XUV-induced reactions in benzene on sub-10 fs timescale: nonadiabatic relaxation and proton migration.

PubMed

Galbraith, M C E; Smeenk, C T L; Reitsma, G; Marciniak, A; Despré, V; Mikosch, J; Zhavoronkov, N; Vrakking, M J J; Kornilov, O; Lépine, F

2017-08-02

Unraveling ultrafast dynamical processes in highly excited molecular species has an impact on our understanding of chemical processes such as combustion or the chemical composition of molecular clouds in the universe. In this article we use short (<7 fs) XUV pulses to produce excited cationic states of benzene molecules and probe their dynamics using few-cycle VIS/NIR laser pulses. The excited states produced by the XUV pulses lie in an especially complex spectral region where multi-electronic effects play a dominant role. We show that very fast τ ≈ 20 fs nonadiabatic processes dominate the relaxation of these states, in agreement with the timescale expected for most excited cationic states in benzene. In the CH 3 + fragmentation channel of the doubly ionized benzene cation we identify pathways that involve structural rearrangement and proton migration to a specific carbon atom. Further, we observe non-trivial transient behavior in this fragment channel, which can be interpreted either in terms of propagation of the nuclear wavepacket in the initially excited electronic state of the cation or as a two-step electronic relaxation via an intermediate state.

TRPP2 ion channels: Critical regulators of organ morphogenesis in health and disease.

PubMed

Busch, Tilman; Köttgen, Michael; Hofherr, Alexis

2017-09-01

Ion channels control the membrane potential and mediate transport of ions across membranes. Archetypical physiological functions of ion channels include processes such as regulation of neuronal excitability, muscle contraction, or transepithelial ion transport. In that regard, transient receptor potential ion channel polycystin 2 (TRPP2) is remarkable, because it controls complex morphogenetic processes such as the establishment of properly shaped epithelial tubules and left-right-asymmetry of organs. The fascinating question of how an ion channel regulates morphogenesis has since captivated the attention of scientists in different disciplines. Four loosely connected key insights on different levels of biological complexity ranging from protein to whole organism have framed our understanding of TRPP2 physiology: 1) TRPP2 is a non-selective cation channel; 2) TRPP2 is part of a receptor-ion channel complex; 3) TRPP2 localizes to primary cilia; and 4) TRPP2 is required for organ morphogenesis. In this review, we will discuss the current knowledge in these key areas and highlight some of the challenges ahead. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

The isolated voltage sensing domain of the Shaker potassium channel forms a voltage-gated cation channel

PubMed Central

Zhao, Juan; Blunck, Rikard

2016-01-01

Domains in macromolecular complexes are often considered structurally and functionally conserved while energetically coupled to each other. In the modular voltage-gated ion channels the central ion-conducting pore is surrounded by four voltage sensing domains (VSDs). Here, the energetic coupling is mediated by interactions between the S4-S5 linker, covalently linking the domains, and the proximal C-terminus. In order to characterize the intrinsic gating of the voltage sensing domain in the absence of the pore domain, the Shaker Kv channel was truncated after the fourth transmembrane helix S4 (Shaker-iVSD). Shaker-iVSD showed significantly altered gating kinetics and formed a cation-selective ion channel with a strong preference for protons. Ion conduction in Shaker-iVSD developed despite identical primary sequence, indicating an allosteric influence of the pore domain. Shaker-iVSD also displays pronounced 'relaxation'. Closing of the pore correlates with entry into relaxation suggesting that the two processes are energetically related. DOI: http://dx.doi.org/10.7554/eLife.18130.001 PMID:27710769

Anion-Cation Permeability Correlates with Hydrated Counterion Size in Glycine Receptor Channels

PubMed Central

Sugiharto, Silas; Lewis, Trevor M.; Moorhouse, Andrew J.; Schofield, Peter R.; Barry, Peter H.

2008-01-01

The functional role of ligand-gated ion channels depends critically on whether they are predominantly permeable to cations or anions. However, these, and other ion channels, are not perfectly selective, allowing some counterions to also permeate. To address the mechanisms by which such counterion permeation occurs, we measured the anion-cation permeabilities of different alkali cations, Li+ Na+, and Cs+, relative to either Cl− or \\documentclass[10pt]{article} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{pmc} \\usepackage[Euler]{upgreek} \\pagestyle{empty} \\oddsidemargin -1.0in \\begin{document} \\begin{equation*}{\\mathrm{NO}}_{3}^{-}\\end{equation*}\\end{document} anions in both a wild-type glycine receptor channel (GlyR) and a mutant GlyR with a wider pore diameter. We hypothesized and showed that counterion permeation in anionic channels correlated inversely with an equivalent or effective hydrated size of the cation relative to the channel pore radius, with larger counterion permeabilities being observed in the wider pore channel. We also showed that the anion component of conductance was independent of the nature of the cation. We suggest that anions and counterion cations can permeate through the pore as neutral ion pairs, to allow the cations to overcome the large energy barriers resulting from the positively charged selectivity filter in small GlyR channels, with the permeability of such ion pairs being dependent on the effective hydrated diameter of the ion pair relative to the pore diameter. PMID:18708455

Ca2+ and Mn2+ Influx Through Receptor-Mediated Activation of Nonspecific Cation Channels in Mast Cells

NASA Astrophysics Data System (ADS)

Fasolato, Cristina; Hoth, Markus; Matthews, Gary; Penner, Reinhold

1993-04-01

Whole-cell patch-clamp recordings of membrane currents and Fura-2 measurements of free intracellular calcium concentration ([Ca2+]_i) were used to study calcium influx through receptor-activated cation channels in rat peritoneal mast cells. Cation channels were activated by the secretagogue compound 48/80, whereas a possible concomitant Ca2+ entry through pathways activated by depletion of calcium stores was blocked by dialyzing cells with heparin. Heparin effectively suppressed the transient Ca2+ release induced by 48/80 and abrogated inositol 1,4,5-trisphosphate-induced calcium influx without affecting activation of 50-pS cation channels. There was a clear correlation between changes in [Ca2+]_i and the activity of 50-pS channels. The changes in [Ca2+]_i increased with elevation of extracellular Ca2+. At the same time, inward currents through 50-pS channels were diminished as more Ca2+ permeated. This effect was due to a decrease in slope conductance and a reduction in the open probability of the cation channels. In physiological solutions, 3.6% of the total current was carried by Ca2+. The cation channels were not only permeable to Ca2+ but also to Mn2+, as evidenced by the quench of Fura-2 fluorescence. Mn2+ current through 50-pS channels could not be resolved at the single-channel level. Our results suggest that 50-pS cation channels partially contribute to sustained increases of [Ca2+]_i in mast cells following receptor activation.

Expression and distribution of voltage-gated ion channels in ferret sinoatrial node.

PubMed

Brahmajothi, Mulugu V; Morales, Michael J; Campbell, Donald L; Steenbergen, Charles; Strauss, Harold C

2010-10-01

Spontaneous diastolic depolarization in the sinoatrial (SA) node enables it to serve as pacemaker of the heart. The variable cell morphology within the SA node predicts that ion channel expression would be heterogeneous and different from that in the atrium. To evaluate ion channel heterogeneity within the SA node, we used fluorescent in situ hybridization to examine ion channel expression in the ferret SA node region and atrial appendage. SA nodal cells were distinguished from surrounding cardiac myocytes by expression of the slow (SA node) and cardiac (surrounding tissue) forms of troponin I. Nerve cells in the sections were identified by detection of GAP-43 and cytoskeletal middle neurofilament. Transcript expression was characterized for the 4 hyperpolarization-activated cation channels, 6 voltage-gated Na(+) channels, 3 voltage-gated Ca(2+) channels, 24 voltage-gated K(+) channel α-subunits, and 3 ancillary subunits. To ensure that transcript expression was representative of protein expression, immunofluorescence was used to verify localization patterns of voltage-dependent K(+) channels. Colocalizations were performed to observe any preferential patterns. Some overlapping and nonoverlapping binding patterns were observed. Measurement of different cation channel transcripts showed heterogeneous expression with many different patterns of expression, attesting to the complexity of electrical activity in the SA node. This study provides insight into the possible role ion channel heterogeneity plays in SA node pacemaker activity.

Signature and Pathophysiology of Non-canonical Pores in Voltage-Dependent Cation Channels.

PubMed

Held, Katharina; Voets, Thomas; Vriens, Joris

2016-01-01

Opening and closing of voltage-gated cation channels allows the regulated flow of cations such as Na(+), K(+), and Ca(2+) across cell membranes, which steers essential physiological processes including shaping of action potentials and triggering Ca(2+)-dependent processes. Classical textbooks describe the voltage-gated cation channels as membrane proteins with a single, central aqueous pore. In recent years, however, evidence has accumulated for the existence of additional ion permeation pathways in this group of cation channels, distinct from the central pore, which here we collectively name non-canonical pores. Whereas the first non-canonical pores were unveiled only after making specific point mutations in the voltage-sensor region of voltage-gated Na(+) and K(+) channels, recent evidence indicates that they may also be functional in non-mutated channels. Moreover, several channelopathies have been linked to mutations that cause the appearance of a non-canonical ion permeation pathway as a new pathological mechanism. This review provides an integrated overview of the biophysical properties of non-canonical pores described in voltage-dependent cation channels (KV, NaV, Cav, Hv1, and TRPM3) and of the (patho)physiological impact of opening of such pores.

Zero kinetic energy photoelectron spectroscopy of tryptamine and the dissociation pathway of the singly hydrated cation cluster.

PubMed

Gu, Quanli; Knee, J L

2012-09-14

The relative ionization energies of tryptamine conformations are determined by zero kinetic energy photoelectron spectroscopy and photoionization efficiency measurements. The relative cationic conformational stabilities are compared to the published results for the neutral molecule. In the cation, the interaction strength changes significantly between amino group and either the phenyl or the pyrrole moiety of the indole chromophore where most of the positive charge is located, leading to different conformational structures and relative conformer energies in the cation. In particular, the measured adiabatic ionization potential of isomer B is 60,928 ± 5 cm(-1), at least 400 cm(-1) higher than any of the 6 other tryptamine isomers which all have ionization potentials within 200 cm(-1) of each other. In addition to the monomer, measurements were made on the A conformer of the tryptamine(+)-H(2)O complex including the ionization threshold and cation dissociation energy measured using a threshold photoionization fragmentation method. The water cluster exhibits an unexpectedly high ionization potential of 60,307 ± 100 cm(-1), close to the conformer A monomer of 60 320 ± 100 cm(-1). It also exhibits surprisingly low dissociation energy of 1750 ± 150 cm(-1) compared to other H-bonding involved cation-H(2)O complexes which are typically several thousands of wavenumbers higher. Quantum chemical calculations indicate that upon ionization the structure of the parent molecule in the water complex remains mostly unchanged due to the rigid intermolecular double hydrogen bonded water molecule bridging the monomer backbone and its side chain thus leading to the high ionization potential in the water cluster. The surprisingly low dissociation energy measured in the cationic water complex is attributed to the formation of a much more stable structural isomer H(+) in the exit channel.

Activation by divalent cations of a Ca2+-activated K+ channel from skeletal muscle membrane.

PubMed

Oberhauser, A; Alvarez, O; Latorre, R

1988-07-01

Several divalent cations were studied as agonists of a Ca2+-activated K+ channel obtained from rat muscle membranes and incorporated into planar lipid bilayers. The effect of these agonists on single-channel currents was tested in the absence and in the presence of Ca2+. Among the divalent cations that activate the channel, Ca2+ is the most effective, followed by Cd2+, Sr2+, Mn2+, Fe2+, and Co2+. Mg2+, Ni2+, Ba2+, Cu2+, Zn2+, Hg2+, and Sn2+ are ineffective. The voltage dependence of channel activation is the same for all the divalent cations. The time-averaged probability of the open state is a sigmoidal function of the divalent cation concentration. The sigmoidal curves are described by a dissociation constant K and a Hill coefficient N. The values of these parameters, measured at 80 mV are: N = 2.1, K = 4 X 10(-7) mMN for Ca2+; N = 3.0, K = 0.02 mMN for Cd2+; N = 1.45, K = 0.63 mMN for Sr2+; N = 1.7, K = 0.94 mMN for Mn2+; N = 1.1, K = 3.0 mMN for Fe2+; and N = 1.1 K = 4.35 mMN for Co2+. In the presence of Ca2+, the divalent cations Cd2+, Co2+, Mn2+, Ni2+, and Mg2+ are able to increase the apparent affinity of the channel for Ca2+ and they increase the Hill coefficient in a concentration-dependent fashion. These divalent cations are only effective when added to the cytoplasmic side of the channel. We suggest that these divalent cations can bind to the channel, unmasking new Ca2+ sites.

The fragmentation of ethanol cation under an electric field: An ab initio/RRKM study

NASA Astrophysics Data System (ADS)

Lu, Hsiu-Feng; Li, F.-Y.; Lin, Chun-Chin; Nagaya, K.; Chao, Ito; Lin, S. H.

2007-08-01

We present a theoretical study of ethanol cation under an electric field due to the existence of laser field in order to understand the influence of electric field on the mass spectrum of ethanol. The electric field was applied to the four major reaction channels of an ethanol cation, such as the conversion between C 2H 5OH + and c-C 2H 5OH +, CH 3-elimination and two α-H-eliminations, respectively. The correlation between product distribution and field strength is quite complex due to the different responses of the reactants and transition states toward the external electric field. This makes the product distribution change as field strength varies.

Roderick MacKinnon - Patents

Science.gov Websites

CHANNEL PROTEINS, MUTANT PROKARYOTIC CATION CHANNEL PROTEINS, AND USES THEREOF - MacKinnon, Roderick cation channel proteins, and potentially have uses in treating conditions related to the function of SENSOR DOMAINS OF VOLTAGE-DEPENDENT ION CHANNEL PROTEINS AND USES THEREOF - MacKinnon, Roderick; et. al

Gating current studies reveal both intra- and extracellular cation modulation of K+ channel deactivation

PubMed Central

Wang, Zhuren; Zhang, Xue; Fedida, David

1999-01-01

The presence of permeant ions can modulate the rate of gating charge return in wild-type human heart K+ (hKv1.5) channels. Here we employ gating current measurements in a non-conducting mutant, W472F, of the hKv1.5 channel to investigate how different cations can modulate charge return and whether the actions can be specifically localized at the internal as well as the external mouth of the channel pore. Intracellular cations were effective at accelerating charge return in the sequence Cs+ > Rb+ > K+ > Na+ > NMG+. Extracellular cations accelerated charge return with the selectivity sequence Cs+ > Rb+ > Na+ = NMG+. Intracellular and extracellular cation actions were of relatively low affinity. The Kd for preventing slowing of the time constant of the off-gating current decay (τoff) was 20.2 mM for intracellular Cs+ (Csi+) and 358 mM for extracellular Cs+ (Cso+). Both intracellular and extracellular cations can regulate the rate of charge return during deactivation of hKv1.5, but intracellular cations are more effective. We suggest that ion crystal radius is an important determinant of this action, with larger ions preventing slowing more effectively. Important parallels exist with cation-dependent modulation of slow inactivation of ionic currents in this channel. However, further experiments are required to understand the exact relationship between acceleration of charge return and the slowing of inactivation of ionic currents by cations. PMID:10050001

Regulation of Transient Receptor Potential channels by the phospholipase C pathway

PubMed Central

Rohacs, Tibor

2013-01-01

Transient Receptor Potential (TRP) channels were discovered while analyzing visual mutants in drosophila. The protein encoded by the transient receptor potential (trp) gene is a Ca2+ permeable cation channel activated downstream of the phospholipase C (PLC) pathway. While searching for homologues in other organisms, a surprisingly large number of mammalian TRP channels were cloned. The regulation of TRP channels is quite diverse, but many of them are either activated downstream of the PLC pathway, or modulated by it. This review will summarize the current knowledge on regulation of TRP channels by the PLC pathway, with special focus on TRPC-s, which can be considered as effectors of the PLC pathway, and the heat and capsaicin sensitive TRPV1, which is modulated by the PLC pathway in a complex manner. PMID:23916247

Size Dependent Cation Channel in Nanoporous Prussian Blue Lattice

NASA Astrophysics Data System (ADS)

Moritomo, Yutaka; Igarashi, Kazuhiro; Kim, Jungeun; Tanaka, Hiroshi

2009-08-01

Cation and/or molecule transfer within nanoporous materials can be utilized in, for example, electrochromic devices, hydrogen storage, molecular sensors, and molecular filters. Here, we investigated the mobilities of cations, Na+, K+, and Rb+, in vacancy-controlled Prussian blue film, NaxCo[Fe(CN)6]1-vzH2O (v is vacancy concentration) with a jungle gym structure. We found that only the smallest Na+ ions pass through the cubic planes of the lattice, while the larger cations, i.e., K+ and Rb+, take a detour channel along the [Fe(CN)6] vacancy. The size-dependent cation channel is well understood in terms of the potential curve derived by an ab initio total energy calculation.

Spectroscopic evidence of 3-hydroxyflavone sorption within MFI type zeolites: ESIPT and metal complexation.

PubMed

Moissette, A; Hureau, M; Kokaislova, A; Le Person, A; Cornard, J P; De Waele, I; Batonneau-Gener, I

2015-10-21

Due to its chemical and photochemical properties and potential applications in numerous domains as a molecular probe, 3-hydroxyflavone (3HF) is a molecule of high interest. In particular, the processes of intramolecular proton transfer in the excited state and metallic complexation are known to be dependent on the chemical environment. In this context, the particular properties of zeolites make these microporous materials an environment adapted to study the reactivity of isolated molecules adsorbed in their porous void space. Thus, this report investigates the incorporation without any solvent of 3HF into the internal volume of various channel-type MFI zeolites. Using complementary techniques (diffuse reflectance UV-vis absorption, Raman scattering, FTIR, fluorescence emission and molecular modelling), very different spectral behaviours are observed in totally dealuminated silicalite-1 and in Al rich MZSM-5 (M = H(+), Na(+), Zn(2+)). In silicalite-1, the non-polar and non-protic internal micro-environment does not induce any valuable interaction between 3HF and the channel walls. Therefore, the molecule shows easy tautomer formation upon excitation. Within HZSM-5, 3HF is adsorbed in close proximity of the acid proton of the zeolite which inhibits the intramolecular proton transfer and then, only the normal form is observed at the excited state. For NaZSM-5, the spectral data show an intermediary behaviour due to the aprotic but polar environment, in agreement with 3HF sorption in close proximity of the Na(+) extra framework cation. After mixing 3HF and ZnZSM-5, the spectral features clearly indicate metallic complexation of the guest molecule. The zeolite dependent reactivity reported here demonstrates the adsorption of the guest within the internal volume because the charge balancing cations which clearly control the reaction are principally located in the zeolite channels. The 3HF incorporation into the internal volume is proved by the decrease of the microporous volume observed by nitrogen adsorption-desorption isotherm measurements. The experimental data are confirmed by Monte Carlo molecular modelling which also predicts 3HF sorption in the zeolite channels in the proximity of charge compensating cations. Consequently, as the molecule dimensions are assumed to be slightly larger than the channel size, the flexibility of the molecule and the lattice deformation have to be considered to allow 3HF penetration into the zeolite void space.

Vinpocetine regulates cation channel permeability of inner retinal neurons in the ischaemic retina.

PubMed

Nivison-Smith, Lisa; Acosta, Monica L; Misra, Stuti; O'Brien, Brendan J; Kalloniatis, Michael

2014-01-01

Vinpocetine is a natural drug which exerts neuroprotective effects in ischaemia of the brain through actions on cation channels, glutamate receptors and other pathways. This study investigated the effect of vinpocetine on cation channel permeability of inner retinal neurons after acute retinal metabolic insult. We focused on amacrine and ganglion cells immunoreactive for calretinin or parvalbumin due to their previously documented susceptibility to ischaemia. Using the probe, 1-amino-4-guanidobutane (AGB), we observed increased cation channel permeability across amacrine and ganglion cells under ischaemia and hypoglycaemia but not anoxia. Calretinin and parvalbumin immunoreactivity was also reduced during ischaemia and hypoglyacemia but not anoxia. Vinpocetine decreased AGB entry into ischaemic and hypoglycaemic ganglion cells indicating that the drug can modulate unregulated cation entry. In addition, vinpocetine prevented the loss of calretinin and parvalbumin immunoreactivity following ischaemia suggesting it may indirectly regulate intracellular calcium. Vinpocetine also reduced AGB permeability in selected amacrine and ganglion cell populations following N-methyl-D-aspartate (NMDA) but not kainate activation suggesting that vinpocetine's regulation of cation channel permeability may partly involve NMDA sensitive glutamate receptors. Copyright © 2014 Elsevier Ltd. All rights reserved.

Molecular beads on a charged molecular string

NASA Astrophysics Data System (ADS)

Zhang, Haizhen; Ferrell, Tyler A.; Asplund, Matthew C.; Dearden, David V.

2007-09-01

Complexes of [alpha],[omega]-alkyldiammonium cations [H3N+(CH2)nNH3+, n = 2-10] with the cyclic, hollow ligand cucurbit[6]uril (CB6) were characterized in the gas phase using Fourier transform ion cyclotron resonance mass spectrometry with energy resolved sustained off-resonance irradiation (SORI) collision induced dissociation, in combination with HF/6-31G* and B3LYP/6-31G* computational methods. All the complexes have the diammonium cation threaded through the cavity of CB6. The modeled supramolecular geometries, the SORI energies required for dissociation of the complexes and for appearance of singly protonated diamine product ions, and the branching ratios for the various dissociation channels all suggest that the optimum [alpha],[omega]-alkyldiammonium chain length for binding CB6 in the gas phase occurs for n = 4. This contrasts with observed complex stability constants in aqueous formic acid, which are maximum for n = 6, reflecting solvent stabilization of the ammonium groups that is not possible in the gas phase. At the B3LYP/6-31G* level of theory, the binding energy for the n = 4 complex with respect to dissociation to singly protonated butanediamine and protonated CB6 is 204 kJ mol-1. The n = 6 complex exhibits especially low dissociation thresholds, perhaps reflecting compression of the diammonium cation upon complexation with CB6, forming a loaded "molecular spring."

Axial stretch-dependent cation entry in dystrophic cardiomyopathy: Involvement of several TRPs channels

PubMed Central

Krzesiak, A.; Lipskaia, L.; Adnot, S.; Hajjar, R.J.; Cognard, C.

2016-01-01

In Duchenne muscular dystrophy (DMD), deficiency of the cytoskeletal protein dystrophin leads to well-described defects in skeletal muscle but also to dilated cardiomyopathy (DCM). In cardiac cells, the subsarcolemmal localization of dystrophin is thought to protect the membrane from mechanical stress. The dystrophin deficiency leads to membrane instability and a high stress-induced Ca2+ influx due to dysregulation of sarcolemmal channels such as stretch-activated channels (SACs). In this work divalent cation entry has been explored in isolated ventricular Wild Type (WT) and mdx cardiomyocytes in two different conditions: at rest and during the application of an axial stretch. At rest, our results suggest that activation of TRPV2 channels participates to a constitutive basal cation entry in mdx cardiomyocytes.Using microcarbon fibres technique, an axial stretchwas applied to mimic effects of physiological conditions of ventricular filling and study on cation influx bythe Mn2+-quenching techniquedemonstrated a high stretch-dependentcationic influx in dystrophic cells, partially due to SACs. Involvement of TRPs channels in this excessive Ca2+ influx has been investigated using specific modulators and demonstratedboth sarcolemmal localization and an abnormal activity of TRPV2 channels. In conclusion, TRPV2 channels are demonstrated here to play a key role in cation influx and dysregulation in dystrophin deficient cardiomyocytes, enhanced in stretching conditions. PMID:26803937

Gap-junctional channel and hemichannel activity of two recently identified connexin 26 mutants associated with deafness.

PubMed

Dalamon, Viviana; Fiori, Mariana C; Figueroa, Vania A; Oliva, Carolina A; Del Rio, Rodrigo; Gonzalez, Wendy; Canan, Jonathan; Elgoyhen, Ana B; Altenberg, Guillermo A; Retamal, Mauricio A

2016-05-01

Gap-junction channels (GJCs) are formed by head-to-head association of two hemichannels (HCs, connexin hexamers). HCs and GJCs are permeable to ions and hydrophilic molecules of up to Mr ~1 kDa. Hearing impairment of genetic origin is common, and mutations of connexin 26 (Cx26) are its major cause. We recently identified two novel Cx26 mutations in hearing-impaired subjects, L10P and G109V. L10P forms functional GJCs with slightly altered voltage dependence and HCs with decrease ATP/cationic dye selectivity. G109V does not form functional GJCs, but forms functional HCs with enhanced extracellular Ca(2+) sensitivity and subtle alterations in voltage dependence and ATP/cationic dye selectivity. Deafness associated with G109V could result from decreased GJCs activity, whereas deafness associated to L10P may have a more complex mechanism that involves changes in HC permeability.

A cool way to live long.

PubMed

Conti, Bruno; Hansen, Malene

2013-02-14

In this issue, Xiao et al. challenge the notion that cold temperatures promote longevity solely through thermodynamic effects. They show that low temperatures activate a cold-sensitive cation channel, TRPA-1, which triggers a complex signaling pathway in both neurons and nonneuronal cells to extend the lifespan of Caenorhabditis elegans. Copyright © 2013 Elsevier Inc. All rights reserved.

Block by Extracellular Divalent Cations of Drosophila Big Brain Channels Expressed in Xenopus Oocytes

PubMed Central

Yanochko, Gina M.; Yool, Andrea J.

2004-01-01

Drosophila Big Brain (BIB) is a transmembrane protein encoded by the neurogenic gene big brain (bib), which is important for early development of the fly nervous system. BIB expressed in Xenopus oocytes is a monovalent cation channel modulated by tyrosine kinase signaling. Results here demonstrate that the BIB conductance shows voltage- and dose-dependent block by extracellular divalent cations Ca2+ and Ba2+ but not by Mg2+ in wild-type channels. Site-directed mutagenesis of negatively charged glutamate (Glu274) and aspartate (Asp253) residues had no effect on divalent cation block. However, mutation of a conserved glutamate at position 71 (Glu71) in the first transmembrane domain (M1) altered channel properties. Mutation of Glu71 to Asp introduced a new sensitivity to block by extracellular Mg2+; substitutions with asparagine or glutamine decreased whole-cell conductance; and substitution with lysine compromised plasma membrane expression. Block by divalent cations is important in other ion channels for voltage-dependent function, enhanced signal resolution, and feedback regulation. Our data show that the wild-type BIB conductance is attenuated by external Ca2+, suggesting that endogenous divalent cation block might be relevant for enhancing signal resolution or voltage dependence for the native signaling process in neuronal cell fate determination. PMID:14990474

Non-selective cation channels in plasma and vacuolar membranes and their contribution to K+ transport.

PubMed

Pottosin, Igor; Dobrovinskaya, Oxana

2014-05-15

Both in vacuolar and plasma membranes, in addition to truly K(+)-selective channels there is a variety of non-selective channels, which conduct K(+) and other ions with little preference. Many non-selective channels in the plasma membrane are active at depolarized potentials, thus, contributing to K(+) efflux rather than to K(+) uptake. They may play important roles in xylem loading or contribute to a K(+) leak, induced by salt or oxidative stress. Here, three currents, expressed in root cells, are considered: voltage-insensitive cation current, non-selective outwardly rectifying current, and low-selective conductance, activated by reactive oxygen species. The latter two do not only poorly discriminate between different cations (like K(+)vs Na(+)), but also conduct anions. Such solute channels may mediate massive electroneutral transport of salts and might be involved in osmotic adjustment or volume decrease, associated with cell death. In the tonoplast two major currents are mediated by SV (slow) and FV (fast) vacuolar channels, respectively, which are virtually impermeable for anions. SV channels conduct mono- and divalent cations indiscriminately and are activated by high cytosolic Ca(2+) and depolarized voltages. FV channels are inhibited by micromolar cytosolic Ca(2+), Mg(2+), and polyamines, and conduct a variety of monovalent cations, including K(+). Strikingly, both SV and FV channels sense the K(+) content of vacuoles, which modulates their voltage dependence, and in case of SV, also alleviates channel's inhibition by luminal Ca(2+). Therefore, SV and FV channels may operate as K(+)-sensing valves, controlling K(+) distribution between the vacuole and the cytosol. Copyright © 2014 Elsevier GmbH. All rights reserved.

TRP Channels

NASA Astrophysics Data System (ADS)

Voets, Thomas; Owsianik, Grzegorz; Nilius, Bernd

The TRP superfamily represents a highly diverse group of cation-permeable ion channels related to the product of the Drosophila trp (transient receptor potential) gene. The cloning and characterization of members of this cation channel family has experienced a remarkable growth during the last decade, uncovering a wealth of information concerning the role of TRP channels in a variety of cell types, tissues, and species. Initially, TRP channels were mainly considered as phospholipase C (PLC)-dependent and/or store-operated Ca2+-permeable cation channels. More recent research has highlighted the sensitivity of TRP channels to a broad array of chemical and physical stimuli, allowing them to function as dedicated biological sensors involved in processes ranging from vision to taste, tactile sensation, and hearing. Moreover, the tailored selectivity of certain TRP channels enables them to play key roles in the cellular uptake and/or transepithelial transport of Ca2+, Mg2+, and trace metal ions. In this chapter we give a brief overview of the TRP channel superfamily followed by a survey of current knowledge concerning their structure and activation mechanisms.

Isolated pores dissected from human two-pore channel 2 are functional

PubMed Central

Penny, Christopher J.; Rahman, Taufiq; Sula, Altin; Miles, Andrew J.; Wallace, B. A.; Patel, Sandip

2016-01-01

Multi-domain voltage-gated ion channels appear to have evolved through sequential rounds of intragenic duplication from a primordial one-domain precursor. Whereas modularity within one-domain symmetrical channels is established, little is known about the roles of individual regions within more complex asymmetrical channels where the domains have undergone substantial divergence. Here we isolated and characterised both of the divergent pore regions from human TPC2, a two-domain channel that holds a key intermediate position in the evolution of voltage-gated ion channels. In HeLa cells, each pore localised to the ER and caused Ca2+ depletion, whereas an ER-targeted pore mutated at a residue that inactivates full-length TPC2 did not. Additionally, one of the pores expressed at high levels in E. coli. When purified, it formed a stable, folded tetramer. Liposomes reconstituted with the pore supported Ca2+ and Na+ uptake that was inhibited by known blockers of full-length channels. Computational modelling of the pore corroborated cationic permeability and drug interaction. Therefore, despite divergence, both pores are constitutively active in the absence of their partners and retain several properties of the wild-type pore. Such symmetrical ‘pore-only’ proteins derived from divergent channel domains may therefore provide tractable tools for probing the functional architecture of complex ion channels. PMID:27941820

Isolated pores dissected from human two-pore channel 2 are functional.

PubMed

Penny, Christopher J; Rahman, Taufiq; Sula, Altin; Miles, Andrew J; Wallace, B A; Patel, Sandip

2016-12-12

Multi-domain voltage-gated ion channels appear to have evolved through sequential rounds of intragenic duplication from a primordial one-domain precursor. Whereas modularity within one-domain symmetrical channels is established, little is known about the roles of individual regions within more complex asymmetrical channels where the domains have undergone substantial divergence. Here we isolated and characterised both of the divergent pore regions from human TPC2, a two-domain channel that holds a key intermediate position in the evolution of voltage-gated ion channels. In HeLa cells, each pore localised to the ER and caused Ca 2+ depletion, whereas an ER-targeted pore mutated at a residue that inactivates full-length TPC2 did not. Additionally, one of the pores expressed at high levels in E. coli. When purified, it formed a stable, folded tetramer. Liposomes reconstituted with the pore supported Ca 2+ and Na + uptake that was inhibited by known blockers of full-length channels. Computational modelling of the pore corroborated cationic permeability and drug interaction. Therefore, despite divergence, both pores are constitutively active in the absence of their partners and retain several properties of the wild-type pore. Such symmetrical 'pore-only' proteins derived from divergent channel domains may therefore provide tractable tools for probing the functional architecture of complex ion channels.

Inversion of membrane surface charge by trivalent cations probed with a cation-selective channel

PubMed Central

Gurnev, Philip A.; Bezrukov, Sergey M.

2014-01-01

We demonstrate that the cation-selective channel formed by gramicidin A can be used as a reliable sensor for studying the multivalent ion accumulation at the surfaces of charged lipid membranes and the “charge inversion” phenomenon. In asymmetrically charged membranes with the individual leaflets formed from pure negative and positive lipids bathed by 0.1 M CsCl solutions the channel exhibits current rectification which is comparable to that of a typical n/p semiconductor diode. We show that even at these highly asymmetrical conditions the channel conductance can be satisfactorily described by the electrodiffusion equation in the constant field approximation but, due to predictable limitations, only when the applied voltages do not exceed 50 mV. Analysis of the changes in the voltage-dependent channel conductance upon addition of trivalent cations allows us to gauge their interactions with the membrane surface. The inversion of the sign of the effective surface charge takes place at the concentrations which correlate with the cation size. Specifically, these concentrations are close to 0.05 mM for lanthanum, 0.25 mM for hexaamminecobalt, and 4 mM for spermidine. PMID:23088396

Inversion of membrane surface charge by trivalent cations probed with a cation-selective channel.

PubMed

Gurnev, Philip A; Bezrukov, Sergey M

2012-11-13

We demonstrate that the cation-selective channel formed by gramicidin A can be used as a reliable sensor for studying the multivalent ion accumulation at the surfaces of charged lipid membranes and the "charge inversion" phenomenon. In asymmetrically charged membranes with the individual leaflets formed from pure negative and positive lipids bathed by 0.1 M CsCl solutions the channel exhibits current rectification, which is comparable to that of a typical n/p semiconductor diode. We show that even at these highly asymmetrical conditions the channel conductance can be satisfactorily described by the electrodiffusion equation in the constant field approximation but, due to predictable limitations, only when the applied voltages do not exceed 50 mV. Analysis of the changes in the voltage-dependent channel conductance upon addition of trivalent cations allows us to gauge their interactions with the membrane surface. The inversion of the sign of the effective surface charge takes place at the concentrations, which correlate with the cation size. Specifically, these concentrations are close to 0.05 mM for lanthanum, 0.25 mM for hexaamminecobalt, and 4 mM for spermidine.

Monovalent Cation Permeation through the Connexin40 Gap Junction Channel

PubMed Central

Beblo, Dolores A.; Veenstra, Richard D.

1997-01-01

The unitary conductances and permeability sequences of the rat connexin40 (rCx40) gap junction channels to seven monovalent cations and anions were studied in rCx40-transfected neuroblastoma 2A (N2A) cell pairs using the dual whole cell recording technique. Chloride salt cation substitutions (115 mM principal salt) resulted in the following junctional maximal single channel current-voltage relationship slope conductances (γj in pS): CsCl (153), RbCl (148), KCl (142), NaCl (115), LiCl (86), TMACl (71), TEACl (63). Reversible block of the rCx40 channel was observed with TBA. Potassium anion salt γj are: Kglutamate (160), Kacetate (160), Kaspartate (158), KNO3 (157), KF (148), KCl (142), and KBr (132). Ion selectivity was verified by measuring reversal potentials for current in rCx40 gap junction channels with asymmetric salt solutions in the two electrodes and using the Goldman-Hodgkin-Katz equation to calculate relative permeabilities. The permeabilities relative to Li+ are: Cs+ (1.38), Rb+ (1.32), K+ (1.31), Na+ (1.16), TMA+ (0.53), TEA+ (0.45), TBA+ (0.03), Cl− (0.19), glutamate− (0.04), and NO3− (0.14), assuming that the monovalent anions permeate the channel by forming ion pairs with permeant monovalent cations within the pore thereby causing proportionate decreases in the channel conductance. This hypothesis can account for why the predicted increasing conductances with increasing ion mobilities in an essentially aqueous channel were not observed for anions in the rCx40 channel. The rCx40 effective channel radius is estimated to be 6.6 Å from a theoretical fit of the relationship of relative permeability and cation radius. PMID:9101408

Intracellular spermine blocks TRPC4 channel via electrostatic interaction with C-terminal negative amino acids.

PubMed

Kim, Jinsung; Moon, Sang Hui; Shin, Young-Cheul; Jeon, Ju-Hong; Park, Kyu Joo; Lee, Kyu Pil; So, Insuk

2016-04-01

Transient receptor potential canonical (TRPC) 4 channels are calcium-permeable, nonselective cation channels and are widely expressed in mammalian tissue, especially in the GI tract and brain. TRPC4 channels are known to be involved in neurogenic contraction of ileal smooth muscle cells via generating cationic current after muscarinic stimulation (muscarinic cationic current (mIcat)). Polyamines exist in numerous tissues and are believed to be involved in cell proliferation, differentiation, scar formation, wound healing, and carcinogenesis. Besides, physiological polyamines are essential to maintain inward rectification of cardiac potassium channels (Kir2.1). At membrane potentials more positive than equilibrium potential, intracellular polyamines plug the cytosolic surface of the Kir2.1 so that potassium ions cannot pass through the pore. Recently, it was reported that polyamines inhibit not only cardiac potassium channels but also nonselective cation channels that mediate the generation of mIcat. Here, we report that TRPC4, a definite mIcat mediator, is inhibited by intracellular spermine with great extent. The inhibition was specific to TRPC4 and TRPC5 channels but was not effective to TRPC1/4, TRPC1/5, and TRPC3 channels. For this inhibition to occur, we found that glutamates at 728th and 729th position of TRPC4 channels are essential whereby we conclude that spermine blocks the TRPC4 channel with electrostatic interaction between negative amino acids at the C-terminus of the channel.

Mechanosensory calcium-selective cation channels in epidermal cells

NASA Technical Reports Server (NTRS)

Ding, J. P.; Pickard, B. G.

1993-01-01

This paper explores the properties and likely functions of an epidermal Ca(2+)-selective cation channel complex activated by tension. As many as eight or nine linked or linkable equivalent conductance units or co-channels can open together. Open time for co-channel quadruplets and quintuplets tends to be relatively long with millimolar Mg2+ (but not millimolar Ca2+) at the cytosolic face of excised plasma membrane. Sensitivity to tension is regulated by transmembrane voltage and temperature. Under some circumstances channel activity is sychronized in rhythmic pulses. Certain lanthanides and a cytoskeleton-disturbing herbicide that inhibit gravitropic reception act on the channel system at low concentrations. Specifically, ethyl-N-phenylcarbamate promotes tension-dependent activity at micromolar levels. With moderate suction, Gd3+ provided at about 0.5 micromole at the extracellular face of the membrane promotes for several seconds but may then become inhibitory. Provision at 1-2 micromoles promotes and subsequently inhibits more vigorously (often abruptly and totally), and at high levels inhibits immediately. La3+, a poor gravitropic inhibitor, acts similarly but much more gradually and only at much higher concentrations. These properties, particularly these susceptibilities to modulation, indicate that in vivo the mechanosensitive channel must be mechanosensory and mechanoregulatory. It could serve to transduce the shear forces generated in the integrated wall-membrane-cytoskeleton system during turgor changes and cell expansion as well as transducing the stresses induced by gravity, touch and flexure. In so far as such transduction is modulated by voltage and temperature, the channels would also be sensors for these modalities as long as the wall-membrane-cytoskeleton system experiences mechanical stress.

The anti-proliferative effect of cation channel blockers in T lymphocytes depends on the strength of mitogenic stimulation.

PubMed

Petho, Zoltan; Balajthy, Andras; Bartok, Adam; Bene, Krisztian; Somodi, Sandor; Szilagyi, Orsolya; Rajnavolgyi, Eva; Panyi, Gyorgy; Varga, Zoltan

2016-03-01

Ion channels are crucially important for the activation and proliferation of T lymphocytes, and thus, for the function of the immune system. Previous studies on the effects of channel blockers on T cell proliferation reported variable effectiveness due to differing experimental systems. Therefore our aim was to investigate how the strength of the mitogenic stimulation influences the efficiency of cation channel blockers in inhibiting activation, cytokine secretion and proliferation of T cells under standardized conditions. Human peripheral blood lymphocytes were activated via monoclonal antibodies targeting the TCR-CD3 complex and the co-stimulator CD28. We applied the blockers of Kv1.3 (Anuroctoxin), KCa3.1 (TRAM-34) and CRAC (2-Apb) channels of T cells either alone or in combination with rapamycin, the inhibitor of the mammalian target of rapamycin (mTOR). Five days after the stimulation ELISA and flow cytometric measurements were performed to determine IL-10 and IFN-γ secretion, cellular viability and proliferation. Our results showed that ion channel blockers and rapamycin inhibit IL-10 and IFN-γ secretion and cell division in a dose-dependent manner. Simultaneous application of the blockers for each channel along with rapamycin was the most effective, indicating synergy among the various activation pathways. Upon increasing the extent of mitogenic stimulation the anti-proliferative effect of the ion channel blockers diminished. This phenomenon may be important in understanding the fine-tuning of T cell activation. Copyright © 2016 European Federation of Immunological Societies. Published by Elsevier B.V. All rights reserved.

TRIC-B channels display labile gating: evidence from the TRIC-A knockout mouse model.

PubMed

Venturi, Elisa; Matyjaszkiewicz, Antoni; Pitt, Samantha J; Tsaneva-Atanasova, Krasimira; Nishi, Miyuki; Yamazaki, Daiju; Takeshima, Hiroshi; Sitsapesan, Rebecca

2013-08-01

Sarcoplasmic/endoplasmic reticulum (SR) and nuclear membranes contain two related cation channels named TRIC-A and TRIC-B. In many tissues, both subtypes are co-expressed, making it impossible to distinguish the distinct single-channel properties of each subtype. We therefore incorporated skeletal muscle SR vesicles derived from Tric-a-knockout mice into bilayers in order to characterise the biophysical properties of native TRIC-B without possible misclassification of the channels as TRIC-A, and without potential distortion of functional properties by detergent purification protocols. The native TRIC-B channels were ideally selective for cations. In symmetrical 210 mM K(+), the maximum (full) open channel level (199 pS) was equivalent to that observed when wild-type SR vesicles were incorporated into bilayers. Analysis of TRIC-B gating revealed complex and variable behaviour. Four main sub-conductance levels were observed at approximately 80 % (161 pS), 60 % (123 pS), 46 % (93 pS), and 30 % (60 pS) of the full open state. Seventy-five percent of the channels were voltage sensitive with Po being markedly reduced at negative holding potentials. The frequent, rapid transitions between TRIC-B sub-conductance states prevented development of reliable gating models using conventional single-channel analysis. Instead, we used mean-variance plots to highlight key features of TRIC-B gating in a more accurate and visually useful manner. Our study provides the first biophysical characterisation of native TRIC-B channels and indicates that this channel would be suited to provide counter current in response to Ca(2+) release from the SR. Further experiments are required to distinguish the distinct functional properties of TRIC-A and TRIC-B and understand their individual but complementary physiological roles.

The TRPC6 channel activator hyperforin induces the release of zinc and calcium from mitochondria.

PubMed

Tu, Peng; Gibon, Julien; Bouron, Alexandre

2010-01-01

Hyperforin, an extract of the medicinal plant hypericum perforatum (also named St John's wort), possesses antidepressant properties. Recent data showed that it elevates the intracellular concentration of Ca(2+) by activating diacylglycerol-sensitive C-class of transient receptor potential (TRPC6) channels without activating the other isoforms (TRPC1, TRPC3, TRPC4, TRPC5, and TRPC7). This study was undertaken to further characterize the cellular neuronal responses induced by hyperforin. Experiments conducted on cortical neurons in primary culture and loaded with fluorescent probes for Ca(2+) (Fluo-4) and Zn(2+) (FluoZin-3) showed that it not only controls the activity of plasma membrane channels but it also mobilizes these two cations from internal pools. Experiments conducted on isolated brain mitochondria indicated that hyperforin, like the inhibitor of oxidative phosphorylation, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), collapses the mitochondrial membrane potential. Furthermore, it promotes the release of Ca(2+) and Zn(2+) from these organelles via a ruthenium red-sensitive transporter. In fact, hyperforin exerts complex actions on CNS neurons. This antidepressant not only triggers the entry of cations via plasma membrane TRPC6 channels but it displays protonophore-like properties. As hyperforin is now use to probe the functions of native TRPC6 channels, our data indicate that caution is required when interpreting results obtained with this antidepressant.

Regulation of Sodium Transport in the Inner Ear

PubMed Central

Kim, Sung Huhn; Marcus, Daniel C.

2011-01-01

Na+ concentrations in endolymph must be controlled to maintain hair cell function since the transduction channels of hair cells are cation-permeable, but not K+-selective. Flooding or fluctuations of the hair cell cytosol with Na+ would be expected to lead to cellular dysfunction, hearing loss and vertigo. This review briefly describes cellular mechanisms known to be responsible for Na+homeostasis in each compartment of the inner ear, including the cochlea, saccule, semicircular canals and endolymphatic sac. The influx of Na+into endolymph of each of the organs is likely via passive diffusion, but these pathways have not yet been identified or characterized. Na+ absorption is controlled by gate -keeper channels in the apical (endolymphatic) membrane of the transporting cells. Highly Na+-selective epithelial sodium channels (ENaC) control absorption by Reissner’s membrane, saccular extramacular epithelium, semicircular canal duct epithelium and endolymphatic sac. ENaC activity is controlled by a number of signal pathways, but most notably by genomic regulation of channel numbers in the membrane via glucocorticoid signaling. Nonselective cation channels in the apical membrane of outer sulcus epithelial cells and vestibular transitional cells mediate Na+ and parasensory K+ absorption. The K+-mediated transduction current in hair cells is also accompanied by a Na+ flux since the transduction channels are nonselective cation channels. Cation absorption by all of these cells is regulated by extracellular ATP via apical nonselective cation channels (P2X receptors). The heterogeneous population of epithelial cells in the endolymphatic sac is thought to have multiple absorptive pathways for Na+ with regulatory pathways that include glucocorticoids and purinergic agonists. PMID:21620939

Tuning the ion selectivity of tetrameric cation channels by changing the number of ion binding sites

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

Derebe, Mehabaw G.; Sauer, David B.; Zeng, Weizhong

2015-11-30

Selective ion conduction across ion channel pores is central to cellular physiology. To understand the underlying principles of ion selectivity in tetrameric cation channels, we engineered a set of cation channel pores based on the nonselective NaK channel and determined their structures to high resolution. These structures showcase an ensemble of selectivity filters with a various number of contiguous ion binding sites ranging from 2 to 4, with each individual site maintaining a geometry and ligand environment virtually identical to that of equivalent sites in K{sup +} channel selectivity filters. Combined with single channel electrophysiology, we show that only themore » channel with four ion binding sites is K{sup +} selective, whereas those with two or three are nonselective and permeate Na{sup +} and K{sup +} equally well. These observations strongly suggest that the number of contiguous ion binding sites in a single file is the key determinant of the channel's selectivity properties and the presence of four sites in K{sup +} channels is essential for highly selective and efficient permeation of K{sup +} ions.« less

Roles of somatic A-type K(+) channels in the synaptic plasticity of hippocampal neurons.

PubMed

Yang, Yoon-Sil; Kim, Kyeong-Deok; Eun, Su-Yong; Jung, Sung-Cherl

2014-06-01

In the mammalian brain, information encoding and storage have been explained by revealing the cellular and molecular mechanisms of synaptic plasticity at various levels in the central nervous system, including the hippocampus and the cerebral cortices. The modulatory mechanisms of synaptic excitability that are correlated with neuronal tasks are fundamental factors for synaptic plasticity, and they are dependent on intracellular Ca(2+)-mediated signaling. In the present review, the A-type K(+) (IA) channel, one of the voltage-dependent cation channels, is considered as a key player in the modulation of Ca(2+) influx through synaptic NMDA receptors and their correlated signaling pathways. The cellular functions of IA channels indicate that they possibly play as integral parts of synaptic and somatic complexes, completing the initiation and stabilization of memory.

Ablation of the Kell/Xk complex alters erythrocyte divalent cation homeostasis.

PubMed

Rivera, Alicia; Kam, Siok Yuen; Ho, Mengfatt; Romero, Jose R; Lee, Soohee

2013-02-01

XK is a putative transporter of unknown function that is ubiquitously expressed and linked through disulfide bonds to Kell protein, an endothelin-3 (ET-3)-converting enzyme. We generated three knockout (KO) mice that lacked either Xk, Kell or both proteins and characterized erythrocyte cation levels, transport and hematological parameters. Absence of Xk or Kell was accompanied by changes in erythrocyte K(+), Mg(2+), Na(+) and Ca(2+) transport that were associated with changes in mean cellular volume and corpuscular hemoglobin concentration mean. Baseline Ca(2+)-ATPase activity was undetected in erythrocytes from all three mouse types but was restored upon pre-incubation with ET-3. Consistent with these alterations in Ca(2+) handling, we observed increased Gardos channel activity in Kel and Xk KO mice. In addition Kel deletion was associated with increased Mg(2+) permeability while Xk deletion blocked Na/Mg exchanger activity. Our results provide evidence that cellular divalent cation regulation is functionally coupled to the Kell/XK system in erythrocytes and loss of this complex may contribute to acanthocytosis formation in McLeod syndrome. Copyright © 2012 Elsevier Inc. All rights reserved.

Ablation of the Kell/Xk complex alters erythrocyte divalent cation homeostasis

PubMed Central

Rivera, Alicia; Kam, Siok Yuen; Ho, Mengfatt; Romero, Jose R.; Lee, Soohee

2012-01-01

XK is a putative transporter of unknown function that is ubiquitously expressed and linked through disulfide bonds to Kell protein, an endothelin-3 (ET-3)-converting enzyme. We generated three knockout (KO) mice that lacked either Xk, Kell or both proteins and characterized erythrocyte cation levels, transport and hematological parameters. Absence of Xk or Kell was accompanied by changes in erythrocyte K+, Mg2+, Na+ and Ca2+ transport that were associated with changes in mean cellular volume and corpuscular hemoglobin concentration mean. Baseline Ca2+-ATPase activity was undetected in erythrocytes from all three mouse types but was restored upon pre-incubation with ET-3. Consistent with these alterations in Ca2+ handling, we observed increased Gardos channel activity in Kel and Xk KO mice. In addition Kel deletion was associated with increased Mg2+ permeability while Xk deletion blocked Na/Mg exchanger activity. Our results provide evidence that cellular divalent cation regulation is functionally coupled to the Kell/XK system in erythrocytes and loss of this complex may contribute to acanthocytosis formation in McLeod syndrome. PMID:23122227

Crystal structure of channelrhodopsin, a light-gated cation channel – all cations lead through the monomer –

PubMed Central

Kato, Hideaki E.; Nureki, Osamu

2013-01-01

Channelrhodopsin (ChR) is a light-gated cation channel derived from green algae. Since the inward flow of cations triggers the neuron firing, neurons expressing ChRs can be optically controlled even within freely moving mammals. Although ChR has been broadly applied to neuro-science research, little is known about its molecular mechanisms. We determined the crystal structure of chimeric ChR at 2.3 Å resolution and revealed its molecular architecture. The integration of structural, electrophysio-logical, and computational analyses provided insight into the molecular basis for the channel function of ChR, and paved the way for the principled design of ChR variants with novel properties. PMID:27493541

The pore properties of human nociceptor channel TRPA1 evaluated in single channel recordings

PubMed Central

Bobkov, Y.V.; Corey, E.A.; Ache, B.W.

2011-01-01

TRPA channels detect stimuli of different sensory modalities, including a broad spectrum of chemosensory stimuli, noxious stimuli associated with tissue damage and inflammation, mechanical stimuli, and thermal stimuli. Despite a growing understanding of potential modulators, agonists, and antagonists for these channels, the exact mechanisms of channel regulation and activation remain mostly unknown or controversial and widely debated. Relatively little is also known about the basic biophysical parameters of both native and heterologously expressed TRPA channels. Here we use conventional single channel inside-out and outside-out patch recording from the human TRPA1 channel transiently expressed in human embryonic kidney 293T cells to characterize the selectivity of the channel for inorganic mono-/divalent and organic monovalent cations in the presence of Allylisothiocyanate (AITC). We show the relative permeability of the hTRPA1 channel to inorganic cations to be: Ca2+(5.1)>Ba2+(3.5)>Mg2+(2.8)>NH4+(1.5)>Li+(1.2)>Na+(1.0)≥K+(0.98)≥Rb+(0.98)>Cs+(0.95); and to organic cations: Na+(1.0)≥Dimethylamine(0.99)>Trimethylamine(0.7)>Tetramethylammonium(0.4)>N-methyl-d-glucamine(0.1). Activation of the hTRPA1 channels by AITC appears to recruit the channels to a conformational state with an increased permeability to large organic cations. The pore of the channels in this state can be characterized as dilated by approximately 1–2.5A. These findings provide important insight into the basic fundamental properties and function of TRPA1 channels in general and human TRPA1 channel in particular. PMID:21195050

Monovalent and divalent cation permeability and block of neuronal nicotinic receptor channels in rat parasympathetic ganglia

PubMed Central

1995-01-01

Acetylcholine-evoked currents mediated by activation of nicotinic receptors in rat parasympathetic neurons were examined using whole-cell voltage clamp. The relative permeability of the neuronal nicotinic acetylcholine (nACh) receptor channel to monovalent and divalent inorganic and organic cations was determined from reversal potential measurements. The channel exhibited weak selectivity among the alkali metals with a selectivity sequence of Cs+ > K+ > Rb+ > Na+ > Li+, and permeability ratios relative to Na+ (Px/PNa) ranging from 1.27 to 0.75. The selectivity of the alkaline earths was also weak, with the sequence of Mg2+ > Sr2+ > Ba2+ > Ca2+, and relative permeabilities of 1.10 to 0.65. The relative Ca2+ permeability (PCa/PNa) of the neuronal nACh receptor channel is approximately fivefold higher than that of the motor endplate channel (Adams, D. J., T. M. Dwyer, and B. Hille. 1980. Journal of General Physiology. 75:493-510). The transition metal cation, Mn2+ was permeant (Px/PNa = 0.67), whereas Ni2+, Zn2+, and Cd2+ blocked ACh-evoked currents with half-maximal inhibition (IC50) occurring at approximately 500 microM, 5 microM and 1 mM, respectively. In contrast to the muscle endplate AChR channel, that at least 56 organic cations which are permeable to (Dwyer et al., 1980), the majority of organic cations tested were found to completely inhibit ACh- evoked currents in rat parasympathetic neurons. Concentration-response curves for guanidinium, ethylammonium, diethanolammonium and arginine inhibition of ACh-evoked currents yielded IC50's of approximately 2.5- 6.0 mM. The organic cations, hydrazinium, methylammonium, ethanolammonium and Tris, were measureably permeant, and permeability ratios varied inversely with the molecular size of the cation. Modeling suggests that the pore has a minimum diameter of 7.6 A. Thus, there are substantial differences in ion permeation and block between the nACh receptor channels of mammalian parasympathetic neurons and amphibian skeletal muscle which represent functional consequences of differences in the primary structure of the subunits of the ACh receptor channel. PMID:7561740

Pharmacology of the human red cell voltage-dependent cation channel; Part I. Activation by clotrimazole and analogues.

PubMed

Barksmann, Trine L; Kristensen, Berit I; Christophersen, Palle; Bennekou, Poul

2004-01-01

The activation and pharmacological modulation of the nonselective voltage-dependent cation (NSVDC) channel from human erythrocytes were studied. Basic channel activation was achieved by suspending red cells in a low Cl(-) Ringer (2 mM), where a positive membrane potential (V(m) = E(Cl)) immediately developed. Voltage- and time-dependent activation of the NSVDC channel occurred, reaching a cation conductance (g+) of 1.5-2.0 microS cm(-2). In the presence of the classical Gárdos channel blocker clotrimazole (0-50 microM), activation occurred faster, and g+ saturated dose-dependently (EC50 = 14 microM) at a value of about 4 microS cm(-2). The clotrimazole analogues TRAM-34, econazole, and miconazole also stimulated the channel, whereas the chemically more distant Gárdos channel inhibitors nitrendipine and cetiedil had no effects. Although the potency for modulation of the NSVDC channel is much lower than the IC50 value for Gárdos channel inhibition, clotrimazole (and its analogues) constitutes the first chemical class of positive modulators of the NSVDC channel. This may be an important pharmacological "fingerprint" in the identification of the cloned equivalent of the erythrocyte channel.

Chloride channel blockers activate an endogenous cationic current in oocytes of Bufo arenarum.

PubMed

Cavarra, M S; del Mónaco, S M; Kotsias, B A

2004-07-01

A two-electrode, voltage-clamp technique was used to measure the effect of the Cl(-) channel blockers, 9-anthracene carboxylic acid and niflumic acid, upon the ionic currents of oocytes of the South American toad Bufo arenarum. The main results were: (1) both blockers produced a reversible increase of the outward currents on a dose-dependent manner; (2) the activated outward current was voltage dependent; (3) the 9-anthracene carboxylic acid-sensitive current was blocked with barium; and (4) the effect of 9-anthracene carboxylic acid was more pronounced in a zero-K(+) solution than in standard (2 mmol l(-1)) or high (20 mmol l(-1)) K(+) solutions, indicating that a K(+) conductance is activated. The effect of the Cl(-) channel blockers could be due to a direct interaction with endogenous cationic channels. Another possible explanation is that Cl(-) that enter the cell during depolarizing steps in control solution inhibit this cationic conductance; thus, the blockade of Cl(-) channels by 9-anthracene carboxylic acid and niflumic acid would remove this inhibition, allowing the cationic current to flow freely.

