), are being developed as a therapeutic option for cancer cachexia syndrome; however, the exact mechanism by which GHS interfere with skeletal muscle is not fully understood. By a multidisciplinary approach ranging from cytofluorometry and electrophysiology to gene expression and histology, we characterized the calcium homeostasis in fast-twitch extensor digitorum longus (EDL) muscle of adult rats with cisplatin-induced cachexia and established the potential beneficial effects of two GHS (hexarelin and JMV2894) at this level. Additionally, in vivo measures of grip strength and of ultrasonography recordings allowed us to evaluate the functional impact of GHS therapeutic intervention. Cisplatin-treated EDL muscle fibres were characterized by a ~18% significant reduction of the muscle weight and fibre diameter together with an up-regulation of atrogin1/Murf-1 genes and a down-regulation of Pgc1-a gene, all indexes of muscle atrophy, and by a two-fold increase in resting intracellular calcium, [Ca 2+ ] i , compared with control rats. Moreover, the amplitude of the calcium transient induced by caffeine or depolarizing high potassium solution as well as the store-operated calcium entry were ~50% significantly reduced in cisplatin-treated rats. Calcium homeostasis dysregulation parallels with changes of functional ex vivo (excitability and resting macroscopic conductance) and in vivo (forelimb force and muscle volume) outcomes in cachectic animals. Administration of hexarelin or JMV2894 markedly reduced the cisplatin-induced alteration of calcium homeostasis by both common as well as drug-specific mechanisms of action. This effect correlated with muscle function preservation as well as amelioration of various atrophic indexes, thus supporting the functional impact of GHS activity on calcium homeostasis. Our findings provide a direct evidence that a dysregulation of calcium homeostasis plays a key role in cisplatin-induced model of cachexia gaining insight into the etiopathogenesis of this form of muscle wasting. Furthermore, our demonstration that GHS administration efficaciously prevents cisplatin-induced calcium homeostasis alteration contributes to elucidate the mechanism of action through which GHS could potentially ameliorate chemotherapy-associated cachexia. © 2017 The Authors. Journal of Cachexia, Sarcopenia and Muscle published by John Wiley & Sons Ltd on behalf of the Society on Sarcopenia, Cachexia and Wasting Disorders.

Targeting Chronic and Neuropathic Pain: The N-type Calcium Channel Comes of Age

PubMed Central

Snutch, Terrance P.

2005-01-01

Summary: The rapid entry of calcium into cells through activation of voltage-gated calcium channels directly affects membrane potential and contributes to electrical excitability, repetitive firing patterns, excitation-contraction coupling, and gene expression. At presynaptic nerve terminals, calcium entry is the initial trigger mediating the release of neurotransmitters via the calcium-dependent fusion of synaptic vesicles and involves interactions with the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex of synaptic release proteins. Physiological factors or drugs that affect either presynaptic calcium channel activity or the efficacy of calcium-dependent vesicle fusion have dramatic consequences on synaptic transmission, including that mediating pain signaling. The N-type calcium channel exhibits a number of characteristics that make it an attractive target for therapeutic intervention concerning chronic and neuropathic pain conditions. Within the past year, both U.S. and European regulatory agencies have approved the use of the cationic peptide Prialt for the treatment of intractable pain. Prialt is the first N-type calcium channel blocker approved for clinical use and represents the first new proven mechanism of action for chronic pain intervention in many years. The present review discusses the rationale behind targeting the N-type calcium channel, some of the limitations confronting the widespread clinical application of Prialt, and outlines possible strategies to improve upon Prialt's relatively narrow therapeutic window. PMID:16489373

Na+/Ca2+ exchange in cardiac myocytes. Effect of ouabain on voltage dependence.

PubMed

Lee, H C; Clusin, W T

1987-02-01

Sarcolemmal sodium/calcium exchange activity was examined in individual chick embryonic myocardial cell aggregates that were loaded with quin 2. The baseline [Ca2+]i was 68 +/- 4 nM (n = 29). Abrupt superfusion with sodium-free lithium solution produced a fourfold increase in steady-state [Ca2+]i to 290 +/- 19 nM, which was reversible upon sodium restitution. Other methods of increasing [Ca2+]i such as KCl-depolarization or caffeine produced a dose-dependent increase in quin 2 fluorescence, accompanied by sustained contracture. The [Ca2+]i increase in zero sodium was linear, and its half-time (t1/2) of 15.1 +/- 0.1 s was similar to that of the sodium-free contracture (t1/2 = 14.4 +/- 0.5 s) under the same conditions. The sodium-dependent [Ca2+]i increase was not significantly greater when potassium served as the sodium substitute instead of lithium. This suggests that sodium/calcium exchange has little voltage dependence in this situation. However, in aggregates pretreated with ouabain (2.5 microM), the [Ca2+]i increase was almost threefold greater with potassium than with lithium (P less than 0.007). Ouabain therefore potentiated the effect of membrane potential on calcium influx. We propose that elevation of [Na2+]i is a prerequisite for voltage dependence of the sodium/calcium exchange under the conditions studied. Sodium loading will then drastically increase calcium influx during the action potential while inducing an outward membrane current that could accelerate repolarization.

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.

Metabotropic and ionotropic glutamate receptors regulate calcium channel currents in salamander retinal ganglion cells

PubMed Central

Shen, Wen; Slaughter, Malcolm M

1998-01-01

Glutamate suppressed high-voltage-activated barium currents (IBa,HVA) in tiger salamander retinal ganglion cells. Both ionotropic (iGluR) and metabotropic (mGluR) receptors contributed to this calcium channel inhibition. Trans-ACPD (1-aminocyclopentane-trans-1S,3R-dicarboxylic acid), a broad-spectrum metabotropic glutamate receptor agonist, suppressed a dihydropyridine-sensitive barium current. Kainate, an ionotropic glutamate receptor agonist, reduced an ω-conotoxin GVIA-sensitive current. The relative effectiveness of selective agonists indicated that the predominant metabotropic receptor was the L-2-amino-4-phosphonobutyrate (l-AP4)-sensitive, group III receptor. This receptor reversed the action of forskolin, but this was not responsible for calcium channel suppression. l-AP4 raised internal calcium concentration. Antagonists of phospholipase C, inositol trisphosphate (IP3) receptors and ryanodine receptors inhibited the action of metabotropic agonists, indicating that group III receptor transduction was linked to this pathway. The action of kainate was partially suppressed by BAPTA, by calmodulin antagonists and by blockers of calmodulin-dependent phosphatase. Suppression by kainate of the calcium channel current was more rapid when calcium was the charge carrier, instead of barium. The results indicate that calcium influx through kainate-sensitive glutamate receptors can activate calmodulin, which stimulates phosphatases that may directly suppress voltage-sensitive calcium channels. Thus, ionotropic and metabotropic glutamate receptors inhibit distinct calcium channels. They could act synergistically, since both increase internal calcium. These pathways provide negative feedback that can reduce calcium influx when ganglion cells are depolarized. PMID:9660896

Mechanisms involved in cardiac sensitization by volatile anesthetics: general applicability to halogenated hydrocarbons?

PubMed

Himmel, Herbert M

2008-01-01

An increased sensitivity of the heart to catecholamines or cardiac sensitization is a recognized risk during acute human exposure to halogenated hydrocarbons used as solvents, foam-blowing or fire-extinguishing agents, refrigerants, and aerosol propellants. Although cardiac sensitization to such "industrial" halocarbons can result in serious arrhythmia and death, research into its mechanistic basis has been limited, whereas the literature on volatile anesthetics (e.g., halothane, chloroform) is comparably extensive. A review of the literature on halocarbons and related volatile anesthetics was conducted. The available experimental evidence suggests that volatile anesthetics at physiologically relevant concentrations interact predominantly with the main repolarizing cardiac potassium channels hERG and I(Ks), as well as with calcium and sodium channels at slightly higher concentrations. On the level of the heart, inhibition of these ion channels is prone to alter both action potential shape (triangulation) and electrical impulse conduction, which may facilitate arrhythmogenesis by volatile anesthetics per se and is potentiated by catecholamines. Action potential triangulation by regionally heterogeneous inhibition of calcium and potassium channels will facilitate catecholamine-induced afterdepolarizations, triggered activity, and enhanced automaticity. Inhibition of cardiac sodium channels will reduce conduction velocity and alter refractory period; this is potentiated by catecholamines and promotes reentry arrhythmias. Other cardiac and/or neuronal mechanisms might also contribute to arrhythmogenesis. The few scattered in vitro data available for halocarbons (e.g., FC-12, halon 1301, trichloroethylene) suggest inhibition of cardiac sodium (conduction), calcium and potassium channels (triangulation), extraneuronal catecholamine reuptake, and various neuronal ion channels. Therefore, it is hypothesized that halocarbons promote cardiac sensitization by similar mechanisms as volatile anesthetics. Experimental approaches for further investigation of these sensitization mechanisms by selected halocarbons are suggested.

All‐optical functional synaptic connectivity mapping in acute brain slices using the calcium integrator CaMPARI

PubMed Central

Sha, Fern; Johenning, Friedrich W.; Schreiter, Eric R.; Looger, Loren L.; Larkum, Matthew E.

2016-01-01

Key points The genetically encoded fluorescent calcium integrator calcium‐modulated photoactivatable ratiobetric integrator (CaMPARI) reports calcium influx induced by synaptic and neural activity. Its fluorescence is converted from green to red in the presence of violet light and calcium.The rate of conversion – the sensitivity to activity – is tunable and depends on the intensity of violet light.Synaptic activity and action potentials can independently initiate significant CaMPARI conversion.The level of conversion by subthreshold synaptic inputs is correlated to the strength of input, enabling optical readout of relative synaptic strength.When combined with optogenetic activation of defined presynaptic neurons, CaMPARI provides an all‐optical method to map synaptic connectivity. Abstract The calcium‐modulated photoactivatable ratiometric integrator (CaMPARI) is a genetically encoded calcium integrator that facilitates the study of neural circuits by permanently marking cells active during user‐specified temporal windows. Permanent marking enables measurement of signals from large swathes of tissue and easy correlation of activity with other structural or functional labels. One potential application of CaMPARI is labelling neurons postsynaptic to specific populations targeted for optogenetic stimulation, giving rise to all‐optical functional connectivity mapping. Here, we characterized the response of CaMPARI to several common types of neuronal calcium signals in mouse acute cortical brain slices. Our experiments show that CaMPARI is effectively converted by both action potentials and subthreshold synaptic inputs, and that conversion level is correlated to synaptic strength. Importantly, we found that conversion rate can be tuned: it is linearly related to light intensity. At low photoconversion light levels CaMPARI offers a wide dynamic range due to slower conversion rate; at high light levels conversion is more rapid and more sensitive to activity. Finally, we employed CaMPARI and optogenetics for functional circuit mapping in ex vivo acute brain slices, which preserve in vivo‐like connectivity of axon terminals. With a single light source, we stimulated channelrhodopsin‐2‐expressing long‐range posteromedial (POm) thalamic axon terminals in cortex and induced CaMPARI conversion in recipient cortical neurons. We found that POm stimulation triggers robust photoconversion of layer 5 cortical neurons and weaker conversion of layer 2/3 neurons. Thus, CaMPARI enables network‐wide, tunable, all‐optical functional circuit mapping that captures supra‐ and subthreshold depolarization. PMID:27861906

Growth hormone secretagogues prevent dysregulation of skeletal muscle calcium homeostasis in a rat model of cisplatin‐induced cachexia

PubMed Central

Conte, Elena; Camerino, Giulia Maria; Mele, Antonietta; De Bellis, Michela; Pierno, Sabata; Rana, Francesco; Fonzino, Adriano; Caloiero, Roberta; Rizzi, Laura; Bresciani, Elena; Ben Haj Salah, Khoubaib; Fehrentz, Jean‐Alain; Martinez, Jean; Giustino, Arcangela; Mariggiò, Maria Addolorata; Coluccia, Mauro; Tricarico, Domenico; Lograno, Marcello Diego; De Luca, Annamaria; Torsello, Antonio; Conte, Diana

2017-01-01

Abstract Background Cachexia is a wasting condition associated with cancer types and, at the same time, is a serious and dose‐limiting side effect of cancer chemotherapy. Skeletal muscle loss is one of the main characteristics of cachexia that significantly contributes to the functional muscle impairment. Calcium‐dependent signaling pathways are believed to play an important role in skeletal muscle decline observed in cachexia, but whether intracellular calcium homeostasis is affected in this situation remains uncertain. Growth hormone secretagogues (GHS), a family of synthetic agonists of ghrelin receptor (GHS‐R1a), are being developed as a therapeutic option for cancer cachexia syndrome; however, the exact mechanism by which GHS interfere with skeletal muscle is not fully understood. Methods By a multidisciplinary approach ranging from cytofluorometry and electrophysiology to gene expression and histology, we characterized the calcium homeostasis in fast‐twitch extensor digitorum longus (EDL) muscle of adult rats with cisplatin‐induced cachexia and established the potential beneficial effects of two GHS (hexarelin and JMV2894) at this level. Additionally, in vivo measures of grip strength and of ultrasonography recordings allowed us to evaluate the functional impact of GHS therapeutic intervention. Results Cisplatin‐treated EDL muscle fibres were characterized by a ~18% significant reduction of the muscle weight and fibre diameter together with an up‐regulation of atrogin1/Murf‐1 genes and a down‐regulation of Pgc1‐a gene, all indexes of muscle atrophy, and by a two‐fold increase in resting intracellular calcium, [Ca2+]i, compared with control rats. Moreover, the amplitude of the calcium transient induced by caffeine or depolarizing high potassium solution as well as the store‐operated calcium entry were ~50% significantly reduced in cisplatin‐treated rats. Calcium homeostasis dysregulation parallels with changes of functional ex vivo (excitability and resting macroscopic conductance) and in vivo (forelimb force and muscle volume) outcomes in cachectic animals. Administration of hexarelin or JMV2894 markedly reduced the cisplatin‐induced alteration of calcium homeostasis by both common as well as drug‐specific mechanisms of action. This effect correlated with muscle function preservation as well as amelioration of various atrophic indexes, thus supporting the functional impact of GHS activity on calcium homeostasis. Conclusions Our findings provide a direct evidence that a dysregulation of calcium homeostasis plays a key role in cisplatin‐induced model of cachexia gaining insight into the etiopathogenesis of this form of muscle wasting. Furthermore, our demonstration that GHS administration efficaciously prevents cisplatin‐induced calcium homeostasis alteration contributes to elucidate the mechanism of action through which GHS could potentially ameliorate chemotherapy‐associated cachexia. PMID:28294567

Hybrid Markov-mass action law model for cell activation by rare binding events: Application to calcium induced vesicular release at neuronal synapses.

PubMed

Guerrier, Claire; Holcman, David

2016-10-18

Binding of molecules, ions or proteins to small target sites is a generic step of cell activation. This process relies on rare stochastic events where a particle located in a large bulk has to find small and often hidden targets. We present here a hybrid discrete-continuum model that takes into account a stochastic regime governed by rare events and a continuous regime in the bulk. The rare discrete binding events are modeled by a Markov chain for the encounter of small targets by few Brownian particles, for which the arrival time is Poissonian. The large ensemble of particles is described by mass action laws. We use this novel model to predict the time distribution of vesicular release at neuronal synapses. Vesicular release is triggered by the binding of few calcium ions that can originate either from the synaptic bulk or from the entry through calcium channels. We report here that the distribution of release time is bimodal although it is triggered by a single fast action potential. While the first peak follows a stimulation, the second corresponds to the random arrival over much longer time of ions located in the synaptic terminal to small binding vesicular targets. To conclude, the present multiscale stochastic modeling approach allows studying cellular events based on integrating discrete molecular events over several time scales.

Intracellular Calcium Mobilization in Response to Ion Channel Regulators via a Calcium-Induced Calcium Release Mechanism

PubMed Central

Petrou, Terry; Olsen, Hervør L.; Thrasivoulou, Christopher; Masters, John R.; Ashmore, Jonathan F.

2017-01-01

Free intracellular calcium ([Ca2+]i), in addition to being an important second messenger, is a key regulator of many cellular processes including cell membrane potential, proliferation, and apoptosis. In many cases, the mobilization of [Ca2+]i is controlled by intracellular store activation and calcium influx. We have investigated the effect of several ion channel modulators, which have been used to treat a range of human diseases, on [Ca2+]i release, by ratiometric calcium imaging. We show that six such modulators [amiodarone (Ami), dofetilide, furosemide (Fur), minoxidil (Min), loxapine (Lox), and Nicorandil] initiate release of [Ca2+]i in prostate and breast cancer cell lines, PC3 and MCF7, respectively. Whole-cell currents in PC3 cells were inhibited by the compounds tested in patch-clamp experiments in a concentration-dependent manner. In all cases [Ca2+]i was increased by modulator concentrations comparable to those used clinically. The increase in [Ca2+]i in response to Ami, Fur, Lox, and Min was reduced significantly (P < 0.01) when the external calcium was reduced to nM concentration by chelation with EGTA. The data suggest that many ion channel regulators mobilize [Ca2+]i. We suggest a mechanism whereby calcium-induced calcium release is implicated; such a mechanism may be important for understanding the action of these compounds. PMID:27980039

Heat stress responses modulate calcium regulations and electrophysiological characteristics in atrial myocytes.

PubMed

Chen, Yao-Chang; Kao, Yu-Hsun; Huang, Chun-Feng; Cheng, Chen-Chuan; Chen, Yi-Jen; Chen, Shih-Ann

2010-04-01

Heat stress-induced responses change the ionic currents and calcium homeostasis. However, the molecular insights into the heat stress responses on calcium homeostasis remain unclear. The purposes of this study were to examine the mechanisms of heat stress responses on calcium handling and electrophysiological characteristics in atrial myocytes. We used indo-1 fluorimetric ratio technique and whole-cell patch clamp to investigate the intracellular calcium, action potentials, and ionic currents in isolated rabbit single atrial cardiomyocytes with or without (control) exposure to heat stress (43 degrees C, 15 min) 5+/-1 h before experiments. The expressions of sarcoplasmic reticulum ATPase (SERCA2a), and Na(+)-Ca(2+) exchanger (NCX) in the control and heat stress-treated atrial myocytes were evaluated by Western blot and real-time PCR. As compared with control myocytes, the heat stress-treated myocytes had larger sarcoplasmic reticulum calcium content and larger intracellular calcium transient with a shorter decay portion. Heat stress-treated myocytes also had larger L-type calcium currents, transient outward potassium currents, but smaller NCX currents. Heat stress responses increased the protein expressions, SERCA2a, NCX, and heat shock protein. However, heat stress responses did not change the RNA expression of SERCA2a and NCX. In conclusion, heat stress responses change calcium handling through protein but not RNA regulation. Copyright (c) 2009 Elsevier Ltd. All rights reserved.

Best time window for the use of calcium-modulating agents to improve functional recovery in injured peripheral nerves-An experiment in rats.

PubMed

Yan, Yuhui; Shen, Feng-Yi; Agresti, Michael; Zhang, Lin-Ling; Matloub, Hani S; LoGiudice, John A; Havlik, Robert; Li, Jifeng; Gu, Yu-Dong; Yan, Ji-Geng

2017-09-01

Peripheral nerve injury can have a devastating effect on daily life. Calcium concentrations in nerve fibers drastically increase after nerve injury, and this activates downstream processes leading to neuron death. Our previous studies showed that calcium-modulating agents decrease calcium accumulation, which aids in regeneration of injured peripheral nerves; however, the optimal therapeutic window for this application has not yet been identified. In this study, we show that calcium clearance after nerve injury is positively correlated with functional recovery in rats suffering from a crushed sciatic nerve injury. After the nerve injury, calcium accumulation increased. Peak volume is from 2 to 8 weeks post injury; calcium accumulation then gradually decreased over the following 24-week period. The compound muscle action potential (CMAP) measurement from the extensor digitorum longus muscle recovered to nearly normal levels in 24 weeks. Simultaneously, real-time polymerase chain reaction results showed that upregulation of calcium-ATPase (a membrane protein that transports calcium out of nerve fibers) mRNA peaked at 12 weeks. These results suggest that without intervention, the peak in calcium-ATPase mRNA expression in the injured nerve occurs after the peak in calcium accumulation, and CMAP recovery continues beyond 24 weeks. Immediately using calcium-modulating agents after crushed nerve injury improved functional recovery. These studies suggest that a crucial time frame in which to initiate effective clinical approaches to accelerate calcium clearance and nerve regeneration would be prior to 2 weeks post injury. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Presynaptic strontium dynamics and synaptic transmission.

PubMed Central

Xu-Friedman, M A; Regehr, W G

1999-01-01

Strontium can replace calcium in triggering neurotransmitter release, although peak release is reduced and the duration of release is prolonged. Strontium has therefore become useful in probing release, but its mechanism of action is not well understood. Here we study the action of strontium at the granule cell to Purkinje cell synapse in mouse cerebellar slices. Presynaptic residual strontium levels were monitored with fluorescent indicators, which all responded to strontium (fura-2, calcium orange, fura-2FF, magnesium green, and mag-fura-5). When calcium was replaced by equimolar concentrations of strontium in the external bath, strontium and calcium both entered presynaptic terminals. Contaminating calcium was eliminated by including EGTA in the extracellular bath, or by loading parallel fibers with EGTA, enabling the actions of strontium to be studied in isolation. After a single stimulus, strontium reached higher peak free levels than did calcium (approximately 1.7 times greater), and decayed more slowly (half-decay time 189 ms for strontium and 32 ms for calcium). These differences in calcium and strontium dynamics are likely a consequence of greater strontium permeability through calcium channels, lower affinity of the endogenous buffer for strontium, and less efficient extrusion of strontium. Measurements of presynaptic divalent levels help to explain properties of release evoked by strontium. Parallel fiber synaptic currents triggered by strontium are smaller in amplitude and longer in duration than those triggered by calcium. In both calcium and strontium, release consists of two components, one more steeply dependent on divalent levels than the other. Strontium drives both components less effectively than does calcium, suggesting that the affinities of the sensors involved in both phases of release are lower for strontium than for calcium. Thus, the larger and slower strontium transients account for the prominent slow component of release triggered by strontium. PMID:10096899

Construction and use of a zebrafish heart voltage and calcium optical mapping system, with integrated electrocardiogram and programmable electrical stimulation

PubMed Central

Lin, Eric; Craig, Calvin; Lamothe, Marcel; Sarunic, Marinko V.; Beg, Mirza Faisal

2015-01-01

Zebrafish are increasingly being used as a model of vertebrate cardiology due to mammalian-like cardiac properties in many respects. The size and fecundity of zebrafish make them suitable for large-scale genetic and pharmacological screening. In larger mammalian hearts, optical mapping is often used to investigate the interplay between voltage and calcium dynamics and to investigate their respective roles in arrhythmogenesis. This report outlines the construction of an optical mapping system for use with zebrafish hearts, using the voltage-sensitive dye RH 237 and the calcium indicator dye Rhod-2 using two industrial-level CCD cameras. With the use of economical cameras and a common 532-nm diode laser for excitation, the rate dependence of voltage and calcium dynamics within the atrial and ventricular compartments can be simultaneously determined. At 140 beats/min, the atrial action potential duration was 36 ms and the transient duration was 53 ms. With the use of a programmable electrical stimulator, a shallow rate dependence of 3 and 4 ms per 100 beats/min was observed, respectively. In the ventricle the action potential duration was 109 ms and the transient duration was 124 ms, with a steeper rate dependence of 12 and 16 ms per 100 beats/min. Synchronous electrocardiograms and optical mapping recordings were recorded, in which the P-wave aligns with the atrial voltage peak and R-wave aligns with the ventricular peak. A simple optical pathway and imaging chamber are detailed along with schematics for the in-house construction of the electrocardiogram amplifier and electrical stimulator. Laboratory procedures necessary for zebrafish heart isolation, cannulation, and loading are also presented. PMID:25740339

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.

Sex Differences in β-Adrenergic Responsiveness of Action Potentials and Intracellular Calcium Handling in Isolated Rabbit Hearts

PubMed Central

Hoeker, Gregory S.; Hood, Ashleigh R.; Katra, Rodolphe P.; Poelzing, Steven; Pogwizd, Steven M.

2014-01-01

Cardioprotection in females, as observed in the setting of heart failure, has been attributed to sex differences in intracellular calcium handling and its modulation by β-adrenergic signaling. However, further studies examining sex differences in β-adrenergic responsiveness have yielded inconsistent results and have mostly been limited to studies of contractility, ion channel function, or calcium handling alone. Given the close interaction of the action potential (AP) and intracellular calcium transient (CaT) through the process of excitation-contraction coupling, the need for studies exploring the relationship between agonist-induced AP and calcium handling changes in female and male hearts is evident. Thus, the aim of this study was to use optical mapping to examine sex differences in ventricular APs and CaTs measured simultaneously from Langendorff-perfused hearts isolated from naïve adult rabbits during β-adrenergic stimulation. The non-selective β-agonist isoproterenol (Iso) decreased AP duration (APD90), CaT duration (CaD80), and the decay constant of the CaT (τ) in a dose-dependent manner (1–316.2 nM), with a plateau at doses ≥31.6 nM. The Iso-induced changes in APD90 and τ (but not CaD80) were significantly smaller in female than male hearts. These sex differences were more significant at faster (5.5 Hz) than resting rates (3 Hz). Treatment with Iso led to the development of spontaneous calcium release (SCR) with a dose threshold of 31.6 nM. While SCR occurrence was similar in female (49%) and male (53%) hearts, the associated ectopic beats had a lower frequency of occurrence (16% versus 40%) and higher threshold (100 nM versus 31.6 nM) in female than male hearts (p<0.05). In conclusion, female hearts had a decreased capacity to respond to β-adrenergic stimulation, particularly under conditions of increased demand (i.e. faster pacing rates and “maximal” levels of Iso effects), however this reduced β-adrenergic responsiveness of female hearts was associated with reduced arrhythmic activity. PMID:25340795

Metabolic and biochemical considerations of bone.

PubMed

Lutwak, L

1975-01-01

Recognition of the dynamic aspects of bone metabolism can lead to a unified concept involving endocrine and nutritional influences. Although most hormones can influence bone metabolism directly or indirectly, the principal ones involved in skeletal metabolism are parathyroid hormone, calcitonin and 1,25-dihydroxy-vitamin D. The actions of parathyroid hormone and 1,25-dihydroxy-vitamin D result in elevations of circulating extracellular fluid calcium concentration through actions directly on bone, intestine, and kidney. Calcitonin leads to decreases in calcium concentration, primarily by action on bone and kidney. The absorption and retention of calcium by the organism is further influenced by the dietary content of calcium, phosphorus, protein, and fluoride. Chronic dietary deficiencies of calcium and excesses of phosphorus may lead to chronic nutritional secondary hyperparathyroidism with resulting skeletal demineralization. In both experimental animals and in man, the earliest manifestation of this condition may be demineralization of the jaw with resultant paradentosis. Experimental studies in animals and in man have shown that this form of demineralization may be completely reversed by increasing dietary calcium and decreasing dietary phosphrous.

The Actions of Calcium on Hair Bundle Mechanics in Mammalian Cochlear Hair Cells

PubMed Central

Beurg, Maryline; Nam, Jong-Hoon; Crawford, Andrew; Fettiplace, Robert

2008-01-01

Sound stimuli excite cochlear hair cells by vibration of each hair bundle, which opens mechanotransducer (MT) channels. We have measured hair-bundle mechanics in isolated rat cochleas by stimulation with flexible glass fibers and simultaneous recording of the MT current. Both inner and outer hair-cell bundles exhibited force-displacement relationships with a nonlinearity that reflects a time-dependent reduction in stiffness. The nonlinearity was abolished, and hair-bundle stiffness increased, by maneuvers that diminished calcium influx through the MT channels: lowering extracellular calcium, blocking the MT current with dihydrostreptomycin, or depolarizing to positive potentials. To simulate the effects of Ca2+, we constructed a finite-element model of the outer hair cell bundle that incorporates the gating-spring hypothesis for MT channel activation. Four calcium ions were assumed to bind to the MT channel, making it harder to open, and, in addition, Ca2+ was posited to cause either a channel release or a decrease in the gating-spring stiffness. Both mechanisms produced Ca2+ effects on adaptation and bundle mechanics comparable to those measured experimentally. We suggest that fast adaptation and force generation by the hair bundle may stem from the action of Ca2+ on the channel complex and do not necessarily require the direct involvement of a myosin motor. The significance of these results for cochlear transduction and amplification are discussed. PMID:18178649

Implications and mechanism of action of gabapentin in neuropathic pain.

PubMed

Kukkar, Ankesh; Bali, Anjana; Singh, Nirmal; Jaggi, Amteshwar Singh

2013-03-01

Gabapentin is an anti-epileptic agent but now it is also recommended as first line agent in neuropathic pain, particularly in diabetic neuropathy and post herpetic neuralgia. α2δ-1, an auxillary subunit of voltage gated calcium channels, has been documented as its main target and its specific binding to this subunit is described to produce different actions responsible for pain attenuation. The binding to α2δ-1 subunits inhibits nerve injury-induced trafficking of α1 pore forming units of calcium channels (particularly N-type) from cytoplasm to plasma membrane (membrane trafficking) of pre-synaptic terminals of dorsal root ganglion (DRG) neurons and dorsal horn neurons. Furthermore, the axoplasmic transport of α2δ-1 subunits from DRG to dorsal horns neurons in the form of anterograde trafficking is also inhibited in response to gabapentin administration. Gabapentin has also been shown to induce modulate other targets including transient receptor potential channels, NMDA receptors, protein kinase C and inflammatory cytokines. It may also act on supra-spinal region to stimulate noradrenaline mediated descending inhibition, which contributes to its anti-hypersensitivity action in neuropathic pain.

Inhibition of Voltage-Gated Calcium Channels as Common Mode of Action for (Mixtures of) Distinct Classes of Insecticides

PubMed Central

Meijer, Marieke; Dingemans, Milou M.L.; van den Berg, Martin; Westerink, Remco H.S.

2014-01-01

Humans are exposed to distinct structural classes of insecticides with different neurotoxic modes of action. Because calcium homeostasis is essential for proper neuronal function and development, we investigated the effects of insecticides from different classes (pyrethroid: (α-)cypermethrin; organophosphate: chlorpyrifos; organochlorine: endosulfan; neonicotinoid: imidacloprid) and mixtures thereof on the intracellular calcium concentration ([Ca2+]i). Effects of acute (20 min) exposure to (mixtures of) insecticides on basal and depolarization-evoked [Ca2+]i were studied in vitro with Fura-2-loaded PC12 cells and high resolution single-cell fluorescence microscopy. The data demonstrate that cypermethrin, α-cypermethrin, endosulfan, and chlorpyrifos concentration-dependently decreased depolarization-evoked [Ca2+]i, with 50% (IC50) at 78nM, 239nM, 250nM, and 899nM, respectively. Additionally, acute exposure to chlorpyrifos or endosulfan (10μM) induced a modest increase in basal [Ca2+]i, amounting to 68 ± 8nM and 53 ± 8nM, respectively. Imidacloprid did not disturb basal or depolarization-evoked [Ca2+]i at 10μM. Following exposure to binary mixtures, effects on depolarization-evoked [Ca2+]i were within the expected effect additivity range, whereas the effect of the tertiary mixture was less than this expected additivity effect range. These results demonstrate that different types of insecticides inhibit depolarization-evoked [Ca2+]i in PC12 cells by inhibiting voltage-gated calcium channels (VGCCs) in vitro at concentrations comparable with human occupational exposure levels. Moreover, the effective concentrations in this study are below those for earlier described modes of action. Because inhibition of VGCCs appears to be a common and potentially additive mode of action of several classes of insecticides, this target should be considered in neurotoxicity risk assessment studies. PMID:24913802

Beat-to-beat variability of cardiac action potential duration: underlying mechanism and clinical implications.

PubMed

Nánási, Péter P; Magyar, János; Varró, András; Ördög, Balázs

2017-10-01

Beat-to-beat variability of cardiac action potential duration (short-term variability, SV) is a common feature of various cardiac preparations, including the human heart. Although it is believed to be one of the best arrhythmia predictors, the underlying mechanisms are not fully understood at present. The magnitude of SV is basically determined by the intensity of cell-to-cell coupling in multicellular preparations and by the duration of the action potential (APD). To compensate for the APD-dependent nature of SV, the concept of relative SV (RSV) has been introduced by normalizing the changes of SV to the concomitant changes in APD. RSV is reduced by I Ca , I Kr , and I Ks while increased by I Na , suggesting that ion currents involved in the negative feedback regulation of APD tend to keep RSV at a low level. RSV is also influenced by intracellular calcium concentration and tissue redox potential. The clinical implications of APD variability is discussed in detail.

Biophysical properties and computational modeling of calcium spikes in serotonergic neurons of the dorsal raphe nucleus.

PubMed

Tuckwell, Henry C

2013-06-01

Serotonergic neurons of the dorsal raphe nuclei, with their extensive innervation of nearly the whole brain have important modulatory effects on many cognitive and physiological processes. They play important roles in clinical depression and other psychiatric disorders. In order to quantify the effects of serotonergic transmission on target cells it is desirable to construct computational models and to this end these it is necessary to have details of the biophysical and spike properties of the serotonergic neurons. Here several basic properties are reviewed with data from several studies since the 1960s to the present. The quantities included are input resistance, resting membrane potential, membrane time constant, firing rate, spike duration, spike and afterhyperpolarization (AHP) amplitude, spike threshold, cell capacitance, soma and somadendritic areas. The action potentials of these cells are normally triggered by a combination of sodium and calcium currents which may result in autonomous pacemaker activity. We here analyse the mechanisms of high-threshold calcium spikes which have been demonstrated in these cells the presence of TTX (tetrodotoxin). The parameters for calcium dynamics required to give calcium spikes are quite different from those for regular spiking which suggests the involvement of restricted parts of the soma-dendritic surface as has been found, for example, in hippocampal neurons. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Impact of magnesium:calcium ratio on calcification of the aortic wall.

PubMed

Villa-Bellosta, Ricardo

2017-01-01

An inverse relationship between serum magnesium concentration and vascular calcification has been reported following observational clinical studies. Moreover, several studies have been suggesting a protective effect of magnesium on the vascular calcification. However, the exact mechanism remains elusive, and investigators have speculated among a myriad of potential actions. The effect of magnesium on calcification of the aortic wall is yet to be investigated. In the present study, the effects of magnesium and calcium on the metabolism of extracellular PPi, the main endogenous inhibitor of vascular calcification, were investigated in the rat aorta. Calcium and magnesium have antagonist effects on PPi hydrolysis in the aortic wall. Km and Ki values for PPi hydrolysis in rat aortic rings were 1.1 mmol/L magnesium and 32 μmol/L calcium, respectively, but ATP hydrolysis was not affected with calcium. Calcium deposition in the rat aortic wall dramatically increased when the magnesium concentration was increased (ratio of Mg:Ca = 1:1; 1.5 mmol/L calcium and 1.5 mmol/L magnesium) respect to low magnesium concentration (ratio Mg:Ca = 1:3, 1.5 mmol/L calcium and 0.75 mmol/L magnesium). Data from observational clinical studies showing that the serum magnesium concentration is inversely correlated with vascular calcification could be reinterpreted as a compensatory regulatory mechanism that reduces both PPi hydrolysis and vascular calcification. The impact of magnesium in vascular calcification in humans could be studied in association with calcium levels, for example, as the magnesium:calcium ratio.

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

Studying the mechanism of neurostimulation by infrared laser light using GCaMP6s and Rhodamine B imaging

NASA Astrophysics Data System (ADS)

Moreau, David; Lefort, Claire; Bardet, Sylvia M.; O'Connor, Rodney P.

2016-03-01

Infrared laser light radiation can be used to depolarize neurons and to stimulate neural activity. The absorption of infrared radiation and heating of biological tissue is thought to be the underlying mechanism of this phenomenon whereby local temperature increases in the plasma membrane of cells either directly influence membrane properties or act via temperature sensitive ion channels. Action potentials are typically measured electrically in neurons with microelectrodes, but they can also be observed using fluorescence microscopy techniques that use synthetic or genetically encoded calcium indicators. In this work, we studied the impact of infrared laser light on neuronal calcium signals to address the mechanism of these thermal effects. Cultured primary mouse hippocampal neurons expressing the genetically encoded calcium indicator GCaMP6s were used in combination with the temperature sensitive fluorophore Rhodamine B to measure calcium signals and temperature changes at the cellular level. Here we present our all-optical strategy for studying the influence of infrared laser light on neuronal activity.

Calcium-regulated nuclear enzymes: potential mediators of phytochrome-induced changes in nuclear metabolism?

NASA Technical Reports Server (NTRS)

Roux, S. J.

1992-01-01

Calcium ions have been proposed to serve as important regulatory elements in stimulus-response coupling for phytochrome responses. An important test of this hypothesis will be to identify specific targets of calcium action that are required for some growth or development process induced by the photoactivated form of phytochrome (Pfr). Initial studies have revealed that there are at least two enzymes in pea nuclei that are stimulated by Pfr in a Ca(2+)-dependent fashion, a calmodulin-regulated nucleoside triphosphatase and a calmodulin-independent but Ca(2+)-dependent protein kinase. The nucleoside triphosphatase appears to be associated with the nuclear envelope, while the protein kinase co-purifies with a nuclear fraction highly enriched for chromatin. This short review summarizes the latest findings on these enzymes and relates them to what is known about Pfr-regulated nuclear metabolism.

Effect of calcium on the hemolytic activity of Stichodactyla helianthus toxin sticholysin II on human erythrocytes.

PubMed

Celedón, Gloria; González, Gustavo; Lissi, Eduardo; Cerda, Tania; Martinez, Diana; Soto, Carmen; Pupo, Mario; Pazos, Fabiola; Lanio, Maria E; Alvarez, Carlos

2009-11-01

Sticholysin II (St II) is a toxin from the sea anemona Stichodactyla helianthus that produces erythrocytes lysis at low concentration and its activity depends on the presence of calcium. Calcium may act modifying toxin interaction with erythrocyte membranes or activating cellular processes which may result in a modified St II lytic action. In this study we are reporting that, in the presence of external K(+), extracellular calcium decreased St II activity on erythrocytes. On the other hand an increase of intracellular calcium promotes Sty II lytic activity. The effect of intracellular calcium was specifically studied in relation to membrane lipid translocation elicited by scramblases and how this action influence St II lytic activity on erythrocytes. We used 0.5 mmol/L calcium and 10 mmol/L A23187, as calcium ionophore, for scramblases activation and found increased St II activity associated to increase of intracellular calcium. N-ethyl maleimide (activator) and 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (inhibitor) were used as scramblases modulators in the assays which produced an increase and a decrease of the calcium effect, respectively. Results reported suggest an improved St II membrane pore-forming capacity promoted by intracellular calcium associated to membrane phospholipids translocation.

Demonstration of the existence of receptor-dependent calcium channels in the platelets

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

Avdonin, P.V.; Bugrii, E.M.; Cheglakov, I.B.

1987-01-01

Recently, with the new methodology of measuring calcium ion concentration in the cytoplasm with the aid of the fluorescent indicator, it has been shown that calcium is a second messenger, mediating the action of many hormones, neuromediators, and other extracellular factors. Another argument in support of the existence of receptor-dependent calcium channels is provided by data on the activation by agonists of the uptake of /sup 45/Ca by the cells. In all the studies cited, the conditions were such that the passage of Ca/sup 2 +/ through the potential-dependent channels was excluded. In this paper, evidence is presented for themore » existence of receptor-dependent calcium channels in the plasma membrane using human platelets as the objects. Two approaches were used. First, the authors determined the binding of /sup 45/Ca by the platelets. In this case, to determine whether /sup 45/Ca passes into the cytoplasm or is adsorbed on the membrane, the authors compared its uptake by simply washed platelets and by platelets in whose cytoplasm buffer capacity for calcium was artificially created with quin 2. The second approach was based on the data of Hallam and Rink, who showed that agonists that increase the calcium level in the platelets induce an intake of Mn/sup 2 +/ ions into the cell in a calcium-free medium.« less

General anesthesia selectively disrupts astrocyte calcium signaling in the awake mouse cortex

PubMed Central

Thrane, Alexander Stanley; Zeppenfeld, Douglas; Lou, Nanhong; Xu, Qiwu; Nagelhus, Erlend Arnulf; Nedergaard, Maiken

2012-01-01

Calcium signaling represents the principle pathway by which astrocytes respond to neuronal activity. General anesthetics are routinely used in clinical practice to induce a sleep-like state, allowing otherwise painful procedures to be performed. Anesthetic drugs are thought to mainly target neurons in the brain and act by suppressing synaptic activity. However, the direct effect of general anesthesia on astrocyte signaling in awake animals has not previously been addressed. This is a critical issue, because calcium signaling may represent an essential mechanism through which astrocytes can modulate synaptic activity. In our study, we performed calcium imaging in awake head-restrained mice and found that three commonly used anesthetic combinations (ketamine/xylazine, isoflurane, and urethane) markedly suppressed calcium transients in neocortical astrocytes. Additionally, all three anesthetics masked potentially important features of the astrocyte calcium signals, such as synchronized widespread transients that appeared to be associated with arousal in awake animals. Notably, anesthesia affected calcium transients in both processes and soma and depressed spontaneous signals, as well as calcium responses, evoked by whisker stimulation or agonist application. We show that these calcium transients are inositol 1,4,5-triphosphate type 2 receptor (IP3R2)-dependent but resistant to a local blockade of glutamatergic or purinergic signaling. Finally, we found that doses of anesthesia insufficient to affect neuronal responses to whisker stimulation selectively suppressed astrocyte calcium signals. Taken together, these data suggest that general anesthesia may suppress astrocyte calcium signals independently of neuronal activity. We propose that these glial effects may constitute a nonneuronal mechanism for sedative action of anesthetic drugs. PMID:23112168

Tibolone protects T98G cells from glucose deprivation.

PubMed

Ávila Rodriguez, Marco; Garcia-Segura, Luis Miguel; Cabezas, Ricardo; Torrente, Daniel; Capani, Francisco; Gonzalez, Janneth; Barreto, George E

2014-10-01

The steroidal drug Tibolone is used for the treatment of climacteric symptoms and osteoporosis in post-menopausal women. Although Tibolone has been shown to exert neuroprotective actions after middle cerebral artery occlusion, its specific actions on glial cells have received very little attention. In the present study we have assessed whether Tibolone exerts protective actions in a human astrocyte cell model, the T98G cells, subjected to glucose deprivation. Our findings indicate that Tibolone decreases the effects of glucose deprivation on cell death, nuclear fragmentation, superoxide ion production, mitochondrial membrane potential, cytoplasmic calcium concentration and morphological parameters. These findings suggest that glial cells may participate in the neuroprotective actions of Tibolone in the brain. Copyright © 2014 Elsevier Ltd. All rights reserved.

Action of Phα1β, a peptide from the venom of the spider Phoneutria nigriventer, on the analgesic and adverse effects caused by morphine in mice.

PubMed

Tonello, Raquel; Rigo, Flávia; Gewehr, Camila; Trevisan, Gabriela; Pereira, Elizete Maria Rita; Gomez, Marcus Vinicius; Ferreira, Juliano

2014-06-01

Opioids are standard therapy for the treatment of pain; however, adverse effects limit their use. Voltage-gated calcium channel blockers may be used to increase opioid analgesia, but their effect on opioid-induced side effects is little known. Thus, the goal of this study was to evaluate the action of the peptide Phα1β, a voltage-gated calcium channel blocker, on the antinociceptive and adverse effects produced by morphine in mice. A single administration of morphine (3-10 mg/kg) was able to reduce heat nociception as well as decrease gastrointestinal transit. The antinociception caused by a single injection of morphine was slightly increased by an intrathecal injection of Phα1β (30 pmol/site). Repeated treatment with morphine caused tolerance, hyperalgesia, withdrawal syndrome, and constipation, and the Phα1β (.1-30 pmol/site, intrathecal) was able to reverse these effects. Finally, the effects produced by the native form of Phα1β were fully mimicked by a recombinant version of this peptide. Taken together, these data show that Phα1β was effective in potentiating the analgesia caused by a single dose of morphine as well as in reducing tolerance and the adverse effects induced by repeated administration of morphine, indicating its potential use as an adjuvant drug in combination with opioids. This article presents preclinical evidence for a useful adjuvant drug in opioid treatment. Phα1β, a peptide calcium channel blocker, could be used not only to potentiate morphine analgesia but also to reduce the adverse effects caused by repeated administration of morphine. Copyright © 2014. Published by Elsevier Inc.

Fluorescence lifetime imaging of calcium flux in neurons in response to pulsed infrared light

NASA Astrophysics Data System (ADS)

Walsh, Alex J.; Sedelnikova, Anna; Tolstykh, Gleb P.; Ibey, Bennett L.; Beier, Hope T.

2017-02-01

Pulsed infrared light can excite action potentials in neurons; yet, the fundamental mechanism underlying this phenomenon is unknown. Previous work has observed a rise in intracellular calcium concentration following infrared exposure, but the source of the calcium and mechanism of release is unknown. Here, we used fluorescence lifetime imaging of Oregon Green BAPTA-1 to study intracellular calcium dynamics in primary rat hippocampal neurons in response to infrared light exposure. The fluorescence lifetime of Oregon Green BAPTA-1 is longer when bound to calcium, and allows robust measurement of intracellular free calcium concentrations. First, a fluorescence lifetime calcium calibration curve for Oregon Green BAPTA-1 was determined in solutions. The normalized amplitude of the short and long lifetimes was calibrated to calcium concentration. Then, neurons were incubated in Oregon Green BAPTA-1 and exposed to pulses of infrared light (0-1 J/cm2; 0-5 ms; 1869 nm). Fluorescence lifetime images were acquired prior to, during, and after the infrared exposure. Fluorescence lifetime images, 64x64 pixels, were acquired at 12 or 24 ms for frame rates of 83 and 42 Hz, respectively. Accurate α1 approximations were achieved in images with low photon counts by computing an α1 index value from the relative probability of the observed decay events. Results show infrared light exposure increases intracellular calcium in neurons. Altogether, this study demonstrates accurate fluorescence lifetime component analysis from low-photon count data for improved imaging speed.

A Double-Blind Randomized Placebo Controlled Trial of Magnesium Oxide for Alleviation of Chronic Low Back Pain

DTIC Science & Technology

1999-01-01

minireview of the interactions between calcium channel blockers and analgesics. In a metaanalysis of several studies, they concluded that calcium ...Philadelphia: W. B. Saunders Company. Miranda, H., & Paeile, C. (1990). Interactions between analgesics and calcium channel blockers. General... calcium access into the cell and the actions of calcium inside the cell. The influx of calcium inside the depolarized presynaptic cell allows for

Sodium and calcium currents shape action potentials in immature mouse inner hair cells

PubMed Central

Marcotti, Walter; Johnson, Stuart L; Rüsch, Alfons; Kros, Corné J

2003-01-01

Before the onset of hearing at postnatal day 12, mouse inner hair cells (IHCs) produce spontaneous and evoked action potentials. These spikes are likely to induce neurotransmitter release onto auditory nerve fibres. Since immature IHCs express both α1D (Cav1.3) Ca2+ and Na+ currents that activate near the resting potential, we examined whether these two conductances are involved in shaping the action potentials. Both had extremely rapid activation kinetics, followed by fast and complete voltage-dependent inactivation for the Na+ current, and slower, partially Ca2+-dependent inactivation for the Ca2+ current. Only the Ca2+ current is necessary for spontaneous and induced action potentials, and 29 % of cells lacked a Na+ current. The Na+ current does, however, shorten the time to reach the action-potential threshold, whereas the Ca2+ current is mainly involved, together with the K+ currents, in determining the speed and size of the spikes. Both currents increased in size up to the end of the first postnatal week. After this, the Ca2+ current reduced to about 30 % of its maximum size and persisted in mature IHCs. The Na+ current was downregulated around the onset of hearing, when the spiking is also known to disappear. Although the Na+ current was observed as early as embryonic day 16.5, its role in action-potential generation was only evident from just after birth, when the resting membrane potential became sufficiently negative to remove a sizeable fraction of the inactivation (half inactivation was at −71 mV). The size of both currents was positively correlated with the developmental change in action-potential frequency. PMID:12937295

Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels

PubMed Central

Hermann, Anton; Sitdikova, Guzel F.; Weiger, Thomas M.

2015-01-01

All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences. PMID:26287261

Ziconotide: neuronal calcium channel blocker for treating severe chronic pain.

PubMed

Miljanich, G P

2004-12-01

Ziconotide (PRIALT) is a neuroactive peptide in the final stages of clinical development as a novel non-opioid treatment for severe chronic pain. It is the synthetic equivalent of omega-MVIIA, a component of the venom of the marine snail, Conus magus. The mechanism of action underlying ziconotide's therapeutic profile derives from its potent and selective blockade of neuronal N-type voltage-sensitive calcium channels (N-VSCCs). Direct blockade of N-VSCCs inhibits the activity of a subset of neurons, including pain-sensing primary nociceptors. This mechanism of action distinguishes ziconotide from all other analgesics, including opioid analgesics. In fact, ziconotide is potently anti-nociceptive in animal models of pain in which morphine exhibits poor anti-nociceptive activity. Moreover, in contrast to opiates, tolerance to ziconotide is not observed. Clinical studies of ziconotide in more than 2,000 patients reveal important correlations to ziconotide's non-clinical pharmacology. For example, ziconotide provides significant pain relief to severe chronic pain sufferers who have failed to obtain relief from opiate therapy and no evidence of tolerance to ziconotide is seen in these patients. Contingent on regulatory approval, ziconotide will be the first in a new class of neurological drugs: the N-type calcium channel blockers, or NCCBs. Its novel mechanism of action as a non-opioid analgesic suggests ziconotide has the potential to play a valuable role in treatment regimens for severe chronic pain. If approved for clinical use, ziconotide will further validate the neuroactive venom peptides as a source of new and useful medicines.

Impact of magnesium:calcium ratio on calcification of the aortic wall

PubMed Central

2017-01-01

Objective An inverse relationship between serum magnesium concentration and vascular calcification has been reported following observational clinical studies. Moreover, several studies have been suggesting a protective effect of magnesium on the vascular calcification. However, the exact mechanism remains elusive, and investigators have speculated among a myriad of potential actions. The effect of magnesium on calcification of the aortic wall is yet to be investigated. In the present study, the effects of magnesium and calcium on the metabolism of extracellular PPi, the main endogenous inhibitor of vascular calcification, were investigated in the rat aorta. Approach and results Calcium and magnesium have antagonist effects on PPi hydrolysis in the aortic wall. Km and Ki values for PPi hydrolysis in rat aortic rings were 1.1 mmol/L magnesium and 32 μmol/L calcium, respectively, but ATP hydrolysis was not affected with calcium. Calcium deposition in the rat aortic wall dramatically increased when the magnesium concentration was increased (ratio of Mg:Ca = 1:1; 1.5 mmol/L calcium and 1.5 mmol/L magnesium) respect to low magnesium concentration (ratio Mg:Ca = 1:3, 1.5 mmol/L calcium and 0.75 mmol/L magnesium). Conclusion Data from observational clinical studies showing that the serum magnesium concentration is inversely correlated with vascular calcification could be reinterpreted as a compensatory regulatory mechanism that reduces both PPi hydrolysis and vascular calcification. The impact of magnesium in vascular calcification in humans could be studied in association with calcium levels, for example, as the magnesium:calcium ratio. PMID:28570619

Mechanistic roles for calcium and vitamin D in the regulation of body weight.

PubMed

Soares, M J; Murhadi, L L; Kurpad, A V; Chan She Ping-Delfos, W L; Piers, L S

2012-07-01

Low intakes of calcium and inadequate vitamin D status often cluster with higher prevalence rates of obesity. Consequently, there has been much interest in the mechanisms by which calcium and vitamin D could regulate body weight and adiposity. This review has focused on randomized controlled trials (RCTs) that have manipulated these nutrients and studied pathways of energy balance. Overall, there is consistent evidence that calcium and vitamin D increase whole body fat oxidation after single and multiple meals, and that calcium promotes a modest energy loss through increased faecal fat excretion. The evidence is equivocal for a greater diet-induced thermogenesis, increased lipolysis, suppression of key lipogenic enzymes, decreased hunger ratings or reduced energy/macronutrient intake. Emerging evidence suggests a potential improvement in insulin sensitivity following vitamin D that would impinge on food intake and substrate oxidation. However, the very few RCTs on supplemental vitamin D and energy balance have not explored postprandial avenues of the hormone's actions. Future efforts in this area need to define the threshold intake of these nutrients that would maximize metabolic and gastrointestinal outcomes. Such studies would provide a platform for endorsing the non-skeletal role of calcium and vitamin D in human pathophysiology. © 2012 The Authors. obesity reviews © 2012 International Association for the Study of Obesity.

Reconstruction of Cell Surface Densities of Ion Pumps, Exchangers, and Channels from mRNA Expression, Conductance Kinetics, Whole-Cell Calcium, and Current-Clamp Voltage Recordings, with an Application to Human Uterine Smooth Muscle Cells

PubMed Central

Atia, Jolene; McCloskey, Conor; Shmygol, Anatoly S.; Rand, David A.; van den Berg, Hugo A.; Blanks, Andrew M.

2016-01-01

Uterine smooth muscle cells remain quiescent throughout most of gestation, only generating spontaneous action potentials immediately prior to, and during, labor. This study presents a method that combines transcriptomics with biophysical recordings to characterise the conductance repertoire of these cells, the ‘conductance repertoire’ being the total complement of ion channels and transporters expressed by an electrically active cell. Transcriptomic analysis provides a set of potential electrogenic entities, of which the conductance repertoire is a subset. Each entity within the conductance repertoire was modeled independently and its gating parameter values were fixed using the available biophysical data. The only remaining free parameters were the surface densities for each entity. We characterise the space of combinations of surface densities (density vectors) consistent with experimentally observed membrane potential and calcium waveforms. This yields insights on the functional redundancy of the system as well as its behavioral versatility. Our approach couples high-throughput transcriptomic data with physiological behaviors in health and disease, and provides a formal method to link genotype to phenotype in excitable systems. We accurately predict current densities and chart functional redundancy. For example, we find that to evoke the observed voltage waveform, the BK channel is functionally redundant whereas hERG is essential. Furthermore, our analysis suggests that activation of calcium-activated chloride conductances by intracellular calcium release is the key factor underlying spontaneous depolarisations. PMID:27105427

Axonal GABAA receptors.

PubMed

Trigo, Federico F; Marty, Alain; Stell, Brandon M

2008-09-01

Type A GABA receptors (GABA(A)Rs) are well established as the main inhibitory receptors in the mature mammalian forebrain. In recent years, evidence has accumulated showing that GABA(A)Rs are prevalent not only in the somatodendritic compartment of CNS neurons, but also in their axonal compartment. Evidence for axonal GABA(A)Rs includes new immunohistochemical and immunogold data: direct recording from single axonal terminals; and effects of local applications of GABA(A)R modulators on action potential generation, on axonal calcium signalling, and on neurotransmitter release. Strikingly, whereas presynaptic GABA(A)Rs have long been considered inhibitory, the new studies in the mammalian brain mostly indicate an excitatory action. Depending on the neuron that is under study, axonal GABA(A)Rs can be activated by ambient GABA, by GABA spillover, or by an autocrine action, to increase either action potential firing and/or transmitter release. In certain neurons, the excitatory effects of axonal GABA(A)Rs persist into adulthood. Altogether, axonal GABA(A)Rs appear as potent neuronal modulators of the mammalian CNS.

Inference of neuronal network spike dynamics and topology from calcium imaging data

PubMed Central

Lütcke, Henry; Gerhard, Felipe; Zenke, Friedemann; Gerstner, Wulfram; Helmchen, Fritjof

2013-01-01

Two-photon calcium imaging enables functional analysis of neuronal circuits by inferring action potential (AP) occurrence (“spike trains”) from cellular fluorescence signals. It remains unclear how experimental parameters such as signal-to-noise ratio (SNR) and acquisition rate affect spike inference and whether additional information about network structure can be extracted. Here we present a simulation framework for quantitatively assessing how well spike dynamics and network topology can be inferred from noisy calcium imaging data. For simulated AP-evoked calcium transients in neocortical pyramidal cells, we analyzed the quality of spike inference as a function of SNR and data acquisition rate using a recently introduced peeling algorithm. Given experimentally attainable values of SNR and acquisition rate, neural spike trains could be reconstructed accurately and with up to millisecond precision. We then applied statistical neuronal network models to explore how remaining uncertainties in spike inference affect estimates of network connectivity and topological features of network organization. We define the experimental conditions suitable for inferring whether the network has a scale-free structure and determine how well hub neurons can be identified. Our findings provide a benchmark for future calcium imaging studies that aim to reliably infer neuronal network properties. PMID:24399936

Impact of nanosecond pulsed electric fields on primary hippocampal neurons

NASA Astrophysics Data System (ADS)

Roth, Caleb C.; Payne, Jason A.; Kuipers, Marjorie A.; Thompson, Gary L.; Wilmink, Gerald J.; Ibey, Bennett L.

2012-02-01

Cellular exposure to nanosecond pulsed electric fields (nsPEF) are believed to cause immediate creation of nanopores in the plasma membrane. These nanopores enable passage of small ions, but remain impermeable to larger molecules like propidium iodide. Previous work has shown that nanopores are stable for minutes after exposure, suggesting that formation of nanopores in excitable cells could lead to prolonged action potential inhibition. Previously, we measured the formation of nanopores in neuroblastoma cells by measuring the influx of extracellular calcium by preloading cells with Calcium Green-AM. In this work, we explored the impact of changing the width of a single nsPEF, at constant amplitude, on uptake of extracellular calcium ions by primary hippocampal neurons (PHN). Calcium Green was again used to measure the influx of extracellular calcium and FM1-43 was used to monitor changes in membrane conformation. The observed thresholds for nanopore formation in PHN by nsPEF were comparable to those measured in neuroblastoma. This work is the first study of nsPEF effects on PHN and strongly suggests that neurological inhibition by nanosecond electrical pulses is highly likely at doses well below irreversible damage.

Cardiac cell: a biological laser?

PubMed

Chorvat, D; Chorvatova, A

2008-04-01

We present a new concept of cardiac cells based on an analogy with lasers, practical implementations of quantum resonators. In this concept, each cardiac cell comprises a network of independent nodes, characterised by a set of discrete energy levels and certain transition probabilities between them. Interaction between the nodes is given by threshold-limited energy transfer, leading to quantum-like behaviour of the whole network. We propose that in cardiomyocytes, during each excitation-contraction coupling cycle, stochastic calcium release and the unitary properties of ionic channels constitute an analogue to laser active medium prone to "population inversion" and "spontaneous emission" phenomena. This medium, when powered by an incoming threshold-reaching voltage discharge in the form of an action potential, responds to the calcium influx through L-type calcium channels by stimulated emission of Ca2+ ions in a coherent, synchronised and amplified release process known as calcium-induced calcium release. In parallel, phosphorylation-stimulated molecular amplification in protein cascades adds tuneable features to the cells. In this framework, the heart can be viewed as a coherent network of synchronously firing cardiomyocytes behaving as pulsed laser-like amplifiers, coupled to pulse-generating pacemaker master-oscillators. The concept brings a new viewpoint on cardiac diseases as possible alterations of "cell lasing" properties.

Effect of inhibition of microsomal Ca(2+)-ATPase on cytoplasmic calcium and enzyme secretion in pancreatic acini.

PubMed

Metz, D C; Pradhan, T K; Mrozinski, J E; Jensen, R T; Turner, R J; Patto, R J; Gardner, J D

1994-01-13

We used thapsigargin (TG), 2,5-di-tert-butyl-1,4-benzohydroquinone (BHQ) and cyclopiazonic acid (CPA), each of which inhibits microsomal Ca(2+)-ATPase, to evaluate the effects of this inhibition on cytoplasmic free calcium ([Ca2+]i) and secretagogue-stimulated enzyme secretion in rat pancreatic acini. Using single-cell microspectrofluorimetry of fura-2-loaded acini we found that all three agents caused a sustained increase in [Ca2+]i by mobilizing calcium from inositol-(1,4,5)-trisphosphate-sensitive intracellular calcium stores and by promoting influx of extracellular calcium. Concentrations of all three agents that increased [Ca2+]i potentiated the stimulation of enzyme secretion caused by secretagogues that activate adenylate cyclase but inhibited the stimulation of enzyme secretion caused by secretagogues that activate phospholipase C. With BHQ, potentiation of adenylate cyclase-mediated enzyme secretion occurred immediately whereas inhibition of phospholipase C-mediated enzyme secretion occurred only after several min of incubation. In addition, the effects of BHQ and CPA on both [Ca2+]i and secretagogue-stimulated enzyme secretion were reversed completely by washing whereas the actions of TG could not be reversed by washing. Concentrations of BHQ in excess of those that caused maximal changes in [Ca2+]i inhibited all modes of stimulated enzyme secretion by a mechanism that was apparently unrelated to changes in [Ca2+]i. Finally, in contrast to the findings with TG and BHQ, CPA inhibited bombesin-stimulated enzyme secretion over a range of concentrations that was at least 10-fold lower than the range of concentrations over which CPA potentiated VIP-stimulated enzyme secretion.

Discovery and Development of Calcium Channel Blockers

PubMed Central

Godfraind, Théophile

2017-01-01

In the mid 1960s, experimental work on molecules under screening as coronary dilators allowed the discovery of the mechanism of calcium entry blockade by drugs later named calcium channel blockers. This paper summarizes scientific research on these small molecules interacting directly with L-type voltage-operated calcium channels. It also reports on experimental approaches translated into understanding of their therapeutic actions. The importance of calcium in muscle contraction was discovered by Sidney Ringer who reported this fact in 1883. Interest in the intracellular role of calcium arose 60 years later out of Kamada (Japan) and Heibrunn (USA) experiments in the early 1940s. Studies on pharmacology of calcium function were initiated in the mid 1960s and their therapeutic applications globally occurred in the the 1980s. The first part of this report deals with basic pharmacology in the cardiovascular system particularly in isolated arteries. In the section entitled from calcium antagonists to calcium channel blockers, it is recalled that drugs of a series of diphenylpiperazines screened in vivo on coronary bed precontracted by angiotensin were initially named calcium antagonists on the basis of their effect in depolarized arteries contracted by calcium. Studies on arteries contracted by catecholamines showed that the vasorelaxation resulted from blockade of calcium entry. Radiochemical and electrophysiological studies performed with dihydropyridines allowed their cellular targets to be identified with L-type voltage-operated calcium channels. The modulated receptor theory helped the understanding of their variation in affinity dependent on arterial cell membrane potential and promoted the terminology calcium channel blocker (CCB) of which the various chemical families are introduced in the paper. In the section entitled tissue selectivity of CCBs, it is shown that characteristics of the drug, properties of the tissue, and of the stimuli are important factors of their action. The high sensitivity of hypertensive animals is explained by the partial depolarization of their arteries. It is noted that they are arteriolar dilators and that they cannot be simply considered as vasodilators. The second part of this report provides key information about clinical usefulness of CCBs. A section is devoted to the controversy on their safety closed by the Allhat trial (2002). Sections are dedicated to their effect in cardiac ischemia, in cardiac arrhythmias, in atherosclerosis, in hypertension, and its complications. CCBs appear as the most commonly used for the treatment of cardiovascular diseases. As far as hypertension is concerned, globally the prevalence in adults aged 25 years and over was around 40% in 2008. Usefulness of CCBs is discussed on the basis of large clinical trials. At therapeutic dosage, they reduce the elevated blood pressure of hypertensive patients but don't change blood pressure of normotensive subjects, as was observed in animals. Those active on both L- and T-type channels are efficient in nephropathy. Alteration of cognitive function is a complication of hypertension recognized nowadays as eventually leading to dementia. This question is discussed together with the efficacy of CCBs in cognitive pathology. In the section entitled beyond the cardiovascular system, CCBs actions in migraine, neuropathic pain, and subarachnoid hemorrhage are reported. The final conclusions refer to long-term effects discovered in experimental animals that have not yet been clearly reported as being important in human pharmacotherapy. PMID:28611661

Neurotoxicity Induced by Bupivacaine via T-Type Calcium Channels in SH-SY5Y Cells

PubMed Central

Wen, Xianjie; Xu, Shiyuan; Liu, Hongzhen; Zhang, Quinguo; Liang, Hua; Yang, Chenxiang; Wang, Hanbing

2013-01-01

There is concern regarding neurotoxicity induced by the use of local anesthetics. A previous study showed that an overload of intracellular calcium is involved in the neurotoxic effect of some anesthetics. T-type calcium channels, which lower the threshold of action potentials, can regulate the influx of calcium ions. We hypothesized that T-type calcium channels are involved in bupivacaine-induced neurotoxicity. In this study, we first investigated the effects of different concentrations of bupivacaine on SH-SY5Y cell viability, and established a cell injury model with 1 mM bupivacaine. The cell viability of SH-SY5Y cells was measured following treatment with 1 mM bupivacaine and/or different dosages (10, 50, or 100 µM) of NNC 55-0396 dihydrochloride, an antagonist of T-type calcium channels for 24 h. In addition, we monitored the release of lactate dehydrogenase, cytosolic Ca2+ ([Ca2+]i), cell apoptosis and caspase-3 expression. SH-SY5Y cells pretreated with different dosages (10, 50, or 100 µM) of NNC 55-0396 dihydrochloride improved cell viability, reduced lactate dehydrogenase release, inhibited apoptosis, and reduced caspase-3 expression following bupivacaine exposure. However, the protective effect of NNC 55-0396 dihydrochloride plateaued. Overall, our results suggest that T-type calcium channels may be involved in bupivacaine neurotoxicity. However, identification of the specific subtype of T calcium channels involved requires further investigation. PMID:23658789

A possible molecular mechanism of the action of digitalis: ouabain action on calcium binding to sites associated with a purified sodium-potassium-activated adenosine triphosphatase from kidney.

PubMed

Gervais, A; Lane, L K; Anner, B M; Lindenmayer, G E; Schwartz, A

1977-01-01

Calcium binding at 0 degrees C to a purified sheep kidney Na+,K+-ATPase was described by linear Scatchard plots. Binding at saturating free calcium was 65-80 nmol/mg of protein, or 30-40 mol of calcium/mol of enzyme. Aqueous emulsions of lipids extracted from Na+,K+-ATPase yielded dissociation constants and maximum calcium-binding values that were similar to those for native Na+,K+-ATPase. Phospholipase A treatment markedly reduced calcium binding. Pretreatment of native Na+,K+-ATPase with ouabain increased the dissociation constant for calcium binding from 131 +/- 7 to 192 +/- 7 muM without altering maximum calcium binding. Ouabain pretreatment did not affect calcium binding to extracted phospholipids, ouabain-insensitive ATPases, or heat denatured Na+,K+-ATPase, Na+ and K+ (5-20 mM) increased the dissociation constants for calcium, which suggests competition between the monovalent cations and calcium for the binding sites. At higher concentrations of monovalent cations, ouabain increased the apparent affinity of binding sites for calcium. Extrapolation to physiological cation concentrations revealed that the ouabain-induced increase in apparent affinity for calcium may be as much as 2- to 3-fold. These results suggest: (1) calcium binds to phospholipids associated with Na+,K+-ATPase; (2) ouabain interaction with Na+,K+-ATPase induces a perturbation that is transmitted to adjacent phospholipids, altering their affinity for calcium; and (3) at physiological concentrations of Na+ or K+, or both, ouabain interaction with Na+,K+-ATPase may lead to an increased pool of membrane-bound calcium.

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.

[Calciotropic actions of parathyroid hormone and vitamin D-endocrine system].

PubMed

Avila, Euclides; Barrera, David; Díaz, Lorenza

2007-01-01

Parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D [1,25-(OH)zD] participate in systemic regulation of calcium homeostasis through endocrine effects mediated via the specific receptors PTHR1 and VDR, expressed in bone, kidney, intestine and parathyroid glands. In bone, both hormones PTH and 1,25-(OH)2D promote calcium release into the circulation; however, they also have anabolic effects in this tissue. In kidney, PTH controls 1,25-(OH)2D synthesis, and together both hormones stimulate calcium reabsorption. The most important calciotropic action of 1,25-(OH)2D is stimulation of intestinal calcium absorption. In the parathyroid glands, 1,25-(OH)2D regulates PTH synthesis through a negative feedback mechanism, while modulating the gland growth. Finally, a general overview of the maternal adaptations regarding calcium homeostasis during pregnancy and lactation is presented.

In Vitro Screen for Cyanide Antidotes

DTIC Science & Technology

1993-05-13

each others actions in the in yiro screen. Known cyanide antidotes (e.g., pyruvate, mercaptopyruvate, alpha - ketoglutarate , naloxone and flunarizine...generation, cytosolic-free calcium ) and inhibition of certain enzymes (catalase, superoxide dismutase and cytochrome oxidase) was evaluated for 39...cyanide, and for this reason other biochemical actions of cyanide [elevated cytosolic calcium (3), peroxide generation (4) and inhibition of

Distant homologs of anti-apoptotic factor HAX1 encode parvalbumin-like calcium binding proteins.

PubMed

Kokoszyńska, Katarzyna; Rychlewski, Leszek; Wyrwicz, Lucjan S

2010-07-15

Apoptosis is a highly ordered and orchestrated multiphase process controlled by the numerous cellular and extra-cellular signals, which executes the programmed cell death via release of cytochrome c alterations in calcium signaling, caspase-dependent limited proteolysis and DNA fragmentation. Besides the general modifiers of apoptosis, several tissue-specific regulators of this process were identified including HAX1 (HS-1 associated protein X-1) - an anti-apoptotic factor active in myeloid cells. Although HAX1 was the subject of various experimental studies, the mechanisms of its action and a functional link connected with the regulation of apoptosis still remains highly speculative. Here we provide the data which suggests that HAX1 may act as a regulator or as a sensor of calcium. On the basis of iterative similarity searches, we identified a set of distant homologs of HAX1 in insects. The applied fold recognition protocol gives us strong evidence that the distant insects' homologs of HAX1 are novel parvalbumin-like calcium binding proteins. Although the whole three EF-hands fold is not preserved in vertebrate our analysis suggests that there is an existence of a potential single EF-hand calcium binding site in HAX1. The molecular mechanism of its action remains to be identified, but the risen hypothesis easily translates into previously reported lines of various data on the HAX1 biology as well as, provides us a direct link to the regulation of apoptosis. Moreover, we also report that other family of myeloid specific apoptosis regulators - myeloid leukemia factors (MLF1, MLF2) share the homologous C-terminal domain and taxonomic distribution with HAX1. Performed structural and active sites analyses gave new insights into mechanisms of HAX1 and MLF families in apoptosis process and suggested possible role of HAX1 in calcium-binding, still the analyses require further experimental verification.

Distant homologs of anti-apoptotic factor HAX1 encode parvalbumin-like calcium binding proteins

PubMed Central

2010-01-01

Background Apoptosis is a highly ordered and orchestrated multiphase process controlled by the numerous cellular and extra-cellular signals, which executes the programmed cell death via release of cytochrome c alterations in calcium signaling, caspase-dependent limited proteolysis and DNA fragmentation. Besides the general modifiers of apoptosis, several tissue-specific regulators of this process were identified including HAX1 (HS-1 associated protein X-1) - an anti-apoptotic factor active in myeloid cells. Although HAX1 was the subject of various experimental studies, the mechanisms of its action and a functional link connected with the regulation of apoptosis still remains highly speculative. Findings Here we provide the data which suggests that HAX1 may act as a regulator or as a sensor of calcium. On the basis of iterative similarity searches, we identified a set of distant homologs of HAX1 in insects. The applied fold recognition protocol gives us strong evidence that the distant insects' homologs of HAX1 are novel parvalbumin-like calcium binding proteins. Although the whole three EF-hands fold is not preserved in vertebrate our analysis suggests that there is an existence of a potential single EF-hand calcium binding site in HAX1. The molecular mechanism of its action remains to be identified, but the risen hypothesis easily translates into previously reported lines of various data on the HAX1 biology as well as, provides us a direct link to the regulation of apoptosis. Moreover, we also report that other family of myeloid specific apoptosis regulators - myeloid leukemia factors (MLF1, MLF2) share the homologous C-terminal domain and taxonomic distribution with HAX1. Conclusions Performed structural and active sites analyses gave new insights into mechanisms of HAX1 and MLF families in apoptosis process and suggested possible role of HAX1 in calcium-binding, still the analyses require further experimental verification. PMID:20633251

Trigeminal ganglion neuron subtype-specific alterations of CaV2.1 calcium current and excitability in a Cacna1a mouse model of migraine

PubMed Central

Fioretti, B; Catacuzzeno, L; Sforna, L; Gerke-Duncan, M B; van den Maagdenberg, A M J M; Franciolini, F; Connor, M; Pietrobon, D

2011-01-01

Abstract Familial hemiplegic migraine type-1 (FHM1), a monogenic subtype of migraine with aura, is caused by gain-of-function mutations in CaV2.1 (P/Q-type) calcium channels. The consequences of FHM1 mutations on the trigeminovascular pathway that generates migraine headache remain largely unexplored. Here we studied the calcium currents and excitability properties of two subpopulations of small-diameter trigeminal ganglion (TG) neurons from adult wild-type (WT) and R192Q FHM1 knockin (KI) mice: capsaicin-sensitive neurons without T-type calcium currents (CS) and capsaicin-insensitive neurons characterized by the expression of T-type calcium currents (CI-T). Small TG neurons retrogradely labelled from the dura are mostly CS neurons, while CI-T neurons were not present in the labelled population. CS and CI-T neurons express CaV2.1 channels with different activation properties, and the CaV2.1 channels are differently affected by the FHM1 mutation in the two TG neuron subtypes. In CI-T neurons from FHM1 KI mice there was a larger P/Q-type current density following mild depolarizations, a larger action potential (AP)-evoked calcium current and a longer AP duration when compared to CI-T neurons from WT mice. In striking contrast, the P/Q-type current density, voltage dependence and kinetics were not altered by the FHM1 mutation in CS neurons. The excitability properties of mutant CS neurons were also unaltered. Congruently, the FHM1 mutation did not alter depolarization-evoked CGRP release from the dura mater, while CGRP release from the trigeminal ganglion was larger in KI compared to WT mice. Our findings suggest that the facilitation of peripheral mechanisms of CGRP action, such as dural vasodilatation and nociceptor sensitization at the meninges, does not contribute to the generation of headache in FHM1. PMID:22005682

Calcium Channel Antagonists as Disease-Modifying Therapy for Parkinson's Disease: Therapeutic Rationale and Current Status.

PubMed

Swart, Tara; Hurley, Michael J

2016-12-01

Parkinson's disease is a disabling hypokinetic neurological movement disorder in which the aetiology is unknown in the majority of cases. Current pharmacological treatments, though effective at restoring movement, are only symptomatic and do nothing to slow disease progression. Electrophysiological, epidemiological and neuropathological studies have implicated Ca V 1.3 subtype calcium channels in the pathogenesis of the disorder, and drugs with some selectivity for this ion channel (brain-penetrant dihydropyridine calcium channel blockers) are neuroprotective in animal models of the disease. Dihydropyridines have been safely used for decades to treat hypertension and other cardiovascular disorders. A phase II clinical trial found that isradipine was safely tolerated by patients with Parkinson's disease, and a phase III trial is currently underway to determine whether treatment with isradipine is neuroprotective and therefore able to slow the progression of Parkinson's disease. This manuscript reviews the current information about the use of dihydropyridines as therapy for Parkinson's disease and discusses the possible mechanism of action of these drugs, highlighting Ca V 1.3 calcium channels as a potential therapeutic target for neuroprotection in Parkinson's disease.

Regulation of insulin exocytosis by calcium-dependent protein kinase C in beta cells.

PubMed

Trexler, Adam J; Taraska, Justin W

2017-11-01

The control of insulin release from pancreatic beta cells helps ensure proper blood glucose level, which is critical for human health. Protein kinase C has been shown to be one key control mechanism for this process. After glucose stimulation, calcium influx into beta cells triggers exocytosis of insulin-containing dense-core granules and activates protein kinase C via calcium-dependent phospholipase C-mediated generation of diacylglycerol. Activated protein kinase C potentiates insulin release by enhancing the calcium sensitivity of exocytosis, likely by affecting two main pathways that could be linked: (1) the reorganization of the cortical actin network, and (2) the direct phosphorylation of critical exocytotic proteins such as munc18, SNAP25, and synaptotagmin. Here, we review what is currently known about the molecular mechanisms of protein kinase C action on each of these pathways and how these effects relate to the control of insulin release by exocytosis. We identify remaining challenges in the field and suggest how these challenges might be addressed to advance our understanding of the regulation of insulin release in health and disease. Published by Elsevier Ltd.

A Neuron-Based Screening Platform for Optimizing Genetically-Encoded Calcium Indicators

PubMed Central

Schreiter, Eric R.; Hasseman, Jeremy P.; Tsegaye, Getahun; Fosque, Benjamin F.; Behnam, Reza; Shields, Brenda C.; Ramirez, Melissa; Kimmel, Bruce E.; Kerr, Rex A.; Jayaraman, Vivek; Looger, Loren L.; Svoboda, Karel; Kim, Douglas S.

2013-01-01

Fluorescent protein-based sensors for detecting neuronal activity have been developed largely based on non-neuronal screening systems. However, the dynamics of neuronal state variables (e.g., voltage, calcium, etc.) are typically very rapid compared to those of non-excitable cells. We developed an electrical stimulation and fluorescence imaging platform based on dissociated rat primary neuronal cultures. We describe its use in testing genetically-encoded calcium indicators (GECIs). Efficient neuronal GECI expression was achieved using lentiviruses containing a neuronal-selective gene promoter. Action potentials (APs) and thus neuronal calcium levels were quantitatively controlled by electrical field stimulation, and fluorescence images were recorded. Images were segmented to extract fluorescence signals corresponding to individual GECI-expressing neurons, which improved sensitivity over full-field measurements. We demonstrate the superiority of screening GECIs in neurons compared with solution measurements. Neuronal screening was useful for efficient identification of variants with both improved response kinetics and high signal amplitudes. This platform can be used to screen many types of sensors with cellular resolution under realistic conditions where neuronal state variables are in relevant ranges with respect to timing and amplitude. PMID:24155972

Peripheral μ-opioid receptor mediated inhibition of calcium signaling and action potential-evoked calcium fluorescent transients in primary afferent CGRP nociceptive terminals.

PubMed

Baillie, Landon D; Schmidhammer, Helmut; Mulligan, Sean J

2015-06-01

While μ-opioid receptor (MOR) agonists remain the most powerful analgesics for the treatment of severe pain, serious adverse side effects that are secondary to their central nervous system actions pose substantial barriers to therapeutic use. Preclinical and clinical evidence suggest that peripheral MORs play an important role in opioid analgesia, particularly under inflammatory conditions. However, the mechanisms of peripheral MOR signaling in primary afferent pain fibres remain to be established. We have recently introduced a novel ex vivo optical imaging approach that, for the first time, allows the study of physiological functioning within individual peripheral nociceptive fibre free nerve endings in mice. In the present study, we found that MOR activation in selectively identified, primary afferent CGRP nociceptive terminals caused inhibition of N-type Ca(2+) channel signaling and suppression of action potential-evoked Ca(2+) fluorescent transients mediated by 'big conductance' Ca(2+)-activated K(+) channels (BKCa). In the live animal, we showed that the peripherally acting MOR agonist HS-731 produced analgesia and that BKCa channels were the major effectors of the peripheral MOR signaling. We have identified two key molecular transducers of MOR activation that mediate significant inhibition of nociceptive signaling in primary afferent terminals. Understanding the mechanisms of peripheral MOR signaling may promote the development of pathway selective μ-opioid drugs that offer improved therapeutic profiles for achieving potent analgesia while avoiding serious adverse central side effects. Copyright © 2015 Elsevier Ltd. All rights reserved.

Pharmacological and clinical properties of calcimimetics: calcium receptor activators that afford an innovative approach to controlling hyperparathyroidism.

PubMed

Nagano, Nobuo

2006-03-01

Circulating levels of calcium ion (Ca2+) are maintained within a narrow physiological range mainly by the action of parathyroid hormone (PTH) secreted from parathyroid gland (PTG) cells. PTG cells can sense small fluctuations in plasma Ca2+ levels by virtue of a cell surface Ca2+ receptor (CaR) that belongs to the superfamily of G protein-coupled receptors (GPCR). Compounds that activate the CaR and inhibit PTH secretion are termed 'calcimimetics' because they mimic or potentiate the effects of extracellular Ca2+ on PTG cell function. Preclinical studies with NPS R-568, a first generation calcimimetic compound that acts as a positive allosteric modulator of the CaR, have demonstrated that oral administration decreases serum levels of PTH and calcium, with a leftward shift in the set-point for calcium-regulated PTH secretion in normal rats. NPS R-568 also suppresses the elevation of serum PTH levels and PTG hyperplasia and can improve bone mineral density (BMD) and strength in rats with chronic renal insufficiency (CRI). Clinical trials with cinacalcet hydrochloride (cinacalcet), a compound with an improved metabolic profile, have shown that long-term treatment continues to suppress the elevation of serum levels of calcium and PTH in patients with primary hyperparathyroidism (1HPT). Furthermore, clinical trials in patients with uncontrolled secondary hyperparathyroidism (2HPT) have demonstrated that cinacalcet not only lowers serum PTH levels, but also the serum phosphorus and calcium x phosphorus product; these are a hallmark of an increased risk of cardiovascular disease and mortality in dialysis patients with end-stage renal disease. Indeed, cinacalcet has already been approved for marketing in several countries. Calcimimetic compounds like cinacalcet have great potential as an innovative medical approach to manage 1HPT and 2HPT.

Electrophysiological, vasoactive, and gastromodulatory effects of stevia in healthy Wistar rats.

PubMed

Yesmine, Saquiba; Connolly, Kylie; Hill, Nicholas; Coulson, Fiona R; Fenning, Andrew S

2013-07-01

Antihypertensive and antidiabetic effects of stevia, Stevia rebaudiana (Asteraceae), have been demonstrated in several human and animal models. The current study aims to define stevia's role in modifying the electrophysiological and mechanical properties of cardiomyocytes, blood vessels, and gastrointestinal smooth muscle. Tissues from thoracic aorta, mesenteric arteries, ileum, and left ventricular papillary muscles were excised from 8-week-old healthy Wistar rats. The effects of stevia (1 × 10-9 M to 1 × 10-4 M) were measured on these tissues. Stevia's effects in the presence of verapamil, 4-AP, and L-NAME were also assessed. In cardiomyocytes, stevia attenuated the force of contraction, decreased the average peak amplitude, and shortened the repolarisation phase of action potential - repolarisation phase of action potential20 by 25 %, repolarisation phase of action potential50 by 34 %, and repolarisation phase of action potential90 by 36 %. Stevia caused relaxation of aortic tissues which was significantly potentiated in the presence of verapamil. In mesenteric arteries, incubation with L-NAME failed to block stevia-induced relaxation indicating the mechanism of action may not be fully via nitric oxide-dependent pathways. Stevia concentration-dependently reduced electrical field stimulated and carbachol-induced contractions in the isolated ileum. This study is the first to show the effectiveness of stevia in reducing cardiac action potential duration at 20 %, 50 %, and 90 % of repolarisation. Stevia also showed beneficial modulatory effects on cardiovascular and gastrointestinal tissues via calcium channel antagonism, activation of the M2 muscarinic receptor function, and enhanced nitric oxide release. Georg Thieme Verlag KG Stuttgart · New York.

Calcium currents and graded synaptic transmission between heart interneurons of the leech.

PubMed

Angstadt, J D; Calabrese, R L

1991-03-01

Synaptic transmission between reciprocally inhibitory heart interneurons (HN cells) of the medicinal leech was examined in the absence of Na-mediated action potentials. Under voltage clamp, depolarizing steps from a holding potential of -60 mV elicited 2 kinetically distinct components of inward current in the presynaptic HN cell: an early transient current that inactivates within 200 msec and a persistent current that only partially decays over several seconds. Both currents begin to activate near -60 mV. Steady-state inactivation occurs over the voltage range between -70 and -45 mV and is completely removed by 1-2-sec hyperpolarizing voltage steps to -80 mV. The inward currents are carried by Ca2+, Ba2+, or Sr2+ ions, but not by Co2+, Mn2+, or Ni2+. These same inward currents underlie the burst-generating plateau potentials previously described in HN cells (Arbas and Calabrese, 1987a,b). With a presynaptic holding potential of -60 mV, the threshold for transmitter release is near -45 mV. Postsynaptic currents in the contralateral HN cell have a reversal potential near -60 mV. The largest postsynaptic currents (300-400 pA) exhibit an initial peak response that is followed by a more slowly decaying component. The persistent component of Ca2+ current in the presynaptic neuron is strongly correlated with the prolonged component of the postsynaptic current, while the transient presynaptic Ca2+ current appears to correspond to the early peak of postsynaptic current. These data are consistent with the hypothesis that voltage-dependent calcium currents contribute to the oscillatory capability of reciprocally inhibitory HN cells by (1) generating the plateau potential that drives the burst of action potentials and (2) underlying the release of inhibitory transmitter onto the contralateral cell.

Repair of Nerve Cell Membrance Damage by Calcium-Dependent, Membrane-Binding Proteins

DTIC Science & Technology

2013-09-01

In acute spinal cord injury the plasma membranes of spinal neurons are torn allowing high concentrations of calcium to enter the cytoplasm, activating...repairing the cell membrane as soon as the increase in intracellular calcium is sensed by calcium -binding proteins. If these repair mechanisms can be...testing the hypothesis that the action of copine, a human calcium -dependent-membrane-binding protein, in model systems can promote a stable repair of

[Classical actions of vitamin D: insights from human genetics and from mouse models on calcium and phosphate homeostasis].

PubMed

Jehan, Frédéric; Voloc, Alexandru

2014-01-01

At the beginning of the 20th century, the discovery of vitamin D by Sir EV McCollum allowed a better comprehension of its origin and its role, and made it possible to cure rickets, a largely prevalent disease at that time. The main role of vitamin D3 is to maintain calcium and phosphate homeostasis through the action of 1,25-dihydroxyvitamin D3, its active form. This underlies physiological functions related to calcium and phosphate, such as bone mineralization or muscle function. Progress in basic research for the last 40 years led to the discovery of the main hydroxylation steps that produce and catabolize the active form of vitamin D. It also uncovered the molecular aspects of vitamin D action, from its nuclear receptor, VDR, to the various target genes of this hormone. Recent progress in human genetics pointed out mutations in genes involved in vitamin D metabolism and 1,25-dihydroxyvitamin D3 actions. It also helped to understand the role of the major actors that control vitamin D production and effects, through 1,25-dihydroxyvitamin D3 actions on phosphate and calcium homeostasis, and on bone biology. Genetical engineering targeting the whole animal or defined tissues or cell types have yielded many mouse models in the past decades. When targeted to tissues important for vitamin D metabolism and activity, these models allowed a more detailed comprehension of vitamin effects on calcium and phosphorus homeostasis. © Société de Biologie, 2014.

The probability of quantal secretion near a single calcium channel of an active zone.

PubMed Central

Bennett, M R; Farnell, L; Gibson, W G

2000-01-01

A Monte Carlo analysis has been made of calcium dynamics and quantal secretion at microdomains in which the calcium reaches very high concentrations over distances of <50 nm from a channel and for which calcium dynamics are dominated by diffusion. The kinetics of calcium ions in microdomains due to either the spontaneous or evoked opening of a calcium channel, both of which are stochastic events, are described in the presence of endogenous fixed and mobile buffers. Fluctuations in the number of calcium ions within 50 nm of a channel are considerable, with the standard deviation about half the mean. Within 10 nm of a channel these numbers of ions can give rise to calcium concentrations of the order of 100 microM. The temporal changes in free calcium and calcium bound to different affinity indicators in the volume of an entire varicosity or bouton following the opening of a single channel are also determined. A Monte Carlo analysis is also presented of how the dynamics of calcium ions at active zones, after the arrival of an action potential and the stochastic opening of a calcium channel, determine the probability of exocytosis from docked vesicles near the channel. The synaptic vesicles in active zones are found docked in a complex with their calcium-sensor associated proteins and a voltage-sensitive calcium channel, forming a secretory unit. The probability of quantal secretion from an isolated secretory unit has been determined for different distances of an open calcium channel from the calcium sensor within an individual unit: a threefold decrease in the probability of secretion of a quantum occurs with a doubling of the distance from 25 to 50 nm. The Monte Carlo analysis also shows that the probability of secretion of a quantum is most sensitive to the size of the single-channel current compared with its sensitivity to either the binding rates of the sites on the calcium-sensor protein or to the number of these sites that must bind a calcium ion to trigger exocytosis of a vesicle. PMID:10777721

Nerve Growth Factor Sensitizes Adult Sympathetic Neurons to the Proinflammatory Peptide Bradykinin

PubMed Central

Vivas, Oscar; Kruse, Martin

2014-01-01

Levels of nerve growth factor (NGF) are elevated in inflamed tissues. In sensory neurons, increases in NGF augment neuronal sensitivity (sensitization) to noxious stimuli. Here, we hypothesized that NGF also sensitizes sympathetic neurons to proinflammatory stimuli. We cultured superior cervical ganglion (SCG) neurons from adult male Sprague Dawley rats with or without added NGF and compared their responsiveness to bradykinin, a proinflammatory peptide. The NGF-cultured neurons exhibited significant depolarization, bursts of action potentials, and Ca2+ elevations after bradykinin application, whereas neurons cultured without NGF showed only slight changes in membrane potential and cytoplasmic Ca2+ levels. The NGF effect, which requires trkA receptors, takes hours to develop and days to reverse. We addressed the ionic mechanisms underlying this sensitization. NGF did not alter bradykinin-induced M-current inhibition or phosphatidylinositol 4,5-bisphosphate hydrolysis. Maxi-K channel-mediated current evoked by depolarizations was reduced by 50% by culturing neurons in NGF. Application of iberiotoxin or paxilline, blockers of Maxi-K channels, mimicked NGF treatment and sensitized neurons to bradykinin application. A calcium channel blocker also mimicked NGF treatment. We found that NGF reduces Maxi-K channel opening by decreasing the activity of nifedipine-sensitive calcium channels. In conclusion, culture in NGF reduces the activity of L-type calcium channels, and secondarily, the calcium-sensitive activity of Maxi-K channels, rendering sympathetic neurons electrically hyper-responsive to bradykinin. PMID:25186743

The effects of crustacean cardioactive peptide on locust oviducts are calcium-dependent.

PubMed

Donini, Andrew; Lange, Angela B

2002-04-01

The role of calcium as a second messenger in the crustacean cardioactive peptide (CCAP)-induced contractions of the locust oviducts was investigated. Incubation of the oviducts in a calcium-free saline containing, a preferential calcium cation chelator, or an extracellular calcium channel blocker, abolished CCAP-induced contractions, indicating that the effects of CCAP on the oviducts are calcium-dependent. In contrast, sodium free saline did not affect CCAP-induced contractions. Co-application of CCAP to the oviducts with preferential L-type voltage-dependent calcium channel blockers reduced CCAP-induced contractions by 32-54%. Two preferential T-type voltage-dependent calcium channel blockers both inhibited CCAP-induced oviduct contractions although affecting different components of the contractions. Amiloride decreased the tonic component of CCAP-induced contractions by 40-55% and flunarizine dihydrochloride decreased the frequency of CCAP-induced phasic contractions by as much as 65%, without affecting tonus. Flunarizine dihydrochloride did not alter the proctolin-induced contractions of the oviducts. Results suggest that the actions of CCAP are partially mediated by voltage-dependent calcium channels similar to vertebrate L-type and T-type channels. High-potassium saline does not abolish CCAP-induced contractions indicating the presence of receptor-operated calcium channels that mediate the actions of CCAP on the oviducts. The involvement of calcium from intracellular stores in CCAP-induced contractions of the oviducts is likely since, an intracellular calcium antagonist decreased CCAP-induced contractions by 30-35%.

Acetylcholine Mediates a Slow Synaptic Potential in Hippocampal Pyramidal Cells

NASA Astrophysics Data System (ADS)

Cole, A. E.; Nicoll, R. A.

1983-09-01

The hippocampal slice preparation was used to study the role of acetylcholine as a synaptic transmitter. Bath-applied acetylcholine had three actions on pyramidal cells: (i) depolarization associated with increased input resistance, (ii) blockade of calcium-activated potassium responses, and (iii) blockade of accommodation of cell discharge. All these actions were reversed by the muscarinic antagonist atropine. Stimulation of sites in the slice known to contain cholinergic fibers mimicked all the actions. Furthermore, these evoked synaptic responses were enhanced by the cholinesterase inhibitor eserine and were blocked by atropine. These findings provide electrophysiological support for the role of acetylcholine as a synaptic transmitter in the brain and demonstrate that nonclassical synaptic responses involving the blockade of membrane conductances exist in the brain.

Roselle Polyphenols Exert Potent Negative Inotropic Effects via Modulation of Intracellular Calcium Regulatory Channels in Isolated Rat Heart.

PubMed

Lim, Yi-Cheng; Budin, Siti Balkis; Othman, Faizah; Latip, Jalifah; Zainalabidin, Satirah

2017-07-01

Roselle (Hibiscus sabdariffa Linn.) calyces have demonstrated propitious cardioprotective effects in animal and clinical studies; however, little is known about its action on cardiac mechanical function. This study was undertaken to investigate direct action of roselle polyphenols (RP) on cardiac function in Langendorff-perfused rat hearts. We utilized RP extract which consists of 12 flavonoids and seven phenolic acids (as shown by HPLC profiling) and has a safe concentration range between 125 and 500 μg/ml in this study. Direct perfusion of RP in concentration-dependent manner lowered systolic function of the heart as shown by lowered LVDP and dP/dt max , suggesting a negative inotropic effect. RP also reduced heart rate (negative chronotropic action) while simultaneously increasing maximal velocity of relaxation (positive lusitropic action). Conversely, RP perfusion increased coronary pressure, an indicator for improvement in coronary blood flow. Inotropic responses elicited by pharmacological agonists for L-type Ca 2+ channel [(±)-Bay K 8644], ryanodine receptor (4-chloro-m-cresol), β-adrenergic receptor (isoproterenol) and SERCA blocker (thapsigargin) were all abolished by RP. In conclusion, RP elicits negative inotropic, negative chronotropic and positive lusitropic responses by possibly modulating calcium entry, release and reuptake in the heart. Our findings have shown the potential use of RP as a therapeutic agent to treat conditions like arrhythmia.

Renal Stone Risk During Spaceflight: Assessment and Countermeasure Validation

NASA Technical Reports Server (NTRS)

Pietrzyk, Robert A.; Whitson, Peggy A.; Sams, Clarence F.; Jones, Jeffery A.; Smith, Scott M.

2009-01-01

This viewgraph presentation describes the risks of renal stone formation in manned space flight. The contents include: 1) Risk; 2) Evidence; 3) Nephrolithiasis -A Multifactorial Disease; 4) Symptoms/signs; 5) Urolithiasis and Stone Passage; 6) Study Objectives; 7) Subjects; 8) Methods; 9) Investigation Results; 10) Potassium Citrate; 11) Calcium Balance; 12) Case Study; 13) Significant Findings; 14) Risk Mitigation Strategies and Recommended Actions; and 15) Future Potential.

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.

Calcium pathway machinery at fertilization in echinoderms

PubMed Central

Ramos, Isabela; Wessel, Gary M.

2016-01-01

Calcium signaling in cells directs diverse physiological processes. The calcium waves triggered by fertilization is a highly conserved calcium signaling event essential for egg activation, and has been documented in every egg tested. This activity is one of the few highly conserved events of egg activation through the course of evolution. Echinoderm eggs, as well as many other cell types, have three main intracellular Ca2+ mobilizing messengers – IP3, cADPR and NAADP. Both cADPR and NAADP were identified as Ca2+ mobilizing messengers using the sea urchin egg homogenate, and this experimental system, along with the intact urchin and starfish oocyte/egg, continues to be a vital tool for investigating the mechanism of action of calcium signals. While many of the major regulatory steps of the IP3 pathway are well resolved, both cADPR and NAADP remain understudied in terms of our understanding of the fundamental process of egg activation at fertilization. Recently, NAADP has been shown to trigger Ca2+ release from acidic vesicles, separately from the ER, and a new class of calcium channels, the two-pore channels (TPCs), was identified as the likely targets for this messenger. Moreover, it was found that both cADPR and NAADP can be synthesized by the same family of enzymes, the ADP-rybosyl cyclases (ARCs). In this context of increasing amount of information, the potential coupling and functional roles of different messengers, intracellular stores and channels in the formation of the fertilization calcium wave in echinoderms will be critically evaluated. PMID:23218671

Isosteviol prevents the prolongation of action potential in hypertrophied cardiomyoctyes by regulating transient outward potassium and L-type calcium channels.

PubMed

Fan, Zhuo; Lv, Nanying; Luo, Xiao; Tan, Wen

2017-10-01

Cardiac hypertrophy is a thickening of the heart muscle that is associated with cardiovascular diseases such as hypertension and myocardial infarction. It occurs initially as an adaptive process against increased workloads and often leads to sudden arrhythmic deaths. Studies suggest that the lethal arrhythmia is attributed to hypertrophy-induced destabilization of cardiac electrical activity, especially the prolongation of the action potential. The reduced activity of I to is demonstrated to be responsible for the ionic mechanism of prolonged action potential duration and arrhythmogeneity. Isosteviol (STV), a derivative of stevioside, plays a protective role in a variety of stress-induced cardiac diseases. Here we report effects of STV on rat ISO-induced hypertrophic cardiomyocytes. STV alleviated ISO-induced hypertrophy of cardiomyocytes by decreasing cell area of hypertrophied cardiomyocytes. STV application prevented the prolongation of action potential which was prominent in hypertrophied cells. The decrease and increase of current densities for I to and I CaL observed in hypertrophied myocytes were both prevented by STV application. In addition, the results of qRT-PCR suggested that the changes of electrophysiological activity of I to and I CaL are correlated to the alterations of the mRNA transcription level. Copyright © 2017. Published by Elsevier B.V.

Calcium-activated potassium channels in insect pacemaker neurons as unexpected target site for the novel fumigant dimethyl disulfide.

PubMed

Gautier, Hélène; Auger, Jacques; Legros, Christian; Lapied, Bruno

2008-01-01

Dimethyl disulfide (DMDS), a plant-derived insecticide, is a promising fumigant as a substitute for methyl bromide. To further understand the mode of action of DMDS, we examined its effect on cockroach octopaminergic neurosecretory cells, called dorsal unpaired median (DUM) neurons, using whole-cell patch-clamp technique, calcium imaging and antisense oligonucleotide strategy. At low concentration (1 microM), DMDS modified spontaneous regular spike discharge into clear bursting activity associated with a decrease of the amplitude of the afterhyperpolarization. This effect led us to suspect alterations of calcium-activated potassium currents (IKCa) and [Ca(2+)](i) changes. We showed that DMDS reduced amplitudes of both peak transient and sustained components of the total potassium current. IKCa was confirmed as a target of DMDS by using iberiotoxin, cadmium chloride, and pSlo antisense oligonucleotide. In addition, we showed that DMDS induced [Ca(2+)](i) rise in Fura-2-loaded DUM neurons. Using calcium-free solution, and (R,S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl-N,N-di-[2-(2,3,4-trimethoxy-phenyl)ethyl]-acetamide (LOE 908) [an inhibitor of transient receptor potential (TRP)gamma], we demonstrated that TRPgamma initiated calcium influx. By contrast, omega-conotoxin GVIA (an inhibitor of N-type high-voltage-activated calcium channels), did not affect the DMDS-induced [Ca(2+)](i) rise. Finally, the participation of the calcium-induced calcium release mechanism was investigated using thapsigargin, caffeine, and ryanodine. Our study revealed that DMDS-induced elevation in [Ca(2+)](i) modulated IKCa in an unexpected bell-shaped manner via intracellular calcium. In conclusion, DMDS affects multiple targets, which could be an effective way to improve pest control efficacy of fumigation.

Modulation of voltage-gated channel currents by harmaline and harmane.

PubMed

Splettstoesser, Frank; Bonnet, Udo; Wiemann, Martin; Bingmann, Dieter; Büsselberg, Dietrich

2005-01-01

Harmala alkaloids are endogenous substances, which are involved in neurodegenerative disorders such as M. Parkinson, but some of them also have neuroprotective effects in the nervous system. While several sites of action at the cellular level (e.g. benzodiazepine receptors, 5-HT and GABA(A) receptors) have been identified, there is no report on how harmala alkaloids interact with voltage-gated membrane channels. The aim of this study was to investigate the effects of harmaline and harmane on voltage-activated calcium- (I(Ca(V))), sodium- (I(Na(V))) and potassium (I(K(V)))-channel currents, using the whole-cell patch-clamp method with cultured dorsal root ganglion neurones of 3-week-old rats. Currents were elicited by voltage steps from the holding potential to different command potentials. Harmaline and harmane reduced I(Ca(V)), I(Na(V)) and I(K(V)) concentration-dependent (10-500 microM) over the voltage range tested. I(Ca(V)) was reduced with an IC(50) of 100.6 microM for harmaline and by a significantly lower concentration of 75.8 microM (P<0.001, t-test) for harmane. The Hill coefficient was close to 1. Threshold concentration was around 10 microM for both substances. The steady state of inhibition of I(Ca(V)) by harmaline or harmane was reached within several minutes. The action was not use-dependent and at least partly reversible. It was mainly due to a reduction in the sustained calcium channel current (I(Ca(L+N))), while the transient voltage-gated calcium channel current (I(Ca(T))) was only partially affected. We conclude that harmaline and harmane are modulators of I(Ca(V)) in vitro. This might be related to their neuroprotective effects.

Modulation of voltage-gated channel currents by harmaline and harmane

PubMed Central

Splettstoesser, Frank; Bonnet, Udo; Wiemann, Martin; Bingmann, Dieter; Büsselberg, Dietrich

2004-01-01

Harmala alkaloids are endogenous substances, which are involved in neurodegenerative disorders such as M. Parkinson, but some of them also have neuroprotective effects in the nervous system. While several sites of action at the cellular level (e.g. benzodiazepine receptors, 5-HT and GABAA receptors) have been identified, there is no report on how harmala alkaloids interact with voltage-gated membrane channels. The aim of this study was to investigate the effects of harmaline and harmane on voltage-activated calcium- (ICa(V)), sodium- (INa(V)) and potassium (IK(V))-channel currents, using the whole-cell patch-clamp method with cultured dorsal root ganglion neurones of 3-week-old rats. Currents were elicited by voltage steps from the holding potential to different command potentials. Harmaline and harmane reduced ICa(V), INa(V) and IK(V) concentration-dependent (10–500 μM) over the voltage range tested. ICa(V) was reduced with an IC50 of 100.6 μM for harmaline and by a significantly lower concentration of 75.8 μM (P<0.001, t-test) for harmane. The Hill coefficient was close to 1. Threshold concentration was around 10 μM for both substances. The steady state of inhibition of ICa(V) by harmaline or harmane was reached within several minutes. The action was not use dependent and at least partly reversible. It was mainly due to a reduction in the sustained calcium channel current (ICa(L+N)), while the transient voltage-gated calcium channel current (ICa(T)) was only partially affected. We conclude that harmaline and harmane are modulators of ICa(V) in vitro. This might be related to their neuroprotective effects. PMID:15644868

Regulation of Contraction by the Thick Filaments in Skeletal Muscle.

PubMed

Irving, Malcolm

2017-12-19

Contraction of skeletal muscle cells is initiated by a well-known signaling pathway. An action potential in a motor nerve triggers an action potential in a muscle cell membrane, a transient increase of intracellular calcium concentration, binding of calcium to troponin in the actin-containing thin filaments, and a structural change in the thin filaments that allows myosin motors from the thick filaments to bind to actin and generate force. This calcium/thin filament mediated pathway provides the "START" signal for contraction, but it is argued that the functional response of the muscle cell, including the speed of its contraction and relaxation, adaptation to the external load, and the metabolic cost of contraction is largely determined by additional mechanisms. This review considers the role of the thick filaments in those mechanisms, and puts forward a paradigm for the control of contraction in skeletal muscle in which both the thick and thin filaments have a regulatory function. The OFF state of the thick filament is characterized by helical packing of most of the myosin head or motor domains on the thick filament surface in a conformation that makes them unavailable for actin binding or ATP hydrolysis, although a small fraction of the myosin heads are constitutively ON. The availability of the majority fraction of the myosin heads for contraction is controlled in part by the external load on the muscle, so that these heads only attach to actin and hydrolyze ATP when they are required. This phenomenon seems to be the major determinant of the well-known force-velocity relationship of muscle, and controls the metabolic cost of contraction. The regulatory state of the thick filament also seems to control the dynamics of both muscle activation and relaxation. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Glutamate and Dynorphin Release from a Subcellular Fraction Enriched in Hippocampal Mossy Fiber Synaptosomes

DTIC Science & Technology

1988-01-01

presence of extrasynaptosomal calcium . while only 3(0- of the evoked release of glutamate was calcium -dependent. D-aspartate. which exchanges glutamate...out of the cytoplasmic pool. virtually eliminated the calcium -independent component of glutamate release. This synaptosomal preparation will be useful...investigation of their presynaptic mechanisms ol action. l" Hippocampus Mossy fiber expansions Synaptosomes Glutamate Dynorphin Peptides Opioids Release Calcium

Neuroprotective action of lithium in disorders of the central nervous system

PubMed Central

CHIU, Chi-Tso; CHUANG, De-Maw

2011-01-01

Substantial in vitro and in vivo evidence of neurotrophic and neuroprotective effects of lithium suggests that it may also have considerable potential for the treatment of neurodegenerative conditions. Lithium's main mechanisms of action appear to stem from its ability to inhibit glycogen synthase kinase-3 activity and also to induce signaling mediated by brain-derived neurotrophic factor. This in turn alters a wide variety of downstream efectors, with the ultimate effect of enhancing pathways to cell survival. In addition, lithium contributes to calcium homeostasis. By inhibiting N-methyl-D-aspartate receptor-mediated calcium influx, for instance, it suppresses the calcium-dependent activation of pro-apoptotic signaling pathways. By inhibiting the activity of phosphoinositol phosphatases, it decreases levels of inositol 1,4,5-trisphosphate, a process recently identified as a novel mechanism for inducing autophagy. These mechanisms alow therapeutic doses of lithium to protect neuronal cells from diverse insults that would otherwise lead to massive cell death. Lithium, moreover, has been shown to improve behavioral and cognitive deficits in animal models of neurodegenerative diseases, including stroke, amyotrophic lateral sclerosis, fragile X syndrome, and Huntington's, Alzheimer's, and Parkinson's diseases. Since lithium is already FDA-approved for the treatment of bipolar disorder, our conclusions support the notion that its clinical relevance can be expanded to include the treatment of several neurological and neurodegenerative-related diseases. PMID:21743136

Calcium-Activated Potassium Channels at Nodes of Ranvier Secure Axonal Spike Propagation

PubMed Central

Gründemann, Jan; Clark, Beverley A.

2015-01-01

Summary Functional connectivity between brain regions relies on long-range signaling by myelinated axons. This is secured by saltatory action potential propagation that depends fundamentally on sodium channel availability at nodes of Ranvier. Although various potassium channel types have been anatomically localized to myelinated axons in the brain, direct evidence for their functional recruitment in maintaining node excitability is scarce. Cerebellar Purkinje cells provide continuous input to their targets in the cerebellar nuclei, reliably transmitting axonal spikes over a wide range of rates, requiring a constantly available pool of nodal sodium channels. We show that the recruitment of calcium-activated potassium channels (IK, KCa3.1) by local, activity-dependent calcium (Ca2+) influx at nodes of Ranvier via a T-type voltage-gated Ca2+ current provides a powerful mechanism that likely opposes depolarizing block at the nodes and is thus pivotal to securing continuous axonal spike propagation in spontaneously firing Purkinje cells. PMID:26344775

An inulin-type fructan enhances calcium absorption primarily via an effect on colonic absorption in humans

USDA-ARS?s Scientific Manuscript database

Calcium absorption efficiency and bone mineral mass are increased in adolescents who regularly consume inulin-type fructans (ITF). The mechanism of action in increasing absorption is unknown but may be related to increased colonic calcium absorption. We conducted a study in young adults designed to ...

Sodium-dependent potassium channels of a Slack-like subtype contribute to the slow afterhyperpolarization in lamprey spinal neurons

PubMed Central

Wallén, Peter; Robertson, Brita; Cangiano, Lorenzo; Löw, Peter; Bhattacharjee, Arin; Kaczmarek, Leonard K; Grillner, Sten

2007-01-01

The slow afterhyperpolarization (sAHP) following the action potential is the main determinant of spike frequency regulation. The sAHP after single action potentials in neurons of the lamprey locomotor network is largely due to calcium-dependent K+ channels (80%), activated by calcium entering the cell during the spike. The residual (20%) component becomes prominent during high level activity (50% of the sAHP). It is not Ca2+ dependent, has a reversal potential like that of potassium, and is not affected by chloride injection. It is not due to rapid activation of Na+/K+-ATPase. This non-KCa-sAHP is reduced markedly in amplitude when sodium ions are replaced by lithium ions, and is thus sodium dependent. Quinidine also blocks this sAHP component, further indicating an involvement of sodium-dependent potassium channels (KNa). Modulators tested do not influence the KNa-sAHP amplitude. Immunofluorescence labelling with an anti-Slack antibody revealed distinct immunoreactivity of medium-sized and large neurons in the grey matter of the lamprey spinal cord, suggesting the presence of a Slack-like subtype of KNa channel. The results strongly indicate that a KNa potassium current contributes importantly to the sAHP and thereby to neuronal frequency regulation during high level burst activity as during locomotion. This is, to our knowledge, the first demonstration of a functional role for the Slack gene in contributing to the slow AHP. PMID:17884929

Get Enough Calcium

MedlinePlus

... Vitamins 3 of 4 sections Take Action: Vitamin D Get enough vitamin D. Vitamin D helps your body absorb (take in) calcium. Find out how much vitamin D you need each day . Your body makes vitamin ...

An open source tool for automatic spatiotemporal assessment of calcium transients and local ‘signal-close-to-noise’ activity in calcium imaging data

PubMed Central

Martin, Corinna; Jablonka, Sibylle

2018-01-01

Local and spontaneous calcium signals play important roles in neurons and neuronal networks. Spontaneous or cell-autonomous calcium signals may be difficult to assess because they appear in an unpredictable spatiotemporal pattern and in very small neuronal loci of axons or dendrites. We developed an open source bioinformatics tool for an unbiased assessment of calcium signals in x,y-t imaging series. The tool bases its algorithm on a continuous wavelet transform-guided peak detection to identify calcium signal candidates. The highly sensitive calcium event definition is based on identification of peaks in 1D data through analysis of a 2D wavelet transform surface. For spatial analysis, the tool uses a grid to separate the x,y-image field in independently analyzed grid windows. A document containing a graphical summary of the data is automatically created and displays the loci of activity for a wide range of signal intensities. Furthermore, the number of activity events is summed up to create an estimated total activity value, which can be used to compare different experimental situations, such as calcium activity before or after an experimental treatment. All traces and data of active loci become documented. The tool can also compute the signal variance in a sliding window to visualize activity-dependent signal fluctuations. We applied the calcium signal detector to monitor activity states of cultured mouse neurons. Our data show that both the total activity value and the variance area created by a sliding window can distinguish experimental manipulations of neuronal activity states. Notably, the tool is powerful enough to compute local calcium events and ‘signal-close-to-noise’ activity in small loci of distal neurites of neurons, which remain during pharmacological blockade of neuronal activity with inhibitors such as tetrodotoxin, to block action potential firing, or inhibitors of ionotropic glutamate receptors. The tool can also offer information about local homeostatic calcium activity events in neurites. PMID:29601577

Photocontrol of Voltage-Gated Ion Channel Activity by Azobenzene Trimethylammonium Bromide in Neonatal Rat Cardiomyocytes

PubMed Central

Frolova, Sheyda R.; Gaiko, Olga; Tsvelaya, Valeriya A.; Pimenov, Oleg Y.; Agladze, Konstantin I.

2016-01-01

The ability of azobenzene trimethylammonium bromide (azoTAB) to sensitize cardiac tissue excitability to light was recently reported. The dark, thermally relaxed trans- isomer of azoTAB suppressed spontaneous activity and excitation propagation speed, whereas the cis- isomer had no detectable effect on the electrical properties of cardiomyocyte monolayers. As the membrane potential of cardiac cells is mainly controlled by activity of voltage-gated ion channels, this study examined whether the sensitization effect of azoTAB was exerted primarily via the modulation of voltage-gated ion channel activity. The effects of trans- and cis- isomers of azoTAB on voltage-dependent sodium (INav), calcium (ICav), and potassium (IKv) currents in isolated neonatal rat cardiomyocytes were investigated using the whole-cell patch-clamp technique. The experiments showed that azoTAB modulated ion currents, causing suppression of sodium (Na+) and calcium (Ca2+) currents and potentiation of net potassium (K+) currents. This finding confirms that azoTAB-effect on cardiac tissue excitability do indeed result from modulation of voltage-gated ion channels responsible for action potential. PMID:27015602

Regulation of the Proteasome by Neuronal Activity and Calcium/Calmodulin-dependent Protein Kinase II*

PubMed Central

Djakovic, Stevan N.; Schwarz, Lindsay A.; Barylko, Barbara; DeMartino, George N.; Patrick, Gentry N.

2009-01-01

Protein degradation via the ubiquitin proteasome system has been shown to regulate changes in synaptic strength that underlie multiple forms of synaptic plasticity. It is plausible, therefore, that the ubiquitin proteasome system is itself regulated by synaptic activity. By utilizing live-cell imaging strategies we report the rapid and dynamic regulation of the proteasome in hippocampal neurons by synaptic activity. We find that the blockade of action potentials (APs) with tetrodotoxin inhibited the activity of the proteasome, whereas the up-regulation of APs with bicuculline dramatically increased the activity of the proteasome. In addition, the regulation of the proteasome is dependent upon external calcium entry in part through N-methyl-d-aspartate receptors and L-type voltage-gated calcium channels and requires the activity of calcium/calmodulin-dependent protein kinase II (CaMKII). Using in vitro and in vivo assays we find that CaMKII stimulates proteasome activity and directly phosphorylates Rpt6, a subunit of the 19 S (PA700) subcomplex of the 26 S proteasome. Our data provide a novel mechanism whereby CaMKII may regulate the proteasome in neurons to facilitate remodeling of synaptic connections through protein degradation. PMID:19638347

Regulation of the proteasome by neuronal activity and calcium/calmodulin-dependent protein kinase II.

PubMed

Djakovic, Stevan N; Schwarz, Lindsay A; Barylko, Barbara; DeMartino, George N; Patrick, Gentry N

2009-09-25

Protein degradation via the ubiquitin proteasome system has been shown to regulate changes in synaptic strength that underlie multiple forms of synaptic plasticity. It is plausible, therefore, that the ubiquitin proteasome system is itself regulated by synaptic activity. By utilizing live-cell imaging strategies we report the rapid and dynamic regulation of the proteasome in hippocampal neurons by synaptic activity. We find that the blockade of action potentials (APs) with tetrodotoxin inhibited the activity of the proteasome, whereas the up-regulation of APs with bicuculline dramatically increased the activity of the proteasome. In addition, the regulation of the proteasome is dependent upon external calcium entry in part through N-methyl-D-aspartate receptors and L-type voltage-gated calcium channels and requires the activity of calcium/calmodulin-dependent protein kinase II (CaMKII). Using in vitro and in vivo assays we find that CaMKII stimulates proteasome activity and directly phosphorylates Rpt6, a subunit of the 19 S (PA700) subcomplex of the 26 S proteasome. Our data provide a novel mechanism whereby CaMKII may regulate the proteasome in neurons to facilitate remodeling of synaptic connections through protein degradation.

Effect of parathyroid hormone on transport by toad and turtle bladder

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

Sabatini, S.; Kurtzman, N.A.

1987-01-01

The authors recently demonstrated that parathyroid hormone (PTH) inhibited both vasopressin- and cyclic AMP-stimulated water transport in the toad bladder. This was associated with an increase in calcium uptake by isolated epithelial cells. They postulated that PTH exerts its action on H/sub 2/O transport by directly stimulating calcium uptake. The current study was designed to compare the effects of PTH and the calcium ionophore, A23187, on H/sub 2/O and Na transport and H..mu.. secretion in toad and turtle bladders. In toad bladder, PTH and A23187 decreased arginine vasopressin (AVP)-stimulated H/sub 2/O flow and short-circuit current (SCC) after 60 min serosalmore » incubation. In turtle bladder A23187 decreased SCC to 79.3 +/- 3.6% of base line (P < 0.05), and significantly decreased RSCC as well. PTH had no effect on SCC or H/sup +/ secretion in turtle bladders. Both PTH and A23187 increased /sup 45/Ca uptake in toad bladder epithelial cells; only A23187 increased /sup 45/Ca uptake in the turtle bladder. The different action of PTH in these two membranes, compared with that of the calcium ionophore, illustrates the selectivity of PTH on membrane transport. PTH increases calcium uptake and decreases transport only in a hormone-sensitive epithelium, whereas the ionophore works in virtually all living membranes. The mode of action of these two agents to increase calcium uptake is, therefore likely different.« less

75 FR 28608 - Calcium Hydroxide; Receipt of Application for Emergency Exemption, Solicitation of Public Comment

Federal Register 2010, 2011, 2012, 2013, 2014

2010-05-21

... ENVIRONMENTAL PROTECTION AGENCY [EPA-HQ-OPP-2010-0411; FRL-8826-7] Calcium Hydroxide; Receipt of... Department of Agriculture to use the pesticide calcium hydroxide (CAS No. 1305-62-0) to treat up to 1,000...: [email protected] . SUPPLEMENTARY INFORMATION: I. General Information A. Does this Action Apply to Me...

Reduced expression of the Ca(2+) transporter protein PMCA2 slows Ca(2+) dynamics in mouse cerebellar Purkinje neurones and alters the precision of motor coordination.

PubMed

Empson, Ruth M; Turner, Paul R; Nagaraja, Raghavendra Y; Beesley, Philip W; Knöpfel, Thomas

2010-03-15

Cerebellar Purkinje neurones (PNs) express high levels of the plasma membrane calcium ATPase, PMCA2, a transporter protein critical for the clearance of calcium from excitable cells. Genetic deletion of one PMCA2 encoding gene in heterozygous PMCA2 knock-out (PMCA2(+/-) mice enabled us to determine how PMCA2 influences PN calcium regulation without the complication of the severe morphological changes associated with complete PMCA2 knock-out (PMCA2(-/-) in these cells. The PMCA2(+/-) cerebellum expressed half the normal levels of PMCA2 and this nearly doubled the time taken for PN dendritic calcium transients to recover (mean fast and slow recovery times increased from 70 ms to 110 ms and from 600 ms to 1100 ms). The slower calcium recovery had distinct consequences for PMCA2(+/-) PN physiology. The PNs exhibited weaker climbing fibre responses, prolonged outward Ca(2+)-dependent K(+) current (mean fast and slow recovery times increased from 136 ms to 192 ms and from 595 ms to 1423 ms) and a slower mean frequency of action potential firing (7.4 Hz compared with 15.8 Hz). Our findings were consistent with prolonged calcium accumulation in the cytosol of PMCA2(+/-) Purkinje neurones. Although PMCA2(+/-) mice exhibited outwardly normal behaviour and little change in their gait pattern, when challenged to run on a narrow beam they exhibited clear deficits in hindlimb coordination. Training improved the motor performance of both PMCA2(+/-) and wild-type mice, although PMCA2(+/-) mice were always impaired. We conclude that reduced calcium clearance perturbs calcium dynamics in PN dendrites and that this is sufficient to disrupt the accuracy of cerebellar processing and motor coordination.

Metabotropic glutamate receptors activate dendritic calcium waves and TRPM channels which drive rhythmic respiratory patterns in mice

PubMed Central

Mironov, S L

2008-01-01

Respiration in vertebrates is generated by a compact network which is located in the lower brainstem but cellular mechanisms which underlie persistent oscillatory activity of the respiratory network are yet unknown. Using two-photon imaging and patch-clamp recordings in functional brainstem preparations of mice containing pre-Bötzinger complex (preBötC), we examined the actions of metabotropic glutamate receptors (mGluR1/5) on the respiratory patterns. The agonist DHPG potentiated and antagonist LY367385 depressed respiration-related activities. In the inspiratory neurons, we observed rhythmic activation of non-selective channels which had a conductance of 24 pS. Their activity was enhanced with membrane depolarization and after elevation of calcium from the cytoplasmic side of the membrane. They were activated by a non-hydrolysable PIP2 analogue and blocked by flufenamate, ATP4− and Gd3+. All these properties correspond well to those of TRPM4 channels. Calcium imaging of functional slices revealed rhythmic transients in small clusters of neurons present in a network. Calcium transients in the soma were preceded by the waves in dendrites which were dependent on mGluR activation. Initiation and propagation of waves required calcium influx and calcium release from internal stores. Calcium waves activated TPRM4-like channels in the soma and promoted generation of inspiratory bursts. Simulations of activity of neurons communicated via dendritic calcium waves showed emerging activity within neuronal clusters and its synchronization between the clusters. The experimental and theoretical data provide a subcellular basis for a recently proposed group-pacemaker hypothesis and describe a novel mechanism of rhythm generation in neuronal networks. PMID:18308826

Modulation of ventricular transient outward K+ current by acidosis and its effects on excitation-contraction coupling

PubMed Central

Saegusa, Noriko; Garg, Vivek

2013-01-01

The contribution of transient outward current (Ito) to changes in ventricular action potential (AP) repolarization induced by acidosis is unresolved, as is the indirect effect of these changes on calcium handling. To address this issue we measured intracellular pH (pHi), Ito, L-type calcium current (ICa,L), and calcium transients (CaTs) in rabbit ventricular myocytes. Intracellular acidosis [pHi 6.75 with extracellular pH (pHo) 7.4] reduced Ito by ∼50% in myocytes with both high (epicardial) and low (papillary muscle) Ito densities, with little effect on steady-state inactivation and activation. Of the two candidate α-subunits underlying Ito, human (h)Kv4.3 and hKv1.4, only hKv4.3 current was reduced by intracellular acidosis. Extracellular acidosis (pHo 6.5) shifted Ito inactivation toward less negative potentials but had negligible effect on peak current at +60 mV when initiated from −80 mV. The effects of low pHi-induced inhibition of Ito on AP repolarization were much greater in epicardial than papillary muscle myocytes and included slowing of phase 1, attenuation of the notch, and elevation of the plateau. Low pHi increased AP duration in both cell types, with the greatest lengthening occurring in epicardial myocytes. The changes in epicardial AP repolarization induced by intracellular acidosis reduced peak ICa,L, increased net calcium influx via ICa,L, and increased CaT amplitude. In summary, in contrast to low pHo, intracellular acidosis has a marked inhibitory effect on ventricular Ito, perhaps mediated by Kv4.3. By altering the trajectory of the AP repolarization, low pHi has a significant indirect effect on calcium handling, especially evident in epicardial cells. PMID:23585132

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.

The blockade of excitation/contraction coupling by nifedipine in patch-clamped rat skeletal muscle cells in culture.

PubMed

Cognard, C; Rivet, M; Raymond, G

1990-04-01

The effects of the dihydropyridine derivative, nifedipine, well known as a blocker of calcium channels, were tested on cultured rat myoballs. Membrane currents and contractions were simultaneously recorded by means of the patch-clamp technique and a photoelectric transducing method. High concentrations of nifedipine (5 microM) inhibited the contractile responses and inward calcium current (ICa) elicited by long depolarizations. In the absence of ICa (1.5 mM cadmium in the bath), nifedipine inhibited both the ICa-independent contractile component and the outward current, supposed to depend on the intracellular calcium released during contraction. At low concentrations (0.5 microM) the blocking effects of nifedipine could be strongly enhanced by shifting the membrane potential towards less negative values (-60 mV) for 50 s prior to the test pulse. A blocking effect of nifedipine, at a usually ineffective concentration (0.1 microM), could also be observed when long-lasting (3 min) prepulses to 0 mV were applied from a reference membrane potential of -60 mV. This effect could be relieved by long-lasting cell hyperpolarizations (-90 mV). The blocking effects of nifedipine unrelated to ICa could be interpreted as an action on a molecule (voltage sensor) in the T-tubule membrane involved in the excitation/contraction coupling process and as a preferential binding of the dihydropyridine derivative on the inactivated form of this molecule, favored by the weak negative potentials or long-lasting depolarizations. The results provide data in favor of the existence of strong similarities between the calcium channels and voltage sensors since their operation was inhibited in a voltage-dependent manner by nifedipine.

Zebrafish CaV2.1 Calcium Channels Are Tailored for Fast Synchronous Neuromuscular Transmission

PubMed Central

Naranjo, David; Wen, Hua; Brehm, Paul

2015-01-01

The CaV2.2 (N-type) and CaV2.1 (P/Q-type) voltage-dependent calcium channels are prevalent throughout the nervous system where they mediate synaptic transmission, but the basis for the selective presence at individual synapses still remains an open question. The CaV2.1 channels have been proposed to respond more effectively to brief action potentials (APs), an idea supported by computational modeling. However, the side-by-side comparison of CaV2.1 and CaV2.2 kinetics in intact neurons failed to reveal differences. As an alternative means for direct functional comparison we expressed zebrafish CaV2.1 and CaV2.2 α-subunits, along with their accessory subunits, in HEK293 cells. HEK cells lack calcium currents, thereby circumventing the need for pharmacological inhibition of mixed calcium channel isoforms present in neurons. HEK cells also have a simplified morphology compared to neurons, which improves voltage control. Our measurements revealed faster kinetics and shallower voltage-dependence of activation and deactivation for CaV2.1. Additionally, recordings of calcium current in response to a command waveform based on the motorneuron AP show, directly, more effective activation of CaV2.1. Analysis of calcium currents associated with the AP waveform indicate an approximately fourfold greater open probability (PO) for CaV2.1. The efficient activation of CaV2.1 channels during APs may contribute to the highly reliable transmission at zebrafish neuromuscular junctions. PMID:25650925

ER Stress-Mediated Signaling: Action Potential and Ca(2+) as Key Players.

PubMed

Bahar, Entaz; Kim, Hyongsuk; Yoon, Hyonok

2016-09-15

The proper functioning of the endoplasmic reticulum (ER) is crucial for multiple cellular activities and survival. Disturbances in the normal ER functions lead to the accumulation and aggregation of unfolded proteins, which initiates an adaptive response, the unfolded protein response (UPR), in order to regain normal ER functions. Failure to activate the adaptive response initiates the process of programmed cell death or apoptosis. Apoptosis plays an important role in cell elimination, which is essential for embryogenesis, development, and tissue homeostasis. Impaired apoptosis can lead to the development of various pathological conditions, such as neurodegenerative and autoimmune diseases, cancer, or acquired immune deficiency syndrome (AIDS). Calcium (Ca(2+)) is one of the key regulators of cell survival and it can induce ER stress-mediated apoptosis in response to various conditions. Ca(2+) regulates cell death both at the early and late stages of apoptosis. Severe Ca(2+) dysregulation can promote cell death through apoptosis. Action potential, an electrical signal transmitted along the neurons and muscle fibers, is important for conveying information to, from, and within the brain. Upon the initiation of the action potential, increased levels of cytosolic Ca(2+) (depolarization) lead to the activation of the ER stress response involved in the initiation of apoptosis. In this review, we discuss the involvement of Ca(2+) and action potential in ER stress-mediated apoptosis.

ELECTRICAL PHENOMENA IN NERVE

PubMed Central

Shanes, Abraham M.

1949-01-01

The action of a number of agents, which may be classified as "stabilizers" and "unstabilizers" on the electrical oscillations and after-potentials in the squid giant axon has been examined. The effects on the spike, "positive overshoot," and "potassium potential" were also observed, but where possible concentrations were employed which left these phenomena unaltered. Veratrine augmented the oscillations and the negative after-potential, particularly with repetitive stimulation. Yohimbine caused a small long lasting positive after-potential and depressed the oscillations, effects also enhanced with repetitive activity. Cocaine and procaine suppressed the oscillations and the negative after-potential but DDT was completely inert. An elevation in the medium calcium depressed the oscillations and the naturally occurring negative after-potential; negative after-potentials induced with veratrine were increased by calcium. A decrease in the potassium augmented the oscillations and the negative after-potential. A hypothesis is presented in which these effects are interpreted in terms of potassium concentration at the fiber surface as regulated by a labile permeability and metabolism. This is discussed in relation to the available evidence for these factors. It is a pleasure to acknowledge the author's indebtedness to Dr. D. E. S. Brown, Director, and to his staff at the Bermuda Biological Station for Research for the cooperation and special facilities provided during the initiation of this work. Dr. T. Baylor of Princeton University very kindly provided the camera and film used in Bermuda. PMID:18139008

Citrate and renal calculi: an update

NASA Technical Reports Server (NTRS)

Pak, C. Y.

1994-01-01

Citrate is an inhibitor of the crystallization of stone-forming calcium salts. Hypocitraturia, frequently encountered in patients with nephrolithiasis, is therefore an important risk factor for stone formation. Potassium citrate provides physiological and physicochemical correction and inhibits new stone formation, not only in hypocitraturic calcium nephrolithiasis but also in uric acid nephrolithiasis. Inhibition of stone recurrence has now been validated by a randomized trial. Ongoing research has disclosed additional causes of hypocitraturia (sodium excess, low intestinal alkali absorption, but not primary citrate malabsorption). Moreover, new insights on potassium citrate action have been shown, notably that some of absorbed citrate escapes oxidation and contributes to the citraturic response, that ingestion with a meal does not sacrifice physiological or physicochemical action, that orange juice mimics but does not completely duplicate its actions, that potassium citrate may have a beneficial bone-sparing effect, that it may reduce stone fragments following ESWL, and that danger of aluminum toxicity is not great in subjects with functioning kidneys. Finally, the research on potassium citrate has led to two promising products, calcium citrate as an optimum calcium supplement and potassium-magnesium citrate which may be superior to potassium citrate in the management of stone disease.

THE M-RNA, EXPRESSION OF SERCA2 AND NCX1 IN THE PROCESS OF PHARMACOLOGICAL CELL PROTECTION IN EXPERIMENTAL ACUTE PANCREATITIS INDUCED BY TAUROCHOLATE.

PubMed

Vasques, Enio Rodrigues; Cunha, José Eduardo Monteiro; Kubrusly, Marcia Saldanha; Coelho, Ana Maria; Sanpietri, Sandra N; Nader, Helena B; Tersariol, Ivarne L S; Lima, Marcelo A; Chaib, Eleazar; D'Albuquerque, Luiz Augusto Carneiro

2018-06-21

Intracellular calcium overload is known to be a precipitating factor of pancreatic cell injury in acute pancreatitis (AP). Intracellular calcium homeostasis depends of Plasmatic Membrane Calcium ATPase (PMCA), Sarcoplasmic Endothelial Reticulum Calcium ATPase 2 (SERCA 2) and the Sodium Calcium Exchanger (NCX1). The antioxidant melatonin (Mel) and Trisulfate Disaccharide (TD) that accelerates NCX1 action could reduce the cell damage determined by the AP. To evaluate m-RNA expressions of SERCA2 and NCX1 in acute pancreatitis induced by sodium taurocholate in Wistar rats pre-treated with melatonin and/or TD. Wistar rats were divided in groups: 1) without AP; 2) AP without pre-treatment; 3) AP and Melatonin; 4) AP and TD; 5) AP and Melatonin associated to TD. Pancreatic tissue samples were collected for detection of SERCA2 and NCX1 m-R NA levels by polymerase chain reaction (PCR). Increased m-RNA expression of SERCA2 in the melatonin treated group, without increase of m-RNA expression of the NCX1. The TD did not affect levels of SERCA2 and NCX1 m-RNA expressions. The combined melatonin and TD treatment reduced the m-RNA expression of SERCA2. The effect of melatonin is restricted to increased m-RNA expression of SERCA2. Although TD does not affect gene expression, its action in accelerating calcium exchanger function can explain the slightest expression of SERCA2 m-RNA when associated with Melatonin, perhaps by a joint action of drugs with different and but possibly complementary mechanisms.

[Aging and homeostasis. Management of disorders in bone and calcium metabolism associated with ageing.

PubMed

Takeuchi, Yasuhiro

Disorders in bone and calcium metabolism associated with aging are based on secondary hyperparathyroidism due to impaired intestinal calcium absorption caused by insufficient vitamin D actions and augmented bone resorption due to sex hormone deficiency. Both of them are involved in the development of osteoporosis that increases risk of fractures. Therefore, the most important thing for management of disorders in bone and calcium metabolism associated with aging is to prevent fractures with appropriate drugs for osteoporosis.

[Interfering effects of radix Salviae miltiorrhizae and lingustrazine on mm-LDL activating BKCa in ECV304 cell].

PubMed

Lin, L; Zheng, Y F; Qu, J H; Bao, G H

2001-08-01

To observe the action of minimally modified low density lipoprotein (mm-LDL) on BKCa in ECV304 cell and the interfering effects of radix salviae miltiorrhizae extract powder 764-3 (30 micrograms/ml) and lingustrazine (200 micrograms/ml) on this action. The cell-attached configuration of patch clamp technique was applied. mm-LDL (100 micrograms/ml) potentiated the activity of BKCa in ECV304. While 764-3 and lingustrazine abolished it. mm-LDL acted on vascular endothelial cell ECV304 could rapidly activate the activity of BKCa and might result in the increase of electro-chemical gradient for the resting Ca2+ influx, thus resting cytoplasmic concentration of calcium could be elevated and endothelial dysfunction would be induced. 764-3 and lingustrazine might have the protective action through decreasing the activity of BKCa.

Sympathetic Nervous Regulation of Calcium and Action Potential Alternans in the Intact Heart.

PubMed

Winter, James; Bishop, Martin J; Wilder, Catherine D E; O'Shea, Christopher; Pavlovic, Davor; Shattock, Michael J

2018-01-01

Rationale: Arrhythmogenic cardiac alternans are thought to be an important determinant for the initiation of ventricular fibrillation. There is limited information on the effects of sympathetic nerve stimulation (SNS) on alternans in the intact heart and the conclusions of existing studies, focused on investigating electrical alternans, are conflicted. Meanwhile, several lines of evidence implicate instabilities in Ca handling, not electrical restitution, as the primary mechanism underpinning alternans. Despite this, there have been no studies on Ca alternans and SNS in the intact heart. The present study sought to address this, by application of voltage and Ca optical mapping for the simultaneous study of APD and Ca alternans in the intact guinea pig heart during direct SNS. Objective : To determine the effects of SNS on APD and Ca alternans in the intact guinea pig heart and to examine the mechanism(s) by which the effects of SNS are mediated. Methods and Results : Studies utilized simultaneous voltage and Ca optical mapping in isolated guinea pig hearts with intact innervation. Alternans were induced using a rapid dynamic pacing protocol. SNS was associated with rate-independent shortening of action potential duration (APD) and the suppression of APD and Ca alternans, as indicated by a shift in the alternans threshold to faster pacing rates. Qualitatively similar results were observed with exogenous noradrenaline perfusion. In contrast with previous reports, both SNS and noradrenaline acted to flatten the slope of the electrical restitution curve. Pharmacological block of the slow delayed rectifying potassium current (I Ks ), sufficient to abolish I Ks -mediated APD-adaptation, partially reversed the effects of SNS on pacing-induced alternans. Treatment with cyclopiazonic acid, an inhibitor of the sarco(endo)plasmic reticulum ATPase, had opposite effects to that of SNS, acting to increase susceptibility to alternans, and suggesting that accelerated Ca reuptake into the sarcoplasmic reticulum is a major mechanism by which SNS suppresses alternans in the guinea pig heart. Conclusions : SNS suppresses calcium and action potential alternans in the intact guinea pig heart by an action mediated through accelerated Ca handling and via increased I Ks .

Piracetam and other structurally related nootropics.

PubMed

Gouliaev, A H; Senning, A

1994-05-01

Nearly three decades have now passed since the discovery of the piracetam-like nootropics, compounds which exhibit cognition-enhancing properties, but for which no commonly accepted mechanism of action has been established. This review covers clinical, pharmacokinetic, biochemical and behavioural results presented in the literature from 1965 through 1992 (407 references) of piracetam, oxiracetam, pramiracetam, etiracetam, nefiracetam, aniracetam and rolziracetam and their structural analogues. The piracetam-like nootropics are capable of achieving reversal of amnesia induced by, e.g., scopolamine, electroconvulsive shock and hypoxia. Protection against barbiturate intoxication is observed and some benefit in clinical studies with patients suffering from mild to moderate degrees of dementia has been demonstrated. No affinity for the alpha 1-, alpha 2-, beta-, muscarinic, 5-hydroxytryptamine-, dopamine, adenosine-A1-, mu-opiate, gamma-aminobutyric acid (GABA) (except for nefiracetam (GABAA)), benzodiazepine and glutamate receptors has been found. The racetams possess a very low toxicity and lack serious side effects. Increased turnover of different neurotransmitters has been observed as well as other biochemical findings, e.g., inhibition of enzymes such as prolylendopeptidase. So far, no generally accepted mechanism of action has, however, emerged. We believe that the effect of the racetams is due to a potentiation of already present neurotransmission and that much evidence points in the direction of a modulated ion flux by, e.g., potentiated calcium influx through non-L-type voltage-dependent calcium channels, potentiated sodium influx through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor gated channels or voltage-dependent channels or decreases in potassium efflux. Effects on carrier mediated ion transport are also possible.

TRICHLOROETHYLENE IHIBITS VOLTAGE-SENSITIVE CALCIUM CURRENTS IN DIFFERENTIATED PC 12 CELLS.

EPA Science Inventory

ABSTRACT BODY: It has been demonstrated recently that volatile organic compounds (VOCs)such as toluene, perchloroethylene and trichloroethylene inhibit function of voltage-sensitive calcium channels (VSSC). Such actions are hypothesized to contribute to the acute neurotoxicity of...

Decreased afferent excitability contributes to synaptic depression during high-frequency stimulation in hippocampal area CA1

PubMed Central

Kim, Eunyoung; Owen, Benjamin; Holmes, William R.