Comparison of the effects of divalent cations on the noradrenaline-evoked cation current in rabbit portal vein smooth muscle cells

PubMed Central

Aromolaran, A S; Large, W A

1999-01-01

The facilitatory effects of external Ca2+, Sr2+ and Ba2+ (Cao2+, Sro2+ and Bao2+) on the noradrenaline-evoked non-selective cation current (Icat) were compared in rabbit portal vein smooth muscle cells using patch pipette techniques. All divalent cations tested potentiated the amplitude of Icat and the potency sequence was Cao2+ > Sro2+ > Bao2+. Cao2+ and Sro2+ increased the amplitude of Icat by about eight times whereas Bao2+ produced only a threefold facilitation. The current-voltage relationship of Icat was not changed by Cao2+, Sro2+ or Bao2+. From noise analysis the single channel conductance (γ) was approximately 10 pS in divalent cation-free solution but was about 20 pS with Cao2+, Sro2+ and Bao2+. From noise and voltage-jump experiments it was apparent that at least three kinetically resolvable channel states are associated with Icat in divalent cation-free solution. Cao2+ and Sro2+ produced marked changes in the characteristics of the power spectrum and relaxations of Icat in response to voltage steps, consistent with a shift in the equilibrium between the channel states, whereas Bao2+ produced minimal effects. The data show that Cao2+, Sro2+ and Bao2+ increase the amplitude of Icat, which results in part from an increase in the single channel conductance. In addition the results suggest that Cao2+ and Sro2+ alter the kinetic behaviour of the single channels whereas Bao2+ has little effect on the equilibrium between the channel states. PMID:10545143

Effects of collision energy and vibrational excitation of CH3 + cations on its reactivity with hydrocarbons: But-2-yne CH3CCCH3 as reagent partner

NASA Astrophysics Data System (ADS)

Cernuto, Andrea; Lopes, Allan; Romanzin, Claire; Cunha de Miranda, Barbara; Ascenzi, Daniela; Tosi, Paolo; Tonachini, Glauco; Maranzana, Andrea; Polášek, Miroslav; Žabka, Jan; Alcaraz, Christian

2017-10-01

The methyl carbocation is ubiquitous in gaseous environments, such as planetary ionospheres, cometary comae, and the interstellar medium, as well as combustion systems and plasma setups for technological applications. Here we report on a joint experimental and theoretical study on the mechanism of the reaction CH3 + + CH3CCCH3 (but-2-yne, also known as dimethylacetylene), by combining guided ion beam mass spectrometry experiments with ab initio calculations of the potential energy hypersurface. Such a reaction is relevant in understanding the chemical evolution of Saturn's largest satellite, Titan. Two complementary setups have been used: in one case, methyl cations are generated via electron ionization, while in the other case, direct vacuum ultraviolet photoionization with synchrotron radiation of methyl radicals is used to study internal energy effects on the reactivity. Absolute reactive cross sections have been measured as a function of collision energy, and product branching ratios have been derived. The two most abundant products result from electron and hydride transfer, occurring via direct and barrierless mechanisms, while other channels are initiated by the electrophilic addition of the methyl cation to the triple bond of but-2-yne. Among the minor channels, special relevance is placed on the formation of C5H7 +, stemming from H2 loss from the addition complex. This is the only observed condensation product with the formation of new C—C bonds, and it might represent a viable pathway for the synthesis of complex organic species in astronomical environments and laboratory plasmas.

The effect of alkaline cations on the Intercalation of Carbon Dioxide in Sepiolite Minerals: a Molecular Dynamics Investigation.

NASA Astrophysics Data System (ADS)

Tavanti, Francesco; Muniz-Miranda, Francesco; Pedone, Alfonso

2018-03-01

The ability of the sepiolite mineral to intercalate CO2 molecules inside its channels in the presence of different alkaline cations (K+, Na+ and Li+) has been studied by classical Molecular Dynamics simulations. Starting from an alkaline-free sepiolite crystalline model we built three models with stoichiometry Mg320Si440Al40O1200(OH)160X+40•480H2O. On these models, we gradually replaced the water molecules present in the channels with carbon dioxide and determined the energy of this exchange reaction as well as the structural organization and dynamics of carbon dioxide in the channels. The adsorption energy shows that the Li-containing sepiolite mineral retains more carbon dioxide with respect to those with sodium and potassium cations in the channels. Moreover, the ordered patterns of CO2 molecules observed in the alkaline-free sepiolite mineral are in part destabilized by the presence of cations decreasing the adsorption capacity of this clay mineral.

Whole-cell and single channel monovalent cation currents through the novel rabbit epithelial Ca2+ channel ECaC

PubMed Central

Nilius, Bernd; Vennekens, Rudi; Prenen, Jean; Hoenderop, Joost G J; Bindels, René J M; Droogmans, Guy

2000-01-01

This study describes properties of monovalent cation currents through ECaC, a recently cloned epithelial Ca2+-permeable channel from rabbit. The kinetics of currents through ECaC was strongly modulated by divalent cations. Currents were inhibited in the presence of extracellular Ca2+. They showed an initial voltage-dependent decay in the presence of 1 mm Mg2+ at hyperpolarizing steps in Ca2+-free solutions, which represents a voltage-dependent Mg2+ block through binding of Mg2+ to a site localized in the electrical field of the membrane (δ = 0.31) and a voltage-dependent binding constant (at 0 mV 3.1 mm Ca2+, obtained from a Woodhull type analysis). Currents were only stable in the absence of divalent cations and showed under these conditions a small time- and voltage-dependent component of activation. Single channel currents in cell-attached and inside-out patches had a conductance of 77.5 ± 4.9 pS (n = 11) and reversed at +14.8 ± 1.6 mV (n = 9) in the absence of divalent cations. The permeation sequence for monovalent cations through ECaC was Na+ > Li+ > K+ > Cs+ > NMDG+ which is identical to the Eisenmann sequence X for a strong field-strength binding site. It is concluded that the permeation profile of ECaC for monovalent cations suggests a strong field-strength binding site that may be involved in Ca2+ permeation and Mg2+ block. PMID:10970426

Single-Walled Carbon Nanotubes: Mimics of Biological Ion Channels.

PubMed

Amiri, Hasti; Shepard, Kenneth L; Nuckolls, Colin; Hernández Sánchez, Raúl

2017-02-08

Here we report on the ion conductance through individual, small diameter single-walled carbon nanotubes. We find that they are mimics of ion channels found in natural systems. We explore the factors governing the ion selectivity and permeation through single-walled carbon nanotubes by considering an electrostatic mechanism built around a simplified version of the Gouy-Chapman theory. We find that the single-walled carbon nanotubes preferentially transported cations and that the cation permeability is size-dependent. The ionic conductance increases as the absolute hydration enthalpy decreases for monovalent cations with similar solid-state radii, hydrated radii, and bulk mobility. Charge screening experiments using either the addition of cationic or anionic polymers, divalent metal cations, or changes in pH reveal the enormous impact of the negatively charged carboxylates at the entrance of the single-walled carbon nanotubes. These observations were modeled in the low-to-medium concentration range (0.1-2.0 M) by an electrostatic mechanism that mimics the behavior observed in many biological ion channel-forming proteins. Moreover, multi-ion conduction in the high concentration range (>2.0 M) further reinforces the similarity between single-walled carbon nanotubes and protein ion channels.

The electrostatics of VDAC: implications for selectivity and gating.

PubMed

Choudhary, Om P; Ujwal, Rachna; Kowallis, William; Coalson, Rob; Abramson, Jeff; Grabe, Michael

2010-02-26

The voltage-dependent anion channel (VDAC) is the major pathway mediating the transfer of metabolites and ions across the mitochondrial outer membrane. Two hallmarks of the channel in the open state are high metabolite flux and anion selectivity, while the partially closed state blocks metabolites and is cation selective. Here we report the results from electrostatics calculations carried out on the recently determined high-resolution structure of murine VDAC1 (mVDAC1). Poisson-Boltzmann calculations show that the ion transfer free energy through the channel is favorable for anions, suggesting that mVDAC1 represents the open state. This claim is buttressed by Poisson-Nernst-Planck calculations that predict a high single-channel conductance indicative of the open state and an anion selectivity of 1.75--nearly a twofold selectivity for anions over cations. These calculations were repeated on mutant channels and gave selectivity changes in accord with experimental observations. We were then able to engineer an in silico mutant channel with three point mutations that converted mVDAC1 into a channel with a preference for cations. Finally, we investigated two proposals for how the channel gates between the open and the closed state. Both models involve the movement of the N-terminal helix, but neither motion produced the observed voltage sensitivity, nor did either model result in a cation-selective channel, which is observed experimentally. Thus, we were able to rule out certain models for channel gating, but the true motion has yet to be determined. Copyright (c) 2009. Elsevier Ltd. All rights reserved.

Determinants of cation transport selectivity: Equilibrium binding and transport kinetics

PubMed Central

2015-01-01

The crystal structures of channels and transporters reveal the chemical nature of ion-binding sites and, thereby, constrain mechanistic models for their transport processes. However, these structures, in and of themselves, do not reveal equilibrium selectivity or transport preferences, which can be discerned only from various functional assays. In this Review, I explore the relationship between cation transport protein structures, equilibrium binding measurements, and ion transport selectivity. The primary focus is on K+-selective channels and nonselective cation channels because they have been extensively studied both functionally and structurally, but the principles discussed are relevant to other transport proteins and molecules. PMID:26078056

A structural, functional, and computational analysis suggests pore flexibility as the base for the poor selectivity of CNG channels

PubMed Central

Napolitano, Luisa Maria Rosaria; Bisha, Ina; De March, Matteo; Marchesi, Arin; Arcangeletti, Manuel; Demitri, Nicola; Mazzolini, Monica; Rodriguez, Alex; Magistrato, Alessandra; Onesti, Silvia; Laio, Alessandro; Torre, Vincent

2015-01-01

Cyclic nucleotide-gated (CNG) ion channels, despite a significant homology with the highly selective K+ channels, do not discriminate among monovalent alkali cations and are permeable also to several organic cations. We combined electrophysiology, molecular dynamics (MD) simulations, and X-ray crystallography to demonstrate that the pore of CNG channels is highly flexible. When a CNG mimic is crystallized in the presence of a variety of monovalent cations, including Na+, Cs+, and dimethylammonium (DMA+), the side chain of Glu66 in the selectivity filter shows multiple conformations and the diameter of the pore changes significantly. MD simulations indicate that Glu66 and the prolines in the outer vestibule undergo large fluctuations, which are modulated by the ionic species and the voltage. This flexibility underlies the coupling between gating and permeation and the poor ionic selectivity of CNG channels. PMID:26100907

Structural and functional characterization of a calcium-activated cation channel from Tsukamurella paurometabola

NASA Astrophysics Data System (ADS)

Dhakshnamoorthy, Balasundaresan; Rohaim, Ahmed; Rui, Huan; Blachowicz, Lydia; Roux, Benoît

2016-09-01

The selectivity filter is an essential functional element of K+ channels that is highly conserved both in terms of its primary sequence and its three-dimensional structure. Here, we investigate the properties of an ion channel from the Gram-positive bacterium Tsukamurella paurometabola with a selectivity filter formed by an uncommon proline-rich sequence. Electrophysiological recordings show that it is a non-selective cation channel and that its activity depends on Ca2+ concentration. In the crystal structure, the selectivity filter adopts a novel conformation with Ca2+ ions bound within the filter near the pore helix where they are coordinated by backbone oxygen atoms, a recurrent motif found in multiple proteins. The binding of Ca2+ ion in the selectivity filter controls the widening of the pore as shown in crystal structures and in molecular dynamics simulations. The structural, functional and computational data provide a characterization of this calcium-gated cationic channel.

A structural, functional, and computational analysis suggests pore flexibility as the base for the poor selectivity of CNG channels.

PubMed

Napolitano, Luisa Maria Rosaria; Bisha, Ina; De March, Matteo; Marchesi, Arin; Arcangeletti, Manuel; Demitri, Nicola; Mazzolini, Monica; Rodriguez, Alex; Magistrato, Alessandra; Onesti, Silvia; Laio, Alessandro; Torre, Vincent

2015-07-07

Cyclic nucleotide-gated (CNG) ion channels, despite a significant homology with the highly selective K(+) channels, do not discriminate among monovalent alkali cations and are permeable also to several organic cations. We combined electrophysiology, molecular dynamics (MD) simulations, and X-ray crystallography to demonstrate that the pore of CNG channels is highly flexible. When a CNG mimic is crystallized in the presence of a variety of monovalent cations, including Na(+), Cs(+), and dimethylammonium (DMA(+)), the side chain of Glu66 in the selectivity filter shows multiple conformations and the diameter of the pore changes significantly. MD simulations indicate that Glu66 and the prolines in the outer vestibule undergo large fluctuations, which are modulated by the ionic species and the voltage. This flexibility underlies the coupling between gating and permeation and the poor ionic selectivity of CNG channels.

First-Row Transition Metal Doping in Calcium Phosphate Bioceramics: A Detailed Crystallographic Study

PubMed Central

Renaudin, Guillaume; Gomes, Sandrine; Nedelec, Jean-Marie

2017-01-01

Doped calcium phosphate bioceramics are promising materials for bone repair surgery because of their chemical resemblance to the mineral constituent of bone. Among these materials, BCP samples composed of hydroxyapatite (Ca10(PO4)6(OH)2) and β-TCP (Ca3(PO4)2) present a mineral analogy with the nano-multi-substituted hydroxyapatite bio-mineral part of bones. At the same time, doping can be used to tune the biological properties of these ceramics. This paper presents a general overview of the doping mechanisms of BCP samples using cations from the first-row transition metals (from manganese to zinc), with respect to the applied sintering temperature. The results enable the preparation of doped synthetic BCP that can be used to tailor biological properties, in particular by tuning the release amounts upon interaction with biological fluids. Intermediate sintering temperatures stabilize the doping elements in the more soluble β-TCP phase, which favors quick and easy release upon integration in the biological environment, whereas higher sintering temperatures locate the doping elements in the weakly soluble HAp phase, enabling a slow and continuous supply of the bio-inspired properties. An interstitial doping mechanism in the HAp hexagonal channel is observed for the six investigated cations (Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) with specific characteristics involving a shift away from the center of the hexagonal channel (Fe3+, Co2+), cationic oxidation (Mn3+, Co3+), and also cationic reduction (Cu+). The complete crystallochemical study highlights a complex HAp doping mechanism, mainly realized by an interstitial process combined with calcium substitution for the larger cations of the series leading to potentially calcium deficient HAp. PMID:28772452

Erythrocyte ion channels in regulation of apoptosis.

PubMed

Lang, Florian; Birka, Christina; Myssina, Svetlana; Lang, Karl S; Lang, Philipp A; Tanneur, Valerie; Duranton, Christophe; Wieder, Thomas; Huber, Stephan M

2004-01-01

Erythrocytes lack mitochondria and nuclei, key organelles in the regulation of apoptosis. Until recently, erythrocytes were thus not considered subject to this type of cell death. However, exposure of erythrocytes to the Ca2+ ionophore ionomycin was shown to induce cell shrinkage, cell membrane blebbing and breakdown of phosphatidylserine asymmetry with subsequent phosphatidylserine exposure at the cell surface, all typical features of apoptosis. Further studies revealed the participation of ion channels in the regulation of erythrocyte "apoptosis." Osmotic shock, oxidative stress and energy depletion all activate a Ca2(+)-permeable non-selective cation channel in the erythrocyte cell membrane. The subsequent increase of Ca2+ concentration stimulates a scramblase leading to breakdown of cell membrane phosphatidylserine asymmetry and activates Ca2+ sensitive K+ (Gardos) channels leading to KCl loss and (further) cell shrinkage. Phosphatidylserine exposure and cell shrinkage are blunted in the nominal absence of extracellular Ca2+, in the presence of the cation channel inhibitors amiloride or ethylisopropylamiloride, at increased extracellular K+ or in the presence of the Gardos channel inhibitors clotrimazole or charybdotoxin. Thus, increase of cytosolic Ca2+ and cellular loss of K+ participate in the triggering of erythrocyte scramblase. Nevertheless, phosphatidylserine exposure is not completely abrogated in the nominal absence of Ca2+, pointing to additional Ca2(+)-independent pathways. One of those is activation of sphingomyelinase with subsequent formation of ceramide which in turn leads to stimulation of erythrocyte scramblase. The exposure of phosphatidylserine at the extracellular face of the cell membrane stimulates phagocytes to engulf the apoptotic erythrocytes. Thus, sustained activation of the cation channels eventually leads to clearance of affected erythrocytes from peripheral blood. Erythropoietin inhibits the non-selective cation channel and thus interferes with erythrocyte "apoptosis." Susceptibility to scramblase activation is enhanced in thalassemia, sickle cell disease and glucose-6-phosphate dehydrogenase deficiency. Infection with Plasmodium falciparum leads to activation of the cation channel eventually triggering erythrocyte "apoptosis."

Binding symmetry of extracellular divalent cations to conduction pore studied using tandem dimers of a CNG channel.

PubMed

Kwon, Ryuk-Jun; Ha, Tal Soo; Kim, Wonjae; Park, Chul-Seung

2002-11-08

Cyclic nucleotide-gated (CNG) channels are composed of the tetramer of alpha-subunit alone or alpha- and beta-subunits. The alpha-subunits of these channels have a conserved glutamate (Glu) residue within the pore-forming region and the residue determines the selectivity as well as the affinity for the extracellular divalent cations. Using the high-affinity mutant (E363D) of bovine retinal CNG channel in which the Glu at position 363 was replaced to Asp, we constructed tandem dimers and investigated the binding characteristics of divalent cations to the site. The gating and permeation characteristics of individual homomeric tandem dimers are indistinguishable to those of homo-tetramers formed by parental monomers. The heteromeric tandem dimers showed the binding affinity for Sr(2+) identical to the geometric mean of the affinities for two parent channels, indicating the energy additive and thus the simultaneous interaction. On the other hand, the binding affinity for Mg(2+) followed the harmonic mean of those parent channels indicating that Mg(2+) interacts more strongly with the subunit bearing Asp residue at the position. Thus the results strongly suggest that the Glu363 residues in the CNG channel pore be flexible enough to adapt different binding symmetries for different divalent cations. Moreover, the simultaneous interaction between the four Glu residues and Sr(2+) provides an important structural constraint to the CNG channel outer vestibule of unknown structure.

Cation-limited kinetic model for microbial extracellular electron transport via an outer membrane cytochrome C complex

PubMed Central

Okamoto, Akihiro; Tokunou, Yoshihide; Saito, Junki

2016-01-01

Outer-membrane c-type cytochrome (OM c-Cyt) complexes in several genera of iron-reducing bacteria, such as Shewanella and Geobacter, are capable of transporting electrons from the cell interior to extracellular solids as a terminal step of anaerobic respiration. The kinetics of this electron transport has implications for controlling the rate of microbial electron transport during bioenergy or biochemical production, iron corrosion, and natural mineral cycling. Herein, we review the findings from in-vivo and in-vitro studies examining electron transport kinetics through single OM c-Cyt complexes in Shewanella oneidensis MR-1. In-vitro electron flux via a purified OM c-Cyt complex, comprised of MtrA, B, and C proteins from S. oneidensis MR-1, embedded in a proteoliposome system is reported to be 10- to 100-fold faster compared with in-vivo estimates based on measurements of electron flux per cell and OM c-Cyts density. As the proteoliposome system is estimated to have 10-fold higher cation flux via potassium channels than electrons, we speculate that the slower rate of electron-coupled cation transport across the OM is responsible for the significantly lower electron transport rate that is observed in-vivo. As most studies to date have primarily focused on the energetics or kinetics of interheme electron hopping in OM c-Cyts in this microbial electron transport mechanism, the proposed model involving cation transport provides new insight into the rate detemining step of EET, as well as the role of self-secreted flavin molecules bound to OM c-Cyt and proton management for energy conservation and production in S. oneidensis MR-1. PMID:27924259

Long-pore Electrostatics in Inward-rectifier Potassium Channels

PubMed Central

Robertson, Janice L.; Palmer, Lawrence G.; Roux, Benoît

2008-01-01

Inward-rectifier potassium (Kir) channels differ from the canonical K+ channel structure in that they possess a long extended pore (∼85 Å) for ion conduction that reaches deeply into the cytoplasm. This unique structural feature is presumably involved in regulating functional properties specific to Kir channels, such as conductance, rectification block, and ligand-dependent gating. To elucidate the underpinnings of these functional roles, we examine the electrostatics of an ion along this extended pore. Homology models are constructed based on the open-state model of KirBac1.1 for four mammalian Kir channels: Kir1.1/ROMK, Kir2.1/IRK, Kir3.1/GIRK, and Kir6.2/KATP. By solving the Poisson-Boltzmann equation, the electrostatic free energy of a K+ ion is determined along each pore, revealing that mammalian Kir channels provide a favorable environment for cations and suggesting the existence of high-density regions in the cytoplasmic domain and cavity. The contribution from the reaction field (the self-energy arising from the dielectric polarization induced by the ion's charge in the complex geometry of the pore) is unfavorable inside the long pore. However, this is well compensated by the electrostatic interaction with the static field arising from the protein charges and shielded by the dielectric surrounding. Decomposition of the static field provides a list of residues that display remarkable correspondence with existing mutagenesis data identifying amino acids that affect conduction and rectification. Many of these residues demonstrate interactions with the ion over long distances, up to 40 Å, suggesting that mutations potentially affect ion or blocker energetics over the entire pore. These results provide a foundation for understanding ion interactions in Kir channels and extend to the study of ion permeation, block, and gating in long, cation-specific pores. PMID:19001143

Effect of flecainide derivatives on sarcoplasmic reticulum calcium release suggests a lack of direct action on the cardiac ryanodine receptor.

PubMed

Bannister, Mark L; Alvarez-Laviada, Anita; Thomas, N Lowri; Mason, Sammy A; Coleman, Sharon; du Plessis, Christo L; Moran, Abbygail T; Neill-Hall, David; Osman, Hasnah; Bagley, Mark C; MacLeod, Kenneth T; George, Christopher H; Williams, Alan J

2016-08-01

Flecainide is a use-dependent blocker of cardiac Na(+) channels. Mechanistic analysis of this block showed that the cationic form of flecainide enters the cytosolic vestibule of the open Na(+) channel. Flecainide is also effective in the treatment of catecholaminergic polymorphic ventricular tachycardia but, in this condition, its mechanism of action is contentious. We investigated how flecainide derivatives influence Ca(2) (+) -release from the sarcoplasmic reticulum through the ryanodine receptor channel (RyR2) and whether this correlates with their effectiveness as blockers of Na(+) and/or RyR2 channels. We compared the ability of fully charged (QX-FL) and neutral (NU-FL) derivatives of flecainide to block individual recombinant human RyR2 channels incorporated into planar phospholipid bilayers, and their effects on the properties of Ca(2) (+) sparks in intact adult rat cardiac myocytes. Both QX-FL and NU-FL were partial blockers of the non-physiological cytosolic to luminal flux of cations through RyR2 channels but were significantly less effective than flecainide. None of the compounds influenced the physiologically relevant luminal to cytosol cation flux through RyR2 channels. Intracellular flecainide or QX-FL, but not NU-FL, reduced Ca(2) (+) spark frequency. Given its inability to block physiologically relevant cation flux through RyR2 channels, and its lack of efficacy in blocking the cytosolic-to-luminal current, the effect of QX-FL on Ca(2) (+) sparks is likely, by analogy with flecainide, to result from Na(+) channel block. Our data reveal important differences in the interaction of flecainide with sites in the cytosolic vestibules of Na(+) and RyR2 channels. © 2016 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.

LiBi{sub 3}S{sub 5}—A lithium bismuth sulfide with strong cation disorder

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

Nakhal, Suliman; Wiedemann, Dennis, E-mail: dennis.wiedemann@chem.tu-berlin.de; Stanje, Bernhard

Among chalcogenide semiconductors for thermoelectric applications, alkali-metal bismuth compounds occur in many complex compositions favorable for high performance. Although LiBi{sub 3}S{sub 5} had been announced in 1977, the potential 1D lithium-ion conductor has hitherto eluded selective synthesis and structure determination. In this study, we present a solid-state route to phase-pure LiBi{sub 3}S{sub 5} powder starting from LiBiS{sub 2} and Bi{sub 2}S{sub 3}. Neutron diffractograms and lithium NMR spectra reveal its crystal structure to be a cation-disordered variety of the AgBi{sub 3}S{sub 5} type (synthetic pavonite; monoclinic, C2/m). Topological analyses and lithium NMR relaxometry suggest that correlated lithium-ion diffusion with activationmore » energies up to 0.66(2) eV occurs along the channels in b direction including tetrahedral voids. Because of cation disorder, immobile bismuth(III) ions clog these pathways, making LiBi{sub 3}S{sub 5} a moderate to poor ionic conductor. The synthesis route reported is nonetheless promising for new lithium bismuth sulfides with, possibly ordered, structure types of the pavonite homologous series. - Graphical abstract: Phase-pure LiBi{sub 3}S{sub 5} has been synthesized and shown to crystallize in cation-disordered variety of the AgBi{sub 3}S{sub 5} type (synthetic pavonite, C2/m) using neutron diffractometry. Topological analyses and NMR relaxometry suggest that immobile Bi{sup 3+} ions clog migration channels along b, making the material a poor lithium conductor. Display Omitted - Highlights: • Phase-pure LiBi{sub 3}S{sub 5} has been synthesized using a promising solid-state route. • LiBi{sub 3}S{sub 5} crystallizes in a cation-disordered variant of the AgBi{sub 3}S{sub 5} type. • Topological analyses suggest lithium diffusion in channels along b. • NMR relaxometry finds activation energies of diffusion as high as 0.66(2) eV. • Because of disorder, LiBi{sub 3}S{sub 5} is a moderate to poor lithium-ion conductor.« less

Dynamics of receptor-operated Ca(2+) currents through TRPC channels controlled via the PI(4,5)P2-PLC signaling pathway.

PubMed

Mori, Masayuki X; Itsuki, Kyohei; Hase, Hideharu; Sawamura, Seishiro; Kurokawa, Tatsuki; Mori, Yasuo; Inoue, Ryuji

2015-01-01

Transient receptor potential canonical (TRPC) channels are Ca(2+)-permeable, nonselective cation channels that carry receptor-operated Ca(2+) currents (ROCs) triggered by receptor-induced, phospholipase C (PLC)-catalyzed hydrolysis of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. Within the vasculature, TRPC channel ROCs contribute to smooth muscle cell depolarization, vasoconstriction, and vascular remodeling. However, TRPC channel ROCs exhibit a variable response to receptor-stimulation, and the regulatory mechanisms governing TRPC channel activity remain obscure. The variability of ROCs may be explained by their complex regulation by PI(4,5)P2 and its metabolites, which differentially affect TRPC channel activity. To resolve the complex regulation of ROCs, the use of voltage-sensing phosphoinositide phosphatases and model simulation have helped to reveal the time-dependent contribution of PI(4,5)P2 and the possible role of PI(4,5)P2 in the regulation of ROCs. These approaches may provide unprecedented insight into the dynamics of PI(4,5)P2 regulation of TRPC channels and the fundamental mechanisms underlying transmembrane ion flow. Within that context, we summarize the regulation of TRPC channels and their coupling to receptor-mediated signaling, as well as the application of voltage-sensing phosphoinositide phosphatases to this research. We also discuss the controversial bidirectional effects of PI(4,5)P2 using a model simulation that could explain the complicated effects of PI(4,5)P2 on different ROCs.

Activation of a Ca2+-dependent cation conductance with properties of TRPM2 by reactive oxygen species in lens epithelial cells.

PubMed

Keckeis, Susanne; Wernecke, Laura; Salchow, Daniel J; Reichhart, Nadine; Strauß, Olaf

2017-08-01

Ion channels are crucial for maintenance of ion homeostasis and transparency of the lens. The lens epithelium is the metabolically and electrophysiologically active cell type providing nutrients, ions and water to the lens fiber cells. Ca 2+ -dependent non-selective ion channels seem to play an important role for ion homeostasis. The aim of the study was to identify and characterize Ca 2+ - and reactive oxygen species (ROS)-dependent non-selective cation channels in human lens epithelial cells. RT-PCR revealed gene expression of the Ca 2+ -activated non-selective cation channels TRPC3, TRPM2, TRPM4 and Ano6 in both primary lens epithelial cells and the cell line HLE-B3, whereas TRPM5 mRNA was only found in HLE-B3 cells. Using whole-cell patch-clamp technique, ionomycin evoked non-selective cation currents with linear current-voltage relationship in both cell types. The current was decreased by flufenamic acid (FFA), 2-APB, 9-phenanthrol and miconazole, but insensitive to DIDS, ruthenium red, and intracellularly applied spermine. H 2 O 2 evoked a comparable current, abolished by FFA. TRPM2 protein expression in HLE-B3 cells was confirmed by means of immunocytochemistry and western blot. In summary, we conclude that lens epithelial cells functionally express Ca 2+ - and H 2 O 2 -activated non-selective cation channels with properties of TRPM2. Copyright © 2017. Published by Elsevier Ltd.

El Tor hemolysin of Vibrio cholerae O1 forms channels in planar lipid bilayer membranes.

PubMed

Ikigai, H; Ono, T; Iwata, M; Nakae, T; Shimamura, T

1997-05-15

We investigated the channel formation by El Tor hemolysin (molecular mass, 65 kDa) of Vibrio cholerae O1 biotype El Tor in planar lipid bilayers. The El Tor hemolysin channel exhibited asymmetric and hyperbolic membrane current with increasing membrane potential, meaning that the channel is voltage dependent. The zero-current membrane potential measured in KCI solution showed that permeability ratio PK+/PCl- was 0.16, indicating that the channel is 6-fold more anion selective over cation. The hemolysin channel frequently flickered in the presence of divalent cations, suggesting that the channel spontaneously opens and closes. These data imply that the El Tor hemolysin damages target cells by the formation of transmembrane channels and, consequently, is the cause of osmotic cytolysis.

Tic20 forms a channel independent of Tic110 in chloroplasts

PubMed Central

2011-01-01

Background The Tic complex (Translocon at the inner envelope membrane of chloroplasts) mediates the translocation of nuclear encoded chloroplast proteins across the inner envelope membrane. Tic110 forms one prominent protein translocation channel. Additionally, Tic20, another subunit of the complex, was proposed to form a protein import channel - either together with or independent of Tic110. However, no experimental evidence for Tic20 channel activity has been provided so far. Results We performed a comprehensive biochemical and electrophysiological study to characterize Tic20 in more detail and to gain a deeper insight into its potential role in protein import into chloroplasts. Firstly, we compared transcript and protein levels of Tic20 and Tic110 in both Pisum sativum and Arabidopsis thaliana. We found the Tic20 protein to be generally less abundant, which was particularly pronounced in Arabidopsis. Secondly, we demonstrated that Tic20 forms a complex larger than 700 kilodalton in the inner envelope membrane, which is clearly separate from Tic110, migrating as a dimer at about 250 kilodalton. Thirdly, we defined the topology of Tic20 in the inner envelope, and found its N- and C-termini to be oriented towards the stromal side. Finally, we successfully reconstituted overexpressed and purified full-length Tic20 into liposomes. Using these Tic20-proteoliposomes, we could demonstrate for the first time that Tic20 can independently form a cation selective channel in vitro. Conclusions The presented data provide first biochemical evidence to the notion that Tic20 can act as a channel protein within the chloroplast import translocon complex. However, the very low abundance of Tic20 in the inner envelope membranes indicates that it cannot form a major protein translocation channel. Furthermore, the independent complex formation of Tic20 and Tic110 argues against a joint channel formation. Thus, based on the observed channel activity of Tic20 in proteoliposomes, we speculate that the chloroplast inner envelope contains multiple (at least two) translocation channels: Tic110 as the general translocation pore, whereas Tic20 could be responsible for translocation of a special subset of proteins. PMID:21961525

Mechanosensitive cation channels in human leukaemia cells: calcium permeation and blocking effect

PubMed Central

Staruschenko, Alexandr V; Vedernikova, Elena A

2002-01-01

Cell-attached and inside-out patch-clamp methods were employed to identify and characterize mechanosensitive (MS) ionic channels in the plasma membrane of human myeloid leukaemia K562 cells. A reversible activation of gadolinium-blockable mechanogated currents in response to negative pressure application was found in 58 % of stable patches (n = 317). I-V relationships measured with a sodium-containing pipette solution showed slight inward rectification. Data analysis revealed the presence of two different populations of channels that were distinguishable by their conductance properties (17.2 ± 0.3 pS and 24.5 ± 0.5 pS), but were indistinguishable with regard to their selective and pharmacological properties. Ion-substitution experiments indicated that MS channels in leukaemia cells were permeable to cations but not to anions and do not discriminate between Na+ and K+. The channels were fully impermeable to large organic cations such as Tris+ and N-methyl-d-glucamine ions (NMDG+). Ca2+ permeation and blockade of MS channels were examined using pipettes containing different concentrations of Ca2+. In the presence of 2 mm CaCl2, when other cations were impermeant, both outward and inward single-channel currents were observed; the I-V relationship showed a unitary conductance of 7.7 ± 1.0 pS. The relative permeability value, PCa/PK, was equal to 0.75, as estimated at physiological Ca2+ concentrations. Partial or full inhibition of inward Ca2+ currents through MS channels was observed at higher concentrations of external Ca2+ (10 or 20 mm). No MS channels were activated when using a pipette containing 90 mm CaCl2. Monovalent mechanogated currents were not significantly affected by extracellular Ca2+ at concentrations within the physiological range (0-2 mm), and at some higher Ca2+ concentrations. PMID:12015421

Effect of Alkali Metal Cations on Slow Inactivation of Cardiac Na+ Channels

PubMed Central

Townsend, Claire; Horn, Richard

1997-01-01

Human heart Na+ channels were expressed transiently in both mammalian cells and Xenopus oocytes, and Na+ currents measured using 150 mM intracellular Na+. The kinetics of decaying outward Na+ current in response to 1-s depolarizations in the F1485Q mutant depends on the predominant cation in the extracellular solution, suggesting an effect on slow inactivation. The decay rate is lower for the alkali metal cations Li+, Na+, K+, Rb+, and Cs+ than for the organic cations Tris, tetramethylammonium, N-methylglucamine, and choline. In whole cell recordings, raising [Na+]o from 10 to 150 mM increases the rate of recovery from slow inactivation at −140 mV, decreases the rate of slow inactivation at relatively depolarized voltages, and shifts steady-state slow inactivation in a depolarized direction. Single channel recordings of F1485Q show a decrease in the number of blank (i.e., null) records when [Na+]o is increased. Significant clustering of blank records when depolarizing at a frequency of 0.5 Hz suggests that periods of inactivity represent the sojourn of a channel in a slow-inactivated state. Examination of the single channel kinetics at +60 mV during 90-ms depolarizations shows that neither open time, closed time, nor first latency is significantly affected by [Na+]o. However raising [Na+]o decreases the duration of the last closed interval terminated by the end of the depolarization, leading to an increased number of openings at the depolarized voltage. Analysis of single channel data indicates that at a depolarized voltage a single rate constant for entry into a slow-inactivated state is reduced in high [Na+]o, suggesting that the binding of an alkali metal cation, perhaps in the ion-conducting pore, inhibits the closing of the slow inactivation gate. PMID:9234168

Basally activated nonselective cation currents regulate the resting membrane potential in human and monkey colonic smooth muscle

PubMed Central

Dwyer, Laura; Rhee, Poong-Lyul; Lowe, Vanessa; Zheng, Haifeng; Peri, Lauren; Ro, Seungil; Sanders, Kenton M.

2011-01-01

Resting membrane potential (RMP) plays an important role in determining the basal excitability of gastrointestinal smooth muscle. The RMP in colonic muscles is significantly less negative than the equilibrium potential of K+, suggesting that it is regulated not only by K+ conductances but by inward conductances such as Na+ and/or Ca2+. We investigated the contribution of nonselective cation channels (NSCC) to the RMP in human and monkey colonic smooth muscle cells (SMC) using voltage- and current-clamp techniques. Qualitative reverse transcriptase-polymerase chain reaction was performed to examine potential molecular candidates for these channels among the transient receptor potential (TRP) channel superfamily. Spontaneous transient inward currents and holding currents were recorded in human and monkey SMC. Replacement of extracellular Na+ with equimolar tetraethylammonium or Ca2+ with Mn2+ inhibited basally activated nonselective cation currents. Trivalent cations inhibited these channels. Under current clamp, replacement of extracellular Na+ with N-methyl-d-glucamine or addition of trivalent cations caused hyperpolarization. Three unitary conductances of NSCC were observed in human and monkey colonic SMC. Molecular candidates for basally active NSCC were TRPC1, C3, C4, C7, M2, M4, M6, M7, V1, and V2 in human and monkey SMC. Comparison of the biophysical properties of these TRP channels with basally active NSCC (bINSCC) suggests that TRPM4 and specific TRPC heteromultimer combinations may underlie the three single-channel conductances of bINSCC. In conclusion, these findings suggest that basally activated NSCC contribute to the RMP in human and monkey colonic SMC and therefore may play an important role in determining basal excitability of colonic smooth muscle. PMID:21566016

Biophysics of object segmentation in a collision-detecting neuron

PubMed Central

Dewell, Richard Burkett

2018-01-01

Collision avoidance is critical for survival, including in humans, and many species possess visual neurons exquisitely sensitive to objects approaching on a collision course. Here, we demonstrate that a collision-detecting neuron can detect the spatial coherence of a simulated impending object, thereby carrying out a computation akin to object segmentation critical for proper escape behavior. At the cellular level, object segmentation relies on a precise selection of the spatiotemporal pattern of synaptic inputs by dendritic membrane potential-activated channels. One channel type linked to dendritic computations in many neural systems, the hyperpolarization-activated cation channel, HCN, plays a central role in this computation. Pharmacological block of HCN channels abolishes the neuron's spatial selectivity and impairs the generation of visually guided escape behaviors, making it directly relevant to survival. Additionally, our results suggest that the interaction of HCN and inactivating K+ channels within active dendrites produces neuronal and behavioral object specificity by discriminating between complex spatiotemporal synaptic activation patterns. PMID:29667927

Gibbs-Donnan ratio and channel conductance of Tetrahymena cilia in mixed solution of K+ and Ca2+.

PubMed Central

Oosawa, Y; Kasai, M

1988-01-01

A single cation-channel from Tetrahymena cilia was incorporated into planar lipid bilayers. This channel was voltage-independent and is permeable to K+ and Ca2+. In the experiments with mixed solutions where the concentrations of K+ and Ca2+ were varied, the single-channel conductance was found to be influenced by the Gibbs-Donnan ratio. The data are explained by assuming that the binding sites of this channel were always occupied by two potassium ions or one calcium ion under the present experimental conditions (5 mM-90 mM K+ and 0.5 mM-35 mM Ca2+) and these bound cations determined the channel conductivity. PMID:2462927

Characterization of a C-type natriuretic peptide (CNP-39)-formed cation-selective channel from platypus (Ornithorhynchus anatinus) venom

PubMed Central

Kourie, Joseph I

1999-01-01

The lipid bilayer technique is used to characterize the biophysical and pharmacological properties of a novel, fast, cation-selective channel formed by incorporating platypus (Ornithorhynchus anatinus) venom (OaV) into lipid membranes.A synthetic C-type natriuretic peptide OaCNP-39, which is identical to that present in platypus venom, mimics the conductance, kinetics, selectivity and pharmacological properties of the OaV-formed fast cation-selective channel. The N-terminal fragment containing residues 1-17, i.e. OaCNP-39(1-17), induces the channel activity.The current amplitude of the TEACl-insensitive fast cation-selective channel is dependent on cytoplasmic K+, [K+]cis. The increase in the current amplitude, as a function of increasing [K+]cis, is non-linear and can be described by the Michaelis-Menten equation. At +140 mV, the values of γmax and KS are 63·1 pS and 169 mM, respectively, whereas at 0 mV the values of γmax and KS are 21·1 pS and 307 mM, respectively. γmax and KS are maximal single channel conductance and concentration for half-maximal γ, respectively. The calculated permeability ratios, PK:PRb:PNa: PCs:PLi, were 1:0·76:0·21:0·09:0·03, respectively.The probability of the fast channel being open, Po, increases from 0·15 at 0 mV to 0·75 at +140 mV. In contrast, the channel frequency, Fo, decreases from 400 to 180 events per second for voltages between 0 mV and +140. The mean open time, To, increases as the bilayer is made more positive, between 0 and +140 mV. The mean values of the voltage-dependent kinetic parameters, Po, Fo, To and mean closed time (Tc), are independent of [KCl]cis between 50 and 750 mM (P > 0·05).It is proposed that some of the symptoms of envenomation by platypus venom may be caused partly by changes in cellular functions mediated via the OaCNP-39-formed fast cation-selective channel, which affects signal transduction. PMID:10381585

Channel-forming activity in the venom of the cockroach-hunting wasp, Ampulex compressa.

PubMed

Gincel, Dan; Haspel, Gal; Libersat, Frederic

2004-05-01

The parasitoid solitary wasp Ampulex compressa uses the cockroach Periplaneta americana as a food supply for its larvae. To subdue its prey, the wasp injects a venom cocktail into the brain of the cockroach. We investigated channel activity of A. compressa venom by collecting venom and incorporating it into a planar lipid bilayer. The venom, reconstituted into the bilayer, showed ion channel activity, forming a fast-fluctuating channel with a small conductance of 20+/-0.1pS, with no voltage sensitivity. These channels were not observed when the venom was digested with proteases before application to the bilayer, but were not affected by exposure to protease after their incorporation into the bilayer, indicating that the active venom component is a peptide. The channels were found to be cation selective with similar selectivity for the monovalent cations K(+), Li(+) and Na(+), but showed high selectivity against anions (Cl(-)) and divalent cations (Ca(2+) and Mg(2+)). This study is the first demonstration and biophysical characterization of channel activity in the venom of A. compressa. The possible functional significance of this channel activity is discussed in light of the unusual nature of the effects of this wasp venom on the behavior of its prey.

Implications of hydrogen/halogen-bond in the stabilization of confined water and anion-water clusters by a cationic receptor

NASA Astrophysics Data System (ADS)

Hoque, Md. Najbul; Das, Gopal

2016-03-01

Anion complexation of benzene capped flexible tripodal receptor and solid state stabilization of discrete hybrid anion-water or infinite water clusters by various supramolecular interactions are reported here. The crystal structure of the receptor in protonated states shows all the three arms projected in one direction. We structurally demonstrate discrete fluoride-water cluster [F2-H2O]2- and square shaped chloride-water cluster [Cl2-(H2O)2]2- inside the cationic channel of the receptor. Structural analysis also reveals that these clusters are stabilized inside the channel through active participation of N/C/Ow‧H⋯Ow, N/C/Ow‧H⋯X- (X- = F-, Cl- and I-) H-bonds and electrostatic interactions. Moreover, C-H⋯π and π⋯π types weak intermolecular interactions appear to play crucial role in supramolecular assembly of receptor. Additionally, on treatment with hydroiodic acid (HI) L resulted zwitterionic iodide complex. Crystal structure reveals the presence of S···I halogen bonded dimer, I2···I halogen bond, 1D infinite water chain and neutral iodine molecules. It is comprehensible that ligand basal structure (benzene capped and N-bridge head in two tripodal) play crucial roles in the formation of diverse halide-water cluster. All structures were well examined by different techniques such as NMR, IR, TGA, DSC, PXRD and XRD.

Interactions of divalent cations with calcium binding sites of BK channels reveal independent motions within the gating ring.

PubMed

Miranda, Pablo; Giraldez, Teresa; Holmgren, Miguel

2016-12-06

Large-conductance voltage- and calcium-activated K + (BK) channels are key physiological players in muscle, nerve, and endocrine function by integrating intracellular Ca 2+ and membrane voltage signals. The open probability of BK channels is regulated by the intracellular concentration of divalent cations sensed by a large structure in the BK channel called the "gating ring," which is formed by four tandems of regulator of conductance for K + (RCK1 and RCK2) domains. In contrast to Ca 2+ that binds to both RCK domains, Mg 2+ , Cd 2+ , or Ba 2+ interact preferentially with either one or the other. Interaction of cations with their binding sites causes molecular rearrangements of the gating ring, but how these motions occur remains elusive. We have assessed the separate contributions of each RCK domain to the cation-induced gating-ring structural rearrangements, using patch-clamp fluorometry. Here we show that Mg 2+ and Ba 2+ selectively induce structural movement of the RCK2 domain, whereas Cd 2+ causes motions of RCK1, in all cases substantially smaller than those elicited by Ca 2+ By combining divalent species interacting with unique sites, we demonstrate that RCK1 and RCK2 domains move independently when their specific binding sites are occupied. Moreover, binding of chemically distinct cations to both RCK domains is additive, emulating the effect of fully occupied Ca 2+ binding sites.

Heme Regulates Allosteric Activation of the Slo1 BK Channel

PubMed Central

Horrigan, Frank T.; Heinemann, Stefan H.; Hoshi, Toshinori

2005-01-01

Large conductance calcium-dependent (Slo1 BK) channels are allosterically activated by membrane depolarization and divalent cations, and possess a rich modulatory repertoire. Recently, intracellular heme has been identified as a potent regulator of Slo1 BK channels (Tang, X.D., R. Xu, M.F. Reynolds, M.L. Garcia, S.H. Heinemann, and T. Hoshi. 2003. Nature. 425:531–535). Here we investigated the mechanism of the regulatory action of heme on heterologously expressed Slo1 BK channels by separating the influences of voltage and divalent cations. In the absence of divalent cations, heme generally decreased ionic currents by shifting the channel's G–V curve toward more depolarized voltages and by rendering the curve less steep. In contrast, gating currents remained largely unaffected by heme. Simulations suggest that a decrease in the strength of allosteric coupling between the voltage sensor and the activation gate and a concomitant stabilization of the open state account for the essential features of the heme action in the absence of divalent ions. At saturating levels of divalent cations, heme remained similarly effective with its influence on the G–V simulated by weakening the coupling of both Ca2+ binding and voltage sensor activation to channel opening. The results thus show that heme dampens the influence of allosteric activators on the activation gate of the Slo1 BK channel. To account for these effects, we consider the possibility that heme binding alters the structure of the RCK gating ring and thereby disrupts both Ca2+- and voltage-dependent gating as well as intrinsic stability of the open state. PMID:15955873

Permeation of internal and external monovalent cations through the catfish cone photoreceptor cGMP-gated channel

PubMed Central

1995-01-01

The permeation of monovalent cations through the cGMP-gated channel of catfish cone outer segments was examined by measuring permeability and conductance ratios under biionic conditions. For monovalent cations presented on the cytoplasmic side of the channel, the permeability ratios with respect to extracellular Na followed the sequence NH4 > K > Li > Rb = Na > Cs while the conductance ratios at +50 mV followed the sequence Na approximately NH4 > K > Rb > Li = Cs. These patterns are broadly similar to the amphibian rod channel. The symmetry of the channel was tested by presenting the test ion on the extracellular side and using Na as the common reference ion on the cytoplasmic side. Under these biionic conditions, the permeability ratios with respect to Na at the intracellular side followed the sequence NH4 > Li > K > Na > Rb > Cs while the conductance ratios at +50 mV followed the sequence NH4 > K approximately Na > Rb > Li > Cs. Thus, the channel is asymmetric with respect to external and internal cations. Under symmetrical 120 mM ionic conditions, the single-channel conductance at +50 mV ranged from 58 pS in NH4 to 15 pS for Cs and was in the order NH4 > Na > K > Rb > Cs. Unexpectedly, the single-channel current-voltage relation showed sufficient outward rectification to account for the rectification observed in multichannel patches without invoking voltage dependence in gating. The concentration dependence of the reversal potential for K showed that chloride was impermeant. Anomalous mole fraction behavior was not observed, nor, over a limited concentration range, were multiple dissociation constants. An Eyring rate theory model with a single binding site was sufficient to explain these observations. PMID:8786344

Mechanism of sodium channel block by local anesthetics, antiarrhythmics, and anticonvulsants

PubMed Central

Tikhonov, Denis B.

2017-01-01

Local anesthetics, antiarrhythmics, and anticonvulsants include both charged and electroneutral compounds that block voltage-gated sodium channels. Prior studies have revealed a common drug-binding region within the pore, but details about the binding sites and mechanism of block remain unclear. Here, we use the x-ray structure of a prokaryotic sodium channel, NavMs, to model a eukaryotic channel and dock representative ligands. These include lidocaine, QX-314, cocaine, quinidine, lamotrigine, carbamazepine (CMZ), phenytoin, lacosamide, sipatrigine, and bisphenol A. Preliminary calculations demonstrated that a sodium ion near the selectivity filter attracts electroneutral CMZ but repels cationic lidocaine. Therefore, we further docked electroneutral and cationic drugs with and without a sodium ion, respectively. In our models, all the drugs interact with a phenylalanine in helix IVS6. Electroneutral drugs trap a sodium ion in the proximity of the selectivity filter, and this same site attracts the charged group of cationic ligands. At this position, even small drugs can block the permeation pathway by an electrostatic or steric mechanism. Our study proposes a common pharmacophore for these diverse drugs. It includes a cationic moiety and an aromatic moiety, which are usually linked by four bonds. PMID:28258204

Mechanism of sodium channel block by local anesthetics, antiarrhythmics, and anticonvulsants.

PubMed

Tikhonov, Denis B; Zhorov, Boris S

2017-04-03

Local anesthetics, antiarrhythmics, and anticonvulsants include both charged and electroneutral compounds that block voltage-gated sodium channels. Prior studies have revealed a common drug-binding region within the pore, but details about the binding sites and mechanism of block remain unclear. Here, we use the x-ray structure of a prokaryotic sodium channel, NavMs, to model a eukaryotic channel and dock representative ligands. These include lidocaine, QX-314, cocaine, quinidine, lamotrigine, carbamazepine (CMZ), phenytoin, lacosamide, sipatrigine, and bisphenol A. Preliminary calculations demonstrated that a sodium ion near the selectivity filter attracts electroneutral CMZ but repels cationic lidocaine. Therefore, we further docked electroneutral and cationic drugs with and without a sodium ion, respectively. In our models, all the drugs interact with a phenylalanine in helix IVS6. Electroneutral drugs trap a sodium ion in the proximity of the selectivity filter, and this same site attracts the charged group of cationic ligands. At this position, even small drugs can block the permeation pathway by an electrostatic or steric mechanism. Our study proposes a common pharmacophore for these diverse drugs. It includes a cationic moiety and an aromatic moiety, which are usually linked by four bonds. © 2017 Tikhonov and Zhorov.

Conformational plasticity in the selectivity filter of the TRPV2 ion channel.

PubMed

Zubcevic, Lejla; Le, Son; Yang, Huanghe; Lee, Seok-Yong

2018-05-01

Transient receptor potential vanilloid (TRPV) channels are activated by ligands and heat and are involved in various physiological processes. In contrast to the architecturally related voltage-gated cation channels, TRPV1 and TRPV2 subtypes possess another activation gate at the selectivity filter that can open widely enough to permeate large organic cations. Despite recent structural advances, the mechanism of selectivity filter gating and permeation for both metal ions and large molecules by TRPV1 or TRPV2 is not well known. Here, we determined two crystal structures of rabbit TRPV2 in its Ca 2+ -bound and resiniferatoxin (RTx)- and Ca 2+ -bound forms, to 3.9 Å and 3.1 Å, respectively. Notably, our structures show that RTx binding leads to two-fold symmetric opening of the selectivity filter of TRPV2 that is wide enough for large organic cation permeation. Combined with functional characterizations, our studies reveal a structural basis for permeation of Ca 2+ and large organic cations in TRPV2.

Structures of Hydrated Alkali Metal Cations, M+(H2O)nAr (m = Li, Na, K, rb and Cs, n = 3-5), Using Infrared Photodissociation Spectroscopy and Thermodynamic Analysis

NASA Astrophysics Data System (ADS)

Ke, Haochen; van der Linde, Christian; Lisy, James M.

2014-06-01

Alkali metal cations play vital roles in chemical and biochemical systems. Lithium is widely used in psychiatric treatment of manic states and bipolar disorder; Sodium and potassium are essential elements, having major biological roles as electrolytes, balancing osmotic pressure on body cells and assisting the electroneurographic signal transmission; Rubidium has seen increasing usage as a supplementation for manic depression and depression treatment; Cesium doped compounds are used as essential catalysts in chemical production and organic synthesis. Since hydrated alkali metal cations are ubiquitous and the basic form of the alkali metal cations in chemical and biochemical systems, their structural and thermodynamic properties serve as the foundation for modeling more complex chemical and biochemical processes, such as ion transport and ion size-selectivity of ionophores and protein channels. By combining mass spectrometry and infrared photodissociation spectroscopy, we have characterized the structures and thermodynamic properties of the hydrated alkali metal cations, i.e. M+(H2O)nAr, (M = Li, Na, K, Rb and Cs, n = 3-5). Ab initio calculations and RRKM-EE (evaporative ensemble) calculations were used to assist in the spectral assignments and thermodynamic analysis. Results showed that the structures of hydrated alkali metal cations were determined predominantly by the competition between non-covalent interactions, i.e. the water---water hydrogen bonding interactions and the water---cation electrostatic interactions. This balance, however, is very delicate and small changes, i.e. different cations, different levels of hydration and different effective temperatures clearly impact the balance.

Single mechanically-gated cation channel currents can trigger action potentials in neocortical and hippocampal pyramidal neurons.

PubMed

Nikolaev, Yury A; Dosen, Peter J; Laver, Derek R; van Helden, Dirk F; Hamill, Owen P

2015-05-22

The mammalian brain is a mechanosensitive organ that responds to different mechanical forces ranging from intrinsic forces implicated in brain morphogenesis to extrinsic forces that can cause concussion and traumatic brain injury. However, little is known of the mechanosensors that transduce these forces. In this study we use cell-attached patch recording to measure single mechanically-gated (MG) channel currents and their affects on spike activity in identified neurons in neonatal mouse brain slices. We demonstrate that both neocortical and hippocampal pyramidal neurons express stretch-activated MG cation channels that are activated by suctions of ~25mm Hg, have a single channel conductance for inward current of 50-70pS and show weak selectivity for alkali metal cations (i.e., Na(+)

Double C-H activation of ethane by metal-free SO2*+ radical cations.

PubMed

de Petris, Giulia; Cartoni, Antonella; Troiani, Anna; Barone, Vincenzo; Cimino, Paola; Angelini, Giancarlo; Ursini, Ornella

2010-06-01

The room-temperature C-H activation of ethane by metal-free SO(2)(*+) radical cations has been investigated under different pressure regimes by mass spectrometric techniques. The major reaction channel is the conversion of ethane to ethylene accompanied by the formation of H(2)SO(2)(*+), the radical cation of sulfoxylic acid. The mechanism of the double C-H activation, in the absence of the single activation product HSO(2)(+), is elucidated by kinetic studies and quantum chemical calculations. Under near single-collision conditions the reaction occurs with rate constant k=1.0 x 10(-9) (+/-30%) cm(3) s(-1) molecule(-1), efficiency=90%, kinetic isotope effect k(H)/k(D)=1.1, and partial H/D scrambling. The theoretical analysis shows that the interaction of SO(2)(*+) with ethane through an oxygen atom directly leads to the C-H activation intermediate. The interaction through sulfur leads to an encounter complex that rapidly converts to the same intermediate. The double C-H activation occurs by a reaction path that lies below the reactants and involves intermediates separated by very low energy barriers, which include a complex of the ethyl cation suitable to undergo H/D scrambling. Key issues in the observed reactivity are electron-transfer processes, in which a crucial role is played by geometrical constraints. The work shows how mechanistic details disclosed by the reactions of metal-free electrophiles may contribute to the current understanding of the C-H activation of ethane.

Ionic selectivity of native ATP-activated (P2X) receptor channels in dissociated neurones from rat parasympathetic ganglia

PubMed Central

Liu, Dong-Mei; Adams, David J

2001-01-01

The relative permeability of the native P2X receptor channel to monovalent and divalent inorganic and organic cations was determined from reversal potential measurements of ATP-evoked currents in parasympathetic neurones dissociated from rat submandibular ganglia using the dialysed whole-cell patch clamp technique. The P2X receptor-channel exhibited weak selectivity among the alkali metals with a selectivity sequence of Na+ > Li+ > Cs+ > Rb+ > K+, and permeability ratios relative to Cs+ (PX/PCs) ranging from 1.11 to 0.86. The selectivity for the divalent alkaline earth cations was also weak with the sequence Ca2+ > Sr2+ > Ba2+ > Mn2+ > Mg2+. ATP-evoked currents were strongly inhibited when the extracellular divalent cation concentration was increased. The calculated permeability ratios of different ammonium cations are higher than those of the alkali metal cations. The permeability sequence obtained for the saturated organic cations is inversely correlated with the size of the cation. The unsaturated organic cations have a higher permeability than that predicted by molecular size. Acidification to pH 6.2 increased the ATP-induced current amplitude twofold, whereas alkalization to 8.2 and 9.2 markedly reduced current amplitude. Cell dialysis with either anti-P2X2 and/or anti-P2X4 but not anti-P2X1 antibodies attenuated the ATP-evoked current amplitude. Taken together, these data are consistent with homomeric and/or heteromeric P2X2 and P2X4 receptor subtypes expressed in rat submandibular neurones. The permeability ratios for the series of monovalent organic cations, with the exception of unsaturated cations, were approximately related to the ionic size. The relative permeabilities of the monovalent inoganic and organic cations tested are similar to those reported previously for cloned rat P2X2 receptors expressed in mammalian cells. PMID:11454961

An elevation in physical coupling of type 1 inositol 1,4,5-trisphosphate (IP3) receptors to transient receptor potential 3 (TRPC3) channels constricts mesenteric arteries in genetic hypertension.