2012-01-01

Long-term potentiation (LTP) is often induced experimentally by continuous high-frequency afferent stimulation (HFS), typically at 100 Hz for 1 s. Induction of LTP requires postsynaptic depolarization and voltage-dependent calcium influx. Induction is more effective if the same number of stimuli are given as a series of short bursts rather than as continuous HFS, in part because excitatory postsynaptic potentials (EPSPs) become strongly depressed during HFS, reducing postsynaptic depolarization. In this study, we examined mechanisms of EPSP depression during HFS in area CA1 of rat hippocampal brain slices. We tested for presynaptic terminal vesicle depletion by examining minimal stimulation-evoked excitatory postsynaptic currents (EPSCs) during 100-Hz HFS. While transmission failures increased, consistent with vesicle depletion, EPSC latencies also increased during HFS, suggesting a decrease in afferent excitability. Extracellular recordings of Schaffer collateral fiber volleys confirmed a decrease in afferent excitability, with decreased fiber volley amplitudes and increased latencies during HFS. To determine the mechanism responsible for fiber volley changes, we recorded antidromic action potentials in single CA3 pyramidal neurons evoked by stimulating Schaffer collateral axons. During HFS, individual action potentials decreased in amplitude and increased in latency, and these changes were accompanied by a large increase in the probability of action potential failure. Time derivative and phase-plane analyses indicated decreases in both axon initial segment and somato-dendritic components of CA3 neuron action potentials. Our results indicate that decreased presynaptic axon excitability contributes to depression of excitatory synaptic transmission during HFS at synapses between Schaffer collaterals and CA1 pyramidal neurons. PMID:22773781

Despite differences in cytosolic calcium regulation, lidocaine toxicity is similar in adult and neonatal rat dorsal root ganglia in vitro.

PubMed

Doan, Lisa V; Eydlin, Olga; Piskoun, Boris; Kline, Richard P; Recio-Pinto, Esperanza; Rosenberg, Andrew D; Blanck, Thomas J J; Xu, Fang

2014-01-01

Neuraxial local anesthetics may have neurological complications thought to be due to neurotoxicity. A primary site of action of local anesthetics is the dorsal root ganglia (DRG) neuron. Physiologic differences have been noted between young and adult DRG neurons; hence, the authors examined whether there were any differences in lidocaine-induced changes in calcium and lidocaine toxicity in neonatal and adult rat DRG neurons. DRG neurons were cultured from postnatal day 7 (P7) and adult rats. Lidocaine-induced changes in cytosolic calcium were examined with the calcium indicator Fluo-4. Cells were incubated with varying concentrations of lidocaine and examined for viability using calcein AM and ethidium homodimer-1 staining. Live imaging of caspase-3/7 activation was performed after incubation with lidocaine. The mean KCl-induced calcium transient was greater in P7 neurons (P < 0.05), and lidocaine significantly inhibited KCl-induced calcium responses in both ages (P < 0.05). Frequency distribution histograms of KCl-evoked calcium increases were more heterogeneous in P7 than in adult neurons. With lidocaine, KCl-induced calcium transients in both ages became more homogeneous but remained different between the groups. Interestingly, cell viability was decreased by lidocaine in a dose-dependent manner similarly in both ages. Lidocaine treatment also activated caspase-3/7 in a dose- and time-dependent manner similarly in both ages. Despite physiological differences in P7 and adult DRG neurons, lidocaine cytotoxicity is similar in P7 and adult DRG neurons in vitro. Differences in lidocaine- and KCl-evoked calcium responses suggest the similarity in lidocaine cytotoxicity involves other actions in addition to lidocaine-evoked effects on cytosolic calcium responses.

Despite Differences in Cytosolic Calcium Regulation, Lidocaine Toxicity Is Similar in Adult and Neonatal Rat Dorsal Root Ganglia in Vitro

PubMed Central

Doan, Lisa V.; Eydlin, Olga; Piskoun, Boris; Kline, Richard P; Recio-Pinto, Esperanza; Rosenberg, Andrew D; Blanck, Thomas JJ; Xu, Fang

2013-01-01

Background Neuraxial local anesthetics may have neurological complications thought to be due to neurotoxicity. A primary site of action for local anesthetics is the dorsal root ganglia (DRG) neuron. Physiologic differences have been noted between young and adult DRG neurons; hence, we examined whether there were differences in lidocaine-induced changes in calcium and lidocaine toxicity in neonatal and adult rat DRG neurons. Methods DRG neurons were cultured from postnatal day 7 (P7) and adult rats. Lidocaine-induced changes in cytosolic calcium were examined with the calcium indicator Fluo-4. Cells were incubated with varying concentrations of lidocaine and examined for viability using calcein AM and ethidium homodimer-1 staining. Live imaging of caspase-3/7 activation was performed after incubation with lidocaine. Results The mean KCl-induced calcium transient was greater in P7 neurons (p < 0.05), and lidocaine significantly inhibited KCl-induced calcium responses in both ages (p < 0.05). Frequency distribution histograms of KCl-evoked calcium increases were more heterogeneous in P7 than in adult neurons. With lidocaine, KCl-induced calcium transients in both ages became more homogeneous but remained different between the groups. Interestingly cell viability was decreased by lidocaine in a dose-dependent manner similarly in both ages. Lidocaine treatment also activated caspase-3/7 in a dose- and time-dependent manner similarly in both ages. Conclusions Despite physiological differences in P7 and adult DRG neurons, lidocaine cytotoxicity is similar in P7 and adult DRG neurons in vitro. Differences in lidocaine- and KCl-evoked calcium responses suggest the similarity in lidocaine cytotoxicity involves other actions in addition to lidocaine-evoked effects on cytosolic calcium responses. PMID:23851347

How theories evolved concerning the mechanism of action of barbiturates.

PubMed

Löscher, Wolfgang; Rogawski, Michael A

2012-12-01

The barbiturate phenobarbital has been in use in the treatment of epilepsy for 100 years. It has long been recognized that barbiturates act by prolonging and potentiating the action of γ-aminobutyric acid (GABA) on GABA(A) receptors and at higher concentrations directly activating the receptors. A large body of data supports the concept that GABA(A) receptors are the primary central nervous system target for barbiturates, including the finding that transgenic mice with a point mutation in the β3 GABA(A) -receptor subunit exhibit diminished sensitivity to the sedative and immobilizing actions of the anesthetic barbiturate pentobarbital. Although phenobarbital is only modestly less potent as a GABA(A) -receptor modulator than pentobarbital, phenobarbital is minimally sedating at effective anticonvulsant doses. Possible explanations for the reduced sedative effect of phenobarbital include more regionally restricted action; partial agonist activity; reduced propensity to directly activate GABA(A) receptors (possibly including extrasynaptic receptors containing δ subunits); and reduced activity at other ion channel targets, including voltage-gated calcium channels. In recent years, substantial progress has been made in defining the structural features of GABA(A) receptors responsible for gating and allosteric modulation by drugs. Although the precise sites of action of barbiturates have not yet been defined, the second and third transmembrane domains of the β subunit appear to be critical; binding may involve a pocket formed by β-subunit methionine 286 as well as α-subunit methionine 236. In addition to effects on GABA(A) receptors, barbiturates block AMPA/kainate receptors, and they inhibit glutamate release through an effect on P/Q-type high-voltage activated calcium channels. The combination of these various actions likely accounts for their diverse clinical activities. Despite the remarkable progress of the last century, there is still much to learn about the actions of barbiturates that can be applied to the discovery of new, more therapeutically useful agents. Wiley Periodicals, Inc. © 2012 International League Against Epilepsy.

Drug action of benzocaine on the sarcoplasmic reticulum Ca-ATPase from fast-twitch skeletal muscle.

PubMed

Di Croce, D; Trinks, P W; Grifo, M B; Takara, D; Sánchez, G A

2015-11-01

The effect of the local anesthetic benzocaine on sarcoplasmic reticulum membranes isolated from fast-twitch muscles was tested. The effects on Ca-ATPase activity, calcium binding and uptake, phosphoenzyme accumulation and decomposition were assessed using radioisotopic methods. The calcium binding to the Ca-ATPase was noncompetitively inhibited, and the enzymatic activity decreased in a concentration-dependent manner (IC50 47.1 mM). The inhibition of the activity depended on the presence of the calcium ionophore calcimycin and the membrane protein concentration. The pre-exposure of the membranes to benzocaine enhanced the enzymatic activity in the absence of calcimycin, supporting the benzocaine permeabilizing effect, which was prevented by calcium. Benzocaine also interfered with the calcium transport capability by decreasing the maximal uptake (IC50 40.3 mM) without modification of the calcium affinity for the ATPase. It inhibited the phosphorylation of the enzyme, and at high benzocaine concentration, the dephosphorylation step became rate-limiting as suggested by the biphasic profile of phosphoenzyme accumulation at different benzocaine concentrations. The data reported in this paper revealed a complex pattern of inhibition involving two sites for interaction with low and high benzocaine concentrations. It is concluded that benzocaine not only exerts an indirect action on the membrane permeability to calcium but also affects key steps of the Ca-ATPase enzymatic cycle.

Efficacy of colestilan in the treatment of hyperphosphataemia in renal disease patients.

PubMed

Locatelli, Francesco; Dimkovic, Nada; Spasovski, Goce

2014-07-01

Hyperphosphataemia is common in chronic kidney disease (CKD), particularly in the late stages and is associated with secondary hyperparathyroidism, abnormal bone mineralisation and increased cardiovascular morbidity/mortality. At present, there is a range of phosphate binders designed to keep serum phosphate at normal or near normal levels. Colestilan is a new binder that offers additional actions that may afford further benefits over simply lowering phosphate. This paper reviews the pharmacology and clinical data currently available in the use of colestilan to treat hyperphosphataemia in CKD stage 5 patients on dialysis. Available phosphate binders lower serum phosphorus levels to a clinically relevant extent. The balance between the risks and the potential benefits associated with each agent must be considered when choosing a binder. Calcium-based binders can lead to hypercalcaemia and/or positive calcium balance and cardiovascular calcification. Like sevelamer, colestilan is not absorbed and there is no evidence of any risk of hypercalcaemia. In addition, a significant lowering of low-density lipoprotein-cholesterol, similar to simvastatin, a reduction in plasma uric acid and a reduction in high glycosylated haemoglobin values suggest additional beneficial actions that may convert to reductions in mortality.

Inhibition of Sphingosine Kinase 1 Ameliorates Angiotensin II-Induced Hypertension and Inhibits Transmembrane Calcium Entry via Store-Operated Calcium Channel

PubMed Central

Wilson, Parker C.; Fitzgibbon, Wayne R.; Garrett, Sara M.; Jaffa, Ayad A.; Luttrell, Louis M.; Brands, Michael W.

2015-01-01

Angiotensin II (AngII) plays a critical role in the regulation of vascular tone and blood pressure mainly via regulation of Ca2+ mobilization. Several reports have implicated sphingosine kinase 1 (SK1)/sphingosine 1-phosphate (S1P) in the mobilization of intracellular Ca2+ through a yet-undefined mechanism. Here we demonstrate that AngII-induces biphasic calcium entry in vascular smooth muscle cells, consisting of an immediate peak due to inositol tris-phosphate-dependent release of intracellular calcium, followed by a sustained transmembrane Ca2+ influx through store-operated calcium channels (SOCs). Inhibition of SK1 attenuates the second phase of transmembrane Ca2+ influx, suggesting a role for SK1 in AngII-dependent activation of SOC. Intracellular S1P triggers SOC-dependent Ca2+ influx independent of S1P receptors, whereas external application of S1P stimulated S1P receptor-dependent Ca2+ influx that is insensitive to inhibitors of SOCs, suggesting that the SK1/S1P axis regulates store-operated calcium entry via intracellular rather than extracellular actions. Genetic deletion of SK1 significantly inhibits both the acute hypertensive response to AngII in anaesthetized SK1 knockout mice and the sustained hypertensive response to continuous infusion of AngII in conscious animals. Collectively these data implicate SK1 as the missing link that connects the angiotensin AT1A receptor to transmembrane Ca2+ influx and identify SOCs as a potential intracellular target for SK1. PMID:25871850

Paclitaxel Induces Apoptosis in Breast Cancer Cells through Different Calcium—Regulating Mechanisms Depending on External Calcium Conditions

PubMed Central

Pan, Zhi; Avila, Andrew; Gollahon, Lauren

2014-01-01

Previously, we reported that endoplasmic reticulum calcium stores were a direct target for paclitaxel initiation of apoptosis. Furthermore, the actions of paclitaxel attenuated Bcl-2 resistance to apoptosis through endoplasmic reticulum-mediated calcium release. To better understand the calcium-regulated mechanisms of paclitaxel-induced apoptosis in breast cancer cells, we investigated the role of extracellular calcium, specifically; whether influx of extracellular calcium contributed to and/or was necessary for paclitaxel-induced apoptosis. Our results demonstrated that paclitaxel induced extracellular calcium influx. This mobilization of extracellular calcium contributed to subsequent cytosolic calcium elevation differently, depending on dosage. Under normal extracellular calcium conditions, high dose paclitaxel induced apoptosis-promoting calcium influx, which did not occur in calcium-free conditions. In the absence of extracellular calcium an “Enhanced Calcium Efflux” mechanism in which high dose paclitaxel stimulated calcium efflux immediately, leading to dramatic cytosolic calcium decrease, was observed. In the absence of extracellular calcium, high dose paclitaxel’s stimulatory effects on capacitative calcium entry and apoptosis could not be completely restored. Thus, normal extracellular calcium concentrations are critical for high dose paclitaxel-induced apoptosis. In contrast, low dose paclitaxel mirrored controls, indicating that it occurs independent of extracellular calcium. Thus, extracellular calcium conditions only affect efficacy of high dose paclitaxel-induced apoptosis. PMID:24549172

An integrated platform for simultaneous multi-well field potential recording and Fura-2-based calcium transient ratiometry in human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes.

PubMed

Rast, Georg; Weber, Jürgen; Disch, Christoph; Schuck, Elmar; Ittrich, Carina; Guth, Brian D

2015-01-01

Human induced pluripotent stem cell-derived cardiomyocytes are available from various sources and they are being evaluated for safety testing. Several platforms are available offering different assay principles and read-out parameters: patch-clamp and field potential recording, imaging or photometry, impedance measurement, and recording of contractile force. Routine use will establish which assay principle and which parameters best serve the intended purpose. We introduce a combination of field potential recording and calcium ratiometry from spontaneously beating cardiomyocytes as a novel assay providing a complementary read-out parameter set. Field potential recording is performed using a commercial multi-well multi-electrode array platform. Calcium ratiometry is performed using a fiber optic illumination and silicon avalanche photodetectors. Data condensation and statistical analysis are designed to enable statistical inference of differences and equivalence with regard to a solvent control. Simultaneous recording of field potentials and calcium transients from spontaneously beating monolayers was done in a nine-well format. Calcium channel blockers (e.g. nifedipine) and a blocker of calcium store release (ryanodine) can be recognized and discriminated based on the calcium transient signal. An agonist of L-type calcium channels, FPL 64176, increased and prolonged the calcium transient, whereas BAY K 8644, another L-type calcium channel agonist, had no effect. Both FPL 64176 and various calcium channel antagonists have chronotropic effects, which can be discriminated from typical "chronotropic" compounds, like (±)isoprenaline (positive) and arecaidine propargyl ester (negative), based on their effects on the calcium transient. Despite technical limitations in temporal resolution and exact matching of composite calcium transient with the field potential of a subset of cells, the combined recording platform enables a refined interpretation of the field potential recording and a more reliable identification of drug effects on calcium handling. Copyright © 2015 Elsevier Inc. All rights reserved.

Influence of pre-, post-, and simultaneous perfusion of elevated calcium on the effect of ascending concentrations of lead on digoxin-induced cardiac arrest in isolated frog heart

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

Krishnamoorthy, M.S.; Muthu, P.; Parthiban, N.

1995-10-01

Cardiotoxicity of lead, a ubiquitous environmental pollutant, has already been documented as a potentially lethal, although rarely recognized, complication of lead intoxication. Further, it has already been reported from this laboratory that lead acetate (LA) preperfusion potentiated cardiotoxicity of digoxin (DGN) in isolated frog heart preparation and that exposure to elevated calcium (elev. Ca{sup 2+}) prior to, and simultaneously with LA at 10{sup {minus}7} M concentration, attenuated this potentiation. As an extension of this work, it was considered of interest to study the effect of perfusion of elev. Ca{sup 2+} (6.5 mM) prior to, after and simultaneously with ascending concentrationsmore » of lead (10{sup {minus}9}, 10{sup {minus}7} and 10{sup {minus}5}M) on DGN induced cardiac arrest (CA) in isolated frog heart, since Pb{sup 2+} and Ca{sup 2+} ions are known to compete with each other for the same target sites at the cellular level, an instance of competitive mass action effect. 15 refs., 1 fig., 1 tab.« less

Paired-pulse facilitation and depression at unitary synapses in rat hippocampus: quantal fluctuation affects subsequent release.

PubMed Central

Debanne, D; Guérineau, N C; Gähwiler, B H; Thompson, S M

1996-01-01

1. Excitatory synaptic transmission between pairs of monosynaptically coupled pyramidal cells was examined in rat hippocampal slice cultures. Action potentials were elicited in single CA3 pyramidal cells impaled with microelectrodes and unitary excitatory postsynaptic currents (EPSCs) were recorded in whole-cell voltage-clamped CA1 or CA3 cells. 2. The amplitude of successive unitary EPSCs in response to single action potentials varied. The amplitude of EPSCs was altered by adenosine or changes in the [Mg2+]/[CA2+] ratio. We conclude that single action potentials triggered the release of multiple quanta of glutamate. 3. When two action potentials were elicited in the presynaptic cell, the amplitude of the second EPSC was inversely related to the amplitude of the first. Paired-pulse facilitation (PPF) was observed when the first EPSC was small, i.e. the second EPSC was larger than the first, whereas paired-pulse depression (PPD) was observed when the first EPSC was large. 4. The number of trials displaying PPD was greater when release probability was increased, and smaller when release probability was decreased. 5. PPD was not postsynaptically mediated because it was unaffected by decreasing ionic flux with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or receptor desensitization with aniracetam. 6. PPF was maximal at an interstimulus interval of 70 ms and recovered within 500 ms. Recovery from PPD occurred within 5 s. 7. We propose that multiple release sites are formed by the axon of a CA3 pyramidal cell and a single postsynaptic CA1 or CA3 cell. PPF is observed if the first action potential fails to release transmitter at most release sites. PPD is observed if the first action potential successfully triggers release at most release sites. 8. Our observations of PPF are consistent with the residual calcium hypothesis. We conclude that PPD results from a decrease in quantal content, perhaps due to short-term depletion of readily releasable vesicles. PMID:9011608

Chronic alcohol feeding potentiates hormone-induced calcium signalling in hepatocytes.

PubMed

Bartlett, Paula J; Antony, Anil Noronha; Agarwal, Amit; Hilly, Mauricette; Prince, Victoria L; Combettes, Laurent; Hoek, Jan B; Gaspers, Lawrence D

2017-05-15

Chronic alcohol consumption causes a spectrum of liver diseases, but the pathogenic mechanisms driving the onset and progression of disease are not clearly defined. We show that chronic alcohol feeding sensitizes rat hepatocytes to Ca 2+ -mobilizing hormones resulting in a leftward shift in the concentration-response relationship and the transition from oscillatory to more sustained and prolonged Ca 2+ increases. Our data demonstrate that alcohol-dependent adaptation in the Ca 2+ signalling pathway occurs at the level of hormone-induced inositol 1,4,5 trisphosphate (IP 3 ) production and does not involve changes in the sensitivity of the IP 3 receptor or size of internal Ca 2+ stores. We suggest that prolonged and aberrant hormone-evoked Ca 2+ increases may stimulate the production of mitochondrial reactive oxygen species and contribute to alcohol-induced hepatocyte injury. ABSTRACT: 'Adaptive' responses of the liver to chronic alcohol consumption may underlie the development of cell and tissue injury. Alcohol administration can perturb multiple signalling pathways including phosphoinositide-dependent cytosolic calcium ([Ca 2+ ] i ) increases, which can adversely affect mitochondrial Ca 2+ levels, reactive oxygen species production and energy metabolism. Our data indicate that chronic alcohol feeding induces a leftward shift in the dose-response for Ca 2+ -mobilizing hormones resulting in more sustained and prolonged [Ca 2+ ] i increases in both cultured hepatocytes and hepatocytes within the intact perfused liver. Ca 2+ increases were initiated at lower hormone concentrations, and intercellular calcium wave propagation rates were faster in alcoholics compared to controls. Acute alcohol treatment (25 mm) completely inhibited hormone-induced calcium increases in control livers, but not after chronic alcohol-feeding, suggesting desensitization to the inhibitory actions of ethanol. Hormone-induced inositol 1,4,5 trisphosphate (IP 3 ) accumulation and phospholipase C (PLC) activity were significantly potentiated in hepatocytes from alcohol-fed rats compared to controls. Removal of extracellular calcium, or chelation of intracellular calcium did not normalize the differences in hormone-stimulated PLC activity, indicating calcium-dependent PLCs are not upregulated by alcohol. We propose that the liver 'adapts' to chronic alcohol exposure by increasing hormone-dependent IP 3 formation, leading to aberrant calcium increases, which may contribute to hepatocyte injury. © 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.

Estimating the duration of intracellular action potentials in muscle fibres from single-fibre extracellular potentials.

PubMed

Rodríguez, Javier; Navallas, Javier; Gila, Luis; Dimitrova, Nonna Alexandrovna; Malanda, Armando

2011-04-30

In situ recording of the intracellular action potential (IAP) of human muscle fibres is not yet possible, and consequently, knowledge concerning certain IAP characteristics is still limited. According to the core-conductor theory, close to a fibre, a single fibre action potential (SFAP) can be assumed to be proportional to the IAP second derivative. Thus, we might expect to be able to derive some characteristics of the IAP, such as the duration of its spike, from the SFAP waveform. However, SFAP properties not only depend on the IAP shape but also on the fibre-to-electrode (radial) distance and other physiological properties of the fibre. In this paper we, first, propose an SFAP parameter (the negative phase duration, NPD) appropriate for estimating the IAP spike duration and, second, show that this parameter is largely independent of changes in radial distance and muscle fibre propagation velocity. Estimation of the IAP spike duration from a direct measurement taken from the SFAP waveform provides a possible way to enhance the accuracy of SFAP models. Because IAP spike duration is known to be sensitive to the effects of fatigue and calcium accumulation, the proposed SFAP parameter, the NPD, has potential value in electrodiagnosis and as an indicator of IAP profile changes due to peripheral fatigue. Copyright © 2011 Elsevier B.V. All rights reserved.

78 FR 40147 - Scientific Information Request on Vitamin D and Calcium

Federal Register 2010, 2011, 2012, 2013, 2014

2013-07-03

... DEPARTMENT OF HEALTH AND HUMAN SERVICES Agency for Healthcare Research and Quality Scientific Information Request on Vitamin D and Calcium AGENCY: Agency for Healthcare Research and Quality (AHRQ), HHS. ACTION: Request for Scientific Information Submissions. SUMMARY: The Agency for Healthcare Research and...

78 FR 42952 - Scientific Information Request on Vitamin D and Calcium

Federal Register 2010, 2011, 2012, 2013, 2014

2013-07-18

... DEPARTMENT OF HEALTH AND HUMAN SERVICES Agency for Healthcare Research and Quality Scientific Information Request on Vitamin D and Calcium AGENCY: Agency for Healthcare Research and Quality (AHRQ), HHS. ACTION: Request for scientific information submissions. SUMMARY: The Agency for Healthcare Research and...

Background norepinephrine primes astrocytic calcium responses to subsequent norepinephrine stimuli in the cerebral cortex.

PubMed

Nuriya, Mutsuo; Takeuchi, Miyabi; Yasui, Masato

2017-01-29

Norepinephrine (NE) levels in the cerebral cortex are regulated in two modes; the brain state is correlated with slow changes in background NE concentration, while salient stimuli induce transient NE spikes. Previous studies have revealed their diverse neuromodulatory actions; however, the modulatory role of NE on astrocytic activity has been poorly characterized thus far. In this study, we evaluated the modulatory action of background NE on astrocytic responses to subsequent stimuli, using two-photon calcium imaging of acute murine cortical brain slices. We find that subthreshold background NE significantly augments calcium responses to subsequent pulsed NE stimulation in astrocytes. This priming effect is independent of neuronal activity and is mediated by the activation of β-adrenoceptors and the downstream cAMP pathway. These results indicate that background NE primes astrocytes for subsequent calcium responses to NE stimulation and suggest a novel gliomodulatory role for brain state-dependent background NE in the cerebral cortex. Copyright © 2016 Elsevier Inc. All rights reserved.

Role of dihydropyridinic calcium channel blockers in the management of hypertension.

PubMed

Coca, Antonio; Mazón, Pilar; Aranda, Pedro; Redón, Josep; Divisón, Juan Antonio; Martínez, Javier; Calvo, Carlos; Galcerán, Josep María; Barrios, Vivencio; Roca-Cusachs I Coll, Alexandre

2013-01-01

Dihydropyridinic calcium channel blockers are a subclass of antihypertensive drugs with growing significance in the therapeutic armamentarium. Early studies in the 1990s had aroused certain fears with regard to the safety of the first drugs from this class, since they had a fast onset of action and a short half-life, and thus they were associated with reflex adrenergic activation. New molecules with long half-lives and high lipophilia have shown safety and efficacy in the control of blood pressure, as well as in the reduction of several end points related to hypertension. Moreover, these new molecules, which block special subtypes of calcium channel receptors, provide drugs not only with an action profile that goes beyond the antihypertensive effect, but also with a lower rate of side effects. Therefore, in the light of new studies that include calcium channel blockers alone or in combination, these agents will probably be used even more extensively for the management of hypertension in the following years.

Ghrelin potentiates cardiac reactivity to stress by modulating sympathetic control and beta-adrenergic response.

PubMed

Camargo-Silva, Gabriel; Turones, Larissa Córdova; da Cruz, Kellen Rosa; Gomes, Karina Pereira; Mendonça, Michelle Mendanha; Nunes, Allancer; de Jesus, Itamar Guedes; Colugnati, Diego Basile; Pansani, Aline Priscila; Pobbe, Roger Luis Henschel; Santos, Robson; Fontes, Marco Antônio Peliky; Guatimosim, Silvia; de Castro, Carlos Henrique; Ianzer, Danielle; Ferreira, Reginaldo Nassar; Xavier, Carlos Henrique

2018-03-01

Prior evidence indicates that ghrelin is involved in the integration of cardiovascular functions and behavioral responses. Ghrelin actions are mediated by the growth hormone secretagogue receptor subtype 1a (GHS-R1a), which is expressed in peripheral tissues and central areas involved in the control of cardiovascular responses to stress. In the present study, we assessed the role of ghrelin - GHS-R1a axis in the cardiovascular reactivity to acute emotional stress in rats. Ghrelin potentiated the tachycardia evoked by restraint and air jet stresses, which was reverted by GHS-R1a blockade. Evaluation of the autonomic balance revealed that the sympathetic branch modulates the ghrelin-evoked positive chronotropy. In isolated hearts, the perfusion with ghrelin potentiated the contractile responses caused by stimulation of the beta-adrenergic receptor, without altering the amplitude of the responses evoked by acetylcholine. Experiments in isolated cardiomyocytes revealed that ghrelin amplified the increases in calcium transient changes evoked by isoproterenol. Taken together, our results indicate that the Ghrelin-GHS-R1a axis potentiates the magnitude of stress-evoked tachycardia by modulating the autonomic nervous system and peripheral mechanisms, strongly relying on the activation of cardiac calcium transient and beta-adrenergic receptors. Copyright © 2018 Elsevier Inc. All rights reserved.

[Mechanisms of action of voltage-gated sodium channel ligands].

PubMed

Tikhonov, D B

2007-05-01

The voltage-gated sodium channels play a key role in the generation of action potential in excitable cells. Sodium channels are targeted by a number of modulating ligands. Despite numerous studies, the mechanisms of action of many ligands are still unknown. The main cause of the problem is the absence of the channel structure. Sodium channels belong to the superfamily of P-loop channels that also the data abowt includes potassium and calcium channels and the channels of ionotropic glutamate receptors. Crystallization of several potassium channels has opened a possibility to analyze the structure of other members of the superfamily using the homology modeling approach. The present study summarizes the results of several recent modelling studies of such sodium channel ligands as tetrodotoxin, batrachotoxin and local anesthetics. Comparison of available experimental data with X-ray structures of potassium channels has provided a new level of understanding of the mechanisms of action of sodium channel ligands and has allowed proposing several testable hypotheses.

A new design for a green calcium indicator with a smaller size and a reduced number of calcium-binding sites

PubMed Central

Barykina, Natalia V.; Subach, Oksana M.; Doronin, Danila A.; Sotskov, Vladimir P.; Roshchina, Marina A.; Kunitsyna, Tatiana A.; Malyshev, Aleksey Y.; Smirnov, Ivan V.; Azieva, Asya M.; Sokolov, Ilya S.; Piatkevich, Kiryl D.; Burtsev, Mikhail S.; Varizhuk, Anna M.; Pozmogova, Galina E.; Anokhin, Konstantin V.; Subach, Fedor V.; Enikolopov, Grigori N.

2016-01-01

Genetically encoded calcium indicators (GECIs) are mainly represented by two- or one-fluorophore-based sensors. One type of two-fluorophore-based sensor, carrying Opsanus troponin C (TnC) as the Ca2+-binding moiety, has two binding sites for calcium ions, providing a linear response to calcium ions. One-fluorophore-based sensors have four Ca2+-binding sites but are better suited for in vivo experiments. Herein, we describe a novel design for a one-fluorophore-based GECI with two Ca2+-binding sites. The engineered sensor, called NTnC, uses TnC as the Ca2+-binding moiety, inserted in the mNeonGreen fluorescent protein. Monomeric NTnC has higher brightness and pH-stability in vitro compared with the standard GECI GCaMP6s. In addition, NTnC shows an inverted fluorescence response to Ca2+. Using NTnC, we have visualized Ca2+ dynamics during spontaneous activity of neuronal cultures as confirmed by control NTnC and its mutant, in which the affinity to Ca2+ is eliminated. Using whole-cell patch clamp, we have demonstrated that NTnC dynamics in neurons are similar to those of GCaMP6s and allow robust detection of single action potentials. Finally, we have used NTnC to visualize Ca2+ neuronal activity in vivo in the V1 cortical area in awake and freely moving mice using two-photon microscopy or an nVista miniaturized microscope. PMID:27677952

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.

Store-operated Ca²⁺ entry and depolarization explain the anomalous behaviour of myometrial SR: effects of SERCA inhibition on electrical activity, Ca²⁺ and force.

PubMed

Noble, Debbie; Borysova, Lyudmyla; Wray, Susan; Burdyga, Theodor

2014-09-01

In the myometrium SR Ca(2+) depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca(2+) sparks-STOCs coupling mechanism to explain this. Given the importance of the control of contractility for successful parturition, we have examined, in pregnant rat myometrium, the effects of SR Ca(2+)-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca(2+) transients and force. Simultaneous recording of electrical activity, calcium and force showed that SERCA inhibition, by cyclopiazonic acid (CPA 20 μM), caused time-dependent changes in excitability, most noticeably depolarization and elevations of baseline [Ca(2+)]i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca(2+) spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca(2+) and depolarization continued a point was reached when electrical and Ca(2+) spikes and phasic contractions ceased, and a maintained, tonic force and Ca(2+) was produced. Lanthanum, a non-selective blocker of store-operated Ca(2+) entry, but not the L-type Ca(2+) channel blocker nifedipine (1-10 μM), could abolish the maintained force and calcium. Application of the agonist, carbachol, produced similar effects to CPA, i.e. depolarization, elevation of force and calcium. A brief, high concentration of carbachol, to cause SR Ca(2+) depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca(2+) release is coupled to marked Ca(2+) entry, via store operated Ca(2+) channels, leading to depolarization and enhanced electrical and mechanical activity. Copyright © 2014. Published by Elsevier Ltd.

NMDA-receptor dependent synaptic activation of TRPC channels in olfactory bulb granule cells

PubMed Central

Stroh, Olga; Freichel, Marc; Kretz, Oliver; Birnbaumer, Lutz; Hartmann, Jana; Egger, Veronica

2012-01-01

TRPC channels are widely expressed throughout the nervous system including the olfactory bulb where their function is largely unknown. Here we describe their contribution to central synaptic processing at the reciprocal mitral and tufted cell - granule cell microcircuit, the most abundant synapse of the mammalian olfactory bulb. Suprathreshold activation of the synapse causes sodium action potentials in mouse granule cells and a subsequent long-lasting depolarization (LLD) linked to a global dendritic postsynaptic calcium signal recorded with two-photon laser scanning microscopy. These signals are not observed after action potentials evoked by current injection in the same cells. The LLD persists in the presence of group I metabotropic glutamate receptor antagonists but is entirely absent from granule cells deficient for the NMDA receptor subunit NR1. Moreover, both depolarization and Ca2+ rise are sensitive to the blockade of NMDA receptors. The LLD and the accompanying Ca2+ rise are also absent in granule cells from mice deficient for both TRPC channel subtypes 1 and 4, whereas the deletion of either TRPC1 or TRPC4 results in only a partial reduction of the LLD. Recordings from mitral cells in the absence of both subunits reveal a reduction of asynchronous neurotransmitter release from the granule cells during recurrent inhibition. We conclude that TRPC1 and TRPC4 can be activated downstream of NMDA receptor activation and contribute to slow synaptic transmission in the olfactory bulb, including the calcium dynamics required for asynchronous release from the granule cell spine. PMID:22539836

Primary hyperparathyroidism is associated with subclinical peripheral neural alterations.

PubMed

Diniz, Erik Trovão; Bandeira, Francisco; Lins, Otávio Gomes; Cavalcanti, Érica Nogueira Bezerra; de Arruda, Tiago Matos; Januário, Alexandre Medeiros Sampaio; Diniz, Kaisa Trovão; Marques, Thyciara Fontenele; Azevedo, Hildo

2013-01-01

Some case reports have suggested primary hyperparathyroidism (PHPT) and peripheral polyneuropathy (PPN) are associated; however, there are no reports of studies examining this possible relationship. The aim of this study was to evaluate peripheral nerve conduction in subjects with PHPT. The study involved 17 patients with PHPT. Mean patient age was 60.5 ± 12.9 years, serum calcium concentration was 11.5 ± 1.0 mg/dL, and the serum parathyroid hormone (PTH) level was 315 ± 569 pg/dL. The control group comprised 17 individuals without PHPT. The mean age of controls was 60.8 ± 12.5 years and the serum calcium concentration was 9.8 ± 0.3 mg/dL. Motor and sensory nerve conduction was assessed by electroneurography (ENG). The following ENG parameters differed significantly between the PHPT and control groups: right (R) sural sensory nerve action potential conduction velocity (52.7 ± 6.3 m/s versus 58.0 ± 8.0 m/s; P = .041); R median compound muscle action potential (CMAP) amplitude (7.4 ± 1.6 mV versus 8.9 ± 1.7 mV; P = .002); R median CMAP latency (4.3 ± 1.2 ms versus 3.6 ± 0.6 ms; P = .032); R tibial CMAP latency (4.2 ± 1.1 ms versus 3.3 ± 0.4 ms; P = .001). The neurological examination was normal in all patients. Our data demonstrate an association between PHPT and peripheral neurological alterations, consistent with subclinical sensory-motor PPN.

An integrate-and-fire model for synchronized bursting in a network of cultured cortical neurons.

PubMed

French, D A; Gruenstein, E I

2006-12-01

It has been suggested that spontaneous synchronous neuronal activity is an essential step in the formation of functional networks in the central nervous system. The key features of this type of activity consist of bursts of action potentials with associated spikes of elevated cytoplasmic calcium. These features are also observed in networks of rat cortical neurons that have been formed in culture. Experimental studies of these cultured networks have led to several hypotheses for the mechanisms underlying the observed synchronized oscillations. In this paper, bursting integrate-and-fire type mathematical models for regular spiking (RS) and intrinsic bursting (IB) neurons are introduced and incorporated through a small-world connection scheme into a two-dimensional excitatory network similar to those in the cultured network. This computer model exhibits spontaneous synchronous activity through mechanisms similar to those hypothesized for the cultured experimental networks. Traces of the membrane potential and cytoplasmic calcium from the model closely match those obtained from experiments. We also consider the impact on network behavior of the IB neurons, the geometry and the small world connection scheme.

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.

ICI 182,780 has agonistic effects and synergizes with estradiol-17 beta in fish liver, but not in testis.

PubMed

Pinto, Patrícia I S; Singh, Pratap B; Condeça, João B; Teodósio, Helena R; Power, Deborah M; Canário, Adelino V M

2006-12-27

ICI 182,780 (ICI) belongs to a new class of antiestrogens developed to be pure estrogen antagonists and, in addition to its therapeutic use, it has been used to knock-out estrogen and estrogen receptor (ER) actions in several mammalian species. In the present study, the effects and mechanism of action of ICI were investigated in the teleost fish, sea bream (Sparus auratus). Three independent in vivo experiments were performed in which mature male tilapia (Oreochromis mossambicus) or sea bream received intra-peritoneal implants containing estradiol-17 beta (E2), ICI or a combination of both compounds. The effects of E2 and ICI on plasma calcium levels were measured and hepatic and testicular gene expression of the three ER subtypes, ER alpha, ER beta a and ER beta b, and the estrogen-responsive genes, vitellogenin II and choriogenin L, were analyzed by semi-quantitative RT-PCR in sea bream. E2 treatment caused an increase in calcium levels in tilapia, while ICI alone had no noticeable effect, as expected. However, pretreatment with ICI synergistically potentiated the effect of E2 on plasma calcium in both species. ICI mimicked some E2 actions in gene expression in sea bream liver upregulating ER alpha, vitellogenin II and choriogenin L, although, unlike E2, it did not downregulate ER beta a and ER beta b. In contrast, no effects of E2 or ICI alone were detected in the expression of ERs in testis, while vitellogenin II and choriogenin L were upregulated by E2 but not ICI. Finally, pretreatment with ICI had a synergistic effect on the hepatic E2 down-regulation of ER beta b, but apparently blocked the ER alpha up-regulation by E2. These results demonstrate that ICI has agonistic effects on several typical estrogenic responses in fish, but its actions are tissue-specific. The mechanisms for the ICI agonistic activity are still unknown; although the ICI induced up-regulation of ER alpha mRNA could be one of the factors contributing to the cellular response.

ICI 182,780 has agonistic effects and synergizes with estradiol-17 beta in fish liver, but not in testis

PubMed Central

Pinto, Patrícia IS; Singh, Pratap B; Condeça, João B; Teodósio, Helena R; Power, Deborah M; Canário, Adelino VM

2006-01-01

Background ICI 182,780 (ICI) belongs to a new class of antiestrogens developed to be pure estrogen antagonists and, in addition to its therapeutic use, it has been used to knock-out estrogen and estrogen receptor (ER) actions in several mammalian species. In the present study, the effects and mechanism of action of ICI were investigated in the teleost fish, sea bream (Sparus auratus). Methods Three independent in vivo experiments were performed in which mature male tilapia (Oreochromis mossambicus) or sea bream received intra-peritoneal implants containing estradiol-17 beta (E2), ICI or a combination of both compounds. The effects of E2 and ICI on plasma calcium levels were measured and hepatic and testicular gene expression of the three ER subtypes, ER alpha, ER beta a and ER beta b, and the estrogen-responsive genes, vitellogenin II and choriogenin L, were analyzed by semi-quantitative RT-PCR in sea bream. Results E2 treatment caused an increase in calcium levels in tilapia, while ICI alone had no noticeable effect, as expected. However, pretreatment with ICI synergistically potentiated the effect of E2 on plasma calcium in both species. ICI mimicked some E2 actions in gene expression in sea bream liver upregulating ER alpha, vitellogenin II and choriogenin L, although, unlike E2, it did not downregulate ER beta a and ER beta b. In contrast, no effects of E2 or ICI alone were detected in the expression of ERs in testis, while vitellogenin II and choriogenin L were upregulated by E2 but not ICI. Finally, pretreatment with ICI had a synergistic effect on the hepatic E2 down-regulation of ER beta b, but apparently blocked the ER alpha up-regulation by E2. Conclusion These results demonstrate that ICI has agonistic effects on several typical estrogenic responses in fish, but its actions are tissue-specific. The mechanisms for the ICI agonistic activity are still unknown; although the ICI induced up-regulation of ER alpha mRNA could be one of the factors contributing to the cellular response. PMID:17192186

Allosteric Effects of the Anti-Psychotic Drug Trifluoperazine on the Energetics of Calcium Binding by Calmodulin

PubMed Central

Feldkamp, Michael D.; O'Donnell, Susan E.; Yu, Liping; Shea, Madeline A.

2010-01-01

Trifluoperazine (TFP; Stelazine™) is an antagonist of calmodulin (CaM), an essential regulator of calcium-dependent signal transduction. Reports differ regarding whether, or where, TFP binds to apo CaM. Three crystallographic structures (1CTR, 1A29, 1LIN) show TFP bound to (Ca2+)4-CaM in ratios of 1, 2 or 4 TFP per CaM. In all of these, CaM domains adopt the “open” conformation seen in CaM-kinase complexes having increased calcium affinity. Most reports suggest TFP also increases calcium affinity of CaM. To compare TFP binding to apo CaM and (Ca2+)4-CaM, and explore differential effects on the N- and C-domains of CaM, stoichiometric TFP titrations of CaM were monitored by 15N-HSQC NMR. Two TFP bound to apo CaM, while four bound to (Ca2+)4-CaM. In both cases, the preferred site was in the C-domain. During the titrations, biphasic responses for some resonances suggested inter-site interactions. TFP-binding sites in apo CaM appeared distinct from those in (Ca2+)4-CaM. In equilibrium calcium titrations at defined ratios of TFP:CaM, TFP reduced calcium affinity at most levels tested; this is similar to the effect of many IQ-motifs on CaM. However, at the highest level tested, TFP raised the calcium affinity of the N-domain of CaM. A model of conformational switching is proposed to explain how TFP can exert opposing allosteric effects on calcium affinity by binding to different sites in the “closed”, “semi-open” and “open” domains of CaM. In physiological processes, apo CaM, as well as (Ca2+)4-CaM, needs to be considered a potential target of drug action. PMID:20544963

Regulation of ghrelin secretion and action.

PubMed

Camiña, Jesus P; Carreira, Marcos C; Micic, Dragan; Pombo, Manuel; Kelestimur, Fahrettin; Dieguez, Carlos; Casanueva, Felipe F

2003-10-01

The pulsatile release of growth hormone (GH) from anterior pituitary gland is regulated by the interplay of at least two hypothalamic hormones, GH-releasing hormone (GHRH) and somatostatin, via their engagement with specific cell surface receptors on the anterior pituitary somatotroph. Furthermore, release of GH in vivo may also be controlled by a third type of receptor, the growth hormone secretagogue receptor, a G-protein-coupled receptor, called GHS receptor type 1a (GHSR1a), which was identified in the pituitary and the hypothalamus in humans using a nonpeptidyl growth hormone secretagogue (MK-0677). Ghrelin, the endogenous ligand for the GHS-R1a, is a 28-amino-acid peptide isolated from human stomach that is modified by a straight chain octanoyl group covalently linked to Ser3, which is essential for its endocrine activity. This hormone, predominantly expressed and secreted by the stomach, has a dual action on GH secretion and food intake, showing interdependency between these actions. The finding that fasting and food intake, respectively, increase and decrease the secretion of ghrelin suggests that this hormone may be the bridge connecting somatic growth and body composition with energy metabolism, and appears to play a role in the alteration of energy homeostasis and body weight in pathophysiological states such as hypothyroidism and hyperthyroidism. Despite this, little is known about the intracellular signaling through which ghrelin exerts its regulatory actions. Activation of intracellular calcium mobilization is one of the earliest known cellular signals elicited by ghrelin. In HEK- 293 cells expressing the GHS-R1a, ghrelin induces a biphasic cytosolic calcium elevation characterized by a spike phase of the response, which reflects Ins(1,4,5)P3- dependent calcium mobilization of intracellular stores, and a sustained phase of the response, which is due to calcium influx across the plasma membrane triggered by aperture of capacitative calcium channels (store-operated calcium channels). Upon repeated administration, ghrelin showed a marked suppression of ghrelin-mediated elevations of intracellular calcium. This homologous desensitization represents an important physiological mechanism that modulates receptor responsiveness and acts as an information filter for intracellular signaling system. The discovery of ghrelin adds a new component to the complex machinery responsible for regulation of GH secretion in connection with the regulation of appetite and energy homeostasis.

Leaf and Root Extracts from Campomanesia adamantium (Myrtaceae) Promote Apoptotic Death of Leukemic Cells via Activation of Intracellular Calcium and Caspase-3

PubMed Central

Campos, Jaqueline F.; Espindola, Priscilla P. de Toledo; Torquato, Heron F. V.; Vital, Wagner D.; Justo, Giselle Z.; Silva, Denise B.; Carollo, Carlos A.; de Picoli Souza, Kely; Paredes-Gamero, Edgar J.; dos Santos, Edson L.

2017-01-01

Phytochemical studies are seeking new alternatives to prevent or treat cancer, including different types of leukemias. Campomanesia adamantium, commonly known as guavira or guabiroba, exhibits pharmacological properties including antioxidant, antimicrobial, and antiproliferative activities. Considering the anticancer potential of this plant species, the aim of this study was to evaluate the antileukemic activity and the chemical composition of aqueous extracts from the leaves (AECL) and roots (AECR) of C. adamantium and their possible mechanisms of action. The extracts were analyzed by LC-DAD-MS, and their constituents were identified based on the UV, MS, and MS/MS data. The AECL and AECR showed different chemical compositions, which were identified as main compounds glycosylated flavonols from AECL and ellagic acid and their derivatives from AECR. The cytotoxicity promoted by these extracts were evaluated using human peripheral blood mononuclear cells and Jurkat leukemic cell line. The cell death profile was evaluated using annexin-V-FITC and propidium iodide labeling. Changes in the mitochondrial membrane potential, the activity of caspases, and intracellular calcium levels were assessed. The cell cycle profile was evaluated using propidium iodide. Both extracts caused concentration-dependent cytotoxicity only in Jurkat cells via late apoptosis. This activity was associated with loss of the mitochondrial membrane potential, activation of caspases-9 and -3, changes in intracellular calcium levels, and cell cycle arrest in S-phase. Therefore, the antileukemic activity of the AECL and AECR is mediated by mitochondrial dysfunction and intracellular messengers, which activate the intrinsic apoptotic pathway. Hence, aqueous extracts of the leaves and roots of C. adamantium show therapeutic potential for use in the prevention and treatment of diseases associated the proliferation of tumor cell. PMID:28855870

The Relative Influences of Phosphometabolites and pH on Action Potential Morphology during Myocardial Reperfusion: A Simulation Study

PubMed Central

Roberts, Byron N.; Christini, David J.

2012-01-01

Myocardial ischemia-reperfusion (IR) injury represents a constellation of pathological processes that occur when ischemic myocardium experiences a restoration of perfusion. Reentrant arrhythmias, which represent a particularly lethal manifestation of IR injury, can result when ischemic tissue exhibits decreased excitability and/or changes of action potential duration (APD), conditions that precipitate unidirectional conduction block. Many of the cellular components that are involved with IR injury are modulated by pH and/or phosphometabolites such as ATP and phosphocreatine (PCr), all of which can be manipulated in vivo and potentially in the clinical setting. Using a mathematical model of the cardiomyocyte that we previously developed to study ischemia and reperfusion, we performed a series of simulations with the aim of determining whether pH- or phosphometabolite-related processes play a more significant role in generating changes in excitability and action potential morphology that are associated with the development of reentry. In our simulations, persistent shortening of APD, action potential amplitude (APA), and depolarization of the resting membrane potential were more severe when ATP and PCr availability were suppressed during reperfusion than when extracellular pH recovery was inhibited. Reduced phosphometabolite availability and pH recovery affected multiple ion channels and exchangers. Some of these effects were the result of direct modulation by phosphometabolites and/or acidosis, while others resulted from elevated sodium and calcium loads during reperfusion. In addition, increasing ATP and PCr availability during reperfusion was more beneficial in terms of increasing APD and APA than was increasing the amount of pH recovery. Together, these results suggest that therapies directed at increasing ATP and/or PCr availability during reperfusion may be more beneficial than perturbing pH recovery with regard to mitigating action potential changes that increase the likelihood of reentrant arrhythmias. PMID:23144801

Klotho Up-regulates Renal Calcium Channel Transient Receptor Potential Vanilloid 5 (TRPV5) by Intra- and Extracellular N-glycosylation-dependent Mechanisms*

PubMed Central

Wolf, Matthias T. F.; An, Sung-Wan; Nie, Mingzhu; Bal, Manjot S.; Huang, Chou-Long

2014-01-01

The anti-aging protein Klotho is a type 1 membrane protein produced predominantly in the distal convoluted tubule. The ectodomain of Klotho is cleaved and secreted into the urine to regulate several ion channels and transporters. Secreted Klotho (sKL) up-regulates the TRPV5 calcium channel from the cell exterior by removing sialic acids from N-glycan of the channel and inhibiting its endocytosis. Because TRPV5 and Klotho coexpress in the distal convoluted tubule, we investigated whether Klotho regulates TRPV5 action from inside the cell. Whole-cell TRPV5-mediated channel activity was recorded in HEK cells coexpressing TRPV5 and sKL or membranous Klotho (mKL). Transfection of sKL, but not mKL, produced detectable Klotho protein in cell culture media. As for sKL, mKL increased TRPV5 current density. The role of sialidase activity of mKL acting inside is supported by findings that mutations of putative sialidase activity sites in sKL and mKL abrogated the regulation of TRPV5 but that the extracellular application of a sialidase inhibitor prevented the regulation of TRPV5 by sKL only. Mechanistically, coexpression with a dominant-negative dynamin II prevented the regulation of TRPV5 by sKL but not by mKL. In contrast, blocking forward trafficking by brefeldin A prevented the effect with mKL but not with sKL. Therefore, Klotho up-regulates TRPV5 from both the inside and outside of cells. The intracellular action of Klotho is likely due to enhanced forward trafficking of channel proteins, whereas the extracellular action is due to inhibition of endocytosis. Both effects involve putative Klotho sialidase activity. These effects of Klotho may play important roles regarding calcium reabsorption in the kidney. PMID:25378396

Altered profile of mRNA expression in atrioventricular node of streptozotocin-induced diabetic rats

PubMed Central

Howarth, Frank Christopher; Parekh, Khatija; Jayaprakash, Petrilla; Inbaraj, Edward Samuel; Oz, Murat; Dobrzynski, Halina; Adrian, Thomas Edward

2017-01-01

Prolonged action potential duration, reduced action potential firing rate, upstroke velocity and rate of diastolic depolarization have been demonstrated in atrioventricular node (AVN) cells from streptozotocin (STZ)-induced diabetic rats. To further clarify the molecular basis of these electrical disturbances, the mRNA profiles encoding a variety of proteins associated with the generation and conduction of electrical activity in the AVN, were evaluated in the STZ-induced diabetic rat heart. Expression of mRNA was measured in AVN biopsies using reverse transcription-quantitative polymerase chain reaction techniques. Notable differences in mRNA expression included upregulation of genes encoding membrane and intracellular Ca2+ transport, including solute carrier family 8 member A1, transient receptor potential channel 1, ryanodine receptor 2/3, hyperpolarization-activated cyclic-nucleotide 2 and 3, calcium channel voltage-dependent, β2 subunit and sodium channels 3a, 4a, 7a and 3b. In addition to this, potassium channels potassium voltage-gated channel subfamily A member 4, potassium channel calcium activated intermediate/small conductance subfamily N α member 2, potassium voltage-gated channel subfamily J members 3, 5, and 11, potassium channel subfamily K members 1, 2, 3 and natriuretic peptide B (BNP) were upregulated in AVN of STZ heart, compared with controls. Alterations in gene expression were associated with upregulation of various proteins including the inwardly rectifying, potassium channel Kir3.4, NCX1 and BNP. The present study demonstrated notable differences in the profile of mRNA encoding proteins associated with the generation, conduction and regulation of electrical signals in the AVN of the STZ-induced diabetic rat heart. These data will provide a basis for a substantial range of future studies to investigate whether variations in mRNA translate into alterations in electrophysiological function. PMID:28731153

Mechanism of As2O3-Induced Action Potential Prolongation and Using hiPS-CMs to Evaluate the Rescue Efficacy of Drugs With Different Rescue Mechanism.

PubMed

Yan, Meng; Feng, Lifang; Shi, Yanhui; Wang, Junnan; Liu, Yan; Li, Fengmei; Li, Baoxin

2017-08-01

Arsenic trioxide (As2O3) has been verified as a breakthrough in the management of acute promyelocytic leukemia in recent decades. However, cardiotoxicity, especially long QT syndrome (LQTS) has become the most important issue during As2O3 treatment. The characterized mechanisms behind this adverse effect are inhibition of cardiac hERG channel trafficking and increase of cardiac calcium currents. In our study, we found a new pathway underlying As2O3-induced cardiotoxicity that As2O3 accelerates lysosomal degradation of hERG on plasma membrane after using brefeldin A (BFA) to block protein trafficking. Then we explored pharmacological rescue strategies on As2O3-induced LQTS, and found that 4 therapeutic agents exert rescue efficacy via 3 different pathways: fexofenadine and astemizole facilitate hERG trafficking via promotion of channel-chaperone formation after As2O3 incubation; ranolazine slows hERG degradation in the presence of As2O3; and resveratrol shows significant attenuation on calcium current increase triggered by As2O3. Moreover, we used human-induced pluripotent stem cell derived cardiomyocytes (hiPS-CMs) to evaluate the rescue effects of the above agents on As2O3-induced prolongation of action potential duration (APD) and demonstrated that fexofenadine and resveratrol significantly ameliorate the prolonged APD. These observations suggested that pharmacological chaperone like fexofenadine and resveratrol might have the potential to protect against the cardiotoxicity of As2O3. © The Author 2017. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

The effect of immobilization and 3 (beta-aminoethyl)-1, 2, 4 triazol on the calcium content in gastric tissues of guinea pigs during the formation of experimental ulcers

NASA Technical Reports Server (NTRS)

Grechishkin, L. L.; Ritling, K.

1980-01-01

A sharp fall in the concentration of calcium in gastric tissues upon immobilization and after administration of the histamine analog was recorded. Similar shifts were seen to occur in the blood plasma as well. This implies that under the effect of different action, tissue dystrophy develops by following a common mechanism involving not only the adenyl cyclase system, but that of calcium ion metabolism as well. The calcium ion content in the blood plasma and gastric tissues were measured by atomic absorption spectrophotometry.

A Dynamical Threshold for Cardiac Delayed Afterdepolarization-Mediated Triggered Activity.

PubMed

Liu, Michael B; Ko, Christopher Y; Song, Zhen; Garfinkel, Alan; Weiss, James N; Qu, Zhilin

2016-12-06

Ventricular myocytes are excitable cells whose voltage threshold for action potential (AP) excitation is ∼-60 mV at which I Na is activated to give rise to a fast upstroke. Therefore, for a short stimulus pulse to elicit an AP, a stronger stimulus is needed if the resting potential lies further away from the I Na threshold, such as in hypokalemia. However, for an AP elicited by a long duration stimulus or a diastolic spontaneous calcium release, we observed that the stimulus needed was lower in hypokalemia than in normokalemia in both computer simulations and experiments of rabbit ventricular myocytes. This observation provides insight into why hypokalemia promotes calcium-mediated triggered activity, despite the resting potential lying further away from the I Na threshold. To understand the underlying mechanisms, we performed bifurcation analyses and demonstrated that there is a dynamical threshold, resulting from a saddle-node bifurcation mainly determined by I K1 and I NCX . This threshold is close to the voltage at which I K1 is maximum, and lower than the I Na threshold. After exceeding this dynamical threshold, the membrane voltage will automatically depolarize above the I Na threshold due to the large negative slope of the I K1 -V curve. This dynamical threshold becomes much lower in hypokalemia, especially with respect to calcium, as predicted by our theory. Because of the saddle-node bifurcation, the system can automatically depolarize even in the absence of I Na to voltages higher than the I Ca,L threshold, allowing for triggered APs in single myocytes with complete I Na block. However, because I Na is important for AP propagation in tissue, blocking I Na can still suppress premature ventricular excitations in cardiac tissue caused by calcium-mediated triggered activity. This suppression is more effective in normokalemia than in hypokalemia due to the difference in dynamical thresholds. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Flavonoids inhibit histamine release and expression of proinflammatory cytokines in mast cells.

PubMed

Park, Hyo-Hyun; Lee, Soyoung; Son, Hee-Young; Park, Seung-Bin; Kim, Mi-Sun; Choi, Eun-Ju; Singh, Thoudam S K; Ha, Jeoung-Hee; Lee, Maan-Gee; Kim, Jung-Eun; Hyun, Myung Chul; Kwon, Taeg Kyu; Kim, Yeo Hyang; Kim, Sang-Hyun

2008-10-01

Mast cells participate in allergy and inflammation by secreting inflammatory mediators such as histamine and proinflammatory cytokines. Flavonoids are naturally occurring molecules with antioxidant, cytoprotective, and antiinflammatory actions. However, effect of flavonoids on the release of histamine and proinflammatory mediator, and their comparative mechanism of action in mast cells were not well defined. Here, we compared the effect of six flavonoids (astragalin, fisetin, kaempferol, myricetin, quercetin, and rutin) on the mast cell-mediated allergic inflammation. Fisetin, kaempferol, myricetin, quercetin, and rutin inhibited IgE or phorbol-12-myristate 13-acetate and calcium ionophore A23187 (PMACI)-mediated histamine release in RBL-2H3 cells. These five flavonoids also inhibited elevation of intracellular calcium. Gene expressions and secretion of proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, and IL-8 were assessed in PMACI-stimulated human mast cells (HMC-1). Fisetin, quercetin, and rutin decreased gene expression and production of all the proinflammatory cytokines after PMACI stimulation. Myricetin attenuated TNF-alpha and IL-6 but not IL-1beta and IL-8. Fisetin, myricetin, and rutin suppressed activation of NF-kappaB indicated by inhibition of nuclear translocation of NF-kappaB, NF-kappaB/DNA binding, and NF-kappaB-dependent gene reporter assay. The pharmacological actions of these flavonoids suggest their potential activity for treatment of allergic inflammatory diseases through the down-regulation of mast cell activation.

Calcium signalling silencing in atrial fibrillation.

PubMed

Greiser, Maura

2017-06-15

Subcellular calcium signalling silencing is a novel and distinct cellular and molecular adaptive response to rapid cardiac activation. Calcium signalling silencing develops during short-term sustained rapid atrial activation as seen clinically during paroxysmal atrial fibrillation (AF). It is the first 'anti-arrhythmic' adaptive response in the setting of AF and appears to counteract the maladaptive changes that lead to intracellular Ca 2+ signalling instability and Ca 2+ -based arrhythmogenicity. Calcium signalling silencing results in a failed propagation of the [Ca 2+ ] i signal to the myocyte centre both in patients with AF and in a rabbit model. This adaptive mechanism leads to a substantial reduction in the expression levels of calcium release channels (ryanodine receptors, RyR2) in the sarcoplasmic reticulum, and the frequency of Ca 2+ sparks and arrhythmogenic Ca 2+ waves remains low. Less Ca 2+ release per [Ca 2+ ] i transient, increased fast Ca 2+ buffering strength, shortened action potentials and reduced L-type Ca 2+ current contribute to a substantial reduction of intracellular [Na + ]. These features of Ca 2+ signalling silencing are distinct and in contrast to the changes attributed to Ca 2+ -based arrhythmogenicity. Some features of Ca 2+ signalling silencing prevail in human AF suggesting that the Ca 2+ signalling 'phenotype' in AF is a sum of Ca 2+ stabilizing (Ca 2+ signalling silencing) and Ca 2+ destabilizing (arrhythmogenic unstable Ca 2+ signalling) factors. Calcium signalling silencing is a part of the mechanisms that contribute to the natural progression of AF and may limit the role of Ca 2+ -based arrhythmogenicity after the onset of AF. © 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.

Verapamil Protects Dopaminergic Neuron Damage through a Novel Anti-inflammatory Mechanism by Inhibition of Microglial Activation

PubMed Central

Liu, Yuxin; Lo, Yi-Ching; Qian, Li; Crews, Fulton Tim; Wilson, Belinda; Chen, Hui-Ling; Wu, Hung-Ming; Chen, Shih-Heng; Wei, Ke; Lu, Ru-Band; Ali, Syed; Hong, Jau-Shyong

2010-01-01

Verapamil has been shown to be neuroprotective in several acute neurotoxicity models due to blockade of calcium entry into neurons. However, the potential use of verapamil to treat chronic neurodegenerative diseases has not been reported. Using rat primary mesencephalic neuron/glia cultures, we report that verapamil significantly inhibited LPS-induced dopaminergic neurotoxicity in both pre- and post-treatment experiments. Reconstituted culture studies revealed that the presence of microglia was essential in verapamil-elicited neuroprotection. Mechanistic studies showed that decreased production of inflammatory mediators from LPS-stimulated microglia underlay neuroprotective property of verapamil. Further studies demonstrated that microglial NADPH oxidase (PHOX), the key superoxide-producing enzyme, but not calcium channel in neurons, is the site of action for the neuroprotective effect of verapamil. This conclusion was supported by the following two observations: 1) Verapamil failed to show protective effect on LPS-induced dopaminergic neurotoxicity in PHOX-deficient (deficient in the catalytic subunit of gp91phox) neuron/glia cultures; 2) Ligand binding studies showed that the binding of [3H]Verapamil onto gp91phox transfected COS-7 cell membranes was higher than the non-transfected control. The calcium channel-independent neuroprotective property of verapamil was further supported by the finding that R(+)-verapamil, a less active form in blocking calcium channel, showed the same potency in neuroprotection, inhibition of pro-inflammatory factors production and binding capacity to gp91phox membranes as R(-)-verapamil, the active isomer of calcium channel blocker. In conclusion, our results demonstrate a new indication of verapamil-mediated neuroprotection through a calcium channel-independent pathway and provide a valuable avenue for the development of therapy for inflammation-related neurodegenerative diseases. PMID:20950631

Inhibition of presynaptic calcium transients in cortical inputs to the dorsolateral striatum by metabotropic GABAB and mGlu2/3 receptors

PubMed Central

Kupferschmidt, David A; Lovinger, David M

2015-01-01

Cortical inputs to the dorsolateral striatum (DLS) are dynamically regulated during skill learning and habit formation, and are dysregulated in disorders characterized by impaired action control. Therefore, a mechanistic investigation of the processes regulating corticostriatal transmission is key to understanding DLS-associated circuit function, behaviour and pathology. Presynaptic GABAB and group II metabotropic glutamate (mGlu2/3) receptors exert marked inhibitory control over corticostriatal glutamate release in the DLS, yet the signalling pathways through which they do so are unclear. We developed a novel approach using the genetically encoded calcium (Ca2+) indicator GCaMP6 to assess presynaptic Ca2+ in corticostriatal projections to the DLS. Using simultaneous photometric presynaptic Ca2+ and striatal field potential recordings, we report that relative to P/Q-type Ca2+ channels, N-type channels preferentially contributed to evoked presynaptic Ca2+ influx in motor cortex projections to, and excitatory transmission in, the DLS. Activation of GABAB or mGlu2/3 receptors inhibited both evoked presynaptic Ca2+ transients and striatal field potentials. mGlu2/3 receptor-mediated depression did not require functional N-type Ca2+ channels, but was attenuated by blockade of P/Q-type channels. These findings reveal presynaptic mechanisms of inhibitory modulation of corticostriatal function that probably contribute to the selection and shaping of behavioural repertoires. Key points Plastic changes at cortical inputs to the dorsolateral striatum (DLS) underlie skill learning and habit formation, so characterizing the mechanisms by which these inputs are regulated is important for understanding the neural basis of action control. We developed a novel approach using the genetically encoded calcium (Ca2+) indicator GCaMP6 and brain slice photometry to assess evoked presynaptic Ca2+ transients in cortical inputs to the DLS and study their regulation by GABAB and mGlu2/3 receptors. GABAB and mGlu2/3 receptor activation caused clear reductions in electrical stimulus-evoked presynaptic Ca2+ transients in corticostriatal inputs to the DLS. Functional P/Q-type voltage-gated Ca2+ channels were required for the normal inhibitory action of corticostriatal mGlu2/3 receptors. We provide direct evidence of presynaptic Ca2+ inhibition by G protein-coupled receptors at corticostriatal projections. PMID:25781000

Voltage Gated Calcium Channel Activation by Backpropagating Action Potentials Downregulates NMDAR Function.

PubMed

Theis, Anne-Kathrin; Rózsa, Balázs; Katona, Gergely; Schmitz, Dietmar; Johenning, Friedrich W

2018-01-01

The majority of excitatory synapses are located on dendritic spines of cortical glutamatergic neurons. In spines, compartmentalized Ca 2+ signals transduce electrical activity into specific long-term biochemical and structural changes. Action potentials (APs) propagate back into the dendritic tree and activate voltage gated Ca 2+ channels (VGCCs). For spines, this global mode of spine Ca 2+ signaling is a direct biochemical feedback of suprathreshold neuronal activity. We previously demonstrated that backpropagating action potentials (bAPs) result in long-term enhancement of spine VGCCs. This activity-dependent VGCC plasticity results in a large interspine variability of VGCC Ca 2+ influx. Here, we investigate how spine VGCCs affect glutamatergic synaptic transmission. We combined electrophysiology, two-photon Ca 2+ imaging and two-photon glutamate uncaging in acute brain slices from rats. T- and R-type VGCCs were the dominant depolarization-associated Ca 2+ conductances in dendritic spines of excitatory layer 2 neurons and do not affect synaptic excitatory postsynaptic potentials (EPSPs) measured at the soma. Using two-photon glutamate uncaging, we compared the properties of glutamatergic synapses of single spines that express different levels of VGCCs. While VGCCs contributed to EPSP mediated Ca 2+ influx, the amount of EPSP mediated Ca 2+ influx is not determined by spine VGCC expression. On a longer timescale, the activation of VGCCs by bAP bursts results in downregulation of spine NMDAR function.

Discrete-State Stochastic Models of Calcium-Regulated Calcium Influx and Subspace Dynamics Are Not Well-Approximated by ODEs That Neglect Concentration Fluctuations

PubMed Central

Weinberg, Seth H.; Smith, Gregory D.

2012-01-01

Cardiac myocyte calcium signaling is often modeled using deterministic ordinary differential equations (ODEs) and mass-action kinetics. However, spatially restricted “domains” associated with calcium influx are small enough (e.g., 10−17 liters) that local signaling may involve 1–100 calcium ions. Is it appropriate to model the dynamics of subspace calcium using deterministic ODEs or, alternatively, do we require stochastic descriptions that account for the fundamentally discrete nature of these local calcium signals? To address this question, we constructed a minimal Markov model of a calcium-regulated calcium channel and associated subspace. We compared the expected value of fluctuating subspace calcium concentration (a result that accounts for the small subspace volume) with the corresponding deterministic model (an approximation that assumes large system size). When subspace calcium did not regulate calcium influx, the deterministic and stochastic descriptions agreed. However, when calcium binding altered channel activity in the model, the continuous deterministic description often deviated significantly from the discrete stochastic model, unless the subspace volume is unrealistically large and/or the kinetics of the calcium binding are sufficiently fast. This principle was also demonstrated using a physiologically realistic model of calmodulin regulation of L-type calcium channels introduced by Yue and coworkers. PMID:23509597

Accumulation of K+ in the synaptic cleft modulates activity by influencing both vestibular hair cell and calyx afferent in the turtle

PubMed Central

Contini, Donatella; Price, Steven D.

2016-01-01

Key points In the synaptic cleft between type I hair cells and calyceal afferents, K+ ions accumulate as a function of activity, dynamically altering the driving force and permeation through ion channels facing the synaptic cleft.High‐fidelity synaptic transmission is possible due to large conductances that minimize hair cell and afferent time constants in the presence of significant membrane capacitance.Elevated potassium maintains hair cells near a potential where transduction currents are sufficient to depolarize them to voltages necessary for calcium influx and synaptic vesicle fusion.Elevated potassium depolarizes the postsynaptic afferent by altering ion permeation through hyperpolarization‐activated cyclic nucleotide‐gated (HCN) channels, and contributes to depolarizing the afferent to potentials where a single EPSP (quantum) can generate an action potential.With increased stimulation, hair cell depolarization increases the frequency of quanta released, elevates [K+]cleft and depolarizes the afferent to potentials at which smaller and smaller EPSPs would be sufficient to trigger APs. Abstract Fast neurotransmitters act in conjunction with slower modulatory effectors that accumulate in restricted synaptic spaces found at giant synapses such as the calyceal endings in the auditory and vestibular systems. Here, we used dual patch‐clamp recordings from turtle vestibular hair cells and their afferent neurons to show that potassium ions accumulating in the synaptic cleft modulated membrane potentials and extended the range of information transfer. High‐fidelity synaptic transmission was possible due to large conductances that minimized hair cell and afferent time constants in the presence of significant membrane capacitance. Increased potassium concentration in the cleft maintained the hair cell near potentials that promoted the influx of calcium necessary for synaptic vesicle fusion. The elevated potassium concentration also depolarized the postsynaptic neuron by altering ion permeation through hyperpolarization‐activated cyclic nucleotide‐gated (HCN) channels. This depolarization enabled the afferent to reliably generate action potentials evoked by single AMPA‐dependent EPSPs. Depolarization of the postsynaptic afferent could also elevate potassium in the synaptic cleft, and would depolarize other hair cells enveloped by the same neuritic process increasing the fidelity of neurotransmission at those synapses as well. Collectively, these data demonstrate that neuronal activity gives rise to potassium accumulation, and suggest that potassium ion action on HCN channels can modulate neurotransmission, preserving the fidelity of high‐speed synaptic transmission by dynamically shifting the resting potentials of both presynaptic and postsynaptic cells. PMID:27633787

Endothelin induces two types of contractions of rat uterus: phasic contractions by way of voltage-dependent calcium channels and developing contractions through a second type of calcium channels

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

Kozuka, M.; Ito, T.; Hirose, S.

1989-02-28

Effects of endothelin on nonvascular smooth muscle have been examined using rat uterine horns and two modes of endothelin action have been revealed. Endothelin (0.3 nM) caused rhythmic contractions of isolated uterus in the presence of extracellular calcium. The rhythmic contractions were completely inhibited by calcium channel antagonists. These characteristics of endothelin-induced contractions were very similar to those induced by oxytocin. Binding assays using /sup 125/I-endothelin showed that endothelin and the calcium channel blockers did not compete for the binding sites. However, endothelin was unique in that it caused, in addition to rhythmic contractions, a slowly developing monophasic contraction thatmore » was insensitive to calcium channel blockers. This developing contraction became dominant at higher concentrations of endothelin and was also calcium dependent.« less

Cardiotonic action of two tannins

PubMed Central

Broadbent, J. L.

1962-01-01

A tannin isolated from Paullinia pinnata Linn., and tannic acid, have cardiotonic actions on the isolated perfused frog heart. Paullinia tannin is more firmly “fixed” than tannic acid. Tannin solutions contain peroxide, but the cardiotonic action is not dependent on this, since drugs believed to prevent peroxide formation, and sodium pyruvate which destroys peroxides, do not prevent the cardiotonic action. Maximal stimulation by tannin greatly reduces subsequent stimulation by ouabain. If calcium is omitted from the Ringer solution tannins cannot stimulate the heart. In this respect they differ from ouabain. However, the ouabain stimulation can be prevented by prior perfusion with tannin. It is suggested that the antagonism between tannin and ouabain is due to the former preventing ouabain from reaching its receptor sites, and that tannin stimulation is dependent on the formation of a calcium-tannin complex at the heart surface. In the isolated perfused mammalian heart preparation tannins increase diastolic tonus and coronary flow. PMID:13873207

A Comparative Study of Ion Diffusion from Calcium Hydroxide with Various Herbal Pastes through Dentin

PubMed Central

Dhirawani, Rajesh B; Marya, Jayant; Dhirawani, Vrinda; Kumar, Vijayendra

2017-01-01

Aim The aim of this study was to evaluate the diffusion ability of ions through dentinal tubules of different nonalcoholic calcium hydroxide-containing herbal pastes and compare it with the calcium hydroxide paste prepared with saline. Materials and methods A total of 36 single-rooted premolar teeth were used in this study. The tooth crowns were removed and the root canals were prepared. Depending on the vehicle to be used for preparing calcium hydroxide pastes, six groups were made: Group I: Ca(OH)2 saline paste (control group), group II: Ca(OH)2 papaya latex paste, group III: Ca(OH)2 coconut water paste, group IV: Ca(OH)2 Ashwagandha (Withania somnifera) paste, group V: Ca(OH)2 Tulsi (Ocimum tenuiflorum) paste, and group VI: Ca(OH)2 garlic (Allium sativum) paste. After biomechanical preparation, calcium hydroxide herbal paste dressings were applied and sealed with resin-based cement. The teeth were placed in containers with deionized water, and the pH of the water was measured at regular intervals over 3, 24, 72, and 168 hours. Results We observed that all herbal pastes allowed the diffusion of ions, but pastes prepared with Ashwagandha and papaya latex showed more ion diffusion after 168 hours and marked increase in pH, depicting better support for calcium hydroxide action. Conclusion We conclude that Ashwagandha and papaya latex allow better diffusion of calcium hydroxide through den-tinal tubules, thus enhancing its action, and advise its use as a vehicle for placing intracanal medicament. How to cite this article Dausage P, Dhirawani RB, Marya J, Dhirawani V, Kumar V. A Comparative Study of Ion Diffusion from Calcium Hydroxide with Various Herbal Pastes through Dentin. Int J Clin Pediatr Dent 2017;10(1):41-44. PMID:28377654

Chronic alcohol feeding potentiates hormone‐induced calcium signalling in hepatocytes

PubMed Central

Bartlett, Paula J.; Antony, Anil Noronha; Agarwal, Amit; Hilly, Mauricette; Prince, Victoria L.; Combettes, Laurent; Hoek, Jan B.

2017-01-01

Key points Chronic alcohol consumption causes a spectrum of liver diseases, but the pathogenic mechanisms driving the onset and progression of disease are not clearly defined.We show that chronic alcohol feeding sensitizes rat hepatocytes to Ca2+‐mobilizing hormones resulting in a leftward shift in the concentration–response relationship and the transition from oscillatory to more sustained and prolonged Ca2+ increases.Our data demonstrate that alcohol‐dependent adaptation in the Ca2+ signalling pathway occurs at the level of hormone‐induced inositol 1,4,5 trisphosphate (IP3) production and does not involve changes in the sensitivity of the IP3 receptor or size of internal Ca2+ stores.We suggest that prolonged and aberrant hormone‐evoked Ca2+ increases may stimulate the production of mitochondrial reactive oxygen species and contribute to alcohol‐induced hepatocyte injury. Abstract ‘Adaptive’ responses of the liver to chronic alcohol consumption may underlie the development of cell and tissue injury. Alcohol administration can perturb multiple signalling pathways including phosphoinositide‐dependent cytosolic calcium ([Ca2+]i) increases, which can adversely affect mitochondrial Ca2+ levels, reactive oxygen species production and energy metabolism. Our data indicate that chronic alcohol feeding induces a leftward shift in the dose–response for Ca2+‐mobilizing hormones resulting in more sustained and prolonged [Ca2+]i increases in both cultured hepatocytes and hepatocytes within the intact perfused liver. Ca2+ increases were initiated at lower hormone concentrations, and intercellular calcium wave propagation rates were faster in alcoholics compared to controls. Acute alcohol treatment (25 mm) completely inhibited hormone‐induced calcium increases in control livers, but not after chronic alcohol‐feeding, suggesting desensitization to the inhibitory actions of ethanol. Hormone‐induced inositol 1,4,5 trisphosphate (IP3) accumulation and phospholipase C (PLC) activity were significantly potentiated in hepatocytes from alcohol‐fed rats compared to controls. Removal of extracellular calcium, or chelation of intracellular calcium did not normalize the differences in hormone‐stimulated PLC activity, indicating calcium‐dependent PLCs are not upregulated by alcohol. We propose that the liver ‘adapts’ to chronic alcohol exposure by increasing hormone‐dependent IP3 formation, leading to aberrant calcium increases, which may contribute to hepatocyte injury. PMID:28220501

Spatiotemporal dynamics of rhythmic spinal interneurons measured with two-photon calcium imaging and coherence analysis.

PubMed

Kwan, Alex C; Dietz, Shelby B; Zhong, Guisheng; Harris-Warrick, Ronald M; Webb, Watt W

2010-12-01

In rhythmic neural circuits, a neuron often fires action potentials with a constant phase to the rhythm, a timing relationship that can be functionally significant. To characterize these phase preferences in a large-scale, cell type-specific manner, we adapted multitaper coherence analysis for two-photon calcium imaging. Analysis of simulated data showed that coherence is a simple and robust measure of rhythmicity for calcium imaging data. When applied to the neonatal mouse hindlimb spinal locomotor network, the phase relationships between peak activity of >1,000 ventral spinal interneurons and motor output were characterized. Most interneurons showed rhythmic activity that was coherent and in phase with the ipsilateral motor output during fictive locomotion. The phase distributions of two genetically identified classes of interneurons were distinct from the ensemble population and from each other. There was no obvious spatial clustering of interneurons with similar phase preferences. Together, these results suggest that cell type, not neighboring neuron activity, is a better indicator of an interneuron's response during fictive locomotion. The ability to measure the phase preferences of many neurons with cell type and spatial information should be widely applicable for studying other rhythmic neural circuits.

Evidence for postsynaptic modulation of muscle contraction by a Drosophila neuropeptide.

PubMed

Clark, Julie; Milakovic, Maja; Cull, Amanda; Klose, Markus K; Mercier, A Joffre

2008-07-01

DPKQDFMRFamide, the most abundant FMRFamide-like peptide in Drosophila melanogaster, has been shown previously to enhance contractions of larval body wall muscles elicited by nerve stimulation and to increase excitatory junction potentials (EJPs). The present work investigated the possibility that this peptide can also stimulate muscle contraction by a direct action on muscle fibers. DPKQDFMRFamide induced slow contractions and increased tonus in body wall muscles of Drosophila larvae from which the central nervous system had been removed. The threshold for this effect was approximately 10(-8)M. The increase in tonus persisted in the presence of 7x10(-3)M glutamate, which desensitized postsynaptic glutamate receptors. Thus, the effect on tonus could not be explained by enhanced release of glutamate from synaptic terminals and, thus, may represent a postsynaptic effect. The effect on tonus was abolished in calcium-free saline and by treatment with L-type calcium channel blockers, nifedipine and nicardipine, but not by T-type blockers, amiloride and flunarizine. The present results provide evidence that this Drosophila peptide can act postsynaptically in addition to its apparent presynaptic effects, and that the postsynaptic effect requires influx through L-type calcium channels.

[Strontium and calcium metabolism. Interaction of strontium and vitamin D].

PubMed

Rousselet, F; El Solh, N; Maurat, J P; Gruson, M; Girard, M L

1975-01-01

Oral administration of strontium to calcium wellfed rats blocks the intestinal absorption of calcium. When high doses of vitamine D are given over long period, the inhibition of calcium intestinal absorption disapears. Under these conditions the absorption of strontium is increased. It is suggested that there is only one absorption mechanism for these two cations. An overdose of the vitamine D increases the renal elimination of strontium but under these conditions the plasma concentration of the strontium is unchanged. Vitamine D brings about the some action on the bone fixation of the strontium as it does on the bone fixation of calcium. The bone fixation is increased with low dosages. The bone fixation is decreased with high dosages.

Calcium ion binding to a soil fulvic acid using a donnan potential model

USGS Publications Warehouse

Marinsky, J.A.; Mathuthu, A.; Ephraim, J.H.; Reddy, M.M.

1999-01-01

Calcium ion binding to a soil fulvic acid (Armadale Bh Horizon) was evaluated over a range of calcium ion concentrations, from pH 3.8 to 7.3, using potentiometric titrations and calcium ion electrode measurements. Fulvic acid concentration was constant (100 milligrams per liter) and calcium ion concentration varied up to 8 X 10-4 moles per liter. Experiments discussed here included: (1) titrations of fulvic acid-calcium ion containing solutions with sodium hydroxide; and (2) titrations of fully neutralized fulvic acid with calcium chloride solutions. Apparent binding constants (expressed as the logarithm of the value, log ??app) vary with solution pH, calcium ion concentration, degree of acid dissociation, and ionic strength (from log ??app = 2.5 to 3.9) and are similar to those reported by others. Fulvic acid charge, and the associated Donnan Potential, influences calcium ion-fulvic acid ion pair formation. A Donnan Potential corrrection term allowed calculation of intrinsic calcium ion-fulvic acid binding constants. Intrinsic binding constants vary from 1.2 to 2.5 (the average value is about log??= 1.6) and are similar to, but somewhat higher than, stability constants for calcium ion-carboxylic acid monodentate complexes. ?? by Oldenbourg Wissenschaftsverlag, Mu??nchen.

Calcium channel currents in bovine adrenal chromaffin cells and their modulation by anaesthetic agents.

PubMed Central

Charlesworth, P; Pocock, G; Richards, C D

1994-01-01

1. The calcium channel currents of bovine adrenal chromaffin cells were characterized using a variety of voltage pulse protocols and selective channel blockers before examination of their modulation by anaesthetic agents. 2. All the anaesthetics studied (halothane, methoxyflurane, etomidate and methohexitone) inhibited the calcium channel currents in a concentration-dependent manner and increased the rate of current decay. 3. The anaesthetics did not shift the current-voltage relation nor did they change the voltage for half-maximal channel activation derived from analysis of the voltage dependence of the tail currents. None of the anaesthetics appeared to alter the time constant of tail current decay. 4. To complement earlier studies of the inhibitory actions of anaesthetics on K(+)-evoked catecholamine secretion and the associated Ca2+ uptake, the IC50 values for etomidate and methohexitone were determined using a biochemical assay. The IC50 values for anaesthetic inhibition of calcium channel currents corresponded closely with those for inhibition of K(+)-evoked calcium uptake and catecholamine secretion. 5. The inhibitory effect of the volatile anaesthetics and etomidate is best explained by dual action: a reduction in the probability of channel opening coupled with an increase in the rate of channel inactivation. Methohexitone appeared to inhibit the currents by a use-dependent slow block. PMID:7707224

Antidiabetic effect of Achillea millefollium through multitarget interactions: α-glucosidases inhibition, insulin sensitization and insulin secretagogue activities.

PubMed

Chávez-Silva, Fabiola; Cerón-Romero, Litzia; Arias-Durán, Luis; Navarrete-Vázquez, Gabriel; Almanza-Pérez, Julio; Román-Ramos, Rubén; Ramírez-Ávila, Guillermo; Perea-Arango, Irene; Villalobos-Molina, Rafael; Estrada-Soto, Samuel

2018-02-15

Achillea millefolium L. (Asteraceae) is a perennial herb used in Mexican folk medicine for treatment of several pathologies, including inflammatory and spasmodic gastrointestinal disorders, hepatobiliary complaints, overactive cardiovascular, respiratory ailments and diabetes. To evaluate the potential antidiabetic effect in vivo and to establish the potential mode of action through in vitro approaches of Achillea millefolium. The antidiabetic effect of hydroalcoholic extract of Achillea millefolium (HAEAm) was evaluated on the oral glucose tolerance tests, in normoglycemic and experimental Type 2 diabetic mice models. In addition, we evaluated the possible mode of action in in vitro assays to determine α-glucosidases inhibition, the insulin secretion and calcium mobilization in RINm5F cells and PPARγ and GLUT4 expression in 3T3-L1 cells. HAEAm showed significant glucose diminution on oral glucose tolerance test and in acute experimental Type 2 diabetic assay with respect to the control (p < 0.05). In addition, HAEAm promoted the α-glucosidases inhibition by 55% at 1mg/ml respect to control. On the other hand, HAEAm increased the PPARγ (five-times) and GLUT4 (two-fold) relative expression than control (p < 0.05). Finally, HAEAm significantly increased the insulin secretion and [Ca 2+ ] i compared with control. The HAEAm possesses in vivo antidiabetic effect, having such effect through multitarget modes of action that involve antihyperglycemic (α-glucosidases inhibition), hypoglycemic (insulin secretion) and potential insulin sensitizer (PPARγ/GLUT4 overexpression) actions. Copyright © 2017 Elsevier B.V. All rights reserved.

Quantifying fat, oil, and grease deposit formation kinetics.

PubMed

Iasmin, Mahbuba; Dean, Lisa O; Ducoste, Joel J

2016-01-01

Fat, oil, and grease (FOG) deposits formed in sanitary sewers are calcium-based saponified solids that are responsible for a significant number of nationwide sanitary sewer overflows (SSOs) across United States. In the current study, the kinetics of lab-based saponified solids were determined to understand the kinetics of FOG deposit formation in sewers for two types of fat (Canola and Beef Tallow) and two types of calcium sources (calcium chloride and calcium sulfate) under three pH (7 ± 0.5, 10 ± 0.5, and ≈14) and two temperature conditions (22 ± 0.5 and 45 ± 0.5 °C). The results of this study displayed quick reactions of a fraction of fats with calcium ions to form calcium based saponified solids. Results further showed that increased palmitic fatty acid content in source fats, the magnitude of the pH, and temperature significantly affect the FOG deposit formation and saponification rates. The experimental data of the kinetics were compared with two empirical models: a) Cotte saponification model and b) Foubert crystallization model and a mass-action based mechanistic model that included alkali driven hydrolysis of triglycerides. Results showed that the mass action based mechanistic model was able to predict changes in the rate of formation of saponified solids under the different experimental conditions compared to both empirical models. The mass-action based saponification model also revealed that the hydrolysis of Beef Tallow was slower compared to liquid Canola fat resulting in smaller quantities of saponified solids. This mechanistic saponification model, with its ability to track the saponified solids chemical precursors, may provide an initial framework to predict the spatial formation of FOG deposits in municipal sewers using system wide sewer collection modeling software. Copyright © 2015 Elsevier Ltd. All rights reserved.

Increasing dietary phosphorus intake from food additives: potential for negative impact on bone health.

PubMed

Takeda, Eiji; Yamamoto, Hironori; Yamanaka-Okumura, Hisami; Taketani, Yutaka

2014-01-01

It is important to consider whether habitual high phosphorus intake adversely affects bone health, because phosphorus intake has been increasing, whereas calcium intake has been decreasing in dietary patterns. A higher total habitual dietary phosphorus intake has been associated with higher serum parathyroid hormone (PTH) and lower serum calcium concentrations in healthy individuals. Higher serum PTH concentrations have been shown in those who consume foods with phosphorus additives. These findings suggest that long-term dietary phosphorus loads and long-term hyperphosphatemia may have important negative effects on bone health. In contrast, PTH concentrations did not increase as a result of high dietary phosphorus intake when phosphorus was provided with adequate amounts of calcium. Intake of foods with a ratio of calcium to phosphorus close to that found in dairy products led to positive effects on bone health. Several randomized controlled trials have shown positive relations between dairy intake and bone mineral density. In our loading test with a low-calcium, high-phosphorus lunch provided to healthy young men, serum PTH concentrations showed peaks at 1 and 6 h, and serum fibroblast growth factor 23 (FGF23) concentrations increased significantly at 8 h after the meal. In contrast, the high-calcium, high-phosphorus meal suppressed the second PTH and FGF23 elevations until 8 h after the meal. This implies that adequate dietary calcium intake is needed to overcome the interfering effects of high phosphorus intake on PTH and FGF23 secretion. FGF23 acts on the parathyroid gland to decrease PTH mRNA and PTH secretion in rats with normal kidney function. However, increased serum FGF23 is an early alteration of mineral metabolism in chronic kidney disease, causing secondary hyperthyroidism, and implying resistance of the parathyroid gland to the action of FGF23 in chronic kidney disease. These findings suggest that long-term high-phosphorus diets may impair bone health mediated by FGF23 resistance both in chronic kidney disease patients and in the healthy population.

Aspects of Solvent Chemistry for Calcium Hydroxide Medicaments

PubMed Central

Athanassiadis, Basil

2017-01-01

Calcium hydroxide pastes have been used in endodontics since 1947. Most current calcium hydroxide endodontic pastes use water as the vehicle, which limits the dissolution of calcium hydroxide that can be achieved and, thereby, the maximum pH that can be achieved within the root canal system. Using polyethylene glycol as a solvent, rather than water, can achieve an increase in hydroxyl ions release compared to water or saline. By adopting non-aqueous solvents such as the polyethylene glycols (PEG), greater dissolution and faster hydroxyl ion release can be achieved, leading to enhanced antimicrobial actions, and other improvements in performance and biocompatibility. PMID:29065542

Ameliorative effect of Vernonia cinerea in vincristine-induced painful neuropathy in rats.

PubMed

Thiagarajan, Venkata Rathina Kumar; Shanmugam, Palanichamy; Krishnan, Uma Maheswari; Muthuraman, Arunachalam

2014-10-01

The present study was designed to investigate the antinociceptive potential of Vernonia cinerea (VC) on vincristine-induced painful neuropathy in rats. A chemotherapeutic agent, vincristine (50 μg/kg intraperitoneally for 10 consecutive days), was administered for the induction of neuropathic pain in rats. The painful behavioral changes were assessed using hot plate, acetone drop, paw pressure, Von Frey hair and tail immersion tests to assess the degree of hyperalgesic and allodynic pain sensation in paw and tail. Tissue biomarker changes including thiobarbituric acid reactive substances (TBARSs), reduced glutathione (GSH) and total calcium levels were estimated in sciatic nerve tissue samples to assess the degree of oxidative stress. Histopathological changes were also observed in transverse sections of rat sciatic nerve tissue. Ethanolic extract of VC leaves and pregabalin were administered for 14 consecutive days from day 0 (day of surgery). Pregabalin served as a positive control in the present study. Vincristine administration resulted in a significant reduction in painful behavioral changes along with a rise in the levels of TBARS, total calcium and decrease in GSH levels when compared with the normal control group. Furthermore, significant histopathological changes were also observed. Pretreatment with VC significantly attenuated vincristine-induced development of painful behavioral, biochemical and histological changes in a dose-dependent manner, which is similar to that of pregabalin-pretreated group. The attenuating effect of VC in vincristine-induced nociceptive painful sensation may be due to its potential of antioxidative, neuroprotective and calcium channel inhibitory action. © The Author(s) 2012.

Mercaptoacetate and fatty acids exert direct and antagonistic effects on nodose neurons via GPR40 fatty acid receptors.

PubMed

Darling, Rebecca A; Zhao, Huan; Kinch, Dallas; Li, Ai-Jun; Simasko, Steven M; Ritter, Sue

2014-07-01

β-mercaptoacetate (MA) is a drug known to block mitochondrial oxidation of medium- and long-chain fatty acids (FAs) and to stimulate feeding. Because MA-induced feeding is vagally dependent, it has been assumed that the feeding response is mediated by MA's antimetabolic action at a peripheral, vagally innervated site. However, MA's site of action has not yet been identified. Therefore, we used fluorescent calcium measurements in isolated neurons from rat nodose ganglia to determine whether MA has direct effects on vagal sensory neurons. We found that MA alone did not alter cytosolic calcium concentrations in nodose neurons. However, MA (60 μM to 6 mM) significantly decreased calcium responses to both linoleic acid (LA; 10 μM) and caprylic acid (C8; 10 μM) in all neurons responsive to LA and C8. GW9508 (40 μM), an agonist of the FA receptor, G protein-coupled receptor 40 (GPR40), also increased calcium levels almost exclusively in FA-responsive neurons. MA significantly inhibited this response to GW9508. MA did not inhibit calcium responses to serotonin, high K(+), or capsaicin, which do not utilize GPRs, or to CCK, which acts on a different GPR. GPR40 was detected in nodose ganglia by RT-PCR. Results suggest that FAs directly activate vagal sensory neurons via GPR40 and that MA antagonizes this effect. Thus, we propose that MA's nonmetabolic actions on GPR40 membrane receptors, expressed by multiple peripheral tissues in addition to the vagus nerve, may contribute to or mediate MA-induced stimulation of feeding. Copyright © 2014 the American Physiological Society.

Effect of calcium and magnesium on the antimicrobial action of enterocin LR/6 produced by Enterococcus faecium LR/6.

PubMed

Kumar, Manoj; Srivastava, Sheela

2011-06-01

Enterococci are well-known producers of antimicrobial peptides (enterocins) that possess potential as biopreservatives in food. In this study, divalent cations and release of intracellular potassium were used to assess the mechanism of interaction and killing of enterocin LR/6 produced by Enterococcus faecium LR/6 on three target Gram-positive and Gram-negative bacteria, namely Micrococcus luteus, Enterococcus sp. strain LR/3 and Escherichia coli K-12. Whilst treatment with enterocin LR/6 in all cases led to a significant loss of viability, suggesting a bactericidal mode of action, E. coli K-12 showed better tolerance than the other two strains. Bacteriocins have generally been reported to create pores in the membrane of sensitive cells and this function is diminished by divalent cations. In this study it was shown that Ca(2+) and Mg(2+) markedly improved the viability of enterocin LR/6-treated cells in a concentration-dependent manner. K(+) release as a sign of membrane leakiness was higher in M. luteus compared with the other two test strains. In agreement with the viability response, pre-exposure to Ca(2+) and Mg(2+) substantially reduced the amount of K(+) leakage by M. luteus and Enterococcus sp.; in the case of E. coli K-12, no leakage of K(+) was recorded. These results suggest that enterocin LR/6, which possesses good antibacterial potential, may not be very effective as a preservative in foods containing high concentrations of calcium and magnesium. Copyright © 2011 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.

Photoaffinity labelling of MSH receptors on Anolis melanophores: effects of catecholamines, calcium and forskolin.

PubMed

Eberle, A N; Girard, J

1985-01-01

Photoaffinity labelling of MSH receptors on Anolis melanophores was used as a tool for studying the effects of catecholamines, calcium and forskolin on hormone-receptor interaction and receptor-adenylate cyclase coupling. Covalent attachment of photoreactive alpha-MSH to its receptor was suppressed in calcium-free buffer but was hardly influenced by catecholamines or forskolin. The longlasting signal generated by the covalent MSH-receptor complex was readily and reversibly abolished by adrenaline, noradrenaline, dopamine or clonidine or by the absence of calcium. The suppression of pigment dispersion by catecholamines was blocked by the simultaneous presence of yohimbine but not prazosin, indicating that the catecholamines antagonize the alpha-MSH signal by inhibitory action on the adenylate cyclase system through an alpha-2 receptor. Forskolin, which stimulates melanophores by direct action on the catalytic unit of the adenylate cyclase and at about the same speed as alpha-MSH, produced a slower and weaker response in the presence of noradrenaline. If MSH receptors were covalently labelled and then exposed to noradrenaline, the characteristics of the forskolin-induced response were identical to those of unlabelled cells that had not been exposed to noradrenaline. This may point to a partial restoration of receptor-adenylate cyclase coupling by forskolin. The results show that the longlasting stimulation of Anolis melanophores by photoaffinity labelling proceeds via a permanently stimulated adenylate-cyclase system whose coupling to the receptor depends on calcium and is abolished by alpha-2 receptor agonists. Calcium is also essential for hormone-receptor binding.

Intracellular calcium: a prerequisite for aldosterone action.

PubMed

Schäfer, C; Shahin, V; Albermann, L; Schillers, H; Hug, M J; Oberleithner, H

2003-12-01

Transport of salt and water in various tissues is under control of the mineralocorticoid hormone aldosterone. As a liphophilic hormone, aldosterone diffuses through the plasma membrane and, then, binds to cytosolic mineralocorticoid receptors in the target cells. After binding to nuclear pore complexes, the activated receptor is translocated to the nucleus where transcription processes are initiated. After a lag period of about 20 minutes hormone-specific early mRNA transcripts leave the nucleus through nuclear pores. Some of the steps in this cascade can be followed by electrophysiology in Xenopus laevis oocyte nuclei. In addition to the genomic pathway, aldosterone exerts a rapid pre-genomic response that involves an increase in intracellular calcium. In this study, we tested for the potential role of Ca(2+) in the genomic response of the hormone. We measured the electrical resistance across the nuclear envelope in response to aldosterone, in presence and absence of intracellular Ca(2+). Nuclear envelope electrical resistance reflects receptor binding to the nuclear pore complexes ("early" resistance peak, 2 minutes after aldosterone), ongoing transcription ("transient" resistance drop, 5-15 minutes after aldosterone) and mRNA export ("late" resistance peak, 20 minutes after aldosterone). Pre-injection of the Ca(2+) chelator EGTA eliminated all electrical responses evoked by aldosterone. The transient resistance drop and the late resistance peak, induced by the hormone, were prevented by the transcription inhibitor actinomycin D, coinjected with aldosterone, while the early resistance peak remained unaffected. We conclude that (i). the presence of intracellular Ca(2+) is a prerequisite for the genomic action of aldosterone. (ii). Intracellular calcium plays a role early in the signaling cascade, either in agonist-receptor interaction, or receptor transport/docking to the nuclear pore complexes.

Occupation of low-affinity cholecystokinin (CCK) receptors by CCK activates signal transduction and stimulates amylase secretion in pancreatic acinar cells.

PubMed

Vinayek, R; Patto, R J; Menozzi, D; Gregory, J; Mrozinski, J E; Jensen, R T; Gardner, J D

1993-03-10

Based on the effects of monensin on binding of 125I-CCK-8 and its lack of effect on CCK-8-stimulated amylase secretion we previously proposed that pancreatic acinar cells possess three classes of CCK receptors: high-affinity receptors, low-affinity receptors and very low-affinity receptors [1]. In the present study we treated pancreatic acini with carbachol to induce a complete loss of high-affinity CCK receptors and then examined the action of CCK-8 on inositol trisphosphate IP3(1,4,5), cytosolic calcium and amylase secretion in an effort to confirm and extend our previous hypothesis. We found that first incubating pancreatic acini with 10 mM carbachol decreased binding of 125I-CCK-8 measured during a second incubation by causing a complete loss of high-affinity CCK receptors with no change in the low-affinity CCK receptors. Carbachol treatment of acini, however, did not alter the action of CCK-8 on IP3(1,4,5), cytosolic calcium or amylase secretion or the action of CCK-JMV-180 on amylase secretion or on the supramaximal inhibition of amylase secretion caused by CCK-8. The present findings support our previous hypothesis that pancreatic acinar cells possess three classes of CCK receptors and suggest that high-affinity CCK receptors do not mediate the action of CCK-8 on enzyme secretion, that low-affinity CCK receptors may mediate the action of CCK on cytosolic calcium that does not involve IP3(1,4,5) and produce the upstroke of the dose-response curve for CCK-8-stimulated amylase secretion and that very low-affinity CCK receptors mediate the actions of CCK on IP3(1,4,5) and cytosolic calcium and produce the downstroke of the dose-response curve for CCK-8-stimulated amylase secretion. Moreover, CCK-JMV-180 is a full agonist for stimulating amylase secretion by acting at low-affinity CCK receptors and is an antagonist at very low-affinity CCK receptors.

High-Throughput Phenotyping of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes and Neurons Using Electric Field Stimulation and High-Speed Fluorescence Imaging

PubMed Central

Daily, Neil J.; Du, Zhong-Wei

2017-01-01

Abstract Electrophysiology of excitable cells, including muscle cells and neurons, has been measured by making direct contact with a single cell using a micropipette electrode. To increase the assay throughput, optical devices such as microscopes and microplate readers have been used to analyze electrophysiology of multiple cells. We have established a high-throughput (HTP) analysis of action potentials (APs) in highly enriched motor neurons and cardiomyocytes (CMs) that are differentiated from human induced pluripotent stem cells (iPSCs). A multichannel electric field stimulation (EFS) device enabled the ability to electrically stimulate cells and measure dynamic changes in APs of excitable cells ultra-rapidly (>100 data points per second) by imaging entire 96-well plates. We found that the activities of both neurons and CMs and their response to EFS and chemicals are readily discerned by our fluorescence imaging-based HTP phenotyping assay. The latest generation of calcium (Ca2+) indicator dyes, FLIPR Calcium 6 and Cal-520, with the HTP device enables physiological analysis of human iPSC-derived samples highlighting its potential application for understanding disease mechanisms and discovering new therapeutic treatments. PMID:28525289

Pharmacology of the Phosphate Binder, Lanthanum Carbonate

PubMed Central

Damment, Stephen JP

2011-01-01

Studies were conducted to compare the phosphate-binding efficacy of lanthanum carbonate directly with other clinically used phosphate binders and to evaluate any potential adverse pharmacology. To examine the phosphate-binding efficacy, rats with normal renal function and chronic renal failure received lanthanum carbonate, aluminum hydroxide, calcium carbonate, or sevelamer hydrochloride in several experimental models. Lanthanum carbonate and aluminum hydroxide markedly increased excretion of [32P]-phosphate in feces and reduced excretion in urine in rats with normal renal function (p < 0.05), indicating good dietary phosphate-binding efficacy. In rats with chronic renal failure, lanthanum carbonate and aluminum hydroxide reduced urinary phosphate excretion to a greater degree and more rapidly than calcium carbonate, which in turn was more effective than sevelamer hydrochloride. The potential to induce adverse pharmacological effects was assessed systematically in mice, rats, and dogs with normal renal function using standard in vivo models. There was no evidence of any adverse secondary pharmacological effects of lanthanum carbonate on the central nervous, cardiovascular, respiratory, or gastrointestinal systems. These studies indicate that lanthanum carbonate is the more potent of the currently available dietary phosphate binders. No adverse secondary pharmacological actions were observed in vivo in a systematic evaluation at high doses. PMID:21332344

Cytoprotective mechanism of action of curcumin against cataract.

PubMed

Raman, Thiagarajan; Ramar, Manikandan; Arumugam, Munusamy; Nabavi, Seyed Mohammad; Varsha, Mosur Kumaraswamy Nagarajan Sai

2016-06-01

This review discusses the relationship between oxidative stress and cataract formation, molecular mechanism of curcumin action and potential benefits of treatment with the antioxidant curcumin. The first section deals with curcumin and endogenous antioxidants. The second section focuses on the action of curcumin on lipid peroxidation. Calcium homeostasis and curcumin will be discussed in the third section. The fourth section discusses the role of crystallin proteins that are responsible for maintaining lens transparency and the role of curcumin in regulating crystallin expression. The interaction of curcumin with transcription factors will be dealt in the fifth section. The final section will focus on the effect of curcumin on aldose reductase, which is associated with hyperglycemia and cataract. One of the strongest antioxidants is curcumin which has been shown to be very effective against cataract. This compound is better than other antioxidants in preventing cataract but its limited bioavailability can be addressed by employing nanotechnology. Copyright © 2016 Institute of Pharmacology, Polish Academy of Sciences. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.

[Current Topics on Vitamin D. The vitamin D functions in keratinocytes and its therapeutic applications].

PubMed

Sawatsubashi, Shun

2015-03-01

1,25 (OH) 2D and calcium have been shown to promote epidermal keratinocyte differentiation and prevent proliferation. These prodifferentiation and antiproliferative effects of 1,25 (OH) 2D have led to its clinical use in the treatment of psoriasis. However, the mechanism of vitamin D action on keratinocytes remains largely unknown. While the actions of calcium and the vitamin D receptor signaling pathways on epidermal keratinocyte differentiation are redundant, their effects on the hair follicle are not. In this review, we discuss how the vitamin D and its receptor contribute to skin and hair follicle homeostasis.

Calcium kinetics during bed rest with artificial gravity and exercise countermeasures

USDA-ARS?s Scientific Manuscript database

We assessed the potential for countermeasures to lessen the loss of bone calcium during bed rest. Subjects ingested less calcium during bed rest, and with artificial gravity, they also absorbed less calcium. With exercise, they excreted less calcium. To retain bone during bed rest, calcium intake ne...

In vitro study of the effect of a dentifrice containing 8% arginine, calcium carbonate, and sodium monofluorophosphate on acid-softened enamel.

PubMed

Rege, Aarti; Heu, Rod; Stranick, Michael; Sullivan, Richard J

2014-01-01

To investigate the possible mode of action of a dentifrice containing 8% arginine and calcium carbonate (Pro-Argin Technology), and sodium monofluorophosphate in delivering the benefits of preventing acid erosion and rehardening acid-softened enamel. The surfaces of acid-softened bovine enamel specimens were evaluated after application of a dentifrice containing 8% arginine, calcium carbonate, and sodium monofluorophosphate in vitro. Scanning Electron Microscopy (SEM), Electronic Spectrometry for Chemical Analysis (ESCA), and Secondary Ion Mass Spectrometry (SIMS) were used to characterize the enamel surfaces. Exposure of pristine enamel surfaces to citric acid resulted in clear roughening of the surface. Multiple applications of a dentifrice containing 8% arginine, calcium carbonate, and sodium monofluorophosphate to the surface of the enamel resulted in the disappearance of the microscopic voids observed by SEM as a function of treatment applications. The ESCA analysis demonstrated that both the nitrogen and carbonate levels increased as the number of treatments increased, which provides evidence that arginine and calcium carbonate were bound to the surface. Observance of arginine's signature mass fragmentation pattern by SIMS analysis confirmed the identity of arginine on the enamel surface. A series of in vitro experiments has demonstrated a possible mode of action by which a dentifrice containing 8% arginine, calcium carbonate, and sodium monofluorophosphate delivers the benefits of preventing acid erosion and rehardening acid-softened enamel. The combination of arginine and calcium carbonate adheres to the enamel surface and helps to fill the microscopic gaps created by acid, which in turn helps repair the enamel and provides a protective coating against future acid attacks.

Effects of Calcium Spikes in the Layer 5 Pyramidal Neuron on Coincidence Detection and Activity Propagation

PubMed Central

Chua, Yansong; Morrison, Abigail

2016-01-01

The role of dendritic spiking mechanisms in neural processing is so far poorly understood. To investigate the role of calcium spikes in the functional properties of the single neuron and recurrent networks, we investigated a three compartment neuron model of the layer 5 pyramidal neuron with calcium dynamics in the distal compartment. By performing single neuron simulations with noisy synaptic input and occasional large coincident input at either just the distal compartment or at both somatic and distal compartments, we show that the presence of calcium spikes confers a substantial advantage for coincidence detection in the former case and a lesser advantage in the latter. We further show that the experimentally observed critical frequency phenomenon, in which action potentials triggered by stimuli near the soma above a certain frequency trigger a calcium spike at distal dendrites, leading to further somatic depolarization, is not exhibited by a neuron receiving realistically noisy synaptic input, and so is unlikely to be a necessary component of coincidence detection. We next investigate the effect of calcium spikes in propagation of spiking activities in a feed-forward network (FFN) embedded in a balanced recurrent network. The excitatory neurons in the network are again connected to either just the distal, or both somatic and distal compartments. With purely distal connectivity, activity propagation is stable and distinguishable for a large range of recurrent synaptic strengths if the feed-forward connections are sufficiently strong, but propagation does not occur in the absence of calcium spikes. When connections are made to both the somatic and the distal compartments, activity propagation is achieved for neurons with active calcium dynamics at a much smaller number of neurons per pool, compared to a network of passive neurons, but quickly becomes unstable as the strength of recurrent synapses increases. Activity propagation at higher scaling factors can be stabilized by increasing network inhibition or introducing short term depression in the excitatory synapses, but the signal to noise ratio remains low. Our results demonstrate that the interaction of synchrony with dendritic spiking mechanisms can have profound consequences for the dynamics on the single neuron and network level. PMID:27499740

Effects of Calcium Spikes in the Layer 5 Pyramidal Neuron on Coincidence Detection and Activity Propagation.

PubMed

Chua, Yansong; Morrison, Abigail

2016-01-01

The role of dendritic spiking mechanisms in neural processing is so far poorly understood. To investigate the role of calcium spikes in the functional properties of the single neuron and recurrent networks, we investigated a three compartment neuron model of the layer 5 pyramidal neuron with calcium dynamics in the distal compartment. By performing single neuron simulations with noisy synaptic input and occasional large coincident input at either just the distal compartment or at both somatic and distal compartments, we show that the presence of calcium spikes confers a substantial advantage for coincidence detection in the former case and a lesser advantage in the latter. We further show that the experimentally observed critical frequency phenomenon, in which action potentials triggered by stimuli near the soma above a certain frequency trigger a calcium spike at distal dendrites, leading to further somatic depolarization, is not exhibited by a neuron receiving realistically noisy synaptic input, and so is unlikely to be a necessary component of coincidence detection. We next investigate the effect of calcium spikes in propagation of spiking activities in a feed-forward network (FFN) embedded in a balanced recurrent network. The excitatory neurons in the network are again connected to either just the distal, or both somatic and distal compartments. With purely distal connectivity, activity propagation is stable and distinguishable for a large range of recurrent synaptic strengths if the feed-forward connections are sufficiently strong, but propagation does not occur in the absence of calcium spikes. When connections are made to both the somatic and the distal compartments, activity propagation is achieved for neurons with active calcium dynamics at a much smaller number of neurons per pool, compared to a network of passive neurons, but quickly becomes unstable as the strength of recurrent synapses increases. Activity propagation at higher scaling factors can be stabilized by increasing network inhibition or introducing short term depression in the excitatory synapses, but the signal to noise ratio remains low. Our results demonstrate that the interaction of synchrony with dendritic spiking mechanisms can have profound consequences for the dynamics on the single neuron and network level.

Thapsigargin defines the roles of cellular calcium in secretagogue-stimulated enzyme secretion from pancreatic acini.

PubMed

Metz, D C; Patto, R J; Mrozinski, J E; Jensen, R T; Turner, R J; Gardner, J D

1992-10-15

In the present study we used thapsigargin (TG), an inhibitor of microsomal calcium ATPase, to evaluate the roles of free cytoplasmic calcium and intracellular stored calcium in secretagogue-stimulated enzyme secretion from rat pancreatic acini. Using microspectrofluorimetry of fura-2-loaded pancreatic acini, we found that TG caused a sustained increase in free cytoplasmic calcium by mobilizing calcium from inositol 1,4,5-trisphosphate-sensitive intracellular stores and by increasing influx of extracellular calcium. TG also caused a small increase in basal amylase secretion, inhibited the stimulation of amylase secretion caused by secretagogues that increase inositol 1,4,5-trisphosphate, and potentiated the stimulation of amylase secretion caused by 12-O-tetradecanoylphorbol-13-acetate or secretagogues that increase cyclic adenosine 3',5'-monophosphate. Bombesin, which like TG increased free cytoplasmic calcium, also potentiated the stimulation of amylase secretion caused by secretagogues that increase cyclic adenosine 3',5'-monophosphate, but did not inhibit the stimulation of amylase secretion caused by secretagogues that increase inositol 1,4,5-trisphosphate. Finally, TG inhibited the sustained phase of cholecystokinin-stimulated amylase secretion and potentiated the time course of vasoactive intestinal peptide-stimulated amylase secretion. The present findings indicate that stimulation of amylase secretion by secretagogues that increase inositol 1,4,5-trisphosphate does not depend on increased free cytoplasmic calcium per se. In contrast, TG-induced potentiation of the stimulation of secretagogues that increase cellular cyclic adenosine 3',5'-monophosphate appears to result from increased free cytoplasmic calcium per se.

Burst discharges in neurons of the thalamic reticular nucleus are shaped by calcium-induced calcium release.

PubMed

Coulon, Philippe; Herr, David; Kanyshkova, Tatyana; Meuth, Patrick; Budde, Thomas; Pape, Hans-Christian

2009-01-01

The nucleus reticularis thalami (NRT) is a layer of inhibitory neurons that surrounds the dorsal thalamus. It appears to be the 'pacemaker' of certain forms of slow oscillations in the thalamus and was proposed to be a key determinant of the internal attentional searchlight as well as the origin of hypersynchronous activity during absence seizures. Neurons of the NRT exhibit a transient depolarization termed low threshold spike (LTS) following sustained hyperpolarization. This is caused by the activation of low-voltage-activated Ca2+ channels (LVACC). Although the role of these channels in thalamocortical oscillations was studied in great detail, little is known about the downstream intracellular Ca2+ signalling pathways and their feedback onto the oscillations. A signalling triad consisting of the sarco(endo)plasmic reticulum calcium ATPase (SERCA), Ca2+ activated K+ channels (SK2), and LVACC is active in dendrites of NRT neurons and shapes rhythmic oscillations. The aim of our study was to find out (i) if and how Ca2+-induced Ca2+ release (CICR) via ryanodine receptors (RyR) can be evoked in NRT neurons and (ii) how the released Ca2+ affects burst activity. Combining electrophysiological, immunohistochemical, and two-photon Ca2+ imaging techniques, we show that CICR in NRT neurons takes place by a cell-type specific coupling of LVACC and RyR. CICR could be evoked by the application of caffeine, by activation of LVACC, or by repetitive LTS generation. During the latter, CICR contributed 30% to the resulting build-up of [Ca2+]i. CICR was abolished by cyclopiazonic acid, a specific blocker for SERCA, or by high concentrations of ryanodine (50 microM). Unlike other thalamic nuclei, in the NRT the activation of high-voltage-activated Ca2+ channels failed to evoke CICR. While action potentials contributed little to the build-up of [Ca2+]i upon repetitive LTS generation, the Ca2+ released via RyR significantly reduced the number of action potentials during an LTS and reduced the neurons' low threshold activity, thus potentially reducing hypersynchronicity. This effect persisted in the presence of the SK2 channel blocker apamin. We conclude that the activation of LVACC specifically causes CICR via RyR in neurons of the NRT, thereby adding a Ca2+-dependent intracellular route to the mechanisms determining rhythmic oscillatory bursting in this nucleus.

Depolarizing actions of GABA in immature neurons depend neither on ketone bodies nor on pyruvate.

PubMed

Tyzio, Roman; Allene, Camille; Nardou, Romain; Picardo, Michel A; Yamamoto, Sumii; Sivakumaran, Sudhir; Caiati, Maddalena D; Rheims, Sylvain; Minlebaev, Marat; Milh, Mathieu; Ferré, Pascal; Khazipov, Rustem; Romette, Jean-Louis; Lorquin, Jean; Cossart, Rosa; Khalilov, Ilgam; Nehlig, Astrid; Cherubini, Enrico; Ben-Ari, Yehezkel

2011-01-05

GABA depolarizes immature neurons because of a high [Cl(-)](i) and orchestrates giant depolarizing potential (GDP) generation. Zilberter and coworkers (Rheims et al., 2009; Holmgren et al., 2010) showed recently that the ketone body metabolite DL-3-hydroxybutyrate (DL-BHB) (4 mM), lactate (4 mM), or pyruvate (5 mM) shifted GABA actions to hyperpolarizing, suggesting that the depolarizing effects of GABA are attributable to inadequate energy supply when glucose is the sole energy source. We now report that, in rat pups (postnatal days 4-7), plasma D-BHB, lactate, and pyruvate levels are 0.9, 1.5, and 0.12 mM, respectively. Then, we show that DL-BHB (4 mM) and pyruvate (200 μM) do not affect (i) the driving force for GABA(A) receptor-mediated currents (DF(GABA)) in cell-attached single-channel recordings, (2) the resting membrane potential and reversal potential of synaptic GABA(A) receptor-mediated responses in perforated patch recordings, (3) the action potentials triggered by focal GABA applications, or (4) the GDPs determined with electrophysiological recordings and dynamic two-photon calcium imaging. Only very high nonphysiological concentrations of pyruvate (5 mM) reduced DF(GABA) and blocked GDPs. Therefore, DL-BHB does not alter GABA signals even at the high concentrations used by Zilberter and colleagues, whereas pyruvate requires exceedingly high nonphysiological concentrations to exert an effect. There is no need to alter conventional glucose enriched artificial CSF to investigate GABA signals in the developing brain.

Nicotine-induced stimulation of steroidogenesis in adrenocortical cells of the cat.

PubMed Central

Rubin, R P; Warner, W

1975-01-01

1. The effect of nicotine on steroid production and release from trypsin-dispersed cat adrenocortical cells was investigated. 2. Nicotine, like adrenocorticotrophin (ACTH), elicited a dose-dependent increase in steroidogenesis, which depended upon the presence of calcium in the medium. 3. Augmented steroid production evoked by submaximal concentrations of ACTH monobutyryl cyclic adenosine 3',5'-monophosphate (AMP), or prostaglandin E2 was further enhanced by steroidogenic concentrations of nicotine. 4. These results are discussed in relation to the possible mode of action of nicotine on cortical cells and to the potential consequences of smoking during stress. PMID:165845

The potential beneficial effect of nicardipine in a rat model of transient forebrain ischemia.

PubMed

Alps, B J; Hass, W K

1987-05-01

In a rat 3-day survival model of 10-minute four-vessel occlusion, halothane anesthesia was used to attenuate the ictal blood pressure elevation of the cerebral ischemic response and thereby maintain an isoelectric EEG. Selectively vulnerable regions of the brain were protected by preischemia plus postischemia maintenance treatment with the calcium entry blocker nicardipine. Compared with untreated animals, repeated doses at 500 micrograms/kg IP were markedly more effective than doses of 50 micrograms/kg. Ongoing studies demonstrate a neurocytoprotective action of nicardipine when deferred treatment is given postischemia.

Insights into the activation mechanism of calcium ions on the sericite surface: A combined experimental and computational study

NASA Astrophysics Data System (ADS)

Hu, Yuehua; He, Jianyong; Zhang, Chenhu; Zhang, Chenyang; Sun, Wei; Zhao, Dongbo; Chen, Pan; Han, Haisheng; Gao, Zhiyong; Liu, Runqing; Wang, Li

2018-01-01

The adsorption behaviors and the activation mechanism of calcium ions (Ca2+) on sericite surface have been investigated by Zeta potential measurements, Fourier transform infrared spectroscopy (FT-IR), Micro-flotation tests and First principle calculations. Zeta potential tests results show that the sericite surface potential increases due to the adsorption of calcium ions on the surface. Micro-flotation tests demonstrate that sericite recovery remarkably rise by 10% due to the calcium ions activation on sericite surface. However, the characteristic adsorption bands of calcium oleate do not appear in the FT-IR spectrum, suggesting that oleate ions just physically adsorb on the sericite surface. The first principle calculations based on the density functional theory (DFT) further reveals the microscopic adsorption mechanism of calcium ions on the sericite surface before and after hydration.

Selective inhibitory action of Biginelli-type dihydropyrimidines on depolarization-induced arterial smooth muscle contraction.

PubMed

Cernecka, Hana; Veizerova, Lucia; Mensikova, Lucia; Svetlik, Jan; Krenek, Peter

2012-05-01

Dihydropyridine calcium channel blockers have some disadvantages such as light sensitivity and relatively short plasma half-lives. Stability of dihydropyrimidines analogues could be of advantage, yet they remain less well characterized. We aimed to test four newly synthesized Biginelli-type dihydropyrimidines for their calcium channel blocking activity on rat isolated aorta. Dihydropyrimidines (compounds A-D) were prepared by the Biginelli-like three-component condensation of benzaldehydes with urea/thiourea and dimethyl or diethyl acetone-1,3-dicarboxylate, and their physicochemical properties and effects on depolarization-induced and noradrenaline-induced contractions of rat isolated aorta were evaluated. Dihydropyrimidines A and C blocked KCl-induced contraction only weakly (-log(IC50)=5.03 and 3.73, respectively), while dihydropyrimidine D (-log(IC50)=7.03) was almost as potent as nifedipine (-log(IC50)=8.14). Washout experiments revealed that dihydropyrimidine D may bind strongly to the L-type calcium channel or remains bound to membrane. All tested dihydropyrimidines only marginally inhibited noradrenaline-induced contractions of rat isolated aorta (20% reduction of noradrenaline E(max) ), indicating a more selective action on L-type calcium channel than nifedipine with 75% inhibition of noradrenaline E(max) at 10(-4) m nifedipine). Compounds A and, particularly, D are potent calcium channel blockers in vitro, with a better selectivity in inhibiting depolarization-induced arterial smooth muscle contraction than nifedipine. © 2012 The Authors. JPP © 2012 Royal Pharmaceutical Society.

Background norepinephrine primes astrocytic calcium responses to subsequent norepinephrine stimuli in the cerebral cortex

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

Nuriya, Mutsuo; Keio Advanced Research Center for Water Biology and Medicine, Keio University, Shinjuku, Tokyo, 160-8582; Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama, Kanagawa, 240-8501

Norepinephrine (NE) levels in the cerebral cortex are regulated in two modes; the brain state is correlated with slow changes in background NE concentration, while salient stimuli induce transient NE spikes. Previous studies have revealed their diverse neuromodulatory actions; however, the modulatory role of NE on astrocytic activity has been poorly characterized thus far. In this study, we evaluated the modulatory action of background NE on astrocytic responses to subsequent stimuli, using two-photon calcium imaging of acute murine cortical brain slices. We find that subthreshold background NE significantly augments calcium responses to subsequent pulsed NE stimulation in astrocytes. This primingmore » effect is independent of neuronal activity and is mediated by the activation of β-adrenoceptors and the downstream cAMP pathway. These results indicate that background NE primes astrocytes for subsequent calcium responses to NE stimulation and suggest a novel gliomodulatory role for brain state-dependent background NE in the cerebral cortex. - Highlights: • Background NE augments the responsiveness of astrocytes to subsequent NE stimulation. • The priming effect is independent of neuronal activity and mediated by βadrenoceptor. • Background subthreshold NE may play gliomodulatory roles in the cerebral cortex.« less

Azadirachtin blocks the calcium channel and modulates the cholinergic miniature synaptic current in the central nervous system of Drosophila.

PubMed

Qiao, Jingda; Zou, Xiaolu; Lai, Duo; Yan, Ying; Wang, Qi; Li, Weicong; Deng, Shengwen; Xu, Hanhong; Gu, Huaiyu

2014-07-01

Azadirachtin is a botanical pesticide, which possesses conspicuous biological actions such as insecticidal, anthelmintic, antifeedancy, antimalarial effects as well as insect growth regulation. Deterrent for chemoreceptor functions appears to be the main mechanism involved in the potent biological actions of Azadirachtin, although the cytotoxicity and subtle changes to skeletal muscle physiology may also contribute to its insecticide responses. In order to discover the effects of Azadirachtin on the central nervous system (CNS), patch-clamp recording was applied to Drosophila melanogaster, which has been widely used in neurological research. Here, we describe the electrophysiological properties of a local neuron located in the suboesophageal ganglion region of D. melanogaster using the whole brain. The patch-clamp recordings suggested that Azadirachtin modulates the properties of cholinergic miniature excitatory postsynaptic current (mEPSC) and calcium currents, which play important roles in neural activity of the CNS. The frequency of mEPSC and the peak amplitude of the calcium currents significantly decreased after application of Azadirachtin. Our study indicates that Azadirachtin can interfere with the insect's CNS via inhibition of excitatory cholinergic transmission and partly blocking the calcium channel. © 2013 Society of Chemical Industry.

Network-specific mechanisms may explain the paradoxical effects of carbamazepine and phenytoin.

PubMed

Thomas, Evan A; Petrou, Steven

2013-07-01

A common notion of the mechanism by which the antiepileptic drugs (AEDs) carbamazepine and phenytoin act is that they block sodium channels by binding preferentially to the inactivated state, thereby allowing normal neuronal firing while blocking ictal activity. However, these drugs have unpredictable efficacy and, in some cases, may exacerbate seizures. Previous studies have suggested that reducing sodium channel availability in the dentate gyrus (DG) paradoxically increases excitability. We used a biophysically detailed computer model of the DG to test the hypothesis that AEDs increase excitability by disproportionately reducing negative feedback mechanisms. We built a Markov model of sodium channel gating that reproduces responses to voltage clamp experiments in the presence of carbamazepine and phenytoin. We incorporated this validated Markov model into a biophysically realistic computer model of DG neurons and networks. Simulated drug concentrations were similar to those measured in cerebral spinal fluid in medicated patients. Single neuron models were stimulated with current injections, and networks were stimulated with perforant path synaptic input. In the network model, environmental effects were studied by introducing mossy fiber sprouting. As expected, drugs reduced sodium channel availability, which in turn reduced action potential amplitude. This had only a small effect on action potential (AP) firing rate during brief (100 msec) current injections. Paradoxically, long current injections (2,500 msec) increased AP firing rates. This was caused by reduced calcium entry and consequently reduced activation of calcium activated potassium channels. It is important to note that the main determinant of drug effect was resting membrane potential (RMP) and not action potential firing rate. Binding of phenytoin and carbamazepine is slow and, thus drug effects are largely determined by the long term state of the RMP. This paradoxical AP firing increase was dependent on the unusually large calcium-activated potassium conductances expressed by DG granule cells. This predicts that drug efficacy in a given network will depend on the precise makeup of conductances in the network. RMP is expected to vary with the level of activity in the network. We simulated the effects of drugs on single shot stimulus responses in networks with mossy fiber sprouting and varied the RMP in all neurons as a model for network activity. For an RMP of -50 mV, representing an active network, drugs had no effect, or in some cases, increased excitability. Drugs had an increasingly larger inhibitory effect on network responses as RMP decreased. An important prediction is that drugs will be unable to block ictal activity invading an active network. Our key findings are that drug effects depend on both intrinsic properties of the network and its behavioral state. This may explain the paradoxical and unpredictable effects of some AEDs on seizure control in some patients. Wiley Periodicals, Inc. © 2013 International League Against Epilepsy.

Purification and immunolocalization of an annexin-like protein in pea seedlings

NASA Technical Reports Server (NTRS)

Clark, G. B.; Dauwalder, M.; Roux, S. J.

1992-01-01

As part of a study to identify potential targets of calcium action in plant cells, a 35-kDa, annexin-like protein was purified from pea (Pisum sativum L.) plumules by a method used to purify animal annexins. This protein, called p35, binds to a phosphatidylserine affinity column in a calcium-dependent manner and binds 45Ca2+ in a dot-blot assay. Preliminary sequence data confirm a relationship for p35 with the annexin family of proteins. Polyclonal antibodies have been raised which recognize p35 in Western and dot blots. Immunofluorescence and immunogold techniques were used to study the distribution and subcellular localization of p35 in pea plumules and roots. The highest levels of immunostain were found in young developing vascular cells producing wall thickenings and in peripheral root-cap cells releasing slime. This localization in cells which are actively involved in secretion is of interest because one function suggested for the animal annexins is involvement in the mediation of exocytosis.

Oxidant Induced Changes in Mitochondria and Calcium Dynamicsin the Pathophysiology of Alzheimer's Disease

PubMed Central

Gibson, Gary E.; Karuppagounder, Saravanan S.; Shi, Qingli

2009-01-01

Considerable data supports the hypothesis that mitochondrial abnormalities link gene defects and/or environmental insults to the neurodegenerative process The interaction of oxidants with calcium and the mitochondrial enzymes of the tricarboxylic acid (TCA) cycle are central to that relationship. Abnormalities that were discovered in brains or fibroblasts from patients with Alzheimer's Disease (AD) have been modeled in vitro and in vivo to assess their pathophysiological importance and to determine how they might be reversed. The conclusions are consistent with the hypothesis that the AD-related abnormalities result from oxidative stress. The selection of compounds for reversal is complex because the actions of the relevant compounds vary under different conditions such as cell redox states and acute vs chronic changes. However, the models that have been developed are useful for testing the effectiveness of the potential medications. The results suggest that the reversal of the mitochondrial deficits and a reduction in oxidative stress will reduce the clinical and pathological changes and benefit patients. PMID:19076444

Fall prevention and vitamin D in the elderly: an overview of the key role of the non-bone effects

PubMed Central

2010-01-01

Preventing falls and fall-related fractures in the elderly is an objective yet to be reached. There is increasing evidence that a supplementation of vitamin D and/or of calcium may reduce the fall and fracture rates. A vitamin D-calcium supplement appears to have a high potential due to its simple application and its low cost. However, published studies have shown conflicting results as some studies failed to show any effect, while others reported a significant decrease of falls and fractures. Through a 15-year literature overview, and after a brief reminder on mechanism of falls in older adults, we reported evidences for a vitamin D action on postural adaptations - i.e., muscles and central nervous system - which may explain the decreased fall and bone fracture rates and we underlined the reasons for differences and controversies between published data. Vitamin D supplementation should thus be integrated into primary and secondary fall prevention strategies in older adults. PMID:20937091

Short infrared (IR) laser pulses can induce nanoporation

NASA Astrophysics Data System (ADS)

Roth, Caleb C.; Barnes, Ronald A.; Ibey, Bennett L.; Glickman, Randolph D.; Beier, Hope T.

2016-03-01

Short infrared (IR) laser pulses on the order of hundreds of microseconds to single milliseconds with typical wavelengths of 1800-2100 nm, have shown the capability to reversibly stimulate action potentials (AP) in neuronal cells. While the IR stimulation technique has proven successful for several applications, the exact mechanism(s) underlying the AP generation has remained elusive. To better understand how IR pulses cause AP stimulation, we determined the threshold for the formation of nanopores in the plasma membrane. Using a surrogate calcium ion, thallium, which is roughly the same shape and charge, but lacks the biological functionality of calcium, we recorded the flow of thallium ions into an exposed cell in the presence of a battery of channel antagonists. The entry of thallium into the cell indicated that the ions entered via nanopores. The data presented here demonstrate a basic understanding of the fundamental effects of IR stimulation and speculates that nanopores, formed in response to the IR exposure, play an upstream role in the generation of AP.

Carbon monoxide effects on human ventricle action potential assessed by mathematical simulations

PubMed Central

Trenor, Beatriz; Cardona, Karen; Saiz, Javier; Rajamani, Sridharan; Belardinelli, Luiz; Giles, Wayne R.

2013-01-01

Carbon monoxide (CO) that is produced in a number of different mammalian tissues is now known to have significant effects on the cardiovascular system. These include: (i) vasodilation, (ii) changes in heart rate and strength of contractions, and (iii) modulation of autonomic nervous system input to both the primary pacemaker and the working myocardium. Excessive CO in the environment is toxic and can initiate or mediate life threatening cardiac rhythm disturbances. Recent reports link these ventricular arrhythmias to an increase in the slowly inactivating, or “late” component of the Na+ current in the mammalian heart. The main goal of this paper is to explore the basis of this pro-arrhythmic capability of CO by incorporating changes in CO-induced ion channel activity with intracellular signaling pathways in the mammalian heart. To do this, a quite well-documented mathematical model of the action potential and intracellular calcium transient in the human ventricular myocyte has been employed. In silico iterations based on this model provide a useful first step in illustrating the cellular electrophysiological consequences of CO that have been reported from mammalian heart experiments. Specifically, when the Grandi et al. model of the human ventricular action potential is utilized, and after the Na+ and Ca2+ currents in a single myocyte are modified based on the experimental literature, early after-depolarization (EAD) rhythm disturbances appear, and important elements of the underlying causes of these EADs are revealed/illustrated. Our modified mathematical model of the human ventricular action potential also provides a convenient digital platform for designing future experimental work and relating these changes in cellular cardiac electrophysiology to emerging clinical and epidemiological data on CO toxicity. PMID:24146650

Nociceptive neuronal Fc-gamma receptor I is involved in IgG immune complex induced pain in the rat.

PubMed

Jiang, Haowu; Shen, Xinhua; Chen, Zhiyong; Liu, Fan; Wang, Tao; Xie, Yikuan; Ma, Chao

2017-05-01

Antigen-specific immune diseases such as rheumatoid arthritis are often accompanied by pain and hyperalgesia. Our previous studies have demonstrated that Fc-gamma-receptor type I (FcγRI) is expressed in a subpopulation of rat dorsal root ganglion (DRG) neurons and can be directly activated by IgG immune complex (IgG-IC). In this study we investigated whether neuronal FcγRI contributes to antigen-specific pain in the naïve and rheumatoid arthritis model rats. In vitro calcium imaging and whole-cell patch clamp recordings in dissociated DRG neurons revealed that only the small-, but not medium- or large-sized DRG neurons responded to IgG-IC. Accordingly, in vivo electrophysiological recordings showed that intradermal injection of IgG-IC into the peripheral receptive field could sensitize only the C- (but not A-) type sensory neurons and evoke action potential discharges. Pain-related behavioral tests showed that intradermal injection of IgG-IC dose-dependently produced mechanical and thermal hyperalgesia in the hindpaw of rats. These behavioral effects could be alleviated by localized administration of non-specific IgG or an FcγRI antibody, but not by mast cell stabilizer or histamine antagonist. In a rat model of antigen-induced arthritis (AIA) produced by methylated bovine serum albumin, FcγRI were found upregulated exclusively in the small-sized DRG neurons. In vitro calcium imaging revealed that significantly more small-sized DRG neurons responded to IgG-IC in the AIA rats, although there was no significant difference between the AIA and control rats in the magnitude of calcium changes in the DRG neurons. Moreover, in vivo electrophysiological recordings showed that C-nociceptive neurons in the AIA rats exhibited a greater incidence of action potential discharges and stronger responses to mechanical stimuli after IgG-IC was injected to the receptive fields. These results suggest that FcγRI expressed in the peripheral nociceptors might be directly activated by IgG-IC and contribute to antigen-specific pain in pathological conditions. Copyright © 2017 Elsevier Inc. All rights reserved.

Defective calcium inactivation causes long QT in obese insulin-resistant rat.

PubMed

Lin, Yen-Chang; Huang, Jianying; Kan, Hong; Castranova, Vincent; Frisbee, Jefferson C; Yu, Han-Gang

2012-02-15

The majority of diabetic patients who are overweight or obese die of heart disease. We suspect that the obesity-induced insulin resistance may lead to abnormal cardiac electrophysiology. We tested this hypothesis by studying an obese insulin-resistant rat model, the obese Zucker rat (OZR). Compared with the age-matched control, lean Zucker rat (LZR), OZR of 16-17 wk old exhibited an increase in QTc interval, action potential duration, and cell capacitance. Furthermore, the L-type calcium current (I(CaL)) in OZR exhibited defective inactivation and lost the complete inactivation back to the closed state, leading to increased Ca(2+) influx. The current density of I(CaL) was reduced in OZR, whereas the threshold activation and the current-voltage relationship of I(CaL) were not significantly altered. L-type Ba(2+) current (I(BaL)) in OZR also exhibited defective inactivation, and steady-state inactivation was not significantly altered. However, the current-voltage relationship and activation threshold of I(BaL) in OZR exhibited a depolarized shift compared with LZR. The total and membrane protein expression levels of Cav1.2 [pore-forming subunit of L-type calcium channels (LTCC)], but not the insulin receptors, were decreased in OZR. The insulin receptor was found to be associated with the Cav1.2, which was weakened in OZR. The total protein expression of calmodulin was reduced, but that of Cavβ2 subunit was not altered in OZR. Together, these results suggested that the 16- to 17-wk-old OZR has 1) developed cardiac hypertrophy, 2) exhibited altered electrophysiology manifested by the prolonged QTc interval, 3) increased duration of action potential in isolated ventricular myocytes, 4) defective inactivation of I(CaL) and I(BaL), 5) weakened the association of LTCC with the insulin receptor, and 6) decreased protein expression of Cav1.2 and calmodulin. These results also provided mechanistic insights into a remodeled cardiac electrophysiology under the condition of insulin resistance, enhancing our understanding of long QT associated with obese type 2 diabetic patients.

Extracellular calcium (Ca2+(o))-sensing receptor in a murine bone marrow-derived stromal cell line (ST2): potential mediator of the actions of Ca2+(o) on the function of ST2 cells

NASA Technical Reports Server (NTRS)

Yamaguchi, T.; Chattopadhyay, N.; Kifor, O.; Brown, E. M.; O'Malley, B. W. (Principal Investigator)

1998-01-01

The calcium-sensing receptor (CaR) is a G protein-coupled receptor that plays key roles in extracellular calcium ion (Ca2+(o)) homeostasis by mediating the actions of Ca2+(o) on parathyroid gland and kidney. Bone marrow stromal cells support the formation of osteoclasts from their progenitors as well as the growth of hematopoietic stem cells by secreting humoral factors and through cell to cell contact. Stromal cells also have the capacity to differentiate into bone-forming osteoblasts. Bone resorption by osteoclasts probably produces substantial local increases in Ca2+(o) that could provide a signal for stromal cells in the immediate vicinity, leading us to determine whether such stromal cells express the CaR. In this study, we used the murine bone marrow-derived, stromal cell line, ST2. Both immunocytochemistry and Western blot analysis, using an antiserum specific for the CaR, detected CaR protein in ST2 cells. We also identified CaR transcripts in ST2 cells by Northern analysis using a CaR-specific probe and by RT-PCR with CaR-specific primers, followed by nucleotide sequencing of the amplified products. Exposure of ST2 cells to high Ca2+(o) (4.8 mM) or to the polycationic CaR agonists, neomycin (300 microM) or gadolinium (100 microM), stimulated both chemotaxis and DNA synthesis in ST2 cells. Therefore, taken together, our data strongly suggest that the bone marrow-derived stromal cell line, ST2, possesses both CaR protein and messenger RNA that are very similar if not identical to those in parathyroid and kidney. Furthermore, as ST2 cells have the potential to differentiate into osteoblasts, the CaR in stromal cells could participate in bone turnover by stimulating the proliferation and migration of such cells to sites of bone resorption as a result of local, osteoclast-mediated release of Ca2+(o) and, thereafter, initiating bone formation after their differentiation into osteoblasts.

The analgesic effect of trans-resveratrol is regulated by calcium channels in the hippocampus of mice.

PubMed

Wang, Weijie; Yu, Yingcong; Li, Jing; Wang, Lin; Li, Zhi; Zhang, Chong; Zhen, Linlin; Ding, Lianshu; Wang, Gang; Sun, Xiaoyang; Xu, Ying

2017-08-01

Resveratrol has been widely studied in terms of it's potential to slow the progression of many diseases. But little is known about the mechanism of action in neuropathic pain. Neuropathic pain is the main type of chronic pain associated with tissue injury. Calcium channels and calcium/caffeine-sensitive pools are associated with analgesic pathway involving neuropathic pain. Our previous study suggested that the antinociceptive effect of resveratrol was involved in Ca 2+ /calmodulin-dependent signaling in the spinal cord of mice. The aim of this study was to explore the involvement of Ca 2+ in analgesic effects of trans-resveratrol in neuropathic pain and signal pathway in hippocampus. Hot plate test was used to assess antinociceptive response when mice were treated with trans-resveratrol alone or in combination with Mk 801, nimodipine, CaCl 2 , ryanodine or EGTA. The effects of trans-resveratrol and the combination on Ca 2+ /calmodulin-dependent protein kinase II (CaMKII) and BDNF (brain-derived neurotrophic factor) expression in hippocampus were also investigated. The results showed that trans-resveratrol increased paw withdraw latency in the hot plate test. The effect of resveratrol was enhanced by Mk 801 and nimodipine. Central administration of Ca 2+ , however, abolished the antinociceptive effects of resveratrol. In contrast, centrally administered EGTA or ryanodine improved trans-resveratrol induced antinociception. There was a significant increase in p-CaMKII and BDNF expression in the hippocampus when resveratrol were combined with Mk 801, nimodipine, ryanodine and EGTA. Administration of CaCl 2 blocked changes in p-CaMKII and BDNF levels in the hippocampus. These findings suggest that trans-resveratrol exerts the effects of antinociception through regulation of calcium channels and calcium/caffeine-sensitive pools.