PubMed

Adebiyi, Adebowale; Thomas-Gatewood, Candice M; Leo, M Dennis; Kidd, Michael W; Neeb, Zachary P; Jaggar, Jonathan H

2012-11-01

Hypertension is associated with an elevation in agonist-induced vasoconstriction, but mechanisms involved require further investigation. Many vasoconstrictors bind to phospholipase C-coupled receptors, leading to an elevation in inositol 1,4,5-trisphosphate (IP(3)) that activates sarcoplasmic reticulum IP(3) receptors. In cerebral artery myocytes, IP(3) receptors release sarcoplasmic reticulum Ca(2+) and can physically couple to canonical transient receptor potential 3 (TRPC3) channels in a caveolin-1-containing macromolecular complex, leading to cation current activation that stimulates vasoconstriction. Here, we investigated mechanisms by which IP(3) receptors control vascular contractility in systemic arteries and IP(3)R involvement in elevated agonist-induced vasoconstriction during hypertension. Total and plasma membrane-localized TRPC3 protein was ≈2.7- and 2-fold higher in mesenteric arteries of spontaneously hypertensive rats (SHRs) than in Wistar-Kyoto (WKY) rat controls, respectively. In contrast, IP(3)R1, TRPC1, TRPC6, and caveolin-1 expression was similar. TRPC3 expression was also similar in arteries of pre-SHRs and WKY rats. Control, IP(3)-induced and endothelin-1 (ET-1)-induced fluorescence resonance energy transfer between IP3R1 and TRPC3 was higher in SHR than WKY myocytes. IP3-induced cation current was ≈3-fold larger in SHR myocytes. Pyr3, a selective TRPC3 channel blocker, and calmodulin and IP(3) receptor binding domain peptide, an IP(3)R-TRP physical coupling inhibitor, reduced IP(3)-induced cation current and ET-1-induced vasoconstriction more in SHR than WKY myocytes and arteries. Thapsigargin, a sarcoplasmic reticulum Ca(2+)-ATPase blocker, did not alter ET-1-stimulated vasoconstriction in SHR or WKY arteries. These data indicate that ET-1 stimulates physical coupling of IP(3)R1 to TRPC3 channels in mesenteric artery myocytes, leading to vasoconstriction. Furthermore, an elevation in IP(3)R1 to TRPC3 channel molecular coupling augments ET-1-induced vasoconstriction during hypertension.

The permeability of the endplate channel to organic cations in frog muscle

PubMed Central

1980-01-01

The relative permeability of endplate channels to many organic cations was determined by reversal-potential criteria. Endplate currents induced by iontophoretic "puffs" of acetylcholine were studied by a Vaseline gap, voltage clamp method in cut muscle fibers. Reversal potential changes were measured as the NaCl of the bathing medium was replaced by salts of organic cations, and permeability ratios relative to Na+ ions were calculated from the Goldman-Hodgkin-Katz equation. 40 small monovalent organic cations had permeability ratios larger than 0.1. The most permeant including NH4+, hydroxylamine, hydrazine, methylamine, guanidine, and several relatives of guanidine had permeability ratios in the range 1.3--2.0. However, even cations such as imidazole, choline, tris(hydroxymethyl)aminomethane, triethylamine, and glycine methylester were appreciably permeant with permeability ratios of 0.13--0.95. Four compounds with two charged nitrogen groups were also permeant. Molecular models of the permeant ions suggest that the smallest cross-section of the open pore must be at least as large as a square, 6.5 A x 6.5 A. Specific chemical factors seem to be less important than access or friction in determining the ionic selectivity of the endplate channel. PMID:6247422

The Permeability of the Sodium Channel to Metal Cations in Myelinated Nerve

PubMed Central

Hille, Bertil

1972-01-01

The relative permeability of sodium channels to eight metal cations is studied in myelinated nerve fibers. Ionic currents under voltage-clamp conditions are measured in Na-free solutions containing the test ion. Measured reversal potentials and the Goldman equation are used to calculate the permeability sequence: Na+ ≈ Li+ > Tl+ > K+. The ratio P K/P Na is 1/12. The permeabilities to Rb+, Cs+, Ca++, and Mg++ are too small to measure. The permeability ratios agree with observations on the squid giant axon and show that the reversal potential E Na differs significantly from the Nernst potential for Na+ in normal axons. Opening and closing rates for sodium channels are relatively insensitive to the ionic composition of the bathing medium, implying that gating is a structural property of the channel rather than a result of the movement or accumulation of particular ions around the channel. A previously proposed pore model of the channel accommodates the permeant metal cations in a partly hydrated form. The observed sequence of permeabilities follows the order expected for binding to a high field strength anion in Eisenman's theory of ion exchange equilibria. PMID:5025743

Divalent cations potentiate TRPV1 channel by lowering the heat activation threshold

PubMed Central

Cao, Xu; Ma, Linlin; Yang, Fan

2014-01-01

Transient receptor potential vanilloid type 1 (TRPV1) channel responds to a wide spectrum of physical and chemical stimuli. In doing so, it serves as a polymodal cellular sensor for temperature change and pain. Many chemicals are known to strongly potentiate TRPV1 activation, though how this is achieved remains unclear. In this study we investigated the molecular mechanism underlying the gating effects of divalent cations Mg2+ and Ba2+. Using a combination of fluorescence imaging and patch-clamp analysis, we found that these cations potentiate TRPV1 gating by most likely promoting the heat activation process. Mg2+ substantially lowers the activation threshold temperature; as a result, a significant fraction of channels are heat-activated at room temperature. Although Mg2+ also potentiates capsaicin- and voltage-dependent activation, these processes were found either to be not required (in the case of capsaicin) or insufficient (in the case of voltage) to mediate the activating effect. In support of a selective effect on heat activation, Mg2+ and Ba2+ cause a Ca2+-independent desensitization that specifically prevents heat-induced channel activation but does not prevent capsaicin-induced activation. These results can be satisfactorily explained within an allosteric gating framework in which divalent cations strongly promote the heat-dependent conformational change or its coupling to channel activation, which is further coupled to the voltage- and capsaicin-dependent processes. PMID:24344247

Fragmentation of tetrahydrofuran molecules by H(+), C(+), and O(+) collisions at the incident energy range of 25-1000 eV.

PubMed

Wasowicz, Tomasz J; Pranszke, Bogusław

2015-01-29

We have studied fragmentation processes of the gas-phase tetrahydrofuran (THF) molecules in collisions with the H(+), C(+), and O(+) cations. The collision energies have been varied between 25 and 1000 eV and thus covered a velocity range from 10 to 440 km/s. The following excited neutral fragments of THF have been observed: the atomic hydrogen H(n), n = 4-9, carbon atoms in the 2p3s (1)P1, 2p4p (1)D2, and 2p4p (3)P states and vibrationally and rotationally excited diatomic CH fragments in the A(2)Δ and B(2)Σ(-) states. Fragmentation yields of these excited fragments have been measured as functions of the projectile energy (velocity). Our results show that the fragmentation mechanism depends on the projectile cations and is dominated by electron transfer from tetrahydrofuran molecules to cations. It has been additionally hypothesized that in the C(+)+THF collisions a [C-C4H8O](+) complex is formed prior to dissociation. The possible reaction channels involved in fragmentation of THF under the H(+), C(+), and O(+) cations impact are also discussed.

The Kinetics and the Permeation Properties of Piezo Channels.

PubMed

Gnanasambandam, R; Gottlieb, P A; Sachs, F

2017-01-01

Piezo channels are eukaryotic, cation-selective mechanosensitive channels (MSCs), which show rapid activation and voltage-dependent inactivation. The kinetics of these channels are largely consistent across multiple cell types and different stimulation paradigms with some minor variability. No accessory subunits that associate with Piezo channels have been reported. They are homotrimers and each ∼300kD monomer has an N-terminal propeller blade-like mechanosensing module, which can confer mechanosensing capabilities on ASIC-1 (the trimeric non-MSC, acid-sensing ion channel-1) and a C-terminal pore module, which influences conductance, selectivity, and channel inactivation. Repeated stimulation can cause domain fracture and diffusion of these channels leading to synchronous loss of inactivation. The reconstituted channels spontaneously open only in asymmetric bilayers but lack inactivation. Mutations that cause hereditary xerocytosis alter PIEZO1 kinetics. The kinetics of the wild-type PIEZO1 and alterations thereof in mutants (M2225R, R2456K, and DhPIEZO1) are summarized in the form of a quantitative model and hosted online. The pore is permeable to alkali ions although Li + permeates poorly. Divalent cations, notably Ca 2+ , traverse the channel and inhibit the flux of monovalents. The large monovalent organic cations such as tetramethyl ammonium and tetraethyl ammonium can traverse the channel, but slowly, suggesting a pore diameter of ∼8Å, and the estimated in-plane area change upon opening is around 6-20nm 2 . Ruthenium red can enter the channel only from the extracellular side and seems to bind in a pocket close to residue 2496. Copyright © 2017 Elsevier Inc. All rights reserved.

Early markers of retinal degeneration in rd/rd mice.

PubMed

Acosta, Monica L; Fletcher, Erica L; Azizoglu, Serap; Foster, Lisa E; Farber, Debora B; Kalloniatis, Michael

2005-09-06

In the rd/rd mouse, the cell death of rod photoreceptors has been correlated to abnormal levels of the cyclic nucleotide cGMP within photoreceptors. Given that cGMP is required for opening of the cationic channels, there is the possibility that a high cGMP concentration would maintain these channels open, at a high energy cost for the retina. We investigated whether cation channels were maintained in an open state in the rd/rd mouse retina by determining the labeling pattern of an organic cationic probe (agmatine, AGB) which selectively enters cells through open cationic channels. The metabolic activity of the rd/rd mice was measured by assaying lactate dehydrogenase (LDH) activity in several tissues and Na+/K+ ATPase activity was measured as a function of development and degeneration of the retina. AGB neuronal labeling showed a systematic increase consistent with the known neuronal functional maturation in the normal retina. There was a significant higher AGB labeling of photoreceptors in the rd/rd mouse retina from P6 supporting the possibility of open cationic channels from an early age. There were no changes in the LDH activity of tissues that contain PDE6 or that have a similar LDH distribution as the retina. However, LDH activity was significantly higher in the rd/rd mouse retina than in those of control mice from birth to P6, and it dramatically decreased from P9 as the photoreceptors degenerated. The predominant LDH isoenzyme changes and loss after degeneration appeared to be LDH5. ATPase activity increased with age, reaching adult levels by P16. Unlike LDH activity, there was no significant difference in Na+/K+ ATPase activity between control and rd/rd mice at any age examined. We conclude that AGB is a useful marker of photoreceptors destined to degenerate. We discard the possibility of a generalized metabolic effect in the rd/rd mice. However, the elevated LDH activity present before photoreceptor differentiation indicated altered retinal metabolic activity that could not be associated with open cationic channels alone. Therefore, altered metabolic activity as indicated by LDH measurements in the retina appeared to be the earliest sensitive sign of future photoreceptor dysfunction in the rd/rd mice.

TMEM16A Channels Contribute to the Myogenic Response in Cerebral Arteries

PubMed Central

Bulley, Simon; Neeb, Zachary P.; Burris, Sarah K.; Bannister, John P.; Thomas-Gatewood, Candice M.; Jangsangthong, Wanchana; Jaggar, Jonathan H.

2013-01-01

Rationale Pressure-induced arterial depolarization and constriction (the myogenic response), is a smooth muscle cell (myocyte)-specific mechanism that controls regional organ blood flow and systemic blood pressure. Several different non-selective cation channels contribute to pressure-induced depolarization, but signaling mechanisms involved are unclear. Similarly uncertain is the contribution of anion channels to the myogenic response and physiological functions and mechanisms of regulation of recently discovered transmembrane 16A (TMEM16A) chloride (Cl−) channels in arterial myocytes. Objective Investigate the hypothesis that myocyte TMEM16A channels control membrane potential and contractility and contribute to the myogenic response in cerebral arteries. Methods and Results Cell swelling induced by hyposmotic bath solution stimulated Cl− currents in arterial myocytes that were blocked by TMEM16A channel inhibitory antibodies, RNAi-mediated selective TMEM16A channel knockdown, removal of extracellular calcium (Ca2+), replacement of intracellular EGTA with BAPTA, a fast Ca2+ chelator, and Gd3+ and SKF-96365, non-selective cation channel blockers. In contrast, nimodipine, a voltage-dependent Ca2+ channel inhibitor, or thapsigargin, which depletes intracellular Ca2+ stores, did not alter swelling-activated TMEM16A currents. Pressure (−40 mmHg)-induced membrane stretch activated ion channels in arterial myocyte cell-attached patches that were inhibited by TMEM16A antibodies and were of similar amplitude to recombinant TMEM16A channels. TMEM16A knockdown reduced intravascular pressure-induced depolarization and vasoconstriction, but did not alter depolarization (60 mmol/L K+)-induced vasoconstriction. Conclusions Membrane stretch activates arterial myocyte TMEM16A channels, leading to membrane depolarization and vasoconstriction. Data also provide a mechanism by which a local Ca2+ signal generated by non-selective cation channels stimulates TMEM16A channels to induce myogenic constriction. PMID:22872152

Cation–cation interactions and cation exchange in a series of isostructural framework uranyl tungstates

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

Balboni, Enrica; Burns, Peter C., E-mail: pburns@nd.edu; Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556

2014-05-01

The isotypical compounds (UO{sub 2}){sub 3}(WO{sub 6})(H{sub 2}O){sub 5} (1), Ag(UO{sub 2}){sub 3}(WO{sub 6})(OH)(H{sub 2}O){sub 3} (2), K(UO{sub 2}){sub 3}(WO{sub 6})OH(H{sub 2}O){sub 4} (3), Rb(UO{sub 2}){sub 3}(WO{sub 6})(OH)(H{sub 2}O){sub 3.5} (4), and Cs(UO{sub 2}){sub 3}(WO{sub 6})OH(H{sub 2}O){sub 3} (5) were synthesized, characterized, and their structures determined. Each crystallizes in space group Cc. (1): a=12.979 (3), b=10.238 (2), c=11.302 (2), β=102.044 (2); (2): a=13.148 (2), b=9.520 (1), c=11.083 (2), β=101.568 (2); (3): a=13.111 (8), b=9.930 (6), c=11.242 (7), β=101.024 (7); (4): a=12.940 (2), b=10.231 (2), c=11.259(2), β=102.205 (2); (5): a=12.983 (3), b=10.191 (3), c=11.263 (4), β=101.661 (4). Compounds 1–5 are amore » framework of uranyl and tungsten polyhedra containing cation–cation interactions. The framework has three symmetrically distinct U(VI) cations, one tungsten, sixteen to eighteen oxygen atoms, and in 2–5, one monovalent cation. Each atom occupies a general position. Each U(VI) cation is present as a typical (UO{sub 2}){sup 2+} uranyl ion in an overall pentagonal bipyramidal coordination environment. Each pentagonal bipyramid shares two equatorial edges with two other pentagonal bipyramids, forming a trimer. Trimers are connected into chains by edge-sharing with WO{sub 6} octahedra. Chains are linked through cation–cation interactions between two symmetrically independent uranyl ions. This yields a remarkably complex system of intersecting channels that extend along [0 0 1] and [−1 1 0]. The cation exchange properties of 2 and 3 were characterized at room temperature and at 140 °C. - Graphical abstract: Chains of uranium and tungsten polyhedra are connected into a three dimensional framework by cation–cation interactions occurring between two symmetrically independent uranyl pentagonal bipyramids. Monovalent cations present in channels within the structure can be exchanged by room temperature or mild hydrothermal treatments. The framework of these compounds is robust to cation exchange and heat. (yellow polyhedra=uranium pentagonal bipyramids; blue polyhedra=tungsten octahedral, purple balls=K; yellow balls=Na; grey balls=Tl). - Highlights: • Five isostructural uranyl tungstates compounds were synthesized hydrothermally. • The structures consist of a chains of uranium and tungstate polyhedral. • Chains are connected into a framework by cation–cation interactions. • Cation exchange does not alter the structural integrity of the compounds. • Cation exchange was successful at room temperature and mild hydrothermal conditions.« less

Induction of divalent cation permeability by heterologous expression of a voltage sensor domain.

PubMed

Arima, Hiroki; Tsutsui, Hidekazu; Sakamoto, Ayako; Yoshida, Manabu; Okamura, Yasushi

2018-01-06

The voltage sensor domain (VSD) is a protein domain that confers sensitivity to membrane potential in voltage-gated ion channels as well as the voltage-sensing phosphatase. Although VSDs have long been considered to function as regulatory units acting on adjacent effectors, recent studies have revealed the existence of direct ion permeation paths in some mutated VSDs and in the voltage-gated proton channel. In this study, we show that calcium currents are evoked upon membrane hyperpolarization in cells expressing a VSD derived from an ascidian voltage-gated ion channel superfamily. Unlike the previously reported omega-pore in the Shaker K + channel and rNav1.4, mutations are not required. From electrophysiological experiments in heterologous expression systems, we found that the conductance is directly mediated by the VSD itself and is carried by both monovalent and divalent cations. This is the first report of divalent cation permeation through a VSD-like structure. Copyright © 2018 Elsevier B.V. All rights reserved.

Lysine and the Na+/K+ Selectivity in Mammalian Voltage-Gated Sodium Channels.

PubMed

Li, Yang; Liu, Huihui; Xia, Mengdie; Gong, Haipeng

2016-01-01

Voltage-gated sodium (Nav) channels are critical in the generation and transmission of neuronal signals in mammals. The crystal structures of several prokaryotic Nav channels determined in recent years inspire the mechanistic studies on their selection upon the permeable cations (especially between Na+ and K+ ions), a property that is proposed to be mainly determined by residues in the selectivity filter. However, the mechanism of cation selection in mammalian Nav channels lacks direct explanation at atomic level due to the difference in amino acid sequences between mammalian and prokaryotic Nav homologues, especially at the constriction site where the DEKA motif has been identified to determine the Na+/K+ selectivity in mammalian Nav channels but is completely absent in the prokaryotic counterparts. Among the DEKA residues, Lys is of the most importance since its mutation to Arg abolishes the Na+/K+ selectivity. In this work, we modeled the pore domain of mammalian Nav channels by mutating the four residues at the constriction site of a prokaryotic Nav channel (NavRh) to DEKA, and then mechanistically investigated the contribution of Lys in cation selection using molecular dynamics simulations. The DERA mutant was generated as a comparison to understand the loss of ion selectivity caused by the K-to-R mutation. Simulations and free energy calculations on the mutants indicate that Lys facilitates Na+/K+ selection by electrostatically repelling the cation to a highly Na+-selective location sandwiched by the carboxylate groups of Asp and Glu at the constriction site. In contrast, the electrostatic repulsion is substantially weakened when Lys is mutated to Arg, because of two intrinsic properties of the Arg side chain: the planar geometric design and the sparse charge distribution of the guanidine group.

The permeability of the cGMP-activated channel to organic cations in retinal rods of the tiger salamander.

PubMed Central

Picco, C; Menini, A

1993-01-01

1. The permeability of the channel activated by guanosine 3',5'-cyclic monophosphate (cGMP) to many organic monovalent cations was determined by recording macroscopic currents in excised inside-out patches of plasma membrane from isolated retinal rod outer segments of the tiger salamander. 2. Current-voltage relations were measured when the NaCl of the bathing medium was replaced by salts of organic cations. Permeability ratios relative to Na+ ions were calculated with the Goldman-Hodgkin-Katz potential equation from the measured changes of reversal potentials. 3. Hydroxylammonium+, hydrazinium+ and methylammonium+, which are molecules of very similar shape and size, permeate the channel with very different permeability ratios: 5.92, 1.99 and 0.60 respectively. 4. Methylated and ethylated ammonium+ compounds were investigated. It was found that, not only methylammonium+, but also dimethylammonium+ and ethylammonium+ were permeant with permeability ratios of 0.6, 0.14 and 0.16 respectively. Trimethylammonium+, tetramethylammonium+, diethylammonium+, triethylammonium+, and tetraethylammonium+ were not permeant. 5. Guanidinium+ and its derivatives formamidinium+, aminoguanidinium+, acetamidinium+ and methylguanidinium+ were all permeant with permeability ratios 1.12, 1.00, 0.63, 0.36 and 0.33 respectively. 6. The cGMP-activated channel was found to be permeable to at least thirteen organic cations. Molecular models of the permeant cations indicate that the cross-section of the narrowest part of the pore must be at least as large as a rectangle of 0.38 x 0.5 nm dimensions. PMID:7683718

Ultrasound enhances in vivo tumor expression of plasmid DNA by PEG-introduced cationized dextran.

PubMed

Hosseinkhani, Hossein; Tabata, Yasuhiko

2005-11-28

This study is an investigation to experimentally confirm whether or not ultrasound (US) irradiation is effective in enhancing the in vivo gene expression of plasmid DNA in tumor. Dextran was cationized by introducing spermine to the hydroxyl groups to allow to polyionically complex with a plasmid DNA. The cationized dextran prepared was additionally modified with poly(ethylene glycol) (PEG) molecules which have an active ester and methoxy groups at each terminal, to obtain cationized dextran with different percentages of PEG introduced. Various cationized dextrans with or without PEG introduction were mixed with a plasmid DNA of LacZ to form cationized dextran-plasmid DNA complexes. Electrophoretical examination revealed that the plasmid DNA was complexed both with the cationized dextran and PEG-introduced cationized dextran, irrespective of the PEG introduction percentage, although the higher N/P ratio was needed for plasmid DNA complexation with the latter. By complexation with the cationized dextran, the zeta potential of plasmid DNA was changed to be positive. The charge of PEG-introduced cationized dextran-plasmid DNA complexes became close to 0 mV as their percentage of PEG introduced increased, although the molecular size was about 250 nm, irrespective of the PEG introduction. When cationized dextran-plasmid DNA complexes with or without PEG introduction were intravenously injected to mice carrying a subcutaneous Meth-AR-1 fibrosarcoma mass and the subsequent US irradiation to the tumor mass percutaneously, the PEG-introduced cationized dextran-plasmid DNA complex plus US irradiation enhanced the tumor level of gene expression to a significantly high extent compared with the cationized dextran-plasmid DNA complex and free plasmid DNA with or without US irradiation. The enhanced level depended on the time period and timing of US irradiation. Fluorescent microscopic studies revealed that the localization of plasmid DNA and the gene expression were observed in the tumor tissue injected with the PEG-introduced cationized dextran-plasmid DNA complex plus the subsequent US irradiation. We conclude that complexation with the PEG-introduced cationized dextran combined with US irradiation is a promising way to target the plasmid DNA to the tumor for gene expression.

PEGylation enhances tumor targeting of plasmid DNA by an artificial cationized protein with repeated RGD sequences, Pronectin.

PubMed

Hosseinkhani, Hossein; Tabata, Yasuhiko

2004-05-31

The objective of this study is to investigate feasibility of a non-viral gene carrier with repeated RGD sequences (Pronectin F+) in tumor targeting for gene expression. The Pronectin F+ was cationized by introducing spermine (Sm) to the hydroxyl groups to allow to polyionically complex with plasmid DNA. The cationized Pronectin F+ prepared was additionally modified with poly(ethylene glycol) (PEG) molecules which have active ester and methoxy groups at the terminal, to form various PEG-introduced cationized Pronectin F+. The cationized Pronectin F+ with or without PEGylation at different extents was mixed with a plasmid DNA of LacZ to form respective cationized Pronectin F+-plasmid DNA complexes. The plasmid DNA was electrophoretically complexed with cationized Pronectin F+ and PEG-introduced cationized Pronectin F+, irrespective of the PEGylation extent, although the higher N/P ratio of complexes was needed for complexation with the latter Pronectin F+. The molecular size and zeta potential measurements revealed that the plasmid DNA was reduced in size to about 250 nm and the charge was changed to be positive by the complexation with cationized Pronectin F+. For the complexation with PEG-introduced cationized Pronectin F+, the charge of complex became neutral being almost 0 mV with the increasing PEGylation extents, while the molecular size was similar to that of cationized Pronectin F+. When cationized Pronectin F+-plasmid DNA complexes with or without PEGylation were intravenously injected to mice carrying a subcutaneous Meth-AR-1 fibrosarcoma mass, the PEG-introduced cationized Pronectin F+-plasmid DNA complex specifically enhanced the level of gene expression in the tumor, to a significantly high extent compared with the cationized Pronectin F+-plasmid DNA complexes and free plasmid DNA. The enhanced level of gene expression depended on the percentage of PEG introduced, the N/P ratio, and the plasmid DNA dose. A fluorescent microscopic study revealed that the localization of plasmid DNA in the tumor tissue was observed only for the PEG-introduced cationized Pronectin F+-plasmid DNA complex injected. We conclude that the PEGylation of cationized Pronectin F+ is a promising way to enable the plasmid DNA to target to the tumor for gene expression. Coyright 2004 Elsevier B.V.

Receptor heteromeric assembly-how it works and why it matters: the case of ionotropic glutamate receptors.

PubMed

Herguedas, Beatriz; Krieger, James; Greger, Ingo H

2013-01-01

The composition and spatial arrangement of subunits in ion channels are essential for their function. Diverse stoichiometries are possible in a multitude of channels. These depend upon cell type-specific subunit expression, which can be tuned in a developmentally regulated manner and in response to activity, on subunit stability in the endoplasmic reticulum, intersubunit affinities, and potentially subunit diffusion within the ER membrane. In concert, these parameters shape channel biogenesis and ultimately tune cellular response properties. The complexity of this assembly process is particularly well illustrated by the ionotropic glutamate receptors, the main mediators of excitatory neurotransmission. These tetrameric cation channels predominantly assemble into heteromers, which is "obligatory" for some iGluR subfamilies but "preferential" for others. Here, we discuss recent insights into the rules underlying these two pathways, the role of individual domains based on an ever increasing list of crystal structures, and how these assembly parameters tune assembly across diverse receptor oligomers. Copyright © 2013 Elsevier Inc. All rights reserved.

Substance P modulation of TRPC3/7 channels improves respiratory rhythm regularity and ICAN-dependent pacemaker activity.

PubMed

Ben-Mabrouk, Faiza; Tryba, Andrew K

2010-04-01

Neuromodulators, such as substance P (SubP), play an important role in modulating many rhythmic activities driven by central pattern generators (e.g. locomotion, respiration). However, the mechanism by which SubP enhances breathing regularity has not been determined. Here, we used mouse brainstem slices containing the pre-Bötzinger complex to demonstrate, for the first time, that SubP activates transient receptor protein canonical (TRPC) channels to enhance respiratory rhythm regularity. Moreover, SubP enhancement of network regularity is accomplished via selective enhancement of ICAN (inward non-specific cation current)-dependent intrinsic bursting properties. In contrast to INaP (persistent sodium current)-dependent pacemakers, ICAN-dependent pacemaker bursting activity is TRPC-dependent. Western Blots reveal TRPC3 and TRPC7 channels are expressed in rhythmically active ventral respiratory group island preparations. Taken together, these data suggest that SubP-mediated activation of TRPC3/7 channels underlies rhythmic ICAN-dependent pacemaker activity and enhances the regularity of respiratory rhythm activity.

Knockout of the ASIC2 channel in mice does not impair cutaneous mechanosensation, visceral mechanonociception and hearing

PubMed Central

Roza, Carolina; Puel, Jean-Luc; Kress, Michaela; Baron, Anne; Diochot, Sylvie; Lazdunski, Michel; Waldmann, Rainer

2004-01-01

Mechanosensitive cation channels are thought to be crucial for different aspects of mechanoperception, such as hearing and touch sensation. In the nematode C. elegans, the degenerins MEC-4 and MEC-10 are involved in mechanosensation and were proposed to form mechanosensitive cation channels. Mammalian degenerin homologues, the H+-gated ASIC channels, are expressed in sensory neurones and are therefore interesting candidates for mammalian mechanosensors. We investigated the effect of an ASIC2 gene knockout in mice on hearing and on cutaneous mechanosensation and visceral mechanonociception. However, our data do not support a role of ASIC2 in those facets of mechanoperception. PMID:15169849

NMR studies of cation transport across membranes

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

Shochet, N.R.

1985-01-01

/sup 23/Na NMR Studies of cation transport across membranes were conducted both on model and biological membranes. Two ionophores, the carrier monensin and the channel-former gramicidin, were chosen to induce cation transport in large unilamellar phosphatidylcholine vesicles. The distinction between the NMR signals arising from the two sides of the membrane was achieved by the addition of an anionic paramagnetic shift reagent to the outer solution. The kinetics of the cation transport across the membrane was observed simultaneously monitoring the changes in the /sup 23/Na NMR signals of both compartments. Two mathematical models were developed for the estimation of themore » transport parameters of the monensin- and gramicidin-induced cation transport. The models were able to fit the experimental data very well. A new method for the estimation of the volume trapped inside the vesicles was developed. The method uses the relative areas of the intra- and extravesicular NMR signals arising from a suspension of vesicles bathed in the same medium they contain, as a measure for the relative volumes of these compartments. Sodium transport across biological membranes was studied by /sup 23/ NMR, using suspensions of cultured nerve cells. The sodium influx through voltage-gated channels was studied using the channel modifier batrachotoxin in combination with scorpion toxin.« less

Riparian soil development linked to forest succession above and below dams along the Elwha River, Washington, USA

USGS Publications Warehouse

Perry, Laura G; Shafroth, Patrick B.; Perakis, Steven

2017-01-01

Riparian forest soils can be highly dynamic, due to frequent fluvial disturbance, erosion, and sediment deposition, but effects of dams on riparian soils are poorly understood. We examined soils along toposequences within three river segments located upstream, between, and downstream of two dams on the Elwha River to evaluate relationships between riparian soil development and forest age, succession, and channel proximity, explore dam effects on riparian soils, and provide a baseline for the largest dam removal in history. We found that older, later-successional forests and geomorphic surfaces contained soils with finer texture and greater depth to cobble, supporting greater forest floor mass, mineral soil nutrient levels, and cation exchange. Forest stand age was a better predictor than channel proximity for many soil characteristics, though elevation and distance from the channel were often also important, highlighting how complex interactions between fluvial disturbance, sediment deposition, and biotic retention regulate soil development in this ecosystem. Soils between the dams, and to a lesser extent below the lower dam, had finer textures and higher mineral soil carbon, nitrogen, and cation exchange than above the dams. These results suggested that decreased fluvial disturbance below the dams, due to reduced sediment supply and channel stabilization, accelerated soil development. In addition, reduced sediment supply below the dams may have decreased soil phosphorus. Soil δ15N suggested that salmon exclusion by the dams had no discernable effect on nitrogen inputs to upstream soils. Recent dam removal may alter riparian soils further, with ongoing implications for riparian ecosystems.

Effect of Vibrio parahaemolyticus haemolysin on human erythrocytes.

PubMed

Lang, Philipp A; Kaiser, Stephanie; Myssina, Swetlana; Birka, Christina; Weinstock, Christof; Northoff, Hinnak; Wieder, Thomas; Lang, Florian; Huber, Stephan M

2004-04-01

Haemolysin Kanagawa, a toxin from Vibrio parahaemolyticus, is known to trigger haemolysis. Flux studies indicated that haemolysin forms a cation channel. In the present study, channel properties were elucidated by patch clamp and functional significance of ion fluxes by fluorescence-activated cell sorting (FACS) analysis. Treatment of human erythrocytes with 1 U ml-1 haemolysin within minutes induces a non-selective cation permeability. Moreover, haemolysin activates clotrimazole-sensitive K+ channels, pointing to stimulation of Ca2+-sensitive Gardos channels. Haemolysin (1 U ml-1) leads within 5 min to slight cell shrinkage, which is reversed in Ca2+-free saline. Erythrocytes treated with haemolysin (0.1 U ml-1) do not undergo significant haemolysis within the first 60 min. Replacement of extracellular Na+ with NMDG+ leads to slight cell shrinkage, which is potentiated by 0.1 U ml-1 haemolysin. According to annexin binding, treatment of erythrocytes with 0.1 U ml-1 haemolysin leads within 30 min to breakdown of phosphatidylserine asymmetry of the cell membrane, a typical feature of erythrocyte apoptosis. The annexin binding is significantly blunted at increased extracellular K+ concentrations and by K+ channel blocker clotrimazole. In conclusion, haemolysin Kanagawa induces cation permeability and activates endogenous Gardos K+ channels. Consequences include breakdown of phosphatidylserine asymmetry, which depends at least partially on cellular loss of K+.

A theoretical study of complexes formed between cations and curved aromatic systems: electrostatics does not always control cation-π interaction.

PubMed

Carrazana-García, Jorge A; Cabaleiro-Lago, Enrique M; Rodríguez-Otero, Jesús

2017-04-19

The present work studies the interaction of two extended curved π-systems (corannulene and sumanene) with various cations (sodium, potassium, ammonium, tetramethylammonium, guanidinium and imidazolium). Polyatomic cations are models of groups found in important biomolecules in which cation-π interaction plays a fundamental role. The results indicate an important size effect: with extended π systems and cations of the size of potassium and larger, dispersion is much more important than has been generally recognized for cation-π interactions. In most of the systems studied here, the stability of the cation-π complexes is the result of a balanced combination of electrostatic, induction and dispersion contributions. None of the systems studied here owes its stability to the electrostatic interaction more than 42%. Induction dominates stabilization in complexes with sodium, and in some of the potassium and ammonium complexes. In complexes with large cations and with flat cations dispersion is the major stabilizing contribution and can provide more than 50% of the stabilization energy. This implies that theoretical studies of the cation-π interaction involving large or even medium-size fragments require a level of calculation capable of properly modelling dispersion. The separation between the cation and the π system is another important factor to take into account, especially when the fragments of the cation-π complex are bound (for example, to a protein backbone) and cannot interact at the most favourable distance.

Strong activation of bile acid-sensitive ion channel (BASIC) by ursodeoxycholic acid

PubMed Central

Wiemuth, Dominik; Sahin, Hacer; Lefèvre, Cathérine M.T.; Wasmuth, Hermann E.; Gründer, Stefan

2013-01-01

Bile acid-sensitive ion channel (BASIC) is a member of the DEG/ENaC gene family of unknown function. Rat BASIC (rBASIC) is inactive at rest. We have recently shown that cholangiocytes, the epithelial cells lining the bile ducts, are the main site of BASIC expression in the liver and identified bile acids, in particular hyo- and chenodeoxycholic acid, as agonists of rBASIC. Moreover, it seems that extracellular divalent cations stabilize the resting state of rBASIC, because removal of extracellular divalent cations opens the channel. In this addendum, we demonstrate that removal of extracellular divalent cations potentiates the activation of rBASIC by bile acids, suggesting an allosteric mechanism. Furthermore, we show that rBASIC is strongly activated by the anticholestatic bile acid ursodeoxycholic acid (UDCA), suggesting that BASIC might mediate part of the therapeutic effects of UDCA. PMID:23064163

Ion Channels in Innate and Adaptive Immunity

PubMed Central

Feske, Stefan; Wulff, Heike; Skolnik, Edward Y.

2016-01-01

Ion channels and transporters mediate the transport of charged ions across hydrophobic lipid membranes. In immune cells, divalent cations such as calcium, magnesium, and zinc have important roles as second messengers to regulate intracellular signaling pathways. By contrast, monovalent cations such as sodium and potassium mainly regulate the membrane potential, which indirectly controls the influx of calcium and immune cell signaling. Studies investigating human patients with mutations in ion channels and transporters, analysis of gene-targeted mice, or pharmacological experiments with ion channel inhibitors have revealed important roles of ionic signals in lymphocyte development and in innate and adaptive immune responses. We here review the mechanisms underlying the function of ion channels and transporters in lymphocytes and innate immune cells and discuss their roles in lymphocyte development, adaptive and innate immune responses, and autoimmunity, as well as recent efforts to develop pharmacological inhibitors of ion channels for immunomodulatory therapy. PMID:25861976

VUV photoionization and dissociative photoionization of the prebiotic molecule acetyl cyanide: Theory and experiment

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

Bellili, A.; Hochlaf, M., E-mail: hochlaf@univ-mlv.fr, E-mail: martin.schwell@lisa.u-pec.fr; Schwell, M., E-mail: hochlaf@univ-mlv.fr, E-mail: martin.schwell@lisa.u-pec.fr

2014-10-07

The present combined theoretical and experimental investigation concerns the single photoionization of gas-phase acetyl cyanide and the fragmentation pathways of the resulting cation. Acetyl cyanide (AC) is inspired from both the chemistry of cyanoacetylene and the Strecker reaction which are thought to be at the origin of medium sized prebiotic molecules in the interstellar medium. AC can be formed by reaction from cyanoacetylene and water but also from acetaldehyde and HCN or the corresponding radicals. In view of the interpretation of vacuum ultraviolet (VUV) experimental data obtained using synchrotron radiation, we explored the ground potential energy surface (PES) of acetylmore » cyanide and of its cation using standard and recently implemented explicitly correlated methodologies. Our PES covers the regions of tautomerism (between keto and enol forms) and of the lowest fragmentation channels. This allowed us to deduce accurate thermochemical data for this astrobiologically relevant molecule. Unimolecular decomposition of the AC cation turns out to be very complex. The implications for the evolution of prebiotic molecules under VUV irradiation are discussed.« less

TRPV2.

PubMed

Kojima, Itaru; Nagasawa, Masahiro

2014-01-01

Transient receptor potential vanilloid type 2, TRPV2, is a calcium-permeable cation channel belonging to the TRPV channel family. This channel is activated by heat (>52 °C), various ligands, and mechanical stresses. In most of the cells, a large portion of TRPV2 is located in the endoplasmic reticulum under unstimulated conditions. Upon stimulation of the cells with phosphatidylinositol 3-kinase-activating ligands, TRPV2 is translocated to the plasma membrane and functions as a cation channel. Mechanical stress may also induce translocation of TRPV2 to the plasma membrane. The expression of TRPV2 is high in some types of cells including neurons, neuroendocrine cells, immune cells involved in innate immunity, and certain types of cancer cells. TRPV2 may modulate various cellular functions in these cells.

Modulation of mechanosensitive calcium-selective cation channels by temperature

NASA Technical Reports Server (NTRS)

Ding, J. P.; Pickard, B. G.

1993-01-01

Gating of associations of mechanosensitive Ca(2+)-selective cation co-channels in the plasmalemma of onion epidermis has a strong and unusual temperature dependence. Tension-dependent activity rises steeply as temperature is lowered from 25 degrees C to about 6 degrees C, but drops to a low level at about 5 degrees C. Under the conditions tested (with Mg2+ and K+ at the cytosolic face of outside-out membrane patches), promotion results both from more bursting at all observed linkage levels and from longer duration of bursts of co-channels linked as quadruplets and quintuplets. Co-channel conductance decreases linearly, but only modestly, with declining temperature. It is proposed that these and related mechanosensitive channels may participate in a variety of responses to temperature, including thermonasty, thermotropism, hydrotropism, and both cold damage and cold acclimation.

Cation-π interaction of the univalent sodium cation with [2.2.2]paracyclophane: Experimental and theoretical study

NASA Astrophysics Data System (ADS)

Makrlík, Emanuel; Sýkora, David; Böhm, Stanislav; Vaňura, Petr

2018-02-01

By employing electrospray ionization mass spectrometry (ESI-MS), it was proven experimentally that the univalent sodium cation (Na+) forms with [2.2.2]paracyclophane (C24H24) the cationic complex [Na(C24H24)]+. Further, applying quantum chemical DFT calculations, the most probable structure of the [Na(C24H24)]+ complex was derived. In the resulting complex with a symmetry very close to C3, the "central" cation Na+, fully located in the cavity of the parent [2.2.2]paracyclophane ligand, is bound to all three benzene rings of [2.2.2]paracyclophane via cation-π interaction. Finally, the interaction energy, E(int), of the considered cation-π complex [Na(C24H24)]+ was found to be -267.3 kJ/mol, confirming the formation of this fascinating complex species as well.

A Change in the Ion Selectivity of Ligand-Gated Ion Channels Provides a Mechanism to Switch Behavior.

PubMed

Pirri, Jennifer K; Rayes, Diego; Alkema, Mark J

2015-01-01

Behavioral output of neural networks depends on a delicate balance between excitatory and inhibitory synaptic connections. However, it is not known whether network formation and stability is constrained by the sign of synaptic connections between neurons within the network. Here we show that switching the sign of a synapse within a neural circuit can reverse the behavioral output. The inhibitory tyramine-gated chloride channel, LGC-55, induces head relaxation and inhibits forward locomotion during the Caenorhabditis elegans escape response. We switched the ion selectivity of an inhibitory LGC-55 anion channel to an excitatory LGC-55 cation channel. The engineered cation channel is properly trafficked in the native neural circuit and results in behavioral responses that are opposite to those produced by activation of the LGC-55 anion channel. Our findings indicate that switches in ion selectivity of ligand-gated ion channels (LGICs) do not affect network connectivity or stability and may provide an evolutionary and a synthetic mechanism to change behavior.

Permeation and block of TRPV1 channels by the cationic lidocaine derivative QX-314

PubMed Central

Puopolo, Michelino; Binshtok, Alexander M.; Yao, Gui-Lan; Oh, Seog Bae; Woolf, Clifford J.

2013-01-01

QX-314 (N-ethyl-lidocaine) is a cationic lidocaine derivative that blocks voltage-dependent sodium channels when applied internally to axons or neuronal cell bodies. Coapplication of external QX-314 with the transient receptor potential vanilloid 1 protein (TRPV1) agonist capsaicin produces long-lasting sodium channel inhibition in TRPV1-expressing neurons, suggestive of QX-314 entry into the neurons. We asked whether QX-314 entry occurs directly through TRPV1 channels or through a different pathway (e.g., pannexin channels) activated downstream of TRPV1 and whether QX-314 entry requires the phenomenon of “pore dilation” previously reported for TRPV1. With external solutions containing 10 or 20 mM QX-314 as the only cation, inward currents were activated by stimulation of both heterologously expressed and native TRPV1 channels in rat dorsal root ganglion neurons. QX-314-mediated inward current did not require pore dilation, as it activated within several seconds and in parallel with Cs-mediated outward current, with a reversal potential consistent with PQX-314/PCs = 0.12. QX-314-mediated current was no different when TRPV1 channels were expressed in C6 glioma cells, which lack expression of pannexin channels. Rapid addition of QX-314 to physiological external solutions produced instant partial inhibition of inward currents carried by sodium ions, suggesting that QX-314 is a permeant blocker. Maintained coapplication of QX-314 with capsaicin produced slowly developing reduction of outward currents carried by internal Cs, consistent with intracellular accumulation of QX-314 to concentrations of 50–100 μM. We conclude that QX-314 is directly permeant in the “standard” pore formed by TRPV1 channels and does not require either pore dilation or activation of additional downstream channels for entry. PMID:23303863

Purified ryanodine receptor from rabbit skeletal muscle is the calcium- release channel of sarcoplasmic reticulum

PubMed Central

1988-01-01

The ryanodine receptor of rabbit skeletal muscle sarcoplasmic reticulum was purified as a single 450,000-dalton polypeptide from CHAPS- solubilized triads using immunoaffinity chromatography. The purified receptor had a [3H]ryanodine-binding capacity (Bmax) of 490 pmol/mg and a binding affinity (Kd) of 7.0 nM. Using planar bilayer recording techniques, we show that the purified receptor forms cationic channels selective for divalent ions. Ryanodine receptor channels were identical to the Ca-release channels described in native sarcoplasmic reticulum using the same techniques. In the present work, four criteria were used to establish this identity: (a) activation of channels by micromolar Ca and millimolar ATP and inhibition by micromolar ruthenium red, (b) a main channel conductance of 110 +/- 10 pS in 54 mM trans Ca, (c) a long- term open state of lower unitary conductance induced by ryanodine concentrations as low as 20 nM, and (d) a permeability ratio PCa/PTris approximately equal to 14. In addition, we show that the purified ryanodine receptor channel displays a saturable conductance in both monovalent and divalent cation solutions (gamma max for K and Ca = 1 nS and 172 pS, respectively). In the absence of Ca, channels had a broad selectivity for monovalent cations, but in the presence of Ca, they were selectively permeable to Ca against K by a permeability ratio PCa/PK approximately equal to 6. Receptor channels displayed several equivalent conductance levels, which suggest an oligomeric pore structure. We conclude that the 450,000-dalton polypeptide ryanodine receptor is the Ca-release channel of the sarcoplasmic reticulum and is the target site of ruthenium red and ryanodine. PMID:2459298

Substituent and Solvent Effects on the Absorption Spectra of Cation-π Complexes of Benzene and Borazine: A Theoretical Study.

PubMed

Sarmah, Nabajit; Bhattacharyya, Pradip Kr; Bania, Kusum K

2014-05-29

Time-dependent density functional theory (TDDFT) has been used to predict the absorption spectra of cation-π complexes of benzene and borazine. Both polarized continuum model (PCM) and discrete solvation model (DSM) and a combined effect of PCM and DSM on the absorption spectra have been elucidated. With decrease in size of the cation, the π → π* transitions of benzene and borazine are found to undergo blue and red shift, respectively. A number of different substituents (both electron-withdrawing and electron-donating) and a range of solvents (nonpolar to polar) have been considered to understand the effect of substituent and solvents on the absorption spectra of the cation-π complexes of benzene and borazine. Red shift in the absorption spectra of benzene cation-π complexes are observed with both electron-donating groups (EDGs) and electron-withdrawing groups (EWGs). The same trend has not been observed in the case of substituted borazine cation-π complexes. The wavelength of the electronic transitions corresponding to cation-π complexes correlates well with the Hammet constants (σ p and σ m ). This correlation indicates that the shifting of spectral lines of the cation-π complexes on substitution is due to both resonance and inductive effect. On incorporation of solvent phases, significant red or blue shifting in the absorption spectra of the complexes has been observed. Kamlet-Taft multiparametric equation has been used to explain the effect of solvent on the absorption spectra of complexes. Polarity and polarizability are observed to play an important role in the solvatochromism of the cation-π complexes.

Sodium Fluxes through Nonselective Cation Channels in the Plasma Membrane of Protoplasts from Arabidopsis Roots1

PubMed Central

Demidchik, Vadim; Tester, Mark

2002-01-01

The aim of the present work was to characterize Na+ currents through nonselective cation channels (NSCCs) in protoplasts derived from root cells of Arabidopsis. The procedure of the protoplast isolation was modified to increase the stability of Arabidopsis root protoplasts in low external Ca2+ by digesting tissue in elevated Ca2+. Experiments in whole-cell and outside-out modes were carried out. We found that Na+ currents in Arabidopsis root protoplasts were mediated by cation channels that were insensitive to externally applied tetraethylammonium+ and verapamil, had no time-dependent activation (permanently opened or completely activated within 1–2 ms), were voltage independent, and were weakly selective for monovalent cations. The selectivity sequence was as follows: K+ (1.49) > NH4+ (1.24) > Rb+ (1.15) ≈ Cs+ (1.10) ≈ Na+ (1.00) > Li+ (0.73) > tetraethylammonium+ (0.47). Arabidopsis root NSCCs were blocked by H+ (pK ≈ 6.0), Ca2+ (K1/2 ≈ 0.1 mm), Ba2+, Zn2+, La3+, Gd3+, quinine, and the His modifier diethylpyrocarbonate. They were insensitive to most organic blockers (nifedipine, verapamil, flufenamate, and amiloride) and to the SH-group modifier p-chloromercuriphenyl sulfonic acid. Voltage-insensitive, Ca2+-sensitive single channels were also resolved. Properties of Arabidopsis root NSCCs are discussed and compared with characteristics of similar conductances studied previously in plants and animals. It is suggested that NSCCs present a distinct group of plant ion channels, mediating toxic Na+ influx to the cell and probably having other important roles in physiological processes of plants. PMID:11842142

Heavy metal cations permeate the TRPV6 epithelial cation channel.

PubMed

Kovacs, Gergely; Danko, Tamas; Bergeron, Marc J; Balazs, Bernadett; Suzuki, Yoshiro; Zsembery, Akos; Hediger, Matthias A

2011-01-01

TRPV6 belongs to the vanilloid family of the transient receptor potential channel (TRP) superfamily. This calcium-selective channel is highly expressed in the duodenum and the placenta, being responsible for calcium absorption in the body and fetus. Previous observations have suggested that TRPV6 is not only permeable to calcium but also to other divalent cations in epithelial tissues. In this study, we tested whether TRPV6 is indeed also permeable to cations such as zinc and cadmium. We found that the basal intracellular calcium concentration was higher in HEK293 cells transfected with hTRPV6 than in non-transfected cells, and that this difference almost disappeared in nominally calcium-free solution. Live cell imaging experiments with Fura-2 and NewPort Green DCF showed that overexpression of human TRPV6 increased the permeability for Ca(2+), Ba(2+), Sr(2+), Mn(2+), Zn(2+), Cd(2+), and interestingly also for La(3+) and Gd(3+). These results were confirmed using the patch clamp technique. (45)Ca uptake experiments showed that cadmium, lanthanum and gadolinium were also highly efficient inhibitors of TRPV6-mediated calcium influx at higher micromolar concentrations. Our results suggest that TRPV6 is not only involved in calcium transport but also in the transport of other divalent cations, including heavy metal ions, which may have toxicological implications. Copyright © 2010 Elsevier Ltd. All rights reserved.

Gating behavior of endoplasmic reticulum potassium channels of rat hepatocytes in diabetes.

PubMed

Ghasemi, Maedeh; Khodaei, Naser; Salari, Sajjad; Eliassi, Afsaneh; Saghiri, Reza

2014-07-01

Defects in endoplasmic reticulum homeostasis are common occurrences in different diseases, such as diabetes, in which the function of endoplasmic reticulum is disrupted. It is now well established that ion channels of endoplasmic reticulum membrane have a critical role in endoplasmic reticulum luminal homeostasis. Our previous studies showed the presence of an ATP-sensitive cationic channel in endoplasmic reticulum. Therefore, in this study, we examined and compared the activities of this channel in control and diabetic rats using single-channel recording techniques. Male Wistar rats were made diabetic for 2 weeks with a single dose injection of streptozotocin (45 mg/kg). Ion channel incorporation of rough endoplasmic reticulum of diabetic hepatocytes into the bilayer lipid membrane allowed the characterization of K+ channel. Ion channel incorporation of rough endoplasmic reticulum vesicles into the bilayer lipid revealed that the channel current-voltage (I-V) relation with a mean slope conductance of 520 ± 19 pS was unaffected in diabetes. Interestingly, the channel Po-voltage relation was significantly lower in diabetic rats at voltages above +30 mV. We concluded that the endoplasmic reticulum cationic channel is involved in diabetes. Also, this finding could be considered as a goal for further therapeutic plans.

Reversal of Ion Charge Selectivity Renders the Pentameric Ligand-Gated Ion Channel GLIC Insensitive to Anesthetics

PubMed Central

Tillman, Tommy; Cheng, Mary H.; Chen, Qiang; Tang, Pei; Xu, Yan

2014-01-01

Pentameric ligand gated ion channels (pLGICs) are a family of structurally homologous cationic and anionic channels involved in neurotransmission. Cationic members of the pLGIC family are typically inhibited by general anesthetics, while anionic members are potentiated. GLIC is a prokaryotic cationic pLGIC and can be inhibited by clinical concentrations of general anesthetics. The introduction of three mutations, Y221A (Y–3′A), E222P (E–2′P) and N224R (N0′R), at the selectivity filter and one, A237T (A13′T), at the hydrophobic gate, converted GLIC to an anion channel. The mutated GLIC (GLIC4) became insensitive to the anesthetics propofol and etomidate as well as the channel blocker picrotoxin. Molecular dynamics (MD) simulations revealed changes in the structure and dynamics of GLIC4 in comparison to GLIC, particularly in the tilting angles of the pore-lining helix (TM2) that consequently resulted in different pore radius and hydration profiles. Propofol binding to an intra-subunit site of GLIC shifted the tilting angles of TM2 towards closure at the hydrophobic gate region, consistent with propofol inhibition of GLIC. In contrast, the pore of GLIC4 was much more resilient to perturbation from propofol binding. This study underscores the importance of pore dynamics and conformation to anesthetic effects on channel functions. PMID:22978431

Energetic and dynamic analysis of transport of Na + and K + through a cyclic peptide nanotube in water and in lipid bilayers

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

Song, Yeonho; Lee, Ji Hye; Hwang, Hoon

Potential of mean force (PMF) profiles and position-dependent diffusion coefficients of Na + and K + are calculated to elucidate the translocation of ions through a cyclic peptide nanotube, composed of 8 × cyclo[-(D-Leu-Trp) 4-] rings, in water and in hydrated DMPC bilayers. The PMF profiles and PMF decomposition analysis for the monovalent cations show that favorable interactions of the cations with the CPN as well as the lipid bilayer and dehydration free energy penalties are two major competing factors which determine the free energy surface for ion transport through CPNs both in water and lipid bilayers, and that themore » selectivity of CPNs to cations mainly arises from favorable interaction energies of cations with CPNs and lipid bilayers that are more dominant than the dehydration penalties. Calculations of the position-dependent diffusion coefficients and dynamic friction kernels of the cations indicate that the dehydration process along with the molecular rearrangements occurring outside the channel and the coupling of the ion motions with the chain-structured water movements inside the channel lead to decrease of the diffusion coefficients far away from the channel entrance and also reduced coefficients inside the channel. Here the PMF and diffusivity profiles for Na + and K + reveal that the energetics of ion transport through the CPN are governed by global interactions of ions with all the components in the system while the diffusivity of ions through the channel is mostly determined by local interactions of ions with the confined water molecules inside the channel. Comparison of Na + and K + ion distributions based on overdamped Brownian dynamics simulations based on the PMF and diffusivity profiles with the corresponding results from molecular dynamics shows good agreement, indicating accuracy of the Bayesian inference method for determining diffusion coefficients in this application. In addition this work shows that position-dependent diffusion coefficients of ions are required to explain the dynamics and conductance of ions through the CPN properly.« less

Energetic and dynamic analysis of transport of Na + and K + through a cyclic peptide nanotube in water and in lipid bilayers

DOE PAGES

Song, Yeonho; Lee, Ji Hye; Hwang, Hoon; ...

2016-11-04

Potential of mean force (PMF) profiles and position-dependent diffusion coefficients of Na + and K + are calculated to elucidate the translocation of ions through a cyclic peptide nanotube, composed of 8 × cyclo[-(D-Leu-Trp) 4-] rings, in water and in hydrated DMPC bilayers. The PMF profiles and PMF decomposition analysis for the monovalent cations show that favorable interactions of the cations with the CPN as well as the lipid bilayer and dehydration free energy penalties are two major competing factors which determine the free energy surface for ion transport through CPNs both in water and lipid bilayers, and that themore » selectivity of CPNs to cations mainly arises from favorable interaction energies of cations with CPNs and lipid bilayers that are more dominant than the dehydration penalties. Calculations of the position-dependent diffusion coefficients and dynamic friction kernels of the cations indicate that the dehydration process along with the molecular rearrangements occurring outside the channel and the coupling of the ion motions with the chain-structured water movements inside the channel lead to decrease of the diffusion coefficients far away from the channel entrance and also reduced coefficients inside the channel. Here the PMF and diffusivity profiles for Na + and K + reveal that the energetics of ion transport through the CPN are governed by global interactions of ions with all the components in the system while the diffusivity of ions through the channel is mostly determined by local interactions of ions with the confined water molecules inside the channel. Comparison of Na + and K + ion distributions based on overdamped Brownian dynamics simulations based on the PMF and diffusivity profiles with the corresponding results from molecular dynamics shows good agreement, indicating accuracy of the Bayesian inference method for determining diffusion coefficients in this application. In addition this work shows that position-dependent diffusion coefficients of ions are required to explain the dynamics and conductance of ions through the CPN properly.« less

Pentavalent neptunyl ([OΞNpΞO] +) cation–cation interactions in aqueous/polar organic mixed-solvent media

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

Burn, Adam G.; Martin, Leigh R.; Nash, Kenneth L.

Bonding interactions between polyvalent cations and oxo-anions are well known and characterized by predictably favorable Gibbs energies in solution-phase coordination chemistry. In contrast, interactions between ions of like charge are generally expected to be repulsive and strongly influenced by cation solvation. An exception to this instinctive rule is found in the existence of complexes resulting from interactions of pentavalent actinyl cations ([O≡An≡O] +) with selected polyvalent cations. Such cation–cation complexes have been known to exist since the 1960s, when they were first reported by Sullivan and co-workers. The weak actinyl cation–cation complex, resulting from a bonding interaction between a pentavalentmore » linear dioxo actinyl cation donor and hexavalent actinyl or trivalent/tetravalent metal cation acceptor, has been most commonly seen in media in which water activities are reduced, principally highly-salted aqueous media. Such interactions of pentavalent actinides are of relevance in ongoing research that focuses on advanced nuclear fuel processing systems based on the upper oxidation states of americium. This investigation focuses on exploring the thermodynamic stability of complexes between selected highly-charged metal cations (Al 3+, Sc 3+, Cr 3+, Fe 3+, In 3+ and UO 2+ 2) and the pentavalent neptunyl cation (NpO + 2, whose coordination chemistry is similar to that of AmO + 2 while exhibiting significantly greater oxidation state stability) in aqueous–polar organic mixed-solvents. As a result, the Gibbs energies for the cation–cation complexation reactions are correlated with general features of electrostatic bonding models; the NpO + 2 • Cr 3+ complex exhibits unexpectedly strong interactions that may indicate significant covalency in the cation–cation bonding interaction.« less

Pentavalent neptunyl ([OΞNpΞO] +) cation–cation interactions in aqueous/polar organic mixed-solvent media

DOE PAGES

Burn, Adam G.; Martin, Leigh R.; Nash, Kenneth L.

2017-06-17

Bonding interactions between polyvalent cations and oxo-anions are well known and characterized by predictably favorable Gibbs energies in solution-phase coordination chemistry. In contrast, interactions between ions of like charge are generally expected to be repulsive and strongly influenced by cation solvation. An exception to this instinctive rule is found in the existence of complexes resulting from interactions of pentavalent actinyl cations ([O≡An≡O] +) with selected polyvalent cations. Such cation–cation complexes have been known to exist since the 1960s, when they were first reported by Sullivan and co-workers. The weak actinyl cation–cation complex, resulting from a bonding interaction between a pentavalentmore » linear dioxo actinyl cation donor and hexavalent actinyl or trivalent/tetravalent metal cation acceptor, has been most commonly seen in media in which water activities are reduced, principally highly-salted aqueous media. Such interactions of pentavalent actinides are of relevance in ongoing research that focuses on advanced nuclear fuel processing systems based on the upper oxidation states of americium. This investigation focuses on exploring the thermodynamic stability of complexes between selected highly-charged metal cations (Al 3+, Sc 3+, Cr 3+, Fe 3+, In 3+ and UO 2+ 2) and the pentavalent neptunyl cation (NpO + 2, whose coordination chemistry is similar to that of AmO + 2 while exhibiting significantly greater oxidation state stability) in aqueous–polar organic mixed-solvents. As a result, the Gibbs energies for the cation–cation complexation reactions are correlated with general features of electrostatic bonding models; the NpO + 2 • Cr 3+ complex exhibits unexpectedly strong interactions that may indicate significant covalency in the cation–cation bonding interaction.« less

ATP transport through VDAC and the VDAC-tubulin complex probed by equilibrium and nonequilibrium MD simulations.

PubMed

Noskov, Sergei Yu; Rostovtseva, Tatiana K; Bezrukov, Sergey M

2013-12-23

Voltage-dependent anion channel (VDAC), the major channel of the mitochondrial outer membrane, serves as a principal pathway for ATP, ADP, and other respiratory substrates across this membrane. Using umbrella-sampling simulations, we established the thermodynamic and kinetic components governing ATP transport across the VDAC1 channel. We found that there are several low-affinity binding sites for ATP along the translocation pathway and that the main barrier for ATP transport is located around the center of the channel and is formed predominantly by residues in the N-terminus. The binding affinity of ATP to an open channel was found to be in the millimolar to micromolar range. However, we show that this weak binding increases the ATP translocation probability by about 10-fold compared with the VDAC pore in which attractive interactions were artificially removed. Recently, it was found that free dimeric tubulin induces a highly efficient, reversible blockage of VDAC reconstituted into planar lipid membranes. It was proposed that by blocking VDAC permeability for ATP/ADP and other mitochondrial respiratory substrates tubulin controls mitochondrial respiration. Using the Rosetta protein-protein docking algorithm, we established a tentative structure of the VDAC-tubulin complex. An extensive set of equilibrium and nonequilibrium (under applied electric field) molecular dynamics (MD) simulations was used to establish the conductance of the open and blocked channel. It was found that the presence of the unstructured C-terminal tail of tubulin in the VDAC pore decreases its conductance by more than 40% and switches its selectivity from anionic to cationic. The subsequent 1D potential of mean force (PMF) computations for the VDAC-tubulin complex show that the state renders ATP transport virtually impossible. A number of residues pivotal for tubulin binding to the channel were identified that help to clarify the molecular details of VDAC-tubulin interaction and to provide new insight into the mechanism of the control of mitochondria respiration by VDAC.

Choline but not its derivative betaine blocks slow vacuolar channels in the halophyte Chenopodium quinoa: implications for salinity stress responses.

PubMed

Pottosin, Igor; Bonales-Alatorre, Edgar; Shabala, Sergey

2014-11-03

Activity of tonoplast slow vacuolar (SV, or TPC1) channels has to be under a tight control, to avoid undesirable leak of cations stored in the vacuole. This is particularly important for salt-grown plants, to ensure efficient vacuolar Na(+) sequestration. In this study we show that choline, a cationic precursor of glycine betaine, efficiently blocks SV channels in leaf and root vacuoles of the two chenopods, Chenopodium quinoa (halophyte) and Beta vulgaris (glycophyte). At the same time, betaine and proline, two major cytosolic organic osmolytes, have no significant effect on SV channel activity. Physiological implications of these findings are discussed. Copyright © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Flammutoxin, a cytolysin from the edible mushroom Flammulina velutipes, forms two different types of voltage-gated channels in lipid bilayer membranes.

PubMed

Tadjibaeva, G; Sabirov, R; Tomita, T

2000-08-25

Flammutoxin, a 31-kDa cardiotoxic and cytolytic protein from the edible mushroom Flammulina velutipes, has been shown to assemble into a pore-forming annular oligomer with outer and inner diameters of 10 and 5 nm on the target cells [Tomita et al., Biochem. J. 333 (1998) 129-137]. Here we studied electrophysiological properties of flammutoxin channels using planar lipid bilayer technique, and found that flammutoxin formed two types of moderately cation-selective, voltage-gated channels with smaller and larger current amplitudes (1-4.5 pA and 20-30 pA, respectively, at 20 mV) in the lipid bilayers composed of phospholipid and cholesterol. The larger-conductance single channel showed the properties of a wide water-filled pore such as a linear relationship between channel conductance and salt concentration of the bathing solution. The functional diameter of the larger-conductance channel was estimated to be 4-5 nm by measuring the current conductance in the presence of polyethylene glycols of various sizes. In contrast, the smaller-conductance single channels showed a non-linear current to voltage curve and a saturating conductance to increasing salt concentration. These results suggest that the larger-conductance channel of flammutoxin corresponds to the hemolytic pore complex, while the smaller-conductance channel may reflect the intermediate state(s) of the assembling toxin.

TRPV1 Channels Are Functionally Coupled with BK(mSlo1) Channels in Rat Dorsal Root Ganglion (DRG) Neurons

PubMed Central

Yan, Zonghe; Kong, Wenjuan; Liu, Beiying; Li, Xia; Yao, Jing; Zhang, Yuexuan; Qin, Feng; Ding, Jiuping

2013-01-01

The transient receptor potential vanilloid receptor 1 (TRPV1) channel is a nonselective cation channel activated by a variety of exogenous and endogenous physical and chemical stimuli, such as temperature (≥42 °C), capsaicin, a pungent compound in hot chili peppers, and allyl isothiocyanate. Large-conductance calcium- and voltage-activated potassium (BK) channels regulate the electric activities and neurotransmitter releases in excitable cells, responding to changes in membrane potentials and elevation of cytosolic calcium ions (Ca2+). However, it is unknown whether the TRPV1 channels are coupled with the BK channels. Using patch-clamp recording combined with an infrared laser device, we found that BK channels could be activated at 0 mV by a Ca2+ influx through TRPV1 channels not the intracellular calcium stores in submilliseconds. The local calcium concentration around BK is estimated over 10 μM. The crosstalk could be affected by 10 mM BAPTA, whereas 5 mM EGTA was ineffectual. Fluorescence and co-immunoprecipitation experiments also showed that BK and TRPV1 were able to form a TRPV1-BK complex. Furthermore, we demonstrated that the TRPV1-BK coupling also occurs in dosal root ganglion (DRG) cells, which plays a critical physiological role in regulating the “pain” signal transduction pathway in the peripheral nervous system. PMID:24147119

Aluminium and hydrogen ions inhibit a mechanosensory calcium-selective cation channel

NASA Technical Reports Server (NTRS)

Ding, J. P.; Pickard, B. G.

1993-01-01

The tension-dependent activity of mechanosensory calcium-selective cation channels in excised plasmalemmal patches from onion bulb scale epidermis is modulated by pH in the physiologically meaningful range between 4.5 and 7.2. It is rapidly lowered by lowering pH and rapidly raised by raising pH. Channel activity is effectively inhibited by low levels of aluminium ions and activity can be partially restored by washing for a few minutes. We suggest that under normal conditions the sensitivity of the mechanosensory channels to pH of the wall free space plays important roles in regulation of plant activities such as growth. We further suggest that, when levels of acid and aluminium ions in the soil solution are high, they might inhibit similar sensory channels in cells of the root tip, thus contributing critically to the acid soil syndrome.

Ion channel-mediated uptake of cationic vital dyes into live cells: a potential source of error when assessing cell viability.

PubMed

Bukhari, Maurish; Burm, Hayley; Samways, Damien S K

2016-10-01

Ionic "vital dyes" are commonly used to assess cell viability based on the idea that their permeation is contingent on a loss of membrane integrity. However, the possibility that dye entry is conducted into live cells by endogenous membrane transporters must be recognized and controlled for. Several cation-selective plasma membrane-localized ion channels, including the adenosine 5'-triphosphate (ATP)-gated P2X receptors, have been reported to conduct entry of the DNA-binding fluorescence dye, YO-PRO-1, into live cells. Extracellular ATP often becomes elevated as a result of release from dying cells, and so it is possible that activation of P2X channels on neighboring live cells could lead to exaggerated estimation of cytotoxicity. Here, we screened a number of fluorescent vital dyes for ion channel-mediated uptake in HEK293 cells expressing recombinant P2X2, P2X7, or TRPV1 channels. Our data shows that activation of all three channels caused substantial uptake and nuclear accumulation of YO-PRO-1, 4',6-diamidino-2-phenylindole (DAPI), and Hoechst 33258 into transfected cells and did so well within the time period usually used for incubation of cells with vital dyes. In contrast, channel activation in the presence of propidium iodide and SYTOX Green caused no measurable uptake and accumulation during a 20-min exposure, suggesting that these dyes are not likely to exhibit measurable uptake through these particular ion channels during a conventional cell viability assay. Caution is encouraged when choosing and employing cationic dyes for the purpose of cell viability assessment, particularly when there is a likelihood of cells expressing ion channels permeable to large ions.

Properties of complexes formed by Na(+), Mg(2+), and Fe(2+) binding with benzene molecules.

PubMed

Kolakkandy, Sujitha; Pratihar, Subha; Aquino, Adelia J A; Wang, Hai; Hase, William L

2014-10-09

A theoretical investigation was performed to study cation-π interactions in complexes of benzene (Bz) with cations, that is, M(z+)(Bz)n for M(z+) = Na(+), Mg(2+), Fe(2+) and n = 1-3, using MP2 theory with the 6-31+G* and 6-311++G** basis sets and the DFT/(B3LYP and B3LYP-D)/6-311++G** methods. Binding energies and structures of the complexes are reported. The splitting between the quintet and single states of the Fe(2+) complexes was found to depend on the number of benzene molecules in the complex and the complex's structure. All of the M(z+)(Bz) complexes prefer a half-sandwich geometry. A geometry with the cation sandwiched between the two benzene rings was found for the M(z+)(Bz)2 complexes, with the benzene rings either in an eclipsed or staggered conformation. An approximate cyclic structure, with the cation at its center, was found for three benzene molecules interacting with the cation. The cation-benzene binding energy is substantial and equal to 22, 108, and 151 kcal/mol for the Na(+)(Bz), Mg(2+)(Bz), and Fe(2+)(Bz) complexes, respectively. The strength of the interaction of the cation with an individual benzene molecule decreases as the number of benzene molecules bound to the cation increases; for example, it is 108 kcal/mol for Mg(2+)(Bz), but only 71 kcal/mol for Mg(2+)(Bz)3. There is a range of values for the M(z+)(Bz)n intermolecular vibrational frequencies; for example, they are ∼230-360 and ∼10-330 cm(-1) for the Mg(2+)(Bz) and Mg(2+)(Bz)3 complexes, respectively. Binding of the cation to benzene both red and blue shifts the benzene vibrational frequencies. This shifting is larger for the Mg(2+) and Fe(2+) complexes, as compared to those for Na(+), as a result of the former's stronger cation-benzene binding. The present study is an initial step to understand the possible importance of cation-π interactions for polycyclic aromatic hydrocarbon aggregation processes during soot formation.

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

Polyakova, I. N., E-mail: polyakova@igic.ras.ru; Baulin, V. E.; Ivanova, I. S.

The coordination compounds of Er{sup 3+} with 1-(methoxydiphenylphosphoryl)-2-diphenylphosphorylbenzene [ErL{sub 2}{sup 1}(NO{sub 3}){sub 2}]{sub 2}[Er(NO{sub 3}){sub 2}(H{sub 2}O){sub 5}]{sub 0.333}(NO{sub 3}){sub 2.333} · 2.833H{sub 2}O (I) and its ethyl substituted derivative [ErL{sub 2}{sup 2}(NO{sub 3}){sub 2}][Er(NO{sub 3}){sub 5}]{sub 0.5} · 0.5H{sub 2}O (II) are synthesized and their crystal structures are studied. I and II contain [ErL{sub 2}(NO{sub 3}){sub 2}]{sup +} complex cations of identical composition and close structure. The eight-vertex polyhedron of the Er atom in the shape of a distorted octahedron with two split trans vertices is formed by the O atoms of the phosphoryl groups of L ligands andmore » nitrate anions. L ligands close nine-membered metallocycles. The structures contain spacious channels which are populated differently, namely, by disordered [Er(NO{sub 3}){sub 2}(H{sub 2}O){sub 5}]{sup +} complex cations, NO{sub 3}{sup −} anions, and crystallization water molecules in I and disordered [Er(NO{sub 3}){sub 5}]{sup 2−} complex anions and crystallization water molecules in II. The IR spectra of I and II are studied.« less

Solvation Effect on Complexation of Alkali Metal Cations by a Calix[4]arene Ketone Derivative.

PubMed

Požar, Josip; Nikšić-Franjić, Ivana; Cvetnić, Marija; Leko, Katarina; Cindro, Nikola; Pičuljan, Katarina; Borilović, Ivana; Frkanec, Leo; Tomišić, Vladislav

2017-09-14

The medium effect on the complexation of alkali metal cations with a calix[4]arene ketone derivative (L) was systematically examined in methanol, ethanol, N-methylformamide, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile. In all solvents the binding of Na + cation by L was rather efficient, whereas the complexation of other alkali metal cations was observed only in methanol and acetonitrile. Complexation reactions were enthalpically controlled, while ligand dissolution was endothermic in all cases. A notable influence of the solvent on NaL + complex stability could be mainly attributed to the differences in complexation entropies. The higher NaL + stability in comparison to complexes with other alkali metal cations in acetonitrile was predominantly due to a more favorable complexation enthalpy. The 1 H NMR investigations revealed a relatively low affinity of the calixarene sodium complex for inclusion of the solvent molecule in the calixarene hydrophobic cavity, with the exception of acetonitrile. Differences in complex stabilities in the explored solvents, apart from N,N-dimethylformamide and acetonitrile, could be mostly explained by taking into account solely the cation and complex solvation. A considerable solvent effect on the complexation equilibria was proven to be due to an interesting interplay between the transfer enthalpies and entropies of the reactants and the complexes formed.

Coxsackievirus and adenovirus receptor (CAR) mediates trafficking of acid sensing ion channel 3 (ASIC3) via PSD-95.

PubMed

Excoffon, Katherine J D A; Kolawole, Abimbola O; Kusama, Nobuyoshi; Gansemer, Nicholas D; Sharma, Priyanka; Hruska-Hageman, Alesia M; Petroff, Elena; Benson, Christopher J

2012-08-17

We have previously shown that the Coxsackievirus and adenovirus receptor (CAR) can interact with post-synaptic density 95 (PSD-95) and localize PSD-95 to cell-cell junctions. We have also shown that activity of the acid sensing ion channel (ASIC3), a H(+)-gated cation channel that plays a role in mechanosensation and pain signaling, is negatively modulated by PSD-95 through a PDZ-based interaction. We asked whether CAR and ASIC3 simultaneously interact with PSD-95, and if so, whether co-expression of these proteins alters their cellular distribution and localization. Results indicate that CAR and ASIC3 co-immunoprecipitate only when co-expressed with PSD-95. CAR also brings both PSD-95 and ASIC3 to the junctions of heterologous cells. Moreover, CAR rescues PSD-95-mediated inhibition of ASIC3 currents. These data suggest that, in addition to activity as a viral receptor and adhesion molecule, CAR can play a role in trafficking proteins, including ion channels, in a PDZ-based scaffolding complex. Copyright © 2012 Elsevier Inc. All rights reserved.

Structure-function study on a de novo synthetic hydrophobic ion channel.

PubMed Central

Qi, Z; Sokabe, M; Donowaki, K; Ishida, H

1999-01-01

Ion conduction properties of a de novo synthesized channel, formed from cyclic octa-peptides consisting of four alternate L-alanine (Ala) and N'-acylated 3-aminobenzoic acid (Aba) moieties, were studied in bilayer membranes. The single-channel conductance was 9 pS in symmetrical 500 mM KCl. The channel favored permeation of cations over anions with a permeability ratio (PCl-/PK+) of 0.15. The selectivity sequence among monovalent cations based on permeability ratio (PX+/PK+) fell into an order: NH4+(1.4) > Cs+(1. 1) >/= K+(1.0) > Na+(0.4) >> Li+(0). The conductance-activity relationship of the channel in K+ solutions followed simple Michaelis-Menten kinetics with a half-maximal saturating activity of 8 mM and a maximal conductance of 9 pS. The permeability ratio PNa+/PK+ remained constant ( approximately 0.40) under biionic concentrations from 10 to 500 mM. These results suggests that the channel is a one-ion channel. The pore diameter probed by a set of organic cations was approximately 6 A. The single-channel current was blocked by Ca2+ in a dose-dependent manner that followed a single-site titration curve with a voltage-dependent dissociation constant of 0.6 mM at 100 mV. The electric distance of the binding site for Ca2+ was 0.07 from both entrances of the channel, indicating the presence of two symmetrical binding sites in each vicinity of the channel entrance. Correlations between conduction properties and structural aspects of the channel are discussed in terms of a three-barrier and two-binding-site (3B2S) model of Eyring rate theory. All available structural information supported an idea that the channel was formed from a tail-to-tail associated dimer of the molecule, the pore of which was lined with hydrophobic acyl chains. This is the first report to have made a systematic analysis of ion permeation through a hydrophobic pore. PMID:9929469

[2.2.2]Paracyclophane as a receptor for the cesium cation in the gas phase

NASA Astrophysics Data System (ADS)

Makrlík, Emanuel; Sýkora, David; Böhm, Stanislav; Vaňura, Petr

2017-10-01

By using electrospray ionisation mass spectrometry, it was proven experimentally that the cesium cation (Cs+) forms with [2.2.2]paracyclophane (C24H24) the cationic complex [Cs(C24H24)]+. Further, applying quantum chemical calculations, the most probable structure of the [Cs(C24H24)]+ complex was derived. In the resulting complex with a symmetry very close to C3, the 'central' cation Cs+, fully located in the cavity of the parent [2.2.2]paracyclophane ligand, is bound to all three benzene rings of [2.2.2]paracyclophane via cation-π interaction. Finally, the interaction energy, E(int), of the considered cation-π complex [Cs(C24H24)]+ was found to be -73.2 kJ/mol, confirming the formation of this fascinating complex species as well. This means that [2.2.2]paracyclophane can be considered as a receptor for the Cs+ cation in the gas phase.

Overcharging below the nanoscale: Multivalent cations reverse the ion selectivity of a biological channel

NASA Astrophysics Data System (ADS)

García-Giménez, Elena; Alcaraz, Antonio; Aguilella, Vicente M.

2010-02-01

We report charge inversion within a nanoscopic biological protein ion channel in salts of multivalent ions. The presence of positive divalent and trivalent counterions reverses the cationic selectivity of the OmpF channel, a general diffusion porin located in the outer membrane of E. coli. We discuss the conditions under which charge inversion can be inferred from the change in sign of the measured quantity, the channel zero current potential. By comparing experimental results in protein channels whose charge has been modified after site-directed mutagenesis, the predictions of current theories of charge inversion are critically examined. It is emphasized that charge inversion does not necessarily increase with the bare surface charge density of the interface and that even this concept of surface charge density may become meaningless in some biological ion channels. Thus, any theory based on electrostatic correlations or chemical binding should explicitly take into account the particular structure of the charged interface.

Ion Permeation and Mechanotransduction Mechanisms of Mechanosensitive Piezo Channels.

PubMed

Zhao, Qiancheng; Wu, Kun; Geng, Jie; Chi, Shaopeng; Wang, Yanfeng; Zhi, Peng; Zhang, Mingmin; Xiao, Bailong

2016-03-16

Piezo proteins have been proposed as the long-sought-after mechanosensitive cation channels in mammals that play critical roles in various mechanotransduction processes. However, the molecular bases that underlie their ion permeation and mechanotransduction have remained functionally undefined. Here we report our finding of the miniature pore-forming module of Piezo1 that resembles the pore architecture of other trimeric channels and encodes the essential pore properties. We further identified specific residues within the pore module that determine unitary conductance, pore blockage and ion selectivity for divalent and monovalent cations and anions. The non-pore-containing region of Piezo1 confers mechanosensitivity to mechano-insensitive trimeric acid-sensing ion channels, demonstrating that Piezo1 channels possess intrinsic mechanotransduction modules separate from their pore modules. In conclusion, this is the first report on the bona fide pore module and mechanotransduction components of Piezo channels, which define their ion-conducting properties and gating by mechanical stimuli, respectively. Copyright © 2016 Elsevier Inc. All rights reserved.

Uptake of photosensitizers by bacteria is influenced by the presence of cations

NASA Astrophysics Data System (ADS)

Kishen, A.; George, S.

2007-05-01

This investigation studies the influence of cations on photosensitizer uptake by Enterococcus faecalis (gram positive) and Actinobacillus actinomycetemcomitans (gram negative). Methods- The uptake of Methylene blue (MB) and Indocyanine Green (ICG), by bacteria were studied under the influence of divalent cations (CaCl II & MgCl II) and EDTA. Further, E. faecalis cells subjected to trypsinisation and calcium channel blocker (verapamil) were also analysed for MB and ICG uptake inorder to understand the mechanism of photosensitizer uptake. Results- Uptake of ICG was enhanced in the presence of divalent cations in E. faecalis and A. actinomycetemcomitans. Treating cells with EDTA had no significant effect on the photosensitizer uptake, although the highest concentration tested showed an enhancement of uptake. In contrast to ICG, MB showed a decreased uptake by bacterial cells on subjecting them to divalent cations and EDTA. Calcium channel blocker had no significant inhibitory effect on photosensitizers uptake. However, trypsin treatment resulted in significant reduction of ICG uptake. The result suggested that ICG uptake by bacteria is mediated through specific transporter protein while MB is associated with the outer surface structures of bacterial cells.

Na, K, Rb, and Cs Exchange in Heulandite Single-Crystals: X-Ray Structure Refinements at 100 K

NASA Astrophysics Data System (ADS)

Yang, Ping; Armbruster, Thomas

1996-04-01

The crystal structures of Na-, K-, Rb-, and Cs-exchanged varieties of the zeolite heulandite with the simplified compositionM+9Al9Si27O72·nH2O were studied by single-crystal X-ray diffraction at 100 K. The structure refinements of Na-, K-, and Rb-exchanged heulandite were performed in space groupC2/mwith resultantRvalues of 3.8, 3.0, and 4.9%, respectively. Cs-exchanged heulandite was refined in space groupC[formula], yielding anRvalue of 3.4%. X-ray single-crystal data of the Cs-exchanged variety indicated that many reflections of typeh k lwere not equivalent toh -k las expected for monoclinic symmetry. With increasing radius of the incorporated channel cations, thebaxis increases from 17.93 to 18.09 Å leading to a slight widening of the channels. The number of H2O molecules also decreases with increasing cation radius due to space limitations. Three general cation positions (II-1,C3, andB4) were found in the four exchanged heulandite samples. For Rb- and Cs-exchanged crystals, the additional cation siteA2 occurs. In Cs-exchanged heulandite symmetry lowering is due to partial Si, Al ordering in the framework accompanied with a more asymmetric arrangement of channel Cs. Only if heavy elements in the channels are present the symmetry information of the framework is enforced, thus partial Si, Al ordering can be resolved.

Barbiturates Bind in the GLIC Ion Channel Pore and Cause Inhibition by Stabilizing a Closed State*♦

PubMed Central

Fourati, Zaineb; Ruza, Reinis Reinholds; Laverty, Duncan; Drège, Emmanuelle; Delarue-Cochin, Sandrine; Joseph, Delphine; Koehl, Patrice; Smart, Trevor; Delarue, Marc

2017-01-01

Barbiturates induce anesthesia by modulating the activity of anionic and cationic pentameric ligand-gated ion channels (pLGICs). Despite more than a century of use in clinical practice, the prototypic binding site for this class of drugs within pLGICs is yet to be described. In this study, we present the first X-ray structures of barbiturates bound to GLIC, a cationic prokaryotic pLGIC with excellent structural homology to other relevant channels sensitive to general anesthetics and, as shown here, to barbiturates, at clinically relevant concentrations. Several derivatives of barbiturates containing anomalous scatterers were synthesized, and these derivatives helped us unambiguously identify a unique barbiturate binding site within the central ion channel pore in a closed conformation. In addition, docking calculations around the observed binding site for all three states of the receptor, including a model of the desensitized state, showed that barbiturates preferentially stabilize the closed state. The identification of this pore binding site sheds light on the mechanism of barbiturate inhibition of cationic pLGICs and allows the rationalization of several structural and functional features previously observed for barbiturates. PMID:27986812

A9C sensitive Cl− - accumulation in A. thaliana root cells during salt stress is controlled by internal and external calcium

PubMed Central

Saleh, Livia; Plieth, Christoph

2013-01-01

The involvement of chloride in salt stress symptoms and salt tolerance mechanisms in plants has been less investigated in the past. Therefore, we studied the salt-induced chloride influx in Arabidopsis expressing the GFP-based anion indicator Clomeleon. High salt concentrations induce two phases of chloride influx. The fast kinetic phase is likely caused by membrane depolarization, and is assumed to be mediated by channels. This is followed by a slower "saturation" phase, where chloride is accumulated in the cytoplasm. Both phases of chloride uptake are dependent on the presence of external calcium. In general: with high [Ca2+] less chloride is accumulated in the cytoplasm. Surprisingly, also the internal calcium availability has an impact on chloride transport. A complete block of the second phase of chloride influx is achieved by the anion channel blocker A9C and trivalent cations (La3+, Gd3+, and Al3+). Other channel blockers and diuretics were found to inhibit the process partially. The results suggest that several transporter species are involved here, including electroneutral cation-chloride-cotransporters, and a part of chloride possibly enters the cells through cation channels after salt application. PMID:23603974

Synthetic ion channels via self-assembly: a route for embedding porous polyoxometalate nanocapsules in lipid bilayer membranes.

PubMed

Carr, Rogan; Weinstock, Ira A; Sivaprasadarao, Asipu; Müller, Achim; Aksimentiev, Aleksei

2008-11-01

Porous polyoxometalate nanocapsules of Keplerate type are known to exhibit the functionality of biological ion channels; however, their use as an artificial ion channel is tempered by the high negative charge of the capsules, which renders their spontaneous incorporation into a lipid bilayer membrane unlikely. In this Letter we report coarse-grained molecular dynamics simulations that demonstrate a route for embedding negatively charged nanocapsules into lipid bilayer membranes via self-assembly. A homogeneous mixture of water, cationic detergent, and phospholipid was observed to spontaneously self-assemble around the nanocapsule into a layered, liposome-like structure, where the nanocapsule was enveloped by a layer of cationic detergent followed by a layer of phospholipid. Fusion of such a layered liposome with a lipid bilayer membrane was observed to embed the nanocapsule into the lipid bilayer. The resulting assembly was found to remain stable even after the surface of the capsule was exposed to electrolyte. In the latter conformation, water was observed to flow into and out of the capsule as Na(+) cations entered, suggesting that a polyoxometalate nanocapsule can form a functional synthetic ion channel in a lipid bilayer membrane.

Synthetic Ion Channels via Self-Assembly: a Route for Embedding Porous Polyoxometalate Nanocapsules in Lipid Bilayer Membranes

PubMed Central

Carr, Rogan; Weinstock, Ira A.; Sivaprasadarao, Asipu; Müller, Achim; Aksimentiev, Aleksei

2010-01-01

Porous polyoxometalate nanocapsules of Keplerate type are known to exhibit the functionality of biological ion channels, however, their use as artificial ion channel is tempered by the high negative charge of the capsules, which renders their spontaneous incorporation into a lipid bilayer membrane unlikely. In this letter we report coarse-grained molecular dynamics simulations that demonstrate a route for embedding negatively charged nanocapsules into lipid bilayer membranes via self-assembly. A homogeneous mixture of water, cationic detergent, and phospholipid was observed to spontaneously self-assemble around the nanocapsule into a layered, liposome-like structure, where the nanocapsule was enveloped by a layer of cationic detergent followed by a layer of phospholipid. Fusion of such a layered liposome with a lipid bilayer membrane was observed to embed the nanocapsule into the lipid bilayer. The resulting assembly was found to remain stable even after the surface of the capsule was exposed to electrolyte. In the latter conformation, water was observed to flow into and out of the capsule as Na+ cations entered, suggesting that a polyoxometalate nanocapsule can form a functional synthetic ion channel in a lipid bilayer membrane. PMID:18844424

Synthetic cation-selective nanotube: permeant cations chaperoned by anions.

PubMed

Hilder, Tamsyn A; Gordon, Dan; Chung, Shin-Ho

2011-01-28

The ability to design ion-selective, synthetic nanotubes which mimic biological ion channels may have significant implications for the future treatment of bacteria, diseases, and as ultrasensitive biosensors. We present the design of a synthetic nanotube made from carbon atoms that selectively allows monovalent cations to move across and rejects all anions. The cation-selective nanotube mimics some of the salient properties of biological ion channels. Before practical nanodevices are successfully fabricated it is vital that proof-of-concept computational studies are performed. With this in mind we use molecular and stochastic dynamics simulations to characterize the dynamics of ion permeation across a single-walled (10, 10), 36 Å long, carbon nanotube terminated with carboxylic acid with an effective radius of 5.08 Å. Although cations encounter a high energy barrier of 7 kT, its height is drastically reduced by a chloride ion in the nanotube. The presence of a chloride ion near the pore entrance thus enables a cation to enter the pore and, once in the pore, it is chaperoned by the resident counterion across the narrow pore. The moment the chaperoned cation transits the pore, the counterion moves back to the entrance to ferry another ion. The synthetic nanotube has a high sodium conductance of 124 pS and shows linear current-voltage and current-concentration profiles. The cation-anion selectivity ratio ranges from 8 to 25, depending on the ionic concentrations in the reservoirs.

Mechanosensitive Piezo Channels in the Gastrointestinal Tract

PubMed Central

Alcaino, C.; Farrugia, G.; Beyder, A.

2017-01-01

Sensation of mechanical forces is critical for normal function of the gastrointestinal (GI) tract and abnormalities in mechanosensation are linked to GI pathologies. In the GI tract there are several mechanosensitive cell types—epithelial enterochromaffin cells, intrinsic and extrinsic enteric neurons, smooth muscle cells and interstitial cells of Cajal. These cells use mechanosensitive ion channels that respond to mechanical forces by altering transmembrane ionic currents in a process called mechanoelectrical coupling. Several mechanosensitive ionic conductances have been identified in the mechano-sensory GI cells, ranging from mechanosensitive voltage-gated sodium and calcium channels to the mechanogated ion channels, such as the two-pore domain potassium channels K2P (TREK-1) and nonselective cation channels from the transient receptor potential family. The recently discovered Piezo channels are increasingly recognized as significant contributors to cellular mechanosensitivity. Piezo1 and Piezo2 are nonselective cationic ion channels that are directly activated by mechanical forces and have well-defined biophysical and pharmacologic properties. The role of Piezo channels in the GI epithelium is currently under investigation and their role in the smooth muscle syncytium and enteric neurons is still not known. In this review, we outline the current state of knowledge on mechanosensitive ion channels in the GI tract, with a focus on the known and potential functions of the Piezo channels. PMID:28728818

Gating Behavior of Endoplasmic Reticulum Potassium Channels of Rat Hepatocytes in Diabetes

PubMed Central

Ghasemi, Maedeh; Khodaei, Naser; Salari, Sajjad; Eliassi, Afsaneh; Saghiri, Reza

2014-01-01

Background: Defects in endoplasmic reticulum homeostasis are common occurrences in different diseases, such as diabetes, in which the function of endoplasmic reticulum is disrupted. It is now well established that ion channels of endoplasmic reticulum membrane have a critical role in endoplasmic reticulum luminal homeostasis. Our previous studies showed the presence of an ATP-sensitive cationic channel in endoplasmic reticulum. Therefore, in this study, we examined and compared the activities of this channel in control and diabetic rats using single-channel recording techniques. Method: Male Wistar rats were made diabetic for 2 weeks with a single dose injection of streptozotocin (45 mg/kg). Ion channel incorporation of rough endoplasmic reticulum of diabetic hepatocytes into the bilayer lipid membrane allowed the characterization of K+ channel. Results: Ion channel incorporation of rough endoplasmic reticulum vesicles into the bilayer lipid revealed that the channel current-voltage (I-V) relation with a mean slope conductance of 520 ± 19 pS was unaffected in diabetes. Interestingly, the channel Po-voltage relation was significantly lower in diabetic rats at voltages above +30 mV. Conclusion: We concluded that the endoplasmic reticulum cationic channel is involved in diabetes. Also, this finding could be considered as a goal for further therapeutic plans. PMID:24842143

Metal-organic complexes in geochemical processes: temperature dependence of the standard thermodynamic properties of aqueous complexes between metal cations and dicarboxylate ligands

NASA Astrophysics Data System (ADS)

Prapaipong, Panjai; Shock, Everett L.; Koretsky, Carla M.

1999-10-01

By combining results from regression and correlation methods, standard state thermodynamic properties for aqueous complexes between metal cations and divalent organic acid ligands (oxalate, malonate, succinate, glutarate, and adipate) are evaluated and applied to geochemical processes. Regression of experimental standard-state equilibrium constants with the revised Helgeson-Kirkham-Flowers (HKF) equation of state yields standard partial molal entropies (S¯°) of aqueous metal-organic complexes, which allow determination of thermodynamic properties of the complexes at elevated temperatures. In cases where S¯° is not available from either regression or calorimetric measurement, the values of S¯° can be estimated from a linear correlation between standard partial molal entropies of association (ΔS¯°r) and standard partial molal entropies of aqueous cations (S¯°M). The correlation is independent of cation charge, which makes it possible to predict S¯° for complexes between divalent organic acids and numerous metal cations. Similarly, correlations between standard Gibbs free energies of association of metal-organic complexes (ΔḠ°r) and Gibbs free energies of formation (ΔḠ°f) for divalent metal cations allow estimates of standard-state equilibrium constants where experimental data are not available. These correlations are found to be a function of ligand structure and cation charge. Predicted equilibrium constants for dicarboxylate complexes of numerous cations were included with those for inorganic and other organic complexes to study the effects of dicarboxylate complexes on the speciation of metals and organic acids in oil-field brines. Relatively low concentrations of oxalic and malonic acids affect the speciation of cations more than similar concentrations of succinic, glutaric, and adipic acids. However, the extent to which metal-dicarboxylate complexes contribute to the speciation of dissolved metals depends on the type of dicarboxylic acid ligand; relative concentration of inorganic, mono-, and dicarboxylate ligands; and the type of metal cation. As an example, in the same solution, dicarboxylic acids have a greater influence on the speciation of Fe+2 and Mg+2 than on the speciation of Zn+2 and Mn+2.

Sculpting Nanoscale Functional Channels in Complex Oxides Using Energetic Ions and Electrons

DOE PAGES

Sachan, Ritesh; Zarkadoula, Eva; Ou, Xin; ...

2018-04-26

The formation of metastable phases has attracted significant attention because of their unique properties and potential functionalities. In the present study, we demonstrate the phase conversion of energetic-ion-induced amorphous nanochannels/tracks into a metastable defect fluorite in A 2B 2O 7 structured complex oxides by electron irradiation. Through in situ electron irradiation experiments in a scanning transmission electron microscope, we observe electron-induced epitaxial crystallization of the amorphous nanochannels in Yb 2Ti 2O 7 into the defect fluorite. This energetic-electron-induced phase transformation is attributed to the coupled effect of ionization-induced electronic excitations and local heating, along with subthreshold elastic energy transfers. Wemore » also show the role of ionic radii of A-site cations (A = Yb, Gd, and Sm) and B-site cations (Ti and Zr) in facilitating the electron-beam-induced crystallization of the amorphous phase to the defect-fluorite structure. The formation of the defect-fluorite structure is eased by the decrease in the difference between ionic radii of A- and B-site cations in the lattice. Molecular dynamics simulations of thermal annealing of the amorphous phase nanochannels in A 2B 2O 7 draw parallels to the electron-irradiation-induced crystallization and confirm the role of ionic radii in lowering the barrier for crystallization. Furthermore, these results suggest that employing guided electron irradiation with atomic precision is a useful technique for selected area phase formation in nanoscale printed devices.« less

Sculpting Nanoscale Functional Channels in Complex Oxides Using Energetic Ions and Electrons

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

Sachan, Ritesh; Zarkadoula, Eva; Ou, Xin

The formation of metastable phases has attracted significant attention because of their unique properties and potential functionalities. In the present study, we demonstrate the phase conversion of energetic-ion-induced amorphous nanochannels/tracks into a metastable defect fluorite in A 2B 2O 7 structured complex oxides by electron irradiation. Through in situ electron irradiation experiments in a scanning transmission electron microscope, we observe electron-induced epitaxial crystallization of the amorphous nanochannels in Yb 2Ti 2O 7 into the defect fluorite. This energetic-electron-induced phase transformation is attributed to the coupled effect of ionization-induced electronic excitations and local heating, along with subthreshold elastic energy transfers. Wemore » also show the role of ionic radii of A-site cations (A = Yb, Gd, and Sm) and B-site cations (Ti and Zr) in facilitating the electron-beam-induced crystallization of the amorphous phase to the defect-fluorite structure. The formation of the defect-fluorite structure is eased by the decrease in the difference between ionic radii of A- and B-site cations in the lattice. Molecular dynamics simulations of thermal annealing of the amorphous phase nanochannels in A 2B 2O 7 draw parallels to the electron-irradiation-induced crystallization and confirm the role of ionic radii in lowering the barrier for crystallization. Furthermore, these results suggest that employing guided electron irradiation with atomic precision is a useful technique for selected area phase formation in nanoscale printed devices.« less

Hydrogen release reactions of Al-based complex hydrides enhanced by vibrational dynamics and valences of metal cations

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

Sato, T.; Ramirez-Cuesta, Anibal J.; Daemen, Luke L.

2016-08-31

Hydrogen release from Al-based complex hydrides composed of metal cation(s) and [AlH4] – was investigated using inelastic neutron scattering viewed from vibrational dynamics. Here, the hydrogen release followed the softening of translational and [AlH4] – librational modes, which was enhanced by vibrational dynamics and the valence(s) of the metal cation(s).

Insights into dynamic processes of cations in pyrochlores and other complex oxides

DOE PAGES

Uberuaga, Blas Pedro; Perriot, Romain

2015-08-26

Complex oxides are critical components of many key technologies, from solid oxide fuel cells and superionics to inert matrix fuels and nuclear waste forms. In many cases, understanding mass transport is important for predicting performance and, thus, extensive effort has been devoted to understanding mass transport in these materials. However, most work has focused on the behavior of oxygen while cation transport has received relatively little attention, even though cation diffusion is responsible for many phenomena, including sintering, radiation damage evolution, and deformation processes. Here, we use accelerated molecular dynamics simulations to examine the kinetics of cation defects in onemore » class of complex oxides, A₂B₂O₇ pyrochlore. In some pyrochlore chemistries, B cation defects are kinetically unstable, transforming to A cation defects and antisites at rates faster than they can diffuse. When this occurs, transport of B cations occurs through defect processes on the A sublattice. Further, these A cation defects, either interstitials or vacancies, can interact with antisite disorder, reordering the material locally, though this process is much more efficient for interstitials than vacancies. Whether this behavior occurs in a given pyrochlore depends on the A and B chemistry. Pyrochlores with a smaller ratio of cation radii exhibit this complex behavior, while those with larger ratios exhibit direct migration of B interstitials. Similar behavior has been reported in other complex oxides such as spinels and perovskites, suggesting that this coupling of transport between the A and B cation sublattices, while not universal, occurs in many complex oxide.« less

Claudin-16 and claudin-19 interact and form a cation-selective tight junction complex

PubMed Central

Hou, Jianghui; Renigunta, Aparna; Konrad, Martin; Gomes, Antonio S.; Schneeberger, Eveline E.; Paul, David L.; Waldegger, Siegfried; Goodenough, Daniel A.

2008-01-01

Tight junctions (TJs) play a key role in mediating paracellular ion reabsorption in the kidney. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is an inherited disorder caused by mutations in the genes encoding the TJ proteins claudin-16 (CLDN16) and CLDN19; however, the mechanisms underlying the roles of these claudins in mediating paracellular ion reabsorption in the kidney are not understood. Here we showed that in pig kidney epithelial cells, CLDN19 functioned as a Cl– blocker, whereas CLDN16 functioned as a Na+ channel. Mutant forms of CLDN19 that are associated with FHHNC were unable to block Cl– permeation. Coexpression of CLDN16 and CLDN19 generated cation selectivity of the TJ in a synergistic manner, and CLDN16 and CLDN19 were observed to interact using several criteria. In addition, disruption of this interaction by introduction of FHHNC-causing mutant forms of either CLDN16 or CLDN19 abolished their synergistic effect. Our data show that CLDN16 interacts with CLDN19 and that their association confers a TJ with cation selectivity, suggesting a mechanism for the role of mutant forms of CLDN16 and CLDN19 in the development of FHHNC. PMID:18188451

Reagent Anions for Charge Inversion of Polypeptide/Protein Cations in the Gas Phase

PubMed Central

He, Min; Emory, Joshua F.; McLuckey, Scott A.

2005-01-01

Various reagent anions capable of converting polypeptide cations to anions via ion/ion reactions have been investigated. The major charge inversion reaction channels include multiple proton transfer and adduct formation. Dianions composed of sulfonate groups as the negative charge carriers show essentially exclusive adduct formation in converting protonated peptides and proteins to anions. Dianions composed of carboxylate groups, on the other hand, show far more charge inversion via multiple proton transfer, with the degree of adduct formation dependent upon both the size of the polypeptide and the spacings between carboxylate groups in the dianion. More highly charged carboxylate-containing anions, such as those derived from carboxylate-terminated polyamidoamine half-generation dendrimers show charge inversion to give anion charges as high in magnitude as −4, with the degree of adduct formation being inversely related to dendrimer generation. All observations can be interpreted on the basis of charge inversion taking place via a long-lived chemical complex. The lifetime of this complex is related to the strengths and numbers of the interactions of the reactants in the complex. Calculations with model systems are fully consistent with sulfonate groups giving rise to more stable complexes. The kinetic stability of the complex can also be affected by the presence of electrostatic repulsion if it is multiply charged. In general, this situation destabilizes the complex and reduces the likelihood for observation of adducts. The findings highlight the characteristics of multiply charged anions that play roles in determining the nature of charge inversion products associated with protonated peptides and proteins. PMID:15889906

High-pressure alchemy on a small-pore zeolite

NASA Astrophysics Data System (ADS)

Lee, Y.

2011-12-01

While an ever-expanding variety of zeolites with a wide range of framework topology is available, it is desirable to have a way to tailor the chemistry of the zeolitic nanopores for a given framework topology via controlling both the coordination-inclusion chemistry and framework distortion/relaxation. This is, however, subjected to the ability of a zeolitic nanopore to allow the redistribution of cations-water assembly and/or insertion of foreign molecules into the pores and channels. Small-pore zeolites such as natrolite (Na16Al16Si24O80x16H2O), however, have been known to show very limited capacity for any changes in the confinement chemistry. We have recently shown that various cation-exchanged natrolites can be prepared under modest conditions from natural sodium natrolite and exhibit cation-dependent volume expansions by up to 18.5% via converting the elliptical channels into progressively circular ones. Here, we show that pressure can be used as a unique and clean tool to further manipulate the chemistry of the natrolite nanopores. Our recent crystallographic and spectroscopic studies of pressure-insertion of foreign molecules, trivalent-cation exchange under pressure, and pressure-induced inversion of cation-water coordination and pore geometry in various cation-exchanged natrolites will be presented.

What Hinders Electron Transfer Dissociation (ETD) of DNA Cations?

NASA Astrophysics Data System (ADS)

Hari, Yvonne; Leumann, Christian J.; Schürch, Stefan

2017-12-01

Radical activation methods, such as electron transfer dissociation (ETD), produce structural information complementary to collision-induced dissociation. Herein, electron transfer dissociation of 3-fold protonated DNA hexamers was studied to gain insight into the fragmentation mechanism. The fragmentation patterns of a large set of DNA hexamers confirm cytosine as the primary target of electron transfer. The reported data reveal backbone cleavage by internal electron transfer from the nucleobase to the phosphate linker leading either to a•/ w or d/ z• ion pairs. This reaction pathway contrasts with previous findings on the dissociation processes after electron capture by DNA cations, suggesting multiple, parallel dissociation channels. However, all these channels merely result in partial fragmentation of the precursor ion because the charge-reduced DNA radical cations are quite stable. Two hypotheses are put forward to explain the low dissociation yield of DNA radical cations: it is either attributed to non-covalent interactions between complementary fragments or to the stabilization of the unpaired electron in stacked nucleobases. MS3 experiments suggest that the charge-reduced species is the intact oligonucleotide. Moreover, introducing abasic sites significantly increases the dissociation yield of DNA cations. Consequently, the stabilization of the unpaired electron by π-π-stacking provides an appropriate rationale for the high intensity of DNA radical cations after electron transfer. [Figure not available: see fulltext.

Effects of ginger and its pungent constituents on transient receptor potential channels.

PubMed

Kim, Young-Soo; Hong, Chan Sik; Lee, Sang Weon; Nam, Joo Hyun; Kim, Byung Joo

2016-12-01

Ginger extract is used as an analeptic in herbal medicine and has been reported to exert antioxidant effects. Transient receptor potential (TRP) canonical 5 (TRPC5), TRP cation channel, subfamily M, member 7 (TRPM7; melastatin 7), and TRP cation channel, subfamily A, member 1 (TRPA1; ankyrin 1) are non-selective cation channels that are modulated by reactive oxygen/nitrogen species (ROS/RNS) and subsequently control various cellular processes. The aim of this study was to evaluate whether ginger and its pungent constituents modulate these channels and exert antioxidant effects. It was found that TRPC5 and TRPA1 currents were modulated by ginger extract and by its pungent constituents, [6]-gingerol, zingerone and [6]-shogaol. In particular, [6]-shogaol markedly and dose-dependently inhibited TRPC5 currents with an IC50 of value of ~18.3 µM. Furthermore, the strong dose-dependent activation of TRPA1 currents by [6]-shogaol was abolished by A‑967079 (a selective TRPA1 inhibitor). However, ginger extract and its pungent constituents had no effect on TRPM7 currents. These results suggest the antioxidant effects of ginger extract and its pungent constituents are mediated through TRPC5 and TRPA1, and that [6]-shogaol is predominantly responsible for the regulation of TRPC5 and TRPA1 currents by ginger extract.

Pillared-layer microporous metal-organic frameworks constructed by robust hydrogen bonds. Synthesis, characterization, and magnetic and adsorption properties of 2,2'-biimidazole and carboxylate complexes.

PubMed

Ding, Bing-Bing; Weng, Yan-Qin; Mao, Zong-Wan; Lam, Chi-Keung; Chen, Xiao-Ming; Ye, Bao-Hui

2005-11-28

Two new isostructural complexes [M(H2biim)3][M(btc)(Hbiim)].2H2O (M = Co, (1); M = Ni, (2)) (btc = 1,3,5-benzenetricarboxylate; H2biim = 2,2'-biimidazole) have been synthesized and characterized by single-crystal X-ray diffraction. They present a unique structure consisting of two distinct units: the monomeric cations [M(H2biim)3]2+ and the two-dimensional (2D) anionic polymer [M(Hbiim)(btc)]2-. In the anionic moiety, the Hbiim- monoanion is simultaneously coordinated to one metal atom in a bidentate mode and further to another metal atom in a monodentate mode. The imidazolate groups bridge the two adjacent metal ions into a helical chain which is further arranged in left- and right-handed manners. These chains are bridged by btc ligands into a 2D brick wall structure. The most interesting aspect is that the [M(H2biim)3]2+ cations act as pillars and link the anionic layers via robust heteromeric hydrogen-bonded synthons (9) and (7) formed by the uncoordinated oxygen atoms of carboxylate groups and the H2biim ligands, resulting in a microporous metal-organic framework with one-dimensional (1D) channels (ca. 11.85 angstroms x 11.85 angstroms for 1 and 11.43 angstroms x 11.43 angstroms for 2). Magnetic properties of these two complexes have also been studied in the temperature range of 2-300 K, and their magnetic susceptibilities obey the Curie-Weiss law in the temperature range of 20-300 K (for 1) and 2-300 K (for 2), respectively, showing anti-ferromagnetic coupling through imidazolate bridging. Taking into consideration the Heisenberg infinite chain model as well as the possibility of chain-to-chain and chain-to-cation interactions, the anti-ferromagnetic exchange of 2 is analyzed via a correction for the molecular field, giving the values of g(cat) = 2.296, g(Ni) = 2.564, J = -13.30 cm(-1), and zJ' = -0.017 cm(-1). The microporous frameworks are stable at ca. 350 degrees C. They do not collapse after removal of the guest water molecules in the channels, and they adsorb methanol molecules selectively.

A cardiac pathway of cyclic GMP-independent signaling of guanylyl cyclase A, the receptor for atrial natriuretic peptide

PubMed Central

Klaiber, Michael; Dankworth, Beatrice; Kruse, Martin; Hartmann, Michael; Nikolaev, Viacheslav O.; Yang, Ruey-Bing; Völker, Katharina; Gaßner, Birgit; Oberwinkler, Heike; Feil, Robert; Freichel, Marc; Groschner, Klaus; Skryabin, Boris V.; Frantz, Stefan; Birnbaumer, Lutz; Pongs, Olaf; Kuhn, Michaela

2011-01-01

Cardiac atrial natriuretic peptide (ANP) regulates arterial blood pressure, moderates cardiomyocyte growth, and stimulates angiogenesis and metabolism. ANP binds to the transmembrane guanylyl cyclase (GC) receptor, GC-A, to exert its diverse functions. This process involves a cGMP-dependent signaling pathway preventing pathological [Ca2+]i increases in myocytes. In chronic cardiac hypertrophy, however, ANP levels are markedly increased and GC-A/cGMP responses to ANP are blunted due to receptor desensitization. Here we show that, in this situation, ANP binding to GC-A stimulates a unique cGMP-independent signaling pathway in cardiac myocytes, resulting in pathologically elevated intracellular Ca2+ levels. This pathway involves the activation of Ca2+‐permeable transient receptor potential canonical 3/6 (TRPC3/C6) cation channels by GC-A, which forms a stable complex with TRPC3/C6 channels. Our results indicate that the resulting cation influx activates voltage-dependent L-type Ca2+ channels and ultimately increases myocyte Ca2+i levels. These observations reveal a dual role of the ANP/GC-A–signaling pathway in the regulation of cardiac myocyte Ca2+i homeostasis. Under physiological conditions, activation of a cGMP-dependent pathway moderates the Ca2+i-enhancing action of hypertrophic factors such as angiotensin II. By contrast, a cGMP-independent pathway predominates under pathophysiological conditions when GC-A is desensitized by high ANP levels. The concomitant rise in [Ca2+]i might increase the propensity to cardiac hypertrophy and arrhythmias. PMID:22027011

TRPC6 G757D Loss-of-Function Mutation Associates with FSGS

PubMed Central

Riehle, Marc; Büscher, Anja K.; Gohlke, Björn-Oliver; Kaßmann, Mario; Kolatsi-Joannou, Maria; Bräsen, Jan H.; Nagel, Mato; Becker, Jan U.; Winyard, Paul; Hoyer, Peter F.; Preissner, Robert; Krautwurst, Dietmar; Gollasch, Maik

2016-01-01

FSGS is a CKD with heavy proteinuria that eventually progresses to ESRD. Hereditary forms of FSGS have been linked to mutations in the transient receptor potential cation channel, subfamily C, member 6 (TRPC6) gene encoding a nonselective cation channel. Most of these TRPC6 mutations cause a gain-of-function phenotype, leading to calcium–triggered podocyte cell death, but the underlying molecular mechanisms are unclear. We studied the molecular effect of disease-related mutations using tridimensional in silico modeling of tetrameric TRPC6. Our results indicated that G757 is localized in a domain forming a TRPC6-TRPC6 interface and predicted that the amino acid exchange G757D causes local steric hindrance and disruption of the channel complex. Notably, functional characterization of model interface domain mutants suggested a loss-of-function phenotype. We then characterized 19 human FSGS–related TRPC6 mutations, the majority of which caused gain-of-function mutations. However, five mutations (N125S, L395A, G757D, L780P, and R895L) caused a loss-of-function phenotype. Coexpression of wild-type TRPC6 and TRPC6 G757D, mimicking heterozygosity observed in patients, revealed a dominant negative effect of TRPC6 G757D. Our comprehensive analysis of human disease–causing TRPC6 mutations reveals loss of TRPC6 function as an additional concept of hereditary FSGS and provides molecular insights into the mechanism responsible for the loss-of-function phenotype of TRPC6 G757D in humans. PMID:26892346

Binding of Capsaicin to the TRPV1 Ion Channel.

PubMed

Darré, Leonardo; Domene, Carmen

2015-12-07

Transient receptor potential (TRP) ion channels constitute a notable family of cation channels involved in the ability of an organisms to detect noxious mechanical, thermal, and chemical stimuli that give rise to the perception of pain, taste, and changes in temperature. One of the most experimentally studied agonist of TRP channels is capsaicin, which is responsible for the burning sensation produced when chili pepper is in contact with organic tissues. Thus, understanding how this molecule interacts and regulates TRP channels is essential to high impact pharmacological applications, particularly those related to pain treatment. The recent publication of a three-dimensional structure of the vanilloid receptor 1 (TRPV1) in the absence and presence of capsaicin from single particle electron cryomicroscopy experiments provides the opportunity to explore these questions at the atomic level. In the present work, molecular docking and unbiased and biased molecular dynamics simulations were employed to generate a structural model of the capsaicin-channel complex. In addition, the standard free energy of binding was estimated using alchemical transformations coupled with conformational, translational, and orientational restraints on the ligand. Key binding modes consistent with previous experimental data are identified, and subtle but essential dynamical features of the binding site are characterized. These observations shed some light into how TRPV1 interacts with capsaicin, and may help to refine design parameters for new TRPV1 antagonists, and potentially guide further developments of TRP channel modulators.

Podocyte Purinergic P2X4 Channels Are Mechanotransducers That Mediate Cytoskeletal Disorganization.