Role of chloride transport proteins in the vasorelaxant action of nitroprusside in isolated rat aorta.

PubMed

Valero, Marta; Pereboom, Désirée; Garay, Ricardo P; Alda, José Octavio

2006-12-28

Chloride ions play a key role in smooth muscle contraction, but little is known concerning their role in smooth muscle relaxation. Here we investigated the effect of chloride transport inhibitors on the vasorelaxant responses to nitroprusside in isolated and endothelium-denuded rat aorta, precontracted with phenylephrine 1 muM. Incubation of aortic rings in NO(3)(-) media strongly potentiated the vasorelaxant responses to nitroprusside. Bumetanide, DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) and acetazolamide strongly potentiated the vasorelaxant responses to nitroprusside (by 70-100%). EC(50) were 2.3+/-0.5 microM for bumetanide, 26+/-15 microM for DIDS and 510+/-118 microM for acetazolamide (n=6 for condition). Niflumic acid, a selective inhibitor of ClCa (calcium-activated chloride channels), potentiated nitroprusside relaxation to a similar extent as chloride transport inhibitors, in a non-additive manner. Zinc and nickel ions, both modestly potentiated nitroprusside vasorelaxation (by 20-30%). Cobaltum had negligible effect on nitroprusside vasorelaxation. CPA (p-chlorophenoxy-acetic acid), an inhibitor of volume-sensitive chloride channels (ClC), slightly potentiated nitroprusside vasorelaxation (by 15%), and the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel inhibitors CFTR(inh)172 (5-[(4-Carboxyphenyl)methylene]-2-thioxo-3-[(3-trifluoromethyl)phenyl-4-thiazolidinone), DPC (diphenylamine-2,2'-dicarboxylic acid) and glibenclamide were without significant effect. In conclusion, inhibition of chloride transport proteins strongly potentiates the vasorelaxant responses to nitroprusside in isolated rat aorta. This effect seems mediated by chloride depletion and inhibition of a chloride channel activated by both, calcium and cyclic GMP (cGMP).

Resveratrol Interferes with Fura-2 Intracellular Calcium Measurements.

PubMed

Kopp, Richard F; Leech, Colin A; Roe, Michael W

2014-03-01

Resveratrol, a naturally occurring polyphenol found in some fruits and especially in grapes, has been reported to provide diverse health benefits. Resveratrol's mechanism of action is the subject of many investigations, and some studies using the ratiometric calcium indicator Fura-2 suggest that it modulates cellular calcium responses. In the current study, contradictory cellular calcium responses to resveratrol applied at concentrations exceeding 10 μM were observed during in vitro imaging studies depending on the calcium indicator used, with Fura-2 indicating an increase in intracellular calcium while Fluo-4 and the calcium biosensor YC3.60 indicated no response. When cells loaded with Fura-2 were treated with 100 μM resveratrol, excitation at 340 nm resulted in a large intensity increase at 510 nm, but the expected concurrent decline with 380 nm excitation was not observed. Pre-treatment of cells with the calcium chelator BAPTA-AM did not prevent a rise in the 340/380 ratio when resveratrol was present, but it did prevent an increase in 340/380 when ATP was applied, suggesting that the resveratrol response was an artifact. Cautious data interpretation is recommended from imaging experiments using Fura-2 concurrently with resveratrol in calcium imaging experiments.

Physiology of Calcium, Phosphate, Magnesium and Vitamin D.

PubMed

Allgrove, Jeremy

2015-01-01

The physiology of calcium and the other minerals involved in its metabolism is complex and intimately linked to the physiology of bone. Five principal humoral factors are involved in maintaining plasma concentrations of calcium, magnesium and phosphate and in coordinating the balance between their content in bone. The transmembrane transport of these elements is dependent on a series of complex mechanisms that are partly controlled by these hormones. The plasma concentration of calcium is initially sensed by a calcium-sensing receptor, which then sets up a cascade of events that initially determines parathyroid hormone secretion and eventually results in a specific action within the target organs, mainly bone and kidney. This chapter describes the physiology of these humoral factors and relates them to the pathological processes that give rise to disorders of calcium, phosphate and magnesium metabolism as well as of bone metabolism. This chapter also details the stages in the calcium cascade, describes the effects of calcium on the various target organs, gives details of the processes by which phosphate and magnesium are controlled and summarises the metabolism of vitamin D. The pathology of disorders of bone and calcium metabolism is described in detail in the relevant chapters. © 2015 S. Karger AG, Basel.

Transient compartment-like syndrome and normokalaemic periodic paralysis due to a Cav1.1 mutation

PubMed Central

Fan, Chunxiang; Lehmann-Horn, Frank; Weber, Marc-André; Bednarz, Marcin; Groome, James R.; Jonsson, Malin K. B.

2013-01-01

We studied a two-generation family presenting with conditions that included progressive permanent weakness, myopathic myopathy, exercise-induced contracture before normokalaemic periodic paralysis or, if localized to the tibial anterior muscle group, transient compartment-like syndrome (painful acute oedema with neuronal compression and drop foot). 23Na and 1H magnetic resonance imaging displayed myoplasmic sodium overload, and oedema. We identified a novel familial Cav1.1 calcium channel mutation, R1242G, localized to the third positive charge of the domain IV voltage sensor. Functional expression of R1242G in the muscular dysgenesis mouse cell line GLT revealed a 28% reduced central pore inward current and a −20 mV shift of the steady-state inactivation curve. Both changes may be at least partially explained by an outward omega (gating pore) current at positive potentials. Moreover, this outward omega current of 27.5 nS/nF may cause the reduction of the overshoot by 13 mV and slowing of the upstroke of action potentials by 36% that are associated with muscle hypoexcitability (permanent weakness and myopathic myopathy). In addition to the outward omega current, we identified an inward omega pore current of 95 nS/nF at negative membrane potentials after long depolarizing pulses that shifts the R1242G residue above the omega pore constriction. A simulation reveals that the inward current might depolarize the fibre sufficiently to trigger calcium release in the absence of an action potential and therefore cause an electrically silent depolarization-induced muscle contracture. Additionally, evidence of the inward current can be found in 23Na magnetic resonance imaging-detected sodium accumulation and 1H magnetic resonance imaging-detected oedema. We hypothesize that the episodes are normokalaemic because of depolarization-induced compensatory outward potassium flux through both delayed rectifiers and omega pore. We conclude that the position of the R1242G residue before elicitation of the omega current is decisive for its conductance: if the residue is located below the gating pore as in the resting state then outward currents are observed; if the residue is above the gating pore because of depolarization, as in the inactivated state, then inward currents are observed. This study shows for the first time that functional characterization of omega pore currents is possible using a cultured cell line expressing mutant Cav1.1 channels. Likewise, it is the first calcium channel mutation for complicated normokalaemic periodic paralysis. PMID:24240197

Calcium and cAMP directly modulate the speed of the Drosophila circadian clock.

PubMed

Palacios-Muñoz, Angelina; Ewer, John

2018-06-01

Circadian clocks impose daily periodicities to animal behavior and physiology. At their core, circadian rhythms are produced by intracellular transcriptional/translational feedback loops (TTFL). TTFLs may be altered by extracellular signals whose actions are mediated intracellularly by calcium and cAMP. In mammals these messengers act directly on TTFLs via the calcium/cAMP-dependent transcription factor, CREB. In the fruit fly, Drosophila melanogaster, calcium and cAMP also regulate the periodicity of circadian locomotor activity rhythmicity, but whether this is due to direct actions on the TTFLs themselves or are a consequence of changes induced to the complex interrelationship between different classes of central pacemaker neurons is unclear. Here we investigated this question focusing on the peripheral clock housed in the non-neuronal prothoracic gland (PG), which, together with the central pacemaker in the brain, controls the timing of adult emergence. We show that genetic manipulations that increased and decreased the levels of calcium and cAMP in the PG caused, respectively, a shortening and a lengthening of the periodicity of emergence. Importantly, knockdown of CREB in the PG caused an arrhythmic pattern of eclosion. Interestingly, the same manipulations directed at central pacemaker neurons caused arrhythmicity of eclosion and of adult locomotor activity, suggesting a common mechanism. Our results reveal that the calcium and cAMP pathways can alter the functioning of the clock itself. In the PG, these messengers, acting as outputs of the clock or as second messengers for stimuli external to the PG, could also contribute to the circadian gating of adult emergence.

Theory of the development of alternans in the heart during controlled diastolic interval pacing

NASA Astrophysics Data System (ADS)

Otani, Niels F.

2017-09-01

The beat-to-beat alternation in action potential durations (APDs) in the heart, called APD alternans, has been linked to the development of serious cardiac rhythm disorders, including ventricular tachycardia and fibrillation. The length of the period between action potentials, called the diastolic interval (DI), is a key dynamical variable in the standard theory of alternans development. Thus, methods that control the DI may be useful in preventing dangerous cardiac rhythms. In this study, we examine the dynamics of alternans during controlled-DI pacing using a series of single-cell and one-dimensional (1D) fiber models of alternans dynamics. We find that a model that combines a so-called memory model with a calcium cycling model can reasonably explain two key experimental results: the possibility of alternans during constant-DI pacing and the phase lag of APDs behind DIs during sinusoidal-DI pacing. We also find that these results can be replicated by incorporating the memory model into an amplitude equation description of a 1D fiber. The 1D fiber result is potentially concerning because it seems to suggest that constant-DI control of alternans can only be effective over only a limited region in space.

Aging-associated changes in L-type calcium channels in the left atria of dogs.

PubMed

Gan, Tian-Yi; Qiao, Weiwei; Xu, Guo-Jun; Zhou, Xian-Hui; Tang, Bao-Peng; Song, Jian-Guo; Li, Yao-Dong; Zhang, Jian; Li, Fa-Peng; Mao, Ting; Jiang, Tao

2013-10-01

Action potential (AP) contours vary considerably between the fibers of normal adult and aged left atria. The underlying ionic and molecular mechanisms that mediate these differences remain unknown. The aim of the present study was to investigate whether the L-type calcium current (I Ca.L ) and the L-type Ca 2+ channel of the left atria may be altered with age to contribute to atrial fibrillation (AF). Two groups of mongrel dogs (normal adults, 2-2.5 years old and older dogs, >8 years old) were used in this study. The inducibility of AF was quantitated using the cumulative window of vulnerability (WOV). A whole-cell patch-clamp was used to record APs and I Ca.L in left atrial (LA) cells obtained from the two groups of dogs. Protein and mRNA expression levels of the a1C (Cav1.2) subunit of the L-type calcium channel were assessed using western blotting and quantitative PCR (qPCR), respectively. Although the resting potential, AP amplitude and did not differ with age, the plateau potential was more negative and the APD 90 was longer in the aged cells compared with that in normal adult cells. Aged LA cells exhibited lower peak I Ca.L current densities than normal adult LA cells (P<0.05). In addition, the Cav1.2 mRNA and protein expression levels in LA cells were decreased in the aged group compared with those in the normal adult group. The lower AP plateau potential and the decreased I Ca.L of LA cells in aged dogs may contribute to the slow and discontinuous conduction of the left atria. Furthermore, the reduction of the expression levels of Cav1.2 with age may be the molecular mechanism that mediates the decline in I Ca.L with increasing age.

Calcium-deficiency assessment and biomarker identification by an integrated urinary metabonomics analysis

PubMed Central

2013-01-01

Background Calcium deficiency is a global public-health problem. Although the initial stage of calcium deficiency can lead to metabolic alterations or potential pathological changes, calcium deficiency is difficult to diagnose accurately. Moreover, the details of the molecular mechanism of calcium deficiency remain somewhat elusive. To accurately assess and provide appropriate nutritional intervention, we carried out a global analysis of metabolic alterations in response to calcium deficiency. Methods The metabolic alterations associated with calcium deficiency were first investigated in a rat model, using urinary metabonomics based on ultra-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry and multivariate statistical analysis. Correlations between dietary calcium intake and the biomarkers identified from the rat model were further analyzed to confirm the potential application of these biomarkers in humans. Results Urinary metabolic-profiling analysis could preliminarily distinguish between calcium-deficient and non-deficient rats after a 2-week low-calcium diet. We established an integrated metabonomics strategy for identifying reliable biomarkers of calcium deficiency using a time-course analysis of discriminating metabolites in a low-calcium diet experiment, repeating the low-calcium diet experiment and performing a calcium-supplement experiment. In total, 27 biomarkers were identified, including glycine, oxoglutaric acid, pyrophosphoric acid, sebacic acid, pseudouridine, indoxyl sulfate, taurine, and phenylacetylglycine. The integrated urinary metabonomics analysis, which combined biomarkers with regular trends of change (types A, B, and C), could accurately assess calcium-deficient rats at different stages and clarify the dynamic pathophysiological changes and molecular mechanism of calcium deficiency in detail. Significant correlations between calcium intake and two biomarkers, pseudouridine (Pearson correlation, r = 0.53, P = 0.0001) and citrate (Pearson correlation, r = -0.43, P = 0.001), were further confirmed in 70 women. Conclusions To our knowledge, this is the first report of reliable biomarkers of calcium deficiency, which were identified using an integrated strategy. The identified biomarkers give new insights into the pathophysiological changes and molecular mechanisms of calcium deficiency. The correlations between calcium intake and two of the biomarkers provide a rationale or potential for further assessment and elucidation of the metabolic responses of calcium deficiency in humans. PMID:23537001

Communication Between the Calcium and cAMP Pathways Regulate the Expression of the TSH Receptor: TRPC2 in the Center of Action

PubMed Central

Löf, Christoffer; Sukumaran, Pramod; Viitanen, Tero; Vainio, Minna; Kemppainen, Kati; Pulli, Ilari; Näsman, Johnny; Kukkonen, Jyrki P.

2012-01-01

Transient receptor potential (TRP) cation channels are widely expressed and function in many physiologically important processes. Perturbations in the expression or mutations of the channels have implications for diseases. Many thyroid disorders, as excessive growth or disturbed thyroid hormone production, can be a result of dysregulated TSH signaling. In the present study, we found that of TRP canonicals (TRPCs), only TRPC2 was expressed in Fischer rat thyroid low-serum 5% cells (FRTL-5 cells). To investigate the physiological importance of the channel, we developed stable TRPC2 knockdown cells using short hairpin RNA (shTRPC2 cells). In these cells, the ATP-evoked entry of calcium was significantly decreased. This led to increased cAMP production, because inhibitory signals from calcium to adenylate cyclase 5/6 were decreased. Enhanced cAMP signaling projected to Ras-related protein 1-MAPK kinase 1 (MAPK/ERK kinase 1) pathway leading to phosphorylation of ERK1/2. The activated ERK1/2 pathway increased the expression of the TSH receptor. In contrast, secretion of thyroglobulin was decreased in shTRPC2 cells, due to improper folding and glycosylation of the protein. We show here a novel role for TRPC2 in regulating thyroid cell function. PMID:23015753

TRPV1 variants impair intracellular Ca2+ signaling and may confer susceptibility to malignant hyperthermia.

PubMed

Abeele, Fabien Vanden; Lotteau, Sabine; Ducreux, Sylvie; Dubois, Charlotte; Monnier, Nicole; Hanna, Amy; Gkika, Dimitra; Romestaing, Caroline; Noyer, Lucile; Flourakis, Matthieu; Tessier, Nolwenn; Al-Mawla, Ribal; Chouabe, Christophe; Lefai, Etienne; Lunardi, Joël; Hamilton, Susan; Fauré, Julien; Van Coppenolle, Fabien; Prevarskaya, Natalia

2018-06-21

Malignant hyperthermia (MH) is a pharmacogenetic disorder arising from uncontrolled muscle calcium release due to an abnormality in the sarcoplasmic reticulum (SR) calcium-release mechanism triggered by halogenated inhalational anesthetics. However, the molecular mechanisms involved are still incomplete. We aimed to identify transient receptor potential vanilloid 1 (TRPV1) variants within the entire coding sequence in patients who developed sensitivity to MH of unknown etiology. In vitro and in vivo functional studies were performed in heterologous expression system, trpv1 -/- mice, and a murine model of human MH. We identified TRPV1 variants in two patients and their heterologous expression in muscles of trpv1 -/- mice strongly enhanced calcium release from SR upon halogenated anesthetic stimulation, suggesting they could be responsible for the MH phenotype. We confirmed the in vivo significance by using mice with a knock-in mutation (Y524S) in the type I ryanodine receptor (Ryr1), a mutation analogous to the Y522S mutation associated with MH in humans. We showed that the TRPV1 antagonist capsazepine slows the heat-induced hypermetabolic response in this model. We propose that TRPV1 contributes to MH and could represent an actionable therapeutic target for prevention of the pathology and also be responsible for MH sensitivity when mutated.

Teaching Calcium-Induced Calcium Release in Cardiomyocytes Using a Classic Paper by Fabiato

ERIC Educational Resources Information Center

Liang, Willmann

2008-01-01

This teaching paper utilizes the materials presented by Dr. Fabiato in his review article entitled "Calcium-induced release of calcium from the cardiac sarcoplasmic reticulum." In the review, supporting evidence of calcium-induced calcium release (CICR) is presented. Data concerning potential objections to the CICR theory are discussed as well. In…

Involvement of peripheral mechanism in the verapamil-induced potentiation of morphine analgesia in mice.

PubMed

Shimizu, Norifumi; Kishioka, Shiroh; Maeda, Takehiko; Fukazawa, Yohji; Dake, Yoshihiro; Yamamoto, Chizuko; Ozaki, Masanobu; Yamamoto, Hiroyuki

2004-08-01

Morphine's analgesic actions are thought to be mediated through both the central and peripheral nervous systems. L-type calcium channel blockers have been reported to potentiate the analgesic effects of morphine, but the locus of this interaction is not known. In this experiment, we examined the site of verapamil-induced potentiation of morphine analgesia in mice using the quaternary opioid receptor antagonist naloxone-methiodide (NLX-M). Subcutaneous injections of morphine increased locomotor activity and serum corticosterone level, which are mediated by the central nervous system. These central effects were not antagonized by 0.1 mg/kg of NLX-M, whereas this dose of NLX-M partially antagonized the analgesic effect of morphine. Treatment with verapamil potentiated morphine analgesia in a dose-dependent manner. The verapamil-induced potentiation of morphine analgesia was abolished by pretreatment with NLX-M (0.1 and 1 mg/kg). These findings suggest that peripheral mechanisms partially contribute to morphine analgesia and mediate the potentiation of morphine analgesia by verapamil.

Action of cholecystokinin and cholinergic agents on calcium transport in isolated pancreatic acinar cells.

PubMed Central

Gardner, J D; Conlon, T P; Kleveman, H L; Adams, T D; Ondetti, M A

1975-01-01

COOH-terminal octapeptide of cholecystokinin (CCK-octapeptide) and the cholinergic agent carbamylcholine each produced a fourfold stimulation of calcium outflux in guinea pig isolated pancreatic acinar cells. Neither agent altered calcium influx. Stimulation of calcium outflux was rapid and specific, was abolished by reducing the incubation temperature to 4 degrees C, and was a saturable function of the secretagogue concentration. The concentrations of CCK-octapeptide and carbamylcholine that produced half-maximal stimulation of calcium outflux were 3.1 x 10(-10) M and 4.9 x 10(-5) M, respectively. The cholinergic antagonist antropine competitively inhibited carbamylcholine stimulation of calcium outflux but did not alter stimulation produced by CCK-octapeptide. Stimulation of calcium outflux by maximal concentrations of carbamycholine plus CCK-octapeptide was the same as that produced by a maximal concentration of either agent alone.Calcium outflux became refractory to stimulation by secretagogues, and incubation with either CCK-ostapeptide or carbamylcholine produced a refractoriness to both agents. The relative potencies with CCK and its related fragments stimulated calcium outflux were CCK-octapeptide greater than heptapeptide greater than CCK greater than hexapeptide = gastrin. Secretin, glucagon, and vasoactive intestinal peptide, at concentrations as high as 10(-5) M, failed to alter calcium outflux and did not affect stimulation by CCK-octapeptide or by carbamycholine. Images PMID:1150877

Inhibition of parathyroid hormone release by maitotoxin, a calcium channel activator

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

Fitzpatrick, L.A.; Yasumoto, T.; Aurbach, G.D.

1989-01-01

Maitotoxin, a toxin derived from a marine dinoflagellate, is a potent activator of voltage-sensitive calcium channels. To further test the hypothesis that inhibition of PTH secretion by calcium is mediated via a calcium channel we studied the effect of maitotoxin on dispersed bovine parathyroid cells. Maitotoxin inhibited PTH release in a dose-dependent fashion, and inhibition was maximal at 1 ng/ml. Chelation of extracellular calcium by EGTA blocked the inhibition of PTH by maitotoxin. Maitotoxin enhanced the effects of the dihydropyridine calcium channel agonist (+)202-791 and increased the rate of radiocalcium uptake in parathyroid cells. Pertussis toxin, which ADP-ribosylates and inactivatesmore » a guanine nucleotide regulatory protein that interacts with calcium channels in the parathyroid cell, did not affect the inhibition of PTH secretion by maitotoxin. Maitotoxin, by its action on calcium channels allows entry of extracellular calcium and inhibits PTH release. Our results suggest that calcium channels are involved in the release of PTH. Inhibition of PTH release by maitotoxin is not sensitive to pertussis toxin, suggesting that maitotoxin may act distal to the site interacting with a guanine nucleotide regulatory protein, or maitotoxin could interact with other ions or second messengers to inhibit PTH release.« less

Antibacterial effect of coffee: calcium concentration in a culture containing teeth/biofilm exposed to Coffea Canephora aqueous extract.

PubMed

Meckelburg, N; Pinto, K C; Farah, A; Iorio, N L P; Pierro, V S S; dos Santos, K R N; Maia, L C; Antonio, A G

2014-09-01

This study determined the changes of calcium concentration in a medium containing teeth/biofilm exposed to Coffea canephora extract (CCE). Enamel fragments were randomly fixed into two 24-well polystyrene plates containing BHI. Pooled human saliva was added to form biofilm on fragments. Specimens were divided into treatment groups (G, n = 8 per group) and treated with 50 μl daily for 1 min per week, as follows: G1, 20% CCE; G2, Milli-Q water (negative control); G3, antibiotic (positive control). Six fragments represented the blank control (G4). The calcium content was observed at baseline, 4 and 7 days of treatment by atomic-absorption spectrophotometry. Cross-sectional hardness of enamel was a demineralization indicator. Calcium increased in the medium after 4 and 7 days of treatment in G1 (3·80 ± 1·3 mg l(-1) and 4·93 ± 2·1 mg l(-1) , respectively) and G3 (4th day = 5·7 ± 1·8 mg l(-1) ; 7th day = 6·7 ± 3·5 mg l(-1) ) (P > 0·05). Calcium from G2 decreased after 7 days, which was different from G3 (P < 0·05). The lower calcium content, at the end of the experiment, was represented by G4, 2·16 ± 0·2 mg l(-1) . The increase in calcium after treatment with CCE is probably due to its antibacterial effect, which caused the bacterial lysis and consequent release of calcium in the medium. This study revealed an inhibitory action of Coffea canephora against dental biofilm. This coffee species caused bacterial lysis and consequent release of calcium into the medium. Furthermore, the advantage of coffee as an antibacterial beverage is that it is consumed in a concentrated form (6-10%) as opposed to various medicinal infusions that have shown such effect in vitro and are usually consumed at 1-2%. Therefore, a light roasted C. canephora aqueous extract can be considered as a potential anticariogenic substance. © 2014 The Society for Applied Microbiology.

BPA Directly Decreases GnRH Neuronal Activity via Noncanonical Pathway.

PubMed

Klenke, Ulrike; Constantin, Stephanie; Wray, Susan

2016-05-01

Peripheral feedback of gonadal estrogen to the hypothalamus is critical for reproduction. Bisphenol A (BPA), an environmental pollutant with estrogenic actions, can disrupt this feedback and lead to infertility in both humans and animals. GnRH neurons are essential for reproduction, serving as an important link between brain, pituitary, and gonads. Because GnRH neurons express several receptors that bind estrogen, they are potential targets for endocrine disruptors. However, to date, direct effects of BPA on GnRH neurons have not been shown. This study investigated the effects of BPA on GnRH neuronal activity using an explant model in which large numbers of primary GnRH neurons are maintained and express many of the receptors found in vivo. Because oscillations in intracellular calcium have been shown to correlate with electrical activity in GnRH neurons, calcium imaging was used to assay the effects of BPA. Exposure to 50μM BPA significantly decreased GnRH calcium activity. Blockage of γ-aminobutyric acid ergic and glutamatergic input did not abrogate the inhibitory BPA effect, suggesting direct regulation of GnRH neurons by BPA. In addition to estrogen receptor-β, single-cell RT-PCR analysis confirmed that GnRH neurons express G protein-coupled receptor 30 (G protein-coupled estrogen receptor 1) and estrogen-related receptor-γ, all potential targets for BPA. Perturbation studies of the signaling pathway revealed that the BPA-mediated inhibition of GnRH neuronal activity occurred independent of estrogen receptors, GPER, or estrogen-related receptor-γ, via a noncanonical pathway. These results provide the first evidence of a direct effect of BPA on GnRH neurons.

Current and potential treatment options for hyperphosphatemia.

PubMed

Carfagna, Fabio; Del Vecchio, Lucia; Pontoriero, Giuseppe; Locatelli, Francesco

2018-06-01

Hyperphosphatemia is common in late stages of chronic kidney disease and is often associated with elevated parathormone levels, abnormal bone mineralization, extra-osseous calcification, and increased risk of cardiovascular events and death. Several classes of oral phosphate binders are available to help control plasma phosphorus levels. Although effective at lowering serum phosphorus, they all have safety, tolerability, and compliance issues that need to be considered when selecting which one to use. Areas covered: This paper reviews the most established treatment options for hyperphosphatemia, in patients with chronic kidney disease, focusing on the new inhibitors of active phosphate absorption. Expert opinion: The prevention and the treatment of hyperphosphatemia is today far to be satisfactory. Nonetheless, an extending range of phosphate binders are now available. Aluminum has potentially serious toxic risks. Calcium-based binders are very effective but can lead to hypercalcemia and/or positive calcium balance and progression of cardiovascular calcification. No long-term data are available for the new calcium acetate/magnesium combination product. Lanthanum is an effective phosphate binder, and long-term effects of tissue deposition seem clinically irrelevant. Sevelamer, appear to have profiles that would lead to pleiotropic effects and reduced progression of vascular calcification, and the main adverse events seen with these agents are gastrointestinal. Iron has a powerful capability of binding phosphate, thus numerous preparations are available, both with and without significant systemic absorption of the iron component. The inhibitors of active intestinal phosphate transport, with their very selective mechanism of action and low pill burden seem the most interesting approach; however, do not seem at present to be effective alone, in reducing serum phosphorus levels.

Calcium released by photolysis of DM-nitrophen stimulates transmitter release at squid giant synapse.

PubMed

Delaney, K R; Zucker, R S

1990-07-01

1. Transmitter release at the squid giant synapse was stimulated by photolytic release of Ca2+ from the 'caged' Ca2+ compound DM-nitrophen (Kaplan & Ellis-Davies, 1988) inserted into presynaptic terminals. 2. Competing binding reactions cause the amount of Ca2+ released by DM-nitrophen photolysis to depend on the concentrations of DM-nitrophen, total Ca2+, Mg+, ATP and native cytoplasmic Ca2+ buffer. Measurements of presynaptic [Ca2+] changes by co-injection of the fluorescent indicator dye Fura-2 show that DM-nitrophen photolysis causes a transient rise in Ca2+ followed by decay within about 150 ms to an increased steady-state level. 3. Rapid photolysis of Ca2(+)-loaded nitrophen within the presynaptic terminal was followed in less than a millisecond by depolarization of the postsynaptic membrane. As with action potential-evoked excitatory postsynaptic potentials (EPSPs), the light-evoked response was partially and reversibly blocked by 1-3 mM-kainic acid which desensitizes postsynaptic glutamate receptors. 4. Release was similar in magnitude and rate to normal action potential-mediated EPSPs. 5. The release of transmitter by photolysis of Ca2(+)-loaded DM-nitrophen was not affected by removal of Ca2+ from the saline or addition of tetrodotoxin. Photolysis of DM-nitrophen injected into presynaptic terminals without added Ca2+ did not stimulate release of transmitter nor did it interfere with normal action potential-mediated release. 6. Stimulation of presynaptic action potentials in Ca2(+)-free saline during the light-evoked response did not elicit increased release of transmitter if the ganglion was bathed in Ca2(+)-free saline, i.e. in the absence of Ca2+ influx. Increasing the intensity of the light or stimulating presynaptic action potentials in Ca2(+)-containing saline increased the release of transmitter. Therefore the failure of presynaptic voltage change to increase transmitter release resulting from release of caged Ca2+ was not due to saturation or inhibition of the release mechanism by light-released Ca2+. 7. Decreasing the temperature of the preparation increased the delay to onset of the light-evoked response and reduced its amplitude and rate of rise to an extent similar to that observed for action potential-evoked EPSPs.

Muscle paralyzing effect of the juice from the trunk of the banana tree.

PubMed

Singh, Y N; Dryden, W F

1985-01-01

The effect of an extract from the trunk of the banana tree (Musa sapientum) was investigated in isolated skeletal muscle preparations from the chick, mouse and frog using twitch tension and intracellular recording techniques. The extract produced, in the same concentration range and after an initial period of twitch augmentation, paralysis of skeletal muscle in both directly and indirectly stimulated preparations. It also had a dose-dependent stimulant effect on the muscle causing a contracture. The neuromuscular blockade was reversed by calcium, but only when added before complete paralysis of the muscle. On the other hand, neostigmine usually hastened the blockade and aggravated the contracture. The frequency of the miniature endplate potential in the mouse phrenic nerve-diaphragm preparation greatly increased initially, declining to an elevated plateau. Effects on quantal content of endplate potentials (e.p.p.s) were studied in the transected mouse phrenic nerve-hemidiaphragm using trains of e.p.p.s. In the presence of the extract, only a few e.p.p. trains could normally be evoked, probably due to nerve terminal block. When quantal content could be measured at low concentrations of the extract, an increase was usually obtained. Muscle action potentials in the frog sartorius muscle were decreased in amplitude until no further potentials could be generated. The results suggest that the nature of the block produced by the extract resembles that of a potent local anaesthetic with an initial atypical labilizing effect on cell calcium rather than a conventional curariform block.

Role of glycolysis in maintenance of the action potential duration and contractile activity in isolated perfused rat heart.

PubMed

Opie, L H; Tuschmidt, R; Bricknell, O; Girardier, L

1980-01-01

1. Changing substrates from glucose to pyruvate in paced isolated rat hearts, perfused by the Langendorff technique at 65 cm H2O with a Krebs-Henseleit bicarbonate buffer, produced effects which are opposite to those of ouabain treatment: negative inotropy, decreased work efficiency, hyperpolarization, increased maximum rate of rise and amplitude of the action potential, increased conduction velocity. 2. All the effects resulting from perfusion with pyruvate can be reversed by adding ouabain at a concentration of 100 microM. 3. The correlation between various tissue metabolises and change in contractile force (delta F), rate of tension development [maximum + (dF/dt)] and rate of relaxation [maximum -(dF/dt)] was studied by multiple linear regression. No significant correlation was found with either glycogen content and tissue lactate or with cAMP and cGMP. A weak negative correlation was found with ATP and phosphocreatine. The strongest correlation was found 76 to 807 nM/g in passing from glucose- to pyruvate-containing perfusion solution. 4. In vitro tests performed with a solution containing high energy phosphates and magnesium at concentrations equal to their calculated values in the cytosol (pH 7.0) showed that a significant negative correlation exists between citrate concentration (range: 1 and 1500 M) and free calcium concentration in the micromole range. 5. It is concluded that the effects of pyruvate (non glucose substrate) perfusion could be mediated by a decrease in cytosolic-free calcium resulting from an increase in intracellular citrate. The observation that all these effects can be reversed by ouabain is taken as a circumstantial evidence of a common mechanism.

The statistics of calcium-mediated focal excitations on a one-dimensional cable.

PubMed

Chen, Wei; Asfaw, Mesfin; Shiferaw, Yohannes

2012-02-08

It is well known that various cardiac arrhythmias are initiated by an ill-timed excitation that originates from a focal region of the heart. However, up to now, it is not known what governs the timing, location, and morphology of these focal excitations. Recent studies have shown that these excitations can be caused by abnormalities in the calcium (Ca) cycling system. However, the cause-and-effect relationships linking subcellular Ca dynamics and focal activity in cardiac tissue is not completely understood. In this article, we present a minimal model of Ca-mediated focal excitations in cardiac tissue. This model accounts for the stochastic nature of spontaneous Ca release on a one-dimensional cable of cardiac cells. Using this model, we show that the timing of focal excitations is equivalent to a first passage time problem in a spatially extended system. In particular, we find that for a short cable the mean first passage time increases exponentially with the number of cells in tissue, and is critically dependent on the ratio of inward to outward currents near the threshold for an action potential. For long cables excitations occurs due to ectopic foci that occur on a length scale determined by the minimum length of tissue that can induce an action potential. Furthermore, we find that for long cables the mean first passage time decreases as a power law in the number cells. These results provide precise criteria for the occurrence of focal excitations in cardiac tissue, and will serve as a guide to determine the propensity of Ca-mediated triggered arrhythmias in the heart. Copyright © 2012 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Calcium sensor regulation of the CaV2.1 Ca2+ channel contributes to short-term synaptic plasticity in hippocampal neurons.

PubMed

Nanou, Evanthia; Sullivan, Jane M; Scheuer, Todd; Catterall, William A

2016-01-26

Short-term synaptic plasticity is induced by calcium (Ca(2+)) accumulating in presynaptic nerve terminals during repetitive action potentials. Regulation of voltage-gated CaV2.1 Ca(2+) channels by Ca(2+) sensor proteins induces facilitation of Ca(2+) currents and synaptic facilitation in cultured neurons expressing exogenous CaV2.1 channels. However, it is unknown whether this mechanism contributes to facilitation in native synapses. We introduced the IM-AA mutation into the IQ-like motif (IM) of the Ca(2+) sensor binding site. This mutation does not alter voltage dependence or kinetics of CaV2.1 currents, or frequency or amplitude of spontaneous miniature excitatory postsynaptic currents (mEPSCs); however, synaptic facilitation is completely blocked in excitatory glutamatergic synapses in hippocampal autaptic cultures. In acutely prepared hippocampal slices, frequency and amplitude of mEPSCs and amplitudes of evoked EPSCs are unaltered. In contrast, short-term synaptic facilitation in response to paired stimuli is reduced by ∼ 50%. In the presence of EGTA-AM to prevent global increases in free Ca(2+), the IM-AA mutation completely blocks short-term synaptic facilitation, indicating that synaptic facilitation by brief, local increases in Ca(2+) is dependent upon regulation of CaV2.1 channels by Ca(2+) sensor proteins. In response to trains of action potentials, synaptic facilitation is reduced in IM-AA synapses in initial stimuli, consistent with results of paired-pulse experiments; however, synaptic depression is also delayed, resulting in sustained increases in amplitudes of later EPSCs during trains of 10 stimuli at 10-20 Hz. Evidently, regulation of CaV2.1 channels by CaS proteins is required for normal short-term plasticity and normal encoding of information in native hippocampal synapses.

Bupivacaine-induced cellular entry of QX-314 and its contribution to differential nerve block

PubMed Central

Brenneis, C; Kistner, K; Puopolo, M; Jo, S; Roberson, DP; Sisignano, M; Segal, D; Cobos, EJ; Wainger, BJ; Labocha, S; Ferreirós, N; Hehn, C; Tran, J; Geisslinger, G; Reeh, PW; Bean, BP; Woolf, C J

2014-01-01

Background and Purpose: Selective nociceptor fibre block is achieved by introducing the cell membrane impermeant sodium channel blocker lidocaine N-ethyl bromide (QX-314) through transient receptor potential V1 (TRPV1) channels into nociceptors. We screened local anaesthetics for their capacity to activate TRP channels, and characterized the nerve block obtained by combination with QX-314. Experimental Approach: We investigated TRP channel activation in dorsal root ganglion (DRG) neurons by calcium imaging and patch-clamp recordings, and cellular QX-314 uptake by MS. To characterize nerve block, compound action potential (CAP) recordings from isolated nerves and behavioural responses were analysed. Key Results: Of the 12 compounds tested, bupivacaine was the most potent activator of ruthenium red-sensitive calcium entry in DRG neurons and activated heterologously expressed TRPA1 channels. QX-314 permeated through TRPA1 channels and accumulated intracellularly after activation of these channels. Upon sciatic injections, QX-314 markedly prolonged bupivacaine's nociceptive block and also extended (to a lesser degree) its motor block. Bupivacaine's blockade of C-, but not A-fibre, CAPs in sciatic nerves was extended by co-application of QX-314. Surprisingly, however, this action was the same in wild-type, TRPA1-knockout and TRPV1/TRPA1-double knockout mice, suggesting a TRP-channel independent entry pathway. Consistent with this, high doses of bupivacaine promoted a non-selective, cellular uptake of QX-314. Conclusions and Implications: Bupivacaine, combined with QX-314, produced a long-lasting sensory nerve block. This did not require QX-314 permeation through TRPA1, although bupivacaine activated these channels. Regardless of entry pathway, the greatly extended duration of block produced by QX-314 and bupivacaine may be clinically useful. PMID:24117225

A novel CaV2.2 channel inhibition by piracetam in peripheral and central neurons.

PubMed

Bravo-Martínez, Jorge; Arenas, Isabel; Vivas, Oscar; Rebolledo-Antúnez, Santiago; Vázquez-García, Mario; Larrazolo, Arturo; García, David E

2012-10-01

No mechanistic actions for piracetam have been documented to support its nootropic effects. Voltage-gated calcium channels have been proposed as a promising pharmacological target of nootropic drugs. In this study, we investigated the effect of piracetam on Ca(V)2.2 channels in peripheral neurons, using patch-clamp recordings from cultured superior cervical ganglion neurons. In addition, we tested if Ca(V)2.2 channel inhibition could be related with the effects of piracetam on central neurons. We found that piracetam inhibited native Ca(V)2.2 channels in superior cervical ganglion neurons in a dose-dependent manner, with an IC(50) of 3.4 μmol/L and a Hill coefficient of 1.1. GDPβS dialysis did not prevent piracetam-induced inhibition of Ca(V)2.2 channels and G-protein-coupled receptor activation by noradrenaline did not occlude the piracetam effect. Piracetam altered the biophysical characteristics of Ca(V)2.2 channel such as facilitation ratio. In hippocampal slices, piracetam and ω-conotoxin GVIA diminished the frequency of excitatory postsynaptic potentials and action potentials. Our results provide evidence of piracetam's actions on Ca(V)2.2 channels in peripheral neurons, which might explain some of its nootropic effects in central neurons.

Exopolysaccharides regulate calcium flow in cariogenic biofilms

PubMed Central

Varenganayil, Muth M.; Decho, Alan W.

2017-01-01

Caries-associated biofilms induce loss of calcium from tooth surfaces in the presence of dietary carbohydrates. Exopolysaccharides (EPS) provide a matrix scaffold and an abundance of primary binding sites within biofilms. The role of EPS in binding calcium in cariogenic biofilms is only partially understood. Thus, the aim of the present study is to investigate the relationship between the calcium dissolution rates and calcium tolerance of caries-associated bacteria and yeast as well as to examine the properties of EPS to quantify its binding affinity for dissolved calcium. Calcium dissolution was measured by dissolution zones on Pikovskaya’s agar. Calcium tolerance was assessed by isothermal microcalorimetry (IMC) by adding CaCl2 to the bacterial cultures. Acid-base titration and Fourier transform infrared (FTIR) spectroscopy were used to identify possible functional groups responsible for calcium binding, which was assessed by isothermal titration calorimetry (ITC). Lactobacillus spp. and mutans streptococci demonstrated calcium dissolution in the presence of different carbohydrates. All strains that demonstrated high dissolution rates also revealed higher rates of calcium tolerance by IMC. In addition, acidic functional groups were predominantly identified as possible binding sites for calcium ions by acid-base titration and FTIR. Finally, ITC revealed EPS to have a higher binding affinity for calcium compared, for example, to lactic acid. In conclusion, this study illustrates the role of EPS in terms of the calcium tolerance of cariogenic microbiota by determining the ability of EPS to control free calcium concentrations within the biofilms as a self-regulating mode of action in the pathogenesis of dental caries. PMID:29023506

Dimethylaminoethanol affects the viability of human cultured fibroblasts.

PubMed

Gragnani, Alfredo; Giannoccaro, Fabiana Bocci; Sobral, Christiane S; Moraes, A A F; França, Jeronimo P; Ferreira, A T; Ferreira, Lydia Masako

2007-01-01

In clinical practice, dimethylaminoethanol (DMAE) has been used in the fight against wrinkles and flaccidity in the cervicofacial region. The firming action of DMAE is explained by the fact that its molecule, considered to be a precursor of acetylcholine, alters muscle contraction. However, no experimental studies have confirmed this theory. Because the actual mechanism of DMAE action was not defined and there were no references in the literature regarding its direct action on fibroblasts, this study was performed to evaluate the direct action of DMAE on cultured human fibroblasts. Human fibroblasts obtained from discarded fragments of total skin from patients undergoing plastic or reconstructive surgical procedures performed within the Plastic Surgery Division at the Federal University of São Paulo were used for this study. The explant technique was used. The culture medium was supplemented with different concentrations of DMAE on the fourth cell passage, and the cell proliferation rate, cytosolic calcium levels, and cell cycle were evaluated. Statistical analysis was performed using analysis of variance (ANOVA) followed by a Newman-Keuls test for multiple comparisons. A decrease in fibroblast proliferation was associated with an increase in DMAE concentration. A longer treatment time with trypsin was required for the groups treated with DMAE in a dose-dependent manner. In the presence of DMAE, cytosolic calcium increased in a dose-dependent manner. Apoptosis also increased in groups treated with DMAE. Dimethylaminoethanol reduced the proliferation of fibroblasts, increased cytosolic calcium, and changed the cell cycle, causing an increase in apoptosis in cultured human fibroblasts.

Calcium and Bone Metabolism Indices.

PubMed

Song, Lu

2017-01-01

Calcium and inorganic phosphate are of critical importance for many body functions, thus the regulations of their plasma concentrations are tightly controlled by the concerted actions of reabsorption/excretion in the kidney, absorption in the intestines, and exchange from bone, the major reservoir for calcium and phosphate in the body. Parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (1,25(OH) 2 D) control calcium homeostasis, whereas PTH, 1,25(OH) 2 D, and bone-derived fibroblast growth factor 23 (FGF 23) control phosphate homeostasis. Hypoparathyroidism can cause hypocalcemia and hyperphosphatemia, whereas deficient vitamin D actions can cause osteomalacia in adults and rickets in children. Hyperparathyroidism, alternatively, can cause hypercalcemia and hypophosphatemia. Laboratory tests of calcium, phosphate, PTH, and 25-hydroxyvitamin D are very useful in the diagnosis of abnormalities associated with calcium and/or phosphate metabolisms. Bone is constantly remodeled throughout life in response to mechanical stress and a need for calcium in extracellular fluids. Metabolic bone diseases such as osteoporosis, osteomalacia in adults or rickets in children, and renal osteodystrophy develop when bone resorption exceeds bone formation. Bone turnover markers (BTM) such as serum N-terminal propeptide of type I procollagen (P1NP) and C-terminal collagen cross-link (CTX) may be useful in predicting future fracture risk or monitoring the response to anti-resorptive therapy. There is a need to standardize sample collection protocols because certain BTMs exhibit large circadian variations and tend to be influenced by food intakes. In the United States, a project to standardize BTM sample collection protocols and to establish the reference intervals for serum P1NP and serum CTX is ongoing. We anticipate the outcome of this project to shine lights on the standardization of BTM assays, sample collection protocols, reference intervals in relation to age, sex, and ethnic origins, and clinical utilities of BTMs. This review will briefly discuss the regulations of calcium and phosphate homeostasis, laboratory's role in the diagnosis, and monitoring of bone and calcium metabolism, as well as the usefulness and controversies of the utilities of BTMs in the diagnosis and monitoring of metabolic bone diseases. © 2017 Elsevier Inc. All rights reserved.

The origin of high sodium bicarbonate waters in the Atlantic and Gulf Coastal Plains

USGS Publications Warehouse

Foster, M.D.

1950-01-01

Some sodium bicarbonate waters at depth in the Atlantic and Gulf Coastal Plains have the same bicarbonate content as the shallower calcium bicarbonate waters in the same formation and appear to be the result of replacement of calcium by sodium through the action of base-exchange minerals. Others, however, contain several hundred parts per million more of bicarbonate than any of the calcium bicarbonate waters and much more bicarbonate than can be attributed to solution of calcium carbonate through the action of carbon dioxide derived from the air and soil. As the waters in the Potomac group (Cretaceous) are all low in sulphate and as the environmental conditions under which the sediments of the Potomac group were deposited do not indicate that large amounts of sulphate are available for solution, it does not seem probable that carbon dioxide generated by chemical or biochemical breakdown of sulphate is responsible for the high sodium bicarbonate waters in this area. Sulphate as a source of oxygen is not necessary for the generation of carbon dioxide by carbonaceous material. Oxygen is an important constituent of carbonaceous material and carbon dioxide is a characteristic decomposition product of such material-as, for example, peat and lignite. Experimental work showed that distilled water, calcium bicarbonate water, and sodium bicarbonate water, after contact with lignite, calcium carbonate, and permutite (a base-exchange material), had all increased greatly in sodium bicarbonate content and had become similar in chemical character and in mineral content to high sodium bicarbonate waters found in the Coastal Plain. The tests indicated that carbonaceous material can act as a source of carbon dioxide, which, when dissolved in water, enables it to take into solution more calcium carbonate. If base-exchange materials are also present to replace calcium with sodium, a still greater amount of bicarbonate can be held in solution. The presence of carbonaceous material, together with calcium carbonate and base-exchange minerals in a formation is, therefore, sufficient to account for the occurrence in it of high sodium bicarbonate waters. ?? 1950.

Increasing Dietary Phosphorus Intake from Food Additives: Potential for Negative Impact on Bone Health123

PubMed Central

Takeda, Eiji; Yamamoto, Hironori; Yamanaka-Okumura, Hisami; Taketani, Yutaka

2014-01-01

It is important to consider whether habitual high phosphorus intake adversely affects bone health, because phosphorus intake has been increasing, whereas calcium intake has been decreasing in dietary patterns. A higher total habitual dietary phosphorus intake has been associated with higher serum parathyroid hormone (PTH) and lower serum calcium concentrations in healthy individuals. Higher serum PTH concentrations have been shown in those who consume foods with phosphorus additives. These findings suggest that long-term dietary phosphorus loads and long-term hyperphosphatemia may have important negative effects on bone health. In contrast, PTH concentrations did not increase as a result of high dietary phosphorus intake when phosphorus was provided with adequate amounts of calcium. Intake of foods with a ratio of calcium to phosphorus close to that found in dairy products led to positive effects on bone health. Several randomized controlled trials have shown positive relations between dairy intake and bone mineral density. In our loading test with a low-calcium, high-phosphorus lunch provided to healthy young men, serum PTH concentrations showed peaks at 1 and 6 h, and serum fibroblast growth factor 23 (FGF23) concentrations increased significantly at 8 h after the meal. In contrast, the high-calcium, high-phosphorus meal suppressed the second PTH and FGF23 elevations until 8 h after the meal. This implies that adequate dietary calcium intake is needed to overcome the interfering effects of high phosphorus intake on PTH and FGF23 secretion. FGF23 acts on the parathyroid gland to decrease PTH mRNA and PTH secretion in rats with normal kidney function. However, increased serum FGF23 is an early alteration of mineral metabolism in chronic kidney disease, causing secondary hyperthyroidism, and implying resistance of the parathyroid gland to the action of FGF23 in chronic kidney disease. These findings suggest that long-term high-phosphorus diets may impair bone health mediated by FGF23 resistance both in chronic kidney disease patients and in the healthy population. PMID:24425727

Vasopressin regulates renal calcium excretion in humans

PubMed Central

Hanouna, Guillaume; Haymann, Jean-Philippe; Baud, Laurent; Letavernier, Emmanuel

2015-01-01

Antidiuretic hormone or arginine vasopressin (AVP) increases water reabsorption in the collecting ducts of the kidney. Three decades ago, experimental models have shown that AVP may increase calcium reabsorption in rat kidney. The objective of this study was to assess whether AVP modulates renal calcium excretion in humans. We analyzed calcium, potassium, and sodium fractional excretion in eight patients affected by insipidus diabetes (nephrogenic or central) under acute vasopressin receptor agonist action and in 10 patients undergoing oral water load test affected or not by inappropriate antidiuretic hormone secretion (SIADH). Synthetic V2 receptor agonist (dDAVP) reduced significantly calcium fractional excretion from 1.71% to 0.58% (P < 0.05) in patients with central diabetes insipidus. In patients with nephrogenic diabetes insipidus (resistant to AVP), calcium fractional excretion did not change significantly after injection (0.48–0.68%, P = NS). In normal subjects undergoing oral water load test, calcium fractional excretion increased significantly from 1.02% to 2.54% (P < 0.05). Patients affected by SIADH had a high calcium fractional excretion at baseline that remained stable during test from 3.30% to 3.33% (P = NS), possibly resulting from a reduced calcium absorption in renal proximal tubule. In both groups, there was a significant correlation between urine output and calcium renal excretion. In humans, dDAVP decreases calcium fractional excretion in the short term. Conversely, water intake, which lowers AVP concentration, increases calcium fractional excretion. The correlation between urine output and calcium excretion suggests that AVP-related antidiuresis increases calcium reabsorption in collecting ducts. PMID:26620256

The role of Rho-kinase and calcium ions in constriction triggered by ET-1.

PubMed

Wiciński, Michał; Szadujkis-Szadurska, Katarzyna; Węclewicz, Mateusz M; Malinowski, Bartosz; Matusiak, Grzegorz; Walczak, Maciej; Wódkiewicz, Eryk; Grześk, Grzegorz; Pawlak-Osińska, Katarzyna

2018-05-05

Endothelin-1 (ET-1) is one of the key factors regulating tension of smooth muscles in blood vessels. It is believed that ET-1 plays an important role in pathogenesis of hypertension, and cardiovascular diseases; therefore, research in order to limit ET-1-mediated action is still in progress. The main objective of this paper was to evaluate the role of Rho-kinase in the ET-1-induced constriction of arteries. The analysis also included significance of intra- and extracellular pool of calcium ions in constriction triggered by ET-1. The studies were performed on perfused Wistar rat tail arteries. Concentration response curve (CRC) was determined for ET-1 in the presence of increased concentrations of Rho-kinase inhibitor (Y-27632) and IP3-receptor antagonist (2APB), both in reference to constriction triggered by solely ET-1. Afterwards, the influence of calcium ions present in the perfusion fluid was evaluated in terms of the effect triggered by 2APB and occurring in arteries constricted by ET-1. ET-1, in concentration dependent manner, leads to increase in perfusion pressure. Y-27632 and 2APB lead to shift of the concentration response curve for ET-1 to the right with simultaneously lowered maximum effect. There was no difference in reaction of the artery constricted by ET-1 and treated with 2APB in solution containing calcium and in calcium-free solution. Vasoconstrictive action of endothelin is not significantly dependent on the inflow of extracellular calcium, but it is proportional to inflow of Ca 2+ related to activation of IP3 receptors and to Rho-kinase activity. Copyright © 2018. Published by Elsevier Inc.

Beyond faithful conduction: short-term dynamics, neuromodulation, and long-term regulation of spike propagation in the axon

PubMed Central

Bucher, Dirk; Goaillard, Jean-Marc

2011-01-01

Most spiking neurons are divided into functional compartments: a dendritic input region, a soma, a site of action potential initiation, an axon trunk and its collaterals for propagation of action potentials, and distal arborizations and terminals carrying the output synapses. The axon trunk and lower order branches are probably the most neglected and are often assumed to do nothing more than faithfully conducting action potentials. Nevertheless, there are numerous reports of complex membrane properties in non-synaptic axonal regions, owing to the presence of a multitude of different ion channels. Many different types of sodium and potassium channels have been described in axons, as well as calcium transients and hyperpolarization-activated inward currents. The complex time- and voltage-dependence resulting from the properties of ion channels can lead to activity-dependent changes in spike shape and resting potential, affecting the temporal fidelity of spike conduction. Neural coding can be altered by activity-dependent changes in conduction velocity, spike failures, and ectopic spike initiation. This is true under normal physiological conditions, and relevant for a number of neuropathies that lead to abnormal excitability. In addition, a growing number of studies show that the axon trunk can express receptors to glutamate, GABA, acetylcholine or biogenic amines, changing the relative contribution of some channels to axonal excitability and therefore rendering the contribution of this compartment to neural coding conditional on the presence of neuromodulators. Long-term regulatory processes, both during development and in the context of activity-dependent plasticity may also affect axonal properties to an underappreciated extent. PMID:21708220

Ameliorative potential of Vernonia cinerea on chronic constriction injury of sciatic nerve induced neuropathic pain in rats.

PubMed

Thiagarajan, Venkata R K; Shanmugam, Palanichamy; Krishnan, Uma M; Muthuraman, Arunachalam

2014-08-29

The aim of the present study is to investigate the ameliorative potential of ethanolic extract of whole plant of Vernonia cinerea in the chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in rats. Behavioral parameters such as a hot plate, acetone drop, paw pressure, Von Frey hair and tail immersion tests were performed to assess the degree of thermal, chemical and mechanical hyperalgesia and allodynia. Biochemical changes in sciatic nerve tissue were ruled out by estimating thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and total calcium levels. Ethanolic extract of Vernonia cinerea and pregabalin were administered for 14 consecutive days starting from the day of surgery. CCI of sciatic nerve has been shown to induce significant changes in behavioral, biochemical and histopathological assessments when compared to the sham control group. Vernonia cinerea attenuated in a dose dependent manner the above pathological changes induced by CCI of the sciatic nerve, which is similar to attenuation of the pregabalin pretreated group. The ameliorating effect of ethanolic extract of Vernonia cinerea against CCI of sciatic nerve induced neuropathic pain may be due to the presence of flavonoids and this effect is attributed to anti-oxidative, neuroprotective and calcium channel modulator actions of these compounds.

Ameliorative potential of Vernonia cinerea on chronic constriction injury of sciatic nerve induced neuropathic pain in rats.

PubMed

Thiagarajan, Venkata R K; Shanmugam, Palanichamy; Krishnan, Uma M; Muthuraman, Arunachalam

2014-09-01

The aim of the present study is to investigate the ameliorative potential of ethanolic extract of whole plant of Vernonia cinerea in the chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in rats. Behavioral parameters such as a hot plate, acetone drop, paw pressure, Von Frey hair and tail immersion tests were performed to assess the degree of thermal, chemical and mechanical hyperalgesia and allodynia. Biochemical changes in sciatic nerve tissue were ruled out by estimating thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and total calcium levels. Ethanolic extract of Vernonia cinerea and pregabalin were administered for 14 consecutive days starting from the day of surgery. CCI of sciatic nerve has been shown to induce significant changes in behavioral, biochemical and histopathological assessments when compared to the sham control group. Vernonia cinerea attenuated in a dose dependent manner the above pathological changes induced by CCI of the sciatic nerve, which is similar to attenuation of the pregabalin pretreated group. The ameliorating effect of ethanolic extract of Vernonia cinerea against CCI of sciatic nerve induced neuropathic pain may be due to the presence of flavonoids and this effect is attributed to anti-oxidative, neuroprotective and calcium channel modulator actions of these compounds.

Ripk3 regulates cardiac microvascular reperfusion injury: The role of IP3R-dependent calcium overload, XO-mediated oxidative stress and F-action/filopodia-based cellular migration.

PubMed

Zhou, Hao; Wang, Jin; Zhu, Pingjun; Hu, Shunying; Ren, Jun

2018-05-01

Ripk3-mediated cellular apoptosis is a major contributor to the pathogenesis of myocardial ischemia reperfusion (IR) injury. However, the mechanisms by which Ripk3 influences microvascular homeostasis and endothelial apoptosis are not completely understood. In this study, loss of Ripk3 inhibited endothelial apoptosis, alleviated luminal swelling, maintained microvasculature patency, reduced the expression of adhesion molecules and limited the myocardial inflammatory response. In vitro, Ripk3 deficiency protected endothelial cells from apoptosis and migratory arrest induced by HR injury. Mechanistically, Ripk3 had the ability to migrate onto the endoplasmic reticulum (ER), leading to ER damage, as evidenced by increased IP3R and XO expression. The higher IP3R content was associated with cellular calcium overload, and increased XO expression was involved in cellular oxidative injury. Furthermore, IP3R-mediated calcium overload and XO-dependent oxidative damage were able to initiate cellular apoptosis. More importantly, IP3R and XO also caused F-actin degradation into G-actin via post-transcriptional modification of cofilin, impairing the formation of the filopodia and limiting the migratory response of endothelial cells. Altogether, our data confirmed that Ripk3 was involved in microvascular IR injury via regulation of IP3R-mediated calcium overload, XO-dependent oxidative damage and filopodia-related cellular migration, ultimately leading to endothelial apoptosis and migratory inhibition. These findings provide a potential target for treating cardiac microcirculatory IR injury. Copyright © 2018 Elsevier Inc. All rights reserved.

The utility of levosimendan in the treatment of heart failure.

PubMed

Lehtonen, Lasse; Põder, Pentti

2007-01-01

Calcium sensitizers are a new group of inotropic drugs. Levosimendan is the only calcium sensitizer in clinical use in Europe. Its mechanism of action includes both calcium sensitization of contractile proteins and the opening of adenosine triphosphate (ATP)-dependent potassium channels as mechanism of vasodilation. The combination of K-channel opening with positive inotropy offers potential benefits in comparison to currently available intravenous inotropes, since K-channel opening protects myocardium during ischemia. Due to the calcium-dependent binding of levosimendan to troponin C, the drug increases contractility without negative lusitropic effects. In patients with heart failure levosimendan dose-dependently increases cardiac output and reduces pulmonary capillary wedge pressure. Since levosimendan has an active metabolite OR-1896 with a half-life of some 80 hours, the duration of the hemodynamic effects significantly exceeds the 1-hour half-life of the parent compound. The hemodynamic effects of the levosimendan support its use in acute and postoperative heart failure. Several moderate-size trials (LIDO, RUSSLAN, CASINO) have previously suggested that the drug might even improve the prognosis of patients with decompensated heart failure. These trials were carried out in patients with high filling pressures. Recently two larger trials (SURVIVE and REVIVE) in patients who were hospitalized because of worsening heart failure have been finalized. These trials did not require filling pressures to be measured. The two trials showed that levosimendan improves the symptoms of heart failure, but does not improve survival. The results raise the question whether a 24-hour levosimendan infusion can be used without invasive hemodynamic monitoring.

The Influence of Glutamate on Axonal Compound Action Potential In Vitro.

PubMed

Abouelela, Ahmed; Wieraszko, Andrzej

2016-01-01

Background  Our previous experiments demonstrated modulation of the amplitude of the axonal compound action potential (CAP) by electrical stimulation. To verify assumption that glutamate released from axons could be involved in this phenomenon, the modification of the axonal CAP induced by glutamate was investigated. Objectives  The major objective of this research is to verify the hypothesis that axonal activity would trigger the release of glutamate, which in turn would interact with specific axonal receptors modifying the amplitude of the action potential. Methods  Segments of the sciatic nerve were exposed to exogenous glutamate in vitro, and CAP was recorded before and after glutamate application. In some experiments, the release of radioactive glutamate analog from the sciatic nerve exposed to exogenous glutamate was also evaluated. Results  The glutamate-induced increase in CAP was blocked by different glutamate receptor antagonists. The effect of glutamate was not observed in Ca-free medium, and was blocked by antagonists of calcium channels. Exogenous glutamate, applied to the segments of sciatic nerve, induced the release of radioactive glutamate analog, demonstrating glutamate-induced glutamate release. Immunohistochemical examination revealed that axolemma contains components necessary for glutamatergic neurotransmission. Conclusion  The proteins of the axonal membrane can under the influence of electrical stimulation or exogenous glutamate change membrane permeability and ionic conductance, leading to a change in the amplitude of CAP. We suggest that increased axonal activity leads to the release of glutamate that results in changes in the amplitude of CAPs.

Studies on the cardiac actions of flosequinan in vitro.

PubMed Central

Gristwood, R. W.; Beleta, J.; Bou, J.; Cardelús, I.; Fernández, A. G.; Llenas, J.; Berga, P.

1992-01-01

1. We have investigated the in vitro cardiac actions of flosequinan and of its major metabolite in man, BTS 53554. 2. Positive inotropic activity was seen with flosequinan in guinea-pig isolated ventricles, the threshold concentration for effect being less than 1 x 10(-5) M. BTS 53554 was approximately half as potent as the parent compound. 3. In guinea-pig working whole hearts flosequinan increased left ventricular dp/dtmax, indicating a positive inotropic action. This effect was accompanied by increases in heart rate, cardiac output and stroke volume. 4. The virtual complete inhibition of inotropic responses to flosequinan and BTS 53554 by carbachol suggests that these responses are adenosine 3':5'-cyclic monophosphate (cyclic AMP)-mediated. 5. Flosequinan was shown to increase calcium inward current in guinea-pig ventricle, an action consistent with a cyclic AMP involvement in the response. 6. The inotropic activity of flosequinan was not potentiated by the selective phosphodiesterase (PDE) III inhibitor SK&F 94120, a result which indicates that flosequinan does not increase cyclic AMP concentrations via stimulation of adenylate cyclase. 7. Flosequinan inotropic responses were potentiated by rolipram, a selective PDE IV inhibitor, a result consistent with flosequinan being itself a PDE III inhibitor. 8. Biochemical studies with purified enzymes confirmed that flosequinan and BTS 53554 are relatively selective inhibitors of PDE III. 9. A comparison of pharmacological and biochemical data for both flosequinan and BTS 53554 indicates that their PDE III inhibitory potency is sufficient to account for their inotropic activity. PMID:1324061

Ketamine produces antidepressant-like effects through phosphorylation-dependent nuclear export of histone deacetylase 5 (HDAC5) in rats

PubMed Central

Choi, Miyeon; Lee, Seung Hoon; Wang, Sung Eun; Ko, Seung Yeon; Song, Mihee; Choi, June-Seek; Duman, Ronald S.; Son, Hyeon

2015-01-01

Ketamine produces rapid antidepressant-like effects in animal assays for depression, although the molecular mechanisms underlying these behavioral actions remain incomplete. Here, we demonstrate that ketamine rapidly stimulates histone deacetylase 5 (HDAC5) phosphorylation and nuclear export in rat hippocampal neurons through calcium/calmodulin kinase II- and protein kinase D-dependent pathways. Consequently, ketamine enhanced the transcriptional activity of myocyte enhancer factor 2 (MEF2), which leads to regulation of MEF2 target genes. Transfection of a HDAC5 phosphorylation-defective mutant (Ser259/Ser498 replaced by Ala259/Ala498, HDAC5-S/A), resulted in resistance to ketamine-induced nuclear export, suppression of ketamine-mediated MEF2 transcriptional activity, and decreased expression of MEF2 target genes. Behaviorally, viral-mediated hippocampal knockdown of HDAC5 blocked or occluded the antidepressant effects of ketamine both in unstressed and stressed animals. Taken together, our results reveal a novel role of HDAC5 in the actions of ketamine and suggest that HDAC5 could be a potential mechanism contributing to the therapeutic actions of ketamine. PMID:26647181

Effect of Calcium Ions on the Disintegration of Enteric-Coated Solid Dosage Forms.

PubMed

Al-Gousous, Jozef; Langguth, Peter

2016-02-01

To investigate the effect of calcium ions on the disintegration of enteric-coated dosage forms, disintegration testing was performed on enteric-coated aspirin tablets in the presence and absence of calcium in the test media. The results show that the presence of calcium ions retards the disintegration of enteric-coated dosage forms. This finding, which has not been reported in scientific literature, sheds light on the importance of conducting well-designed detailed investigations into the potential of calcium from dietary sources, calcium supplements, antacids, and/or phosphate binders affecting the absorption of drugs formulated into enteric-coated dosage forms. Moreover, it shows the necessity to investigate the potential of the occurrence of additional nutrient-excipient interactions. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Calcium supplementation in osteoporosis: useful or harmful?

PubMed

Chiodini, Iacopo; Bolland, Mark J

2018-04-01

Osteoporosis and fragility fractures are important social and economic problems worldwide and are due to both the loss of bone mineral density and sarcopenia. Indeed, fragility fractures are associated with increased disability, morbidity and mortality. It is known that a normal calcium balance together with a normal vitamin D status is important for maintaining well-balanced bone metabolism, and for many years, calcium and vitamin D have been considered crucial in the prevention and treatment of osteoporosis. However, recently, the usefulness of calcium supplementation (alone or with concomitant vitamin D) has been questioned, since some studies reported only weak efficacy of these supplementations in reducing fragility fracture risk. On the other hand, besides the gastrointestinal side effects of calcium supplements and the risk of kidney stones related to use of co-administered calcium and vitamin D supplements, other recent data suggested potential adverse cardiovascular effects from calcium supplementation. This debate article is focused on the evidence regarding both the possible usefulness for bone health and the potential harmful effects of calcium and/or calcium with vitamin D supplementation. © 2018 European Society of Endocrinology.

Calcium Biofortification: Three Pronged Molecular Approaches for Dissecting Complex Trait of Calcium Nutrition in Finger Millet (Eleusine coracana) for Devising Strategies of Enrichment of Food Crops

PubMed Central

Sharma, Divya; Jamra, Gautam; Singh, Uma M.; Sood, Salej; Kumar, Anil

2017-01-01

Calcium is an essential macronutrient for plants and animals and plays an indispensable role in structure and signaling. Low dietary intake of calcium in humans has been epidemiologically linked to various diseases which can have serious health consequences over time. Major staple food-grains are poor source of calcium, however, finger millet [Eleusine coracana (L.) Gaertn.], an orphan crop has an immense potential as a nutritional security crop due to its exceptionally high calcium content. Understanding the existing genetic variation as well as molecular mechanisms underlying the uptake, transport, accumulation of calcium ions (Ca2+) in grains is of utmost importance for development of calcium bio-fortified crops. In this review, we have discussed molecular mechanisms involved in calcium accumulation and transport thoroughly, emphasized the role of molecular breeding, functional genomics and transgenic approaches to understand the intricate mechanism of calcium nutrition in finger millet. The objective is to provide a comprehensive up to date account of molecular mechanisms regulating calcium nutrition and highlight the significance of bio-fortification through identification of potential candidate genes and regulatory elements from finger millet to alleviate calcium malnutrition. Hence, finger millet could be used as a model system for explaining the mechanism of elevated calcium (Ca2+) accumulation in its grains and could pave way for development of nutraceuticals or designer crops. PMID:28144246

Calcium Biofortification: Three Pronged Molecular Approaches for Dissecting Complex Trait of Calcium Nutrition in Finger Millet (Eleusine coracana) for Devising Strategies of Enrichment of Food Crops.

PubMed

Sharma, Divya; Jamra, Gautam; Singh, Uma M; Sood, Salej; Kumar, Anil

2016-01-01

Calcium is an essential macronutrient for plants and animals and plays an indispensable role in structure and signaling. Low dietary intake of calcium in humans has been epidemiologically linked to various diseases which can have serious health consequences over time. Major staple food-grains are poor source of calcium, however, finger millet [ Eleusine coracana (L.) Gaertn.], an orphan crop has an immense potential as a nutritional security crop due to its exceptionally high calcium content. Understanding the existing genetic variation as well as molecular mechanisms underlying the uptake, transport, accumulation of calcium ions (Ca 2+ ) in grains is of utmost importance for development of calcium bio-fortified crops. In this review, we have discussed molecular mechanisms involved in calcium accumulation and transport thoroughly, emphasized the role of molecular breeding, functional genomics and transgenic approaches to understand the intricate mechanism of calcium nutrition in finger millet. The objective is to provide a comprehensive up to date account of molecular mechanisms regulating calcium nutrition and highlight the significance of bio-fortification through identification of potential candidate genes and regulatory elements from finger millet to alleviate calcium malnutrition. Hence, finger millet could be used as a model system for explaining the mechanism of elevated calcium (Ca 2+ ) accumulation in its grains and could pave way for development of nutraceuticals or designer crops.