PubMed

Forst, Anna-Lena; Olteanu, Vlad Sorin; Mollet, Géraldine; Wlodkowski, Tanja; Schaefer, Franz; Dietrich, Alexander; Reiser, Jochen; Gudermann, Thomas; Mederos y Schnitzler, Michael; Storch, Ursula

2016-03-01

Podocytes are specialized, highly differentiated epithelial cells in the kidney glomerulus that are exposed to glomerular capillary pressure and possible increases in mechanical load. The proteins sensing mechanical forces in podocytes are unconfirmed, but the classic transient receptor potential channel 6 (TRPC6) interacting with the MEC-2 homolog podocin may form a mechanosensitive ion channel complex in podocytes. Here, we observed that podocytes respond to mechanical stimulation with increased intracellular calcium concentrations and increased inward cation currents. However, TRPC6-deficient podocytes responded in a manner similar to that of control podocytes, and mechanically induced currents were unaffected by genetic inactivation of TRPC1/3/6 or administration of the broad-range TRPC blocker SKF-96365. Instead, mechanically induced currents were significantly decreased by the specific P2X purinoceptor 4 (P2X4) blocker 5-BDBD. Moreover, mechanical P2X4 channel activation depended on cholesterol and podocin and was inhibited by stabilization of the actin cytoskeleton. Because P2X4 channels are not intrinsically mechanosensitive, we investigated whether podocytes release ATP upon mechanical stimulation using a fluorometric approach. Indeed, mechanically induced ATP release from podocytes was observed. Furthermore, 5-BDBD attenuated mechanically induced reorganization of the actin cytoskeleton. Altogether, our findings reveal a TRPC channel-independent role of P2X4 channels as mechanotransducers in podocytes. Copyright © 2016 by the American Society of Nephrology.

The TiPS/TINS lecture: the molecular biology of mammalian glutamate receptor channels.

PubMed

Seeburg, P H

1993-08-01

In native brain membranes the principal excitatory neurotransmitter L-glutamate activates cation-conducting channels with distinct biophysical and pharmacological properties. Molecular cloning has revealed the existence of 16 channel subunits that can assemble in homomeric or heteromeric configurations in vitro to form receptor channels with disparate functional properties. This review describes the different channel types obtained by recombinant means and the genetic mechanisms controlling the expression of functionally important channel structures.

The TINS/TiPS Lecture. The molecular biology of mammalian glutamate receptor channels.

PubMed

Seeburg, P H

1993-09-01

In native brain membranes the principal excitatory neurotransmitter L-glutamate activates cation-conducting channels with distinct biophysical and pharmacological properties. Molecular cloning has revealed the existence of 16 channel subunits that can assemble in homomeric or heteromeric configurations in vitro to form receptor channels with disparate functional properties. This review describes the different channel types obtained by recombinant means and the genetic mechanisms controlling the expression of functionally important channel structures.

NEUROSCIENCE. Natural light-gated anion channels: A family of microbial rhodopsins for advanced optogenetics.

PubMed

Govorunova, Elena G; Sineshchekov, Oleg A; Janz, Roger; Liu, Xiaoqin; Spudich, John L

2015-08-07

Light-gated rhodopsin cation channels from chlorophyte algae have transformed neuroscience research through their use as membrane-depolarizing optogenetic tools for targeted photoactivation of neuron firing. Photosuppression of neuronal action potentials has been limited by the lack of equally efficient tools for membrane hyperpolarization. We describe anion channel rhodopsins (ACRs), a family of light-gated anion channels from cryptophyte algae that provide highly sensitive and efficient membrane hyperpolarization and neuronal silencing through light-gated chloride conduction. ACRs strictly conducted anions, completely excluding protons and larger cations, and hyperpolarized the membrane of cultured animal cells with much faster kinetics at less than one-thousandth of the light intensity required by the most efficient currently available optogenetic proteins. Natural ACRs provide optogenetic inhibition tools with unprecedented light sensitivity and temporal precision. Copyright © 2015, American Association for the Advancement of Science.

Mosaic expression of claudins in thick ascending limbs of Henle results in spatial separation of paracellular Na+ and Mg2+ transport

PubMed Central

Wulfmeyer, Vera Christine; Drewell, Hoora; Mutig, Kerim; Hou, Jianghui; Breiderhoff, Tilman; Müller, Dominik; Fromm, Michael; Bleich, Markus; Günzel, Dorothee

2017-01-01

The thick ascending limb (TAL) of Henle’s loop drives paracellular Na+, Ca2+, and Mg2+ reabsorption via the tight junction (TJ). The TJ is composed of claudins that consist of four transmembrane segments, two extracellular segments (ECS1 and -2), and one intracellular loop. Claudins interact within the same (cis) and opposing (trans) plasma membranes. The claudins Cldn10b, -16, and -19 facilitate cation reabsorption in the TAL, and their absence leads to a severe disturbance of renal ion homeostasis. We combined electrophysiological measurements on microperfused mouse TAL segments with subsequent analysis of claudin expression by immunostaining and confocal microscopy. Claudin interaction properties were examined using heterologous expression in the TJ-free cell line HEK 293, live-cell imaging, and Förster/FRET. To reveal determinants of interaction properties, a set of TAL claudin protein chimeras was created and analyzed. Our main findings are that (i) TAL TJs show a mosaic expression pattern of either cldn10b or cldn3/cldn16/cldn19 in a complex; (ii) TJs dominated by cldn10b prefer Na+ over Mg2+, whereas TJs dominated by cldn16 favor Mg2+ over Na+; (iii) cldn10b does not interact with other TAL claudins, whereas cldn3 and cldn16 can interact with cldn19 to form joint strands; and (iv) further claudin segments in addition to ECS2 are crucial for trans interaction. We suggest the existence of at least two spatially distinct types of paracellular channels in TAL: a cldn10b-based channel for monovalent cations such as Na+ and a spatially distinct site for reabsorption of divalent cations such as Ca2+ and Mg2+. PMID:28028216

Water insoluble and soluble lipids for gene delivery.

PubMed

Mahato, Ram I

2005-04-05

Among various synthetic gene carriers currently in use, liposomes composed of cationic lipids and co-lipids remain the most efficient transfection reagents. Physicochemical properties of lipid/plasmid complexes, such as cationic lipid structure, cationic lipid to co-lipid ratio, charge ratio, particle size and zeta potential have significant influence on gene expression and biodistribution. However, most cationic lipids are toxic and cationic liposomes/plasmid complexes do not disperse well inside the target tissues because of their large particle size. To overcome the problems associated with cationic lipids, we designed water soluble lipopolymers for gene delivery to various cells and tissues. This review provides a critical discussion on how the components of water insoluble and soluble lipids affect their transfection efficiency and biodistribution of lipid/plasmid complexes.

Crystal structure of the ATP-gated P2X[subscript 4] ion channel in the closed state

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

Kawate, Toshimitsu; Michel, Jennifer Carlisle; Birdsong, William T.

2009-08-13

P2X receptors are cation-selective ion channels gated by extracellular ATP, and are implicated in diverse physiological processes, from synaptic transmission to inflammation to the sensing of taste and pain. Because P2X receptors are not related to other ion channel proteins of known structure, there is at present no molecular foundation for mechanisms of ligand-gating, allosteric modulation and ion permeation. Here we present crystal structures of the zebrafish P2X{sub 4} receptor in its closed, resting state. The chalice-shaped, trimeric receptor is knit together by subunit-subunit contacts implicated in ion channel gating and receptor assembly. Extracellular domains, rich in {beta}-strands, have largemore » acidic patches that may attract cations, through fenestrations, to vestibules near the ion channel. In the transmembrane pore, the 'gate' is defined by an {approx}8 {angstrom} slab of protein. We define the location of three non-canonical, intersubunit ATP-binding sites, and suggest that ATP binding promotes subunit rearrangement and ion channel opening.« less

Synthesis and SMM behaviour of trinuclear versus dinuclear 3d-5f uranyl(v)-cobalt(ii) cation-cation complexes.

PubMed

Chatelain, Lucile; Tuna, Floriana; Pécaut, Jacques; Mazzanti, Marinella

2017-05-02

Trinuclear versus dinuclear heterodimetallic U V O 2 + Co 2+ complexes were selectively assembled via a cation-cation interaction by tuning the ligand. The trimeric complex 2, with a linear [Co-O[double bond, length as m-dash]U[double bond, length as m-dash]O-Co] core, exhibits magnetic exchange and slow relaxation with a reversal barrier of 30.5 ± 0.9 K providing the first example of a U-Co exchange-coupled SMM.

Pre-treatment with vinpocetine protects against retinal ischemia.

PubMed

Nivison-Smith, Lisa; Khoo, Pauline; Acosta, Monica L; Kalloniatis, Michael

2017-01-01

Vinpocetine has been shown to have beneficial effects for tissues of the central nervous system subjected to ischemia and other related metabolic insults. We recently showed vinpocetine promotes glucose availability, prevents unregulated cation channel permeability and regulates glial reactivity when present during retinal ischemia. Less is known however about the ability of vinpocetine to protect against future ischemic insults. This study explores the effect of vinpocetine when used as a pre-treatment in an ex vivo model for retinal ischemia using cation channel permeability of agmatine (AGB) combined with immunohistochemistry as a measure for cell functionality. We found that vinpocetine pre-treatment reduced cation channel permeability and apoptotic marker immunoreactivity in the GCL and increased parvalbumin immunoreactivity of inner retinal neurons in the inner nuclear layer following ischemic insult. Vinpocetine pre-treatment also reduced Müller cell reactivity following ischemic insults of up to 120 min compared to untreated controls. Many of vinpocetine's effects however were transient in nature suggesting the drug can protect retinal neurons against future ischemic damage but may have limited long-term applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

TRPC6 counteracts TRPC3-Nox2 protein complex leading to attenuation of hyperglycemia-induced heart failure in mice.

PubMed

Oda, Sayaka; Numaga-Tomita, Takuro; Kitajima, Naoyuki; Toyama, Takashi; Harada, Eri; Shimauchi, Tsukasa; Nishimura, Akiyuki; Ishikawa, Tatsuya; Kumagai, Yoshito; Birnbaumer, Lutz; Nishida, Motohiro

2017-08-08

Excess production of reactive oxygen species (ROS) caused by hyperglycemia is a major risk factor for heart failure. We previously reported that transient receptor potential canonical 3 (TRPC3) channel mediates pressure overload-induced maladaptive cardiac fibrosis by forming stably functional complex with NADPH oxidase 2 (Nox2). Although TRPC3 has been long suggested to form hetero-multimer channels with TRPC6 and function as diacylglycerol-activated cation channels coordinately, the role of TRPC6 in heart is still obscure. We here demonstrated that deletion of TRPC6 had no impact on pressure overload-induced heart failure despite inhibiting interstitial fibrosis in mice. TRPC6-deficient mouse hearts 1 week after transverse aortic constriction showed comparable increases in fibrotic gene expressions and ROS production but promoted inductions of inflammatory cytokines, compared to wild type hearts. Treatment of TRPC6-deficient mice with streptozotocin caused severe reduction of cardiac contractility with enhancing urinary and cardiac lipid peroxide levels, compared to wild type and TRPC3-deficient mice. Knockdown of TRPC6, but not TRPC3, enhanced basal expression levels of cytokines in rat cardiomyocytes. TRPC6 could interact with Nox2, but the abundance of TRPC6 was inversely correlated with that of Nox2. These results strongly suggest that Nox2 destabilization through disrupting TRPC3-Nox2 complex underlies attenuation of hyperglycemia-induced heart failure by TRPC6.

Temperature and Voltage Coupling to Channel Opening in Transient Receptor Potential Melastatin 8 (TRPM8)*♦

PubMed Central

Raddatz, Natalia; Castillo, Juan P.; Gonzalez, Carlos; Alvarez, Osvaldo; Latorre, Ramon

2014-01-01

Expressed in somatosensory neurons of the dorsal root and trigeminal ganglion, the transient receptor potential melastatin 8 (TRPM8) channel is a Ca2+-permeable cation channel activated by cold, voltage, phosphatidylinositol 4,5-bisphosphate, and menthol. Although TRPM8 channel gating has been characterized at the single channel and macroscopic current levels, there is currently no consensus regarding the extent to which temperature and voltage sensors couple to the conduction gate. In this study, we extended the range of voltages where TRPM8-induced ionic currents were measured and made careful measurements of the maximum open probability the channel can attain at different temperatures by means of fluctuation analysis. The first direct measurements of TRPM8 channel temperature-driven conformational rearrangements provided here suggest that temperature alone is able to open the channel and that the opening reaction is voltage-independent. Voltage is a partial activator of TRPM8 channels, because absolute open probability values measured with fully activated voltage sensors are less than 1, and they decrease as temperature rises. By unveiling the fast temperature-dependent deactivation process, we show that TRPM8 channel deactivation is well described by a double exponential time course. The fast and slow deactivation processes are temperature-dependent with enthalpy changes of 27.2 and 30.8 kcal mol−1. The overall Q10 for the closing reaction is about 33. A three-tiered allosteric model containing four voltage sensors and four temperature sensors can account for the complex deactivation kinetics and coupling between voltage and temperature sensor activation and channel opening. PMID:25352597

Acetylcholine-evoked currents in cultured neurones dissociated from rat parasympathetic cardiac ganglia.

PubMed Central

Fieber, L A; Adams, D J

1991-01-01

1. The properties of acetylcholine (ACh)-activated ion channels of parasympathetic neurones from neonatal rat cardiac ganglia grown in tissue culture were examined using patch clamp recording techniques. Membrane currents evoked by ACh were mimicked by nicotine, attenuated by neuronal bungarotoxin, and unaffected by atropine, suggesting that the ACh-induced currents are mediated by nicotinic receptor activation. 2. The current-voltage (I-V) relationship for whole-cell ACh-evoked currents exhibited strong inward rectification and a reversal (zero current) potential of -3 mV (NaCl outside, CsCl inside). The rectification was not alleviated by changing the main permeant cation or by removal of divalent cations from the intracellular or extracellular solutions. Unitary ACh-activated currents exhibited a linear I-V relationship with slope conductances of 32 pS in cell-attached membrane patches and 38 pS in excised membrane patches with symmetrical CsCl solutions. 3. Acetylcholine-induced currents were reversibly inhibited in a dose-dependent manner by the ganglionic antagonists, mecamylamine (Kd = 37 nM) and hexamethonium (IC50 approximately 1 microM), as well as by the neuromuscular relaxant, d-tubocurarine (Kd = 3 microM). Inhibition of ACh-evoked currents by hexamethonium could not be described by a simple blocking model for drug-receptor interaction. 4. The amplitude of the ionic current through the open channel was dependent on the extracellular Na+ concentration. The direction of the shift in reversal potential upon replacement of NaCl by mannitol indicates that the neuronal nicotinic receptor channel is cation selective and the magnitude suggests a high cation to anion permeability ratio. The cation permeability (PX/PNa) followed the ionic selectivity sequence Cs+ (1.06) greater than Na+ (1.0) greater than Ca2+ (0.93). Anion substitution experiments showed a relative anion permeability, PCl/PNa less than or equal to 0.05. 5. The nicotinic ACh-activated channels described mediate the responses of postganglionic parasympathetic neurones of the mammalian heart to vagal stimulation. PMID:1708819

Immune complexes with cationic antibodies deposit in glomeruli more effectively than cationic antibodies alone.

PubMed

Mannik, M; Gauthier, V J; Stapleton, S A; Agodoa, L Y

1987-06-15

In previously published studies, highly cationized antibodies alone and in immune complexes bound to glomeruli by charge-charge interaction, but only immune complexes persisted in glomeruli. Because normal IgG does not deposit in glomeruli, studies were conducted to determine whether cationized antibodies can be prepared which deposit in glomeruli when bound to antigen but not when free in circulation. A series of cationized rabbit antiHSA was prepared with the number of added amino groups ranging from 13.3 to 60.2 per antibody molecule. Antibodies alone or in preformed soluble immune complexes, prepared at fivefold or 50-fold antigen excess, were administered to mice. With the injection of a fixed dose of 100 micrograms per mouse, antibodies alone did not deposit in glomeruli with less than 29.6 added amino groups by immunofluorescence microscopy. In contrast, 100 micrograms of antibodies with 23.5 added amino groups in immune complexes, made at fivefold antigen excess, formed immune deposits in glomeruli. With selected preparations of cationized, radiolabeled antibodies, deposition in glomeruli was quantified by isolation of mouse glomeruli. These quantitative data were in good agreement with the results of immunofluorescence microscopy. Immune complexes made at 50-fold antigen excess, containing only small-latticed immune complexes with no more than two antibody molecules per complex, deposited in glomeruli similar to antibodies alone. Selected cationized antibodies alone or in immune complexes were administered to mice in varying doses. In these experiments, glomerular deposition of immune complexes, made at fivefold antigen excess, was detected with five- to 10-fold smaller doses than the deposition of the same antibodies alone. These studies demonstrate that antibody molecules in immune complexes are more likely to deposit in glomeruli by charge-charge interactions than antibodies alone.

Copper and protons directly activate the zinc-activated channel.

PubMed

Trattnig, Sarah M; Gasiorek, Agnes; Deeb, Tarek Z; Ortiz, Eydith J Comenencia; Moss, Stephen J; Jensen, Anders A; Davies, Paul A

2016-03-01

The zinc-activated channel (ZAC) is a cationic ion channel belonging to the superfamily of Cys-loop receptors, which consists of pentameric ligand-gated ion channels. ZAC is the least understood member of this family so in the present study we sought to characterize the properties of this channel further. We demonstrate that not only zinc (Zn(2+)) but also copper (Cu(2+)) and protons (H(+)) are agonists of ZAC, displaying potencies and efficacies in the rank orders of H(+)>Cu(2+)>Zn(2+) and H(+)>Zn(2+)>Cu(2+), respectively. The responses elicited by Zn(2+), Cu(2+) and H(+) through ZAC are all characterized by low degrees of desensitization. In contrast, currents evoked by high concentrations of the three agonists comprise distinctly different activation and decay components, with transitions to and from an open state being significantly faster for H(+) than for the two metal ions. The permeabilities of ZAC for Na(+) and K(+) relative to Cs(+) are indistinguishable, whereas replacing all of extracellular Na(+) and K(+) with the divalent cations Ca(2+) or Mg(2+) results in complete elimination of Zn(2+)-activated currents at both negative and positive holding potentials. This indicates that ZAC is non-selectively permeable to monovalent cations, whereas Ca(2+) and Mg(2+) inhibit the channel. In conclusion, this is the first report of a Cys-loop receptor being gated by Zn(2+), Cu(2+) and H(+). ZAC could be an important mediator of some of the wide range of physiological functions regulated by or involving Zn(2+), Cu(2+) and H(+). Copyright © 2016 Elsevier Inc. All rights reserved.

Transient Receptor Potential Channels in the Vasculature

PubMed Central

Earley, Scott; Brayden, Joseph E.

2015-01-01

The mammalian genome encodes 28 distinct members of the transient receptor potential (TRP) superfamily of cation channels, which exhibit varying degrees of selectivity for different ionic species. Multiple TRP channels are present in all cells and are involved in diverse aspects of cellular function, including sensory perception and signal transduction. Notably, TRP channels are involved in regulating vascular function and pathophysiology, the focus of this review. TRP channels in vascular smooth muscle cells participate in regulating contractility and proliferation, whereas endothelial TRP channel activity is an important contributor to endothelium-dependent vasodilation, vascular wall permeability, and angiogenesis. TRP channels are also present in perivascular sensory neurons and astrocytic endfeet proximal to cerebral arterioles, where they participate in the regulation of vascular tone. Almost all of these functions are mediated by changes in global intracellular Ca2+ levels or subcellular Ca2+ signaling events. In addition to directly mediating Ca2+ entry, TRP channels influence intracellular Ca2+ dynamics through membrane depolarization associated with the influx of cations or through receptor- or store-operated mechanisms. Dysregulation of TRP channels is associated with vascular-related pathologies, including hypertension, neointimal injury, ischemia-reperfusion injury, pulmonary edema, and neurogenic inflammation. In this review, we briefly consider general aspects of TRP channel biology and provide an in-depth discussion of the functions of TRP channels in vascular smooth muscle cells, endothelial cells, and perivascular cells under normal and pathophysiological conditions. PMID:25834234

Mechanosensitive Piezo Channels in the Gastrointestinal Tract.

PubMed

Alcaino, C; Farrugia, G; Beyder, A

2017-01-01

Sensation of mechanical forces is critical for normal function of the gastrointestinal (GI) tract and abnormalities in mechanosensation are linked to GI pathologies. In the GI tract there are several mechanosensitive cell types-epithelial enterochromaffin cells, intrinsic and extrinsic enteric neurons, smooth muscle cells and interstitial cells of Cajal. These cells use mechanosensitive ion channels that respond to mechanical forces by altering transmembrane ionic currents in a process called mechanoelectrical coupling. Several mechanosensitive ionic conductances have been identified in the mechanosensory GI cells, ranging from mechanosensitive voltage-gated sodium and calcium channels to the mechanogated ion channels, such as the two-pore domain potassium channels K2P (TREK-1) and nonselective cation channels from the transient receptor potential family. The recently discovered Piezo channels are increasingly recognized as significant contributors to cellular mechanosensitivity. Piezo1 and Piezo2 are nonselective cationic ion channels that are directly activated by mechanical forces and have well-defined biophysical and pharmacologic properties. The role of Piezo channels in the GI epithelium is currently under investigation and their role in the smooth muscle syncytium and enteric neurons is still not known. In this review, we outline the current state of knowledge on mechanosensitive ion channels in the GI tract, with a focus on the known and potential functions of the Piezo channels. Copyright © 2017 Elsevier Inc. All rights reserved.

Bonding and Mobility of Alkali Metals in Helicenes.

PubMed

Barroso, Jorge; Murillo, Fernando; Martínez-Guajardo, Gerardo; Ortíz-Chi, Filiberto; Pan, Sudip; Fernández-Herrera, María A; Merino, Gabriel

2018-06-04

In this work, we analyze the interaction of alkali metal cations with [6]- and [14]helicene and the cation mobility of therein. We found that the distortion of the carbon skeleton is the cause that some of the structures that are local minima for the smallest cations are not energetically stable for K+, Rb+, and Cs+. Also, the most favorable complexes are those where the cation is interacting with two rings forming a metallocene-like structure, except for the largest cation Cs+, where the distortion provoked by the size of the cation desestabilizes the complex. As far as mobility is concerned, the smallest cations, particularly Na+, are the ones that can move most efficiently. In [6]helicene, the mobility is limited by the capture of the cation forming the metallocene-like structure. In larger helicenes, the energy barriers for the cation to move are similar both inside and outside the helix. However, complexes with the cation between two layers are more energetically favored so that the movement will be preferred in that region. The bonding analysis reveals that interactions with no less than 50% of orbitalic contribution are taking place for the series of E+-[6]helicene. Particularly, the complexes of Li+ stand out showing a remarkably orbitalic character bonding (72.5 - 81.6%). © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Impaired endocytosis of the ion channel TRPM4 is associated with human progressive familial heart block type I.

PubMed

Kruse, Martin; Schulze-Bahr, Eric; Corfield, Valerie; Beckmann, Alf; Stallmeyer, Birgit; Kurtbay, Güven; Ohmert, Iris; Schulze-Bahr, Ellen; Brink, Paul; Pongs, Olaf

2009-09-01

Progressive familial heart block type I (PFHBI) is a progressive cardiac bundle branch disease in the His-Purkinje system that exhibits autosomal-dominant inheritance. In 3 branches of a large South African Afrikaner pedigree with an autosomal-dominant form of PFHBI, we identified the mutation c.19G-->A in the transient receptor potential cation channel, subfamily M, member 4 gene (TRPM4) at chromosomal locus 19q13.3. This mutation predicted the amino acid substitution p.E7K in the TRPM4 amino terminus. TRPM4 encodes a Ca2+-activated nonselective cation (CAN) channel that belongs to the transient receptor potential melastatin ion channel family. Quantitative analysis of TRPM4 mRNA content in human cardiac tissue showed the highest expression level in Purkinje fibers. Cellular expression studies showed that the c.19G-->A missense mutation attenuated deSUMOylation of the TRPM4 channel. The resulting constitutive SUMOylation of the mutant TRPM4 channel impaired endocytosis and led to elevated TRPM4 channel density at the cell surface. Our data therefore revealed a gain-of-function mechanism underlying this type of familial heart block.

Impaired endocytosis of the ion channel TRPM4 is associated with human progressive familial heart block type I

PubMed Central

Kruse, Martin; Schulze-Bahr, Eric; Corfield, Valerie; Beckmann, Alf; Stallmeyer, Birgit; Kurtbay, Güven; Ohmert, Iris; Schulze-Bahr, Ellen; Brink, Paul; Pongs, Olaf

2009-01-01

Progressive familial heart block type I (PFHBI) is a progressive cardiac bundle branch disease in the His-Purkinje system that exhibits autosomal-dominant inheritance. In 3 branches of a large South African Afrikaner pedigree with an autosomal-dominant form of PFHBI, we identified the mutation c.19G→A in the transient receptor potential cation channel, subfamily M, member 4 gene (TRPM4) at chromosomal locus 19q13.3. This mutation predicted the amino acid substitution p.E7K in the TRPM4 amino terminus. TRPM4 encodes a Ca2+-activated nonselective cation (CAN) channel that belongs to the transient receptor potential melastatin ion channel family. Quantitative analysis of TRPM4 mRNA content in human cardiac tissue showed the highest expression level in Purkinje fibers. Cellular expression studies showed that the c.19G→A missense mutation attenuated deSUMOylation of the TRPM4 channel. The resulting constitutive SUMOylation of the mutant TRPM4 channel impaired endocytosis and led to elevated TRPM4 channel density at the cell surface. Our data therefore revealed a gain-of-function mechanism underlying this type of familial heart block. PMID:19726882

Nonredundant functions of Arabidopsis LecRK-V.2 and LecRK-VII.1 in controlling stomatal immunity and jasmonate-mediated stomatal closure.

PubMed

Yekondi, Shweta; Liang, Fu-Chun; Okuma, Eiji; Radziejwoski, Amandine; Mai, Hsien-Wei; Swain, Swadhin; Singh, Prashant; Gauthier, Mathieu; Chien, Hsiao-Chiao; Murata, Yoshiyuki; Zimmerli, Laurent

2018-04-01

Stomatal immunity restricts bacterial entry to leaves through the recognition of microbe-associated molecular patterns (MAMPs) by pattern-recognition receptors (PRRs) and downstream abscisic acid and salicylic acid signaling. Through a reverse genetics approach, we characterized the function of the L-type lectin receptor kinase-V.2 (LecRK-V.2) and -VII.1 (LecRK-VII.1). Analyses of interactions with the PRR FLAGELLIN SENSING2 (FLS2) were performed by co-immunoprecipitation and bimolecular fluorescence complementation and whole-cell patch-clamp analyses were used to evaluate guard cell Ca 2+ -permeable cation channels. The Arabidopsis thaliana LecRK-V.2 and LecRK-VII.1 and notably their kinase activities were required for full activation of stomatal immunity. Knockout lecrk-V.2 and lecrk-VII.1 mutants were hyper-susceptible to Pseudomonas syringae infection and showed defective stomatal closure in response to bacteria or to the MAMPs flagellin and EF-Tu. By contrast, Arabidopsis over-expressing LecRK-V.2 or LecRK-VII.1 demonstrated a potentiated stomatal immunity. LecRK-V.2 and LecRK-VII.1 are shown to be part of the FLS2 PRR complex. In addition, LecRK-V.2 and LecRK-VII.1 were critical for methyl jasmonate (MeJA)-mediated stomatal closure, notably for MeJA-induced activation of guard cell Ca 2+ -permeable cation channels. This study highlights the role of LecRK-V.2 and LecRK-VII.1 in stomatal immunity at the FLS2 PRR complex and in MeJA-mediated stomatal closure. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Crystal structure of (4-cyano­pyridine-κN){5,10,15,20-tetrakis[4-(benzoyloxy)phenyl]porphyrinato-κ4 N}zinc–4-cyano­pyridine (1/1)

PubMed Central

Nasri, Soumaya; Amiri, Nesrine; Turowska-Tyrk, Ilona; Daran, Jean-Claude; Nasri, Habib

2016-01-01

In the title compound, [Zn(C72H44N4O8)(C6H4N2)]·C6H4N2 or [Zn(TPBP)(4-CNpy]·(4-CNpy) [where TPBP and 4-CNpy are 5,10,15,20-(tetra­phenyl­benzoate)porphyrinate and 4-cyano­pyridine, respectively], the ZnII cation is chelated by four pyrrole-N atoms of the porphyrinate anion and coordinated by a pyridyl-N atom of the 4-CNpy axial ligand in a distorted square-pyramidal geometry. The average Zn—N(pyrrole) bond length is 2.060 (6) Å and the Zn—N(4-CNpy) bond length is 2.159 (2) Å. The zinc cation is displaced by 0.319 (1) Å from the N4C20 mean plane of the porphyrinate anion toward the 4-cyano­pyridine axial ligand. This porphyrinate macrocycle exhibits major saddle and moderate ruffling and doming deformations. In the crystal, the [Zn(TPBP)(4-CNpy)] complex mol­ecules are linked together via weak C—H⋯N, C—H⋯O and C—H⋯π inter­actions, forming supra­molecular channels parallel to the c axis. The non-coordinating 4-cyano­pyridine mol­ecules are located in the channels and linked with the complex mol­ecules, via weak C—H⋯N inter­actions and π-π stacking or via weak C—H⋯O and C—H⋯π inter­actions. The non-coordinating 4-cyano­pyridine mol­ecule is disordered over two positions with an occupancy ratio of 0.666 (4):0.334 (4). PMID:26958379

Insights into the early evolution of animal calcium signaling machinery: A unicellular point of view

PubMed Central

Cai, Xinjiang; Wang, Xiangbing; Patel, Sandip; Clapham, David E.

2014-01-01

The basic principles of Ca2+ regulation emerged early in prokaryotes. Ca2+ signaling acquired more extensive and varied functions when life evolved into multicellular eukaryotes with intracellular organelles. Animals, fungi and plants display differences in the mechanisms that control cytosolic Ca2+ concentrations. The aim of this review is to examine recent findings from comparative genomics of Ca2+ signaling molecules in close unicellular relatives of animals and in common unicellular ancestors of animals and fungi. Also discussed are the evolution and origins of the sperm-specific CatSper channel complex, cation/Ca2+ exchangers and four-domain voltage-gated Ca2+ channels. Newly identified evolutionary evidence suggests that the distinct Ca2+ signaling machineries in animals, plants and fungi likely originated from an ancient Ca2+ signaling machinery prior to early eukaryotic radiation. PMID:25498309

A melanosomal two-pore sodium channel regulates pigmentation

PubMed Central

Bellono, Nicholas W.; Escobar, Iliana E.; Oancea, Elena

2016-01-01

Intracellular organelles mediate complex cellular functions that often require ion transport across their membranes. Melanosomes are organelles responsible for the synthesis of the major mammalian pigment melanin. Defects in melanin synthesis result in pigmentation defects, visual deficits, and increased susceptibility to skin and eye cancers. Although genes encoding putative melanosomal ion transporters have been identified as key regulators of melanin synthesis, melanosome ion transport and its contribution to pigmentation remain poorly understood. Here we identify two-pore channel 2 (TPC2) as the first reported melanosomal cation conductance by directly patch-clamping skin and eye melanosomes. TPC2 has been implicated in human pigmentation and melanoma, but the molecular mechanism mediating this function was entirely unknown. We demonstrate that the vesicular signaling lipid phosphatidylinositol bisphosphate PI(3,5)P2 modulates TPC2 activity to control melanosomal membrane potential, pH, and regulate pigmentation. PMID:27231233

Insights into the early evolution of animal calcium signaling machinery: a unicellular point of view.

PubMed

Cai, Xinjiang; Wang, Xiangbing; Patel, Sandip; Clapham, David E

2015-03-01

The basic principles of Ca(2+) regulation emerged early in prokaryotes. Ca(2+) signaling acquired more extensive and varied functions when life evolved into multicellular eukaryotes with intracellular organelles. Animals, fungi and plants display differences in the mechanisms that control cytosolic Ca(2+) concentrations. The aim of this review is to examine recent findings from comparative genomics of Ca(2+) signaling molecules in close unicellular relatives of animals and in common unicellular ancestors of animals and fungi. Also discussed are the evolution and origins of the sperm-specific CatSper channel complex, cation/Ca(2+) exchangers and four-domain voltage-gated Ca(2+) channels. Newly identified evolutionary evidence suggests that the distinct Ca(2+) signaling machineries in animals, plants and fungi likely originated from an ancient Ca(2+) signaling machinery prior to early eukaryotic radiation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Thermotaxis, circadian rhythms, and TRP channels in Drosophila

PubMed Central

Bellemer, Andrew

2015-01-01

The fruit fly Drosophila melanogaster is a poikilothermic organism that must detect and respond to both fine and coarse changes in environmental temperature in order maintain optimal body temperature, synchronize behavior to daily temperature fluctuations, and to avoid potentially injurious environmental hazards. Members of the Transient Receptor Potential (TRP) family of cation channels are well known for their activation by changes in temperature and their essential roles in sensory transduction in both invertebrates and vertebrates. The Drosophila genome encodes 13 TRP channels, and several of these have key sensory transduction and modulatory functions in allowing larval and adult flies to make fine temperature discriminations to attain optimal body temperature, detect and avoid large environmental temperature fluctuations, and make rapid escape responses to acutely noxious stimuli. Drosophila use multiple, redundant signaling pathways and neural circuits to execute these behaviors in response to both increases and decreases in temperature of varying magnitudes and time scales. A plethora of powerful molecular and genetic tools and the fly's simple, well-characterized nervous system have given Drosophila neurobiologists a powerful platform to study the cellular and molecular mechanisms of TRP channel function and how these mechanisms are conserved in vertebrates, as well as how these channels function within sensorimotor circuits to generate both simple and complex thermosensory behaviors. PMID:27227026

Mutual influence between triel bond and cation-π interactions: an ab initio study

NASA Astrophysics Data System (ADS)

Esrafili, Mehdi D.; Mousavian, Parisasadat

2017-12-01

Using ab initio calculations, the cooperative and solvent effects on cation-π and B...N interactions are studied in some model ternary complexes, where these interactions coexist. The nature of the interactions and the mechanism of cooperativity are investigated by means of quantum theory of atoms in molecules (QTAIM), noncovalent interaction (NCI) index and natural bond orbital analysis. The results indicate that all cation-π and B...N binding distances in the ternary complexes are shorter than those of corresponding binary systems. The QTAIM analysis reveals that ternary complexes have higher electron density at their bond critical points relative to the corresponding binary complexes. In addition, according to the QTAIM analysis, the formation of cation-π interaction increases covalency of B...N bonds. The NCI analysis indicates that the cooperative effects in the ternary complexes make a shift in the location of the spike associated with each interaction, which can be regarded as an evidence for the reinforcement of both cation-π and B...N interactions in these systems. Solvent effects on the cooperativity of cation-π and B...N interactions are also investigated.

Fascinating interaction of the ammonium cation with [2.2.2]paracyclophane: experimental and theoretical study

NASA Astrophysics Data System (ADS)

Makrlík, Emanuel; Sýkora, David; Böhm, Stanislav; Kvíčalová, Magdalena; Vaňura, Petr

2018-05-01

By means of electrospray ionisation mass spectrometry, it was evidenced experimentally that the ammonium cation (NH4+) reacts with the electroneutral [2.2.2]paracyclophane ligand (C24H24) to form the cationic complex [NH4(C24H24)]+. Moreover, applying quantum chemical calculations, the most probable conformation of the proven [NH4(C24H24)]+ complex was solved. In the complex [NH4(C24H24)]+ having a symmetry very close to C3, the 'central' cation NH4+ is coordinated by three strong bifurcated intramolecular hydrogen bonds to the corresponding six carbon atoms from the three benzene rings of [2.2.2]paracyclophane via cation-π interaction. Finally, the interaction energy, E(int), of the considered complex [NH4(C24H24)]+ was evaluated as -625.8 kJ/mol, confirming the formation of this fascinating complex species as well. It means that the [2.2.2]paracyclophane ligand can be considered as an effective receptor for the ammonium cation in the gas phase.

TRP channels: sensors and transducers of gasotransmitter signals

PubMed Central

Takahashi, Nobuaki; Kozai, Daisuke; Mori, Yasuo

2012-01-01

The transient receptor potential (trp) gene superfamily encodes cation channels that act as multimodal sensors for a wide variety of stimuli from outside and inside the cell. Upon sensing, they transduce electrical and Ca2+ signals via their cation channel activities. These functional features of TRP channels allow the body to react and adapt to different forms of environmental changes. Indeed, members of one class of TRP channels have emerged as sensors of gaseous messenger molecules that control various cellular processes. Nitric oxide (NO), a vasoactive gaseous molecule, regulates TRP channels directly via cysteine (Cys) S-nitrosylation or indirectly via cyclic GMP (cGMP)/protein kinase G (PKG)-dependent phosphorylation. Recent studies have revealed that changes in the availability of molecular oxygen (O2) also control the activation of TRP channels. Anoxia induced by O2-glucose deprivation and severe hypoxia (1% O2) activates TRPM7 and TRPC6, respectively, whereas TRPA1 has recently been identified as a novel sensor of hyperoxia and mild hypoxia (15% O2) in vagal and sensory neurons. TRPA1 also detects other gaseous molecules such as hydrogen sulfide (H2S) and carbon dioxide (CO2). In this review, we focus on how signaling by gaseous molecules is sensed and integrated by TRP channels. PMID:22934072

meso-Octamethylcalix[4]pyrrole as an effective macrocyclic receptor for the univalent thallium cation in the gas phase: Experimental and theoretical study

NASA Astrophysics Data System (ADS)

Polášek, Miroslav; Makrlík, Emanuel; Kvíčala, Jaroslav; Křížová, Věra; Vaňura, Petr

2018-02-01

By using electrospray ionization mass spectrometry (ESI-MS), it was proven experimentally that the univalent thallium cation (Tl+) forms with meso-octamethylcalix[4]pyrrole (1) the cationic complex species 1 Tl+. When this kinetically stable cation-π complex 1 Tl+ is collisionally activated, it decomposes by elimination of the whole ligand 1 or small meso-octamethylcalix[4]pyrrole fragments. Further, applying quantum chemical DFT calculations, four different conformations of the resulting complex 1 Tl+ were derived. It means that under the present experimental conditions, this ligand 1 can be considered as a very effective macrocyclic receptor for the thallium cation.

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

Studies on the System Regulating Proton Movement across the Chloroplast Envelope 1

PubMed Central

Peters, Jeanne S.; Berkowitz, Gerald A.

1991-01-01

Studies were undertaken to further characterize the spinach (Spinacea oleracea) chloroplast envelope system, which facilitates H+ movement into and out of the stroma, and, hence, modulates photosynthetic activity by regulating stromal pH. It was demonstrated that high envelope-bound Mg2+ causes stromal acidification and photosynthetic inhibition. High envelope-bound Mg2+ was also found to necessitate the activity of a digitoxinand oligomycin-sensitive ATPase for the maintenance of high stromal pH and photosynthesis in the illuminated chloroplast. In chloroplasts that had high envelope Mg2+ and inhibited envelope ATPase activity, 2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide was found to raise stromal pH and stimulate photosynthesis. 2-(Diethylamino)-N-(2,6-dimethylphenyl)acetamide is an amine anesthetic that is known to act as a monovalent cation channel blocker in mammalian systems. We postulate that the system regulating cation and H+ fluxes across the plastid envelope includes a monovalent cation channel in the envelope, some degree of (envelope-bound Mg2+ modulated) H+ flux linked to monovalent cation antiport, and ATPase-dependent H+ efflux. PMID:16668116

Thermosensitive transient receptor potential channels (thermo-TRPs) in human corneal epithelial cells

PubMed Central

Mergler, Stefan; Garreis, Fabian; Sahlmüller, Monika; Reinach, Peter S.; Paulsen, Friedrich; Pleyer, Uwe

2010-01-01

Thermosensitive transient receptor potential proteins (TRPs) such as TRPV1-TRPV4 are all heat-activated non-selective cation channels that are modestly permeable to Ca2+. TRPV1, TRPV3 and TRPV4 functional expression were previously identified in human corneal epithelial cells (HCEC). However, the membrane currents were not described underlying their activation by either selective agonists or thermal variation. This study characterized the membrane currents and [Ca 2+]i transients induced by thermal and agonist TRPV1 and 4 stimulation. TRPV1 and 4 expressions were confirmed by RT-PCR and TRPV2 transcripts were also detected. In fura2-loaded HCEC, a TRPV1-3 selective agonist, 100 µM 2-aminoethoxydiphenyl borate (2-APB), induced intracellular Ca2+ transients and an increase in non-selective cation outward currents that were suppressed by ruthenium-red (RuR) (10–20 µM), a nonselective TRPV channel blocker. These changes were also elicited by rises in ambient temperature from 25 °C to over 40 °C. RuR (5 µM) and a selective TRPV1 channel blocker capsazepine (CPZ) (10 µM) or another related blocker, lanthanum chloride (La3+) (100 µM) suppressed these temperature-induced Ca2+ increases. Planar patch-clamp technique was used to characterize the currents underlying Ca2+ transients. Increasing the temperature to over 40 °C induced reversible rises in non-selective cation currents. Moreover, a hypotonic challenge (25 %) increased non-selective cation currents confirming TRPV4 activity. We conclude that HCEC possess in addition to thermo-sensitive TRPV3 activity TRPV1, TRPV2 and TRPV4 activity. Their activation confers temperature sensitivity at the ocular surface, which may protect the cornea against such stress. PMID:21506114

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

PubMed Central

Ishihara, K; Hiraoka, M; Ochi, R

1996-01-01

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

In vitro biopharmaceutical evaluation of ciprofloxacin/metal cation complexes for pulmonary administration.

PubMed

Brillault, J; Tewes, F; Couet, W; Olivier, J C

2017-01-15

Pulmonary delivery of fluoroquinolones (FQs) is an interesting approach to treat lung infections as it may lead to high local concentrations while minimizing systemic exposure. However, FQs have a rapid diffusion through the lung epithelium giving the pulmonary route no advantage compared to the oral route. Interactions between FQs and metal cations form complexes which limit the diffusion through the epithelial barrier and would reduce the absorption of FQs and maintain high concentrations in the lung. The effects of this complexation depend on the FQ and the metal cations and optimum partners should be selected through in vitro experiments prior to aerosol drug formulation. In this study, CIP was chosen as a representative FQ and 5 cations (Ca 2+ , Mg 2+ , Zn 2+ , Al 3+ , Cu 2+ ) were selected to study the complexation and its effects on permeability, antimicrobial efficacy and cell toxicity. The results showed that the apparent association constants between CIP and cations ranked with the descending order: Cu 2+ >Al 3+ >Zn 2+ >Mg 2+ >Ca 2+ . When a target of 80% complexation was reached with the adequate concentrations of cations, the CIP permeability through the Calu-3 lung epithelial cells was decreased of 50%. Toxicity of the CIP on the Calu-3 cells, with an EC50 evaluated at 7μM, was not significantly affected by the presence of the cations. The minimum inhibitory concentration of CIP for Pseudomonas aeruginosa was not affected or slightly increased in the range of cation concentrations tested, except for Mg 2+ . In conclusion, permeability was the main parameter that was affected by the metal cation complexation while cell toxicity and antimicrobial activity were not or slightly modified. Cu 2+ , with the highest apparent constant of association and with no effect on cell toxicity and antimicrobial activity of the CIP, appeared as a promising cation for the development of a controlled-permeability formulation of CIP for lung treatment. Copyright © 2016 Elsevier B.V. All rights reserved.

Spectroscopic Identification of the Carbyne Hydride Structure of the Dehydrogenation Product of Methane Activation by Osmium Cations

NASA Astrophysics Data System (ADS)

Armentrout, P. B.; Kuijpers, Stach E. J.; Lushchikova, Olga V.; Hightower, Randy L.; Boles, Georgia C.; Bakker, Joost M.

2018-04-01

The present work explores the structures of species formed by dehydrogenation of methane (CH4) and perdeuterated methane (CD4) by the 5d transition metal cation osmium (Os+). Using infrared multiple photon dissociation (IRMPD) action spectroscopy and density functional theory (DFT), the structures of the [Os,C,2H]+ and [Os,C,2D]+ products are explored. This study complements previous work on the related species formed by dehydrogenation of methane by four other 5d transition metal cations (M+ = Ta+, W+, Ir+, and Pt+). Osmium cations are formed in a laser ablation source, react with methane pulsed into a reaction channel downstream, and the resulting products spectroscopically characterized through photofragmentation using the Free-Electron Laser for IntraCavity Experiments (FELICE) in the 300-1800 cm-1 range. Photofragmentation was monitored by the loss of H2/D2. Comparison of the experimental spectra and DFT calculated spectra leads to identification of the ground state carbyne hydride, HOsCH+ (2A') as the species formed, as previously postulated theoretically. Further, a full description of the systematic spectroscopic shifts observed for deuterium labeling of these complexes, some of the smallest systems to be studied using IRMPD action spectroscopy, is achieved. A full rotational contour analysis explains the observed linewidths as well as the observation of doublet structures in several bands, consistent with previous observations for HIrCH+ (2A'). [Figure not available: see fulltext.

Calcium, mitochondria and oxidative stress in neuronal pathology. Novel aspects of an enduring theme.

PubMed

Chinopoulos, Christos; Adam-Vizi, Vera

2006-02-01

The interplay among reactive oxygen species (ROS) formation, elevated intracellular calcium concentration and mitochondrial demise is a recurring theme in research focusing on brain pathology, both for acute and chronic neurodegenerative states. However, causality, extent of contribution or the sequence of these events prior to cell death is not yet firmly established. Here we review the role of the alpha-ketoglutarate dehydrogenase complex as a newly identified source of mitochondrial ROS production. Furthermore, based on contemporary reports we examine novel concepts as potential mediators of neuronal injury connecting mitochondria, increased [Ca2+]c and ROS/reactive nitrogen species (RNS) formation; specifically: (a) the possibility that plasmalemmal nonselective cationic channels contribute to the latent [Ca2+]c rise in the context of glutamate-induced delayed calcium deregulation; (b) the likelihood of the involvement of the channels in the phenomenon of 'Ca2+ paradox' that might be implicated in ischemia/reperfusion injury; and (c) how ROS/RNS and mitochondrial status could influence the activity of these channels leading to loss of ionic homeostasis and cell death.

The TRPM7 chanzyme is cleaved to release a chromatin modifying kinase

PubMed Central

Krapivinsky, Grigory; Krapivinsky, Luba; Manasian, Yunona; Clapham, David E.

2014-01-01

SUMMARY TRPM7 is a ubiquitous ion channel and kinase, a unique ‘chanzyme’, required for proper early embryonic development. It conducts Zn2+, Mg2+, Ca2+ as well as monovalent cations, and contains a functional serine/threonine kinase at its carboxyl terminus. Here, we show that in normal tissues and cell lines, the kinase is proteolytically cleaved from the channel domain in a cell type-specific manner. These TRPM7 Cleaved Kinase fragments (M7CKs) translocate to the nucleus and bind multiple components of chromatin remodeling complexes, including Polycomb group proteins. In the nucleus, the kinase phosphorylates specific serines/threonines of histones. M7CK-dependent phosphorylation of H3Ser10 at promoters of TRPM7-dependent genes correlates with their activity. We also demonstrate that cytosolic free [Zn2+] is TRPM7-dependent and regulates M7CK binding to transcription factors containing zinc-finger domains. These findings suggest that TRPM7-mediated modulation of intracellular Zn2+ concentration couples ion channel signaling to epigenetic chromatin covalent modifications that affect gene expression patterns. PMID:24855944

Examination of the effect of the annealing cation on higher order structures containing guanine or isoguanine repeats

PubMed Central

Pierce, Sarah E.; Wang, Junmei; Jayawickramarajah, Janarthanan; Hamilton, Andrew D.; Brodbelt, Jennifer S.

2010-01-01

Isoguanine (2-oxo-6-amino-guanine), a natural but non-standard base, exhibits unique self-association properties compared to its isomer, guanine, and results in formation of different higher order DNA structures. In this work, the higher order structures formed by oligonucleotides containing guanine repeats or isoguanine repeats after annealing in solutions containing various cations are evaluated by electrospray ionization mass spectrometry (ESI-MS) and circular dichroism (CD) spectroscopy. The guanine-containing strand (G9) consistently formed quadruplexes upon annealing, whereas the isoguanine strand (Ig9) formed both pentaplexes and quadruplexes depending on the annealing cation. Quadruplex formation with G9 showed some dependence on the identity of the cation present during annealing with high relative quadruplex formation detected with six of ten cations. Analogous annealing experiments with Ig9 resulted in complex formation with all ten cations, and the majority of the resulting complexes were pentaplexes. CD results indicated most of the original complexes survived the desalting process necessary for ESI-MS analysis. In addition, several complexes, especially the pentaplexes, were found to be capable of cation exchange with ammonium ions. Ab initio calculations were conducted for isoguanine tetrads and pentads coordinated with all ten cations to predict the most energetically stable structures of the complexes in the gas phase. The observed preference of forming quadruplexes versus pentaplexes as a function of the coordinated cation can be interpreted by the calculated reaction energies of both the tetrads and pentads in combination with the distortion energies of tetrads. PMID:19746468

The Physiology of Mechanoelectrical Transduction Channels in Hearing

PubMed Central

Fettiplace, Robert; Kim, Kyunghee X.

2014-01-01

Much is known about the mechanotransducer (MT) channels mediating transduction in hair cells of the vertrbrate inner ear. With the use of isolated preparations, it is experimentally feasible to deliver precise mechanical stimuli to individual cells and record the ensuing transducer currents. This approach has shown that small (1–100 nm) deflections of the hair-cell stereociliary bundle are transmitted via interciliary tip links to open MT channels at the tops of the stereocilia. These channels are cation-permeable with a high selectivity for Ca2+; two channels are thought to be localized at the lower end of the tip link, each with a large single-channel conductance that increases from the low- to high-frequency end of the cochlea. Ca2+ influx through open channels regulates their resting open probability, which may contribute to setting the hair cell resting potential in vivo. Ca2+ also controls transducer fast adaptation and force generation by the hair bundle, the two coupled processes increasing in speed from cochlear apex to base. The molecular intricacy of the stereocilary bundle and the transduction apparatus is reflected by the large number of single-gene mutations that are linked to sensorineural deafness, especially those in Usher syndrome. Studies of such mutants have led to the discovery of many of the molecules of the transduction complex, including the tip link and its attachments to the stereociliary core. However, the MT channel protein is still not firmly identified, nor is it known whether the channel is activated by force delivered through accessory proteins or by deformation of the lipid bilayer. PMID:24987009

Nonselective Currents and Channels in Plasma Membranes of Protoplasts from Coats of Developing Seeds of Bean1

PubMed Central

Zhang, Wen-Hao; Skerrett, Martha; Walker, N. Alan; Patrick, John W.; Tyerman, Stephen D.

2002-01-01

In developing bean (Phaseolus vulgaris) seeds, phloem-imported nutrients move in the symplast from sieve elements to the ground parenchyma cells where they are transported across the plasma membrane into the seed apoplast. To study the mechanisms underlying this transport, channel currents in ground parenchyma protoplasts were characterized using patch clamp. A fast-activating outward current was found in all protoplasts, whereas a slowly activating outward current was observed in approximately 25% of protoplasts. The two currents had low selectivity for univalent cations, but the slow current was more selective for K+ over Cl− (PK:PCl = 3.6–4.2) than the fast current (PK:PCl = 1.8–2.5) and also displayed Ca2+ selectivity. The slow current was blocked by Ba2+, whereas both currents were blocked by Gd3+ and La3+. Efflux of K+ from seed coat halves was inhibited 25% by Gd3+ and La3+ but was stimulated by Ba2+ and Cs+, suggesting that only the fast current may be a component in the pathway for K+ release. An “instantaneous” inward current observed in all protoplasts exhibited similar pharmacology and permeability for univalent cations to the fast outward current. In outside-out patches, two classes of depolarization-activated cation-selective channels were observed: one slowly activating of low conductance (determined from nonstationary noise to be 2.4 pS) and another with conductances 10-fold higher. Both channels occurred at high density. The higher conductance channel in 10 mm KCl had PK:PCl = 2.8. Such nonselective channels in the seed coat ground parenchyma cell could function to allow some of the efflux of phloem-imported univalent ions into the seed apoplast. PMID:11842143

Piezo channels and GsMTx4: Two milestones in our understanding of excitatory mechanosensitive channels and their role in pathology.

PubMed

Suchyna, Thomas M

2017-11-01

Discovery of Piezo channels and the reporting of their sensitivity to the inhibitor GsMTx4 were important milestones in the study of non-selective cationic mechanosensitive channels (MSCs) in normal physiology and pathogenesis. GsMTx4 had been used for years to investigate the functional role of cationic MSCs, especially in muscle tissue, but with little understanding of its target or inhibitory mechanism. The sensitivity of Piezo channels to bilayer stress and its robust mechanosensitivity when expressed in heterologous systems were keys to determining GsMTx4's mechanism of action. However, questions remain regarding Piezo's role in muscle function due to the non-selective nature of GsMTx4 inhibition toward membrane mechanoenzymes and the implication of MCS channel types by genetic knockdown. Evidence supporting Piezo like activity, at least in the developmental stages of muscle, is presented. While the MSC targets of GsMTx4 in muscle pathology are unclear, its muscle protective effects are clearly demonstrated in two recent in situ studies on normal cardiomyocytes and dystrophic skeletal muscle. The muscle protective function may be due to the combined effect of GsMTx4's inhibitory action on cationic MSCs like Piezo and TRP, and its potentiation of repolarizing K + selective MSCs like K2P and SAKCa. Paradoxically, the potent in vitro action of GsMTx4 on many physiological functions seems to conflict with its lack of in situ side-effects on normal animal physiology. Future investigations into cytoskeletal control of sarcolemma mechanics and the suspected inclusion of MSCs in membrane micro/nano sized domains with distinct mechanical properties will aide our understanding of this dichotomy. Published by Elsevier Ltd.

TRPV2 Channels Contribute to Stretch-Activated Cation Currents and Myogenic Constriction in Retinal Arterioles.

PubMed

McGahon, Mary K; Fernández, José A; Dash, Durga P; McKee, Jon; Simpson, David A; Zholos, Alex V; McGeown, J Graham; Curtis, Tim M

2016-10-01

Activation of the transient receptor potential channels, TRPC6, TRPM4, and TRPP1 (PKD2), has been shown to contribute to the myogenic constriction of cerebral arteries. In the present study we sought to determine the potential role of various mechanosensitive TRP channels to myogenic signaling in arterioles of the rat retina. Rat retinal arterioles were isolated for RT-PCR, Fura-2 Ca2+ microfluorimetry, patch-clamp electrophysiology, and pressure myography studies. In some experiments, confocal immunolabeling of wholemount preparations was used to examine the localization of specific mechanosensitive TRP channels in retinal vascular smooth muscle cells (VSMCs). Reverse transcription-polymerase chain reaction analysis demonstrated mRNA expression for TRPC1, M7, V1, V2, V4, and P1, but not TRPC6 or M4, in isolated retinal arterioles. Immunolabeling revealed plasma membrane, cytosolic and nuclear expression of TRPC1, M7, V1, V2, V4, and P1 in retinal VSMCs. Hypoosmotic stretch-induced Ca2+ influx in retinal VSMCs was reversed by the TRPV2 inhibitor tranilast and the nonselective TRPP1/V2 antagonist amiloride. Inhibitors of TRPC1, M7, V1, and V4 had no effect. Hypoosmotic stretch-activated cation currents were similar in Na+ and Cs+ containing solutions suggesting no contribution by TRPP1 channels. Direct plasma membrane stretch triggered cation current activity that was blocked by tranilast and specific TRPV2 pore-blocking antibodies and mimicked by the TRPV2 activator, Δ9-tetrahydrocannabinol. Preincubation of retinal arterioles with TRPV2 blocking antibodies prevented the development of myogenic tone. Our results suggest that retinal VSMCs express a range of mechanosensitive TRP channels, but only TRPV2 appears to contribute to myogenic signaling in this vascular bed.

Endolysosomal Cation Channels and Cancer-A Link with Great Potential.

PubMed

Grimm, Christian; Bartel, Karin; Vollmar, Angelika M; Biel, Martin

2018-01-05

The endolysosomal system (ES) consists of lysosomes; early, late, and recycling endosomes; and autophagosomes. It is a key regulator not only of macromolecule degradation and recycling, plasma membrane repair, homeostasis, and lipid storage, but also of antigen presentation, immune defense, cell motility, cell death signaling, tumor growth, and cancer progression. In addition, it plays a critical role in autophagy, and the autophagy-lysosome pathway is intimately associated with the hallmarks of cancer, such as escaping cell death pathways, evading immune surveillance, and deregulating metabolism. The function of endolysosomes is critically dependent on both soluble and endolysosomal membrane proteins such as ion channels and transporters. Cation channels found in the ES include members of the TRP (transient receptor potential) channel superfamily, namely TRPML channels (mucolipins) as well as two-pore channels (TPCs). In recent studies, these channels have been found to play crucial roles in endolysosomal trafficking, lysosomal exocytosis, and autophagy. Mutation or loss of these channel proteins can impact multiple endolysosomal trafficking pathways. A role for TPCs in cancer cell migration and metastasis, linked to distinct defects in endolysosomal trafficking such as integrin trafficking, has been recently established. In this review, we give an overview on the function of lysosomes in cancer with a particular focus on the roles which TPCs and TRPML channels play in the ES and how this can affect cancer cells.