Computational analysis of the human sinus node action potential: model development and effects of mutations

PubMed Central

Fabbri, Alan; Fantini, Matteo; Wilders, Ronald

2017-01-01

Key points We constructed a comprehensive mathematical model of the spontaneous electrical activity of a human sinoatrial node (SAN) pacemaker cell, starting from the recent Severi–DiFrancesco model of rabbit SAN cells.Our model is based on electrophysiological data from isolated human SAN pacemaker cells and closely matches the action potentials and calcium transient that were recorded experimentally.Simulated ion channelopathies explain the clinically observed changes in heart rate in corresponding mutation carriers, providing an independent qualitative validation of the model.The model shows that the modulatory role of the ‘funny current’ (I f) in the pacing rate of human SAN pacemaker cells is highly similar to that of rabbit SAN cells, despite its considerably lower amplitude.The model may prove useful in the design of experiments and the development of heart‐rate modulating drugs. Abstract The sinoatrial node (SAN) is the normal pacemaker of the mammalian heart.  Over several decades, a large amount of data on the ionic mechanisms underlying the spontaneous electrical activity of SAN pacemaker cells has been obtained, mostly in experiments on single cells isolated from rabbit SAN. This wealth of data has allowed the development of mathematical models of the electrical activity of rabbit SAN pacemaker cells. The present study aimed to construct a comprehensive model of the electrical activity of a human SAN pacemaker cell using recently obtained electrophysiological data from human SAN pacemaker cells.  We based our model on the recent Severi–DiFrancesco model of a rabbit SAN pacemaker cell. The action potential and calcium transient of the resulting model are close to the experimentally recorded values. The model has a much smaller ‘funny current’ (I f) than do rabbit cells, although its modulatory role is highly similar. Changes in pacing rate upon the implementation of mutations associated with sinus node dysfunction agree with the clinical observations. This agreement holds for both loss‐of‐function and gain‐of‐function mutations in the HCN4, SCN5A and KCNQ1 genes, underlying ion channelopathies in I f, fast sodium current and slow delayed rectifier potassium current, respectively. We conclude that our human SAN cell model can be a useful tool in the design of experiments and the development of drugs that aim to modulate heart rate. PMID:28185290

[Aging-related ionic remodeling of L-type voltage dependent calcium channel in left atria of canine].

PubMed

Zhou, Xian-hui; Zhang, Jian; Gan, Tian-yi; Xu, Guo-jun; Tang, Bao-peng

2012-04-01

To investigate aging-related ionic remodeling of L-type voltage dependent calcium channel (LVDCC) in left atria of canine. Seven adult (2.0 - 2.5 years) and 10 aged (> 8 years) dogs were used. The current of LVDCC was recorded by patch clamp technique in the whole cell mode. The action potential duration (APD(90)), amplitude of action potential plateau (APA), I(Ca-L) peak current density of LVDCC were recorded. The mRNA and protein expressions of α1c subunit (Ca(V1.2)), sarcoplasmic reticulum Ca(2+)-ATPase (SECRA(2)), Calpain-I, ryanodine receptor (RYR(2)) were detected by quantitative RT-PCR and Western blot, respectively. I(Ca-L) peak current density [(-8.11 ± 0.54) pA/pF vs. (-14.04 ± 0.82) pA/pF, P < 0.05] was significantly reduced and action potential duration to 90% repolarization (APD(90)) significantly prolonged [(340.5 ± 10.1) ms vs. (320.0 ± 7.9) ms, P < 0.05] in aged group than in adult group. The mRNA gene expression level of Ca(V1.2) was significantly lower (0.90 ± 0.35 vs. 2.38 ± 0.40, P < 0.05) while mRNA expression of RYR(2) was significantly higher (4.39 ± 4.68 vs. 1.49 ± 1.69, P < 0.05) in the aged dogs than in the adult dogs. mRNA expression of SECRA(2) and Calpain-I was similar between the two groups. Similarly, the protein expression level of Ca(V1.2) was significantly lower (0.13 ± 0.10 vs. 0.29 ± 0.12, P < 0.05) while the protein expression level of RYR(2) was significantly higher (0.18 ± 0.21 vs. 0.08 ± 0.36, P < 0.05) in the aged dogs than in the adult dogs. Again, protein expression of SECRA(2), PLN(1) and Calpain-I was similar between the two groups. These data suggest that aging could induce mRNA and protein expression changes of Ca(V1.2) and RYR(2) of LVDCC which might serve as the molecular basis of I(Ca-L) remodeling in aged dogs and might be linked to the increased likelihood of developing atrial fibrillation (AF) in aged dogs.

Molecular Dynamics Simulations of Membrane-Bound STIM1 to Investigate Conformational Changes during STIM1 Activation upon Calcium Release.

PubMed

Mukherjee, Sreya; Karolak, Aleksandra; Debant, Marjolaine; Buscaglia, Paul; Renaudineau, Yves; Mignen, Olivier; Guida, Wayne C; Brooks, Wesley H

2017-02-27

Calcium is involved in important intracellular processes, such as intracellular signaling from cell membrane receptors to the nucleus. Typically, calcium levels are kept at less than 100 nM in the nucleus and cytosol, but some calcium is stored in the endoplasmic reticulum (ER) lumen for rapid release to activate intracellular calcium-dependent functions. Stromal interacting molecule 1 (STIM1) plays a critical role in early sensing of changes in the ER's calcium level, especially when there is a sudden release of stored calcium from the ER. Inactive STIM1, which has a bound calcium ion, is activated upon ion release. Following activation of STIM1, there is STIM1-assisted initiation of extracellular calcium entry through channels in the cell membrane. This extracellular calcium entering the cell then amplifies intracellular calcium-dependent actions. At the end of the process, ER levels of stored calcium are reestablished. The main focus of this work was to study the conformational changes accompanying homo- or heterodimerization of STIM1. For this purpose, the ER luminal portion of STIM1 (residues 58-236), which includes the sterile alpha motif (SAM) domain plus the calcium-binding EF-hand domains 1 and 2 attached to the STIM1 transmembrane region (TM), was modeled and embedded in a virtual membrane. Next, molecular dynamics simulations were performed to study the conformational changes that take place during STIM1 activation and subsequent protein-protein interactions. Indeed, the simulations revealed exposure of residues in the EF-hand domains, which may be important for dimerization steps. Altogether, understanding conformational changes in STIM1 can help in drug discovery when targeting this key protein in intracellular calcium functions.

The Ca2+/H+ antiporter TMEM165 expression, localization in the developing, lactating and involuting mammary gland parallels the secretory pathway Ca2+ATPase (SPCA1)

USDA-ARS?s Scientific Manuscript database

Plasma membrane Ca2+-ATPase 2 (PMCA2) knockout mice showed that ~ 60 % of calcium in milk is transported across the mammary cells apical membrane by PMCA2. The remaining milk calcium is thought to arrive via the secretory pathway through the actions of secretory pathway Ca2+-ATPase’s 1 and/or 2 (SP...

Membrane Potential and Calcium Dynamics in Beta Cells from Mouse Pancreas Tissue Slices: Theory, Experimentation, and Analysis.

PubMed

Dolenšek, Jurij; Špelič, Denis; Klemen, Maša Skelin; Žalik, Borut; Gosak, Marko; Rupnik, Marjan Slak; Stožer, Andraž

2015-10-28

Beta cells in the pancreatic islets of Langerhans are precise biological sensors for glucose and play a central role in balancing the organism between catabolic and anabolic needs. A hallmark of the beta cell response to glucose are oscillatory changes of membrane potential that are tightly coupled with oscillatory changes in intracellular calcium concentration which, in turn, elicit oscillations of insulin secretion. Both membrane potential and calcium changes spread from one beta cell to the other in a wave-like manner. In order to assess the properties of the abovementioned responses to physiological and pathological stimuli, the main challenge remains how to effectively measure membrane potential and calcium changes at the same time with high spatial and temporal resolution, and also in as many cells as possible. To date, the most wide-spread approach has employed the electrophysiological patch-clamp method to monitor membrane potential changes. Inherently, this technique has many advantages, such as a direct contact with the cell and a high temporal resolution. However, it allows one to assess information from a single cell only. In some instances, this technique has been used in conjunction with CCD camera-based imaging, offering the opportunity to simultaneously monitor membrane potential and calcium changes, but not in the same cells and not with a reliable cellular or subcellular spatial resolution. Recently, a novel family of highly-sensitive membrane potential reporter dyes in combination with high temporal and spatial confocal calcium imaging allows for simultaneously detecting membrane potential and calcium changes in many cells at a time. Since the signals yielded from both types of reporter dyes are inherently noisy, we have developed complex methods of data denoising that permit for visualization and pixel-wise analysis of signals. Combining the experimental approach of high-resolution imaging with the advanced analysis of noisy data enables novel physiological insights and reassessment of current concepts in unprecedented detail.

Cellular Mechanisms of Calcium-Mediated Triggered Activity

NASA Astrophysics Data System (ADS)

Song, Zhen

Life-threatening cardiac arrhythmias continue to pose a major health problem. Ventricular fibrillation, which is a complex form of electrical wave turbulence in the lower chambers of the heart, stops the heart from pumping and is the largest cause of natural death in the United States. Atrial fibrillation, a related form of wave turbulence in the upper heart chambers, is in turn the most common arrhythmia diagnosed in clinical practice. Despite extensive research to date, mechanisms of cardiac arrhythmias remain poorly understood. It is well established that both spatial disorder of the refractory period of heart cells and triggered activity (TA) jointly contribute to the initiation and maintenance of arrhythmias. TA broadly refers to the abnormal generation of a single or a sequence of abnormal excitation waves from a small submillimeter region of the heart in the interval of time between two normal waves generated by the heart's natural pacemaker (the sinoatrial node). TA has been widely investigated experimentally and occurs in several pathological conditions where the intracellular concentration of free Ca2+ ions in heart cells becomes elevated. Under such conditions, Ca2+ can be spontaneously released from intracellular stores, thereby driving an electrogenic current that exchanges 3Na+ ions for one Ca2+ ion across the cell membrane. This current in turn depolarizes the membrane of heart cells after a normal excitation. If this calcium-mediated "delayed after depolarization'' (DAD) is sufficiently large, it can generate an action potential. While the arrhythmogenic importance of spontaneous Ca2+ release and DADs is well appreciated, the conditions under which they occur in heart pathologies remain poorly understood. Calcium overload is only one factor among several other factors that can promote DADs, including sympathetic nerve stimulation, different expression levels of membrane ion channels and calcium handling proteins, and different mutations of those proteins. How those various factors interact synergistically to promote DADs is not well understood. Furthermore, at an even more basic level, it remains unclear to what degree spontaneous Ca2+ release and the appearance of DADs are deterministic, meaning reproducible under identical conditions, or inherently stochastic like nucleation in the physical context of phase transitions. In this thesis, we use and further develop a biologically detailed computational model to investigate basic aspects of TA in isolated heart cells (cardiac myocytes). Isolated cells can be obtained by enzymatic dissociation of heart tissue and studied experimentally using standard electrophysiological recording methods and confocal imaging of Ca2+ dynamics. Hence they provide a well controlled setting to investigate the generation of DADs under well controlled conditions. Our computational model captures essential aspects of the hierarchical architecture of ventricular myocytes, which consists of a large number of approximately 20,000 to 50,000 regularly spaced submicron regions containing clusters of 50-100 Ryanodine receptor (RyR) Ca2+ release channels. Each of those regions acts as a discrete "calcium release unit'' (CRU). Therefore our model allows us to address for the first time quantitatively the fundamental question of whether Ca2+ release, which is highly stochastic at the level of a single calcium release unit, is stochastic or deterministic at the whole cell level where the Ca 2+ signal is the summation of releases from a large number of units. Addressing this question is the focus of the first part of this thesis. Our results demonstrate that both the initiation and termination of TA are highly stochastic at the whole cell level due to the spatiotemporal organization of discrete release events into multiple Ca2+ waves. Our results allow us to characterize the probability distributions that govern the number of DADs preceding a triggered action potential and the number of triggered action potentials after termination of periodic stimulation. We show that a limit cycle underlies the bi-directionally coupled dynamics of membrane of voltage and Ca2+ when TA is sustained for long intervals. Furthermore, we construct a simple theoretical model that allows us to relate the shape of those distributions to the statistics and properties of Ca 2+ waves. The second part of this thesis focuses on investigating TA in the context of a specific mutation of a calcium buffering protein calsequestrin (CSQN). This mutation underlies catecholaminergic polymorphic ventricular tachycardia (CPVT), which is a pathophysiological condition that affects a subset of the human population. Our results shed light on the mechanisms by which altered Ca2+ buffering and altered kinetics of RyR Ca 2+ release channels as a direct and indirect effect of this mutation, respectively, promote TA.

A comparison of the effects of commercially available hawthorn preparations on calcium transients of isolated cardiomyocytes.

PubMed

Rodriguez, Michelle E; Poindexter, Brian J; Bick, Roger J; Dasgupta, Amitava

2008-12-01

We studied the potential cardiac effects of two alcohol extracts of commercially available hawthorn using rat cardiomyocytes and measuring calcium transients by real-time fluorescence spectrophotometry. One preparation was a blend of hawthorn flowers, leaves, and berries (extract #1), and the other (extract #2) was from a "berries-only" preparation. Fluorescent images and calcium transients were acquired concurrently. Addition of extract #1 resulted in the initiation of robust calcium transients and eventual calcium overload, while addition of extract #2 caused increased calcium sparking, initiation of calcium transients, and an increased beating rate but no calcium overload. To identify the mechanisms of increased calcium influx, adult rat cardiomyocytes were challenged with 10 microM ouabain, a Na(+),K(+)-ATPase inhibitor, and the calcium channel blocker nifedipine. The findings revealed that equal volumes of the two readily available hawthorn preparations demonstrated markedly different effects on isolated adult rat cardiomyocytes, suggesting important implications for patients who are using these preparations to supplement or even replace their prescribed cardiac medications as to which preparation(s) to use, and potential dire consequences, particularly in cardiac patients. Our study indicates that the mechanism of cardiac activity of hawthorn is via the Na(+),K(+)-ATPase and intracellular calcium concentrations are influenced.

Induction of calcium-dependent nitric oxide synthases by sex hormones.

PubMed

Weiner, C P; Lizasoain, I; Baylis, S A; Knowles, R G; Charles, I G; Moncada, S

1994-05-24

We have examined the effects of pregnancy and sex hormones on calcium-dependent and calcium-independent nitric oxide synthases (NOSs) in the guinea pig. Pregnancy (near term) caused a > 4-fold increase in the activity of calcium-dependent NOS in the uterine artery and at least a doubling in the heart, kidney, skeletal muscle, esophagus, and cerebellum. The increase in NOS activity in the cerebellum during pregnancy was inhibited by the estrogen-receptor antagonist tamoxifen. Treatment with estradiol (but not progesterone) also increased calcium-dependent NOS activity in the tissues examined from both females and males. Testosterone increased calcium-dependent NOS only in the cerebellum. No significant change in calcium-independent NOS activity was observed either during pregnancy or after the administration of any sex hormone. Both pregnancy and estradiol treatment increased the amount of mRNAs for NOS isozymes eNOS and nNOS in skeletal muscle, suggesting that the increases in NOS activity result from enzyme induction. Thus both eNOS and nNOS are subject to regulation by estrogen, an action that could explain some of the changes that occur during pregnancy and some gender differences in physiology and pathophysiology.

Direct stimulation of the transcellular and paracellular calcium transport in the rat cecum by prolactin.

PubMed

Kraidith, Kamonshanok; Jantarajit, Walailuk; Teerapornpuntakit, Jarinthorn; Nakkrasae, La-iad; Krishnamra, Nateetip; Charoenphandhu, Narattaphol

2009-09-01

Prolactin (PRL) is reported to stimulate calcium absorption in the rat's small intestine. However, little is known regarding its effects on the cecum, a part of the large intestine with the highest rate of intestinal calcium transport. We demonstrated herein by quantitative real-time polymerase chain reaction and Western blot analysis that the cecum could be a target organ of PRL since cecal epithelial cells strongly expressed PRL receptors. In Ussing chamber experiments, PRL enhanced the transcellular cecal calcium absorption in a biphasic dose-response manner. PRL also increased the paracellular calcium permeability and passive calcium transport in the cecum, which could be explained by the PRL-induced decrease in transepithelial resistance and increase in cation selectivity of the cecal epithelium. PRL actions in the cecum were abolished by inhibitors of phosphoinositide 3-kinase (PI3K), protein kinase C (PKC), and RhoA-associated coiled-coil forming kinase (ROCK), but not inhibitors of gene transcription and protein biosynthesis. In conclusion, PRL directly enhanced the transcellular and paracellular calcium transport in the rat cecum through the nongenomic signaling pathways involving PI3K, PKC, and ROCK.

BPA Directly Decreases GnRH Neuronal Activity via Noncanonical Pathway

PubMed Central

Klenke, Ulrike; Constantin, Stephanie

2016-01-01

Peripheral feedback of gonadal estrogen to the hypothalamus is critical for reproduction. Bisphenol A (BPA), an environmental pollutant with estrogenic actions, can disrupt this feedback and lead to infertility in both humans and animals. GnRH neurons are essential for reproduction, serving as an important link between brain, pituitary, and gonads. Because GnRH neurons express several receptors that bind estrogen, they are potential targets for endocrine disruptors. However, to date, direct effects of BPA on GnRH neurons have not been shown. This study investigated the effects of BPA on GnRH neuronal activity using an explant model in which large numbers of primary GnRH neurons are maintained and express many of the receptors found in vivo. Because oscillations in intracellular calcium have been shown to correlate with electrical activity in GnRH neurons, calcium imaging was used to assay the effects of BPA. Exposure to 50μM BPA significantly decreased GnRH calcium activity. Blockage of γ-aminobutyric acid ergic and glutamatergic input did not abrogate the inhibitory BPA effect, suggesting direct regulation of GnRH neurons by BPA. In addition to estrogen receptor-β, single-cell RT-PCR analysis confirmed that GnRH neurons express G protein-coupled receptor 30 (G protein-coupled estrogen receptor 1) and estrogen-related receptor-γ, all potential targets for BPA. Perturbation studies of the signaling pathway revealed that the BPA-mediated inhibition of GnRH neuronal activity occurred independent of estrogen receptors, GPER, or estrogen-related receptor-γ, via a noncanonical pathway. These results provide the first evidence of a direct effect of BPA on GnRH neurons. PMID:26934298

Calcium mobilization and phosphoinositide turnover in fluoride-activated human neutrophils

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

Strnad, C.F.; Wong, K.

1986-05-01

Fluoride ion, at concentrations above 10 mM, has been found to activate a superoxide production response in human neutrophils which is strongly dependent on the presence of extracellular calcium. In an attempt to further explore the calcium requirement of fluoride-induced neutrophil activation, intracellular calcium concentrations were monitored through use of the fluorescent calcium probe, Quin 2. Fluoride ion, at concentrations between 10 and 20 mM, was found to elicit a rise in intracellular calcium levels which was characterized by a lag period of 4 to 10 min and a prolonged duration of action (greater than 20 min). In contrast, themore » chemotactic peptide, formylmethionyl-leucyl-phenylalanine (FMLP), induced a rise in intracellular calcium concentration which peaked within 1 min. Preincubation of cells with 1 ..mu..g/ml pertussis toxin resulted in inhibition of the FMLP-induced response, but not that elicited by fluoride. Furthermore, anion exchange chromatography indicated that inositol phosphate accumulation occurred in fluoride-treated cells in association with calcium mobilization. Recent evidence suggests that the FMLP receptor is coupled to phospholipase C and phosphoinositide turnover through a guanine nucleotide binding protein susceptible to inhibition by pertussis toxin. Present results suggest that fluoride ion may serve to activate this protein in a manner resistant to inhibition by pertussis toxin.« less

Calcium-dependent inactivation of calcium channels in cochlear hair cells of the chicken.

PubMed

Lee, Seunghwan; Briklin, Olga; Hiel, Hakim; Fuchs, Paul

2007-09-15

Voltage-gated calcium channels support both spontaneous and sound-evoked neurotransmitter release from ribbon synapses of cochlear hair cells. A variety of regulatory mechanisms must cooperate to ensure the appropriate level of activity in the restricted pool of synaptic calcium channels ( approximately 100) available to each synaptic ribbon. One potential feedback mechanism, calcium-dependent inactivation (CDI) of voltage-gated, L-type calcium channels, can be modulated by calmodulin-like calcium-binding proteins. CDI of voltage-gated calcium current was studied in hair cells of the chicken's basilar papilla (analogous to the mammalian cochlea) after blocking the predominant potassium conductances. For inactivating currents produced by 2.5 s steps to the peak of the current-voltage relation (1 mm EGTA internal calcium buffer), single exponential fits yielded an average decay time constant of 1.92 +/- 0.18 s (mean +/- s.e.m., n = 12) at 20-22 degrees C, while recovery occurred with a half-time of approximately 10 s. Inactivation produced no change in reversal potential, arguing that the observed relaxation did not result from alternative processes such as calcium accumulation or activation of residual potassium currents. Substitution of external calcium with barium greatly reduced inactivation, while inhibition of endoplasmic calcium pumps with t-benzohydroquinone (BHQ) or thapsigargin made inactivation occur faster and to a greater extent. Raising external calcium 10-fold (from 2 to 20 mm) increased peak current 3-fold, but did not alter the extent or time course of CDI. However, increasing levels of internal calcium buffer consistently reduced the rate and extent of inactivation. With 1 mm EGTA buffering and in 2 mm external calcium, the available pool of calcium channels was half-inactivated near the resting membrane potential (-50 mV). CDI may be further regulated by calmodulin-like calcium-binding proteins (CaBPs). mRNAs for several CaBPs are expressed in chicken cochlear tissue, and antibodies to CaBP4 label hair cells, but not supporting cells, equivalent to the pattern seen in mammalian cochlea. Thus, molecular mechanisms that underlie CDI appeared to be conserved across vertebrate species, may provide a means to adjust calcium channel open probability, and could serve to maintain the set-point for spontaneous release from the ribbon synapse.

Calcium-dependent inactivation of calcium channels in cochlear hair cells of the chicken

PubMed Central

Lee, Seunghwan; Briklin, Olga; Hiel, Hakim; Fuchs, Paul

2007-01-01

Voltage-gated calcium channels support both spontaneous and sound-evoked neurotransmitter release from ribbon synapses of cochlear hair cells. A variety of regulatory mechanisms must cooperate to ensure the appropriate level of activity in the restricted pool of synaptic calcium channels (∼100) available to each synaptic ribbon. One potential feedback mechanism, calcium-dependent inactivation (CDI) of voltage-gated, L-type calcium channels, can be modulated by calmodulin-like calcium-binding proteins. CDI of voltage-gated calcium current was studied in hair cells of the chicken's basilar papilla (analogous to the mammalian cochlea) after blocking the predominant potassium conductances. For inactivating currents produced by 2.5 s steps to the peak of the current–voltage relation (1 mm EGTA internal calcium buffer), single exponential fits yielded an average decay time constant of 1.92 ± 0.18 s (mean ±s.e.m., n = 12) at 20–22°C, while recovery occurred with a half-time of ∼10 s. Inactivation produced no change in reversal potential, arguing that the observed relaxation did not result from alternative processes such as calcium accumulation or activation of residual potassium currents. Substitution of external calcium with barium greatly reduced inactivation, while inhibition of endoplasmic calcium pumps with t-benzohydroquinone (BHQ) or thapsigargin made inactivation occur faster and to a greater extent. Raising external calcium 10-fold (from 2 to 20 mm) increased peak current 3-fold, but did not alter the extent or time course of CDI. However, increasing levels of internal calcium buffer consistently reduced the rate and extent of inactivation. With 1 mm EGTA buffering and in 2 mm external calcium, the available pool of calcium channels was half-inactivated near the resting membrane potential (−50 mV). CDI may be further regulated by calmodulin-like calcium-binding proteins (CaBPs). mRNAs for several CaBPs are expressed in chicken cochlear tissue, and antibodies to CaBP4 label hair cells, but not supporting cells, equivalent to the pattern seen in mammalian cochlea. Thus, molecular mechanisms that underlie CDI appeared to be conserved across vertebrate species, may provide a means to adjust calcium channel open probability, and could serve to maintain the set-point for spontaneous release from the ribbon synapse. PMID:17656437

Protein tyrosine phosphatase 1B is a mediator of cyclic ADP ribose-induced Ca2+ signaling in ventricular myocytes.

PubMed

Park, Seon-Ah; Hong, Bing-Zhe; Ha, Ki-Chan; Kim, Uh-Hyun; Han, Myung-Kwan; Kwak, Yong-Geun

2017-06-02

Cyclic ADP-ribose (cADPR) releases Ca 2+ from ryanodine receptor (RyR)-sensitive calcium pools in various cell types. In cardiac myocytes, the physiological levels of cADPR transiently increase the amplitude and frequency of Ca 2+ (that is, a rapid increase and decrease of calcium within one second) during the cardiac action potential. In this study, we demonstrated that cADPR levels higher than physiological levels induce a slow and gradual increase in the resting intracellular Ca 2+ ([Ca 2+ ] i ) level over 10 min by inhibiting the sarcoendoplasmic reticulum Ca 2+ ATPase (SERCA). Higher cADPR levels mediate the tyrosine-dephosphorylation of α-actin by protein tyrosine phosphatase 1B (PTP1B) present in the endoplasmic reticulum. The tyrosine dephosphorylation of α-actin dissociates phospholamban, the key regulator of SERCA, from α-actin and results in SERCA inhibition. The disruption of the integrity of α-actin by cytochalasin B and the inhibition of α-actin tyrosine dephosphorylation by a PTP1B inhibitor block cADPR-mediated Ca 2+ increase. Our results suggest that levels of cADPR that are relatively higher than normal physiological levels modify calcium homeostasis through the dephosphorylation of α-actin by PTB1B and the subsequent inhibition of SERCA in cardiac myocytes.

Functional proteins involved in regulation of intracellular Ca(2+) for drug development: the extracellular calcium receptor and an innovative medical approach to control secondary hyperparathyroidism by calcimimetics.

PubMed

Nagano, Nobuo; Nemeth, Edward F

2005-03-01

Circulating levels of calcium ion (Ca(2+)) are maintained within a narrow physiological range mainly by the action of parathyroid hormone (PTH) secreted from parathyroid cells. Parathyroid cells can sense small fluctuations in plasma Ca(2+) levels by virtue of a cell surface Ca(2+) receptor (CaR) that belongs to the superfamily of G-protein-coupled receptors. Calcimimetics are positive allosteric modulators that activate the CaR on parathyroid cells and thereby immediately suppress PTH secretion. Pre-clinical studies with NPS R-568, a first generation calcimimetic compound, have demonstrated that daily oral administration inhibits the elevation of plasma PTH levels and parathyroid gland hyperplasia and ameliorates impaired bone qualities in rats with chronic renal insufficiency. The results of clinical trials with cinacalcet hydrochloride, a second generation calcimimetic compound, have shown that calcimimetics possess lowering effects not only on serum PTH levels but also on serum calcium x phosphorus product levels, a hallmark of an increased risk for cardiovascular death in dialysis patients with end-stage renal disease (ESRD). Thus, calcimimetics have considerable potential as an innovative medical approach to manage secondary hyperparathyroidism associated with ESRD. Indeed, cinacalcet hydrochloride has been approved in several countries and is the first positive allosteric modulator of any G protein-coupled receptor to reach the market.

Paradoxical Effects of Sodium-Calcium Exchanger Inhibition on Torsade de Pointes and Early Afterdepolarization in a Heart Failure Rabbit Model.

PubMed

Chang, Po-Cheng; Lu, Yu-Ying; Lee, Hui-Ling; Lin, Shien-Fong; Chu, Yen; Wen, Ming-Shien; Chou, Chung-Chuan

2018-05-03

Calcium homeostasis plays an important role in development of early afterdepolarizations (EADs) and torsade de pointes (TdP). The role of sodium-calcium exchanger (NCX) inhibition in genesis secondary Ca rise and EADs-TdP is still debated. Dual voltage and intracellular Ca optical mapping were conducted in 6 control and 9 failing rabbit hearts. After baseline electrophysiological and optical mapping studies, E4031 was given to simulate long QT syndrome. ORM-10103 was then administrated to examine the electrophysiological effects on EAD-TdP development. E4031 enhanced secondary Ca rise, EADs development and TdP inducibility in both control and failing hearts. The results showed that ORM-10103 reduced premature ventricular beats (PVBs) but was unable to suppress the inducibility of TdP or EADs. The electrophysiological effects of ORM-10103 included prolongation of action potential duration (APD) and increased APD heterogeneity in failing hearts. ORM10103 had a neutral effect on the amplitude of secondary Cai rise in control and HF groups. In this model, most EADs generated from the long-short APD junction area. In conclusion, highly selective NCX inhibition with ORM-10103 reduced PVB burden but was unable to suppress secondary Ca rise, EADs development nor inducibility of TdP. The possible electrophysiological mechanisms include APD prolongation and increased APD heterogeneity.

Vitamin K3 inhibits mouse uterine contraction in vitro via interference with the calcium transfer and the potassium channels.

PubMed

Zhang, Xian-Xia; Lu, Li-Min; Wang, Li

2016-08-05

Previous studies have demonstrated vitamin K3 had a great relief to smooth muscle spastic disorders, but no researches have yet pinpointed its possible anti-contractile activity in the uterus. Here, we evaluated the effect of vitamin K3 on myometrial contractility and explored the possible mechanisms of vitamin K3 action. Myograph apparatus were used to record the changes in contractility of isolated mouse uterine strips in a tissue bath. Uterine strips were exposed to vitamin K3 or vehicle. Vitamin K3 suppressed spontaneous contractions in a concentration dependent manner. It significantly decreased the contractile frequency induced by PGF2ɑ but not their amplitude (expect 58.0 μM). Prior incubation with vitamin K3 reduced the effectiveness of PGF2ɑ-induced contraction. The antispasmodic effect of vitamin K3 was also sensitive to potassium channel blockers, such as tetraethylammonium, 4-aminopyridine, iberiotoxin) but not to the nitric oxide related pathway blockers. High concentrations (29.0, 58.0 μM) of vitamin K3 weakened the Ca(2+) dose response and inhibited phase 1 contraction (intracellular stored calcium release). These dates suggest that vitamin K3 specifically suppresses myometrial contractility by affecting calcium and potassium channels; thus, this approach has potential therapy for uterine contractile activity related disorders. Copyright © 2016 Elsevier Inc. All rights reserved.

The Physiology, Pathology, and Pharmacology of Voltage-Gated Calcium Channels and Their Future Therapeutic Potential

PubMed Central

Zamponi, Gerald W.; Striessnig, Joerg; Koschak, Alexandra

2015-01-01

Voltage-gated calcium channels are required for many key functions in the body. In this review, the different subtypes of voltage-gated calcium channels are described and their physiologic roles and pharmacology are outlined. We describe the current uses of drugs interacting with the different calcium channel subtypes and subunits, as well as specific areas in which there is strong potential for future drug development. Current therapeutic agents include drugs targeting L-type CaV1.2 calcium channels, particularly 1,4-dihydropyridines, which are widely used in the treatment of hypertension. T-type (CaV3) channels are a target of ethosuximide, widely used in absence epilepsy. The auxiliary subunit α2δ-1 is the therapeutic target of the gabapentinoid drugs, which are of value in certain epilepsies and chronic neuropathic pain. The limited use of intrathecal ziconotide, a peptide blocker of N-type (CaV2.2) calcium channels, as a treatment of intractable pain, gives an indication that these channels represent excellent drug targets for various pain conditions. We describe how selectivity for different subtypes of calcium channels (e.g., CaV1.2 and CaV1.3 L-type channels) may be achieved in the future by exploiting differences between channel isoforms in terms of sequence and biophysical properties, variation in splicing in different target tissues, and differences in the properties of the target tissues themselves in terms of membrane potential or firing frequency. Thus, use-dependent blockers of the different isoforms could selectively block calcium channels in particular pathologies, such as nociceptive neurons in pain states or in epileptic brain circuits. Of important future potential are selective CaV1.3 blockers for neuropsychiatric diseases, neuroprotection in Parkinson’s disease, and resistant hypertension. In addition, selective or nonselective T-type channel blockers are considered potential therapeutic targets in epilepsy, pain, obesity, sleep, and anxiety. Use-dependent N-type calcium channel blockers are likely to be of therapeutic use in chronic pain conditions. Thus, more selective calcium channel blockers hold promise for therapeutic intervention. PMID:26362469

[Effects of desulfurization waste on calcium distribution, Ca(2+)-ATPase activity, and antioxidant characteristics of rice leaf under alkali stress].

PubMed

Mao, Gui-Lian; Xu, Xing; Zeng, Jin; Yue, Zi-Hui; Yang, Shu-Juan

2012-02-01

To approach the action mechanisms of desulfurization waste on alleviating alkali stress-induced injury of rice, a pot experiment was conducted to study the variations of leaf total calcium content, calcium distribution, plasma membrane Ca(2+)-ATPase activity, and reactive oxygen content of rice seedlings under alkali stress after the application of desulfurization waste. In the control, a few calcium particulates scattered in the cell wall and chloroplasts, while applying desulfurization waste or CaSO4 increased the calcium particulates in the plasma membrane, intercellular space, cell wall, and vacuole significantly. With the increasing application rate of desulfurization waste or CaSO4, the leaf total calcium content increased, Ca(2+)-ATPase activity in plasma membrane and tonoplast presented an increasing trend, plasma membrane relative permeability, MDA content, and O2 production rate decreased, and SOD and POD activities increased. The desulfurization waste could relieve the alkali stress to rice in some extent, and the main reactive compound in the waste could be CaSO4.

Prolactin-induced neuroprotection against glutamate excitotoxicity is mediated by the reduction of [Ca2+]i overload and NF-κB activation

PubMed Central

Rivero-Segura, Nadia A.; Flores-Soto, Edgar; García de la Cadena, Selene; Coronado-Mares, Isabel; Gomez-Verjan, Juan C.; Ferreira, Diana G.; Cabrera-Reyes, Erika Alejandra; Lopes, Luísa V.; Massieu, Lourdes

2017-01-01

Prolactin (PRL) is a peptidic hormone that displays pleiotropic functions in the organism including different actions in the brain. PRL exerts a neuroprotective effect against excitotoxicity produced by glutamate (Glu) or kainic acid in both in vitro and in vivo models. It is well known that Glu excitotoxicity causes cell death through apoptotic or necrotic pathways due to intracellular calcium ([Ca2+] i) overload. Therefore, the aim of the present study was to assess the molecular mechanisms by which PRL maintains cellular viability of primary cultures of rat hippocampal neurons exposed to Glu excitotoxicity. We determined cell viability by monitoring mitochondrial activity and using fluorescent markers for viable and dead cells. The intracellular calcium level was determined by a fluorometric assay and proteins involved in the apoptotic pathway were determined by immunoblot. Our results demonstrated that PRL afforded neuroprotection against Glu excitotoxicity, as evidenced by a decrease in propidium iodide staining and by the decrease of the LDH activity. In addition, the MTT assay shows that PRL maintains normal mitochondrial activity even in neurons exposed to Glu. Furthermore, the Glu-induced intracellular [Ca2+]i overload was attenuated by PRL. These data correlate with the reduction found in the level of active caspase-3 and the pro-apoptotic ratio (Bax/Bcl-2). Concomitantly, PRL elicited the nuclear translocation of the transcriptional factor NF-κB, which was detected by immunofluorescence and confocal microscopy. To our knowledge, this is the first report demonstrating that PRL prevents Glu excitotoxicity by a mechanism involving the restoration of the intracellular calcium homeostasis and mitochondrial activity, as well as an anti-apoptotic action possibly mediated by the activity of NF-κB. Overall, the current results suggest that PRL could be of potential therapeutic advantage in the treatment of neurodegenerative diseases. PMID:28475602

Kv1.1 channelopathy abolishes presynaptic spike width modulation by subthreshold somatic depolarization

PubMed Central

Vivekananda, Umesh; Novak, Pavel; Bello, Oscar D.; Korchev, Yuri E.; Krishnakumar, Shyam S.; Volynski, Kirill E.; Kullmann, Dimitri M.

2017-01-01

Although action potentials propagate along axons in an all-or-none manner, subthreshold membrane potential fluctuations at the soma affect neurotransmitter release from synaptic boutons. An important mechanism underlying analog–digital modulation is depolarization-mediated inactivation of presynaptic Kv1-family potassium channels, leading to action potential broadening and increased calcium influx. Previous studies have relied heavily on recordings from blebs formed after axon transection, which may exaggerate the passive propagation of somatic depolarization. We recorded instead from small boutons supplied by intact axons identified with scanning ion conductance microscopy in primary hippocampal cultures and asked how distinct potassium channels interact in determining the basal spike width and its modulation by subthreshold somatic depolarization. Pharmacological or genetic deletion of Kv1.1 broadened presynaptic spikes without preventing further prolongation by brief depolarizing somatic prepulses. A heterozygous mouse model of episodic ataxia type 1 harboring a dominant Kv1.1 mutation had a similar broadening effect on basal spike shape as deletion of Kv1.1; however, spike modulation by somatic prepulses was abolished. These results argue that the Kv1.1 subunit is not necessary for subthreshold modulation of spike width. However, a disease-associated mutant subunit prevents the interplay of analog and digital transmission, possibly by disrupting the normal stoichiometry of presynaptic potassium channels. PMID:28193892

Effects of Nicotinamide Adenine Dinucleotide (NAD(+)) and Diadenosine Tetraphosphate (Ap4A) on Electrical Activity of Working and Pacemaker Atrial Myocardium in Guinea Pigs.

PubMed

Pustovit, K B; Abramochkin, D V

2016-04-01

Effects of nucleotide polyphosphate compounds (nicotinamide adenine dinucleotide, NAD(+); diadenosine tetraphosphate, Ap4A) on the confi guration of action potentials were studied in isolated preparations of guinea pig sinoatrial node and right atrial appendage (auricle). In the working myocardium, NAD(+) and Ap4A in concentrations of 10(-5) and 10(-4) M had no effect on resting potential, but significantly reduced the duration of action potentials; the most pronounced decrease was found at 25% repolarization. In the primary pacemaker of the sinoatrial node, both concentrations of NAD(+) and Ap4A induced hyperpolarization and reduction in the rate of slow diastolic depolarization, but significant slowing of the sinus rhythm was produced by these substances only in the concentration of 10(-4) M. Moreover, AP shortening and marked acceleration of AP upstroke were observed in the pacemaker myocardium after application of polyphosphates. Comparative analysis of the effects of NAD(+) and Ap4A in the working and pacemaker myocardium drove us to a hypothesis on inhibitory effects of these substances on L-type calcium current accompanied by stimulation of one or several potassium currents, which induce enhancement of repolarization and hyperpolarization of membranes probably mediated by the activation of purine receptors.

Defects in the calcium-binding region drastically affect the cadherin-like domains of RET tyrosine kinase.

PubMed

Gao, Chunxia; Grøtli, Morten; Eriksson, Leif A

2016-03-28

Mutations in the rearranged during transfection (RET) tyrosine kinase gene leading to gain or loss of function have been associated with the development of several human cancers and Hirschsprung's disease (HSCR). However, to what extent these mutations affect individual bio-molecular functions remains unclear. In this article, the functionally significant mutations in the RET CLD1-4 calcium-binding site which lead to HSCR, and depletion of calcium ions in the RET CLD1-4 calcium binding site, were investigated by molecular dynamics simulations--to understand the mechanistic action of the mutations or loss of calcium ions in altering the protein kinase structure, dynamics, and stability. The mutations or loss of calcium ions change the local conformation and change the free energy landscape. Specifically, the mutations and loss of calcium ions decrease the radius of gyration of the whole structure, leading to improper protein folding and GFL-GFRα contact site reduction. Furthermore, based on the most populated conformation in the wildtype MD simulations, a pharmacophore was generated by fragment docking to identify key features of the possible inhibitors targeting the calcium binding site. Overall, the findings may provide useful structural insights into the molecular mechanism underlying RET calcium-binding site mutations and assist in development of novel drugs targeting the extracellular ligand contact site of wildtype RET.

Inhibition of spontaneous activity of rabbit atrioventricular node cells by KB-R7943 and inhibitors of sarcoplasmic reticulum Ca2+ ATPase

PubMed Central

Cheng, Hongwei; Smith, Godfrey L.; Hancox, Jules C.; Orchard, Clive H.

2011-01-01

The atrioventricular node (AVN) can act as a subsidiary cardiac pacemaker if the sinoatrial node fails. In this study, we investigated the effects of the Na–Ca exchange (NCX) inhibitor KB-R7943, and inhibition of the sarcoplasmic reticulum calcium ATPase (SERCA), using thapsigargin or cyclopiazonic acid (CPA), on spontaneous action potentials (APs) and [Ca2+]i transients from cells isolated from the rabbit AVN. Spontaneous [Ca2+]i transients were monitored from undialysed AVN cells at 37 °C using Fluo-4. In separate experiments, spontaneous APs and ionic currents were recorded using the whole-cell patch clamp technique. Rapid application of 5 μM KB-R7943 slowed or stopped spontaneous APs and [Ca2+]i transients. However, in voltage clamp experiments in addition to blocking NCX current (INCX) KB-R7943 partially inhibited L-type calcium current (ICa,L). Rapid reduction of external [Na+] also abolished spontaneous activity. Inhibition of SERCA (using 2.5 μM thapsigargin or 30 μM CPA) also slowed or stopped spontaneous APs and [Ca2+]i transients. Our findings are consistent with the hypothesis that sarcoplasmic reticulum (SR) Ca2+ release influences spontaneous activity in AVN cells, and that this occurs via [Ca2+]i-activated INCX; however, the inhibitory action of KB-R7943 on ICa,L means that care is required in the interpretation of data obtained using this compound. PMID:21163524

[The effect of modulators of SK channels on simple spike firing frequency in the discharge of the cerebellar Purkinje cells in laboratory mice].

PubMed

Egorova, P A; Karelina, T V; Vlasova, O L; Antonov, S M; Besprozvanny, I B

2014-01-01

The effect of CyPPA, a positive modulator of small conductance calcium-activated potassium channels of type 3 and 2 (SK3/SK2), and of NS309, an activator of intermediate and small conductance calcium-activated potassium channels (IK/SK), on the activity of cerebellar Purkinje cells was studied in 2-month-old male mice. The use of 1 mM of CyPPA has led to a decrease of simple spike firing frequency in the discharge of Purkinje cells by 25%, on average, during 1 h after application. At the same time, application of 100 μM of NS309 has promoted a decrease in simple spike firing frequency by 47 %, on average, during 1 h after the beginning of the action. The obtained results confirm the hypothesis that SK channels participate in regulation of simple spike firing frequency in the discharge of Purkinje cells and are responsible for restriction of signal frequency. The effect of NS309 on simple spike firing frequency was more pronounced; therefore, the IK/SK channels may be suggested to play the cardinal role in regulation of spike activity of Purkinje cells. Since increasing simple spike frequency in the discharge of Purkinje cells is observed at many disturbances of motor activity, in particular, at spinocerebellar ataxia, it can be suggested that the studied compounds or substances of similar action are of interest as potential medicinal agents.

Regulation of ACh release from guinea pig bladder urothelial cells: potential role in bladder filling sensations.

PubMed

McLatchie, L M; Young, J S; Fry, C H

2014-07-01

The aim of this study was to quantify and characterize the mechanism of non-neuronal ACh release from bladder urothelial cells and to determine if urothelial cells could be a site of action of anti-muscarinic drugs. A novel technique was developed whereby ACh could be measured from freshly isolated guinea pig urothelial cells in suspension following mechanical stimulation. Various agents were used to manipulate possible ACh release pathways in turn and to study the effects of muscarinic receptor activation and inhibition on urothelial ATP release. Minimal mechanical stimulus achieved full ACh release, indicating a small dynamic range and possible all-or-none signal. ACh release involved a mechanism dependent on the anion channel CFTR and intracellular calcium concentration, but was independent of extracellular calcium, vesicular trafficking, connexins or pannexins, organic cation transporters and was not affected by botulinum-A toxin. Stimulating ACh receptors increased ATP production and antagonizing them reduced ATP release, suggesting a link between ACh and ATP release. These results suggest that release of non-neuronal ACh from the urothelium is large enough and well located to act as a modulator of ATP release. It is hypothesized that this pathway may contribute to the actions of anti-muscarinic drugs in reducing the symptoms of lower urinary tract syndromes. Additionally the involvement of CFTR in ACh release suggests an exciting new direction for the treatment of these conditions. © 2014 The British Pharmacological Society.

Role of phospholipase A2 pathway in regulating activation of Bufo arenarum oocytes.

PubMed

Ajmat, M T; Bonilla, F; Hermosilla, P C; Zelarayán, L; Bühler, M I

2013-08-01

Transient increases in the concentration of cytosolic Ca(2+) are essential for triggering egg activation events. Increased Ca(2+) results from its rapid release from intracellular stores, mainly mediated by one or both intracellular calcium channels: the inositol trisphosphate receptor (IP3R) and the ryanodine receptor (RyR). Several regulatory pathways that tailor the response of these channels to the specific cell type have been proposed. Among its many modulatory actions, calcium can serve as an activator of a cytosolic phospholipase A(2) (cPLA2), which releases arachidonic acid from phospholipids of the endoplasmic reticulum as well as from the nuclear envelope. Previous studies have suggested that arachidonic acid and/or its metabolites were able to modulate the activity of several ion channels. Based on these findings, we have studied the participation of the phospholipase A(2) (PLA(2)) pathway in the process of Bufo arenarum oocyte activation and the interrelation between any of its metabolites and the ion channels involved in the calcium release from the intracellular reservoirs at fertilization. We found that addition of both melittin, a potent PLA(2) activator, and arachidonic acid, the main PLA(2) reaction metabolite, was able to induce activation events in a bell-shaped manner. Differential regulation of IP3Rs and RyRs by arachidonic acid and its products could explain melittin and arachidonic acid behaviour in Bufo arenarum egg activation. The concerted action of arachidonic acid and/or its metabolites could provide controlled mobilization of calcium from intracellular reservoirs and useful tools for understanding calcium homeostasis in eggs that express both types of receptors.

Peripheral gabapentin regulates mosquito allergy-induced itch in mice.

PubMed

Akiyama, Tasuku; Andoh, Tsugunobu; Ohtsuka, Eiji; Nojima, Hiroshi; Ouchi, Hidekazu; Takahata, Hiroki; Kuraishi, Yasushi

2018-05-26

The antipruritic activity of gabapentin, an anticonvulsant, was studied in a mouse model of allergic itch. In mice sensitized by an extract of the salivary glands of the mosquito (ESGM), an intradermal injection of ESGM elicited scratching and increased peripheral nerve firing. Oral or intradermal administration of gabapentin at the ESGM injection site inhibited ESGM-induced scratching and peripheral nerve firing. However, gabapentin did not affect histamine-induced scratching. The distributions of immunoreactivity to the voltage-dependent calcium channel α 2 δ-1 subunit, a site of gabapentin action, and the histamine H 1 receptor differed in the mouse dorsal root ganglia. The α 2 δ-1 subunit was mainly found in neurons that were 15-20 µm in diameter, whereas the H 1 receptor was mainly in 20-30 µm neurons. In addition, α 2 δ-1 subunit immunoreactivity co-localized with that of transient receptor potential vanilloid 1 (TRPV1). These results suggest that gabapentin regulates allergic itch by acting on the calcium channel α 2 δ-1 subunit in peripheral TRPV1-positive neurons. Copyright © 2018 Elsevier B.V. All rights reserved.

The influence of methionine-5-enkephalin on calcium uptake by the bovine aortic media.

PubMed

Kokkas, B; Kotoula, M; Kouyoumtzis, A; Kouvelas, D; Papadopoulos, K; Paradelis, A G

1990-04-01

The influence of methionine-5-enkephalin (M-5-E), an endogenous opioid receptor agonist, on calcium uptake by bovine aortic media was investigated in vitro. 45Ca was used and radioactivity was counted in a beta scintillation counter. M-5-E increases Ca2+ uptake by the preparation. This action is inhibited by naloxone and that is proof that an opioid receptor is stimulated. A comparative study showed that phenylephrine, an alpha-adrenoceptor agonist, exhibits the same action as M-5-E, whereas morphine's action is negligible. Phenylephrine contracts the deendotheliazed ring of the bovine aorta, whereas M-5-E fails to do so. It is concluded that an opioid receptor was identified at the bovine aortic smooth muscle. This receptor is stimulated by M-5-E resulting in an increase of the extracellular Ca2+ entrance. Although no relationship was observed between the receptor and the contraction mechanism, a possible role of M-5-E in the maintenance of the vascular tone cannot be excluded.

Potentiostatic pulse-deposition of calcium phosphate on magnesium alloy for temporary implant applications--an in vitro corrosion study.

PubMed

Kannan, M Bobby; Wallipa, O

2013-03-01

In this study, a magnesium alloy (AZ91) was coated with calcium phosphate using potentiostatic pulse-potential and constant-potential methods and the in vitro corrosion behaviour of the coated samples was compared with the bare metal. In vitro corrosion studies were carried out using electrochemical impedance spectroscopy and potentiodynamic polarization in simulated body fluid (SBF) at 37 °C. Calcium phosphate coatings enhanced the corrosion resistance of the alloy, however, the pulse-potential coating performed better than the constant-potential coating. The pulse-potential coating exhibited ~3 times higher polarization resistance than that of the constant-potential coating. The corrosion current density obtained from the potentiodynamic polarization curves was significantly less (~60%) for the pulse-deposition coating as compared to the constant-potential coating. Post-corrosion analysis revealed only slight corrosion on the pulse-potential coating, whereas the constant-potential coating exhibited a large number of corrosion particles attached to the coating. The better in vitro corrosion performance of the pulse-potential coating can be attributed to the closely packed calcium phosphate particles. Copyright © 2012 Elsevier B.V. All rights reserved.

Molecular and biochemical evidence for the involvement of calcium/calmodulin in auxin action

NASA Technical Reports Server (NTRS)

Yang, T.; Poovaiah, B. W.

2000-01-01

The use of (35)S-labeled calmodulin (CaM) to screen a corn root cDNA expression library has led to the isolation of a CaM-binding protein, encoded by a cDNA with sequence similarity to small auxin up RNAs (SAURs), a class of early auxin-responsive genes. The cDNA designated as ZmSAUR1 (Zea mays SAURs) was expressed in Escherichia coli, and the recombinant protein was purified by CaM affinity chromatography. The CaM binding assay revealed that the recombinant protein binds to CaM in a calcium-dependent manner. Deletion analysis revealed that the CaM binding site was located at the NH(2)-terminal domain. A synthetic peptide of amino acids 20-45, corresponding to the potential CaM binding region, was used for calcium-dependent mobility shift assays. The synthetic peptide formed a stable complex with CaM only in the presence of calcium. The CaM affinity assay indicated that ZmSAUR1 binds to CaM with high affinity (K(d) approximately 15 nM) in a calcium-dependent manner. Comparison of the NH(2)-terminal portions of all of the characterized SAURs revealed that they all contain a stretch of the basic alpha-amphiphilic helix similar to the CaM binding region of ZmSAUR1. CaM binds to the two synthetic peptides from the NH(2)-terminal regions of Arabidopsis SAUR-AC1 and soybean 10A5, suggesting that this is a general phenomenon for all SAURs. Northern analysis was carried out using the total RNA isolated from auxin-treated corn coleoptile segments. ZmSAUR1 gene expression began within 10 min, increased rapidly between 10 and 60 min, and peaked around 60 min after 10 microM alpha-naphthaleneacetic acid treatment. These results indicate that ZmSAUR1 is an early auxin-responsive gene. The CaM antagonist N-(6-aminohexyl)5-chloro-1-naphthalenesulfonamide hydrochloride inhibited the auxin-induced cell elongation but not the auxin-induced expression of ZmSAUR1. This suggests that calcium/CaM do not regulate ZmSAUR1 at the transcriptional level. CaM binding to ZmSAUR1 in a calcium-dependent manner suggests that calcium/CaM regulate ZmSAUR1 at the post-translational level. Our data provide the first direct evidence for the involvement of calcium/CaM-mediated signaling in auxin-mediated signal transduction.

Bone Is a Major Target of PTH/PTHrP Receptor Signaling in Regulation of Fetal Blood Calcium Homeostasis

PubMed Central

Hirai, Takao; Kobayashi, Tatsuya; Nishimori, Shigeki; Karaplis, Andrew C.; Goltzman, David

2015-01-01

The blood calcium concentration during fetal life is tightly regulated within a narrow range by highly interactive homeostatic mechanisms that include transport of calcium across the placenta and fluxes in and out of bone; the mechanisms of this regulation are poorly understood. Our findings that endochondral bone-specific PTH/PTHrP receptor (PPR) knockout (KO) mice showed significant reduction of fetal blood calcium concentration compared with that of control littermates at embryonic day 18.5 led us to focus on bone as a possibly major determinant of fetal calcium homeostasis. We found that the fetal calcium concentration of Runx2 KO mice was significantly higher than that of control littermates, suggesting that calcium flux into bone had a considerable influence on the circulating calcium concentration. Moreover, Runx2:PTH double mutant fetuses showed calcium levels similar to those of Runx2 KO mice, suggesting that part of the fetal hypocalcemia in PTH KO mice was caused by the increment of the mineralized bone mass allowed by the formation of osteoblasts. Finally, Rank:PTH double mutant mice had a blood calcium concentration even lower than that of the either Rank KO or PTH KO mice alone at embryonic day 18.5. These observations in our genetic models suggest that PTH/PTHrP receptor signaling in bones has a significant role of the regulation of fetal blood calcium concentration and that both placental transport and osteoclast activation contribute to PTH's hypercalcemic action. They also show that PTH-independent deposition of calcium in bone is the major controller of fetal blood calcium level. PMID:26052897

Relationship of calcium and membrane guanylate cyclase in adrenocorticotropin-induced steroidogenesis.

PubMed

Nambi, P; Aiyar, N V; Roberts, A N; Sharma, R K

1982-07-01

Chlorpromazine, when incubated with isolated adrenal cells, inhibited the ACTH-stimulated formation of cGMP and corticosterone production. It also inhibited the ACTH-stimulated membrane guanylate cyclase, but did not affect the binding of ACTH to the membrane receptors. cGMP-induced steroidogenesis was not affected by the drug. These data indicate that chlorpromazine interferes with adrenal steroid metabolism at a site between the hormone receptor and guanylate cyclase and also show that guanylate cyclase is composed of separate receptor and catalytic components. Furthermore, based on the premise that chlorpromazine exerts its inhibitory action by blocking the binding of a calcium receptor protein, such as calmodulin, to the receptor-coupled guanylate cyclase, it is proposed that the interaction of calcium, presumably through a calcium-binding protein, is essential for ACTH-dependent guanylate cyclase.

Are Ca2+ channels targets of praziquantel action?

PubMed

Greenberg, Robert M

2005-01-01

Praziquantel is the current drug of choice for the control of schistosomiasis. It is highly effective against all species of schistosomes and shows minimal adverse effects. Though introduced for the treatment of schistosomiasis more than 20 years ago, the mode of action of praziquantel remains to be elucidated. This review will focus on advances in defining the molecular target of praziquantel action, with particular emphasis on recent work indicating an important role for voltage-gated calcium channels.

Reliable, responsive pacemaking and pattern generation with minimal cell numbers: the crustacean cardiac ganglion.

PubMed

Cooke, Ian M

2002-04-01

Investigations of the electrophysiology of crustacean cardiac ganglia over the last half-century are reviewed for their contributions to elucidating the cellular mechanisms and interactions by which a small (as few as nine cells) neuronal network accomplishes extremely reliable, rhythmical, patterned activation of muscular activity-in this case, beating of the neurogenic heart. This ganglion is thus a model for pacemaking and central pattern generation. Favorable anatomy has permitted voltage- and space-clamp analyses of voltage-dependent ionic currents that endow each neuron with the intrinsic ability to respond with rhythmical, patterned impulse activity to nonpatterned stimulation. The crustacean soma and initial axon segment do not support impulse generation but integrate input from stretch-sensitive dendrites and electrotonic and chemically mediated synapses on axonal processes in neuropils. The soma and initial axon produce a depolarization-activated, calcium-mediated, sustained potential, the "driver potential," so-called because it drives a train of impulses at the "trigger zone" of the axon. Extreme reliability results from redundancy and the electrotonic coupling and synaptic interaction among all the neurons. Complex modulation by central nervous system inputs and by neurohormones to adjust heart pumping to physiological demands has long been demonstrated, but much remains to be learned about the cellular and molecular mechanisms of action. The continuing relevance of the crustacean cardiac ganglion as a relatively simple model for pacemaking and central pattern generation is confirmed by the rapidly widening documentation of intrinsic potentials such as plateau potentials in neurons of all major animal groups. The suite of ionic currents (a slowly inactivating calcium current and various potassium currents, with variations) observed for the crustacean cardiac ganglion have been implicated in or proven to underlie a majority of the intrinsic potentials of neurons involved in pattern generation.

Promotion of beta-glucan synthase activity in corn microsomal membranes by calcium and protein phosphorylation

NASA Technical Reports Server (NTRS)

Paliyath, G.; Poovaiah, B. W.

1988-01-01

Regulation of the activity of beta-glucan synthase was studied using microsomal preparations from corn coleoptiles. The specific activity as measured by the incorporation of glucose from uridine diphospho-D-[U-14C]glucose varied between 5 to 15 pmol (mg protein)-1 min-1. Calcium promoted beta-glucan synthase activity and the promotion was observed at free calcium concentrations as low as 1 micromole. Kinetic analysis of substrate-velocity curve showed an apparent Km of 1.92 x 10(-4) M for UDPG. Calcium increased the Vmax from 5.88 x 10(-7) mol liter-1 min-1 in the absence of calcium to 9.52 x 10(-7) mol liter-1 min-1 and 1.66 x 10(-6) mol liter-1 min-1 in the presence of 0.5 mM and 1 mM calcium, respectively. The Km values remained the same under these conditions. Addition of ATP further increased the activity above the calcium-promoted level. Sodium fluoride, a phosphoprotein phosphatase inhibitor, promoted glucan synthase activity indicating that phosphorylation and dephosphorylation are involved in the regulation of the enzyme activity. Increasing the concentration of sodium fluoride from 0.25 mM to 10 mM increased glucan synthase activity five-fold over the + calcium + ATP control. Phosphorylation of membrane proteins also showed a similar increase under these conditions. Calmodulin, in the presence of calcium and ATP stimulated glucan synthase activity substantially, indicating that calmodulin could be involved in the calcium-dependent phosphorylation and promotion of beta-glucan synthase activity. The role of calcium in mediating auxin action is discussed.

Involvement of cell surface TG2 in the aggregation of K562 cells triggered by gluten.

PubMed

Feriotto, G; Calza, R; Bergamini, C M; Griffin, M; Wang, Z; Beninati, S; Ferretti, V; Marzola, E; Guerrini, R; Pagnoni, A; Cavazzini, A; Casciano, F; Mischiati, C

2017-03-01

Gluten-induced aggregation of K562 cells represents an in vitro model reproducing the early steps occurring in the small bowel of celiac patients exposed to gliadin. Despite the clear involvement of TG2 in the activation of the antigen-presenting cells, it is not yet clear in which compartment it occurs. Herein we study the calcium-dependent aggregation of these cells, using either cell-permeable or cell-impermeable TG2 inhibitors. Gluten induces efficient aggregation when calcium is absent in the extracellular environment, while TG2 inhibitors do not restore the full aggregating potential of gluten in the presence of calcium. These findings suggest that TG2 activity is not essential in the cellular aggregation mechanism. We demonstrate that gluten contacts the cells and provokes their aggregation through a mechanism involving the A-gliadin peptide 31-43. This peptide also activates the cell surface associated extracellular TG2 in the absence of calcium. Using a bioinformatics approach, we identify the possible docking sites of this peptide on the open and closed TG2 structures. Peptide docks with the closed TG2 structure near to the GTP/GDP site, by establishing molecular interactions with the same amino acids involved in stabilization of GTP binding. We suggest that it may occur through the displacement of GTP, switching the TG2 structure from the closed to the active open conformation. Furthermore, docking analysis shows peptide binding with the β-sandwich domain of the closed TG2 structure, suggesting that this region could be responsible for the different aggregating effects of gluten shown in the presence or absence of calcium. We deduce from these data a possible mechanism of action by which gluten makes contact with the cell surface, which could have possible implications in the celiac disease onset.

Imaging extracellular calcium in endolymph

NASA Astrophysics Data System (ADS)

Strimbu, C. Elliott; Fridberger, Anders

2018-05-01

Hair cell mechanoelectrical transduction and adaptation are believed to be regulated by extracellular calcium. However, the majority of experiments addressing calcium's role have been performed on reduced preparations in conditions that do not mimic those present in vivo. We used confocal microscopy and a low affinity (kd ˜11 µM) ratiometric fluorescent indicator to measure the extracellular calcium concentration in scala media in an in vitro preparation of the guinea pig cochlea. Microelectrodes were used to measure the cochlear microphonic potential during acoustic stimulation. The mean calcium concentration is significantly higher in the tectorial membrane (TM) than the surrounding endolymph, suggesting that the membrane acts as a calcium sink. We also observe calcium hot spots along the underside of the TM, near the outer hair cell bundles and near Hensens stripe close to the inner hair cell bundle. This suggests that the local calcium concentration near the hair bundles exceeds 100 µM, significantly higher than the bulk endolymph. These results were corroborated with fluorescence correlation spectroscopy using a second calcium sensitive dye, Oregon Green 488-BAPTA. Following a brief exposure to loud sound, TM calcium drops dramatically and shows recovery on a similar timescale as the microphonic potential. Our results suggest that the extracellular calcium concentration near the hair bundles is much higher than previously believed and may also serve as a partial control parameter for temporary threshold shifts.

Study on the Equilibrium Between Liquid Iron and Calcium Vapor

NASA Astrophysics Data System (ADS)

Berg, Martin; Lee, Jaewoo; Sichen, Du

2017-06-01

The solubility of calcium in liquid iron at 1823 K and 1873 K (1550 °C and 1600 °C) as a function of calcium potential was studied experimentally. The measurements were performed using a closed molybdenum holder in which liquid calcium and liquid iron were held at different temperatures. The results indicate a linear relationship between the activity of calcium, relative to pure liquid calcium, and the mole fraction of dissolved calcium in liquid iron, with a negligible temperature dependency in the ranges studied. The activity coefficient of calcium in liquid iron at infinite dilution, γ_{Ca(l0°, was calculated as 1551.

Electrophysiological effects of FK664, a new cardiotonic agent, on preparations from guinea pig ventricle and from rabbit sino-atrial node.

PubMed

Kodama, I; Anno, T; Sudo, Y; Satake, N; Shibata, S

1989-05-01

Effects of the cardiotonic agent FK664, 6-(3, 4-dimethoxy-phenyl)-1-ethyl-4-mesitylimino-3-methyl-3,4-dihydro-2 (1H)-pyrimidone, on isolated guinea pig ventricular muscles and rabbit sinus node pacemaker cells were studied using micro-electrode techniques. In ventricular muscles driven at 0.5-1.0 Hz, FK664 above 3 mumol.litre-1 caused an increase in contractile force and a shortening of time to peak tension. This positive inotropic effect of FK664 was accompanied by a slight elevation of the early plateau phase of the action potential, while other action potential variables were unaffected. The change in contractile force induced by FK664 was abolished in a low Ca2+ medium (0.12 mmol.litre-1) or by treatment with ryanodine (2 mumol.litre-1), whereas it was relatively well preserved in the preparations pretreated with nefedipine (1 mumol.litre-1). The slow action potentials induced by isoprenaline (0.3 mumol.litre-1) in high K+ medium (30 mmol.litre-1) and the slow inward current measured by single sucrose gap voltage clamp at a holding potential of -40 mV were unaffected by FK664. In sinus node pacemaker cells, FK664 (1-10 mumol.litre-1) caused a dose dependent acceleration of phase 4 depolarisation and a shortening of spontaneous firing cycle length. This positive chronotropic effect of FK664 was markedly inhibited in a low Ca2+ medium (0.3 mmol.litre-1). These findings suggest that FK664 has positive inotropic and chronotropic effects on the heart, due to an enhancement of transsarcolemmal calcium influx through the low threshold, dihydropyridine insensitive Ca2+ channel population.

Pharmacological actions of Uncaria alkaloids, rhynchophylline and isorhynchophylline.

PubMed

Shi, Jing-Shan; Yu, Jun-Xian; Chen, Xiu-Ping; Xu, Rui-Xia

2003-02-01

The pharmacological actions of Uncaria alkaloids, rhynchophylline and isorhynchophylline extracted from Uncaria rhynchophylla Miq Jacks were reviewed. The alkaloids mainly act on cardiovascular system and central nervous system including the hypotension, brachycardia, antiarrhythmia, and protection of cerebral ischemia and sedation. The active mechanisms were related to blocking of calcium channel, opening of potassium channel, and regulating of nerve transmitters transport and metabolism, etc.

Investigation of calcium-dependent activity and conformational dynamics of zebra fish 12-lipoxygenase.

PubMed

Mittal, Monica; Hasan, Mahmudul; Balagunaseelan, Navisraj; Fauland, Alexander; Wheelock, Craig; Rådmark, Olof; Haeggström, Jesper Z; Rinaldo-Matthis, Agnes

2017-08-01

A 12-lipoxygenase in zebra fish (zf12-LOX) was found to be required for normal embryonic development and LOXs are of great interest for targeted drug designing. In this study, we investigate the structural-functional aspects of zf12-LOX in response to calcium. A soluble version of zf12-LOX was created by mutagenesis. Based on multiple sequence alignment, we mutated the putative calcium-responsive amino acids in N-PLAT domain of soluble zf12-LOX. Using a series of biophysical methods, we ascertained the oligomeric state, stability, structural integrity and conformational changes of zf12-LOX in response to calcium. We also compared the biophysical properties of soluble zf12-LOX with the mutant in the absence and presence of calcium. Here we provide a detailed characterization of soluble zf12-LOX and the mutant. Both proteins exist as compact monomers in solution, however the enzyme activity of soluble zf12-LOX is significantly increased in presence of calcium. We find that the stimulatory effect of calcium on zf12-LOX is related to a change in protein structure as observed by SAXS, adopting an open-state. In contrast, enzyme with a mutated calcium regulatory site has reduced activity-response to calcium and restricted large re-modeling, suggesting that it retains a closed-state in response to calcium. Taken together, our study suggests that Ca 2+ -dependent regulation is associated with different domain conformation(s) that might change the accessibility to substrate-binding site in response to calcium. The study can be broadly implicated in better understanding the mode(s) of action of LOXs, and the enzymes regulated by calcium in general. Copyright © 2017 Elsevier B.V. All rights reserved.

Cytosolic calcium rises and related events in ergosterol-treated Nicotiana cells.

PubMed

Vatsa, Parul; Chiltz, Annick; Luini, Estelle; Vandelle, Elodie; Pugin, Alain; Roblin, Gabriel

2011-07-01

The typical fungal membrane component ergosterol was previously shown to trigger defence responses and protect plants against pathogens. Most of the elicitors mobilize the second messenger calcium, to trigger plant defences. We checked the involvement of calcium in response to ergosterol using Nicotiana plumbaginifolia and Nicotiana tabacum cv Xanthi cells expressing apoaequorin in the cytosol. First, it was verified if ergosterol was efficient in these cells inducing modifications of proton fluxes and increased expression of defence-related genes. Then, it was shown that ergosterol induced a rapid and transient biphasic increase of free [Ca²⁺](cyt) which intensity depends on ergosterol concentration in the range 0.002-10 μM. Among sterols, this calcium mobilization was specific for ergosterol and, ergosterol-induced pH and [Ca²⁺](cyt) changes were specifically desensitized after two subsequent applications of ergosterol. Specific modulators allowed elucidating some events in the signalling pathway triggered by ergosterol. The action of BAPTA, LaCl₃, nifedipine, verapamil, neomycin, U73122 and ruthenium red suggested that the first phase was linked to calcium influx from external medium which subsequently triggered the second phase linked to calcium release from internal stores. The calcium influx and the [Ca²⁺](cyt) increase depended on upstream protein phosphorylation. The extracellular alkalinization and ROS production depended on calcium influx but, the ergosterol-induced MAPK activation was calcium-independent. ROS were not involved in cytosolic calcium rise as described in other models, indicating that ROS do not systematically participate in the amplification of calcium signalling. Interestingly, ergosterol-induced ROS production is not linked to cell death and ergosterol does not induce any calcium elevation in the nucleus. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

The saponin monomer of dwarf lilyturf tuber, DT-13, reduces L-type calcium currents during hypoxia in adult rat ventricular myocytes.

PubMed

Tao, Jin; Wang, Hongyi; Zhou, Hong; Li, Shengnan

2005-10-28

The saponin monomer 13 of dwarf lilyturf tuber (DT-13), one of the saponin monomers of dwarf lilyturf tuber, has been found to have potent cardioprotective effects. In order to investigate the effects of DT-13 on L-type calcium currents (I(Ca,L)), exploring the mechanisms of DT-13's cardioprotective effects in the condition of pathophysiology, we directly measured the I(Ca,L) during hypoxia in the adult rat cardiac myocytes exposed to DT-13 using standard whole-cell patch-clamp recording technique. Our previous results showed that DT-13 exerted decreasing effects on the I(Ca,L) of the single adult rat cardiac myocytes. In the condition of hypoxia, the current density was inhibited by about 29% after exposure of the cells to DT-13 (0.1 micromol L(-1)) for 10 min, from 6.96+/-1.05 pA/pF to 4.38+/-0.35 pA/pF (n=5, P<0.05). This I(Ca,L)-inhibiting action of DT-13 was concentration-dependent and showed no frequency-dependence. DT-13 up-shifted the current-voltage (I-V) curve. Steady-state activation of I(Ca,L) was not affected markedly, and the half activation potential (V(0.5)) in the presence of DT-13 (0.1 micromol L(-1)) was also not significantly different. DT-13 at 0.1 micromol L(-1) markedly accelerated the voltage-dependent steady-state inactivation of calcium current and shifted the steady-state inactivation curve of I(Ca,L) to the left. In combination with previous reports, these results suggest that there might be a close relationship between the cardioprotective effects of DT-13 and L-type calcium channels in the condition of hypoxia.