Endolysosomal Cation Channels and Cancer—A Link with Great Potential

PubMed Central

Grimm, Christian; Bartel, Karin; Vollmar, Angelika M.; Biel, Martin

2018-01-01

The endolysosomal system (ES) consists of lysosomes; early, late, and recycling endosomes; and autophagosomes. It is a key regulator not only of macromolecule degradation and recycling, plasma membrane repair, homeostasis, and lipid storage, but also of antigen presentation, immune defense, cell motility, cell death signaling, tumor growth, and cancer progression. In addition, it plays a critical role in autophagy, and the autophagy-lysosome pathway is intimately associated with the hallmarks of cancer, such as escaping cell death pathways, evading immune surveillance, and deregulating metabolism. The function of endolysosomes is critically dependent on both soluble and endolysosomal membrane proteins such as ion channels and transporters. Cation channels found in the ES include members of the TRP (transient receptor potential) channel superfamily, namely TRPML channels (mucolipins) as well as two-pore channels (TPCs). In recent studies, these channels have been found to play crucial roles in endolysosomal trafficking, lysosomal exocytosis, and autophagy. Mutation or loss of these channel proteins can impact multiple endolysosomal trafficking pathways. A role for TPCs in cancer cell migration and metastasis, linked to distinct defects in endolysosomal trafficking such as integrin trafficking, has been recently established. In this review, we give an overview on the function of lysosomes in cancer with a particular focus on the roles which TPCs and TRPML channels play in the ES and how this can affect cancer cells. PMID:29303993

Biophysics and Structure of the Patch and the Gigaseal

PubMed Central

Suchyna, Thomas M.; Markin, Vladislav S.; Sachs, Frederick

2009-01-01

Abstract Interpreting channel behavior in patches requires an understanding of patch structure and dynamics, especially in studies of mechanosensitive channels. High resolution optical studies show that patch formation occurs via blebbing that disrupts normal membrane structure and redistributes in situ components including ion channels. There is a 1–2 μm region of the seal below the patch where proteins are excluded and this may consist of extracted lipids that form the gigaseal. Patch domes often have complex geometries with inhomogeneous stresses due to the membrane-glass adhesion energy (Ea), cytoskeletal forces, and possible lipid subdomains. The resting tension in the patch dome ranges from 1–4 mN/m, a significant fraction of the lytic tension of a bilayer (∼10 mN/m). Thus, all patch experiments are conducted under substantial, and uneven, resting tension that may alter the kinetics of many channels. Ea seems dominated by van der Waals attraction overlaid with a normally repulsive Coulombic force. High ionic strength pipette saline increased Ea and, surprisingly, increased cytoskeletal rigidity in cell-attached patches. Low pH pipette saline also increased Ea and reduced the seal selectivity for cations, presumably by neutralizing the membrane surface charge. The seal is a negatively charged, cation selective, space with a resistance of ∼7 gigohm/μm in 100 mM KCl, and the high resistivity of the space may result from the presence of high viscosity glycoproteins. Patches creep up the pipette over time with voltage independent and voltage dependent components. Voltage-independent creep is expected from the capillary attraction of Ea and the flow of fresh lipids from the cell. Voltage-dependent creep seems to arise from electroosmosis in the seal. Neutralization of negative charges on the seal membrane with low pH decreased the creep rate and reversed the direction of creep at positive pipette potentials. PMID:19651032

Unexpected Actinyl Cation-Directed Structural Variation in Neptunyl(VI) A-Type Tri-lacunary Heteropolyoxotungstate Complexes

DOE PAGES

Berg, John M.; Gaunt, Andrew J.; May, Iain; ...

2015-04-22

A-type tri-lacunary heteropolyoxotungstate anions (e.g., [PW 9O 34] 9-, [AsW 9O 34] 9-, [SiW 9O 34] 10- and [GeW 9O 34] 10-) are multi-dentate oxygen donor ligands that readily form sandwich complexes with actinyl cations ({UO 2} 2+, {NpO 2} +, {NpO 2} 2+ & {PuO 2} 2+) in near neutral/slightly alkaline aqueous solutions. Two or three actinyl cations are sandwiched between two trilacunary anions, with additional cations (Na +, K + or NH 4 +) also often held within the cluster. Studies thus far have indicated that it is these additional +I cations, rather than the specific actinylmore » cation, that direct the structural variation in the complexes formed. We now report the structural characterization of the neptunyl (VI) cluster complex (NH 4) 13 [Na(NpO 2) 2(A-α- PW 9O 34) 2]·12H 2O. The anion in this complex, [Na(NpO 2) 2(PW 9O 34) 2] 13-, contains one Na + cation and two {NpO 2} 2+ cations held between two [PW 9O 34] 9- anions – with an additional partial occupancy NH 4 + or {NpO 2} 2+ cation also present. In the analogous uranium (VI) system, under similar reaction conditions that includes an excess of NH 4Cl in the parent solution, it was previously shown that [(NH 4) 2(U VIO 2) 2(A-PW 9O 34) 2] 12- is the dominant species in both solution and the crystallized salt. Spectroscopic studies provide further proof of differences in the observed chemistry for the {NpO 2} 2+/[PW 9O 34] 9- and {UO 2} 2+/[PW 9O 34] 9- systems, both in solution and in solid state complexes crystallized from comparable salt solutions. The work revealed that varying the actinide element (Np vs. U) can indeed measurably impact structure and complex stability in the cluster chemistry of actinyl (VI) cations with A-type tri-lacunary heteropolyoxotungstate anions.« less

Amylose-Based Cationic Star Polymers for siRNA Delivery.

PubMed

Nishimura, Tomoki; Umezaki, Kaori; Mukai, Sada-atsu; Sawada, Shin-ichi; Akiyoshi, Kazunari

2015-01-01

A new siRNA delivery system using a cationic glyco-star polymer is described. Spermine-modified 8-arm amylose star polymer (with a degree of polymerization of approximately 60 per arm) was synthesized by chemoenzymatic methods. The cationic star polymer effectively bound to siRNA and formed spherical complexes with an average hydrodynamic diameter of 230 nm. The cationic 8-arm star polymer complexes showed superior cellular uptake characteristics and higher gene silencing effects than a cationic 1-arm polymer. These results suggest that amylose-based star polymers are a promising nanoplatform for glycobiomaterials.

Mononuclear bromide complexes of Sb(V): crystal structures and thermal behaviour

NASA Astrophysics Data System (ADS)

Adonin, Sergey A.; Bondarenko, Mikhail A.; Samsonenko, Denis G.; Semitut, Evgeniy Yu; Sokolov, Maxim N.; Fedin, Vladimir P.

2018-05-01

Reactions of Sb2O3 dissolved in HBr/Br2 and bromides of pyridinium-derived cations result in mononuclear complexes of Sb(V) - (cation)[SbBr6] (cation = 2-chloropyridinium (1), 2-bromopyridinium (2)). Thermal behaviour of 1 and 2, as well as similar previously reported complexes Et4N [SbBr6] (3) and (N-EtPy)[SbBr6] (4), was studied and discussed.

Evidence for percolation diffusion of cations and reordering in disordered pyrochlore from accelerated molecular dynamics

DOE PAGES

Perriot, Romain; Uberuaga, Blas P.; Zamora, Richard J.; ...

2017-09-20

Diffusion in complex oxides is critical to ionic transport, radiation damage evolution, sintering, and aging. In complex oxides such as pyrochlores, anionic diffusion is dramatically affected by cation disorder. However, little is known about how disorder influences cation transport. Here, we report results from classical and accelerated molecular dynamics simulations of vacancy-mediated cation diffusion in Gd 2Ti 2O 7 pyrochlore, on the microsecond timescale. We find that diffusion is slow at low levels of disorder, while higher disorder allows for fast diffusion, which is then accompanied by antisite annihilation and reordering, and thus a slowing of cation transport. Cation diffusivitymore » is therefore not constant, but decreases as the material reorders. We also show that fast cation diffusion is triggered by the formation of a percolation network of antisites. This is in contrast with observations from other complex oxides and disordered media models, suggesting a fundamentally different relation between disorder and mass transport.« less

Structural Basis for Xenon Inhibition in a Cationic Pentameric Ligand-Gated Ion Channel

PubMed Central

Sauguet, Ludovic; Fourati, Zeineb; Prangé, Thierry; Delarue, Marc; Colloc'h, Nathalie

2016-01-01

GLIC receptor is a bacterial pentameric ligand-gated ion channel whose action is inhibited by xenon. Xenon has been used in clinical practice as a potent gaseous anaesthetic for decades, but the molecular mechanism of interactions with its integral membrane receptor targets remains poorly understood. Here we characterize by X-ray crystallography the xenon-binding sites within both the open and “locally-closed” (inactive) conformations of GLIC. Major binding sites of xenon, which differ between the two conformations, were identified in three distinct regions that all belong to the trans-membrane domain of GLIC: 1) in an intra-subunit cavity, 2) at the interface between adjacent subunits, and 3) in the pore. The pore site is unique to the locally-closed form where the binding of xenon effectively seals the channel. A putative mechanism of the inhibition of GLIC by xenon is proposed, which might be extended to other pentameric cationic ligand-gated ion channels. PMID:26910105

Structural Basis for Xenon Inhibition in a Cationic Pentameric Ligand-Gated Ion Channel.

PubMed

Sauguet, Ludovic; Fourati, Zeineb; Prangé, Thierry; Delarue, Marc; Colloc'h, Nathalie

2016-01-01

GLIC receptor is a bacterial pentameric ligand-gated ion channel whose action is inhibited by xenon. Xenon has been used in clinical practice as a potent gaseous anaesthetic for decades, but the molecular mechanism of interactions with its integral membrane receptor targets remains poorly understood. Here we characterize by X-ray crystallography the xenon-binding sites within both the open and "locally-closed" (inactive) conformations of GLIC. Major binding sites of xenon, which differ between the two conformations, were identified in three distinct regions that all belong to the trans-membrane domain of GLIC: 1) in an intra-subunit cavity, 2) at the interface between adjacent subunits, and 3) in the pore. The pore site is unique to the locally-closed form where the binding of xenon effectively seals the channel. A putative mechanism of the inhibition of GLIC by xenon is proposed, which might be extended to other pentameric cationic ligand-gated ion channels.

Structural Insight into the Assembly of TRPV Channels

PubMed Central

Huynh, Kevin W.; Cohen, Matthew R.; Chakrapani, Sudha; Holdaway, Heather A.; Stewart, Phoebe L.; Moiseenkova-Bell, Vera Y.

2017-01-01

SUMMARY Transient receptor potential (TRP) proteins are a large family of polymodal nonselective cation channels. The TRP vanilloid (TRPV) subfamily consists of six homologous members with diverse functions. TRPV1–TRPV4 are nonselective cation channels proposed to play a role in nociception, while TRPV5 and TRPV6 are involved in epithelial Ca2+ homeostasis. Here we present the cryo-electron microscopy (cryo-EM) structure of functional, full-length TRPV2 at 13.6 Å resolution. The map reveals that the TRPV2 cytoplasmic domain displays a 4-fold petal-like shape in which high-resolution N-terminal ankyrin repeat domain (ARD) structures can be unambiguously fitted. Fitting of the available ARD structures for other TRPV subfamily members into the TRPV2 EM map suggests that TRPV subfamily members have highly homologous structural topologies. These results allowed us to postulate a structural explanation for the functional diversity among TRPV channels and their differential regulation by proteins and ligands. PMID:24373766

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

Perriot, Romain; Uberuaga, Blas P.; Zamora, Richard J.

Diffusion in complex oxides is critical to ionic transport, radiation damage evolution, sintering, and aging. In complex oxides such as pyrochlores, anionic diffusion is dramatically affected by cation disorder. However, little is known about how disorder influences cation transport. Here, we report results from classical and accelerated molecular dynamics simulations of vacancy-mediated cation diffusion in Gd 2Ti 2O 7 pyrochlore, on the microsecond timescale. We find that diffusion is slow at low levels of disorder, while higher disorder allows for fast diffusion, which is then accompanied by antisite annihilation and reordering, and thus a slowing of cation transport. Cation diffusivitymore » is therefore not constant, but decreases as the material reorders. We also show that fast cation diffusion is triggered by the formation of a percolation network of antisites. This is in contrast with observations from other complex oxides and disordered media models, suggesting a fundamentally different relation between disorder and mass transport.« less

Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain.

PubMed

Jaślan, D; Mueller, T D; Becker, D; Schultz, J; Cuin, T A; Marten, I; Dreyer, I; Schönknecht, G; Hedrich, R

2016-09-01

The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents. Here, we combined bioinformatics, structure modelling, site-directed mutagenesis, and in planta patch clamp studies to elucidate the molecular mechanisms of voltage-dependent channel gating in TPC1 in its native plant background. Structure-function analysis of the Arabidopsis TPC1 channel in planta confirmed that helix S10 operates as the major voltage-sensing site, with Glu450 and Glu478 identified as possible ion-pair partners for voltage-sensing Arg537. The contribution of helix S4 to voltage sensing was found to be negligible. Several conserved negative residues on the luminal site contribute to calcium binding, stabilizing the closed channel. During evolution of plant TPC1s from two separate Shaker-like domains, the voltage-sensing function in the N-terminal Shaker-unit (S1-S4) vanished. © 2016 German Botanical Society and The Royal Botanical Society of the Netherlands.

Human trypanolytic factor APOL1 forms pH-gated cation-selective channels in planar lipid bilayers: Relevance to trypanosome lysis

PubMed Central

Thomson, Russell; Finkelstein, Alan

2015-01-01

Apolipoprotein L-1 (APOL1), the trypanolytic factor of human serum, can lyse several African trypanosome species including Trypanosoma brucei brucei, but not the human-infective pathogens T. brucei rhodesiense and T. brucei gambiense, which are resistant to lysis by human serum. Lysis follows the uptake of APOL1 into acidic endosomes and is apparently caused by colloid-osmotic swelling due to an increased ion permeability of the plasma membrane. Here we demonstrate that nanogram quantities of full-length recombinant APOL1 induce ideally cation-selective macroscopic conductances in planar lipid bilayers. The conductances were highly sensitive to pH: their induction required acidic pH (pH 5.3), but their magnitude could be increased 3,000-fold upon alkalinization of the milieu (pKa = 7.1). We show that this phenomenon can be attributed to the association of APOL1 with the bilayer at acidic pH, followed by the opening of APOL1-induced cation-selective channels upon pH neutralization. Furthermore, the conductance increase at neutral pH (but not membrane association at acidic pH) was prevented by the interaction of APOL1 with the serum resistance-associated protein, which is produced by T. brucei rhodesiense and prevents trypanosome lysis by APOL1. These data are consistent with a model of lysis that involves endocytic recycling of APOL1 and the formation of cation-selective channels, at neutral pH, in the parasite plasma membrane. PMID:25730870

Claudin-2-mediated cation and water transport share a common pore

PubMed Central

Rosenthal, Rita; Günzel, Dorothee; Krug, Susanne M.; Schulzke, Jörg-Dieter; Fromm, Michael; Yu, Alan S.L.

2016-01-01

Aim Claudin-2 is a tight junction protein typically located in “leaky” epithelia exhibiting large paracellular permeabilities like small intestine and proximal kidney tubule. Former studies revealed that claudin-2 forms paracellular channels for small cations like sodium and potassium and also paracellular channels for water. This study analyzes whether the diffusive transport of sodium and water occurs through a common pore of the claudin-2 channel. Methods Wild-type claudin-2 and different claudin-2 mutants were expressed in MDCK I kidney tubule cells using an inducible system. Ion and water permeability and the effect of blocking reagents on both were investigated on different clones of the mutants. Results Neutralization of a negatively charged cation interaction site in the pore with the mutation, D65N, decreased both, sodium permeability and water permeability. Claudin-2 mutants (I66C and S68C) with substitution of the pore-lining amino acids with cysteine were used to test the effect of steric blocking of the claudin-2 pore by thiol-reactive reagents. Addition of thiol-reactive reagents to these mutants simultaneously decreased conductance and water permeability. Remarkably, all experimental perturbations caused parallel changes in ion conductance and water permeability, disproving different or independent passage pathways. Conclusion Our results indicate that claudin-2-mediated cation and water transport are frictionally coupled and share a common pore. This pore is lined and determined in permeability by amino acid residues of the first extracellular loop of claudin-2. PMID:27359349

On the cellular site of two-pore channel TPC1 action in the Poaceae.

PubMed

Dadacz-Narloch, Beata; Kimura, Sachie; Kurusu, Takamitsu; Farmer, Edward E; Becker, Dirk; Kuchitsu, Kazuyuki; Hedrich, Rainer

2013-11-01

The slow vacuolar (SV) channel has been characterized in different dicots by patch-clamp recordings. This channel represents the major cation conductance of the largest organelle in most plant cells. Studies with the tpc1-2 mutant of the model dicot plant Arabidopsis thaliana identified the SV channel as the product of the TPC1 gene. By contrast, research on rice and wheat TPC1 suggested that the monocot gene encodes a plasma membrane calcium-permeable channel. To explore the site of action of grass TPC1 channels, we expressed OsTPC1 from rice (Oryza sativa) and TaTPC1 from wheat (Triticum aestivum) in the background of the Arabidopsis tpc1-2 mutant. Cross-species tpc1 complementation and patch-clamping of vacuoles using Arabidopsis and rice tpc1 null mutants documented that both monocot TPC1 genes were capable of rescuing the SV channel deficit. Vacuoles from wild-type rice but not the tpc1 loss-of-function mutant harbor SV channels exhibiting the hallmark properties of dicot TPC1/SV channels. When expressed in human embryonic kidney (HEK293) cells OsTPC1 was targeted to Lysotracker-Red-positive organelles. The finding that the rice TPC1, just like those from the model plant Arabidopsis and even animal cells, is localized and active in lyso-vacuolar membranes associates this cation channel species with endomembrane function. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.

SEPARATION PROCESS USING COMPLEXING AND ADSORPTION

DOEpatents

Spedding, J.H.; Ayers, J.A.

1958-06-01

An adsorption process is described for separating plutonium from a solution of neutron-irradiated uranium containing ions of a compound of plutonium and other cations. The method consists of forming a chelate complex compound with plutoniunn ions in the solution by adding a derivative of 8- hydroxyquinoline, which derivative contains a sulfonic acid group, and adsorbing the remaining cations from the solution on a cation exchange resin, while the complexed plutonium remains in the solution.

Radiochemical study of reactions of alkyl cations with amines. I. Reactions of methyl and sec-butyl cations with diethylamine

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

Ignat`ev, I.S.; Kochina, T.A.; Nefedov, V.D.

1995-08-10

Ion-molecular gas-phase reactions of free methyl and sec-butyl cations with diethylamine were studied. These reactions proceed via two competing pathways involving formation of a condensation complex or a proton-transfer complex, the latter process predominating. 32 refs., 1 tab.

A simple model for metal cation-phosphate interactions in nucleic acids in the gas phase: alkali metal cations and trimethyl phosphate.

PubMed

Ruan, Chunhai; Huang, Hai; Rodgers, M T

2008-02-01

Threshold collision-induced dissociation techniques are employed to determine the bond dissociation energies (BDEs) of complexes of alkali metal cations to trimethyl phosphate, TMP. Endothermic loss of the intact TMP ligand is the only dissociation pathway observed for all complexes. Theoretical calculations at the B3LYP/6-31G* level of theory are used to determine the structures, vibrational frequencies, and rotational constants of neutral TMP and the M+(TMP) complexes. Theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) level using the B3LYP/6-31G* optimized geometries. The agreement between theory and experiment is reasonably good for all complexes except Li+(TMP). The absolute M+-(TMP) BDEs are found to decrease monotonically as the size of the alkali metal cation increases. No activated dissociation was observed for alkali metal cation binding to TMP. The binding of alkali metal cations to TMP is compared with that to acetone and methanol.

The calcium-permeable non-selective cation channel TRPM2 is modulated by cellular acidification

PubMed Central

Starkus, John G; Fleig, Andrea; Penner, Reinhold

2010-01-01

TRPM2 is a calcium-permeable non-selective cation channel expressed in the plasma membrane and in lysosomes that is critically involved in aggravating reactive oxygen species (ROS)-induced inflammatory processes and has been implicated in cell death. TRPM2 is gated by ADP-ribose (ADPR) and modulated by physiological processes that produce peroxide, cyclic ADP-ribose (cADPR), nicotinamide adenine dinucleotide phosphate (NAADP) and Ca2+. We investigated the role of extra- and intracellular acidification on heterologously expressed TRPM2 in HEK293 cells. Our results show that TRPM2 is inhibited by external acidification with an IC50 of pH 6.5 and is completely suppressed by internal pH of 6. Current inhibition requires channel opening and is strongly voltage dependent, being most effective at negative potentials. In addition, increased cytosolic pH buffering capacity or elevated [Ca2+]i reduces the rate of current inactivation elicited by extracellular acidification, and Na+ and Ca2+ influence the efficacy of proton-induced inactivation. Together, these results suggest that external protons permeate TRPM2 channels to gain access to an intracellular site that regulates channel activity. Consistent with this notion, single-channel measurements in HEK293 cells reveal that internal protons induce channel closure without affecting single-channel conductance, whereas external protons affect channel open probability as well as single-channel conductance of native TRPM2 in neutrophils. We conclude that protons compete with Na+ and Ca2+ for channel permeation and channel closure results from a competitive antagonism of protons at an intracellular Ca2+ binding site. PMID:20194125

The calcium-permeable non-selective cation channel TRPM2 is modulated by cellular acidification.

PubMed

Starkus, John G; Fleig, Andrea; Penner, Reinhold

2010-04-15

TRPM2 is a calcium-permeable non-selective cation channel expressed in the plasma membrane and in lysosomes that is critically involved in aggravating reactive oxygen species (ROS)-induced inflammatory processes and has been implicated in cell death. TRPM2 is gated by ADP-ribose (ADPR) and modulated by physiological processes that produce peroxide, cyclic ADP-ribose (cADPR), nicotinamide adenine dinucleotide phosphate (NAADP) and Ca(2+). We investigated the role of extra- and intracellular acidification on heterologously expressed TRPM2 in HEK293 cells. Our results show that TRPM2 is inhibited by external acidification with an IC(50) of pH 6.5 and is completely suppressed by internal pH of 6. Current inhibition requires channel opening and is strongly voltage dependent, being most effective at negative potentials. In addition, increased cytosolic pH buffering capacity or elevated [Ca(2+)](i) reduces the rate of current inactivation elicited by extracellular acidification, and Na(+) and Ca(2+) influence the efficacy of proton-induced inactivation. Together, these results suggest that external protons permeate TRPM2 channels to gain access to an intracellular site that regulates channel activity. Consistent with this notion, single-channel measurements in HEK293 cells reveal that internal protons induce channel closure without affecting single-channel conductance, whereas external protons affect channel open probability as well as single-channel conductance of native TRPM2 in neutrophils. We conclude that protons compete with Na(+) and Ca(2+) for channel permeation and channel closure results from a competitive antagonism of protons at an intracellular Ca(2+) binding site.

An ATP-gated cation channel with some P2Z-like characteristics in gastric smooth muscle cells of toad.

PubMed Central

Ugur, M; Drummond, R M; Zou, H; Sheng, P; Singer, J J; Walsh, J V

1997-01-01

1. Whole-cell and single-channel currents elicited by extracellular ATP were studied in freshly dissociated smooth muscle cells from the stomach of the toad Bufo marinus using standard patch clamp and microfluorimetric techniques. 2. This ATP-gated cation channel shares a number of pharmacological and functional properties with native rat myometrium receptors, certain native P2Z purinoceptors and the recently cloned P2X7 purinoceptor. But, unlike the last two, the ATP-gated channel does not mediate the formation of large non-specific pores. Thus, it may represent a novel member of the P2X or P2Z class. 3. Extracellular application of ATP (> or = 150 microM) elicited an inward whole-cell current at negative holding potentials that was inwardly rectifying and showed no sign of desensitization. Na+, Cs+ and, to a lesser degree, the organic cation choline served as charge carriers, but Cl- did not. Ratiometric fura-2 measurements indicated that the current is carried in part by Ca2+. The EC50 for ATP was 700 microM in solutions with a low divalent cation concentration. 4. ATP (> or = 100 microM) at the extracellular surface of cell-attached or excised patches elicited inwardly rectifying single-channel currents with a 22 pS conductance. Cl- did not serve as a charge carrier but both Na+ and Cs+ did, as did choline to a lesser extent. The mean open time of the channel was quite long, with a range in hundreds of milliseconds at a holding potential of -70 mV. 5. Mg2+ and Ca2+ decreased the magnitude of the ATP-induced whole-cell currents. Mg2+ decreased both the amplitude and the activity of ATP-activated single-channel currents. 6. ADP, UTP, P1, P5-di-adenosine pentaphosphate (AP5A), adenosine and alpha, beta-methylene ATP (alpha, beta-Me-ATP) did not induce significant whole-cell current. ATP-gamma-S and 2-methylthio ATP (2-Me-S-ATP) were significantly less effective than ATP in inducing whole-cell currents, whereas benzoylbenzoyl ATP (BzATP) was more effective. BzATP, alpha, beta-Me-ATP, ATP-gamma-S and 2-Me-S-ATP induced single-channel currents, but a higher concentration of alpha, beta-Me-ATP was required. 7. BzATP did not induce the formation of large non-specific pores, as assayed using mag-fura-2 as a high molecular mass probe. PMID:9032690

Inhibition of cardiac inward rectifier currents by cationic amphiphilic drugs.

PubMed

van der Heyden, M A G; Stary-Weinzinger, A; Sanchez-Chapula, J A

2013-09-01

Cardiac inward rectifier channels belong to three different classes of the KIR channel protein family. The KIR2.x proteins generate the classical inward rectifier current, IK1, while KIR3 and KIR6 members are responsible for the acetylcholine responsive and ATP sensitive inward rectifier currents IKAch and IKATP, respectively. Aberrant function of these channels has been correlated with severe cardiac arrhythmias, indicating their significant contribution to normal cardiac electrophysiology. A common feature of inward rectifier channels is their dependence on the lipid phosphatidyl-4,5-bisphospate (PIP2) interaction for functional activity. Cationic amphiphilic drugs (CADs) are one of the largest classes of pharmaceutical compounds. Several widely used CADs have been associated with inward rectifier current disturbances, and recent evidence points to interference of the channel-PIP2 interaction as the underlying mechanism of action. Here, we will review how six of these well known drugs, used for treatment in various different conditions, interfere in cardiac inward rectifier functioning. In contrast, KIR channel inhibition by the anionic anesthetic thiopental is achieved by a different mechanism of channel-PIP2 interference. We will discuss the latest basic science insights of functional inward rectifier current characteristics, recently derived KIR channel structures and specific PIP2-receptor interactions at the molecular level and provide insight in how these drugs interfere in the structure-function relationships.

Neutral glycoconjugated amide-based calix[4]arenes: complexation of alkali metal cations in water.

PubMed

Cindro, Nikola; Požar, Josip; Barišić, Dajana; Bregović, Nikola; Pičuljan, Katarina; Tomaš, Renato; Frkanec, Leo; Tomišić, Vladislav

2018-02-07

Cation complexation in water presents a unique challenge in calixarene chemistry, mostly due to the fact that a vast majority of calixarene-based cation receptors is not soluble in water or their solubility has been achieved by introducing functionalities capable of (de)protonation. Such an approach inevitably involves the presence of counterions which compete with target cations for the calixarene binding site, and also rather often requires the use of ion-containing buffer solutions in order to control the pH. Herein we devised a new strategy towards the solution of this problem, based on introducing carbohydrate units at the lower or upper rim of calix[4]arenes which comprise efficient cation binding sites. In this context, we prepared neutral, water-soluble receptors with secondary or tertiary amide coordinating groups, and studied their complexation with alkali metal cations in aqueous and methanol (for the comparison purpose) solutions. Complexation thermodynamics was quantitatively characterized by UV spectrometry and isothermal titration calorimetry, revealing that one of the prepared tertiary amide derivatives is capable of remarkably efficient (log K ≈ 5) and selective binding of sodium cations among alkali metal cations in water. Given the ease of the synthetic procedure used, and thus the variety of accessible analogues, this study can serve as a platform for the development of reagents for diverse purposes in aqueous media.

Amylose-Based Cationic Star Polymers for siRNA Delivery

PubMed Central

Nishimura, Tomoki; Umezaki, Kaori; Mukai, Sada-atsu; Sawada, Shin-ichi; Akiyoshi, Kazunari

2015-01-01

A new siRNA delivery system using a cationic glyco-star polymer is described. Spermine-modified 8-arm amylose star polymer (with a degree of polymerization of approximately 60 per arm) was synthesized by chemoenzymatic methods. The cationic star polymer effectively bound to siRNA and formed spherical complexes with an average hydrodynamic diameter of 230 nm. The cationic 8-arm star polymer complexes showed superior cellular uptake characteristics and higher gene silencing effects than a cationic 1-arm polymer. These results suggest that amylose-based star polymers are a promising nanoplatform for glycobiomaterials. PMID:26539548

Molecular Targets for Antiepileptic Drug Development

PubMed Central

Meldrum, Brian S.; Rogawski, Michael A.

2007-01-01

Summary This review considers how recent advances in the physiology of ion channels and other potential molecular targets, in conjunction with new information on the genetics of idiopathic epilepsies, can be applied to the search for improved antiepileptic drugs (AEDs). Marketed AEDs predominantly target voltage-gated cation channels (the α subunits of voltage-gated Na+ channels and also T-type voltage-gated Ca2+ channels) or influence GABA-mediated inhibition. Recently, α2–δ voltage-gated Ca2+ channel subunits and the SV2A synaptic vesicle protein have been recognized as likely targets. Genetic studies of familial idiopathic epilepsies have identified numerous genes associated with diverse epilepsy syndromes, including genes encoding Na+ channels and GABAA receptors, which are known AED targets. A strategy based on genes associated with epilepsy in animal models and humans suggests other potential AED targets, including various voltage-gated Ca2+ channel subunits and auxiliary proteins, A- or M-type voltage-gated K+ channels, and ionotropic glutamate receptors. Recent progress in ion channel research brought about by molecular cloning of the channel subunit proteins and studies in epilepsy models suggest additional targets, including G-protein-coupled receptors, such as GABAB and metabotropic glutamate receptors; hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel subunits, responsible for hyperpolarization-activated current Ih; connexins, which make up gap junctions; and neurotransmitter transporters, particularly plasma membrane and vesicular transporters for GABA and glutamate. New information from the structural characterization of ion channels, along with better understanding of ion channel function, may allow for more selective targeting. For example, Na+ channels underlying persistent Na+ currents or GABAA receptor isoforms responsible for tonic (extrasynaptic) currents represent attractive targets. The growing understanding of the pathophysiology of epilepsy and the structural and functional characterization of the molecular targets provide many opportunities to create improved epilepsy therapies. PMID:17199015

Cation Effects on the Electron-Acceptor Side of Photosystem II.

PubMed

Khan, Sahr; Sun, Jennifer S; Brudvig, Gary W

2015-06-18

The normal pathway of electron transfer on the electron-acceptor side of photosystem II (PSII) involves electron transfer from quinone A, QA, to quinone B, QB. It is possible to redirect electrons from QA(-) to water-soluble Co(III) complexes, which opens a new avenue for harvesting electrons from water oxidation by immobilization of PSII on electrode surfaces. Herein, the kinetics of electron transfer from QA(-) to [Co(III)(terpy)2](3+) (terpy = 2,2';6',2″-terpyridine) are investigated with a spectrophotometric assay revealing that the reaction follows Michaelis-Menten saturation kinetics, is inhibited by cations, and is not affected by variation of the QA reduction potential. A negatively charged site on the stromal surface of the PSII protein complex, composed of glutamic acid residues near QA, is hypothesized to bind cations, especially divalent cations. The cations are proposed to tune the redox properties of QA through electrostatic interactions. These observations may thus explain the molecular basis of the effect of divalent cations like Ca(2+), Sr(2+), Mg(2+), and Zn(2+) on the redox properties of the quinones in PSII, which has previously been attributed to long-range conformational changes propagated from divalent cations binding to the Ca(II)-binding site in the oxygen-evolving complex on the lumenal side of the PSII complex.

Purification and Characterization of Two Voltage-Dependent Anion Channel Isoforms from Plant Seeds1

PubMed Central

Abrecht, Helge; Wattiez, Ruddy; Ruysschaert, Jean-Marie; Homblé, Fabrice

2000-01-01

Mitochondria were isolated from imbibed seeds of lentil (Lens culinaris) and Phaseolus vulgaris. We copurified two voltage-dependent anion channel from detergent solubilized mitochondria in a single purification step using hydroxyapatite. The two isoforms from P. vulgaris were separated by chromatofocusing chromatography in 4 m urea without any loss of channel activity. Channel activity of each isoform was characterized upon reconstitution into diphytanoyl phosphatidylcholine planar lipid bilayers. Both isoforms form large conductance channels that are slightly anion selective and display cation selective substates. PMID:11080295

Revisiting caffeate's capabilities as a complexation agent to silver cation in mining processes by means of the dual descriptor--a conceptual DFT approach.

PubMed

Martínez-Araya, Jorge Ignacio

2012-09-01

Caffeic acid (C(9)H(8)O(4)) and its conjugate base C(9)H(7)O(4) (-) (anionic form-known as caffeate) were analyzed computationally through the use of quantum chemistry to assess their intrinsic global and local reactivity using the tools of conceptual density functional theory. The anionic form was found to be better at coordinating the silver cation than caffeic acid thus suggesting the use of caffeate as a complexation agent. The complexation capability of caffeate was compared with that of some of the most common ligand agents used to coordinate silver cations. Local reactivity descriptors allowed identification of the preferred sites on caffeate for silver cation coordination thus generating a plausible silver complex. All silver complexes were analyzed thermodynamically considering interaction energies in both gas and aqueous phases; the complexation free energy in aqueous phase was also determined. These results suggest that more attention be paid to the caffeate anion and its derivatives because this work has shed new light on the behavior of this anion in the recovery of silver cations that could be exploited in silver mining processes in a environmentally friendly way.

Association Mechanisms of Unsaturated C2 Hydrocarbons with Their Cations: Acetylene and Ethylene

NASA Technical Reports Server (NTRS)

Bera, Partha P.; Head-Gordon, Martin; Lee, Timothy J.

2013-01-01

The ion-molecule association mechanism of acetylene and ethylene with their cations is investigated by ab initio quantum chemical methods to understand the structures, association energies, and the vibrational and electronic spectra of the products. Stable puckered cyclic isomers are found as the result of first forming less stable linear and bridge isomers. The puckered cyclic complexes are calculated to be strongly bound, by 87, 35 and 56 kcal/mol for acetylene-acetylene cation, ethylene-ethylene cation and acetylene-ethylene cation, respectively. These stable complexes may be intermediates that participate in further association reactions. There are no association barriers, and no significant inter-conversion barriers, so the initial linear and bridge encounter complexes are unlikely to be observable. However, the energy gap between the bridged and cyclic puckered isomers greatly differs from complex to complex: it is 44 kcal/mol in C4H4 +, but only 6 kcal/mol in C4H8 +. The accurate CCSD(T) calculations summarized above are also compared against less computationally expensive MP2 and density functional theory (DFT) calculations for structures, relative energies, and vibrational spectra. Calculated vibrational spectra are compared against available experiments for cyclobutadiene cation. Electronic spectra are also calculated using time-dependent DFT.

Density-dependent changes of the pore properties of the P2X2 receptor channel

PubMed Central

Fujiwara, Yuichiro; Kubo, Yoshihiro

2004-01-01

Ligand-gated ion channels underlie and play important roles in synaptic transmission, and it is generally accepted that the ion channel pores have a rigid structure that enables strict regulation of ion permeation. One exception is the P2X ATP-gated channel. After application of ATP, the ion selectivity of the P2X2 channel time-dependently changes, i.e. permeability to large cations gradually increases, and there is significant cell-to-cell variation in the intensity of inward rectification. Here we show P2X2 channel properties are correlated with the expression level: increasing P2X2 expression level in oocytes increases permeability to large cations, decreases inward rectification and increases ligand sensitivity. We also observed that the inward rectification changed in a dose-dependent manner, i.e. when low concentration of ATP was applied to an oocyte with a high expression level, the intensity of inward rectification of the evoked current was weak. Taken together, these results show that the pore properties of P2X2 channel are not static but change dynamically depending on the open channel density. Furthermore, we identified by mutagenesis study that Ile328 located at the outer mouth of the pore is critical for the density-dependent changes of P2X2. Our findings suggest synaptic transmission can be modulated by the local density-dependent changes of channel properties caused, for example, by the presence of clustering molecules. PMID:15107474

Functional ion channels in human pulmonary artery smooth muscle cells: Voltage-dependent cation channels

PubMed Central

Firth, Amy L.; Remillard, Carmelle V.; Platoshyn, Oleksandr; Fantozzi, Ivana; Ko, Eun A.; Yuan, Jason X.-J.

2011-01-01

The activity of voltage-gated ion channels is critical for the maintenance of cellular membrane potential and generation of action potentials. In turn, membrane potential regulates cellular ion homeostasis, triggering the opening and closing of ion channels in the plasma membrane and, thus, enabling ion transport across the membrane. Such transmembrane ion fluxes are important for excitation–contraction coupling in pulmonary artery smooth muscle cells (PASMC). Families of voltage-dependent cation channels known to be present in PASMC include voltage-gated K+ (Kv) channels, voltage-dependent Ca2+-activated K+ (Kca) channels, L- and T- type voltage-dependent Ca2+ channels, voltage-gated Na+ channels and voltage-gated proton channels. When cells are dialyzed with Ca2+-free K+- solutions, depolarization elicits four components of 4-aminopyridine (4-AP)-sensitive Kvcurrents based on the kinetics of current activation and inactivation. In cell-attached membrane patches, depolarization elicits a wide range of single-channel K+ currents, with conductances ranging between 6 and 290 pS. Macroscopic 4-AP-sensitive Kv currents and iberiotoxin-sensitive Kca currents are also observed. Transcripts of (a) two Na+ channel α-subunit genes (SCN5A and SCN6A), (b) six Ca2+ channel α–subunit genes (α1A, α1B, α1X, α1D, α1Eand α1G) and many regulatory subunits (α2δ1, β1-4, and γ6), (c) 22 Kv channel α–subunit genes (Kv1.1 - Kv1.7, Kv1.10, Kv2.1, Kv3.1, Kv3.3, Kv3.4, Kv4.1, Kv4.2, Kv5.1, Kv 6.1-Kv6.3, Kv9.1, Kv9.3, Kv10.1 and Kv11.1) and three Kv channel β-subunit genes (Kvβ1-3) and (d) four Kca channel α–subunit genes (Sloα1 and SK2-SK4) and four Kca channel β-subunit genes (Kcaβ1-4) have been detected in PASMC. Tetrodotoxin-sensitive and rapidly inactivating Na+ currents have been recorded with properties similar to those in cardiac myocytes. In the presence of 20 mM external Ca2+, membrane depolarization from a holding potential of -100 mV elicits a rapidly inactivating T-type Ca2+ current, while depolarization from a holding potential of -70 mV elicits a slowly inactivating dihydropyridine-sensitive L-type Ca2+ current. This review will focus on describing the electrophysiological properties and molecular identities of these voltage-dependent cation channels in PASMC and their contribution to the regulation of pulmonary vascular function and its potential role in the pathogenesis of pulmonary vascular disease. PMID:21927714

Subtype-specific control of P2X receptor channel signaling by ATP and Mg2+.

PubMed

Li, Mufeng; Silberberg, Shai D; Swartz, Kenton J

2013-09-03

The identity and forms of activating ligands for ion channels are fundamental to their physiological roles in rapid electrical signaling. P2X receptor channels are ATP-activated cation channels that serve important roles in sensory signaling and inflammation, yet the active forms of the nucleotide are unknown. In physiological solutions, ATP is ionized and primarily found in complex with Mg(2+). Here we investigated the active forms of ATP and found that the action of MgATP(2-) and ATP(4-) differs between subtypes of P2X receptors. The slowly desensitizing P2X2 receptor can be activated by free ATP, but MgATP(2-) promotes opening with very low efficacy. In contrast, both free ATP and MgATP(2-) robustly open the rapidly desensitizing P2X3 subtype. A further distinction between these two subtypes is the ability of Mg(2+) to regulate P2X3 through a distinct allosteric mechanism. Importantly, heteromeric P2X2/3 channels present in sensory neurons exhibit a hybrid phenotype, characterized by robust activation by MgATP(2-) and weak regulation by Mg(2+). These results reveal the existence of two classes of homomeric P2X receptors with differential sensitivity to MgATP(2-) and regulation by Mg(2+), and demonstrate that both restraining mechanisms can be disengaged in heteromeric channels to form fast and sensitive ATP signaling pathways in sensory neurons.

Subtype-specific control of P2X receptor channel signaling by ATP and Mg2+

PubMed Central

Li, Mufeng; Silberberg, Shai D.; Swartz, Kenton J.

2013-01-01

The identity and forms of activating ligands for ion channels are fundamental to their physiological roles in rapid electrical signaling. P2X receptor channels are ATP-activated cation channels that serve important roles in sensory signaling and inflammation, yet the active forms of the nucleotide are unknown. In physiological solutions, ATP is ionized and primarily found in complex with Mg2+. Here we investigated the active forms of ATP and found that the action of MgATP2− and ATP4− differs between subtypes of P2X receptors. The slowly desensitizing P2X2 receptor can be activated by free ATP, but MgATP2− promotes opening with very low efficacy. In contrast, both free ATP and MgATP2− robustly open the rapidly desensitizing P2X3 subtype. A further distinction between these two subtypes is the ability of Mg2+ to regulate P2X3 through a distinct allosteric mechanism. Importantly, heteromeric P2X2/3 channels present in sensory neurons exhibit a hybrid phenotype, characterized by robust activation by MgATP2− and weak regulation by Mg2+. These results reveal the existence of two classes of homomeric P2X receptors with differential sensitivity to MgATP2− and regulation by Mg2+, and demonstrate that both restraining mechanisms can be disengaged in heteromeric channels to form fast and sensitive ATP signaling pathways in sensory neurons. PMID:23959888

N,N-Dimethyl-N-propyl-propan-1-aminium chloride monohydrate.

PubMed

Kärnä, Minna; Lahtinen, Manu; Valkonen, Jussi

2008-10-11

The title compound, C(8)H(20)N(+)·Cl(-)·H(2)O, has been prepared by a simple one-pot synthesis route followed by anion exchange using resin. In the crystal structure, the cations are packed in such a way that channels exist parallel to the b axis. These channels are filled by the anions and water mol-ecules, which inter-act via O-H⋯Cl hydrogen bonds [O⋯Cl = 3.285 (3) and 3.239 (3) Å] to form helical chains. The cations are involved in weak inter-molecular C-H⋯Cl and C-H⋯O hydrogen bonds. The title compound is not isomorphous with the bromo or iodo analogues.

Electroregulated Metal-Binding with a Crown Ether Tetrathiafulvalene Derivative: Toward Electrochemically Addressed Metal Cation Sponges.

PubMed

Le Derf, Franck; Mazari, Miloud; Mercier, Nicolas; Levillain, Eric; Richomme, Pascal; Becher, Jan; Garín, Javier; Orduna, Jesus; Gorgues, Alain; Sallé, Marc

1999-12-27

A redox responsive ligand incorporating the tetrathiafulvalene unit has been synthesized. The crystal structure of the free ligand (Z)-1 (C(20)H(30)O(5)S(8), triclinic P&onemacr;, Z = 2, a = 9.087(6) Å, b = 11.637(7) Å, c = 14.370(8) Å, alpha = 65.54(3) degrees, beta = 82.32(5) degrees, gamma = 84.18(6) degrees, V = 1368 Å(3)) shows the redox-active tetrathiafulvalene core to be essentially planar, which allows observation of two reversible one-electron processes upon electrochemical oxidation. The efficiency of this system in the control of the reversible complexation/expulsion sequence of a metallic cation (i.e., Ba(2+)) has been made possible thanks to a combination of (a) an unprecedented high coordination ability among tetrathiafulvalene-based macrocycles as determined by LSI mass spectrometry (log K degrees = 3.5, NBA-matrix) as well as by solution investigations ((1)H NMR and cyclic voltammetry titration studies), which remarkably converge to similar binding constant values (i.e., log K degrees = 4.2-4.3), and (b) reversible metal cation expulsion upon electrochemical oxidation to the dicationic state. A channel-like solid-state structure is observed for the Ba(2+) complex (C(20)H(30)O(5)S(8), Ba(2+)(CF(3)SO(3))(2)(2-), (H(2)O)(2), CD(3)CN, monoclinic C2/c, Z = 8, a = 45.66(1) Å, b = 8.897(5) Å, c = 23.124(8) Å, beta = 105.54(4) degrees, V = 9050 Å(3)), which results from the segregated stacking mode of the crown ether and the redox-active tetrathiafulvalene subunits, respectively.

Effects of acidic pH on voltage-gated ion channels in rat trigeminal mesencephalic nucleus neurons.

PubMed

Han, Jin-Eon; Cho, Jin-Hwa; Choi, In-Sun; Kim, Do-Yeon; Jang, Il-Sung

2017-03-01

The effects of acidic pH on several voltage-dependent ion channels, such as voltage-dependent K + and Ca 2+ channels, and hyperpolarization-gated and cyclic nucleotide-activated cation (HCN) channels, were examined using a whole-cell patch clamp technique on mechanically isolated rat mesencephalic trigeminal nucleus neurons. The application of a pH 6.5 solution had no effect on the peak amplitude of voltage-dependent K + currents. A pH 6.0 solution slightly, but significantly inhibited the peak amplitude of voltage-dependent K + currents. The pH 6.0 also shifted both the current-voltage and conductance-voltage relationships to the depolarization range. The application of a pH 6.5 solution scarcely affected the peak amplitude of membrane currents mediated by HCN channels, which were profoundly inhibited by the general HCN channel blocker Cs + (1 mM). However, the pH 6.0 solution slightly, but significantly inhibited the peak amplitude of HCN-mediated currents. Although the pH 6.0 solution showed complex modulation of the current-voltage and conductance-voltage relationships, the midpoint voltages for the activation of HCN channels were not changed by acidic pH. On the other hand, voltage-dependent Ca 2+ channels were significantly inhibited by an acidic pH. The application of an acidic pH solution significantly shifted the current-voltage and conductance-voltage relationships to the depolarization range. The modulation of several voltage-dependent ion channels by an acidic pH might affect the excitability of mesencephalic trigeminal nucleus neurons, and thus physiological functions mediated by the mesencephalic trigeminal nucleus could be affected in acidic pH conditions.

A Co-operative Regulation of Neuronal Excitability by UNC-7 Innexin and NCA/NALCN Leak Channel

PubMed Central

2011-01-01

Gap junctions mediate the electrical coupling and intercellular communication between neighboring cells. Some gap junction proteins, namely connexins and pannexins in vertebrates, and innexins in invertebrates, may also function as hemichannels. A conserved NCA/Dmα1U/NALCN family cation leak channel regulates the excitability and activity of vertebrate and invertebrate neurons. In the present study, we describe a genetic and functional interaction between the innexin UNC-7 and the cation leak channel NCA in Caenorhabditis elegans neurons. While the loss of the neuronal NCA channel function leads to a reduced evoked postsynaptic current at neuromuscular junctions, a simultaneous loss of the UNC-7 function restores the evoked response. The expression of UNC-7 in neurons reverts the effect of the unc-7 mutation; moreover, the expression of UNC-7 mutant proteins that are predicted to be unable to form gap junctions also reverts this effect, suggesting that UNC-7 innexin regulates neuronal activity, in part, through gap junction-independent functions. We propose that, in addition to gap junction-mediated functions, UNC-7 innexin may also form hemichannels to regulate C. elegans' neuronal activity cooperatively with the NCA family leak channels. PMID:21489288

Interaction between the Pore and a Fast Gate of the Cardiac Sodium Channel

PubMed Central

Townsend, Claire; Horn, Richard

1999-01-01

Permeant ions affect a fast gating process observed in human cardiac sodium channels (Townsend, C., H.A. Hartmann, and R. Horn. 1997. J. Gen. Physiol. 110:11–21). Removal of extracellular permeant ions causes a reduction of open probability at positive membrane potentials. These results suggest an intimate relationship between the ion-conducting pore and the gates of the channel. We tested this hypothesis by three sets of manipulations designed to affect the binding of cations within the pore: application of intracellular pore blockers, mutagenesis of residues known to contribute to permeation, and chemical modification of a native cysteine residue (C373) near the extracellular mouth of the pore. The coupling between extracellular permeant ions and this fast gating process is abolished both by pore blockers and by a mutation that severely affects selectivity. A more superficial pore mutation or chemical modification of C373 reduces single channel conductance while preserving both selectivity of the pore and the modulatory effects of extracellular cations. Our results demonstrate a modulatory gating role for a region deep within the pore and suggest that the structure of the permeation pathway is largely preserved when a channel is closed. PMID:9925827

Diphtheria toxin-induced channels in Vero cells selective for monovalent cations

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

Sandvig, K.; Olsnes, S.

1988-09-05

Ion fluxes associated with translocation of diphtheria toxin across the surface membrane of Vero cells were studied. When cells with surface-bound toxin were exposed to low pH to induce toxin entry, the cells became permeable to Na+, K+, H+, choline+, and glucosamine+. There was no increased permeability to Cl-, SO4(-2), glucose, or sucrose, whereas the uptake of /sup 45/Ca2+ was slightly increased. The influx of Ca2+, which appears to be different from that of monovalent cations, was reduced by several inhibitors of anion transport and by verapamil, Mn2+, Co2+, and Ca2+, but not by Mg2+. The toxin-induced fluxes of N+,more » K+, and protons were inhibited by Cd2+. Cd2+ also protected the cells against intoxication by diphtheria toxin, suggesting that the open cation-selective channel is required for toxin translocation. The involvement of the toxin receptor is discussed.« less

The ionic selectivity and calcium dependence of the light-sensitive pathway in toad rods.

PubMed Central

Hodgkin, A L; McNaughton, P A; Nunn, B J

1985-01-01

A new method is described for determining the effects of rapid changes in ionic concentration on the light-sensitive currents of rod outer segments. Replacing Na with another monovalent cation caused a rapid change in current followed by an exponential decline of time constant 0.5-2 s. From the magnitude of the initial rapid change in current we conclude that Li, Na, and K and Rb ions pass readily through the light-sensitive channel in the presence of 1 mM-Ca, whereas Cs crosses with difficulty and choline, tetramethylammonium and tetraethylammonium not at all. The effect of reducing Ca in the external medium indicates that the residual inward current recorded for a few seconds when Na is replaced by an impermeant ion is carried largely by Ca ions. With 1 microM-Ca in the external medium the relative ability of monovalent cations to carry light-sensitive current is Li:Na:K:Rb:Cs = 1.4:1:0.8:0.6:0.15. The same order applied in the physiological region but the values are less certain. Large transient inward currents are seen if external Ca is raised form 1 microM to 5 mM or more; these currents which are maximal in an isotonic Ca solution are presumably carried by Ca. The effect of monovalent cations on the number of open light-sensitive channels was tested by adding the cation to a solution containing 55 mM-Na. Na ions open light-sensitive channels with a delay, probably by promoting Na-Ca exchange; K and Rb close channels by inhibiting exchange; Li and Cs seem inert in the exchange mechanism. The rate at which inward current declines in low [Na]o or high [Ca]o is accelerated by weak background lights and slowed by 3-isobutyl-1-methylxanthine (IBMX), which inhibits the hydrolysis of cGMP. On returning to Ringer solution after a period in low [Na]o the current recovers with a delay of about 1 s which decreases as the Ca concentration of the low [Na]o medium is reduced. We conclude that intracellular Ca has a strong effect on the number of open light-sensitive channels. None the less, several observations are inconsistent with channel closure being dependent simply on combination with internal Ca. PMID:2580087

Multiplexed electrokinetic sample fractionation, preconcentration and elution for proteomics.

PubMed

Hua, Yujuan; Jemere, Abebaw B; Dragoljic, Jelena; Harrison, D Jed

2013-07-07

Both 6 and 8-channel integrated microfluidic sample pretreatment devices capable of performing "in space" sample fractionation, collection, preconcentration and elution of captured analytes via sheath flow assisted electrokinetic pumping are described. Coatings and monolithic polymer beds were developed for the glass devices to provide cationic surface charge and anodal electroosmotic flow for delivery to an electrospray emitter tip. A mixed cationic ([2-(methacryloyloxy)ethyl] trimethylammonium chloride) (META) and hydrophobic butyl methacrylate-based monolithic porous polymer, photopolymerized in the 6- or 8-fractionation channels, was used to capture and preconcentrate samples. A 0.45 wt% META loaded bed generated comparable anodic electroosmotic flow to the cationic polymer PolyE-323 coated channel segments in the device. The balanced electroosmotic flow allowed stable electrokinetic sheath flow to prevent cross contamination of separated protein fractions, while reducing protein/peptide adsorption on the channel walls. Sequential elution of analytes trapped in the SPE beds revealed that the monolithic columns could be efficiently used to provide sheath flow during elution of analytes, as demonstrated for neutral carboxy SNARF (residual signal, 0.08% RSD, n = 40) and charged fluorescein (residual signal, 2.5% n = 40). Elution from monolithic columns showed reproducible performance with peak area reproducibility of ~8% (n = 6 columns) in a single sequential elution and the run-to-run reproducibility was 2.4-6.7% RSD (n = 4) for elution from the same bed. The demonstrated ability of this device design and operation to elute from multiple fractionation beds into a single exit channel for sample analysis by fluorescence or electrospray mass spectrometry is a crucial component of an integrated fractionation and assay system for proteomics.

Are pacemaker properties required for respiratory rhythm generation in adult turtle brain stems in vitro?

PubMed

Johnson, Stephen M; Wiegel, Liana M; Majewski, David J

2007-08-01

The role of pacemaker properties in vertebrate respiratory rhythm generation is not well understood. To address this question from a comparative perspective, brain stems from adult turtles were isolated in vitro, and respiratory motor bursts were recorded on hypoglossal (XII) nerve rootlets. The goal was to test whether burst frequency could be altered by conditions known to alter respiratory pacemaker neuron activity in mammals (e.g., increased bath KCl or blockade of specific inward currents). While bathed in artificial cerebrospinal fluid (aCSF), respiratory burst frequency was not correlated with changes in bath KCl (0.5-10.0 mM). Riluzole (50 microM; persistent Na(+) channel blocker) increased burst frequency by 31 +/- 5% (P < 0.05) and decreased burst amplitude by 42 +/- 4% (P < 0.05). In contrast, flufenamic acid (FFA, 20-500 microM; Ca(2+)-activated cation channel blocker) reduced and abolished burst frequency in a dose- and time-dependent manner (P < 0.05). During synaptic inhibition blockade with bicuculline (50 microM; GABA(A) channel blocker) and strychnine (50 muM; glycine receptor blocker), rhythmic motor activity persisted, and burst frequency was directly correlated with extracellular KCl (0.5-10.0 mM; P = 0.005). During synaptic inhibition blockade, riluzole (50 microM) did not alter burst frequency, whereas FFA (100 microM) abolished burst frequency (P < 0.05). These data are most consistent with the hypothesis that turtle respiratory rhythm generation requires Ca(2+)-activated cation channels but not pacemaker neurons, which thereby favors the group-pacemaker model. During synaptic inhibition blockade, however, the rhythm generator appears to be transformed into a pacemaker-driven network that requires Ca(2+)-activated cation channels.

Tuning the ion selectivity of two-pore channels

PubMed Central

Guo, Jiangtao; Zeng, Weizhong; Jiang, Youxing

2017-01-01

Organellar two-pore channels (TPCs) contain two copies of a Shaker-like six-transmembrane (6-TM) domain in each subunit and are ubiquitously expressed in plants and animals. Interestingly, plant and animal TPCs share high sequence similarity in the filter region, yet exhibit drastically different ion selectivity. Plant TPC1 functions as a nonselective cation channel on the vacuole membrane, whereas mammalian TPC channels have been shown to be endo/lysosomal Na+-selective or Ca2+-release channels. In this study, we performed systematic characterization of the ion selectivity of TPC1 from Arabidopsis thaliana (AtTPC1) and compared its selectivity with the selectivity of human TPC2 (HsTPC2). We demonstrate that AtTPC1 is selective for Ca2+ over Na+, but nonselective among monovalent cations (Li+, Na+, and K+). Our results also confirm that HsTPC2 is a Na+-selective channel activated by phosphatidylinositol 3,5-bisphosphate. Guided by our recent structure of AtTPC1, we converted AtTPC1 to a Na+-selective channel by mimicking the selectivity filter of HsTPC2 and identified key residues in the TPC filters that differentiate the selectivity between AtTPC1 and HsTPC2. Furthermore, the structure of the Na+-selective AtTPC1 mutant elucidates the structural basis for Na+ selectivity in mammalian TPCs. PMID:28096396

A Functional Nuclear Localization Sequence in the C. elegans TRPV Channel OCR-2

PubMed Central

Ezak, Meredith J.; Ferkey, Denise M.

2011-01-01

The ability to modulate gene expression in response to sensory experience is critical to the normal development and function of the nervous system. Calcium is a key activator of the signal transduction cascades that mediate the process of translating a cellular stimulus into transcriptional changes. With the recent discovery that the mammalian Cav1.2 calcium channel can be cleaved, enter the nucleus and act as a transcription factor to control neuronal gene expression, a more direct role for the calcium channels themselves in regulating transcription has begun to be appreciated. Here we report the identification of a nuclear localization sequence (NLS) in the C. elegans transient receptor potential vanilloid (TRPV) cation channel OCR-2. TRPV channels have previously been implicated in transcriptional regulation of neuronal genes in the nematode, although the precise mechanism remains unclear. We show that the NLS in OCR-2 is functional, being able to direct nuclear accumulation of a synthetic cargo protein as well as the carboxy-terminal cytosolic tail of OCR-2 where it is endogenously found. Furthermore, we discovered that a carboxy-terminal portion of the full-length channel can localize to the nucleus of neuronal cells. These results suggest that the OCR-2 TRPV cation channel may have a direct nuclear function in neuronal cells that was not previously appreciated. PMID:21957475

Tuning the ion selectivity of two-pore channels

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

Guo, Jiangtao; Zeng, Weizhong; Jiang, Youxing

Organellar two-pore channels (TPCs) contain two copies of a Shaker-like six-transmembrane (6-TM) domain in each subunit and are ubiquitously expressed in plants and animals. Interestingly, plant and animal TPCs share high sequence similarity in the filter region, yet exhibit drastically different ion selectivity. Plant TPC1 functions as a nonselective cation channel on the vacuole membrane, whereas mammalian TPC channels have been shown to be endo/lysosomal Na+-selective or Ca2+-release channels. In this study, we performed systematic characterization of the ion selectivity of TPC1 from Arabidopsis thaliana (AtTPC1) and compared its selectivity with the selectivity of human TPC2 (HsTPC2). We demonstrate thatmore » AtTPC1 is selective for Ca2+ over Na+, but nonselective among monovalent cations (Li+, Na+, and K+). Our results also confirm that HsTPC2 is a Na+-selective channel activated by phosphatidylinositol 3,5-bisphosphate. Guided by our recent structure of AtTPC1, we converted AtTPC1 to a Na+-selective channel by mimicking the selectivity filter of HsTPC2 and identified key residues in the TPC filters that differentiate the selectivity between AtTPC1 and HsTPC2. Furthermore, the structure of the Na+-selective AtTPC1 mutant elucidates the structural basis for Na+ selectivity in mammalian TPCs.« less

Pyrrole-coupled salicylimine-based fluorescence "turn on" probe for highly selective recognition of Zn²⁺ ions in mixed aqueous media: Application in living cell imaging.

PubMed

Bhosale, Jitendra; Fegade, Umesh; Bondhopadhyay, Banashree; Kaur, Simanpreet; Singh, Narinder; Basu, Anupam; Dabur, Rajesh; Bendre, Ratnamala; Kuwar, Anil

2015-06-01

Cation sensing behaviour of a pyrrole-based derivative (2-hydroxyl 3 methyl 6 isopropyl benzaldehyde}-3,4-dimethyl-1H-pyrrole-2-carbohydrazide (receptor 3) has been explored and is found to be selective towards Zn(2+) over a variety of tested cations. The receptor 3 has shown high selectivity and sensitivity towards Zn(2+) over the other alkali, alkaline earth and transition metal ions. In the presence of Zn(2+), absorption band of receptor 3 has shown the red shift. The sensing behaviour has been suggested to continue via enhancement process which has further been supported by UV-vis absorption and theoretical density functional theory (DFT) calculations indicating the formation of a 1:1 complex between the pyrrole based receptor 3 and Zn(2+). The present work is presenting a highly selective dual channel colorimetric sensor for zinc with great sensitivity. The developed sensor was successfully applied to image intracellular Zn(2+) in living cells. Copyright © 2015 John Wiley & Sons, Ltd.

Crystal Structure of the Potassium Importing KdpFABC Membrane Complex

PubMed Central

Huang, Ching-Shin; Pedersen, Bjørn Panyella; Stokes, David Lloyd

2017-01-01

Cellular potassium import systems play a fundamental role in osmoregulation, pH homeostasis and membrane potential in all domains of life. In bacteria, the kdp operon encodes a four subunit potassium pump that maintains intracellular homeostasis as well as cell shape and turgor under conditions where potassium is limiting1. This membrane complex, called KdpFABC, has one channel-like subunit (KdpA) belonging to the Superfamily of Potassium Transporters and another pump-like subunit (KdpB) belonging to the Superfamily of P-type ATPases. Although there is considerable structural and functional information about members from both superfamilies, the mechanism by which uphill potassium transport through KdpA is coupled with ATP hydrolysis by KdpB remains poorly understood. Here we report the 2.9 Å X-ray structure of the complete Escherichia coli KdpFABC complex with a potassium ion within the selectivity filter of KdpA as well as a water molecule at a canonical cation site in the transmembrane domain of KdpB. The structure also reveals two structural elements that appear to mediate the coupling between these two subunits. Specifically, a protein-embedded tunnel runs between these potassium and water sites and a helix controlling the cytoplasmic gate of KdpA is linked to the phosphorylation domain of KdpB. Based on these observations, we propose an unprecedented mechanism that repurposes protein channel architecture for active transport across biomembranes. PMID:28636601

Zn2+ currents are mediated by calcium-permeable AMPA/Kainate channels in cultured murine hippocampal neurones

PubMed Central

Jia, Yousheng; Jeng, Jade-Ming; Sensi, Stefano L; Weiss, John H

2002-01-01

Permeation of the endogenous cation Zn2+ through calcium-permeable AMPA/kainate receptor-gated (Ca-A/K) channels might subserve pathological and/or physiological signalling roles. Voltage-clamp recording was used to directly assess Zn2+ flux through these channels on cultured murine hippocampal neurones. Ca-A/K channels were present in large numbers only on a minority of neurones (Ca-A/K(+) neurones), many of which were GABAergic. The presence of these channels was assessed in whole-cell or outside-out patch recording as the degree of inward rectification of kainate-activated currents, quantified via a rectification index (RI = G+40/G-60), which ranged from <0.4 (strongly inwardly rectifying) to >2 (outwardly rectifying). The specificity of a low RI as an indication of robust Ca-A/K channel expression was verified by two other techniques, kainate-stimulated cobalt-uptake labelling, and fluorescence imaging of kainate-induced increases in intracellular Ca2+. In addition, the degree of inward rectification of kainate-activated currents correlated strongly with the positive shift of the reversal potential (Vrev) upon switching to a sodium-free, 10 mm Ca2+ buffer. With Zn2+ (3 mm) as the only permeant extracellular cation, kainate-induced inward currents were only observed in neurones that had previously been identified as Ca-A/K(+). A comparison between the Vrev observed with 3 mm Zn2+ and that observed with Ca2+ as the permeant cation revealed a PCa/PZn of ≈1.8. Inward currents recorded in 3 mm Ca2+ were unaffected by the addition of 0.3 mm Zn2+, while microfluorimetrically detected increases in the intracellular concentration of Zn2+ in Ca-A/K(+) neurones upon kainate exposure in the presence of 0.3 mm Zn2+ were only mildly attenuated by the addition of 1.8 mm Ca2+. These results provide direct evidence that Zn2+ can carry currents through Ca-A/K channels, and that there is little interference between Ca2+ and Zn2+ in permeating these channels. PMID:12181280

Increase in cytosolic Ca2+ produced by hypoxia and other depolarizing stimuli activates a non-selective cation channel in chemoreceptor cells of rat carotid body

PubMed Central

Kang, Dawon; Wang, Jiaju; Hogan, James O; Vennekens, Rudi; Freichel, Marc; White, Carl; Kim, Donghee

2014-01-01

The current model of O2 sensing by carotid body chemoreceptor (glomus) cells is that hypoxia inhibits the outward K+ current and causes cell depolarization, Ca2+ influx via voltage-dependent Ca2+ channels and a rise in intracellular [Ca2+] ([Ca2+]i). Here we show that hypoxia (<5% O2), in addition to inhibiting the two-pore domain K+ channels TASK-1/3 (TASK), indirectly activates an ∼20 pS channel in isolated glomus cells. The 20 pS channel was permeable to K+, Na+ and Cs+ but not to Cl− or Ca2+. The 20 pS channel was not sensitive to voltage. Inhibition of TASK by external acid, depolarization of glomus cells with high external KCl (20 mm) or opening of the Ca2+ channel with FPL64176 activated the 20 pS channel when 1 mm Ca2+ was present in the external solution. Ca2+ (10 μm) applied to the cytosolic side of inside-out patches activated the 20 pS channel. The threshold [Ca2+]i for activation of the 20 pS channel in cell-attached patches was ∼200 nm. The reversal potential of the 20 pS channel was estimated to be −28 mV. Our results reveal a sequential mechanism in which hypoxia (<5% O2) first inhibits the K+ conductance and then activates a Na+-permeable, non-selective cation channel via depolarization-induced rise in [Ca2+]i. Our results suggest that inhibition of K+ efflux and stimulation of Na+ influx both contribute to the depolarization of glomus cells during moderate to severe hypoxia. PMID:24591572

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study.

PubMed

Gardiner, Sara H; Karsili, Tolga N V; Lipciuc, M Laura; Wilman, Edward; Ashfold, Michael N R; Vallance, Claire

2014-02-07

The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C2H5Br(+) and C2H5I(+)) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-of-flight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spin-orbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spin-orbit resolved ab initio calculations of cuts through the potential energy surfaces (along the RC-Br/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C2H5Br(+) cations undergo prompt C-Br bond fission to form predominantly C2H5(+) + Br* products with a near-limiting 'parallel' recoil velocity distribution. The observed C2H3(+) + H2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C2H5(+) products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C2H5I(+), along with an additional energetically accessible C-I bond fission channel to form C2H5 + I(+) products. HX (X = Br, I) elimination from the highly internally excited C2H5X(+) cation is deemed the most probable route to forming the C2H4(+) fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor C-C bond fission process to form CH2X(+) + CH3 products.

The atypical cation-conduction and gating properties of ELIC underscore the marked functional versatility of the pentameric ligand-gated ion-channel fold

PubMed Central

Gonzalez-Gutierrez, Giovanni

2015-01-01

The superfamily of pentameric ligand-gated ion channels (pLGICs) is unique among ionotropic receptors in that the same overall structure has evolved to generate multiple members with different combinations of agonist specificities and permeant-ion charge selectivities. However, aside from these differences, pLGICs have been typically regarded as having several invariant functional properties. These include pore blockade by extracellular quaternary-ammonium cations in the micromolar-to-millimolar concentration range (in the case of the cation-selective members), and a gain-of-function phenotype, which manifests as a slower deactivation time course, as a result of mutations that reduce the hydrophobicity of the transmembrane pore lining. Here, we tested this notion on three distantly related cation-selective members of the pLGIC superfamily: the mouse muscle nicotinic acetylcholine receptor (nAChR), and the bacterial GLIC and ELIC channels. Remarkably, we found that, whereas low millimolar concentrations of TMA+ and TEA+ block the nAChR and GLIC, neither of these two quaternary-ammonium cations blocks ELIC at such concentrations; instead, both carry measurable inward currents when present as the only cations on the extracellular side. Also, we found that, whereas lidocaine binding speeds up the current-decay time courses of the nAChR and GLIC in the presence of saturating concentrations of agonists, the binding of lidocaine to ELIC slows this time course down. Furthermore, whereas mutations that reduce the hydrophobicity of the side chains at position 9′ of the M2 α-helices greatly slowed the deactivation time course of the nAChR and GLIC, these mutations had little effect—or even sped up deactivation—when engineered in ELIC. Our data indicate that caution should be exercised when generalizing results obtained with ELIC to the rest of the pLGICs, but more intriguingly, they hint at the possibility that ELIC is a representative of a novel branch of the superfamily with markedly divergent pore properties despite a well-conserved three-dimensional architecture. PMID:26078054

A computational study of anion-modulated cation-π interactions.

PubMed

Carrazana-García, Jorge A; Rodríguez-Otero, Jesús; Cabaleiro-Lago, Enrique M

2012-05-24

The interaction of anions with cation-π complexes formed by the guanidinium cation and benzene was thoroughly studied by means of computational methods. Potential energy surface scans were performed in order to evaluate the effect of the anion coming closer to the cation-π pair. Several structures of guanidinium-benzene complexes and anion approaching directions were examined. Supermolecule calculations were performed on ternary complexes formed by guanidinium, benzene, and one anion and the interaction energy was decomposed into its different two- and three-body contributions. The interaction energies were further dissected into their electrostatic, exchange, repulsion, polarization and dispersion contributions by means of local molecular orbital energy decomposition analysis. The results confirm that, besides the electrostatic cation-anion attraction, the effect of the anion over the cation-π interaction is mainly due to polarization and can be rationalized following the changes in the anion-π and the nonadditive (three-body) terms of the interaction. When the cation and the anion are on the same side of the π system, the three-body interaction is anticooperative, but when the anion and the cation are on opposite sides of the π system, the three-body interaction is cooperative. As far as we know, this is the first study where this kind of analysis is carried out with a structured cation as guanidinium with a significant biological interest.

Probing vacancy-type free-volume defects in Li2B4O7 single crystal by positron annihilation lifetime spectroscopy

NASA Astrophysics Data System (ADS)

Shpotyuk, O.; Adamiv, V.; Teslyuk, I.; Ingram, A.; Demchenko, P.

2018-01-01

Vacancy-type free-volume defects in lithium tetraborate Li2B4O7 single crystal, grown by the Czochralski technique, are probed with positron annihilation spectroscopy in the lifetime measuring mode. The experimental positron lifetime spectrum is reconstructed within the three-component fitting, involving channels of positron and positronium Ps trapping, as well as within the two-component fitting with a positronium-compensating source input. Structural configurations of the most efficient positron traps are considered using the crystallographic specificity of lithium tetraborate with the main accent on cation-type vacancies. Possible channels of positron trapping are visualized using the electronic structure calculations with density functional theory at the basis of structural parameters proper to Li2B4O7. Spatially-extended positron-trapping complexes involving singly-ionized lithium vacancies, with character lifetime close to 0.32 ns, are responsible for positron trapping in the nominally undoped lithium tetraborate Li2B4O7 crystal.

Structural basis for subtype-specific inhibition of the P2X7 receptor

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

Karasawa, Akira; Kawate, Toshimitsu

The P2X7 receptor is a non-selective cation channel activated by extracellular adenosine triphosphate (ATP). Chronic activation of P2X7 underlies many health problems such as pathologic pain, yet we lack effective antagonists due to poorly understood mechanisms of inhibition. Here we present crystal structures of a mammalian P2X7 receptor complexed with five structurally-unrelated antagonists. Unexpectedly, these drugs all bind to an allosteric site distinct from the ATP-binding pocket in a groove formed between two neighboring subunits. This novel drug-binding pocket accommodates a diversity of small molecules mainly through hydrophobic interactions. Functional assays propose that these compounds allosterically prevent narrowing of themore » drug-binding pocket and the turret-like architecture during channel opening, which is consistent with a site of action distal to the ATP-binding pocket. These novel mechanistic insights will facilitate the development of P2X7-specific drugs for treating human diseases.« less

Multisteric TRPV1 nocisensor: a target for analgesics.

PubMed

Szolcsányi, János; Sándor, Zoltán

2012-12-01

Cloning of the transient receptor potential vanilloid type 1 (TRPV1), the heat-gated cation channel/capsaicin receptor expressed by sensory neurons, has opened the door for development of new types of analgesics that selectively act on nociceptors. Here we summarize mutagenetic evidence for selective loss of responsiveness to vanilloids, protons, and heat stimuli to provide clues for avoiding on-target side effects of hyperthermia and burn risk. It is suggested that the complex chemoceptive thermosensor function of TRPV1 (which is modulated by depolarizing stimuli) can be attributed to multisteric gating functions. In this way, it forms the prototype of a new class of ion channels different from the canonical voltage-gated and ligand-gated ones. Several endogenous lipid ligands activate and inhibit TRPV1 and its gating initiates sensory transducer and mediator-releasing functions. Second generation TRPV1 antagonists that do not induce hyperthermia are under development, and a dermal capsaicin patch is already on the market for long-term treatment of neuropathic pain. Copyright © 2012 Elsevier Ltd. All rights reserved.

Characteristics of inositol trisphosphate mediated Ca/sup 2 +/ release from permeabilized hepatocytes

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

Joseph, S.K.; Williamson, J.R.

1986-05-01

Ca/sup 2 +/ release triggered by inositol trisphosphate (IP/sub 3/) has been measured in saponin-permeabilized hepatocytes with /sup 45/Ca/sup 2 +/ or Quin 2. The initial rate of Ca/sup 2 +/ release was not markedly affected by the incubation temperature (175 +/- 40 pmol/s/mg at 30/sup 0/C versus 133 +/- 24 pmol/s/mg at 4/sup 0/C). This result is consistent with the membrane translocation of Ca/sup 2 +/ occurring through an ion-channel rather than an ion-carrier. The amount of Ca/sup 2 +/ released by IP/sub 3/ was not affected by pH (6.5-8.0) or by compounds that inhibit voltage-gated Ca/sup 2 +/more » channels. La/sup 3 +/ (100 ..mu..M) markedly inhibits the effect of 1 ..mu..M IP/sub 3/. The possibility that La/sup 3 +/ chelates IP/sub 3/ cannot be excluded since the effect of La/sup 3 +/ can be overcome by increasing the IP/sub 3/ concentration. IP/sub 3/-mediated Ca/sup 2 +/ release displays a requirement for a permeant cation in the incubation medium. Optimal release is observed with K/sup +/ gluconate. Other monovalent cations, with the exception of Li/sup +/, can substitute for K/sup +/. Permeant anions, at concentrations above 40 mM, inhibit Ca/sup 2 +/ release produced by IP/sub 3/. Cl/sup -/, Br/sup -/, I/sup -/, and SO/sub 4//sup 2 -/ were equally effective. Ca/sup 2 +/ release was not inhibited by DIDS or Furosemide. /sup 85/Sr/sup 2 +/ and /sup 54/Mn/sup 2 +/ fluxes were also stimulated by IP/sub 3/. These results suggest that IP/sub 3/ acts to gate a divalent cation channel. The translocation of positive charge through this channel is balanced by ancillary movements of monovalent cations and anions across the reticular membrane.« less

Influence of the Selectivity Filter Properties on Proton Selectivity in the Influenza A M2 Channel.

PubMed

Dudev, Todor; Grauffel, Cédric; Lim, Carmay

2016-10-05

The homotetrameric M2 proton channel of influenza A plays a crucial role in the viral life cycle and is thus an important therapeutic target. It selectively conducts protons against a background of other competing cations whose concentrations are up to a million times greater than the proton concentration. Its selectivity is largely determined by a constricted region of its open pore known as the selectivity filter, which is lined by four absolutely conserved histidines. While the mechanism of proton transport through the channel has been studied, the physical principles underlying the selectivity for protons over other cations in the channel's His 4 selectivity filter remain elusive. Furthermore, it is not known if proton selectivity absolutely requires all four histidines with two of the four histidines protonated and if other titratable amino acid residues in lieu of the histidines could bind protons and how they affect proton selectivity. Here, we elucidate how the competition between protons and rival cations such as Na + depends on the selectivity filter's (1) histidine protonation state, (2) solvent exposure, (3) oligomeric state (the number of protein chains and thus the number of His ligands), and (4) ligand composition by evaluating the free energies for replacing monovalent Na + with H 3 O + in various model selectivity filters. We show that tetrameric His 4 filters are more proton-selective than their trimeric His 3 counterparts, and a dicationic His 4 filter where two of the four histidines are protonated is more proton-selective than tetrameric filters with other charge states/composition (different combinations of His protonation states or different metal-ligating ligands). The [His 4 ] 2+ filter achieves proton selectivity by providing suboptimal binding conditions for rival cations such as Na + , which prefers a neutral or negatively charged filter instead of a dicationic one, and three rather than four ligands with oxygen-ligating atoms.

In silico assessment of the conduction mechanism of the Ryanodine Receptor 1 reveals previously unknown exit pathways.

PubMed

Heinz, Leonard P; Kopec, Wojciech; de Groot, Bert L; Fink, Rainer H A

2018-05-02

The ryanodine receptor 1 is a large calcium ion channel found in mammalian skeletal muscle. The ion channel gained a lot of attention recently, after multiple independent authors published near-atomic cryo electron microscopy data. Taking advantage of the unprecedented quality of structural data, we performed molecular dynamics simulations on the entire ion channel as well as on a reduced model. We calculated potentials of mean force for Ba 2+ , Ca 2+ , Mg 2+ , K + , Na + and Cl - ions using umbrella sampling to identify the key residues involved in ion permeation. We found two main binding sites for the cations, whereas the channel is strongly repulsive for chloride ions. Furthermore, the data is consistent with the model that the receptor achieves its ion selectivity by over-affinity for divalent cations in a calcium-block-like fashion. We reproduced the experimental conductance for potassium ions in permeation simulations with applied voltage. The analysis of the permeation paths shows that ions exit the pore via multiple pathways, which we suggest to be related to the experimental observation of different subconducting states.

Formation of Stable Cationic Lipid/DNA Complexes for Gene Transfer

NASA Astrophysics Data System (ADS)

Hofland, Hans E. J.; Shephard, Lee; Sullivan, Sean M.

1996-07-01

Stable cationic lipid/DNA complexes were formed by solubilizing cationic liposomes with 1% octylglucoside and complexing a DNA plasmid with the lipid in the presence of detergent. Removal of the detergent by dialysis yielded a lipid/DNA suspension that was able to transfect tissue culture cells up to 90 days after formation with no loss in activity. Similar levels of gene transfer were obtained by mixing the cationic lipid in a liposome form with DNA just prior to cell addition. However, expression was completely lost 24 hr after mixing. The transfection efficiency of the stable complex in 15% fetal calf serum was 30% of that obtained in the absence of serum, whereas the transient complex was completely inactivated with 2% fetal calf serum. A 90-day stability study comparing various storage conditions showed that the stable complex could be stored frozen or as a suspension at 4 degrees C with no loss in transfection efficiency. Centrifugation of the stable complex produced a pellet that contained approximately 90% of the DNA and 10% of the lipid. Transfection of cells with the resuspended pellet and the supernatant showed that the majority of the transfection activity was in the pellet and all the toxicity was in the supernatant. Formation of a stable cationic lipid/DNA complex has produced a transfection vehicle that can be stored indefinitely, can be concentrated with no loss in transfection efficiency, and the toxicity levels can be greatly reduced when the active complex is isolated from the uncomplexed lipid.

Optimizing Cationic and Neutral Lipids for Efficient Gene Delivery at High Serum Content

PubMed Central

Majzoub, Ramsey N.; Hwu, Yeu-kuang; Liang, Keng S.; Leal, Cecília; Safinya, Cyrus R.

2014-01-01

Background Cationic liposome (CL)-DNA complexes are promising gene delivery vectors with potential applications in gene therapy. A key challenge in creating CL-DNA complexes for applications is that their transfection efficiency (TE) is adversely affected by serum. In particular, little is known about the effects of high serum contents on TE even though this may provide design guidelines for applications in vivo. Methods We prepared CL-DNA complexes in which we varied the neutral lipid (DOPC, glycerol-monooleate (GMO), cholesterol), the headgroup charge and chemical structure of the cationic lipid, and the ratio of neutral to cationic lipid; we then measured the TE of these complexes as a function of serum content and assessed their cytotoxicity. We tested selected formulations in two human cancer cell lines (M21/melanoma and PC-3/prostate cancer). Results In the absence of serum, all CL-DNA complexes of custom-synthesized multivalent lipids show high TE. Certain combinations of multivalent lipids and neutral lipids, such as MVL5(5+)/GMO-DNA complexes or complexes based on the dendritic-headgroup lipid TMVLG3(8+) exhibited high TE both in the absence and presence of serum. Although their TE still dropped to a small extent in the presence of serum, it reached or surpassed that of benchmark commercial transfection reagents, in particular at high serum content. Conclusions Two-component vectors (one multivalent cationic lipid and one neutral lipid) can rival or surpass benchmark reagents at low and high serum contents (up to 50%, v/v). We suggest guidelines for optimizing the serum resistance of CL-DNA complexes based on a given cationic lipid. PMID:24753287

Activation of TRPM7 channels by small molecules under physiological conditions.

PubMed

Hofmann, T; Schäfer, S; Linseisen, M; Sytik, L; Gudermann, T; Chubanov, V

2014-12-01

Transient receptor potential cation channel, subfamily M, member 7 (TRPM7) is a cation channel covalently linked to a protein kinase domain. TRPM7 is ubiquitously expressed and regulates key cellular processes such as Mg(2+) homeostasis, motility, and proliferation. TRPM7 is involved in anoxic neuronal death, cardiac fibrosis, and tumor growth. The goal of this work was to identify small molecule activators of the TRPM7 channel and investigate their mechanism of action. We used an aequorin bioluminescence-based assay to screen for activators of the TRPM7 channel. Valid candidates were further characterized using patch clamp electrophysiology. We identified 20 drug-like compounds with various structural backbones that can activate the TRPM7 channel. Among them, the δ opioid antagonist naltriben was studied in greater detail. Naltriben's action was selective among the TRP channels tested. Naltriben activates TRPM7 currents without prior depletion of intracellular Mg(2+) even under conditions of low PIP2. Moreover, naltriben interfered with the effect of the TRPM7 inhibitor NS8593. Finally, our experiments with TRPM7 variants carrying mutations in the pore, TRP, and kinase domains indicate that the site of TRPM7 activation by this small-molecule ligand is most likely located in or near the TRP domain. In conclusion, we identified the first organic small-molecule activators of TRPM7 channels, thus providing new experimental tools to study TRPM7 function in native cellular environments.

Peptides containing antigenic and cationic domains have enhanced, multivalent immunogenicity when bound to DNA vaccines.

PubMed

Riedl, Petra; Reimann, Jörg; Schirmbeck, Reinhold

2004-02-01

We explored strategies to codeliver DNA- and peptide-based vaccines in a way that enhances the immunogenicity of both components of the combination vaccine for T cells. Specific CD8(+) T cell responses to an antigenic peptide are primed when the peptide is fused to a cationic peptide domain that is bound to plasmid DNA or oligonucleotides (ODN; with or without CpG motifs). Plasmid DNA mixed with antigenic/cationic peptides or histones forms large complexes with different biological properties depending on the molar ratios of peptide/protein and polynucleotide. Complexes containing high (but not low) molar ratios of cationic peptide to DNA facilitate transfection (DNA uptake and expression of the plasmid-encoded product) of cells. In contrast, complexes containing low (but not high) molar ratios of cationic peptide to DNA prime potent multispecific T cell responses after a single intramuscular injection of the complexes. The general validity of this observation was confirmed mixing different antigenic/cationic peptides with different DNA vaccines. In these vaccine formulations, multispecific CD8(+) T cell responses specific for epitopes of the peptide- as well as the DNA-based vaccine were efficiently coprimed, together with humoral antibody responses to conformational determinants of large viral antigens encoded by the DNA vaccine. The data indicate that mixtures of DNA vaccines with antigenic, cationic peptides are immunogenic vaccine formulations particularly suited for the induction of multispecific T cell responses.

Pinocytosis and locomotion of amoebae. XV. Visualization of Ca++-dynamics by chlorotetracycline (CTC) fluorescence during induced pinocytosis in living Amoeba proteus.

PubMed

Gawlitta, W; Stockem, W; Wehland, J; Weber, K

1980-01-01

The dynamics of Ca++ during induced pinocytosis were studied in Amoeba proteus using chlorotetracycline (CTC). The fluorescence of the Ca++ - CTC-complex was monitored by an image intensification system, which has certain advantages over standard equipment: (1) Living cells are not subjected to the damaging influence of intensive microscopic illumination, (2) fluorescent probes are not bleached during observation, and (3) the rapid dynamics of the Ca++ -fluxes can be recorded using short exposure times. The results demonstrate the existence of Ca++ bound to intracellular and extracellular sites of the cell membrane complex in normal locomoting and pinocytotic Amoeba proteus. The application of cations inducing pinocytosis causes a rapid decrease in the external CTC-fluorescence probably due to a release of Ca++ from the mucous layer. The degree of fluorescence intensity is correlated with the capacity of pinocytotic channel formation, i.e., the fluorescence decreases as the number of channels increases. During the phase of vesiculation a distinct fluorescence mainly restricted to the basal region of the channels is observed. Intracellular Ca++ was detected in close vicinity to the plasma membrane after both microinjection and external application of CTC. The internal CTC-fluorescence is slightly decreased during the induction phase of pinocytosis. The observations are in good agreement with previous results on the localization of Ca++ -binding sites at the plasma membrane of Amoeba proteus and demonstrate the important role of Ca++ -fluxes for the process of pinocytosis.

From mucolipidosis type IV to Ebola: TRPML and two-pore channels at the crossroads of endo-lysosomal trafficking and disease.

PubMed

Grimm, Christian; Butz, Elisabeth; Chen, Cheng-Chang; Wahl-Schott, Christian; Biel, Martin

2017-11-01

What do lysosomal storage disorders such as mucolipidosis type IV have in common with Ebola, cancer cell migration, or LDL-cholesterol trafficking? LDL-cholesterol, certain bacterial toxins and viruses, growth factors, receptors, integrins, macromolecules destined for degradation or secretion are all sorted and transported via the endolysosomal system (ES). There are several pathways known in the ES, e.g. the degradation, the recycling, or the retrograde trafficking pathway. The ES comprises early and late endosomes, lysosomes and recycling endosomes as well as autophagosomes and lysosome related organelles. Contact sites between the ES and the endoplasmic reticulum or the Golgi apparatus may also be considered part of it. Dysfunction of this complex intracellular machinery can cause or contribute to the development of a number of diseases ranging from neurodegenerative, infectious, or metabolic diseases to retinal and pigmentation disorders as well as cancer and autophagy-related diseases. Endolysosomal ion channels such as mucolipins (TRPMLs) and two-pore channels (TPCs) play an important role in intracellular cation/calcium signaling and homeostasis and appear to critically contribute to the proper function of the endolysosomal trafficking network. Copyright © 2017 Elsevier Ltd. All rights reserved.

Plant rhamnogalacturonan II complexation of heavy metal cations

DOEpatents

O`Neill, M.A.; Pellerin, P.J.M.; Warrenfeltz, D.; Vidal, S.; Darvill, A.G.; Albersheim, P.

1999-03-02

The present invention provides rhamnogalacturonan-II (RG-II) and relates to its ability to complex specific multivalent heavy metal cations. In the presence of boric acid, RG-II monomers form dimers that are cross-linked by a borate ester. The yield of such borate ester cross-linked dimers of RG-II is enhanced in the presence of specific heavy metal cations. The present invention further relates to the utility of RG-II in assays for the detection of specific heavy metal contamination; as a reagent useful in the removal of specific heavy metal cations contaminating foods and liquids, for example, fish, wines, etc.; as a pharmaceutical composition useful as an antidote in specific heavy metal cation poisoning; as a treatment for the detoxification of specific heavy metal cations from blood and/or tissues; and in a method of remediation of waters and soils contaminated with specific heavy metal cations. 15 figs.

Plant rhamnogalacturonan II complexation of heavy metal cations

DOEpatents

O'Neill, Malcolm A.; Pellerin, Patrice J. M.; Warrenfeltz, Dennis; Vidal, Stephane; Darvill, Alan G.; Albersheim, Peter

1999-01-01

The present invention provides rhamnogalacturonan-II (RG-II) and relates to its ability to complex specific multivalent heavy metal cations. In the presence of boric acid, RG-II monomers form dimers that are cross-linked by a borate ester. The yield of such borate ester cross-linked dimers of RG-II is enhanced in the presence of specific heavy metal cations. The present invention further relates to the utility of RG-II in assays for the detection of specific heavy metal contamination; as a reagent useful in the removal of specific heavy metal cations contaminating foods and liquids, for example, fish, wines, etc.; as a pharmaceutical composition useful as an antidote in specific heavy metal cation poisoning; as a treatment for the detoxification of specific heavy metal cations from blood and/or tissues; and in a method of remediation of waters and soils contaminated with specific heavy metal cations.

Transmission electron microscopy characterization of a large-pore titanium silicate

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

Bozhilov, K.N.; Valtchev, V.P.

1993-11-01

The large-pore titanium silicate ETS-10, synthesized with tetramethylammonium, was characterized by means of TEM. The parameters of an orthorhombic unit cell, a = 14.79 [angstrom], b = 14.5 [angstrom], c = 13.06 [angstrom], were determined based on both electron and x-ray diffraction data. A one-dimensional channel structure is proposed, with channels running parallel to [001]. The cations and molecules occupying channel positions display significant positional disorder.

Repair, Evaluation, Maintenance, and Rehabilitation Research Program. Geotechnical Aspects of Rock Erosion in Emergency Spillway Channels

DTIC Science & Technology

1986-08-01

8217 flooring unlined spillway channels. 115. Rippability was proposed by Weaver (1975) as a rock mass classifi- cation system that enables the assessment...geological. features which govern the as- sessment of rippability are rock type, haidness, weathering, stcucture, and fabric. Saismic P-wave velocity...channel. Rippability should be combined with a factor 84 that describes lithostratigraphic continuity in order to derive the erosion potential of the

A calcium-permeable cGMP-activated cation conductance in hippocampal neurons

NASA Technical Reports Server (NTRS)

Leinders-Zufall, T.; Rosenboom, H.; Barnstable, C. J.; Shepherd, G. M.; Zufall, F.

1995-01-01

Whole-cell patch clamp recordings detected a previously unidentified cGMP-activated membrane conductance in cultured rat hippocampal neurons. This conductance is nonselectively permeable for cations and is completely but reversibly blocked by external Cd2+. The Ca2+ permeability of the hippocampal cGMP-activated conductance was examined in detail, indicating that the underlying ion channels display a high relative permeability for Ca2+. The results indicate that hippocampal neurons contain a cGMP-activated membrane conductance that has some properties similar to the cyclic nucleotide-gated channels previously shown in sensory receptor cells and retinal neurons. In hippocampal neurons this conductance similarly could mediate membrane depolarization and Ca2+ fluxes in response to intracellular cGMP elevation.

Ion transport through lipid bilayers by synthetic ionophores: modulation of activity and selectivity.

PubMed

De Riccardis, Francesco; Izzo, Irene; Montesarchio, Daniela; Tecilla, Paolo

2013-12-17

The ion-coupled processes that occur in the plasma membrane regulate the cell machineries in all the living organisms. The details of the chemical events that allow ion transport in biological systems remain elusive. However, investigations of the structure and function of natural and artificial transporters has led to increasing insights about the conductance mechanisms. Since the publication of the first successful artificial system by Tabushi and co-workers in 1982, synthetic chemists have designed and constructed a variety of chemically diverse and effective low molecular weight ionophores. Despite their relative structural simplicity, ionophores must satisfy several requirements. They must partition in the membrane, interact specifically with ions, shield them from the hydrocarbon core of the phospholipid bilayer, and transport ions from one side of the membrane to the other. All these attributes require amphipathic molecules in which the polar donor set used for ion recognition (usually oxygens for cations and hydrogen bond donors for anions) is arranged on a lipophilic organic scaffold. Playing with these two structural motifs, donor atoms and scaffolds, researchers have constructed a variety of different ionophores, and we describe a subset of interesting examples in this Account. Despite the ample structural diversity, structure/activity relationships studies reveal common features. Even when they include different hydrophilic moieties (oxyethylene chains, free hydroxyl, etc.) and scaffolds (steroid derivatives, neutral or polar macrocycles, etc.), amphipathic molecules, that cannot span the entire phospholipid bilayer, generate defects in the contact zone between the ionophore and the lipids and increase the permeability in the bulk membrane. Therefore, topologically complex structures that span the entire membrane are needed to elicit channel-like and ion selective behaviors. In particular the alternate-calix[4]arene macrocycle proved to be a versatile platform to obtain 3D-structures that can form unimolecular channels in membranes. In these systems, the selection of proper donor groups allows us to control the ion selectivity of the process. We can switch from cation to anion transport by substituting protonated amines for the oxygen donors. Large and stable tubular structures with nanometric sized transmembrane nanopores that provide ample internal space represent a different approach for the preparation of synthetic ion channels. We used the metal-mediated self-assembly of porphyrin ligands with Re(I) corners as a new method for producing to robust channel-like structures. Such structures can survive in the complex membrane environment and show interesting ionophoric behavior. In addition to the development of new design principles, the selective modification of the biological membrane permeability could lead to important developments in medicine and technology.

Channel formation by the binding component of Clostridium botulinum C2 toxin: glutamate 307 of C2II affects channel properties in vitro and pH-dependent C2I translocation in vivo.

PubMed

Blöcker, Dagmar; Bachmeyer, Christoph; Benz, Roland; Aktories, Klaus; Barth, Holger

2003-05-13

The binding component (C2II) of the binary Clostridium botulinum C2 toxin mediates transport of the actin ADP-ribosylating enzyme component (C2I) into the cytosol of target cells. C2II (80 kDa) is activated by trypsin cleavage, and proteolytically activated C2II (60 kDa) oligomerizes to heptamers in solution. Activated C2II forms channels in lipid bilayer membranes which are highly cation selective and voltage-gated. A role for this channel in C2I translocation across the cell membrane into the cytosol is discussed. Amino acid residues 303-331 of C2II contain a conserved pattern of alternating hydrophobic and hydrophilic residues, which likely facilitates membrane insertion and channel formation by creating two antiparallel beta-strands. Some of the residues are in strategic positions within the putative C2II channel, in particular, glutamate 307 (E307) localized in its center and glycine 316 (G316) localized on the trans side of the membrane. Here, single-lysine substitutions of these amino acids and the double mutant E307K/G316K of C2II were analyzed in vivo and in artificial lipid bilayer experiments. The pH dependence of C2I transport across cellular membranes was altered, and a pH of

Structural and energetic study of cation-π-cation interactions in proteins.

PubMed

Pinheiro, Silvana; Soteras, Ignacio; Gelpí, Josep Lluis; Dehez, François; Chipot, Christophe; Luque, F Javier; Curutchet, Carles

2017-04-12

Cation-π interactions of aromatic rings and positively charged groups are among the most important interactions in structural biology. The role and energetic characteristics of these interactions are well established. However, the occurrence of cation-π-cation interactions is an unexpected motif, which raises intriguing questions about its functional role in proteins. We present a statistical analysis of the occurrence, composition and geometrical preferences of cation-π-cation interactions identified in a set of non-redundant protein structures taken from the Protein Data Bank. Our results demonstrate that this structural motif is observed at a small, albeit non-negligible frequency in proteins, and suggest a preference to establish cation-π-cation motifs with Trp, followed by Tyr and Phe. Furthermore, we have found that cation-π-cation interactions tend to be highly conserved, which supports their structural or functional role. Finally, we have performed an energetic analysis of a representative subset of cation-π-cation complexes combining quantum-chemical and continuum solvation calculations. Our results point out that the protein environment can strongly screen the cation-cation repulsion, leading to an attractive interaction in 64% of the complexes analyzed. Together with the high degree of conservation observed, these results suggest a potential stabilizing role in the protein fold, as demonstrated recently for a miniature protein (Craven et al., J. Am. Chem. Soc. 2016, 138, 1543). From a computational point of view, the significant contribution of non-additive three-body terms challenges the suitability of standard additive force fields for describing cation-π-cation motifs in molecular simulations.

On The Molecular Mechanism Of Positive Novolac Resists

NASA Astrophysics Data System (ADS)

Huang, Jian-Ping; Kwei, T. K.; Reiser, Arnost

1989-08-01

A molecular mechanism for the dissolution of novolac is proposed, based on the idea of a critical degree of deprotonation as being the condition for the transfer of polymer into solution. The rate at which the critical deprotonation condition is achieved is controlled by the supply of developer into a thin penetration zone, and depends in particular on the rate of diffusion of the base cations which are the developer component with the lowest mobility. The penetration zone contains phenolate ions and ion-bound water, but it retains the structure of a rigid polymer membrane, as evidenced by the diffusion coefficient of cations in the pene;tration zone which is several orders of magnitude slower than in an open gel of the same material. When the critical degree of deprotonation is reached, the membrane structure unravels and all subsequent events, chain rearrangement and transfer into solution, occur rapidly. The supralinear dependence of dissolution rate on base concentration and the effect of the size of the base cation are plausibly interpreted by the model. The diffusion of developer components is assumed to occur preferentially via hydrophilic sites in the polymer matrix. These sites define a diffusion path which acts like a hydrophilic diffusion channel. Suitably designed hydrophobic molecules can block some of the channels and in this way alter the dissolution rate. They reduce in effect the diffusion crossect ion of the material. Hydrophilic additives, on the other hand, introduce additional channels into the system and promote dissolution. The concept of diffusion channels appears to provide a unified interpretation for a number of common observations.

Cation-Inhibited Transport of Graphene Oxide Nanomaterials in Saturated Porous Media: The Hofmeister Effects.

PubMed

Xia, Tianjiao; Qi, Yu; Liu, Jing; Qi, Zhichong; Chen, Wei; Wiesner, Mark R

2017-01-17

Transport of negatively charged nanoparticles in porous media is largely affected by cations. To date, little is known about how cations of the same valence may affect nanoparticle transport differently. We observed that the effects of cations on the transport of graphene oxide (GO) and sulfide-reduced GO (RGO) in saturated quartz sand obeyed the Hofmeister series; that is, transport-inhibition effects of alkali metal ions followed the order of Na + < K + < Cs + , and those of alkaline earth metal ions followed the order of Mg 2+ < Ca 2+ < Ba 2+ . With batch adsorption experiments and microscopic data, we verified that cations having large ionic radii (and thus being weakly hydrated) interacted with quartz sand and GO and RGO more strongly than did cations of small ionic radii. In particular, the monovalent Cs + and divalent Ca 2+ and Ba 2+ , which can form inner-sphere complexes, resulted in very significant deposition of GO and RGO via cation bridging between quartz sand and GO and RGO, and possibly via enhanced straining, due to the enhanced aggregation of GO and RGO from cation bridging. The existence of the Hofmeister effects was further corroborated with the interesting observation that cation bridging was more significant for RGO, which contained greater amounts of carboxyl and phenolic groups (i.e., metal-complexing moieties) than did GO. The findings further demonstrate that transport of nanoparticles is controlled by the complex interplay between nanoparticle surface functionalities and solution chemistry constituents.

Tight junctions of the proximal tubule and their channel proteins.

PubMed

Fromm, Michael; Piontek, Jörg; Rosenthal, Rita; Günzel, Dorothee; Krug, Susanne M

2017-08-01

The renal proximal tubule achieves the majority of renal water and solute reabsorption with the help of paracellular channels which lead through the tight junction. The proteins forming such channels in the proximal tubule are claudin-2, claudin-10a, and possibly claudin-17. Claudin-2 forms paracellular channels selective for small cations like Na + and K + . Independently of each other, claudin-10a and claudin-17 form anion-selective channels. The claudins form the paracellular "pore pathway" and are integrated, together with purely sealing claudins and other tight junction proteins, in the belt of tight junction strands surrounding the tubular epithelial cells. In most species, the proximal tubular tight junction consists of only 1-2 (pars convoluta) to 3-5 (pars recta) horizontal strands. Even so, they seal the tubule very effectively against leak passage of nutrients and larger molecules. Remarkably, claudin-2 channels are also permeable to water so that 20-25% of proximal water absorption may occur paracellularly. Although the exact structure of the claudin-2 channel is still unknown, it is clear that Na + and water share the same pore. Already solved claudin crystal structures reveal a characteristic β-sheet, comprising β-strands from both extracellular loops, which is anchored to a left-handed four-transmembrane helix bundle. This allowed homology modeling of channel-forming claudins present in the proximal tubule. The surface of cation- and anion-selective claudins differ in electrostatic potentials in the area of the proposed ion channel, resulting in the opposite charge selectivity of these claudins. Presently, while models of the molecular structure of the claudin-based oligomeric channels have been proposed, its full understanding has only started.

Novel regulatory mechanism in human urinary bladder: central role of transient receptor potential melastatin 4 channels in detrusor smooth muscle function

PubMed Central

Hristov, Kiril L.; Smith, Amy C.; Parajuli, Shankar P.; Malysz, John; Rovner, Eric S.

2016-01-01

Transient receptor potential melastatin 4 (TRPM4) channels are Ca2+-activated nonselective cation channels that have been recently identified as regulators of detrusor smooth muscle (DSM) function in rodents. However, their expression and function in human DSM remain unexplored. We provide insights into the functional role of TRPM4 channels in human DSM under physiological conditions. We used a multidisciplinary experimental approach, including RT-PCR, Western blotting, immunohistochemistry and immunocytochemistry, patch-clamp electrophysiology, and functional studies of DSM contractility. DSM samples were obtained from patients without preoperative overactive bladder symptoms. RT-PCR detected mRNA transcripts for TRPM4 channels in human DSM whole tissue and freshly isolated single cells. Western blotting and immunohistochemistry with confocal microscopy revealed TRPM4 protein expression in human DSM. Immunocytochemistry further detected TRPM4 protein expression in DSM single cells. Patch-clamp experiments showed that 9-phenanthrol, a selective TRPM4 channel inhibitor, significantly decreased the transient inward cation currents and voltage step-induced whole cell currents in freshly isolated human DSM cells. In current-clamp mode, 9-phenanthrol hyperpolarized the human DSM cell membrane potential. Furthermore, 9-phenanthrol attenuated the spontaneous phasic, carbachol-induced and nerve-evoked contractions in human DSM isolated strips. Significant species-related differences in TRPM4 channel activity between human, rat, and guinea pig DSM were revealed, suggesting a more prominent physiological role for the TRPM4 channel in the regulation of DSM function in humans than in rodents. In conclusion, TRPM4 channels regulate human DSM excitability and contractility and are critical determinants of human urinary bladder function. Thus, TRPM4 channels could represent promising novel targets for the pharmacological or genetic control of overactive bladder. PMID:26791488

Mechanosensitive Ca²⁺-permeable channels in human leukemic cells: pharmacological and molecular evidence for TRPV2.

PubMed

Pottosin, Igor; Delgado-Enciso, Iván; Bonales-Alatorre, Edgar; Nieto-Pescador, María G; Moreno-Galindo, Eloy G; Dobrovinskaya, Oxana

2015-01-01

Mechanosensitive channels are present in almost every living cell, yet the evidence for their functional presence in T lymphocytes is absent. In this study, by means of the patch-clamp technique in attached and inside-out modes, we have characterized cationic channels, rapidly activated by membrane stretch in Jurkat T lymphoblasts. The half-activation was achieved at a negative pressure of ~50mm Hg. In attached mode, single channel currents displayed an inward rectification and the unitary conductance of ~40 pS at zero command voltage. In excised inside-out patches the rectification was transformed to an outward one. Mechanosensitive channels weakly discriminated between mono- and divalent cations (PCa/PNa~1) and were equally permeable for Ca²⁺ and Mg²⁺. Pharmacological analysis showed that the mechanosensitive channels were potently blocked by amiloride (1mM) and Gd³⁺ (10 μM) in a voltage-dependent manner. They were also almost completely blocked by ruthenium red (1 μM) and SKF 96365 (250 μM), inhibitors of transient receptor potential vanilloid 2 (TRPV2) channels. At the same time, the channels were insensitive to 2-aminoethoxydiphenyl borate (2-APB, 100 μM) or N-(p-amylcinnamoyl)anthranilic acid (ACA, 50 μM), antagonists of transient receptor potential canonical (TRPC) or transient receptor potential melastatin (TRPM) channels, respectively. Human TRPV2 siRNA virtually abolished the stretch-activated current. TRPV2 are channels with multifaceted functions and regulatory mechanisms, with potentially important roles in the lymphocyte Ca²⁺ signaling. Implications of their regulation by mechanical stress are discussed in the context of lymphoid cells functions. Copyright © 2014 Elsevier B.V. All rights reserved.

Local electrostatic interactions determine the diameter of fusion pores

PubMed Central

Guček, Alenka; Jorgačevski, Jernej; Górska, Urszula; Rituper, Boštjan; Kreft, Marko; Zorec, Robert

2015-01-01

In regulated exocytosis vesicular and plasma membranes merge to form a fusion pore in response to stimulation. The nonselective cation HCN channels are involved in the regulation of unitary exocytotic events by at least 2 mechanisms. They can affect SNARE-dependent exocytotic activity indirectly, via the modulation of free intracellular calcium; and/or directly, by altering local cation concentration, which affects fusion pore geometry likely via electrostatic interactions. By monitoring membrane capacitance, we investigated how extracellular cation concentration affects fusion pore diameter in pituitary cells and astrocytes. At low extracellular divalent cation levels predominantly transient fusion events with widely open fusion pores were detected. However, fusion events with predominately narrow fusion pores were present at elevated levels of extracellular trivalent cations. These results show that electrostatic interactions likely help determine the stability of discrete fusion pore states by affecting fusion pore membrane composition. PMID:25835258

Anionized and cationized hemeundecapeptides as probes for cell surface charge and permeability studies: differentiated labeling of endothelial plasmalemmal vesicles

PubMed Central

1985-01-01

To obtain small membrane markers easily accessible to the charged groups of the cell surface, we prepared, from hemeundecapeptide (HUP), three derivatives that maintain the peroxidatic activity: the anionized hemeundecapeptide, Mr 1,963, estimated diameter 1.68 nm, pl 3.5, for the detection of basic groups; and both a cationized hemeundecapeptide containing predominantly tertiary amino groups, Mr 2,215, estimated diameter 1.75 nm, pl 9.0, and a cationized hemeundecapeptide containing only primary amino groups, Mr 2,271, estimated diameter 1.75 nm, pl 10.6, for labeling acidic residues. The markers were perfused in situ in mice to label the luminal surface of fenestrated endothelium of pancreatic capillaries. Specimens were processed through the cytochemical reaction for peroxidatic activity and examined by electron microscopy. The anionized HUP and HUP (pl 4.85) marked the plasmalemma proper, the coated pits, and the membrane and diaphragms of plasmalemmal vesicles and transendothelial channels. The cationized HUP containing predominantly tertiary amino groups (pl 9.0) decorated all cell surface components with the exception of plasmalemmal vesicles and channels; the latter were, however, labeled by the cationized HUP containing only primary groups (pl 10.6), which suggests that these structures contain on their luminal surface very weak acidic residues of high pKa values. The fact that the membrane of plasmalemmal vesicles can discriminate against permeant cationic macromolecules only up to a pl of approximately 9.0 indicates that in the electrostatic restriction there is a charge limit. In the case of fenestrated capillary endothelium, the upper charge limit seems to be a pl of approximately 9.0. In these vessels, the charge discrimination is effective for molecules as small as 2 nm. PMID:3968182

Anionized and cationized hemeundecapeptides as probes for cell surface charge and permeability studies: differentiated labeling of endothelial plasmalemmal vesicles.

PubMed

Ghinea, N; Simionescu, N

1985-02-01

To obtain small membrane markers easily accessible to the charged groups of the cell surface, we prepared, from hemeundecapeptide (HUP), three derivatives that maintain the peroxidatic activity: the anionized hemeundecapeptide, Mr 1,963, estimated diameter 1.68 nm, pl 3.5, for the detection of basic groups; and both a cationized hemeundecapeptide containing predominantly tertiary amino groups, Mr 2,215, estimated diameter 1.75 nm, pl 9.0, and a cationized hemeundecapeptide containing only primary amino groups, Mr 2,271, estimated diameter 1.75 nm, pl 10.6, for labeling acidic residues. The markers were perfused in situ in mice to label the luminal surface of fenestrated endothelium of pancreatic capillaries. Specimens were processed through the cytochemical reaction for peroxidatic activity and examined by electron microscopy. The anionized HUP and HUP (pl 4.85) marked the plasmalemma proper, the coated pits, and the membrane and diaphragms of plasmalemmal vesicles and transendothelial channels. The cationized HUP containing predominantly tertiary amino groups (pl 9.0) decorated all cell surface components with the exception of plasmalemmal vesicles and channels; the latter were, however, labeled by the cationized HUP containing only primary groups (pl 10.6), which suggests that these structures contain on their luminal surface very weak acidic residues of high pKa values. The fact that the membrane of plasmalemmal vesicles can discriminate against permeant cationic macromolecules only up to a pl of approximately 9.0 indicates that in the electrostatic restriction there is a charge limit. In the case of fenestrated capillary endothelium, the upper charge limit seems to be a pl of approximately 9.0. In these vessels, the charge discrimination is effective for molecules as small as 2 nm.

On the permeation of large organic cations through the pore of ATP-gated P2X receptors

PubMed Central

Harkat, Mahboubi; Peverini, Laurie; Dunning, Kate; Beudez, Juline; Martz, Adeline; Calimet, Nicolas; Specht, Alexandre; Cecchini, Marco; Chataigneau, Thierry; Grutter, Thomas

2017-01-01

Pore dilation is thought to be a hallmark of purinergic P2X receptors. The most commonly held view of this unusual process posits that under prolonged ATP exposure the ion pore expands in a striking manner from an initial small-cation conductive state to a dilated state, which allows the passage of larger synthetic cations, such as N-methyl-d-glucamine (NMDG+). However, this mechanism is controversial, and the identity of the natural large permeating cations remains elusive. Here, we provide evidence that, contrary to the time-dependent pore dilation model, ATP binding opens an NMDG+-permeable channel within milliseconds, with a conductance that remains stable over time. We show that the time course of NMDG+ permeability superimposes that of Na+ and demonstrate that the molecular motions leading to the permeation of NMDG+ are very similar to those that drive Na+ flow. We found, however, that NMDG+ “percolates” 10 times slower than Na+ in the open state, likely due to a conformational and orientational selection of permeating molecules. We further uncover that several P2X receptors, including those able to desensitize, are permeable not only to NMDG+ but also to spermidine, a large natural cation involved in ion channel modulation, revealing a previously unrecognized P2X-mediated signaling. Altogether, our data do not support a time-dependent dilation of the pore on its own but rather reveal that the open pore of P2X receptors is wide enough to allow the permeation of large organic cations, including natural ones. This permeation mechanism has considerable physiological significance. PMID:28442564

Transient Receptor Potential Channels as Targets for Phytochemicals

PubMed Central

2015-01-01

To date, 28 mammalian transient receptor potential (TRP) channels have been cloned and characterized. They are grouped into six subfamilies on the basis of their amino acid sequence homology: TRP Ankyrin (TRPA), TRP Canonical (TRPC), TRP Melastatin (TRPM), TRP Mucolipin (TRPML), TRP Polycystin (TRPP), and TRP Vanilloid (TRPV). Most of the TRP channels are nonselective cation channels expressed on the cell membrane and exhibit variable permeability ratios for Ca2+ versus Na+. They mediate sensory functions (such as vision, nociception, taste transduction, temperature sensation, and pheromone signaling) and homeostatic functions (such as divalent cation flux, hormone release, and osmoregulation). Significant progress has been made in our understanding of the specific roles of these TRP channels and their activation mechanisms. In this Review, the emphasis will be on the activation of TRP channels by phytochemicals that are claimed to exert health benefits. Recent findings complement the anecdotal evidence that some of these phytochemicals have specific receptors and the activation of which is responsible for the physiological effects. Now, the targets for these phytochemicals are being unveiled; a specific hypothesis can be proposed and tested experimentally to infer a scientific validity of the claims of the health benefits. The broader and pressing issues that have to be addressed are related to the quantities of the active ingredients in a given preparation, their bioavailability, metabolism, adverse effects, excretion, and systemic versus local effects. PMID:24926802

pH-dependent pore-forming activity of OmpATb from Mycobacterium tuberculosis and characterization of the channel by peptidic dissection.

PubMed

Molle, Virginie; Saint, Nathalie; Campagna, Sylvie; Kremer, Laurent; Lea, Edward; Draper, Philip; Molle, Gérard

2006-08-01

Mycobacteria are characterized by an unusual cell wall that controls nutrient and small hydrophilic compound permeability. Porin-like proteins are necessary to ensure the transport of molecules into the cell. Here, we investigated the pore-forming properties of OmpATb, a porin from Mycobacterium tuberculosis, in lipid bilayers. Multi-channel experiments showed an asymmetric behaviour with channel closures at negative critical voltages (Vc) and a strong decrease in Vc at acidic pH. Single-channel experiments gave conductance values of about 850 +/- 80 pS in 1 M KCl and displayed a weak cationic selectivity in 4-8 pH range. The production and characterization of a series of truncated OmpATb proteins, showed that the central domain (OmpATb73-220) was sufficient to induce the ion channel properties of the native protein in lipid bilayers, i.e. asymmetric insertion, pH-dependent voltage closure, cationic selectivity and similar conductance values in 1 M KCl. Western blot analysis suggests that the presence of OmpATb is only restricted to certain pathogenic species. Therefore, the propensity of channels of native OmpATb to close at low pH may represent an intrinsic property allowing pathogenic mycobacteria to adapt and survive to mildly acidic conditions, such as those encountered within the macrophage phagosome.

The contribution of cationic conductances to the potential of rod photoreceptors.