Transmural Heterogeneity and Remodeling of Ventricular Excitation-Contraction Coupling in Human Heart Failure

PubMed Central

Lou, Qing; Fedorov, Vadim V.; Glukhov, Alexey V.; Moazami, Nader; Fast, Vladimir G.; Efimov, Igor R.

2011-01-01

Background Excitation-contraction (EC) coupling is altered in the end-stage heart failure (HF). However, spatial heterogeneity of this remodeling has not been established at the tissue level in failing human heart. The objective is to study functional remodeling of EC coupling and calcium handling in failing and nonfailing human hearts. Methods and Results We simultaneously optically mapped action potentials (AP) and calcium transients (CaT) in coronary-perfused left ventricular wedge preparations from nonfailing (n = 6) and failing (n = 5) human hearts. Our major findings are: (1) CaT duration minus AP duration was longer at sub-endocardium in failing compared to nonfailing hearts during bradycardia (40 beats/min). (2) The transmural gradient of CaT duration was significantly smaller in failing hearts compared with nonfailing hearts at fast pacing rates (100 beats/min). (3) CaT in failing hearts had a flattened plateau at the midmyocardium; and exhibited a “two-component” slow rise at sub-endocardium in three failing hearts. (4) CaT relaxation was slower at sub-endocardium than that at sub-epicardium in both groups. Protein expression of sarcoplasmic reticulum Ca2+-ATPase 2a (SERCA2a) was lower at sub-endocardium than that at sub-epicardium in both nonfailing and failing hearts. SERCA2a protein expression at sub-endocardium was lower in hearts with ischemic cardiomyopathy compared with nonischemic cardiomyopathy. Conclusions For the first time, we present direct experimental evidence of transmural heterogeneity of EC coupling and calcium handling in human hearts. End-stage HF is associated with the heterogeneous remodeling of EC coupling and calcium handling. PMID:21502574

Curcumin induces crosstalk between autophagy and apoptosis mediated by calcium release from the endoplasmic reticulum, lysosomal destabilization and mitochondrial events

PubMed Central

Moustapha, A; Pérétout, PA; Rainey, NE; Sureau, F; Geze, M; Petit, J-M; Dewailly, E; Slomianny, C; Petit, PX

2015-01-01

Curcumin, a major active component of turmeric (Curcuma longa, L.), has anticancer effects. In vitro studies suggest that curcumin inhibits cancer cell growth by activating apoptosis, but the mechanism underlying these effects is still unclear. Here, we investigated the mechanisms leading to apoptosis in curcumin-treated cells. Curcumin induced endoplasmic reticulum stress causing calcium release, with a destabilization of the mitochondrial compartment resulting in apoptosis. These events were also associated with lysosomal membrane permeabilization and of caspase-8 activation, mediated by cathepsins and calpains, leading to Bid cleavage. Truncated tBid disrupts mitochondrial homeostasis and enhance apoptosis. We followed the induction of autophagy, marked by the formation of autophagosomes, by staining with acridine orange in cells exposed curcumin. At this concentration, only the early events of apoptosis (initial mitochondrial destabilization with any other manifestations) were detectable. Western blotting demonstrated the conversion of LC3-I to LC3-II (light chain 3), a marker of active autophagosome formation. We also found that the production of reactive oxygen species and formation of autophagosomes following curcumin treatment was almost completely blocked by N-acetylcystein, the mitochondrial specific antioxidants MitoQ10 and SKQ1, the calcium chelators, EGTA-AM or BAPTA-AM, and the mitochondrial calcium uniporter inhibitor, ruthenium red. Curcumin-induced autophagy failed to rescue all cells and most cells underwent type II cell death following the initial autophagic processes. All together, these data imply a fail-secure mechanism regulated by autophagy in the action of curcumin, suggesting a therapeutic potential for curcumin. Offering a novel and effective strategy for the treatment of malignant cells. PMID:27551451

Genetically encoded calcium indicators for multi-color neural activity imaging and combination with optogenetics

PubMed Central

Akerboom, Jasper; Carreras Calderón, Nicole; Tian, Lin; Wabnig, Sebastian; Prigge, Matthias; Tolö, Johan; Gordus, Andrew; Orger, Michael B.; Severi, Kristen E.; Macklin, John J.; Patel, Ronak; Pulver, Stefan R.; Wardill, Trevor J.; Fischer, Elisabeth; Schüler, Christina; Chen, Tsai-Wen; Sarkisyan, Karen S.; Marvin, Jonathan S.; Bargmann, Cornelia I.; Kim, Douglas S.; Kügler, Sebastian; Lagnado, Leon; Hegemann, Peter; Gottschalk, Alexander; Schreiter, Eric R.; Looger, Loren L.

2013-01-01

Genetically encoded calcium indicators (GECIs) are powerful tools for systems neuroscience. Here we describe red, single-wavelength GECIs, “RCaMPs,” engineered from circular permutation of the thermostable red fluorescent protein mRuby. High-resolution crystal structures of mRuby, the red sensor RCaMP, and the recently published red GECI R-GECO1 give insight into the chromophore environments of the Ca2+-bound state of the sensors and the engineered protein domain interfaces of the different indicators. We characterized the biophysical properties and performance of RCaMP sensors in vitro and in vivo in Caenorhabditis elegans, Drosophila larvae, and larval zebrafish. Further, we demonstrate 2-color calcium imaging both within the same cell (registering mitochondrial and somatic [Ca2+]) and between two populations of cells: neurons and astrocytes. Finally, we perform integrated optogenetics experiments, wherein neural activation via channelrhodopsin-2 (ChR2) or a red-shifted variant, and activity imaging via RCaMP or GCaMP, are conducted simultaneously, with the ChR2/RCaMP pair providing independently addressable spectral channels. Using this paradigm, we measure calcium responses of naturalistic and ChR2-evoked muscle contractions in vivo in crawling C. elegans. We systematically compare the RCaMP sensors to R-GECO1, in terms of action potential-evoked fluorescence increases in neurons, photobleaching, and photoswitching. R-GECO1 displays higher Ca2+ affinity and larger dynamic range than RCaMP, but exhibits significant photoactivation with blue and green light, suggesting that integrated channelrhodopsin-based optogenetics using R-GECO1 may be subject to artifact. Finally, we create and test blue, cyan, and yellow variants engineered from GCaMP by rational design. This engineered set of chromatic variants facilitates new experiments in functional imaging and optogenetics. PMID:23459413

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Serotonin and the regulation of calcium transport in dairy cows.

PubMed

Hernandez, L L

2017-12-01

The mammary gland regulates maternal metabolism during lactation. Numerous factors within the tissue send signals to shift nutrients to the mammary gland for milk synthesis. Serotonin is a monoamine that has been well documented to regulate several aspects of lactation among species. Maintenance of maternal calcium homeostasis during lactation is a highly evolved process that is elegantly regulated by the interaction of the mammary gland with the bone, gut, and kidney tissues. It is well documented that dietary calcium is insufficient to maintain maternal calcium concentrations during lactation, and mammals must rely on bone resorption to maintain normocalcemia. Our recent work focused on the ability of the mammary gland to function as an accessory parathyroid gland during lactation. It was demonstrated that serotonin acts to stimulate parathyroid hormone-related protein (PTHrP) in the mammary gland during lactation. The main role of mammary-derived PTHrP during mammalian lactation is to stimulate bone resorption to maintain maternal calcium homeostasis during lactation. In addition to regulating PTHrP, it was shown that serotonin appears to directly affect calcium transporters and pumps in the mammary gland. Our current working hypothesis regarding the control of calcium during lactation is as follows: serotonin directly stimulates PTHrP production in the mammary gland through interaction with the sonic hedgehog signaling pathway. Simultaneously, serotonin directly increases calcium movement into the mammary gland and, subsequently, milk. These 2 direct actions of serotonin combine to induce a transient maternal hypocalcemia required to further stimulate PTHrP production and calcium mobilization from bone. Through these 2 routes, serotonin is able to improve maternal calcium concentrations. Furthermore, we have shown that Holstein and Jersey cows appear to regulate calcium in different manners and also respond differently to serotonergic stimulation of the calcium pathway. Our data in rodents and cows indicate that serotonin and calcium are working through a unique feedback loop with PTHrP during lactation to regulate milk calcium and maternal calcium homeostasis.

Cardiomyocyte dysfunction during the chronic phase of Chagas disease.

PubMed

Roman-Campos, Danilo; Sales-Júnior, Policarpo; Duarte, Hugo Leonardo; Gomes, Eneas Ricardo; Guatimosim, Silvia; Ropert, Catherine; Gazzinelli, Ricardo Tostes; Cruz, Jader Santos

2013-04-01

Chagas disease, which is caused by the parasite Trypanosoma cruzi, is an important cause of heart failure. We investigated modifications in the cellular electrophysiological and calcium-handling characteristics of an infected mouse heart during the chronic phase of the disease. The patch-clamp technique was used to record action potentials (APs) and L-type Ca2+ and transient outward K+ currents. [Ca2+]i changes were determined using confocal microscopy. Infected ventricular cells showed prolonged APs, reduced transient outward K+ and L-type Ca2+ currents and reduced Ca2+ release from the sarcoplasmic reticulum. Thus, the chronic phase of Chagas disease is characterised by cardiomyocyte dysfunction, which could lead to heart failure.

Cardiomyocyte dysfunction during the chronic phase of Chagas disease

PubMed Central

Roman-Campos, Danilo; Sales-Júnior, Policarpo; Duarte, Hugo Leonardo; Gomes, Eneas Ricardo; Guatimosim, Silvia; Ropert, Catherine; Gazzinelli, Ricardo Tostes; Cruz, Jader Santos

2013-01-01

Chagas disease, which is caused by the parasite Trypanosoma cruzi, is an important cause of heart failure. We investigated modifications in the cellular electrophysiological and calcium-handling characteristics of an infected mouse heart during the chronic phase of the disease. The patch-clamp technique was used to record action potentials (APs) and L-type Ca2+ and transient outward K+ currents. [Ca2+]i changes were determined using confocal microscopy. Infected ventricular cells showed prolonged APs, reduced transient outward K+ and L-type Ca2+ currents and reduced Ca2+ release from the sarcoplasmic reticulum. Thus, the chronic phase of Chagas disease is characterised by cardiomyocyte dysfunction, which could lead to heart failure. PMID:23579807

Extraction and analysis of neuron firing signals from deep cortical video microscopy

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

Kerekes, Ryan A; Blundon, Jay

We introduce a method for extracting and analyzing neuronal activity time signals from video of the cortex of a live animal. The signals correspond to the firing activity of individual cortical neurons. Activity signals are based on the changing fluorescence of calcium indicators in the cells over time. We propose a cell segmentation method that relies on a user-specified center point, from which the signal extraction method proceeds. A stabilization approach is used to reduce tissue motion in the video. The extracted signal is then processed to flatten the baseline and detect action potentials. We show results from applying themore » method to a cortical video of a live mouse.« less

Neuroprotective effect of novel cognitive enhancer noopept on AD-related cellular model involves the attenuation of apoptosis and tau hyperphosphorylation.

PubMed

Ostrovskaya, Rita U; Vakhitova, Yulia V; Kuzmina, Uliyana Sh; Salimgareeva, Milyausha Kh; Zainullina, Liana F; Gudasheva, Tatiana A; Vakhitov, Vener A; Seredenin, Sergey B

2014-08-06

Noopept (N-phenyl-acetyl-L-prolylglycine ethyl ester) was constructed as a dipeptide analog of the standard cognition enhancer, piracetam. Our previous experiments have demonstrated the cognition restoring effect of noopept in several animal models of Alzheimer disease (AD). Noopept was also shown to prevent ionic disbalance, excitotoxicity, free radicals and pro-inflammatory cytokines accumulation, and neurotrophine deficit typical for different kinds of brain damages, including AD. In this study, we investigated the neuroprotective action of noopept on cellular model of AD, Aβ 25-35-induced toxicity in PC12 cells and revealed the underlying mechanisms. The neuroprotective effect of noopept (added to the medium at 10 μM concentration, 72 hours before Аβ 25-35) was studied on Аβ 25-35-induced injury (5 μM for 24 h) in PC12 cells. The ability of drug to protect the impairments of cell viability, calcium homeostasis, ROS level, mitochondrial function, tau phosphorylation and neurite outgrowth caused by Аβ 25-35 were evaluated. Following the exposure of PC12 cells to Аβ 25-35 an increase of the level of ROS, intracellular calcium, and tau phosphorylation at Ser396 were observed; these changes were accompanied by a decrease in cell viability and an increase of apoptosis. Noopept treatment before the amyloid-beta exposure improved PC12 cells viability, reduced the number of early and late apoptotic cells, the levels of intracellular reactive oxygen species and calcium and enhanced the mitochondrial membrane potential. In addition, pretreatment of PC12 cell with noopept significantly attenuated tau hyperphosphorylation at Ser396 and ameliorated the alterations of neurite outgrowth evoked by Аβ25-35. Taken together, these data provide evidence that novel cognitive enhancer noopept protects PC12 cell against deleterious actions of Aβ through inhibiting the oxidative damage and calcium overload as well as suppressing the mitochondrial apoptotic pathway. Moreover, neuroprotective properties of noopept likely include its ability to decrease tau phosphorylation and to restore the altered morphology of PC12 cells. Therefore, this nootropic dipeptide is able to positively affect not only common pathogenic pathways but also disease-specific mechanisms underlying Aβ-related pathology.

Neuroprotective effect of novel cognitive enhancer noopept on AD-related cellular model involves the attenuation of apoptosis and tau hyperphosphorylation

PubMed Central

2014-01-01

Background Noopept (N-phenyl-acetyl-L-prolylglycine ethyl ester) was constructed as a dipeptide analog of the standard cognition enhancer, piracetam. Our previous experiments have demonstrated the cognition restoring effect of noopept in several animal models of Alzheimer disease (AD). Noopept was also shown to prevent ionic disbalance, excitotoxicity, free radicals and pro-inflammatory cytokines accumulation, and neurotrophine deficit typical for different kinds of brain damages, including AD. In this study, we investigated the neuroprotective action of noopept on cellular model of AD, Aβ25–35-induced toxicity in PC12 cells and revealed the underlying mechanisms. Results The neuroprotective effect of noopept (added to the medium at 10 μM concentration, 72 hours before Аβ25–35) was studied on Аβ25–35-induced injury (5 μM for 24 h) in PC12 cells. The ability of drug to protect the impairments of cell viability, calcium homeostasis, ROS level, mitochondrial function, tau phosphorylation and neurite outgrowth caused by Аβ25–35 were evaluated. Following the exposure of PC12 cells to Аβ25–35 an increase of the level of ROS, intracellular calcium, and tau phosphorylation at Ser396 were observed; these changes were accompanied by a decrease in cell viability and an increase of apoptosis. Noopept treatment before the amyloid-beta exposure improved PC12 cells viability, reduced the number of early and late apoptotic cells, the levels of intracellular reactive oxygen species and calcium and enhanced the mitochondrial membrane potential. In addition, pretreatment of PC12 cell with noopept significantly attenuated tau hyperphosphorylation at Ser396 and ameliorated the alterations of neurite outgrowth evoked by Аβ25–35. Conclusions Taken together, these data provide evidence that novel cognitive enhancer noopept protects PC12 cell against deleterious actions of Aβ through inhibiting the oxidative damage and calcium overload as well as suppressing the mitochondrial apoptotic pathway. Moreover, neuroprotective properties of noopept likely include its ability to decrease tau phosphorylation and to restore the altered morphology of PC12 cells. Therefore, this nootropic dipeptide is able to positively affect not only common pathogenic pathways but also disease-specific mechanisms underlying Aβ-related pathology. PMID:25096780

Antiapolipoprotein A-1 IgG chronotropic effects require nongenomic action of aldosterone on L-type calcium channels.

PubMed

Rossier, Michel F; Pagano, Sabrina; Python, Magaly; Maturana, Andres D; James, Richard W; Mach, François; Roux-Lombard, Pascale; Vuilleumier, Nicolas

2012-03-01

Autoantibodies to apolipoprotein A-1 (antiapoA-1 IgG) have been shown to be associated with higher resting heart rate and morbidity in myocardial infarction patients and to behave as a chronotropic agent in the presence of aldosterone on isolated neonatal rat ventricular cardiomyocytes (NRVC). We aimed at identifying the pathways accounting for this aldosterone-dependent antiapoA-1 IgG-positive chronotropic effect on NRVC. The rate of regular spontaneous contractions was determined on NRVC in the presence of different steroid hormones and antagonists. AntiapoA-1 IgG chronotropic response was maximal within 20 min and observed only in aldosterone-pretreated cells but not in those exposed to other steroids. The positive antiapoA-1 IgG chronotropic effect was already significant after 5 min aldosterone preincubation, was dependent on 3-kinase and protein kinase A activities, was not inhibited by actinomycin D, and was fully abrogated by eplerenone (but not by spironolactone), demonstrating the dependence on a nongenomic action of aldosterone elicited through the mineralocorticoid receptor (MR). Under oxidative conditions (but not under normal redox state), corticosterone mimicked the permissive action of aldosterone on the antiapoA-1 IgG chronotropic response. Pharmacological and patch-clamp studies identified L-type calcium channels as crucial effectors of antiapoA-1 IgG chronotropic action, involving two converging pathways that increase the channel activity. The first one involves the rapid, nongenomic activation of the phosphatidylinositol 3-kinase enzyme by MR, and the second one requires a constitutive basal protein kinase A activity. In conclusion, our results indicate that, on NRVC, the aldosterone-dependent chronotropic effects of antiapoA-1 IgG involve the nongenomic activation of L-type calcium channels.

The inhibitory effect of somatostatin peptides on the rat anococcygeus muscle in vitro.

PubMed Central

Priestley, T.; Woodruff, G. N.

1988-01-01

1. Electrically evoked contractions of the rat anococcygeus muscle were inhibited in a concentration-dependent manner by somatostatin-14 (SS14), -28 (SS28) and two synthetic hexapeptide analogues: L-363,301 (Pro-Phe-D-Trp-Lys-Thr-Phe) and L-363,586 (N-Me-Ala-Tyr-D-Trp-Lys-Val-Phe), with pIC50 values of 7.41, 7.38, 7.07 and 8.34, respectively. 2. The inhibitory effects of SS14 were dependent on stimulation frequency and external calcium ion concentration. Calcium behaved as a non-competitive antagonist of SS14, it reduced the maximal inhibitory effect of the peptide and at a concentration of 5.08 mM it significantly affected the pIC50 value. 3. SS14 (3 x 10(-7) M) did not affect the tonic actions of bath-applied noradrenaline in the absence of field stimulation. 4. The effects of SS14 persisted in naloxone (10(-5) M) and were, therefore, not due to an action at opiate receptors. Furthermore, experiments involving the lyophilization of bath contents, showed no evidence to support an indirect mechanism involving the release of an endogenous inhibitory substance. 5. High concentrations (10(-5) M) of SS14 or L-363,301 inhibited the relaxation response evoked by electrical stimulation of guanethidine (3 x 10(-4) M)-treated preparations. 6. These results are consistent with similar actions of SS14 on other smooth muscle preparations and are presumed to reflect a presynaptic inhibition of transmitter release by a direct action on somatostatin receptors. The antagonistic effect of calcium on this response is discussed with reference to a possible role in receptor desensitization. PMID:2900039

Characterization of adenosine receptors in guinea-pig isolated left atria.

PubMed Central

Jahnel, U.; Nawrath, H.

1989-01-01

1. The effects of purinergic stimulation on action potential, force of contraction, 86Rb efflux and 45Ca uptake were investigated in guinea-pig left atria. 2. Adenosine exerted a negative inotropic effect which was antagonized by adenosine deaminase but enhanced by dipyridamole. 3. The negative inotropic effect of adenosine was mimicked by 5'-(N-ethyl)-carboxamido-adenosine (NECA) and the isomers of N6-(phenyl-isopropyl)-adenosine, R-PIA and S-PIA. NECA and R-PIA were about 100 times more potent than adenosine, whereas R-PIA was about 100 times more potent than S-PIA. 4. The inotropic effects of adenosine (in the presence of dipyridamole), NECA, R-PIA and S-PIA were competitively antagonized either by theophylline (pA2 about 4.5) or 8-phenyltheophylline (pA2 about 6.3). 5. NECA and R-PIA shortened the action potential duration and increased the rate constant of the efflux of 86Rb in a concentration-dependent manner with no differences in potency; the effects were competitively antagonized by 8-phenyltheophylline. 6. Barium ions reduced the efflux of 86Rb under control conditions and antagonized the increase induced by NECA and R-PIA. 7. NECA and R-PIA significantly reduced 45Ca uptake in beating preparations. 8. It is concluded that adenosine, NECA and R-PIA activate a common receptor population (P1 or A3) on the outside of the cell membrane of atrial heart muscle to increase the potassium conductance and to reduce the action potential and, thereby, calcium influx and force of contraction. PMID:2790380

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.

Renal rickets-practical approach

PubMed Central

Sahay, Manisha; Sahay, Rakesh

2013-01-01

Rickets/osteomalacia is an important problem in a tropical country. Many cases are due to poor vitamin D intake or calcium deficient diets and can be corrected by administration of calcium and vitamin D. However, some cases are refractory to vitamin D therapy and are related to renal defects. These include rickets of renal tubular acidosis (RTA), hypophosphatemic rickets, and vitamin D dependent rickets (VDDR). The latter is due to impaired action of 1α-hydroxylase in renal tubule. These varieties need proper diagnosis and specific treatment. PMID:24251212

Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate.

PubMed

Kim, Yi-Yeoun; Hetherington, Nicola B J; Noel, Elizabeth H; Kröger, Roland; Charnock, John M; Christenson, Hugo K; Meldrum, Fiona C

2011-12-23

Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Distribution of the messenger RNA for the small conductance calcium-activated potassium channel SK3 in the adult rat brain and correlation with immunoreactivity.

PubMed

Tacconi, S; Carletti, R; Bunnemann, B; Plumpton, C; Merlo Pich, E; Terstappen, G C

2001-01-01

Small conductance calcium-activated potassium channels are voltage independent potassium channels which modulate the firing patterns of neurons by activating the slow component of the afterhyperpolarization. The genes encoding a family of small conductance calcium-activated potassium channels have been cloned and up to now three known members have been described and named small conductance calcium-activated potassium channel type 1, small conductance calcium-activated potassium channel type 2 and small conductance calcium-activated potassium channel type 3; the distribution of their messenger RNA in the rat CNS has already been performed but only in a limited detail. The present study represents the first detailed analysis of small conductance calcium-activated potassium channel type 3 mRNA distribution in the adult rat brain and resulted in a strong to moderate expression of signal in medial habenular nucleus, substantia nigra compact part, suprachiasmatic nucleus, ventral tegmental area, lateral septum, dorsal raphe and locus coeruleus. Immunohistological experiments were also performed and confirmed the presence of small conductance calcium-activated potassium channel type 3 protein in medial habenular nucleus, locus coeruleus and dorsal raphe. Given the importance of dorsal raphe, locus coeruleus and substantia nigra/ventral tegmental area for serotonergic, noradrenergic and dopaminergic transmission respectively, our results pose the morphological basis for further studies on the action of small conductance calcium-activated potassium channel type 3 in serotonergic, noradrenergic and dopaminergic transmission.

40 CFR Appendix V to Part 265 - Examples of Potentially Incompatible Waste

Code of Federal Regulations, 2013 CFR

2013-07-01

... Calcium Lithium Magnesium Potassium Sodium Zinc powder Other reactive metals and metal hydrides Potential... concentrated waste in Groups 1-A or 1-B Water Calcium Lithium Metal hydrides Potassium SO2Cl2, SOCl2, PCl3...

40 CFR Appendix V to Part 265 - Examples of Potentially Incompatible Waste

Code of Federal Regulations, 2012 CFR

2012-07-01

... Calcium Lithium Magnesium Potassium Sodium Zinc powder Other reactive metals and metal hydrides Potential... concentrated waste in Groups 1-A or 1-B Water Calcium Lithium Metal hydrides Potassium SO2Cl2, SOCl2, PCl3...

40 CFR Appendix V to Part 265 - Examples of Potentially Incompatible Waste

Code of Federal Regulations, 2014 CFR

2014-07-01

... Calcium Lithium Magnesium Potassium Sodium Zinc powder Other reactive metals and metal hydrides Potential... concentrated waste in Groups 1-A or 1-B Water Calcium Lithium Metal hydrides Potassium SO2Cl2, SOCl2, PCl3...

1,25-Dihydroxyvitamin D3 Controls a Cohort of Vitamin D Receptor Target Genes in the Proximal Intestine That Is Enriched for Calcium-regulating Components.

PubMed

Lee, Seong Min; Riley, Erin M; Meyer, Mark B; Benkusky, Nancy A; Plum, Lori A; DeLuca, Hector F; Pike, J Wesley

2015-07-17

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) plays an integral role in calcium homeostasis in higher organisms through its actions in the intestine, kidney, and skeleton. Interestingly, although several intestinal genes are known to play a contributory role in calcium homeostasis, the entire caste of key components remains to be identified. To examine this issue, Cyp27b1 null mice on either a normal or a high calcium/phosphate-containing rescue diet were treated with vehicle or 1,25(OH)2D3 and evaluated 6 h later. RNA samples from the duodena were then subjected to RNA sequence analysis, and the data were analyzed bioinformatically. 1,25(OH)2D3 altered expression of large collections of genes in animals under either dietary condition. 45 genes were found common to both 1,25(OH)2D3-treated groups and were composed of genes previously linked to intestinal calcium uptake, including S100g, Trpv6, Atp2b1, and Cldn2 as well as others. An additional distinct network of 56 genes was regulated exclusively by diet. We then conducted a ChIP sequence analysis of binding sites for the vitamin D receptor (VDR) across the proximal intestine in vitamin D-sufficient normal mice treated with vehicle or 1,25(OH)2D3. The residual VDR cistrome was composed of 4617 sites, which was increased almost 4-fold following hormone treatment. Interestingly, the majority of the genes regulated by 1,25(OH)2D3 in each diet group as well as those found in common in both groups contained frequent VDR sites that likely regulated their expression. This study revealed a global network of genes in the intestine that both represent direct targets of vitamin D action in mice and are involved in calcium absorption. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

1,25-Dihydroxyvitamin D3 Controls a Cohort of Vitamin D Receptor Target Genes in the Proximal Intestine That Is Enriched for Calcium-regulating Components*

PubMed Central

Lee, Seong Min; Riley, Erin M.; Meyer, Mark B.; Benkusky, Nancy A.; Plum, Lori A.; DeLuca, Hector F.; Pike, J. Wesley

2015-01-01

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) plays an integral role in calcium homeostasis in higher organisms through its actions in the intestine, kidney, and skeleton. Interestingly, although several intestinal genes are known to play a contributory role in calcium homeostasis, the entire caste of key components remains to be identified. To examine this issue, Cyp27b1 null mice on either a normal or a high calcium/phosphate-containing rescue diet were treated with vehicle or 1,25(OH)2D3 and evaluated 6 h later. RNA samples from the duodena were then subjected to RNA sequence analysis, and the data were analyzed bioinformatically. 1,25(OH)2D3 altered expression of large collections of genes in animals under either dietary condition. 45 genes were found common to both 1,25(OH)2D3-treated groups and were composed of genes previously linked to intestinal calcium uptake, including S100g, Trpv6, Atp2b1, and Cldn2 as well as others. An additional distinct network of 56 genes was regulated exclusively by diet. We then conducted a ChIP sequence analysis of binding sites for the vitamin D receptor (VDR) across the proximal intestine in vitamin D-sufficient normal mice treated with vehicle or 1,25(OH)2D3. The residual VDR cistrome was composed of 4617 sites, which was increased almost 4-fold following hormone treatment. Interestingly, the majority of the genes regulated by 1,25(OH)2D3 in each diet group as well as those found in common in both groups contained frequent VDR sites that likely regulated their expression. This study revealed a global network of genes in the intestine that both represent direct targets of vitamin D action in mice and are involved in calcium absorption. PMID:26041780

Acquisition of contextual discrimination involves the appearance of a RAS-GRF1/p38 mitogen-activated protein (MAP) kinase-mediated signaling pathway that promotes long term potentiation (LTP).

PubMed

Jin, Shan-Xue; Arai, Junko; Tian, Xuejun; Kumar-Singh, Rajendra; Feig, Larry A

2013-07-26

RAS-GRF1 is a guanine nucleotide exchange factor with the ability to activate RAS and RAC GTPases in response to elevated calcium levels. We previously showed that beginning at 1 month of age, RAS-GRF1 mediates NMDA-type glutamate receptor (NMDAR)-induction of long term depression in the CA1 region of the hippocampus of mice. Here we show that beginning at 2 months of age, when mice first acquire the ability to discriminate between closely related contexts, RAS-GRF1 begins to contribute to the induction of long term potentiation (LTP) in the CA1 hippocampus by mediating the action of calcium-permeable, AMPA-type glutamate receptors (CP-AMPARs). Surprisingly, LTP induction by CP-AMPARs through RAS-GRF1 occurs via activation of p38 MAP kinase rather than ERK MAP kinase, which has more frequently been linked to LTP. Moreover, contextual discrimination is blocked by knockdown of Ras-Grf1 expression specifically in the CA1 hippocampus, infusion of a p38 MAP kinase inhibitor into the CA1 hippocampus, or the injection of an inhibitor of CP-AMPARs. These findings implicate the CA1 hippocampus in the developmentally dependent capacity to distinguish closely related contexts through the appearance of a novel LTP-supporting signaling pathway.

Acquisition of Contextual Discrimination Involves the Appearance of a RAS-GRF1/p38 Mitogen-activated Protein (MAP) Kinase-mediated Signaling Pathway That Promotes Long Term Potentiation (LTP)*

PubMed Central

Jin, Shan-Xue; Arai, Junko; Tian, Xuejun; Kumar-Singh, Rajendra; Feig, Larry A.

2013-01-01

RAS-GRF1 is a guanine nucleotide exchange factor with the ability to activate RAS and RAC GTPases in response to elevated calcium levels. We previously showed that beginning at 1 month of age, RAS-GRF1 mediates NMDA-type glutamate receptor (NMDAR)-induction of long term depression in the CA1 region of the hippocampus of mice. Here we show that beginning at 2 months of age, when mice first acquire the ability to discriminate between closely related contexts, RAS-GRF1 begins to contribute to the induction of long term potentiation (LTP) in the CA1 hippocampus by mediating the action of calcium-permeable, AMPA-type glutamate receptors (CP-AMPARs). Surprisingly, LTP induction by CP-AMPARs through RAS-GRF1 occurs via activation of p38 MAP kinase rather than ERK MAP kinase, which has more frequently been linked to LTP. Moreover, contextual discrimination is blocked by knockdown of Ras-Grf1 expression specifically in the CA1 hippocampus, infusion of a p38 MAP kinase inhibitor into the CA1 hippocampus, or the injection of an inhibitor of CP-AMPARs. These findings implicate the CA1 hippocampus in the developmentally dependent capacity to distinguish closely related contexts through the appearance of a novel LTP-supporting signaling pathway. PMID:23766509

Ionic calcium determination in skim milk with molecular probes and front-face fluorescence spectroscopy: simple linear regression.

PubMed

Gangidi, R R; Metzger, L E

2006-11-01

The purpose of this study was to determine if the ionic calcium content of skim milk could be determined using molecular probes and front-face fluorescence spectroscopy. Current methods for determining ionic calcium are not sensitive, overestimate ionic calcium, or require complex procedures. Molecular probes designed specifically for measuring ionic calcium could potentially be used to determine the ionic calcium content of skim milk. The goal of the current study was to develop foundation methods for future studies to determine ionic calcium directly in skim milk and other dairy products with molecular probes and fluorescence spectroscopy. In this study, the effect of pH on calcium-sensitive fluorescent probe (Rhod-5N and Fluo-5N) performance using various concentrations of skim milk was determined. The pH of diluted skim milk (1.9 to 8.9% skim milk), was adjusted to either 6.2 or 7.0, after which the samples were analyzed with fluorescent probes (1 microM) and front-face fluorescence spectroscopy. The ionic calcium content of each sample was also determined using a calcium ion-selective electrode. The results demonstrated that the ionic calcium content of each sample was highly correlated (R2 > 0.989) with the fluorescence intensities of the probe-calcium adduct using simple linear regression. Higher than suggested ionic calcium contents of 1,207 and 1,973 microM were determined with the probes (Fluo-5N and Rhod-5N) in diluted skim milk with pH 7.0 and 6.2, respectively. The fluorescence intensity of the probe-calcium adduct decreased with a decrease in pH for the same ionic calcium concentration. This study demonstrates that Fluo-5N and Rhod-5N can be used to determine the ionic-calcium content of diluted milk with front-face fluorescence spectroscopy. Furthermore, these probes may also have the potential to determine the ionic calcium content of undiluted skim milk.

Modulation of the activity of midbrain central gray substance neurons by calcium channel agonists and antagonists in vitro.

PubMed

Yakhnitsa, V A; Pilyavskii, A I; Limansky, Y P; Bulgakova, N V

1996-01-01

Changes in the background impulse activity of midbrain central gray substance neurons have been studied on slice preparations from the rat midbrain upon application of calcium-free solution, an activator of calcium channels, BAY-K 8644 (10 nM), organic (verapamil, 40 microM; D600, 10 microM; nifedipine, 1-10 microM; amiloride, 1 microM) and inorganic (Co2+, 1.5 mM) calcium channel blockers. Besides BAY-K 8644, all the substances inhibited most of the neurons studied. Verapamil, BAY-K 8644 and Co2+ also revealed facilitatory effects. Facilitatory action of BAY-K was most effective in silent neurons and in those previously inhibited by amiloride. Latent period values of inhibition in calcium-free solution and upon application of organic and inorganic blockers have the following sequence: D600 > amiloride > verapamil > Co2+ > nifedipine > calcium-free solution. Maximum rise time had the following order: amiloride > D600 > nifedipine > verapamil > Co2+ > calcium-free solution. Complete suppression of the neuronal activity induced by amiloride lasted twice as long as that induced by calcium-free solution, Co2+ and nifedipine, and six times as long as verapamil-induced suppression. Preliminary application of calcium channel blockers reduced facilitatory and increased inhibitory effects of serotonin and substance P. Data obtained are discussed with the supposition in mind that inhibition of the function of calcium channels in central gray substance neurons could be one of the mechanisms underlying the analgesic effect of a series of neurotropic agents after their introduction into this structure.

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA

PubMed Central

1995-01-01

Sarcoplasmic reticulum (SR) Ca release was studied at 13-16 degrees C in cut fibers (sarcomere length, 3.4-3.9 microns) mounted in a double Vaseline-gap chamber. The amplitude and duration of the action- potential stimulated free [Ca] transient were reduced by equilibration with end-pool solutions that contained 20 mM EGTA with 1.76 mM Ca and 0.63 mM phenol red, a maneuver that appeared to markedly reduce the amount of Ca complexed by troponin. A theoretical analysis shows that, under these conditions, the increase in myoplasmic free [Ca] is expected to be restricted to within a few hundred nanometers of the SR Ca release sites and to have a time course that essentially matches that of release. Furthermore, almost all of the Ca that is released from the SR is expected to be rapidly bound by EGTA and exchanged for protons with a 1:2 stoichiometry. Consequently, the time course of SR Ca release can be estimated by scaling the delta pH signal measured with phenol red by -beta/2. The value of beta, the buffering power of myoplasm, was determined in fibers equilibrated with a combination of EGTA, phenol red, and fura-2; its mean value was 22 mM/pH unit. The Ca content of the SR (expressed as myoplasmic concentration) was estimated from the total amount of Ca released by either a train of action potentials or a depleting voltage step; its mean value was 2,685 microM in the action-potential experiments and 2,544 microM in the voltage- clamp experiments. An action potential released, on average, 0.14 of the SR Ca content with a peak rate of release of approximately 5%/ms. A second action potential, elicited 20 ms later, released only 0.6 times as much Ca (expressed as a fraction of the SR content), probably because Ca inactivation of Ca release was produced by the first action potential. During a depolarizing voltage step to 60 mV, the rate of Ca release rapidly increased to a peak value of approximately 3%/ms and then decreased to a quasi-steady level that was only 0.6 times as large; this decrease was also probably due to Ca inactivation of Ca release. SR Ca release was studied with small step depolarizations that open no more than one SR Ca channel in 7,000 and increase the value of spatially averaged myoplasmic free [Ca] by only 0.2 nM. PMID:8537818

Vincristine-sulphate-loaded liposome-templated calcium phosphate nanoshell as potential tumor-targeting delivery system.

PubMed

Thakkar, Hetal Paresh; Baser, Amit Kumar; Parmar, Mayur Prakashbhai; Patel, Ketul Harshadbhai; Ramachandra Murthy, Rayasa

2012-06-01

Vincristine-sulfate-loaded liposomes were prepared with an aim to improve stability, reduce drug leakage during systemic circulation, and increase intracellular uptake. Liposomes were prepared by the thin-film hydration method, followed by coating with calcium phosphate, using the sequential addition approach. Prepared formulations were characterized for size, zeta potential, drug-entrapment efficiency, morphology by transmission electron microscopy (TEM), in vitro drug-release profile, and in vitro cell cytotoxicity study. Effect of formulation variables, such as drug:lipid ratio as well as nature and volume of hydration media, were found to affect drug entrapment, and the concentration of calcium chloride in coating was found to affect size and coating efficiency. Size, zeta potential, and TEM images confirmed that the liposomes were effectively coated with calcium phosphate. The calcium phosphate nanoshell exhibited pH-dependent drug release, showing significantly lower release at pH 7.4, compared to the release at pH 4.5, which is the pH of the tumor interstitium. The in vitro cytotoxicity study done on the lung cancer cell line indicated that coated liposomes are more cytotoxic than plain liposomes and drug solution, indicating their potential for intracellular drug delivery. The cell-uptake study done on the lung cancer cell line indicated that calcium-phosphate-coated liposomes show higher cell uptake than uncoated liposomes.

An Exploration of the Calcium-Binding Mode of Egg White Peptide, Asp-His-Thr-Lys-Glu, and In Vitro Calcium Absorption Studies of Peptide-Calcium Complex.

PubMed

Sun, Na; Jin, Ziqi; Li, Dongmei; Yin, Hongjie; Lin, Songyi

2017-11-08

The binding mode between the pentapeptide (DHTKE) from egg white hydrolysates and calcium ions was elucidated upon its structural and thermodynamics characteristics. The present study demonstrated that the DHTKE peptide could spontaneously bind calcium with a 1:1 stoichiometry, and that the calcium-binding site corresponded to the carboxyl oxygen, amino nitrogen, and imidazole nitrogen atoms of the DHTKE peptide. Moreover, the effect of the DHTKE-calcium complex on improving the calcium absorption was investigated in vitro using Caco-2 cells. Results showed that the DHTKE-calcium complex could facilitate the calcium influx into the cytosol and further improve calcium absorption across Caco-2 cell monolayers by more than 7 times when compared to calcium-free control. This study facilitates the understanding about the binding mechanism between peptides and calcium ions as well as suggests a potential application of egg white peptides as nutraceuticals to improve calcium absorption.

Role of calcium stores and membrane voltage in the generation of slow wave action potentials in guinea-pig gastric pylorus

PubMed Central

Van Helden, D F; Imtiaz, M S; Nurgaliyeva, K; von der Weid, P-Y; Dosen, P J

2000-01-01

Intracellular recordings made in single bundle strips of a visceral smooth muscle revealed rhythmic spontaneous membrane depolarizations termed slow waves (SWs). These exhibited ‘pacemaker’ and ‘regenerative’ components composed of summations of more elementary events termed spontaneous transient depolarizations (STDs). STDs and SWs persisted in the presence of tetrodotoxin, nifedipine and ryanodine, and upon brief exposure to Ca2+-free Cd2+-containing solutions; they were enhanced by ACh and blocked by BAPTA AM, cyclopiazonic acid and caffeine. SWs were also inhibited in heparin-loaded strips. SWs were observed over a wide range of membrane potentials (e.g. −80 to −45 mV) with increased frequencies at more depolarized potentials. Regular spontaneous SW activity in this preparation began after 1–3 h superfusion of the tissue with physiological saline following the dissection procedure. Membrane depolarization applied before the onset of this activity induced bursts of STD-like events (termed the ‘initial’ response) which, when larger than threshold levels initiated regenerative responses. The combined initial-regenerative waveform was termed the SW-like action potential. Voltage-induced responses exhibited large variable latencies (typical range 0.3–4 s), refractory periods of ≈11 s and a pharmacology that was indistinguishable from those of STDs and spontaneous SWs. The data indicate that SWs arise through more elementary inositol 1,4,5-trisphosphate (IP3) receptor-induced Ca2+ release events which rhythmically synchronize to trigger regenerative Ca2+ release and induce inward current across the plasmalemma. The finding that action potentials, which were indistinguishable from SWs, could be evoked by depolarization suggests that membrane potential modulates IP3 production. Voltage feedback on intracellular IP3-sensitive Ca2+ release is likely to have a major influence on the generation and propagation of SWs. PMID:10747196

[Membrane mechanisms of effects of antihypoxic agents bemethyl and almide on neurons of Mollusca].

PubMed

Vislobokov, A I; Marysheva, V V; Shabanov, P D

2003-01-01

Membranotropic effects of the antihypoxants bemithyl and almide, structural analogs of thiobenzimidazole, have been studied on the isolated neuronal preparations of Lymaea stagnalis branchycephalic mollusk. Both drugs in a concentration range of 100-1000 microM produced a reversible, dose-dependent nonselective single-phase blocking action upon the ion channels and completely blocked the channels at a concentration of 10 mM. Therefore, bemithyl and almide are active membranotropic compounds capable (in sufficiently high concentrations) of changing the conductivity of slow sodium, calcium, and potassium ion channels in excitable cells. The protective antihypoxant drug reactions on a systemic level of the organism are probably related to the fact that both drugs in small concentrations are capable of hyperpolarizing the cell membrane, activating the ion channel function, and stabilizing the action potential under hypoxia conditions; in greater concentrations, bemithyl and almide are capable of blocking ion currents, thus reducing the excitability of cells and protecting them from overstress.

Granule fraction inhomogeneity of calcium carbonate/sorbitol in roller compacted granules.

PubMed

Bacher, C; Olsen, P M; Bertelsen, P; Sonnergaard, J M

2008-02-12

The granule fraction inhomogeneity of roller compacted granules was examined on mixtures of three different morphologic forms of calcium carbonate and three particle sizes of sorbitol. The granule fraction inhomogeneity was determined by the distribution of the calcium carbonate in each of the 10 size fractions between 0 and 2000 microm and by calculating the demixing potential. Significant inhomogeneous occurrence of calcium carbonate in the size fractions was demonstrated, depending mostly on the particles sizes of sorbitol but also on the morphological forms of calcium carbonate. The heterogeneous distribution of calcium carbonate was related to the decrease in compactibility of roller compacted granules in comparison to the ungranulated materials. This phenomenon was explained by a mechanism where fracturing of the ribbon during granulation occurred at the weakest interparticulate bonds (the calcium carbonate: calcium carbonate bonds) and consequently exposed the weakest areas of bond formation on the surface of the granules. Accordingly, the non-uniform allocation of the interparticulate attractive forces in a tablet would cause a lowering of the compactibility. Furthermore, the ability of the powder to agglomerate in the roller compactor was demonstrated to be related to the ability of the powder to be compacted into a tablet, thus the most compactable calcium carbonate and the smallest sized sorbitol improved the homogeneity by decreasing the demixing potential.

[Role of calcium ions in the mechanism of action of acetylcholine on energy metabolism in rat liver mitochondria].

PubMed

Vatamaniuk, M Z; Artym, V V; Kuka, O B; Doliba, M M; Shostakovs'ka, I V

1996-01-01

It is shown that administration of acetylcholine to animals (50 micrograms per 100 g of body weight) leads to the activation of respiration and oxidative phosphorylation in the rat liver mitochondria under oxidation of alpha-ketoglutarate; this effect depends on the concentration of calcium ions in the incubation medium of mitochondria. The rate of ADP-stimulated respiration of mitochondria of experimental animals reaches its maximum level under lower concentrations of Ca2+ than in the control animals. The results of investigation of dependence of acetyl choline effect on respiration of mitochondria on the concentration of alpha-ketoglutarate in calcium and calcium-free incubation medium have shown that the half-maximum effect of acetylcholine is observed in calcium medium at lower concentration of the substrate than in calcium-free medium. The latter indicates to the increase of affinity of alpha-ketoglutarate dehydrogenase to alpha-ketoglutarate under these conditions. It is found out that acetylcholine (1.10(-8) M) increases the rate of ADP- and Ca(2+)-stimulated respiration of mitochondria of isolated perfused rat liver, while mutual effect of verapamyl and niphedipin removes this effect.

Calcium current in isolated neonatal rat ventricular myocytes.

PubMed Central

Cohen, N M; Lederer, W J

1987-01-01

1. Calcium currents (ICa) from neonatal rat ventricular heart muscle cells grown in primary culture were examined using the 'whole-cell' voltage-clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). Examination of ICa was limited to one calcium channel type, 'L' type (Nilius, Hess, Lansman & Tsien, 1985), by appropriate voltage protocols. 2. We measured transient and steady-state components of ICa, and could generally describe ICa in terms of the steady-state activation (d infinity) and inactivation (f infinity) parameters. 3. We observed that the reduction of ICa by the calcium channel antagonist D600 can be explained by both a shift of d infinity to more positive potentials as well as a slight reduction of ICa conductance. D600 did not significantly alter either the rate of inactivation of ICa or the voltage dependence of f infinity. 4. The calcium channel modulator BAY K8644 shifted both d infinity and f infinity to more negative potentials. Additionally, BAY K8644 increased the rate of inactivation at potentials between +5 and +55 mV. Furthermore, BAY K8644 also increased ICa conductance, a change consistent with a promotion of 'mode 2' calcium channel activity (Hess, Lansman & Tsien, 1984). 5. We conclude that, as predicted by d infinity and f infinity, there is a significant steady-state component of ICa ('window current') at plateau potentials in neonatal rat heart cells. Modulation of the steady-state and transient components of ICa by various agents can be attributed both to specific alterations in d infinity and f infinity and to more complicated alterations in the mode of calcium channel activity. PMID:2451004

Enhancement of oral bioavailability of atorvastatin calcium by self-emulsifying drug delivery systems (SEDDS).

PubMed

Kadu, Pawan J; Kushare, Sachin S; Thacker, Dhaval D; Gattani, Surendra G

2011-02-01

The aim of the present study was to formulate a self-emulsifying drug delivery system of atorvastatin calcium and its characterization including in vitro and in vivo potential. The solubility of atorvastatin calcium was determined in various vehicles such as Captex 355, Captex 355 EP/NF, Ethyl oleate, Capmul MCM, Capmul PG-8, Gelucire 44/14, Tween 80, Tween 20, and PEG 400. Pseudoternary phase diagrams were plotted on the basis of solubility data of drug in various components to evaluate the microemulsification region. Formulation development and screening was carried out based on results obtained from phase diagrams and characteristics of resultant microemulsion. Prepared formulations were tested for microemulsifying properties and evaluated for clarity, precipitation, viscosity determination, drug content and in vitro dissolution. The optimized formulation further evaluated for particle size distribution, zeta potential, stability studies and in vivo potential. In vivo performance of the optimized formulation was evaluated using a Triton-induced hypercholesterolemia model in male Albino Wistar rats. The formulation significantly reduced serum lipid levels as compared with atorvastatin calcium. Thus studies illustrated the potential use for the delivery of hydrophobic drug such as atorvastatin calcium by oral route.

Effects of inorganic phosphate and ADP on calcium handling by the sarcoplasmic reticulum in rat skinned cardiac muscles.

PubMed

Xiang, J Z; Kentish, J C

1995-03-01

The aim was to investigate whether, and how, increases in inorganic phosphate (Pi) and ADP, similar to those occurring intracellularly during early myocardial ischaemia, affect the calcium handling of the sarcoplasmic reticulum. Rat ventricular trabeculae were permeabilised with saponin. The physiological process of calcium induced calcium release (CICR) from the muscle sarcoplasmic reticulum was triggered via flash photolysis of the "caged Ca2+", nitr-5. Alternatively, calcium release was induced by rapid application of caffeine to give an estimate of sarcoplasmic reticular calcium loading. The initial rate of sarcoplasmic reticular calcium pumping was also assessed by photolysis of caged ATP at saturating [Ca2+]. Myoplasmic [Ca2+] (using fluo-3) and isometric force were measured. Pi (2-20 mM) significantly depressed the magnitude of CICR and the associated force transient. Sarcoplasmic reticular calcium loading was inhibited even more than CICR by Pi, suggesting that reduced calcium loading could account for all of the inhibitory effect of Pi on CICR and that Pi may slightly activate the calcium release mechanism. The reduced sarcoplasmic reticular calcium loading seemed to be due to a fall in the free energy of ATP hydrolysis (delta GATP) available for the calcium pump, since equal decreases in delta GATP produced by adding both Pi and ADP in various ratios caused similar falls in the calcium loading of the sarcoplasmic reticulum. The caged ATP experiments indicated that Pi (20 mM) did not affect the rate constant of sarcoplasmic reticular calcium uptake. ADP (10 mM) alone, or with 1 mM Pi, inhibited calcium loading. In spite of this, ADP (10 mM) did not alter CICR and, when 1 mM Pi was added, ADP increased CICR above control. An increase in intracellular Pi reduces sarcoplasmic reticular calcium loading and thus depresses the CICR. This could be an important contributing factor in the hypoxic or ischaemic contractile failure of the myocardium. However the detrimental effect of Pi may be offset to some extent by a stimulatory action of ADP on the calcium release mechanism of CICR.

Ion channels to inactivate neurons in Drosophila.

PubMed

Hodge, James J L

2009-01-01

Ion channels are the determinants of excitability; therefore, manipulation of their levels and properties provides an opportunity for the investigator to modulate neuronal and circuit function. There are a number of ways to suppress electrical activity in Drosophila neurons, for instance, over-expression of potassium channels (i.e. Shaker Kv1, Shaw Kv3, Kir2.1 and DORK) that are open at resting membrane potential. This will result in increased potassium efflux and membrane hyperpolarisation setting resting membrane potential below the threshold required to fire action potentials. Alternatively over-expression of other channels, pumps or co-transporters that result in a hyperpolarised membrane potential will also prevent firing. Lastly, neurons can be inactivated by, disrupting or reducing the level of functional voltage-gated sodium (Nav1 paralytic) or calcium (Cav2 cacophony) channels that mediate the depolarisation phase of action potentials. Similarly, strategies involving the opposite channel manipulation should allow net depolarisation and hyperexcitation in a given neuron. These changes in ion channel expression can be brought about by the versatile transgenic (i.e. Gal4/UAS based) systems available in Drosophila allowing fine temporal and spatial control of (channel) transgene expression. These systems are making it possible to electrically inactivate (or hyperexcite) any neuron or neural circuit in the fly brain, and much like an exquisite lesion experiment, potentially elucidate whatever interesting behaviour or phenotype each network mediates. These techniques are now being used in Drosophila to reprogram electrical activity of well-defined circuits and bring about robust and easily quantifiable changes in behaviour, allowing different models and hypotheses to be rapidly tested.

A comprehensive search for calcium binding sites critical for TMEM16A calcium-activated chloride channel activity

PubMed Central

Tien, Jason; Peters, Christian J; Wong, Xiu Ming; Cheng, Tong; Jan, Yuh Nung; Jan, Lily Yeh; Yang, Huanghe

2014-01-01

TMEM16A forms calcium-activated chloride channels (CaCCs) that regulate physiological processes such as the secretions of airway epithelia and exocrine glands, the contraction of smooth muscles, and the excitability of neurons. Notwithstanding intense interest in the mechanism behind TMEM16A-CaCC calcium-dependent gating, comprehensive surveys to identify and characterize potential calcium sensors of this channel are still lacking. By aligning distantly related calcium-activated ion channels in the TMEM16 family and conducting systematic mutagenesis of all conserved acidic residues thought to be exposed to the cytoplasm, we identify four acidic amino acids as putative calcium-binding residues. Alterations of the charge, polarity, and size of amino acid side chains at these sites alter the ability of different divalent cations to activate the channel. Furthermore, TMEM16A mutant channels containing double cysteine substitutions at these residues are sensitive to the redox potential of the internal solution, providing evidence for their physical proximity and solvent accessibility. DOI: http://dx.doi.org/10.7554/eLife.02772.001 PMID:24980701

Biophysically realistic minimal model of dopamine neuron

NASA Astrophysics Data System (ADS)

Oprisan, Sorinel

2008-03-01

We proposed and studied a new biophysically relevant computational model of dopaminergic neurons. Midbrain dopamine neurons are involved in motivation and the control of movement, and have been implicated in various pathologies such as Parkinson's disease, schizophrenia, and drug abuse. The model we developed is a single-compartment Hodgkin-Huxley (HH)-type parallel conductance membrane model. The model captures the essential mechanisms underlying the slow oscillatory potentials and plateau potential oscillations. The main currents involved are: 1) a voltage-dependent fast calcium current, 2) a small conductance potassium current that is modulated by the cytosolic concentration of calcium, and 3) a slow voltage-activated potassium current. We developed multidimensional bifurcation diagrams and extracted the effective domains of sustained oscillations. The model includes a calcium balance due to the fundamental importance of calcium influx as proved by simultaneous electrophysiological and calcium imaging procedure. Although there are significant evidences to suggest a partially electrogenic calcium pump, all previous models considered only elecrtogenic pumps. We investigated the effect of the electrogenic calcium pump on the bifurcation diagram of the model and compared our findings against the experimental results.

Active Dendrites and Differential Distribution of Calcium Channels Enable Functional Compartmentalization of Golgi Cells.

PubMed

Rudolph, Stephanie; Hull, Court; Regehr, Wade G

2015-11-25

Interneurons are essential to controlling excitability, timing, and synaptic integration in neuronal networks. Golgi cells (GoCs) serve these roles at the input layer of the cerebellar cortex by releasing GABA to inhibit granule cells (grcs). GoCs are excited by mossy fibers (MFs) and grcs and provide feedforward and feedback inhibition to grcs. Here we investigate two important aspects of GoC physiology: the properties of GoC dendrites and the role of calcium signaling in regulating GoC spontaneous activity. Although GoC dendrites are extensive, previous studies concluded they are devoid of voltage-gated ion channels. Hence, the current view holds that somatic voltage signals decay passively within GoC dendrites, and grc synapses onto distal dendrites are not amplified and are therefore ineffective at firing GoCs because of strong passive attenuation. Using whole-cell recording and calcium imaging in rat slices, we find that dendritic voltage-gated sodium channels allow somatic action potentials to activate voltage-gated calcium channels (VGCCs) along the entire dendritic length, with R-type and T-type VGCCs preferentially located distally. We show that R- and T-type VGCCs located in the dendrites can boost distal synaptic inputs and promote burst firing. Active dendrites are thus critical to the regulation of GoC activity, and consequently, to the processing of input to the cerebellar cortex. In contrast, we find that N-type channels are preferentially located near the soma, and control the frequency and pattern of spontaneous firing through their close association with calcium-activated potassium (KCa) channels. Thus, VGCC types are differentially distributed and serve specialized functions within GoCs. Interneurons are essential to neural processing because they modulate excitability, timing, and synaptic integration within circuits. At the input layer of the cerebellar cortex, a single type of interneuron, the Golgi cell (GoC), carries these functions. The extent of inhibition depends on both spontaneous activity of GoCs and the excitatory synaptic input they receive. In this study, we find that different types of calcium channels are differentially distributed, with dendritic calcium channels being activated by somatic activity, boosting synaptic inputs and enabling bursting, and somatic calcium cannels promoting regular firing. We therefore challenge the current view that GoC dendrites are passive and identify the mechanisms that contribute to GoCs regulating the flow of sensory information in the cerebellar cortex. Copyright © 2015 the authors 0270-6474/15/3515492-13$15.00/0.

Calcium pectate chemistry causes growth to be stored in Chara corallina: a test of the pectate cycle.

PubMed

Proseus, Timothy E; Boyer, John S

2008-08-01

Calcium pectate chemistry was reported to control the growth rate of cells of Chara corallina, and required turgor pressure (P) to do so. Accordingly, this chemistry should account for other aspects of growth, particularly the ability of plants to compensate for brief exposure to low P, that is, to 'store' growth. Live Chara cells or isolated walls were attached to a pressure probe, and P was varied. Low P caused growth to be inhibited in live cells, but when P returned to normal (0.5 MPa), a flush of growth completely compensated for that lost at low P for as long as 23-53 min. This growth storage was absent in isolated walls, mature cells and live cells exposed to cold, indicating that the cytoplasm delivered a metabolically derived growth factor needing P for its action. Because the cytoplasm delivered pectate needing P for its action, pectate was supplied to isolated walls at low P as though the cytoplasm had done so. Growth was stored while otherwise none occurred. It was concluded that a P-dependent cycle of calcium pectate chemistry not only controlled growth rate and new wall deposition, but also accounted for stored growth.

Canonical Transient Receptor Potential Channel 2 (TRPC2) as a Major Regulator of Calcium Homeostasis in Rat Thyroid FRTL-5 Cells

PubMed Central

Sukumaran, Pramod; Löf, Christoffer; Kemppainen, Kati; Kankaanpää, Pasi; Pulli, Ilari; Näsman, Johnny; Viitanen, Tero; Törnquist, Kid

2012-01-01

Mammalian non-selective transient receptor potential cation channels (TRPCs) are important in the regulation of cellular calcium homeostasis. In thyroid cells, including rat thyroid FRTL-5 cells, calcium regulates a multitude of processes. RT-PCR screening of FRTL-5 cells revealed the presence of TRPC2 channels only. Knockdown of TRPC2 using shRNA (shTRPC2) resulted in decreased ATP-evoked calcium peak amplitude and inward current. In calcium-free buffer, there was no difference in the ATP-evoked calcium peak amplitude between control cells and shTRPC2 cells. Store-operated calcium entry was indistinguishable between the two cell lines. Basal calcium entry was enhanced in shTRPC2 cells, whereas the level of PKCβ1 and PKCδ, the activity of sarco/endoplasmic reticulum Ca2+-ATPase, and the calcium content in the endoplasmic reticulum were decreased. Stromal interaction molecule (STIM) 2, but not STIM1, was arranged in puncta in resting shTRPC2 cells but not in control cells. Phosphorylation site Orai1 S27A/S30A mutant and non-functional Orai1 R91W attenuated basal calcium entry in shTRPC2 cells. Knockdown of PKCδ with siRNA increased STIM2 punctum formation and enhanced basal calcium entry but decreased sarco/endoplasmic reticulum Ca2+-ATPase activity in wild-type cells. Transfection of a truncated, non-conducting mutant of TRPC2 evoked similar results. Thus, TRPC2 functions as a major regulator of calcium homeostasis in rat thyroid cells. PMID:23144458

Calcium release rates from tooth enamel treated with dentifrices containing whitening agents and abrasives.

PubMed

Araujo, Danilo Barral; Silva, Luciana Rodrigues; de Araujo, Roberto Paulo Correia

2010-01-01

Tooth whitening agents containing hydrogen peroxide and carbamide peroxide are used frequently in esthetic dental procedures. However, lesions on the enamel surface have been attributed to the action of these products. Using conventional procedures for separating and isolating biological structures, powdered enamel was obtained and treated with hydrogen peroxide, carbamide peroxide, and sodium bicarbonate, ingredients typically found in dentifrices. The enamel was exposed to different pH levels, and atomic emission spectrometry was used to determine calcium release rates. As the pH level increased, the rate of calcium release from enamel treated with dentifrices containing whitening agents decreased. Carbamide peroxide produced the lowest amount of decalcification, while sodium bicarbonate produced the highest release rates at all pH levels.

Emergence of order in visual system development.

PubMed Central

Shatz, C J

1996-01-01

Neural connections in the adult central nervous system are highly precise. In the visual system, retinal ganglion cells send their axons to target neurons in the lateral geniculate nucleus (LGN) in such a way that axons originating from the two eyes terminate in adjacent but nonoverlapping eye-specific layers. During development, however, inputs from the two eyes are intermixed, and the adult pattern emerges gradually as axons from the two eyes sort out to form the layers. Experiments indicate that the sorting-out process, even though it occurs in utero in higher mammals and always before vision, requires retinal ganglion cell signaling; blocking retinal ganglion cell action potentials with tetrodotoxin prevents the formation of the layers. These action potentials are endogenously generated by the ganglion cells, which fire spontaneously and synchronously with each other, generating "waves" of activity that travel across the retina. Calcium imaging of the retina shows that the ganglion cells undergo correlated calcium bursting to generate the waves and that amacrine cells also participate in the correlated activity patterns. Physiological recordings from LGN neurons in vitro indicate that the quasiperiodic activity generated by the retinal ganglion cells is transmitted across the synapse between ganglion cells to drive target LGN neurons. These observations suggest that (i) a neural circuit within the immature retina is responsible for generating specific spatiotemporal patterns of neural activity; (ii) spontaneous activity generated in the retina is propagated across central synapses; and (iii) even before the photoreceptors are present, nerve cell function is essential for correct wiring of the visual system during early development. Since spontaneously generated activity is known to be present elsewhere in the developing CNS, this process of activity-dependent wiring could be used throughout the nervous system to help refine early sets of neural connections into their highly precise adult patterns. Images Fig. 1 Fig. 4 PMID:8570602

Biocalcite, a multifunctional inorganic polymer: Building block for calcareous sponge spicules and bioseed for the synthesis of calcium phosphate-based bone

PubMed Central

Schröder, Heinz C; Müller, Werner E G

2014-01-01

Summary Calcium carbonate is the material that builds up the spicules of the calcareous sponges. Recent results revealed that the calcium carbonate/biocalcite-based spicular skeleton of these animals is formed through an enzymatic mechanism, such as the skeleton of the siliceous sponges, evolutionarily the oldest animals that consist of biosilica. The enzyme that mediates the calcium carbonate deposition has been identified as a carbonic anhydrase (CA) and has been cloned from the calcareous sponge species Sycon raphanus. Calcium carbonate deposits are also found in vertebrate bones besides the main constituent, calcium phosphate/hydroxyapatite (HA). Evidence has been presented that during the initial phase of HA synthesis poorly crystalline carbonated apatite is deposited. Recent data summarized here indicate that during early bone formation calcium carbonate deposits enzymatically formed by CA, act as potential bioseeds for the precipitation of calcium phosphate mineral onto bone-forming osteoblasts. Two different calcium carbonate phases have been found during CA-driven enzymatic calcium carbonate deposition in in vitro assays: calcite crystals and round-shaped vaterite deposits. The CA provides a new target of potential anabolic agents for treatment of bone diseases; a first CA activator stimulating the CA-driven calcium carbonate deposition has been identified. In addition, the CA-driven calcium carbonate crystal formation can be frozen at the vaterite state in the presence of silintaphin-2, an aspartic acid/glutamic acid-rich sponge-specific protein. The discovery that calcium carbonate crystals act as bioseeds in human bone formation may allow the development of novel biomimetic scaffolds for bone tissue engineering. Na-alginate hydrogels, enriched with biosilica, have recently been demonstrated as a suitable matrix to embed bone forming cells for rapid prototyping bioprinting/3D cell printing applications. PMID:24991497

Biocalcite, a multifunctional inorganic polymer: Building block for calcareous sponge spicules and bioseed for the synthesis of calcium phosphate-based bone.

PubMed

Wang, Xiaohong; Schröder, Heinz C; Müller, Werner E G

2014-01-01

Calcium carbonate is the material that builds up the spicules of the calcareous sponges. Recent results revealed that the calcium carbonate/biocalcite-based spicular skeleton of these animals is formed through an enzymatic mechanism, such as the skeleton of the siliceous sponges, evolutionarily the oldest animals that consist of biosilica. The enzyme that mediates the calcium carbonate deposition has been identified as a carbonic anhydrase (CA) and has been cloned from the calcareous sponge species Sycon raphanus. Calcium carbonate deposits are also found in vertebrate bones besides the main constituent, calcium phosphate/hydroxyapatite (HA). Evidence has been presented that during the initial phase of HA synthesis poorly crystalline carbonated apatite is deposited. Recent data summarized here indicate that during early bone formation calcium carbonate deposits enzymatically formed by CA, act as potential bioseeds for the precipitation of calcium phosphate mineral onto bone-forming osteoblasts. Two different calcium carbonate phases have been found during CA-driven enzymatic calcium carbonate deposition in in vitro assays: calcite crystals and round-shaped vaterite deposits. The CA provides a new target of potential anabolic agents for treatment of bone diseases; a first CA activator stimulating the CA-driven calcium carbonate deposition has been identified. In addition, the CA-driven calcium carbonate crystal formation can be frozen at the vaterite state in the presence of silintaphin-2, an aspartic acid/glutamic acid-rich sponge-specific protein. The discovery that calcium carbonate crystals act as bioseeds in human bone formation may allow the development of novel biomimetic scaffolds for bone tissue engineering. Na-alginate hydrogels, enriched with biosilica, have recently been demonstrated as a suitable matrix to embed bone forming cells for rapid prototyping bioprinting/3D cell printing applications.

Safinamide: a new hope for Parkinson's disease?

PubMed

Teixeira, Fábio G; Gago, Miguel F; Marques, Paulo; Moreira, Pedro Silva; Magalhães, Ricardo; Sousa, Nuno; Salgado, António J

2018-03-01

The loss of dopaminergic neurons (DAn) and reduced dopamine (DA) production underlies the reasoning behind the gold standard treatment for Parkinson's disease (PD) using levodopa (L-DOPA). Recently licensed by the European Medicine Agency (EMA) and US Food and Drug Administration (FDA), safinamide [a monoamine oxidase B (MOA-B) inhibitor] is an alternative to L-DOPA; as we discuss here, it enhances dopaminergic transmission with decreased secondary effects compared with L-DOPA. In addition, nondopaminergic actions (neuroprotective effects) have been reported, with safinamide inhibiting glutamate release and sodium/calcium channels, reducing the excitotoxic input to dopaminergic neuronal death. Effects of safinamide have been correlated with the amelioration of non-motor symptoms (NMS), although these remain under discussion. Overall, safinamide can be considered to have potential antidyskinetic and neuroprotective effects and future trials and/or studies should be performed to provide further evidence for its potential as an anti-PD drug. Copyright © 2018 Elsevier Ltd. All rights reserved.

Modulation of Kv7 channels and excitability in the brain.

PubMed

Greene, Derek L; Hoshi, Naoto

2017-02-01

Neuronal Kv7 channels underlie a voltage-gated non-inactivating potassium current known as the M-current. Due to its particular characteristics, Kv7 channels show pronounced control over the excitability of neurons. We will discuss various factors that have been shown to drastically alter the activity of this channel such as protein and phospholipid interactions, phosphorylation, calcium, and numerous neurotransmitters. Kv7 channels locate to key areas for the control of action potential initiation and propagation. Moreover, we will explore the dynamic surface expression of the channel modulated by neurotransmitters and neural activity. We will also focus on known principle functions of neural Kv7 channels: control of resting membrane potential and spiking threshold, setting the firing frequency, afterhyperpolarization after burst firing, theta resonance, and transient hyperexcitability from neurotransmitter-induced suppression of the M-current. Finally, we will discuss the contribution of altered Kv7 activity to pathologies such as epilepsy and cognitive deficits.

Modulation of Kv7 channels and excitability in the brain

PubMed Central

Greene, Derek L; Hoshi, Naoto

2016-01-01

Neuronal Kv7 channels underlie a voltage-gated non-inactivating potassium current known as the M-current. Due to its particular characteristics, Kv7 channels show pronounced control over the excitability of neurons. We will discuss various factors that have been shown to drastically alter the activity of this channel such as protein and phospholipid interactions, phosphorylation, calcium, and numerous neurotransmitters. Kv7 channels locate to key areas for the control of action potential initiation and propagation. Moreover, we will explore the dynamic surface expression of the channel modulated by neurotransmitters and neural activity. We will also focus on known principle functions of neural Kv7 channels: control of resting membrane potential and spiking threshold, setting the firing frequency, afterhyperpolarization after burst firing, theta resonance, and transient hyperexcitability from neurotransmitter-induced suppression of the M-current. Finally, we will discuss the contribution of altered Kv7 activity to pathologies such as epilepsy and cognitive deficits. PMID:27645822

Distinct action of aranidipine and its active metabolite on renal arterioles, with special reference to renal protection.

PubMed

Nakamura, A; Hayashi, K; Fujiwara, K; Ozawa, Y; Honda, M; Saruta, T

2000-06-01

Aranidipine, a newly developed calcium antagonist, possesses unique pharmacologic characteristics in that its metabolite (M-1) still has antihypertensive action. We examined the effects of both agents on renal microcirculation using the isolated perfused hydronephrotic rat kidney. During norepinephrine-induced constriction, the addition of aranidipine dilated both afferent and efferent arterioles in a dose-dependent manner; at 10(-6) M, 83 +/- 6% and 90 +/- 6% reversal, respectively. In contrast, its active metabolite exerted dilator action predominantly on the afferent arteriole (79 +/- 4% vs. 44 +/- 17% at 10(-6) M for afferent and efferent arterioles, respectively). We further examined the long-term (8 weeks) effect of these agents on the development of renal injury in salt-loaded subtotally nephrectomized spontaneously hypertensive rats. Both aranidipine and M-1 reduced blood pressure by a similar magnitude. The decreases in proteinuria were observed in the aranidipine-treated group at weeks 6, 8, and 10, whereas in the M-1 group, significant reduction was attained only at week 6. Histopathologic examination revealed that both treatments improved glomerular and arteriolar sclerosis. Glomerular sclerosis, however, was less pronounced in the aranidipine-treated group than in the M-1 group. In conclusion, aranidipine has dilator action on both arterioles, whereas M-1 caused predominant dilation of afferent arterioles. Such metabolic changes may constitute a determinant of efferent arteriolar action of the calcium antagonist.

Calcium currents, charge movement and dihydropyridine binding in fast- and slow-twitch muscles of rat and rabbit.

PubMed Central

Lamb, G D; Walsh, T

1987-01-01

1. The Vaseline-gap technique was used to record slow calcium currents and asymmetric charge movement in single fibres of fast-twitch muscles (extensor digitorum longus (e.d.l.) and sternomastoid) and slow-twitch muscles (soleus) from rat and rabbit, at a holding potential of -90 mV. 2. The slow calcium current in soleus fibres was about one-third of the size of the current in e.d.l. fibres, but was very similar otherwise. In both e.d.l. and soleus fibres, the dihydropyridine (DHP), nifedipine, suppressed the calcium current entirely. 3. In these normally polarized fibres, nifedipine suppressed only part (qns) of the asymmetric charge movement. The proportion of qns suppressed by various concentrations of nifedipine was linearly related to the associated reduction of the calcium current. Half-maximal suppression of both parameters was obtained with about 0.5 microM-nifedipine. The calcium current and the qns component of the charge movement also were suppressed over the same time course by nifedipine. Another DHP calcium antagonist, (+)PN200/110, was indistinguishable from nifedipine in its effects of suppressing calcium currents and qns. 4. In all muscle types, the total amount of qns in each fibre was linearly related to the size of the calcium current (in the absence of DHP). On average, qns was 3.3 times larger in e.d.l. fibres than in soleus fibres. 5. In contrast to the other dihydropyridines, (-)bay K8644, a calcium channel agonist, did not suppress any asymmetric charge movement. 6. The potential dependence of the slow calcium current implied a minimum gating charge of about five or six electronic charges. The movement of qns occurred over a more negative potential range than the change in calcium conductance. 7. Experiments on the binding of (+)PN200/110 indicated that e.d.l. muscles had between about 2 and 3 times more specific DHP binding sites than did soleus muscle. 8. These results point to a close relationship between slow calcium channels, the qns component of the charge movement and DHP binding sites, in both fast- and slow-twitch mammalian muscle. qns appears to be part of the gating current of the T-system calcium channels. PMID:2451745

Cannabidiol and (−)Δ9-tetrahydrocannabinol are neuroprotective antioxidants

PubMed Central

Hampson, A. J.; Grimaldi, M.; Axelrod, J.; Wink, D.

1998-01-01

The neuroprotective actions of cannabidiol and other cannabinoids were examined in rat cortical neuron cultures exposed to toxic levels of the excitatory neurotransmitter glutamate. Glutamate toxicity was reduced by both cannabidiol, a nonpsychoactive constituent of marijuana, and the psychotropic cannabinoid (−)Δ9-tetrahydrocannabinol (THC). Cannabinoids protected equally well against neurotoxicity mediated by N-methyl-d-aspartate receptors, 2-amino-3-(4-butyl-3-hydroxyisoxazol-5-yl)propionic acid receptors, or kainate receptors. N-methyl-d-aspartate receptor-induced toxicity has been shown to be calcium dependent; this study demonstrates that 2-amino-3-(4-butyl-3-hydroxyisoxazol-5-yl)propionic acid/kainate receptor-type neurotoxicity is also calcium-dependent, partly mediated by voltage sensitive calcium channels. The neuroprotection observed with cannabidiol and THC was unaffected by cannabinoid receptor antagonist, indicating it to be cannabinoid receptor independent. Previous studies have shown that glutamate toxicity may be prevented by antioxidants. Cannabidiol, THC and several synthetic cannabinoids all were demonstrated to be antioxidants by cyclic voltametry. Cannabidiol and THC also were shown to prevent hydroperoxide-induced oxidative damage as well as or better than other antioxidants in a chemical (Fenton reaction) system and neuronal cultures. Cannabidiol was more protective against glutamate neurotoxicity than either ascorbate or α-tocopherol, indicating it to be a potent antioxidant. These data also suggest that the naturally occurring, nonpsychotropic cannabinoid, cannabidiol, may be a potentially useful therapeutic agent for the treatment of oxidative neurological disorders such as cerebral ischemia. PMID:9653176

Geometry-dependent functional changes in iPSC-derived cardiomyocytes probed by functional imaging and RNA sequencing

PubMed Central

Gaublomme, Jellert; Shekhar, Karthik; Butty, Vincent; Yi, B. Alexander; Kralj, Joel M.; Bloxham, William; Boyer, Laurie A.; Regev, Aviv

2017-01-01

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are a promising platform for cardiac studies in vitro, and possibly for tissue repair in humans. However, hiPSC-CM cells tend to retain morphology, metabolism, patterns of gene expression, and electrophysiology similar to that of embryonic cardiomyocytes. We grew hiPSC-CM in patterned islands of different sizes and shapes, and measured the effect of island geometry on action potential waveform and calcium dynamics using optical recordings of voltage and calcium from 970 islands of different sizes. hiPSC-CM in larger islands showed electrical and calcium dynamics indicative of greater functional maturity. We then compared transcriptional signatures of the small and large islands against a developmental time course of cardiac differentiation. Although island size had little effect on expression of most genes whose levels differed between hiPSC-CM and adult primary CM, we identified a subset of genes for which island size drove the majority (58%) of the changes associated with functional maturation. Finally, we patterned hiPSC-CM on islands with a variety of shapes to probe the relative contributions of soluble factors, electrical coupling, and direct cell-cell contacts to the functional maturation. Collectively, our data show that optical electrophysiology is a powerful tool for assaying hiPSC-CM maturation, and that island size powerfully drives activation of a subset of genes involved in cardiac maturation. PMID:28333933

Antimicrobial activity of gallic acid against thermophilic Campylobacter is strain specific and associated with a loss of calcium ions.

PubMed

Sarjit, Amreeta; Wang, Yi; Dykes, Gary A

2015-04-01

Gallic acid has been suggested as a potential antimicrobial for the control of Campylobacter but its effectiveness is poorly studied. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of gallic acid against Campylobacter jejuni (n = 8) and Campylobacter coli (n = 4) strains was determined. Gallic acid inhibited the growth of five C. jejuni strains and three C. coli strains (MIC: 15.63-250 μg mL(-1)). Gallic acid was only bactericidal to two C. coli strains (MBC: 125 and 62.5 μg mL(-1)). The mechanism of the bactericidal effect against these two strains (and selected non-susceptible controls) was investigated by determining decimal reduction times and by monitoring the loss of cellular content and calcium ions, and changes in cell morphology. Gallic acid did not result in a loss of cellular content or morphological changes in the susceptible strains as compared to the controls. Gallic acid resulted in a loss of calcium ions (0.58-1.53 μg mL(-1) and 0.54-1.17 μg mL(-1), respectively, over a 180 min period) from the susceptible strains but not the controls. Gallic acid is unlikely to be an effective antimicrobial against Campylobacter in a practical sense unless further interventions to ensure an effective bactericidal mode of action against all strains are developed. Copyright © 2014 Elsevier Ltd. All rights reserved.

Interpreting experimental data on egg production--applications of dynamic differential equations.

PubMed

France, J; Lopez, S; Kebreab, E; Dijkstra, J

2013-09-01

This contribution focuses on applying mathematical models based on systems of ordinary first-order differential equations to synthesize and interpret data from egg production experiments. Models based on linear systems of differential equations are contrasted with those based on nonlinear systems. Regression equations arising from analytical solutions to linear compartmental schemes are considered as candidate functions for describing egg production curves, together with aspects of parameter estimation. Extant candidate functions are reviewed, a role for growth functions such as the Gompertz equation suggested, and a function based on a simple new model outlined. Structurally, the new model comprises a single pool with an inflow and an outflow. Compartmental simulation models based on nonlinear systems of differential equations, and thus requiring numerical solution, are next discussed, and aspects of parameter estimation considered. This type of model is illustrated in relation to development and evaluation of a dynamic model of calcium and phosphorus flows in layers. The model consists of 8 state variables representing calcium and phosphorus pools in the crop, stomachs, plasma, and bone. The flow equations are described by Michaelis-Menten or mass action forms. Experiments that measure Ca and P uptake in layers fed different calcium concentrations during shell-forming days are used to evaluate the model. In addition to providing a useful management tool, such a simulation model also provides a means to evaluate feeding strategies aimed at reducing excretion of potential pollutants in poultry manure to the environment.

The investigation of the cellular electrophysiological and antiarrhythmic effects of a novel selective sodium-calcium exchanger inhibitor, GYKB-6635, in canine and guinea-pig hearts.

PubMed

Geramipour, Amir; Kohajda, Zsófia; Corici, Claudia; Prorok, János; Szakonyi, Zsolt; Oravecz, Kinga; Márton, Zoltán; Nagy, Norbert; Tóth, András; Acsai, Károly; Virág, László; Varró, András; Jost, Norbert

2016-10-01

The sodium-calcium exchanger (NCX) is considered as the major transmembrane transport mechanism that controls Ca 2+ homeostasis. Its contribution to the cardiac repolarization has not yet been directly studied due to lack of specific inhibitors, so that an urgent need for more selective compounds. In this study, the electrophysiological effects of GYKB-6635, a novel NCX inhibitor, on the NCX, L-type calcium, and main repolarizing potassium currents as well as action potential (AP) parameters were investigated. Ion currents and AP recordings were investigated by applying the whole-cell patch clamp and standard microelectrode techniques in canine heart at 37 °C. Effects of GYKB-6635 were studied in ouabain-induced arrhythmias in isolated guinea-pig hearts. At a concentration of 1 μmol/L, GYKB significantly reduced both the inward and outward NCX currents (57% and 58%, respectively). Even at a high concentration (10 μmol/L), GYKB-6635 did not change the I CaL , the maximum rate of depolarization (dV/dt max ), the main repolarizing K + currents, and the main AP parameters. GYKB-6635 pre-treatment significantly delayed the time to the development of ventricular fibrillation (by about 18%). It is concluded that GYKB-6635 is a potent and highly selective inhibitor of the cardiac NCX and, in addition, it is suggested to also contribute to the prevention of DAD-based arrhythmias.

A facile magnesium-containing calcium carbonate biomaterial as potential bone graft.

PubMed

He, Fupo; Zhang, Jing; Tian, Xiumei; Wu, Shanghua; Chen, Xiaoming

2015-12-01

The calcium carbonate is the main composition of coral which has been widely used as bone graft in clinic. Herein, we readily prepared novel magnesium-containing calcium carbonate biomaterials (MCCs) under the low-temperature conditions based on the dissolution-recrystallization reaction between unstable amorphous calcium carbonate (ACC) and metastable vaterite-type calcium carbonate with water involved. The content of magnesium in MCCs was tailored by adjusting the proportion of ACC starting material that was prepared using magnesium as stabilizer. The phase composition of MCCs with various amounts of magnesium was composed of one, two or three kinds of calcium carbonates (calcite, aragonite, and/or magnesian calcite). The different MCCs differed in topography. The in vitro degradation of MCCs accelerated with increasing amount of introduced magnesium. The MCCs with a certain amount of magnesium not only acquired higher compressive strength, but also promoted in vitro cell proliferation and osteogenic differentiation. Taken together, the facile MCCs shed light on their potential as bone graft. Copyright © 2015 Elsevier B.V. All rights reserved.

Electrosynthesis of Biomimetic Manganese-Calcium Oxides for Water Oxidation Catalysis--Atomic Structure and Functionality.

PubMed

González-Flores, Diego; Zaharieva, Ivelina; Heidkamp, Jonathan; Chernev, Petko; Martínez-Moreno, Elías; Pasquini, Chiara; Mohammadi, Mohammad Reza; Klingan, Katharina; Gernet, Ulrich; Fischer, Anna; Dau, Holger

2016-02-19

Water-oxidizing calcium-manganese oxides, which mimic the inorganic core of the biological catalyst, were synthesized and structurally characterized by X-ray absorption spectroscopy at the manganese and calcium K edges. The amorphous, birnesite-type oxides are obtained through a simple protocol that involves electrodeposition followed by active-site creation through annealing at moderate temperatures. Calcium ions are inessential, but tune the electrocatalytic properties. For increasing calcium/manganese molar ratios, both Tafel slopes and exchange current densities decrease gradually, resulting in optimal catalytic performance at calcium/manganese molar ratios of close to 10 %. Tracking UV/Vis absorption changes during electrochemical operation suggests that inactive oxides reach their highest, all-Mn(IV) oxidation state at comparably low electrode potentials. The ability to undergo redox transitions and the presence of a minor fraction of Mn(III) ions at catalytic potentials is identified as a prerequisite for catalytic activity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Calcium regulation of oxidative phosphorylation in rat skeletal muscle mitochondria.

PubMed

Kavanagh, N I; Ainscow, E K; Brand, M D

2000-02-24

Activation of oxidative phosphorylation by physiological levels of calcium in mitochondria from rat skeletal muscle was analysed using top-down elasticity and regulation analysis. Oxidative phosphorylation was conceptually divided into three subsystems (substrate oxidation, proton leak and phosphorylation) connected by the membrane potential or the protonmotive force. Calcium directly activated the phosphorylation subsystem and (with sub-saturating 2-oxoglutarate) the substrate oxidation subsystem but had no effect on the proton leak kinetics. The response of mitochondria respiring on 2-oxoglutarate at two physiological concentrations of free calcium was quantified using control and regulation analysis. The partial integrated response coefficients showed that direct stimulation of substrate oxidation contributed 86% of the effect of calcium on state 3 oxygen consumption, and direct activation of the phosphorylation reactions caused 37% of the increase in phosphorylation flux. Calcium directly activated phosphorylation more strongly than substrate oxidation (78% compared to 45%) to achieve homeostasis of mitochondrial membrane potential during large increases in flux.

Effect of ticlopidine ex vivo on platelet intracellular calcium mobilization

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

Derian, C.K.; Friedman, P.A.

1988-04-01

The antiplatelet compound ticlopidine exerts its potent inhibitory activity through an as yet undetermined mechanism(s). The goal of this study was to determine the effect, if any, of ticlopidine ex vivo on platelet calcium mobilization. Ticlopidine inhibited ADP-induced platelet aggregation by 50-80%. In the presence of 1 mM EGTA, ticlopidine inhibited ADP- and thrombin-stimulated increases in (Ca2+)i in fura-2 loaded platelets. We evaluated further the effect of ticlopidine on calcium mobilization by examining both agonist-stimulated formation of inositol trisphosphate in intact platelets and the ability of inositol trisphosphate to release /sup 45/Ca from intracellular sites in permeabilized cells. We showmore » here that while ticlopidine significantly affected agonist-induced intracellular calcium mobilization in intact platelets, the drug was without effect on agonist-stimulated formation of inositol trisphosphate in intact platelets and on inositol trisphosphate-induced /sup 45/Ca release in saponin-permeabilized platelets. Our study demonstrates that ticlopidine exerts at least part of its effect via inhibition of intracellular calcium mobilization but that its site of action remains to be determined.« less

Calcium antagonistic activity of Bacopa monniera in guinea-pig trachea.

PubMed

Channa, Shabana; Dar, Ahsana

2012-01-01

To demonstrate the calcium antagonistic property of ethanol extract of Bacopa monniera in guinea-pig trachea. The dose response curves of CaCl(2) (1 × 10(-5) to 1 × 10(-1) M) were constructed in the absence and presence of ethanol extract of Bacopa monniera (100, 500 and 700 μg/ml) or nifedipine (1 × 10(-6) M) in guinea-pig trachea in calcium free high K(+)-MOPS-PSS (3-(N-morpholino)-propanesulphonic acid physiological salt solution). The data was analyzed by ANOVA followed by least significant difference test or by Student's 't' test for unequal variance when appropriate. A probability of at least P < 0.05 was considered statistically significant. The plant extract (500 and 700 μg/ml) significantly (P < 0.05) depressed and shifted the calcium concentration-response curves (1 × 10(-3)- 1 × 10(-1) M) to rightward similar to that of nifedipine. Bacopa monniera extract exhibited calcium channel blocking activity in guinea-pig tracheal smooth muscles that may rationalize its relaxant action on guinea-pig trachea and its traditional use in respiratory disorders.

Mitochondrial membrane permeabilization and cell death during myocardial infarction: roles of calcium and reactive oxygen species

PubMed Central

Webster, Keith A

2013-01-01

Excess generation of reactive oxygen species (ROS) and cytosolic calcium accumulation play major roles in the initiation of programmed cell death during acute myocardial infarction. Cell death may include necrosis, apoptosis and autophagy, and combinations thereof. During ischemia, calcium handling between the sarcoplasmic reticulum and myofilament is disrupted and calcium is diverted to the mitochondria causing swelling. Reperfusion, while essential for survival, reactivates energy transduction and contractility and causes the release of ROS and additional ionic imbalance. During acute ischemia–reperfusion, the principal death pathways are programmed necrosis and apoptosis through the intrinsic pathway, initiated by the opening of the mitochondrial permeability transition pore and outer mitochondrial membrane permeabilization, respectively. Despite intense investigation, the mechanisms of action and modes of regulation of mitochondrial membrane permeabilization are incompletely understood. Extrinsic apoptosis, necroptosis and autophagy may also contribute to ischemia–reperfusion injury. In this review, the roles of dysregulated calcium and ROS and the contributions of Bcl-2 proteins, as well as mitochondrial morphology in promoting mitochondrial membrane permeability change and the ensuing cell death during myocardial infarction are discussed. PMID:23176689

Calcium and 1,25-dihydroxyvitamin D3 modulate genes of immune and inflammatory pathways in the human colon: a human crossover trial.

PubMed

Protiva, Petr; Pendyala, Swaroop; Nelson, Celeste; Augenlicht, Leonard H; Lipkin, Martin; Holt, Peter R

2016-05-01

A high dietary calcium intake with adequate vitamin D status has been linked to lower colorectal cancer risk, but the mechanisms of these effects are poorly understood. The objective of this study was to elucidate the effects of a Western-style diet (WD) and supplemental calcium and/or 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on the colorectal mucosa. We conducted 2 crossover trials to define molecular pathways in the human colorectum altered by 1) a 4-wk WD supplemented with and without 2 g calcium carbonate/d and 2) a 4-wk WD supplemented with 1,25(OH)2D3 (0.5 μg/d) with or without 2 g calcium carbonate/d. The primary study endpoint was genome-wide gene expression in biopsy specimens of the rectosigmoid colonic mucosa. Serum and urinary calcium concentrations were also measured. Changes in urinary calcium accurately reflected calcium consumption. The WD induced modest upregulation of genes involved in inflammatory pathways, including interferon signaling, and calcium supplementation reversed these toward baseline. In contrast, supplementation of the WD with 1,25(OH)2D3 induced striking upregulation of genes involved in inflammation, immune response, extracellular matrix, and cell adhesion. Calcium supplementation largely abrogated these changes. Supplementing 1,25(OH)2D3 to a WD markedly upregulated genes in immune response and inflammation pathways, which were largely reversed by calcium supplementation. This study provides clinical trial evidence of global gene expression changes occurring in the human colorectum in response to calcium and 1,25(OH)2D3 intervention. One action of 1,25(OH)2D3 is to upregulate adaptive immunity. Calcium appears to modulate this effect, pointing to its biological interaction in the mucosa. This trial was registered at clinicaltrials.gov as NCT00298545 Trial protocol is available at http://clinicalstudies.rucares.org (protocol numbers PHO475 and PHO554). © 2016 American Society for Nutrition.

Symmetrical choline-derived dications display strong anti-kinetoplastid activity

PubMed Central

Ibrahim, Hasan M. S.; Al-Salabi, Mohammed I.; El Sabbagh, Nasser; Quashie, Neils B.; Alkhaldi, Abdulsalam A. M.; Escale, Roger; Smith, Terry K.; Vial, Henri J.; de Koning, Harry P.

2011-01-01

Objectives To investigate the anti-kinetoplastid activity of choline-derived analogues with previously reported antimalarial efficacy. Methods From an existing choline analogue library, seven antimalarial compounds, representative of the first-, second- and third-generation analogues previously developed, were assessed for activity against Trypanosoma and Leishmania spp. Using a variety of techniques, the effects of choline analogue exposure on the parasites were documented and a preliminary investigation of their mode of action was performed. Results The activities of choline-derived compounds against Trypanosoma brucei and Leishmania mexicana were determined. The compounds displayed promising anti-kinetoplastid activity, particularly against T. brucei, to which 4/7 displayed submicromolar EC50 values for the wild-type strain. Low micromolar concentrations of most compounds cleared trypanosome cultures within 24–48 h. The compounds inhibit a choline transporter in Leishmania, but their entry may not depend only on this carrier; T. b. brucei lacks a choline carrier and the mode of uptake remains unclear. The compounds had no effect on the overall lipid composition of the cells, cell cycle progression or cyclic adenosine monophosphate production or short-term effects on intracellular calcium levels. However, several of the compounds, displayed pronounced effects on the mitochondrial membrane potential; this action was not associated with production of reactive oxygen species but rather with a slow rise of intracellular calcium levels and DNA fragmentation. Conclusions The choline analogues displayed strong activity against kinetoplastid parasites, particularly against T. b. brucei. In contrast to their antimalarial activity, they did not act on trypanosomes by disrupting choline salvage or phospholipid metabolism, instead disrupting mitochondrial function, leading to chromosomal fragmentation. PMID:21078603

Usefulness of cardiotoxicity assessment using calcium transient in human induced pluripotent stem cell-derived cardiomyocytes.

PubMed

Watanabe, Hitoshi; Honda, Yayoi; Deguchi, Jiro; Yamada, Toru; Bando, Kiyoko

2017-01-01

Monitoring dramatic changes in intracellular calcium ion levels during cardiac contraction and relaxation, known as calcium transient, in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) would be an attractive strategy for assessing compounds on cardiac contractility. In addition, as arrhythmogenic compounds are known to induce characteristic waveform changes in hiPSC-CMs, it is expected that calcium transient would allow evaluation of not only compound-induced effects on cardiac contractility, but also compound arrhythmogenic potential. Using a combination of calcium transient in hiPSC-CMs and a fast kinetic fluorescence imaging detection system, we examined in this study changes in calcium transient waveforms induced by a series of 17 compounds that include positive/negative inotropic agents as well as cardiac ion channel activators/inhibitors. We found that all positive inotropic compounds induced an increase in peak frequency and/or peak amplitude. The effects of a negative inotropic compound could clearly be detected in the presence of a β-adrenergic receptor agonist. Furthermore, most arrhythmogenic compounds raised the ratio of peak decay time to peak rise time (D/R ratio) in calcium transient waveforms. Compound concentrations at which these parameters exceeded cutoff values correlated well with systemic exposure levels at which arrhythmias were reported to be evoked. In conclusion, we believe that peak analysis of calcium transient and determination of D/R ratio are reliable methods for assessing compounds' cardiac contractility and arrhythmogenic potential, respectively. Using these approaches would allow selection of compounds with low cardiotoxic potential at the early stage of drug discovery.

Reduction of calcium flux from the extracellular region and endoplasmic reticulum by amorphous nano-silica particles owing to carboxy group addition on their surface.

PubMed

Onodera, Akira; Yayama, Katsutoshi; Morosawa, Hideto; Ishii, Yukina; Tsutsumi, Yasuo; Kawai, Yuichi

2017-03-01

Several studies have reported that amorphous nano-silica particles (nano-SPs) modulate calcium flux, although the mechanism remains incompletely understood. We thus analyzed the relationship between calcium flux and particle surface properties and determined the calcium flux route. Treatment of Balb/c 3T3 fibroblasts with nano-SPs with a diameter of 70 nm (nSP70) increased cytosolic calcium concentration, but that with SPs with a diameter of 300 or 1000 nm did not. Surface modification of nSP70 with a carboxy group also did not modulate calcium flux. Pretreatment with a general calcium entry blocker almost completely suppressed calcium flux by nSP70. Preconditioning by emptying the endoplasmic reticulum (ER) calcium stores slightly suppressed calcium flux by nSP70. These results indicate that nSP70 mainly modulates calcium flux across plasma membrane calcium channels, with subsequent activation of the ER calcium pump, and that the potential of calcium flux by nano-SPs is determined by the particle surface charge.

Lack of voltage-dependent calcium channel opening during the calcium influx induced by progesterone in human sperm. Effect of calcium channel deactivation and inactivation.

PubMed

Guzmán-Grenfell, Alberto Martín; González-Martínez, Marco T

2004-01-01

Progesterone induces calcium influx and acrosomal exocytosis in human sperm. Pharmacologic evidence suggests that voltage-dependent calcium channels (VDCCs) are involved. In this study, membrane potential (Vm) and intracellular calcium concentration ([Ca(2+)](i)) were monitored simultaneously to assess the effect of VDCC gating on the calcium influx triggered by progesterone. Holding the Vm to values that maintained VDCCs in a deactivated (-71 mV) closed state inhibited the calcium influx induced by progesterone by approximately 40%. At this Vm, the acrosomal reaction induced by progesterone, but not by A23187, was inhibited. However, when the Vm was held at -15 mV (which maintains VDCCs in an inactivated closed state), the progesterone-induced calcium influx was stimulated. Furthermore, the progesterone and voltage-dependent calcium influxes were additive. These findings indicate that progesterone does not produce VDCC gating in human sperm.

The effect of radiopacifiers agents on pH, calcium release, radiopacity, and antimicrobial properties of different calcium hydroxide dressings.

PubMed

Ordinola-Zapata, Ronald; Bramante, Clovis Monteiro; García-Godoy, Franklin; Moldauer, Bertram Ivan; Gagliardi Minotti, Paloma; Tercília Grizzo, Larissa; Duarte, Marco Antonio Hungaro

2015-07-01

The aim of this study was to evaluate the antimicrobial activity, pH level, calcium ion release, and radiopacity of calcium hydroxide pastes associated with three radiopacifying agents (iodoform, zinc oxide, and barium sulfate). For the pH and calcium release tests, 45 acrylic teeth were utilized and immersed in ultrapure water. After 24 h, 72 h, and 7 days the solution was analyzed by using a pH meter and an atomic absorption spectrophotometer. Polyethylene tubes filled with the pastes were used to perform the radiopacity test. For the antimicrobial test, 25 dentin specimens were infected intraorally in order to induce the biofilm colonization and treated with the pastes for 7 days. The Live/Dead technique and a confocal microscope were used to obtain the ratio of live cells. Parametric and nonparametric statistical tests were performed to show differences among the groups (P < 0.05). The pH analysis at 7 days showed significant differences (P < 0.05) among the groups. No differences among the pastes were found in the calcium release test on the 7th day (P > 0.05). The calcium hydroxide/iodoform samples had the highest radiopacity and antimicrobial activity against the biofilm-infected dentin in comparison to the other pastes (P < 0.05). Calcium hydroxide mixed with 17% iodoform and 35% propylene glycol into a paste had the highest pH, calcium ion release, radiopacity, and the greatest antimicrobial action versus similar samples mixed with BaSO4 or ZnO. © 2015 Wiley Periodicals, Inc.

Differential effects of tetracaine on two kinetic components of calcium release in frog skeletal muscle fibres.

PubMed Central

Pizarro, G; Csernoch, L; Uribe, I; Ríos, E

1992-01-01

1. Intramembrane charge movements and changes in intracellular calcium concentration were recorded simultaneously in voltage clamped cut skeletal muscle fibres of the frog in the presence and absence of tetracaine. 2. Extracellular application of 20 microM tetracaine reduced the increase in myoplasmic [Ca2+]. The effect on the underlying calcium release flux from the sarcoplasmic reticulum was to suppress the peak of the release while sparing the steady level attained at the end of 100 ms clamp depolarizations. 3. While the peak of the release flux at corresponding voltages was reduced by 62% after the addition of tetracaine, the rate of inactivation was the same when the pulses elicited release fluxes of similar amplitude. 4. Higher concentrations of tetracaine, 0.2 mM, abolished the calcium signal in stretched fibres whereas in slack fibres this concentration left a non-inactivating calcium release flux. 5. Lowering the extracellular pH antagonized the effect of the drug both on charge movements and on calcium signals. The permanently charged analogue tetracaine methobromide lacked effects on excitation-contraction coupling. 6. These results imply that the two kinetic components of calcium release flux have very different tetracaine sensitivities. They are also consistent with an intracellular site of action of the drug at low concentration. Taken together they strongly suggest that the inactivating and non-inactivating components of calcium release correspond to different pathways: one that inactivates, is sensitive to tetracaine and is controlled by calcium, and another that does not inactivate, is much less sensitive to tetracaine and is directly controlled by voltage. PMID:1297844

Dietary Calcium Intake and Calcium Supplementation in Hungarian Patients with Osteoporosis

PubMed Central

Szamosujvári, Pál; Dombai, Péter; Csóré, Katalin; Mikófalvi, Kinga; Steindl, Tímea; Streicher, Ildikó; Tarsoly, Júlia; Zajzon, Gergely; Somogyi, Péter; Szamosújvári, Pál; Lakatos, Péter

2013-01-01

Purpose. Adequate calcium intake is the basis of osteoporosis therapy—when this proves insufficient, even specific antiosteoporotic agents cannot exert their actions properly. Methods. Our representative survey analyzed the dietary intake and supplementation of calcium in 8033 Hungarian female and male (mean age: 68 years) (68.01 (CI95: 67.81–68.21)) patients with osteoporosis. Results. Mean intake from dietary sources was 665 ± 7.9 mg (68.01 (CI95: 67.81–68.21)) daily. A significant positive relationship could be detected between total dietary calcium intake and lumbar spine BMD (P = 0.045), whereas such correlation could not be demonstrated with femoral T-score. Milk consumption positively correlated with femur (P = 0.041), but not with lumbar BMD. The ingestion of one liter of milk daily increased the T-score by 0.133. Average intake from supplementation was 558 ± 6.2 mg (68.01 (CI95: 67.81–68.21)) daily. The cumulative dose of calcium—from both dietary intake and supplementation—was significantly associated with lumbar (r = 0.024, P = 0.049), but not with femur BMD (r = 0.021, P = 0.107). The currently recommended 1000–1500 mg total daily calcium intake was achieved in 34.5% of patients only. It was lower than recommended in 47.8% of the cases and substantially higher in 17.7% of subjects. Conclusions. We conclude that calcium intake in Hungarian osteoporotic patients is much lower than the current recommendation, while routinely applied calcium supplementation will result in inappropriately high calcium intake in numerous patients. PMID:23737777

Extracellular calcium elicits a chemokinetic response from monocytes in vitro and in vivo

NASA Technical Reports Server (NTRS)

Olszak, I. T.; Poznansky, M. C.; Evans, R. H.; Olson, D.; Kos, C.; Pollak, M. R.; Brown, E. M.; Scadden, D. T.; O'Malley, B. W. (Principal Investigator)

2000-01-01

Recruitment of macrophages to sites of cell death is critical for induction of an immunologic response. Calcium concentrations in extracellular fluids vary markedly, and are particularly high at sites of injury or infection. We hypothesized that extracellular calcium participates in modulating the immune response, perhaps acting via the seven-transmembrane calcium-sensing receptor (CaR) on mature monocytes/macrophages. We observed a dose-dependent increase in monocyte chemotaxis in response to extracellular calcium or the selective allosteric CaR activator NPS R-467. In contrast, monocytes derived from mice deficient in CaR lacked the normal chemotactic response to a calcium gradient. Notably, CaR activation of monocytes bearing the receptor synergistically augmented the transmigration response of monocytes to the chemokine MCP-1 in association with increased cell-surface expression of its cognate receptor, CCR2. Conversely, stimulation of monocytes with MCP-1 or SDF-1alpha reciprocally increased CaR expression, suggesting a dual-enhancing interaction of Ca(2+) with chemokines in recruiting inflammatory cells. Subcutaneous administration in mice of Ca(2+), MCP-1, or (more potently) the combination of Ca(2+) and MCP-1, elicited an inflammatory infiltrate consisting of monocytes/macrophages. Thus extracellular calcium functions as an ionic chemokinetic agent capable of modulating the innate immune response in vivo and in vitro by direct and indirect actions on monocytic cells. Calcium deposition may be both consequence and cause of chronic inflammatory changes at sites of injury, infection, and atherosclerosis.

The potential benefits of dietary and/or supplemental calcium and vitamin D.

PubMed

Moyad, Mark A

2003-01-01

Osteoporosis is a significant problem in women and men. In addition, as osteoporosis has garnered more attention there should be more attention than ever placed on the potential benefits of calcium and vitamin D. Clinicians need to inform patients that there are numerous healthy dietary sources of calcium and vitamin D. Calcium and vitamin D supplements seem to act synergistically to reduce fracture risk in men and women; therefore, they need to be taken together to impact fracture risk. In addition, almost every randomized trial of an effective osteoporosis drug therapy has utilized calcium and vitamin D to enhance the efficacy of the drug itself. Several forms of calcium supplements are commercially available today and clinicians need to understand the similarities and differences between them. Calcium and vitamin D in moderation also have a good safety profile and may actually have benefits far beyond osteoporosis therapy. For example, calcium may increase high-density lipoprotein (HDL), prevent colon polyps, reduce blood pressure, reduce kidney stone recurrence, and may promote weight loss. Vitamin D may reduce the risk of some cancers, provide an enhanced response to some chemotherapeutic agents, prevent type I diabetes, and may reduce tooth loss along with calcium. Clinicians need to encourage individuals to receive the recommended daily allowance of these two agents because they seem to have an impact on numerous health conditions besides osteoporosis.

Effect of the Association of Nonsteroidal Anti-inflammatory and Antibiotic Drugs on Antibiofilm Activity and pH of Calcium Hydroxide Pastes.

PubMed

de Freitas, Rafaela Pignatti; Greatti, Vanessa Raquel; Alcalde, Murilo Priori; Cavenago, Bruno Cavalini; Vivan, Rodrigo Ricci; Duarte, Marco Antonio Hungaro; Weckwerth, Ana Carolina Villas Bôas; Weckwerth, Paulo Henrique

2017-01-01

The objective of the present study was to evaluate the in vitro antibiofilm activity and pH of calcium hydroxide associated with different nonsteroidal anti-inflammatory drugs (NSAIDs). The groups analyzed were as follows: group 1, calcium hydroxide paste with propylene glycol; group 2, calcium hydroxide paste with propylene glycol + 5% diclofenac sodium; group 3, calcium hydroxide paste with propylene glycol + 5% ibuprofen; group 4, calcium hydroxide paste with propylene glycol + 5% ciprofloxacin; and group 6, positive control (without medication). For analysis of the pH, the pastes were inserted into tubes and immersed in flasks containing ultrapure water. At the time intervals of 3, 24, 72, and 168 hours, the pH was measured with a calibrated pH meter. For microbial analysis, biofilm was induced in 30 bovine dentin blocks for 21 days. Subsequently, the pastes were placed on the blocks with biofilm for 7 days. Afterward, the pastes were removed by irrigation with sterile water, and the specimens were analyzed with a laser scanning confocal microscope with the 50 μL Live/Dead BacLight Bacterial Viability solution L7012 Kit (Molecular Probes, Inc, Eugene, OR). Data were subjected to statistical analysis at a significance level of 5%. The highest pH values were found for calcium hydroxide associated with ciprofloxacin in all periods analyzed. With the exception of pure calcium hydroxide paste, the other groups showed statistically significant differences (P < .05) in comparison with the positive control. The association of NSAIDs or antibiotic did not interfere with the pH of calcium hydroxide paste and increased the antimicrobial action of calcium hydroxide paste against Enterococcus faecalis biofilm formation. Published by Elsevier Inc.

Linking physiology and biomineralization processes to ecological inferences on the life history of fishes.

PubMed

Loewen, T N; Carriere, B; Reist, J D; Halden, N M; Anderson, W G

2016-12-01

Biomineral chemistry is frequently used to infer life history events and habitat use in fishes; however, significant gaps remain in our understanding of the underlying mechanisms. Here we have taken a multidisciplinary approach to review the current understanding of element incorporation into biomineralized structures in fishes. Biominerals are primarily composed of calcium-based derivatives such as calcium carbonate found in otoliths and calcium phosphates found in scales, fins and bones. By focusing on non-essential life elements (strontium and barium) and essential life elements (calcium, zinc and magnesium), we attempt to connect several fields of study to synergise how physiology may influence biomineralization and subsequent inference of life history. Data provided in this review indicate that the presence of non-essential elements in biominerals of fish is driven primarily by hypo- and hyper-calcemic environmental conditions. The uptake kinetics between environmental calcium and its competing mimics define what is ultimately incorporated in the biomineral structure. Conversely, circannual hormonally driven variations likely influence essential life elements like zinc that are known to associate with enzyme function. Environmental temperature and pH as well as uptake kinetics for strontium and barium isotopes demonstrate the role of mass fractionation in isotope selection for uptake into fish bony structures. In consideration of calcium mobilisation, the action of osteoclast-like cells on calcium phosphates of scales, fins and bones likely plays a role in fractionation along with transport kinetics. Additional investigations into calcium mobilisation are warranted to understand differing views of strontium, and barium isotope fractionation between calcium phosphates and calcium carbonate structures in fishes. Copyright © 2016 Elsevier Inc. All rights reserved.

The neuromuscular activity of Bothriopsis bilineata smaragdina (forest viper) venom and its toxin Bbil-TX (Asp49 phospholipase A2) on isolated mouse nerve-muscle preparations.

PubMed

Floriano, Rafael Stuani; Rocha, Thalita; Carregari, Victor Corasolla; Marangoni, Sergio; da Cruz-Höfling, Maria Alice; Hyslop, Stephen; Rodrigues-Simioni, Léa; Rowan, Edward G

2015-03-01

The presynaptic action of Bothriopsis bilineata smaragdina (forest viper) venom and Bbil-TX, an Asp49 PLA2 from this venom, was examined in detail in mouse phrenic nerve-muscle (PND) preparations in vitro and in a neuroblastoma cell line (SK-N-SH) in order to gain a better insight into the mechanism of action of the venom and associated Asp49 PLA2. In low Ca(2+) solution, venom (3μg/ml) caused a quadriphasic response in PND twitch height whilst at 10μg/ml the venom additionally induced an abrupt and marked initial contracture followed by neuromuscular facilitation, rhythmic oscillations of nerve-evoked twitches, alterations in baseline and progressive blockade. The venom slowed the relaxation phase of muscle twitches. In low Ca(2+), Bbil-TX [210nM (3μg/ml)] caused a progressive increase in PND twitch amplitude but no change in the decay time constant. Venom (10μg/ml) and Bbil-TX (210nM) caused minor changes in the compound action potential (CAP) amplitude recorded from sciatic nerve preparations, with no significant effect on rise time and latency; tetrodotoxin (3.1nM) blocked the CAP at the end of the experiments. In mouse triangularis sterni nerve-muscle (TSn-m) preparations, venom (10μg/ml) and Bbil-TX (210nM) significantly reduced the perineural waveform associated with the outward K(+) current while the amplitude of the inward Na(+) current was not significantly affected. Bbil-TX (210nM) caused a progressive increase in the quantal content of TSn-m preparations maintained in low Ca(2+) solution. Venom (3μg/ml) and toxin (210nM) increased the calcium fluorescence in SK-N-SH neuroblastoma cells loaded with Fluo3 AM and maintained in low or normal Ca(2+) solution. In normal Ca(2+), the increase in fluorescence amplitude was accompanied by irregular and frequent calcium transients. In TSn-m preparations loaded with Fluo4 AM, venom (10μg/ml) caused an immediate increase in intracellular Ca(2+) followed by oscillations in fluorescence and muscle contracture; Bbil-TX did not change the calcium fluorescence in TSn-m preparations. Immunohistochemical analysis of toxin-treated PND preparations revealed labeling of junctional ACh receptors but a loss of the presynaptic proteins synaptophysin and SNAP25. Together, these data confirm the presynaptic action of Bbil-TX and show that it involves modulation of K(+) channel activity and presynaptic protein expression. Copyright © 2015 Elsevier Ltd. All rights reserved.

Synaptic calcium regulation in hair cells of the chicken basilar papilla.

PubMed

Im, Gi Jung; Moskowitz, Howard S; Lehar, Mohammed; Hiel, Hakim; Fuchs, Paul Albert

2014-12-10

Cholinergic inhibition of hair cells occurs by activation of calcium-dependent potassium channels. A near-membrane postsynaptic cistern has been proposed to serve as a store from which calcium is released to supplement influx through the ionotropic ACh receptor. However, the time and voltage dependence of acetylcholine (ACh)-evoked potassium currents reveal a more complex relationship between calcium entry and release from stores. The present work uses voltage steps to regulate calcium influx during the application of ACh to hair cells in the chicken basilar papilla. When calcium influx was terminated at positive membrane potential, the ACh-evoked potassium current decayed exponentially over ∼100 ms. However, at negative membrane potentials, this current exhibited a secondary rise in amplitude that could be eliminated by dihydropyridine block of the voltage-gated calcium channels of the hair cell. Calcium entering through voltage-gated channels may transit through the postsynaptic cistern, since ryanodine and sarcoendoplasmic reticulum calcium-ATPase blockers altered the time course and magnitude of this secondary, voltage-dependent contribution to ACh-evoked potassium current. Serial section electron microscopy showed that efferent and afferent synaptic structures are juxtaposed, supporting the possibility that voltage-gated influx at afferent ribbon synapses influences calcium homeostasis during long-lasting cholinergic inhibition. In contrast, spontaneous postsynaptic currents ("minis") resulting from stochastic efferent release of ACh were made briefer by ryanodine, supporting the hypothesis that the synaptic cistern serves primarily as a calcium barrier and sink during low-level synaptic activity. Hypolemmal cisterns such as that at the efferent synapse of the hair cell can play a dynamic role in segregating near-membrane calcium for short-term and long-term signaling. Copyright © 2014 the authors 0270-6474/14/3416688-10$15.00/0.

Synaptic Calcium Regulation in Hair Cells of the Chicken Basilar Papilla

PubMed Central

Im, Gi Jung; Moskowitz, Howard S.; Lehar, Mohammed; Hiel, Hakim

2014-01-01

Cholinergic inhibition of hair cells occurs by activation of calcium-dependent potassium channels. A near-membrane postsynaptic cistern has been proposed to serve as a store from which calcium is released to supplement influx through the ionotropic ACh receptor. However, the time and voltage dependence of acetylcholine (ACh)-evoked potassium currents reveal a more complex relationship between calcium entry and release from stores. The present work uses voltage steps to regulate calcium influx during the application of ACh to hair cells in the chicken basilar papilla. When calcium influx was terminated at positive membrane potential, the ACh-evoked potassium current decayed exponentially over ∼100 ms. However, at negative membrane potentials, this current exhibited a secondary rise in amplitude that could be eliminated by dihydropyridine block of the voltage-gated calcium channels of the hair cell. Calcium entering through voltage-gated channels may transit through the postsynaptic cistern, since ryanodine and sarcoendoplasmic reticulum calcium-ATPase blockers altered the time course and magnitude of this secondary, voltage-dependent contribution to ACh-evoked potassium current. Serial section electron microscopy showed that efferent and afferent synaptic structures are juxtaposed, supporting the possibility that voltage-gated influx at afferent ribbon synapses influences calcium homeostasis during long-lasting cholinergic inhibition. In contrast, spontaneous postsynaptic currents (“minis”) resulting from stochastic efferent release of ACh were made briefer by ryanodine, supporting the hypothesis that the synaptic cistern serves primarily as a calcium barrier and sink during low-level synaptic activity. Hypolemmal cisterns such as that at the efferent synapse of the hair cell can play a dynamic role in segregating near-membrane calcium for short-term and long-term signaling. PMID:25505321

Anthropogenic calcium depletion: a unique threat to forest ecosystem health?

Treesearch

Paul G. Schaberg; Donald H. DeHayes; Gary J. Hawley

2001-01-01

Numerous anthropogenic factors can deplete calcium (Ca) from forest ecosystems. Because an adequate supply of Ca is needed to support fundamental biological functions, including cell membrane stability and stress response, the potential for Ca deficiency following the individual, cumulative, or potentially synergistic, influences of anthropogenic factors raises...

Potential molecular markers associated with tuber calcium content in wild potato germplasm

USDA-ARS?s Scientific Manuscript database

High tuber calcium is associated with a reduced incidence of disease and physiological disorders in potato. However, genetic variation for tuber calcium content in cultivated potato is low, limiting opportunities to study the genetic basis of this trait. We utilized wild germplasm to develop a popul...

Deficits in memory and hippocampal long-term potentiation in mice with reduced calbindin D28K expression.

PubMed Central

Molinari, S; Battini, R; Ferrari, S; Pozzi, L; Killcross, A S; Robbins, T W; Jouvenceau, A; Billard, J M; Dutar, P; Lamour, Y; Baker, W A; Cox, H; Emson, P C

1996-01-01

The influx of calcium into the postsynaptic neuron is likely to be an important event in memory formation. Among the mechanisms that nerve cells may use to alter the time course or size of a spike of intracellular calcium are cytosolic calcium binding or "buffering" proteins. To consider the role in memory formation of one of these proteins, calbindin D28K, which is abundant in many neurons, including the CA1 pyramidal cells of the hippocampus, transgenic mice deficient in calbindin D28K have been created. These mice show selective impairments in spatial learning paradigms and fail to maintain long-term potentiation. These results suggest a role for calbindin D28K protein in temporally extending a neuronal calcium signal, allowing the activation of calcium-dependent intracellular signaling pathways underlying memory function. Images Fig. 1 PMID:8755597

Heterogeneity of adult masseter muscle satellite cells with cardiomyocyte differentiation potential.

PubMed

Huang, Wei; Liang, Jialiang; Feng, Yuliang; Jia, Zhanfeng; Jiang, Lin; Cai, Wenfeng; Paul, Christian; Gu, Jianguo G; Stambrook, Peter J; Millard, Ronald W; Zhu, Xiao-Lan; Zhu, Ping; Wang, Yigang

2018-05-26

Although resident cardiac stem cells have been reported, regeneration of functional cardiomyocytes (CMs) remains a challenge. The present study identifies an alternative progenitor source for CM regeneration without the need for genetic manipulation or invasive heart biopsy procedures. Unlike limb skeletal muscles, masseter muscles (MM) in the mouse head are developed from Nkx2-5 mesodermal progenitors. Adult masseter muscle satellite cells (MMSCs) display heterogeneity in developmental origin and cell phenotypes. The heterogeneous MMSCs that can be characterized by cell sorting based on stem cell antigen-1 (Sca1) show different lineage potential. While cardiogenic potential is preserved in Sca1 + MMSCs as shown by expression of cardiac progenitor genes (including Nkx2-5), skeletal myogenic capacity is maintained in Sca1 - MMSCs with Pax7 expression. Sca1 + MMSC-derived beating cells express cardiac genes and exhibit CM-like morphology. Electrophysiological properties of MMSC-derived CMs are demonstrated by calcium transients and action potentials. These findings show that MMSCs could serve as a novel cell source for cardiomyocyte replacement. Copyright © 2018. Published by Elsevier Inc.

The protective effect of lipid emulsion in preventing bupivacaine-induced mitochondrial injury and apoptosis of H9C2 cardiomyocytes.

PubMed

Chen, Zhe; Jin, Zhousheng; Xia, Yun; Zhao, Shishi; Xu, Xuzhong; Papadimos, Thomas J; Wang, Quanguang

2017-11-01

Lipid emulsion (LE) has been shown to be effective in the resuscitation of bupivacaine-induced cardiac arrest, but the precise mechanism of this action has not been fully elucidated. Pursuant to this lack of information on the mechanism in which LE protects the myocardium during bupivacaine-induced toxicity, we explored mitochondrial function and cell apoptosis. H9C2 cardiomyocytes were used in study. Cells were randomly divided in different groups and were cultivated 6 h, 12 h, and 24 h. The mitochondria were extracted and mitochondrial ATP content was measured, as was mitochondrial membrane potential, the concentration of calcium ion (Ca2+), and the activity of Ca2+-ATP enzyme (Ca2+-ATPase). Cells from groups Bup1000, LE group, and Bup1000LE were collected to determine cell viability, cell apoptosis, and electron microscopy scanning of mitochondrial ultrastructure (after 24 h). We found that LE can reverse the inhibition of the mitochondrial function induced by bupivacaine, regulate the concentration of calcium ion in mitochondria, resulting in the protection of myocardial cells from toxicity induced by bupivacaine.

[Features of noradrenaline stimulation of rat liver mitochondria respiration by ADP and calcium ions].

PubMed

Stefankiv, Iu S; Babskyĭ, A M; Shostakovska, Y V

1995-01-01

A single administration of a physiological dose of noradrenaline to animals. in contrast to adrenaline, stimulates the respiration of mitochondria not only under oxidation of FAD-dependent Krebbs cycle substrate of the succinase but also HAD-dependent substrate of alpha-ketoglutarate. In the both cases the phosphorylation rate increases, since the action of noradrenaline, separating the respiration and oxidative phosphorylation, was not found. Noradrenaline increases the capacity of mitochondria to more actively absorb calcium ions under oxidation of succinate than under that of alpha-ketoglutarate.

Preparation and evaluation of cilnidipine microemulsion

PubMed Central

Tandel, Hemal; Raval, Krunal; Nayani, Anil; Upadhay, Manish

2012-01-01

Cilnidipine, a calcium channel blocker having neuroprotective action and BCS Class II drug, hence formulating in Microemulsion will increase solubility, absorption and bioavailability. The formulation was prepared using titration method by tocotrienol, tween 20 and transcutol HP as oil, surfactant and co-surfactant and characterized for dilutability, dye solubility, assay (98.39±0.06), pH (6.6±1.5), Viscosity (98±1.0 cps) and Conductivity (0.2±0.09 μS/cm). The formulation was optimized on basis of percentage transmittance (99.269±0.23 at 700 nm), Globule size (13.31±4.3 nm) and zeta potential (–11.4±2.3 mV). Cilnidipine microemulsion was found to be stable for 3 months. PMID:23066184

Calcium influx is required for endocytotic membrane retrieval

PubMed Central

Vogel, Steven S.; Smith, Robert M.; Baibakov, Boris; Ikebuchi, Yoshihide; Lambert, Nevin A.

1999-01-01

Cells use endocytotic membrane retrieval to compensate for excess surface membrane after exocytosis. Retrieval is thought to be calcium-dependent, but the source of this calcium is not known. We found that, in sea urchin eggs, endocytotic membrane retrieval required extracellular calcium. Inhibitors of P-type calcium channels—cadmium, ω-conotoxin MVIIC, ω-agatoxin IVA, and ω-agatoxin TK—blocked membrane retrieval; selective inhibitors of N-type and L-type channels did not. Treatment with calcium ionophores overcame agatoxin inhibition in a calcium-dependent manner. Cadmium blocked membrane retrieval when applied during the first 5 minutes after fertilization, the period when the membrane potential is depolarized. We conclude that calcium influx through ω-agatoxin-sensitive channels plays a key role in signaling for endocytotic membrane retrieval. PMID:10220411

The role of calcium in the prevention of cardiovascular disease--a review of observational studies and randomized clinical trials.

PubMed

Rautiainen, Susanne; Wang, Lu; Manson, JoAnn E; Sesso, Howard D

2013-11-01

Calcium is a mineral that is important for bone health and has also been suggested to play a role in the prevention of cardiovascular disease (CVD). Lately, the potential effects of both inadequate and excessive calcium intake have received growing attention. In this review, we summarize the evidence from experimental, epidemiologic, and clinical studies investigating the role of calcium intake, either from the diet or from supplements, as well as blood concentrations, in relation to the risk of CVD in adults. In vitro and in vivo laboratory studies suggest that calcium may be involved in CVD development through multiple pathways, including blood cholesterol, insulin secretion and sensitivity, vasodilation, inflammatory profile, thrombosis, obesity, and vascular calcification. Several prospective epidemiologic studies have examined how dietary or supplemental calcium intake is associated with CVD incidence or mortality in middle-aged and older adults, and the results are inconsistent. Prospective studies investigating blood concentrations of calcium have also reported mixed results. However, changes in blood calcium concentrations may reflect a disturbed calcium phosphate balance, which is associated with increased risk of CVD. To date there is no randomized clinical trial that has been designed specifically to test the effect of calcium supplementation on the risk of CVD as the primary end point. Existing trials have performed secondary analyses, and most of them have been conducted among postmenopausal women. These trials suggest that calcium supplementation has no effect on CVD development; however, they do not allow a definitive conclusion to be drawn. The average daily intake of calcium is low in many populations; however, the evidence for a potential role of dietary or supplemental calcium in the prevention of CVD remains insufficient and inconclusive. Only large-scale randomized trials designed to investigate the effects of calcium supplementation on CVD events as the primary end point, as well as short-term trials investigating the effect on coronary biomarkers, can provide a definitive answer.

Calcium intake of rural Gambian infants: a quantitative study of the relative contributions of breast milk and complementary foods at 3 and 12 months of age.

PubMed

Jarjou, L M A; Goldberg, G R; Coward, W A; Prentice, A

2012-06-01

There is a paucity of information from developing countries on total calcium intake during infancy, and potential consequences for growth and bone development. Observational longitudinal study of rural Gambian infants (13 males and 17 females) at 3 and 12 months of age. Breast-milk intake and calcium concentration, weighed dietary intake, anthropometry, midshaft radius bone mineral content (BMC) and bone width (BW). At 3 and 12 months (mean ± s.d.) calcium intake from breast milk was 179 ± 53 and 117 ± 38, and from other foods 12 ± 38 and 73 ± 105 mg/day. There was no difference in total calcium intake; 94% and 62% of calcium came from breast milk. At 3 and 12 months, weight s.d.-scores were -0.441 ± 1.07 and -1.967 ± 1.06; length s.d.-scores were -0.511 ± 1.04 and -1.469 ± 1.13. Breast-milk calcium intake positively predicted weight (P = 0.0002, P ≤ 0.0001) and length (P = 0.056, P = 0.001). These relationships were not independent of breast-milk intake, which positively predicted weight (P ≤ 0.002) and length (P = 0.06, P = 0.004). At 3, but not 12 months, weight and length correlated with total calcium intake. There were no relationships between total calcium intake and breast-milk intake with BW or BMC. The combination of low calcium intake from breast milk and complementary foods resulted in a low total calcium intake close to the estimated biological requirement for bone mineral accretion. Relationships between calcium intake and growth were largely accounted for by breast-milk intake, suggesting that low calcium intake per se was not the limiting factor in the poor growth. These findings have potential implications for deriving calcium requirements in developing countries.

Vitamin D and intestinal calcium transport after bariatric surgery.

PubMed

Schafer, Anne L

2017-10-01

Bariatric surgery is a highly effective treatment for obesity, but it may have detrimental effects on the skeleton. Skeletal effects are multifactorial but mediated in part by nutrient malabsorption. While there is increasing interest in non-nutritional mechanisms such as changes in fat-derived and gut-derived hormones, nutritional factors are modifiable and thus represent potential opportunities to prevent and treat skeletal complications. This review begins with a discussion of normal intestinal calcium transport, including recent advances in our understanding of its regulation by vitamin D, and areas of continued uncertainty. Human and animal studies of vitamin D and intestinal calcium transport after bariatric surgery are then summarized. In humans, even with optimized 25-hydroxyvitamin D levels and recommended calcium intake, fractional calcium absorption decreased dramatically after Roux-en-Y gastric bypass (RYGB). In rats, intestinal calcium absorption was lower after RYGB than after sham surgery, despite elevated 1,25-dihyroxyvitamin D levels and intestinal gene expression evidence of vitamin D responsiveness. Such studies have the potential to shed new light on the physiology of vitamin D and intestinal calcium transport. Moreover, understanding the effects of bariatric surgery on these processes may improve the clinical care of bariatric surgery patients. Published by Elsevier Ltd.

Safety assessment of the calcium-binding protein, apoaequorin, expressed by Escherichia coli.

PubMed

Moran, Daniel L; Tetteh, Afua O; Goodman, Richard E; Underwood, Mark Y

2014-07-01

Calcium-binding proteins are ubiquitous modulators of cellular activity and function. Cells possess numerous calcium-binding proteins that regulate calcium concentration in the cytosol by buffering excess free calcium ion. Disturbances in intracellular calcium homeostasis are at the heart of many age-related conditions making these proteins targets for therapeutic intervention. A calcium-binding protein, apoaequorin, has shown potential utility in a broad spectrum of applications for human health and well-being. Large-scale recombinant production of the protein has been successful; enabling further research and development and commercialization efforts. Previous work reported a 90-day subchronic toxicity test that demonstrated this protein has no toxicity by oral exposure in Sprague-Dawley rodents. The current study assesses the allergenic potential of the purified protein using bioinformatic analysis and simulated gastric digestion. The results from the bioinformatics searches with the apoaequorin sequence show the protein is not a known allergen and not likely to cross-react with known allergens. Apoaequorin is easily digested by pepsin, a characteristic commonly exhibited by many non-allergenic dietary proteins. From these data, there is no added concern of safety due to unusual stability of the protein by ingestion. Copyright © 2014 Elsevier Inc. All rights reserved.

Continuous Modeling of Calcium Transport Through Biological Membranes

NASA Astrophysics Data System (ADS)

Jasielec, J. J.; Filipek, R.; Szyszkiewicz, K.; Sokalski, T.; Lewenstam, A.

2016-08-01

In this work an approach to the modeling of the biological membranes where a membrane is treated as a continuous medium is presented. The Nernst-Planck-Poisson model including Poisson equation for electric potential is used to describe transport of ions in the mitochondrial membrane—the interface which joins mitochondrial matrix with cellular cytosis. The transport of calcium ions is considered. Concentration of calcium inside the mitochondrion is not known accurately because different analytical methods give dramatically different results. We explain mathematically these differences assuming the complexing reaction inside mitochondrion and the existence of the calcium set-point (concentration of calcium in cytosis below which calcium stops entering the mitochondrion).

Vascular targets for cannabinoids: animal and human studies

PubMed Central

Stanley, Christopher; O'Sullivan, Saoirse E

2014-01-01

Application of cannabinoids and endocannabinoids to perfused vascular beds or individual isolated arteries results in changes in vascular resistance. In most cases, the result is vasorelaxation, although vasoconstrictor responses are also observed. Cannabinoids also modulate the actions of vasoactive compounds including acetylcholine, methoxamine, angiotensin II and U46619 (thromboxane mimetic). Numerous mechanisms of action have been proposed including receptor activation, potassium channel activation, calcium channel inhibition and the production of vasoactive mediators such as calcitonin gene-related peptide, prostanoids, NO, endothelial-derived hyperpolarizing factor and hydrogen peroxide. The purpose of this review is to examine the evidence for the range of receptors now known to be activated by cannabinoids. Direct activation by cannabinoids of CB1, CBe, TRPV1 (and potentially other TRP channels) and PPARs in the vasculature has been observed. A potential role for CB2, GPR55 and 5-HT1A has also been identified in some studies. Indirectly, activation of prostanoid receptors (TP, IP, EP1 and EP4) and the CGRP receptor is involved in the vascular responses to cannabinoids. The majority of this evidence has been obtained through animal research, but recent work has confirmed some of these targets in human arteries. Vascular responses to cannabinoids are enhanced in hypertension and cirrhosis, but are reduced in obesity and diabetes, both due to changes in the target sites of action. Much further work is required to establish the extent of vascular actions of cannabinoids and the application of this research in physiological and pathophysiological situations. Linked ArticlesThis article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6 PMID:24329566

Calcium intake, serum vitamin D and obesity in children: is there an association?

PubMed Central

da Cunha, Kelly Aparecida; Magalhães, Elma Izze da Silva; Loureiro, Laís Monteiro Rodrigues; Sant'Ana, Luciana Ferreira da Rocha; Ribeiro, Andréia Queiroz; de Novaes, Juliana Farias

2015-01-01

OBJECTIVE: To evaluate the association between calcium intake and serum vitamin D levels and childhood obesity by an integrative review. DATA SOURCE: The research was conducted in the databases PubMed/medLine, Science Direct and SciELO with 2001 to 2014 publications. We used the combined terms in English: ''children'' and ''calcium'' or ''children'' and ''vitamin D'' associated with the descriptors: ''obesity'', ''adiposity'' or ''body fat'' for all bases. Cross-sectional and cohort studies, as well as clinical trials, were included. Review articles or those that that have not addressed the association of interest were excluded. DATA SYNTHESIS: Eight articles were part of this review, five of which were related to calcium and three to vitamin D. Most studies had a longitudinal design. The analyzed studies found an association between calcium intake and obesity, especially when age and sex were considered. Inverse relationship between serum vitamin D and measures of adiposity in children has been observed and this association was influenced by the sex of the patient and by the seasons of the year. CONCLUSIONS: The studies reviewed showed an association between calcium and vitamin D with childhood obesity. Considering the possible protective effect of these micronutrients in relation to childhood obesity, preventive public health actions should be designed, with emphasis on nutritional education. PMID:25890445

A Discrete Electromechanical Model for Human Cardiac Tissue: Effects of Stretch-Activated Currents and Stretch Conditions on Restitution Properties and Spiral Wave Dynamics

PubMed Central

Weise, Louis D.; Panfilov, Alexander V.

2013-01-01

We introduce an electromechanical model for human cardiac tissue which couples a biophysical model of cardiac excitation (Tusscher, Noble, Noble, Panfilov, 2006) and tension development (adjusted Niederer, Hunter, Smith, 2006 model) with a discrete elastic mass-lattice model. The equations for the excitation processes are solved with a finite difference approach, and the equations of the mass-lattice model are solved using Verlet integration. This allows the coupled problem to be solved with high numerical resolution. Passive mechanical properties of the mass-lattice model are described by a generalized Hooke's law for finite deformations (Seth material). Active mechanical contraction is initiated by changes of the intracellular calcium concentration, which is a variable of the electrical model. Mechanical deformation feeds back on the electrophysiology via stretch-activated ion channels whose conductivity is controlled by the local stretch of the medium. We apply the model to study how stretch-activated currents affect the action potential shape, restitution properties, and dynamics of spiral waves, under constant stretch, and dynamic stretch caused by active mechanical contraction. We find that stretch conditions substantially affect these properties via stretch-activated currents. In constantly stretched medium, we observe a substantial decrease in conduction velocity, and an increase of action potential duration; whereas, with dynamic stretch, action potential duration is increased only slightly, and the conduction velocity restitution curve becomes biphasic. Moreover, in constantly stretched medium, we find an increase of the core size and period of a spiral wave, but no change in rotation dynamics; in contrast, in the dynamically stretching medium, we observe spiral drift. Our results may be important to understand how altered stretch conditions affect the heart's functioning. PMID:23527160

A discrete electromechanical model for human cardiac tissue: effects of stretch-activated currents and stretch conditions on restitution properties and spiral wave dynamics.

PubMed

Weise, Louis D; Panfilov, Alexander V

2013-01-01

We introduce an electromechanical model for human cardiac tissue which couples a biophysical model of cardiac excitation (Tusscher, Noble, Noble, Panfilov, 2006) and tension development (adjusted Niederer, Hunter, Smith, 2006 model) with a discrete elastic mass-lattice model. The equations for the excitation processes are solved with a finite difference approach, and the equations of the mass-lattice model are solved using Verlet integration. This allows the coupled problem to be solved with high numerical resolution. Passive mechanical properties of the mass-lattice model are described by a generalized Hooke's law for finite deformations (Seth material). Active mechanical contraction is initiated by changes of the intracellular calcium concentration, which is a variable of the electrical model. Mechanical deformation feeds back on the electrophysiology via stretch-activated ion channels whose conductivity is controlled by the local stretch of the medium. We apply the model to study how stretch-activated currents affect the action potential shape, restitution properties, and dynamics of spiral waves, under constant stretch, and dynamic stretch caused by active mechanical contraction. We find that stretch conditions substantially affect these properties via stretch-activated currents. In constantly stretched medium, we observe a substantial decrease in conduction velocity, and an increase of action potential duration; whereas, with dynamic stretch, action potential duration is increased only slightly, and the conduction velocity restitution curve becomes biphasic. Moreover, in constantly stretched medium, we find an increase of the core size and period of a spiral wave, but no change in rotation dynamics; in contrast, in the dynamically stretching medium, we observe spiral drift. Our results may be important to understand how altered stretch conditions affect the heart's functioning.

Altered transient outward current in human atrial myocytes of patients with reduced left ventricular function.

PubMed

Schreieck, J; Wang, Y; Overbeck, M; Schömig, A; Schmitt, C

2000-02-01

Electrophysiologic remodeling is involved in the self-perpetuation of atrial fibrillation. To define whether differences in atrial electrophysiology already are present in patients with increased susceptibility for atrial fibrillation, we compared patients in sinus rhythm with and without heart failure. Atrial specimens were obtained from patients with reduced left ventricular ejection fraction (LVEF; n = 10) and normal LVEF (n = 16) who were undergoing aortocoronary bypass surgery and from donor hearts (n = 4). Enzymatically isolated atrial myocytes were investigated by whole cell, patch clamp techniques. Total outward current was significantly larger in myocytes of hearts with low LVEF than normal LVEF (19.4 +/- 1.3 vs 15.1 +/- 1.2 pA/pF at pulses to +60 mV, respectively). Analysis of inactivation time courses of different outward current components revealed that the observed current difference is due to the transient calcium-independent outward current I(to1) which is twice as large in the low LVEF group than in the normal LVEF group (9.4 +/- 0.9 vs 4.7 +/- 0.4 pA/pF at pulses to +60 mV, respectively). I(to1) recovery from inactivation was significantly more rapid in myocytes of hearts with low LVEF, and action potential plateau in these cells was significantly shorter. The results of I(to1) and action potential measurements in atrial myocytes of donor hearts were very similar to the results of patients with preserved heart function. I(to1) in human atrial myocytes of patients with reduced LVEF has an increased density and altered kinetics in sinus rhythm. These differences in outward current may explain the reduced plateau phase of action potentials.

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.

The cariostatic mechanisms of fluoride.

PubMed

Rošin-Grget, Kata; Peroš, Kristina; Sutej, Ivana; Bašić, Krešimir

2013-11-01

This article discusses the possible cariostatic mechanisms of the action of fluoride. In the past, fluoride inhibition of caries was ascribed to reduced solubility of enamel due to incorporation of fluoride (F-) into the enamel minerals. The present evidence from clinical and laboratory studies suggests that the caries-preventive mode of action of fluoride is mainly topical. There is convincing evidence that fluoride has a major effect on demineralisation and remineralisation of dental hard tissue. The source of this fluoride could either be fluorapatite (formed due to the incorporation of fluoride into enamel) or calcium fluoride (CaF2)-like precipitates, which are formed on the enamel and in the plaque after application of topical fluoride. Calcium fluoride deposits are protected from rapid dissolution by a phosphate -protein coating of salivary origin. At lower pH, the coating is lost and an increased dissolution rate of calcium fluoride occurs. The CaF2, therefore, act as an efficient source of free fluoride ions during the cariogenic challenge. The current evidence indicates that fluoride has a direct and indirect effect on bacterial cells, although the in vivo implications of this are still not clear. A better understanding of the mechanisms of the action of fluoride is very important for caries prevention and control. The effectiveness of fluoride as a cariostatic agent depends on the availability of free fluoride in plaque during cariogenic challenge, i.e. during acid production. Thus, a constant supply of low levels of fluoride in biofilm/saliva/dental interference is considered the most beneficial in preventing dental caries. Copyright © 2013 by Academy of Sciences and Arts of Bosnia and Herzegovina.

Decursinol and decursin protect primary cultured rat cortical cells from glutamate-induced neurotoxicity.

PubMed

Kang, So Young; Kim, Young Choong

2007-06-01

We previously reported six neuroprotective decursinol derivatives, coumarins from Angelica gigas (Umbelliferae) roots. To elucidate the action patterns of decursinol derivatives, we investigated the neuroprotective effects of decursinol and decursin, which showed highly significant activity and were major constituents of A. gigas, using primary cultures of rat cortical cells in-vitro. At concentrations of 0.1-10.0 microM, both decursinol and decursin exerted a significant neuroprotective activity pretreatment and throughout treatment. In addition, decursin had a neuroprotective impact in the post-treatment paradigm implying that decursin might possess different action mechanisms from that of decursinol in the protection of neurons against glutamate injury. Both decursinol and decursin effectively reduced the glutamate-induced increased intracellular calcium ([Ca(2+)](i)) in cortical cells, suggesting that these two coumarins may exert neuroprotection by reducing calcium influx by overactivation of glutamate receptors. This suggestion was supported by the result that decursinol and decursin protected neurons against kainic acid (KA)-induced neurotoxicity better than against that induced by N-methyl-D-aspartate (NMDA). Moreover, both decursinol and decursin significantly prevented glutamate-induced decreases in glutathione, a cellular antioxidant, and glutathione peroxidase activity. In addition, both compounds efficiently reduced the overproduction of cellular peroxide in glutamate-injured cortical cells. These results suggested that both decursinol and decursin protected primary cultured rat cortical cells against glutamate-induced oxidative stress by both reducing calcium influx and acting on the cellular antioxidative defence system. Moreover, decursin is considered to probably have a different action mechanism from that of decursinol in protecting cortical cells against glutamate injury.