PubMed

Moriondo, Andrea; Rispoli, Giorgio

2010-05-01

The contribution of cationic conductances in shaping the rod photovoltage was studied in light adapted cells recorded under whole-cell voltage- or current-clamp conditions. Depolarising current steps (of size comparable to the light-regulated current) produced monotonic responses when the prepulse holding potential (V (h)) was -40 mV (i.e. corresponding to the membrane potential in the dark). At V (h) = -60 mV (simulating the steady-state response to an intense background of light) current injections <35 pA (mimicking a light decrement) produced instead an initial depolarisation that declined to a plateau, and voltage transiently overshot V (h) at the stimulus offset. Current steps >40 pA produced a steady depolarisation to approximately -16 mV at both V (h). The difference between the responses at the two V (h) was primarily generated by the slow delayed-rectifier-like K(+) current (I (Kx)), which therefore strongly affects both the photoresponse rising and falling phase. The steady voltage observed at both V (h) in response to large current injections was instead generated by Ca-activated K(+) channels (I (KCa)), as previously found. Both I (Kx) and I (KCa) oppose the cation influx, occurring at the light stimulus offset through the cGMP-gated channels and the voltage-activated Ca(2+) channels (I (Ca)). This avoids that the cation influx could erratically depolarise the rod past its normal resting value, thus allowing a reliable dim stimuli detection, without slowing down the photovoltage recovery kinetics. The latter kinetics was instead accelerated by the hyperpolarisation-activated, non-selective current (I (h)) and I (Ca). Blockade of all K(+) currents with external TEA unmasked a I (Ca)-dependent regenerative behaviour.

Self-Incompatibility in Papaver rhoeas Activates Nonspecific Cation Conductance Permeable to Ca2+ and K+[W

PubMed Central

Wu, Juyou; Wang, Su; Gu, Yuchun; Zhang, Shaoling; Publicover, Stephen J.; Franklin-Tong, Vernonica E.

2011-01-01

Cellular responses rely on signaling. In plant cells, cytosolic free calcium is a major second messenger, and ion channels play a key role in mediating physiological responses. Self-incompatibility (SI) is an important genetically controlled mechanism to prevent self-fertilization. It uses interaction of matching S-determinants from the pistil and pollen to allow “self” recognition, which triggers rejection of incompatible pollen. In Papaver rhoeas, the S-determinants are PrsS and PrpS. PrsS is a small novel cysteine-rich protein; PrpS is a small novel transmembrane protein. Interaction of PrsS with incompatible pollen stimulates S-specific increases in cytosolic free calcium and alterations in the actin cytoskeleton, resulting in programmed cell death in incompatible but not compatible pollen. Here, we have used whole-cell patch clamping of pollen protoplasts to show that PrsS stimulates SI-specific activation of pollen grain plasma membrane conductance in incompatible but not compatible pollen grain protoplasts. The SI-activated conductance does not require voltage activation, but it is voltage sensitive. It is permeable to divalent cations (Ba2+ ≥ Ca2+ > Mg2+) and the monovalent ions K+ and NH4+ and is enhanced at voltages negative to −100 mV. The Ca2+ conductance is blocked by La3+ but not by verapamil; the K+ currents are tetraethylammonium chloride insensitive and do not require Ca2+. We propose that the SI-stimulated conductance may represent a nonspecific cation channel or possibly two conductances, permeable to monovalent and divalent cations. Our data provide insights into signal-response coupling involving a biologically important response. PrsS provides a rare example of a protein triggering alterations in ion channel activity. PMID:21177472

A Lys-Trp cation-π interaction mediates the dimerization and function of the chloride intracellular channel protein 1 transmembrane domain.

PubMed

Peter, Bradley; Polyansky, Anton A; Fanucchi, Sylvia; Dirr, Heini W

2014-01-14

Chloride intracellular channel protein 1 (CLIC1) is a dual-state protein that can exist either as a soluble monomer or in an integral membrane form. The oligomerization of the transmembrane domain (TMD) remains speculative despite it being implicated in pore formation. The extent to which electrostatic and van der Waals interactions drive folding and association of the dimorphic TMD is unknown and is complicated by the requirement of interactions favorable in both aqueous and membrane environments. Here we report a putative Lys37-Trp35 cation-π interaction and show that it stabilizes the dimeric form of the CLIC1 TMD in membranes. A synthetic 30-mer peptide comprising a K37M TMD mutant was examined in 2,2,2-trifluoroethanol, sodium dodecyl sulfate micelles, and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine liposomes using far-ultraviolet (UV) circular dichroism, fluorescence, and UV absorbance spectroscopy. Our data suggest that Lys37 is not implicated in the folding, stability, or membrane insertion of the TMD peptide. However, removal of this residue impairs the formation of dimers and higher-order oligomers. This is accompanied by a 30-fold loss of chloride influx activity, suggesting that dimerization modulates the rate of chloride conductance. We propose that, within membranes, individual TMD helices associate via a Lys37-mediated cation-π interaction to form active dimers. The latter findings are also supported by results of modeling a putative TMD dimer conformation in which Lys37 and Trp35 form cation-π pairs at the dimer interface. Dimeric helix bundles may then associate to form fully active ion channels. Thus, within a membrane-like environment, aromatic interactions involving a polar lysine side chain provide a thermodynamic driving force for helix-helix association.

CASEIN KINASE-MEDIATED PHOSPHORYLATION OF SERINE 839 IS NECESSARY FOR BASOLATERAL LOCALIZATION OF THE Ca2+-ACTIVATED NON-SELECTIVE CATION CHANNEL TRPM4

PubMed Central

Cerda, Oscar; Cáceres, Mónica; Park, Kang-Sik; Leiva-Salcedo, Elías; Romero, Aníbal; Varela, Diego

2014-01-01

TRPM4 is a Ca2+-activated non-selective cation channel expressed in a wide range of human tissues. TRPM4 participates in a variety of physiological processes such as T cell activation, myogenic vasoconstriction and allergic reactions. TRPM4 Ca2+ sensitivity is enhanced by calmodulin (CaM) and phosphathydilinositol 4, 5-biphosphate (PI(4,5)P2) binding, as well as, under certain conditions, PKC activation. However, information as to the mechanisms of modulation of this channel remain unknown, including direct identification of phosphorylation sites on TRPM4 and their role in channel features. Here, we use mass-spectrometric-based proteomic approaches (immunoprecipitation and tandem mass spectrometry), to unambiguously identify S839 as a phosphorylation site present on human TRPM4 expressed in a human cell line. Site-directed mutagenesis employing a serine to alanine mutation to eliminate phosphorylation, and a phospho-mimetic aspartate mutation, as well as biochemical and immunocytochemical experiments, revealed a role for S839 phosphorylation in the basolateral expression of TRPM4 channels in epithelial cells. Moreover, we demonstrated that casein kinase 1 (CK1) phosphorylates S839 and is responsible for the basolateral localization of TRPM4. PMID:25231975

Casein kinase-mediated phosphorylation of serine 839 is necessary for basolateral localization of the Ca²⁺-activated non-selective cation channel TRPM4.

PubMed

Cerda, Oscar; Cáceres, Mónica; Park, Kang-Sik; Leiva-Salcedo, Elías; Romero, Aníbal; Varela, Diego; Trimmer, James S; Stutzin, Andrés

2015-08-01

Transient receptor potential melastatin-like 4 (TRPM4) is a Ca(2+)-activated non-selective cation channel expressed in a wide range of human tissues. TRPM4 participates in a variety of physiological processes such as T cell activation, myogenic vasoconstriction, and allergic reactions. TRPM4 Ca(2+) sensitivity is enhanced by calmodulin (CaM) and phosphathydilinositol 4, 5-bisphosphate (PI(4,5)P2) binding, as well as, under certain conditions, PKC activation. However, information as to the mechanisms of modulation of this channel remains unknown, including direct identification of phosphorylation sites on TRPM4 and their role in channel features. Here, we use mass-spectrometric-based proteomic approaches (immunoprecipitation and tandem mass spectrometry) to unambiguously identify S839 as a phosphorylation site present on human TRPM4 expressed in a human cell line. Site-directed mutagenesis employing a serine to alanine mutation to eliminate phosphorylation, and a phospho-mimetic aspartate mutation, as well as biochemical and immunocytochemical experiments, revealed a role for S839 phosphorylation in the basolateral expression of TRPM4 channels in epithelial cells. Moreover, we demonstrated that casein kinase 1 (CK1) phosphorylates S839 and is responsible for the basolateral localization of TRPM4.

Piezo1 forms mechanosensitive ion channels in the human MCF-7 breast cancer cell line

NASA Astrophysics Data System (ADS)

Li, Chouyang; Rezania, Simin; Kammerer, Sarah; Sokolowski, Armin; Devaney, Trevor; Gorischek, Astrid; Jahn, Stephan; Hackl, Hubert; Groschner, Klaus; Windpassinger, Christian; Malle, Ernst; Bauernhofer, Thomas; Schreibmayer, Wolfgang

2015-02-01

Mechanical interaction between cells - specifically distortion of tensional homeostasis-emerged as an important aspect of breast cancer genesis and progression. We investigated the biophysical characteristics of mechanosensitive ion channels (MSCs) in the malignant MCF-7 breast cancer cell line. MSCs turned out to be the most abundant ion channel species and could be activated by negative pressure at the outer side of the cell membrane in a saturable manner. Assessing single channel conductance (GΛ) for different monovalent cations revealed an increase in the succession: Li+ < Na+ < K+ ~Rb+ ~ Cs+. Divalent cations permeated also with the order: Ca2+ < Ba2+. Comparison of biophysical properties enabled us to identify MSCs in MCF-7 as ion channels formed by the Piezo1 protein. Using patch clamp technique no functional MSCs were observed in the benign MCF-10A mammary epithelial cell line. Blocking of MSCs by GsMTx-4 resulted in decreased motility of MCF-7, but not of MCF-10A cells, underscoring a possible role of Piezo1 in invasion and metastatic propagation. The role of Piezo1 in biology and progression of breast cancer is further substantiated by markedly reduced overall survival in patients with increased Piezo1 mRNA levels in the primary tumor.

Cationic PAMAM dendrimers as pore-blocking binary toxin inhibitors.

PubMed

Förstner, Philip; Bayer, Fabienne; Kalu, Nnanya; Felsen, Susanne; Förtsch, Christina; Aloufi, Abrar; Ng, David Y W; Weil, Tanja; Nestorovich, Ekaterina M; Barth, Holger

2014-07-14

Dendrimers are unique highly branched macromolecules with numerous groundbreaking biomedical applications under development. Here we identified poly(amido amine) (PAMAM) dendrimers as novel blockers for the pore-forming B components of the binary anthrax toxin (PA63) and Clostridium botulinum C2 toxin (C2IIa). These pores are essential for delivery of the enzymatic A components of the internalized toxins from endosomes into the cytosol of target cells. We demonstrate that at low μM concentrations cationic PAMAM dendrimers block PA63 and C2IIa to inhibit channel-mediated transport of the A components, thereby protecting HeLa and Vero cells from intoxication. By channel reconstitution and high-resolution current recording, we show that the PAMAM dendrimers obstruct transmembrane PA63 and C2IIa pores in planar lipid bilayers at nM concentrations. These findings suggest a new potential role for the PAMAM dendrimers as effective polyvalent channel-blocking inhibitors, which can protect human target cells from intoxication with binary toxins from pathogenic bacteria.

A polyoxometalate-encapsulating cationic metal-organic framework as a heterogeneous catalyst for desulfurization.

PubMed

Hao, Xiu-Li; Ma, Yuan-Yuan; Zang, Hong-Ying; Wang, Yong-Hui; Li, Yang-Guang; Wang, En-Bo

2015-02-23

A new cationic triazole-based metal-organic framework encapsulating Keggin-type polyoxometalates, with the molecular formula [Co(BBPTZ)3][HPMo12O40]⋅24 H2O [compound 1; BBPTZ = 4,4'-bis(1,2,4-triazol-1-ylmethyl)biphenyl] is hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. The structure of compound 1 contains a non-interpenetrated 3D CdSO4 (cds)-type framework with two types of channels that are interconnected with each other; straight channels that are occupied by the Keggin-type POM anions, and wavelike channels that contain lattice water molecules. The catalytic activity of compound 1 in the oxidative desulfurization reaction indicates that it is not only an effective and size-selective heterogeneous catalyst, but it also exhibits distinct structural stability in the catalytic reaction system. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cationic PAMAM Dendrimers as Pore-Blocking Binary Toxin Inhibitors

PubMed Central

2015-01-01

Dendrimers are unique highly branched macromolecules with numerous groundbreaking biomedical applications under development. Here we identified poly(amido amine) (PAMAM) dendrimers as novel blockers for the pore-forming B components of the binary anthrax toxin (PA63) and Clostridium botulinum C2 toxin (C2IIa). These pores are essential for delivery of the enzymatic A components of the internalized toxins from endosomes into the cytosol of target cells. We demonstrate that at low μM concentrations cationic PAMAM dendrimers block PA63 and C2IIa to inhibit channel-mediated transport of the A components, thereby protecting HeLa and Vero cells from intoxication. By channel reconstitution and high-resolution current recording, we show that the PAMAM dendrimers obstruct transmembrane PA63 and C2IIa pores in planar lipid bilayers at nM concentrations. These findings suggest a new potential role for the PAMAM dendrimers as effective polyvalent channel-blocking inhibitors, which can protect human target cells from intoxication with binary toxins from pathogenic bacteria. PMID:24954629

Effect of TRPV2 cation channels on the proliferation, migration and invasion of 5637 bladder cancer cells.

PubMed

Liu, Quanliang; Wang, Xinghuan

2013-11-01

Transient receptor potential vanilloid 2 (TRPV2), a nonselective cation channel, has become an attractive target gene for tumor studies due to its wide range of physiological and pathological functions. However, its specific role in bladder cancer development and progression remains unclear. The aim of the present study was to investigate the effects of TRPV2 on the proliferation, migration and invasion of 5637 bladder cancer cells in vitro . Rat TRPV2 cDNA was transfected into 5637 bladder cancer cells and changes in the behavior of the cells were detected. It was observed that TRPV2 enhanced bladder cancer cell migration and invasion; however, it did not affect cell proliferation in vitro . TRPV2 activity, which may be mediated by direct matrix metalloproteinase 2 (MMP2) regulation, is important in bladder tumor development and progression. The results of this study suggest that TRPV2 channels are a potential therapeutic target for bladder carcinoma.

Effect of TRPV2 cation channels on the proliferation, migration and invasion of 5637 bladder cancer cells

PubMed Central

LIU, QUANLIANG; WANG, XINGHUAN

2013-01-01

Transient receptor potential vanilloid 2 (TRPV2), a nonselective cation channel, has become an attractive target gene for tumor studies due to its wide range of physiological and pathological functions. However, its specific role in bladder cancer development and progression remains unclear. The aim of the present study was to investigate the effects of TRPV2 on the proliferation, migration and invasion of 5637 bladder cancer cells in vitro. Rat TRPV2 cDNA was transfected into 5637 bladder cancer cells and changes in the behavior of the cells were detected. It was observed that TRPV2 enhanced bladder cancer cell migration and invasion; however, it did not affect cell proliferation in vitro. TRPV2 activity, which may be mediated by direct matrix metalloproteinase 2 (MMP2) regulation, is important in bladder tumor development and progression. The results of this study suggest that TRPV2 channels are a potential therapeutic target for bladder carcinoma. PMID:24223658

Block ionomer complexes of PEG-block-poly(4-vinylbenzylphosphonate) and cationic surfactants as highly stable, pH responsive drug delivery system.

PubMed

Kamimura, Masao; Kim, Jong Oh; Kabanov, Alexander V; Bronich, Tatiana K; Nagasaki, Yukio

2012-06-28

A new family of block ionomer complexes (BIC) formed by poly(ethylene glycol)-block-poly(4-vinylbenzylphosphonate) (PEG-b-PVBP) and various cationic surfactants was prepared and characterized. These complexes spontaneously self-assembled in aqueous solutions into particles with average size of 40-60nm and remained soluble over the entire range of the compositions of the mixtures including stoichiometric electroneutral complexes. Solution behavior and physicochemical properties of such BIC were very sensitive to the structure of cationic surfactants. Furthermore, such complexation was used for incorporation of cationic anti-cancer drug, doxorubicin (DOX), into the core of BIC with high loading capacity and efficiency. The DOX/PEG-b-PVBP BIC also displayed high stability against dilution, changes in ionic strength. Furthermore, DOX release at the extracellular pH of DOX/PEG-b-PVBP BIC was slow. It was greatly increased at the acidic pH mimicking the endosomal/lysosomal environment. Confocal fluorescence microscopy using live MCF-7 breast cancer cells suggested that DOX/PEG-b-PVBP BICs are transported to lysosomes. Subsequently, the drugs are released and exert cytotoxic effect killing these cancer cells. These findings indicate that the obtained complexes can be attractive candidates for delivery of cationic drugs to tumors. Copyright © 2012 Elsevier B.V. All rights reserved.

[Noncovalent cation-π interactions--their role in nature].

PubMed

Fink, Krzysztof; Boratyński, Janusz

2014-11-07

Non-covalent interactions play an extremely important role in organisms. The main non-covalent interactions in nature are: ion-ion interactions, dipole-dipole interactions, hydrogen bonds, and van der Waals interactions. A new kind of intermolecular interactions--cation-π interactions--is gaining increasing attention. These interactions occur between a cation and a π system. The main contributors to cation-π interactions are electrostatic, polarization and, to a lesser extent, dispersion interactions. At first, cation-π interactions were studied in a gas phase, with metal cation-aromatic system complexes. The characteristics of these complexes are as follows: an increase of cation atomic number leads to a decrease of interaction energy, and an increase of cation charge leads to an increase of interaction energy. Aromatic amino acids bind with metal cations mainly through interactions with their main chain. Nevertheless, cation-π interaction with a hydrophobic side chain significantly enhances binding energy. In water solutions most cations preferentially interact with water molecules rather than aromatic systems. Cation-π interactions occur in environments with lower accessibility to a polar solvent. Cation-π interactions can have a stabilizing role on the secondary, tertiary and quaternary structure of proteins. These interactions play an important role in substrate or ligand binding sites in many proteins, which should be taken into consideration when the screening of effective inhibitors for these proteins is carried out. Cation-π interactions are abundant and play an important role in many biological processes.

Redox chemistry of nickel(II) complexes supported by a series of noninnocent β-diketiminate ligands.

PubMed

Takaichi, June; Morimoto, Yuma; Ohkubo, Kei; Shimokawa, Chizu; Hojo, Takayuki; Mori, Seiji; Asahara, Haruyasu; Sugimoto, Hideki; Fujieda, Nobutaka; Nishiwaki, Nagatoshi; Fukuzumi, Shunichi; Itoh, Shinobu

2014-06-16

Nickel complexes of a series of β-diketiminate ligands ((R)L(-), deprotonated form of 2-substituted N-[3-(phenylamino)allylidene]aniline derivatives (R)LH, R = Me, H, Br, CN, and NO2) have been synthesized and structurally characterized. One-electron oxidation of the neutral complexes [Ni(II)((R)L(-))2] by AgSbF6 or [Ru(III)(bpy)3](PF6)3 (bpy = 2,2'-bipyridine) gave the corresponding metastable cationic complexes, which exhibit an EPR spectrum due to a doublet species (S = 1/2) and a characteristic absorption band in near IR region ascribable to a ligand-to-ligand intervalence charge-transfer (LLIVCT) transition. DFT calculations have indicated that the divalent oxidation state of nickel ion (Ni(II)) is retained, whereas one of the β-diketiminate ligands is oxidized to give formally a mixed-valence complex, [Ni(II)((R)L(-))((R)L(•))](+). Thus, the doublet spin state of the oxidized cationic complex can be explained by taking account of the antiferromagnetic interaction between the high-spin nickel(II) ion (S = 1) and the organic radical (S = 1/2) of supporting ligand. A single-crystal structure of one of the cationic complexes (R = H) has been successfully determined to show that both ligands in the cationic complex are structurally equivalent. On the basis of theoretical analysis of the LLIVCT band and DFT calculations as well as the crystal structure, the mixed-valence complexes have been assigned to Robin-Day class III species, where the radical spin is equally delocalized between the two ligands to give the cationic complex, which is best described as [Ni(II)((R)L(0.5•-))2](+). One-electron reduction of the neutral complexes with decamethylcobaltocene gave the anionic complexes when the ligand has the electron-withdrawing substituent (R = CN, NO2, Br). The generated anionic complexes exhibited EPR spectra due to a doublet species (S = 1/2) but showed no LLIVCT band in the near-IR region. Thus, the reduced complexes are best described as the d(9) nickel(I) complexes supported by two anionic β-diketiminate ligands, [Ni(I)((R)L(-))2](-). This conclusion was also supported by DFT calculations. Substituent effects on the electronic structures of the three oxidation states (neutral, cationic, and anionic) of the complexes are systematically evaluated on the basis of DFT calculations.

Versatile synthesis of cationic N-heterocyclic carbene-gold(i) complexes containing a second ancillary ligand. Design of heterobimetallic ruthenium-gold anticancer agents.

PubMed

Fernández-Gallardo, Jacob; Elie, Benelita T; Sanaú, Mercedes; Contel, María

2016-02-21

We describe a versatile and quick route to cationic gold(i) complexes containing N-heterocyclic carbenes and a second ancillary ligand (such as phosphanes, phosphites, arsines and amines) of interest for the synthesis of compounds with potential catalytic and medicinal applications. The general synthetic strategy has been applied in the preparation of novel cationic heterobimetallic ruthenium(ii)-gold(i) complexes that are highly cytotoxic to renal cancer Caki-1 and colon cancer HCT 116 cell lines while showing a synergistic effect and being more selective than their monometallic counterparts.

Slack, Slick, and Sodium-Activated Potassium Channels

PubMed Central

Kaczmarek, Leonard K.

2013-01-01

The Slack and Slick genes encode potassium channels that are very widely expressed in the central nervous system. These channels are activated by elevations in intracellular sodium, such as those that occur during trains of one or more action potentials, or following activation of nonselective cationic neurotransmitter receptors such as AMPA receptors. This review covers the cellular and molecular properties of Slack and Slick channels and compares them with findings on the properties of sodium-activated potassium currents (termed KNa currents) in native neurons. Human mutations in Slack channels produce extremely severe defects in learning and development, suggesting that KNa channels play a central role in neuronal plasticity and intellectual function. PMID:24319675

Marine Toxins Targeting Ion Channels

PubMed Central

Arias, Hugo R.

2006-01-01

This introductory minireview points out the importance of ion channels for cell communication. The basic concepts on the structure and function of ion channels triggered by membrane voltage changes, the so-called voltage-gated ion channels (VGICs), as well as those activated by neurotransmitters, the so-called ligand-gated ion channel (LGICs), are introduced. Among the most important VGIC superfamiles, we can name the voltage-gated Na+ (NaV), Ca2+ (CaV), and K+ (KV) channels. Among the most important LGIC super families, we can include the Cys-loop or nicotinicoid, the glutamate-activated (GluR), and the ATP-activated (P2XnR) receptor superfamilies. Ion channels are transmembrane proteins that allow the passage of different ions in a specific or unspecific manner. For instance, the activation of NaV, CaV, or KV channels opens a pore that is specific for Na+, Ca2+, or K+, respectively. On the other hand, the activation of certain LGICs such as nicotinic acetylcholine receptors, GluRs, and P2XnRs allows the passage of cations (e.g., Na+, K+, and/or Ca2+), whereas the activation of other LGICs such as type A γ-butyric acid and glycine receptors allows the passage of anions (e.g., Cl− and/or HCO3−). In this regard, the activation of NaV and CaV as well as ligand-gated cation channels produce membrane depolarization, which finally leads to stimulatory effects in the cell, whereas the activation of KV as well as ligand-gated anion channels induce membrane hyperpolarization that finally leads to inhibitory effects in the cell. The importance of these ion channel superfamilies is emphasized by considering their physiological functions throughout the body as well as their pathophysiological implicance in several neuronal diseases. In this regard, natural molecules, and especially marine toxins, can be potentially used as modulators (e.g., inhibitors or prolongers) of ion channel functions to treat or to alleviate a specific ion channel-linked disease (e.g., channelopaties).

A Multi-Level Theoretical Study to Disclose the Binding Mechanisms of Gold(III)-Bipyridyl Compounds as Selective Aquaglyceroporin Inhibitors.

PubMed

Graziani, Valentina; Marrone, Alessandro; Re, Nazzareno; Coletti, Cecilia; Platts, James A; Casini, Angela

2017-10-04

Structural studies have paved the avenue to a deeper understanding of aquaporins (AQPs), small ancient proteins providing efficient transmembrane pathways for water, small uncharged solutes such as glycerol, and possibly gas molecules. Despite the numerous studies, their roles in health and disease remain to be fully disclosed. The recent discovery of Au III complexes as potent and selective inhibitors of aquaglyceroporin isoforms paves the way to their possible therapeutic application. The binding of the selective human AQP3 inhibitor, the cationic complex [Au(bipy)Cl 2 ] + (Aubipy), to the protein channel has been investigated here by means of a multi-level theoretical workflow that includes QM, MD and QM/MM approaches. The hydroxo complex was identified as the prevalent form of Aubipy in physiological media and its binding to AQP3 studied by MD. Both non-covalent and coordinative Aubipy-AQP3 adducts were simulated to probe their role in the modulation of water channel functionality. The electronic structures of representative Aubipy-AQP3 adducts were then analysed to unveil the role played by the metal moiety in their stabilisation. This study spotlights the overall importance of three key aspects for AQP3 inhibition: 1) water speciation of the Au III complex, 2) stability of non-covalent adducts and 3) conformational changes induced within the pore by the coordinative binding of Au III . The obtained results are expected to orient future developments in the design of isoform-selective Au III inhibitors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cationic lipids: molecular structure/ transfection activity relationships and interactions with biomembranes.

PubMed

Koynova, Rumiana; Tenchov, Boris

2010-01-01

Abstract Synthetic cationic lipids, which form complexes (lipoplexes) with polyanionic DNA, are presently the most widely used constituents of nonviral gene carriers. A large number of cationic amphiphiles have been synthesized and tested in transfection studies. However, due to the complexity of the transfection pathway, no general schemes have emerged for correlating the cationic lipid chemistry with their transfection efficacy and the approaches for optimizing their molecular structures are still largely empirical. Here we summarize data on the relationships between transfection activity and cationic lipid molecular structure and demonstrate that the transfection activity depends in a systematic way on the lipid hydrocarbon chain structure. A number of examples, including a large series of cationic phosphatidylcholine derivatives, show that optimum transfection is displayed by lipids with chain length of approximately 14 carbon atoms and that the transfection efficiency strongly increases with increase of chain unsaturation, specifically upon replacement of saturated with monounsaturated chains.

Analysis of the Light-harvesting Pigment-Protein Complex of Wild Type and a Chlorophyll-b-less Mutant of Barley 1

PubMed Central

Burke, John J.; Steinback, Katherine E.; Arntzen, Charles J.

1979-01-01

we have compared chloroplast lamellae isolated from a chlorophyll-b-less mutant and wild type barley (Hordeum vulgare). The results demonstrate that: (a) one of the two major polypeptides comprising the lightharvesting complex (LHC) is present in the chlorophyll-b-less mutant; (b) higher cation concentrations are required to maintain grana stacks in the mutant; and (c) cation effects on excitation energy distribution are present in the chlorophyll-b-less mutant but are reduced in amount and are dependent on higher concentrations of cations. We interpret these data to support the concept that the LHC mediates cation-induced grana stacking and cation regulation of excitation energy distribution between photosystems I and Ii in chloroplast lamellae. A partial LHC complement in the mutant alters the quantitative cation requirement for both phenomena, but not the over-all qualitative response. Images PMID:16660704

Understanding chemical reactions of CO2 and its isoelectronic molecules with 1-butyl-3-methylimidazolium acetate by changing the nature of the cation: the case of CS2 in 1-butyl-1-methylpyrrolidinium acetate studied by NMR spectroscopy and density functional theory calculations.

PubMed

Cabaço, M Isabel; Besnard, Marcel; Chávez, Fabián Vaca; Pinaud, Noël; Sebastião, Pedro J; Coutinho, João A P; Danten, Yann

2014-06-28

NMR spectroscopy ((1)H, (13)C, (15)N) shows that carbon disulfide reacts spontaneously with 1-butyl-1-methylpyrrolidinium acetate ([BmPyrro][Ac]) in the liquid phase. It is found that the acetate anions play an important role in conditioning chemical reactions with CS2 leading, via coupled complex reactions, to the degradation of this molecule to form thioacetate anion (CH3COS(-)), CO2, OCS, and trithiocarbonate (CS3 (2-)). In marked contrast, the cation does not lead to the formation of any adducts allowing to conclude that, at most, its role consists in assisting indirectly these reactions. The choice of the [BmPyrro](+) cation in the present study allows disentangling the role of the anion and the cation in the reactions. As a consequence, the ensemble of results already reported on CS2-[Bmim][Ac] (1), OCS-[Bmim][Ac] (2), and CO2-[Bmim][Ac] (3) systems can be consistently rationalized. It is argued that in system (1) both anion and cation play a role. The CS2 reacts with the acetate anion leading to the formation of CH3COS(-), CO2, and OCS. After these reactions have proceeded the nascent CO2 and OCS interact with the cation to form imidazolium-carboxylate ([Bmim] CO2) and imidazolium-thiocarboxylate ([Bmim] COS). The same scenario also applies to system (2). In contrast, in the CO2-[Bmim] [Ac] system a concerted cooperative process between the cation, the anion, and the CO2 molecule takes place. A carbene issued from the cation reacts to form the [Bmim] CO2, whereas the proton released by the ring interacts with the anion to produce acetic acid. In all these systems, the formation of adduct resulting from the reaction between the solute molecule and the carbene species originating from the cation is expected. However, this species was only observed in systems (2) and (3). The absence of such an adduct in system (1) has been theoretically investigated using DFT calculations. The values of the energetic barrier of the reactions show that the formation of [Bmim] CS2 is unfavoured and that the anion offers a competitive reactive channel via an oxygen-sulphur exchange mechanism with the solute in systems (1) and (2).

Cation and anion dependence of stable geometries and stabilization energies of alkali metal cation complexes with FSA(-), FTA(-), and TFSA(-) anions: relationship with physicochemical properties of molten salts.

PubMed

Tsuzuki, Seiji; Kubota, Keigo; Matsumoto, Hajime

2013-12-19

Stable geometries and stabilization energies (Eform) of the alkali metal complexes with bis(fluorosulfonyl)amide, (fluorosulfonyl)(trifluoromethylslufonyl)amide and bis(trifluoromethylsulfonyl)amide (FSA(-), FTA(-) and TFSA(-)) were studied by ab initio molecular orbital calculations. The FSA(-) complexes prefer the bidentate structures in which two oxygen atoms of two SO2 groups have contact with the metal cation. The FTA(-) and TFSA(-) complexes with Li(+) and Na(+) prefer the bidentate structures, while the FTA(-) and TFSA(-) complexes with Cs(+) prefer tridentate structures in which the metal cation has contact with two oxygen atoms of an SO2 group and one oxygen atom of another SO2 group. The two structures are nearly isoenergetic in the FTA(-) and TFSA(-) complexes with K(+) and Rb(+). The magnitude of Eform depends on the alkali metal cation significantly. The Eform calculated for the most stable TFSA(-) complexes with Li(+), Na(+), K(+), Rb(+) and Cs(+) cations at the MP2/6-311G** level are -137.2, -110.5, -101.1, -89.6, and -84.1 kcal/mol, respectively. The viscosity and ionic conductivity of the alkali TFSA molten salts have strong correlation with the magnitude of the attraction. The viscosity increases and the ionic conductivity decreases with the increase of the attraction. The melting points of the alkali TFSA and alkali BETA molten salts also have correlation with the magnitude of the Eform, which strongly suggests that the magnitude of the attraction play important roles in determining the melting points of these molten salts. The anion dependence of the Eform calculated for the complexes is small (less than 2.9 kcal/mol). This shows that the magnitude of the attraction is not the cause of the low melting points of alkali FTA molten salts compared with those of corresponding alkali TFSA molten salts. The electrostatic interactions are the major source of the attraction in the complexes. The electrostatic energies for the most stable TFSA(-) complexes with the five alkali metal cations are -140.3, -119.4, -104.1, -96.9, and -91.1 kcal/mol, respectively. The induction interactions also contribute to the attraction. In particular, the induction interactions are large in the Li(+) complexes. The induction energies for the five complexes are -46.6, -25.2, -17.5, -13.3, and -10.4 kcal/mol, respectively.

Distinct regions that control ion selectivity and calcium-dependent activation in the bestrophin ion channel.

PubMed

Vaisey, George; Miller, Alexandria N; Long, Stephen B

2016-11-22

Cytoplasmic calcium (Ca 2+ ) activates the bestrophin anion channel, allowing chloride ions to flow down their electrochemical gradient. Mutations in bestrophin 1 (BEST1) cause macular degenerative disorders. Previously, we determined an X-ray structure of chicken BEST1 that revealed the architecture of the channel. Here, we present electrophysiological studies of purified wild-type and mutant BEST1 channels and an X-ray structure of a Ca 2+ -independent mutant. From these experiments, we identify regions of BEST1 responsible for Ca 2+ activation and ion selectivity. A "Ca 2+ clasp" within the channel's intracellular region acts as a sensor of cytoplasmic Ca 2+ . Alanine substitutions within a hydrophobic "neck" of the pore, which widen it, cause the channel to be constitutively active, irrespective of Ca 2+ . We conclude that the primary function of the neck is as a "gate" that controls chloride permeation in a Ca 2+ -dependent manner. In contrast to what others have proposed, we find that the neck is not a major contributor to the channel's ion selectivity. We find that mutation of a cytosolic "aperture" of the pore does not perturb the Ca 2+ dependence of the channel or its preference for anions over cations, but its mutation dramatically alters relative permeabilities among anions. The data suggest that the aperture functions as a size-selective filter that permits the passage of small entities such as partially dehydrated chloride ions while excluding larger molecules such as amino acids. Thus, unlike ion channels that have a single "selectivity filter," in bestrophin, distinct regions of the pore govern anion-vs.-cation selectivity and the relative permeabilities among anions.

Computational Model of the Insect Pheromone Transduction Cascade

PubMed Central

Gu, Yuqiao; Lucas, Philippe; Rospars, Jean-Pierre

2009-01-01

A biophysical model of receptor potential generation in the male moth olfactory receptor neuron is presented. It takes into account all pre-effector processes—the translocation of pheromone molecules from air to sensillum lymph, their deactivation and interaction with the receptors, and the G-protein and effector enzyme activation—and focuses on the main post-effector processes. These processes involve the production and degradation of second messengers (IP3 and DAG), the opening and closing of a series of ionic channels (IP3-gated Ca2+ channel, DAG-gated cationic channel, Ca2+-gated Cl− channel, and Ca2+- and voltage-gated K+ channel), and Ca2+ extrusion mechanisms. The whole network is regulated by modulators (protein kinase C and Ca2+-calmodulin) that exert feedback inhibition on the effector and channels. The evolution in time of these linked chemical species and currents and the resulting membrane potentials in response to single pulse stimulation of various intensities were simulated. The unknown parameter values were fitted by comparison to the amplitude and temporal characteristics (rising and falling times) of the experimentally measured receptor potential at various pheromone doses. The model obtained captures the main features of the dose–response curves: the wide dynamic range of six decades with the same amplitudes as the experimental data, the short rising time, and the long falling time. It also reproduces the second messenger kinetics. It suggests that the two main types of depolarizing ionic channels play different roles at low and high pheromone concentrations; the DAG-gated cationic channel plays the major role for depolarization at low concentrations, and the Ca2+-gated Cl− channel plays the major role for depolarization at middle and high concentrations. Several testable predictions are proposed, and future developments are discussed. PMID:19300479

Direct Binding between Pre-S1 and TRP-like Domains in TRPP Channels Mediates Gating and Functional Regulation by PIP2.

PubMed

Zheng, Wang; Cai, Ruiqi; Hofmann, Laura; Nesin, Vasyl; Hu, Qiaolin; Long, Wentong; Fatehi, Mohammad; Liu, Xiong; Hussein, Shaimaa; Kong, Tim; Li, Jingru; Light, Peter E; Tang, Jingfeng; Flockerzi, Veit; Tsiokas, Leonidas; Chen, Xing-Zhen

2018-02-06

Transient receptor potential (TRP) channels are regulated by diverse stimuli comprising thermal, chemical, and mechanical modalities. They are also commonly regulated by phosphatidylinositol-4,5-bisphosphate (PIP2), with underlying mechanisms largely unknown. We here revealed an intramolecular interaction of the TRPP3 N and C termini (N-C) that is functionally essential. The interaction was mediated by aromatic Trp81 in pre-S1 domain and cationic Lys568 in TRP-like domain. Structure-function analyses revealed similar N-C interaction in TRPP2 as well as TRPM8/-V1/-C4 via highly conserved tryptophan and lysine/arginine residues. PIP2 bound to cationic residues in TRPP3, including K568, thereby disrupting the N-C interaction and negatively regulating TRPP3. PIP2 had similar negative effects on TRPP2. Interestingly, we found that PIP2 facilitates the N-C interaction in TRPM8/-V1, resulting in channel potentiation. The intramolecular N-C interaction might represent a shared mechanism underlying the gating and PIP2 regulation of TRP channels. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

The DEG/ENaC cation channel protein UNC-8 drives activity-dependent synapse removal in remodeling GABAergic neurons

PubMed Central

Miller-Fleming, Tyne W; Petersen, Sarah C; Manning, Laura; Matthewman, Cristina; Gornet, Megan; Beers, Allison; Hori, Sayaka; Mitani, Shohei; Bianchi, Laura; Richmond, Janet; Miller, David M

2016-01-01

Genetic programming and neural activity drive synaptic remodeling in developing neural circuits, but the molecular components that link these pathways are poorly understood. Here we show that the C. elegans Degenerin/Epithelial Sodium Channel (DEG/ENaC) protein, UNC-8, is transcriptionally controlled to function as a trigger in an activity-dependent mechanism that removes synapses in remodeling GABAergic neurons. UNC-8 cation channel activity promotes disassembly of presynaptic domains in DD type GABA neurons, but not in VD class GABA neurons where unc-8 expression is blocked by the COUP/TF transcription factor, UNC-55. We propose that the depolarizing effect of UNC-8-dependent sodium import elevates intracellular calcium in a positive feedback loop involving the voltage-gated calcium channel UNC-2 and the calcium-activated phosphatase TAX-6/calcineurin to initiate a caspase-dependent mechanism that disassembles the presynaptic apparatus. Thus, UNC-8 serves as a link between genetic and activity-dependent pathways that function together to promote the elimination of GABA synapses in remodeling neurons. DOI: http://dx.doi.org/10.7554/eLife.14599.001 PMID:27403890

Enhanced splicing correction effect by an oligo-aspartic acid-PNA conjugate and cationic carrier complexes.

PubMed

Bae, Yun Mi; Kim, Myung Hee; Yu, Gwang Sig; Um, Bong Ho; Park, Hee Kyung; Lee, Hyun-il; Lee, Kang Taek; Suh, Yung Doug; Choi, Joon Sig

2014-02-10

Peptide nucleic acids (PNAs) are synthetic structural analogues of DNA and RNA. They recognize specific cellular nucleic acid sequences and form stable complexes with complementary DNA or RNA. Here, we designed an oligo-aspartic acid-PNA conjugate and showed its enhanced delivery into cells with high gene correction efficiency using conventional cationic carriers, such as polyethylenimine (PEI) and Lipofectamine 2000. The negatively charged oligo-aspartic acid-PNA (Asp(n)-PNA) formed complexes with PEI and Lipofectamine, and the resulting Asp(n)-PNA/PEI and Asp(n)-PNA/Lipofectamine complexes were introduced into cells. We observed significantly enhanced cellular uptake of Asp(n)-PNA by cationic carriers and detected an active splicing correction effect even at nanomolar concentrations. We found that the splicing correction efficiency of the complex depended on the kind of the cationic carriers and on the number of repeating aspartic acid units. By enhancing the cellular uptake efficiency of PNAs, these results may provide a novel platform technology of PNAs as bioactive substances for their biological and therapeutic applications. Copyright © 2013 Elsevier B.V. All rights reserved.

Interaction of the univalent silver cation with [Gly6]-antamanide: Experimental and theoretical study

NASA Astrophysics Data System (ADS)

Makrlík, Emanuel; Böhm, Stanislav; Kvíčala, Jaroslav; Vaňura, Petr; Ruzza, Paolo

2018-03-01

On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Ag+(aq) + 1.Na+(nb) ⇄ 1.Ag+ (nb) + Na+(aq) occurring in the two-phase water - nitrobenzene system (1 = [Gly6]-antamanide; aq = aqueous phase, nb = nitrobenzene phase) was determined as log Kex (Ag+,1·Na+) = 1.5 ± 0.1. Further, the stability constant of the 1·Ag+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb (1·Ag+) = 4.5 ± 0.2. Finally, by using quantum chemical DFT calculations, the most probable structure of the cationic complex species 1·Ag+ was derived. In the resulting complex, the "central" cation Ag+ is coordinated by four noncovalent interactions to the corresponding four carbonyl oxygen atoms of the parent ligand 1. Besides, the whole 1·Ag+ complex structure is stabilized by two intramolecular hydrogen bonds. The interaction energy of the considered 1·Ag+ complex was found to be -465.5 kJ/mol, confirming also the formation of this cationic species.

Effects of countercations on the structures and redox and spectroscopic properties of diruthenium catecholate complexes with ligand-unsupported Ru-Ru bonds.

PubMed

Chang, Ho-Chol; Mochizuki, Katsunori; Kitagawa, Susumu

2005-05-30

The molecular structures and physicochemical properties of diruthenium complexes with ligand-unsupported Ru-Ru bonds, generally formulated as [A2{Ru2(DTBCat)4}] (DTB = 3,5- or 3,6-di-tert-butyl; Cat(2-) = catecholate), were studied in detail by changing the countercations. First, the binding structures of the cations in a family of [{A(DME)n}2{Ru2(3,5-DTBCat)4}] (n = 2 for A+ = Li+ and Na+ and n = 1 for A+ = K+ and Rb+) were systematically examined to reveal the effects of the cations on the molecular structures and electrochemical properties. Second, the complex (n-Bu4N)2[Ru2(3,6-DTBCat)4] with a cation-free structure was synthesized using tetra-n-butylammonium cations. The complex clearly demonstrates first that the ligand-unsupported Ru-Ru bonds are essentially stabilized by the dianionic nature of the catecholate derivatives without any other bridging or supporting species. In contrast, the redox potentials and absorption spectra of the complexes can sensitively respond to the countercations depending upon the polarity of the solvents.

Infrared spectroscopic and theoretical study of the HC2n+1O+ (n = 2-5) cations

NASA Astrophysics Data System (ADS)

Jin, Jiaye; Li, Wei; Liu, Yuhong; Wang, Guanjun; Zhou, Mingfei

2017-06-01

The carbon chain cations, HC2n+1O+ (n = 2-5), are produced via pulsed laser vaporization of a graphite target in supersonic expansions containing carbon monoxide and hydrogen. The infrared spectra are measured via mass-selected infrared photodissociation spectroscopy of the CO "tagged" [HC2n+1O.CO]+ cation complexes in the 1600-3500 cm-1 region. The geometries and electronic ground states of these cation complexes are determined by their infrared spectra compared to the predications of theoretical calculations. All of the HC2n+1O+ (n = 2-5) core cations are characterized to be linear carbon chain derivatives terminated by hydrogen and oxygen, which have the closed-shell singlet ground states with polyyne-like carbon chain structures.

Trivalent Lewis Acidic Cations Govern the Electronic Properties and Stability of Heterobimetallic Complexes of Nickel.

PubMed

Kumar, Amit; Lionetti, Davide; Day, Victor W; Blakemore, James D

2018-01-02

Assembly of heterobimetallic complexes is synthetically challenging due to the propensity of ditopic ligands to bind metals unselectively. Here, we employ a novel divergent approach for selective preparation of a variety of bimetallic complexes within a ditopic macrocyclic ligand platform. In our approach, nickel is readily coordinated to a Schiff base cavity, and then a range of redox-inactive cations (M=Na + , Ca 2+ , Nd 3+ , and Y 3+ ) are installed in a pendant crown-ether-like site. This modular strategy allows access to complexes with the highly Lewis acidic trivalent cations Nd 3+ and Y 3+ , a class of compounds that were previously inaccessible. Spectroscopic and electrochemical studies reveal wide variations in properties that are governed most strongly by the trivalent cations. Exposure to dimethylformamide drives loss of Nd 3+ and Y 3+ from the pendant crown-ether site, suggesting solvent effects must be carefully considered in future applications involving use of highly Lewis acidic metals. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Catalytic Hydroamination of Alkynes and Norbornene with Neutral and Cationic Tantalum Imido Complexes

PubMed Central

Anderson, Laura L.; Arnold, John; Bergman, Robert G.

2005-01-01

Several tantalum imido complexes have been synthesized and shown to efficiently catalyze the hydroamination of internal and terminal alkynes. An unusual hydroamination/hydroarylation reaction of norbornene catalyzed by a highly electrophilic cationic tantalum imido complex is also reported. Factors affecting catalyst activity and selectivity are discussed along with mechanistic insights gained from stoichiometric reactions. PMID:15255680

A modern ionotropic glutamate receptor with a K(+) selectivity signature sequence.

PubMed

Janovjak, H; Sandoz, G; Isacoff, E Y

2011-01-01

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system and gates non-selective cation channels. The origins of glutamate receptors are not well understood as they differ structurally and functionally from simple bacterial ligand-gated ion channels. Here we report the discovery of an ionotropic glutamate receptor that combines the typical eukaryotic domain architecture with the 'TXVGYG' signature sequence of the selectivity filter found in K(+) channels. This receptor exhibits functional properties intermediate between bacterial and eukaryotic glutamate-gated ion channels, suggesting a link in the evolution of ionotropic glutamate receptors.

Complexation of the calcium cation with antamanide: an experimental and theoretical study

NASA Astrophysics Data System (ADS)

Makrlík, Emanuel; Böhm, Stanislav; Vaňura, Petr; Ruzza, Paolo

2015-06-01

By using extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Ca2+(aq) + 1 .Sr2+(nb) ? 1 .Ca2+(nb) + Sr2+(aq) occurring in the two-phase water-nitrobenzene system (1 = antamanide; aq = aqueous phase, nb = nitrobenzene phase) was determined as log Kex (Ca2+, 1 .Sr2+) = 1.6 ± 0.1. Further, the stability constant of the 1 .Ca2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb (1 .Ca2+) = 10.9 ± 0.2. Finally, applying quantum mechanical density functional level of theory calculations, the most probable structure of the cationic complex species 1 .Ca2+ was derived. In the resulting complex, the 'central' cation Ca2+ is bound by six strong bonding interactions to the corresponding six carbonyl oxygen atoms of the parent ligand 1. Besides, the whole 1 .Ca2+ complex structure is stabilised by two intramolecular hydrogen bonds. The interaction energy of the considered 1 .Ca2+ complex, involving the Boys-Bernardi counterpoise corrections of the basis set superposition error, was found to be -1219.3 kJ/mol, confirming the formation of this cationic species.

Evolutionary insights into T-type Ca2+ channel structure, function, and ion selectivity from the Trichoplax adhaerens homologue

PubMed Central

Smith, Carolyn L.; Abdallah, Salsabil; Le, Phuong; Harracksingh, Alicia N.; Artinian, Liana; Tamvacakis, Arianna N.; Rehder, Vincent; Reese, Thomas S.

2017-01-01

Four-domain voltage-gated Ca2+ (Cav) channels play fundamental roles in the nervous system, but little is known about when or how their unique properties and cellular roles evolved. Of the three types of metazoan Cav channels, Cav1 (L-type), Cav2 (P/Q-, N- and R-type) and Cav3 (T-type), Cav3 channels are optimized for regulating cellular excitability because of their fast kinetics and low activation voltages. These same properties permit Cav3 channels to drive low-threshold exocytosis in select neurons and neurosecretory cells. Here, we characterize the single T-type calcium channel from Trichoplax adhaerens (TCav3), an early diverging animal that lacks muscle, neurons, and synapses. Co-immunolocalization using antibodies against TCav3 and neurosecretory cell marker complexin labeled gland cells, which are hypothesized to play roles in paracrine signaling. Cloning and in vitro expression of TCav3 reveals that, despite roughly 600 million years of divergence from other T-type channels, it bears the defining structural and biophysical features of the Cav3 family. We also characterize the channel’s cation permeation properties and find that its pore is less selective for Ca2+ over Na+ compared with the human homologue Cav3.1, yet it exhibits a similar potent block of inward Na+ current by low external Ca2+ concentrations (i.e., the Ca2+ block effect). A comparison of the permeability features of TCav3 with other cloned channels suggests that Ca2+ block is a locus of evolutionary change in T-type channel cation permeation properties and that mammalian channels distinguish themselves from invertebrate ones by bearing both stronger Ca2+ block and higher Ca2+ selectivity. TCav3 is the most divergent metazoan T-type calcium channel and thus provides an evolutionary perspective on Cav3 channel structure–function properties, ion selectivity, and cellular physiology. PMID:28330839

Extraction and characterization of ternary complexes between natural organic matter, cations, and oxyanions from a natural soil.

PubMed

Peel, Hannah R; Martin, David P; Bednar, Anthony J

2017-06-01

Natural organic matter (NOM) can have a significant influence on the mobility and fate of inorganic oxyanions, such as arsenic and selenium, in the environment. There is evidence to suggest that interactions between NOM and these oxyanions are facilitated by bridging cations (primarily Fe 3+ ) through the formation of ternary complexes. Building on previous work characterizing ternary complexes formed in the laboratory using purified NOM, this study describes the extraction and characterization of intact ternary complexes directly from a soil matrix. The complexes are stable to the basic extraction conditions (pH 12) and do not appear to change when the pH of the extract is adjusted back to neutral. The results suggest that ternary complexes between NOM, cations, and inorganic oxyanions exist in natural soils and could play a role in the speciation of inorganic oxyanions in environmental matrices. Published by Elsevier Ltd.

Interaction between water-soluble rhodium complex RhCl(CO)(TPPTS)₂ and surfactants probed by spectroscopic methods.

PubMed

Zhou, Li-Mei; Guo, Cai-Hong; Fu, Hai-Yan; Jiang, Xiao-Hui; Chen, Hua; Li, Rui-Xiang; Li, Xian-Jun

2012-07-01

The interactions of rhodium complex RhCl(CO)(TPPTS)(2) [TPPTS=P(m-C(6)H(4)SO(3)Na)(3)] with cationic, nonionic, and anionic surfactants have been investigated by UV-vis, fluorescence and (1)H NMR measurements. The presence of four different species of RhCl(CO)(TPPTS)(2) in cationic cetyltrimethylammonium (CTAB) solution has been demonstrated: free rhodium complex, rhodium complex bound to CTAB monomer, rhodium complex bound to CTAB premicelles, rhodium complex bound to CTAB micelles. The spectroscopy data show that RhCl(CO)(TPPTS)(2) can adsorb on the interface of cationic CTAB micelles by strong electrostatic attraction, weakly bind to the nonionic polyoxyethylene (20) sorbitan monolaurate (Tween 20) micelles by hydrophobic interaction, and does not interact with anion sodium dodecyl sulfate (SDS) micelles due to the strong electrostatic repulsion. Copyright © 2012 Elsevier B.V. All rights reserved.

Neutral and cationic phosphoramide adducts of silicon tetrachloride: synthesis and characterization of their solution and solid-state structures.

PubMed

Denmark, Scott E; Eklov, Brian M

2008-01-01

The solution and solid-state structures of hexamethylphosphoramide (HMPA) adducts of tetrachlorosilane (SiCl4) are discussed. In solution, the meridional and facial isomers of the hexa-coordinate cationic complex 3 HMPASiCl3 + Cl(-) (2) predominate at all HMPA concentrations, and are in equilibrium with the hexa-coordinate neutral trans- and cis-2 HMPASiCl4 complexes (1), as well as the penta-coordinate cationic cis-2 HMPASiCl3 + Cl(-) (3). Single crystal X-ray analyses are reported for the ionized mer-3 HMPASiCl3 + HCl2 (-) and the neutral trans-2 HMPASiCl4 complexes.

Identifying the elusive link between amino acid sequence and charge selectivity in pentameric ligand-gated ion channels.

PubMed

Cymes, Gisela D; Grosman, Claudio

2016-10-10

Among neurotransmitter-gated ion channels, the superfamily of pentameric ligand-gated ion channels (pLGICs) is unique in that its members display opposite permeant-ion charge selectivities despite sharing the same structural fold. Although much effort has been devoted to the identification of the mechanism underlying the cation-versus-anion selectivity of these channels, a careful analysis of past work reveals that discrepancies exist, that different explanations for the same phenomenon have often been put forth, and that no consensus view has yet been reached. To elucidate the molecular basis of charge selectivity for the superfamily as a whole, we performed extensive mutagenesis and electrophysiological recordings on six different cation-selective and anion-selective homologs from vertebrate, invertebrate, and bacterial origin. We present compelling evidence for the critical involvement of ionized side chains-whether pore-facing or buried-rather than backbone atoms and propose a mechanism whereby not only their charge sign but also their conformation determines charge selectivity. Insertions, deletions, and residue-to-residue mutations involving nonionizable residues in the intracellular end of the pore seem to affect charge selectivity by changing the rotamer preferences of the ionized side chains in the first turn of the M2 α-helices. We also found that, upon neutralization of the charged residues in the first turn of M2, the control of charge selectivity is handed over to the many other ionized side chains that decorate the pore. This explains the long-standing puzzle as to why the neutralization of the intracellular-mouth glutamates affects charge selectivity to markedly different extents in different cation-selective pLGICs.

Dense transient receptor potential cation channel, vanilloid family, type 2 (TRPV2) immunoreactivity defines a subset of motoneurons in the dorsal lateral nucleus of the spinal cord, the nucleus ambiguus and the trigeminal motor nucleus in rat.

PubMed

Lewinter, R D; Scherrer, G; Basbaum, A I

2008-01-02

The transient receptor potential cation channel, vanilloid family, type 2 (TRPV2) is a member of the TRPV family of proteins and is a homologue of the capsaicin/vanilloid receptor (transient receptor potential cation channel, vanilloid family, type 1, TRPV1). Like TRPV1, TRPV2 is expressed in a subset of dorsal root ganglia (DRG) neurons that project to superficial laminae of the spinal cord dorsal horn. Because noxious heat (>52 degrees C) activates TRPV2 in transfected cells this channel has been implicated in the processing of high intensity thermal pain messages in vivo. In contrast to TRPV1, however, which is restricted to small diameter DRG neurons, there is significant TRPV2 immunoreactivity in a variety of CNS regions. The present report focuses on a subset of neurons in the brainstem and spinal cord of the rat including the dorsal lateral nucleus (DLN) of the spinal cord, the nucleus ambiguus, and the motor trigeminal nucleus. Double label immunocytochemistry with markers of motoneurons, combined with retrograde labeling, established that these cells are, in fact, motoneurons. With the exception of their smaller diameter, these cells did not differ from other motoneurons, which are only lightly TRPV2-immunoreactive. As for the majority of DLN neurons, the densely-labeled populations co-express androgen receptor and follow normal DLN ontogeny. The functional significance of the very intense TRPV2 expression in these three distinct spinal cord and brainstem motoneurons groups remains to be determined.

Formation of a physiological complex between TRPV2 and RGA protein promotes cell surface expression of TRPV2.

PubMed

Stokes, Alexander J; Wakano, Clay; Del Carmen, Kimberly A; Koblan-Huberson, Murielle; Turner, Helen

2005-03-01

The transient receptor potential, sub-family Vanilloid (TRPV)(2) cation channel is activated in response to extreme temperature elevations in sensory neurons. However, TRPV2 is widely expressed in tissues with no sensory function, including cells of the immune system. Regulation of GRC, the murine homolog of TRPV2 has been studied in insulinoma cells and myocytes. GRC is activated in response to certain growth factors and neuropeptides, via a mechanism that involves regulated access of the channel to the plasma membrane. This is likely to be an important primary control mechanism for TRPV2 outside the CNS. Here, we report that a regulated trafficking step controls the access of TRPV2 to the cell surface in mast cells. In mast cells, elevations in cytosolic cAMP are sufficient to drive plasma membrane localization of TRPV2. We have previously proposed that the recombinase gene activator protein (RGA), a four-transmembrane domain, intracellular protein, associates with TRPV2 during the biosynthesis and early trafficking of the channel. We use a polyclonal antibody to RGA to confirm the formation of a physiological complex between RGA and TRPV2. Finally, we show that over-expression of the RGA protein potentiates the basal surface localization of TRPV2. We propose that trafficking and activation mechanisms intersect for TRPV2, and that cAMP mobilizing stimuli may regulate TRPV2 localization in non-sensory cells. RGA participates in the control of TRPV2 surface levels, and co-expression of RGA may be a key component of experimental systems that seek to study TRPV2 physiology.

Cationic Phosphorus Dendrimer Enhances Photodynamic Activity of Rose Bengal against Basal Cell Carcinoma Cell Lines.

PubMed

Dabrzalska, Monika; Janaszewska, Anna; Zablocka, Maria; Mignani, Serge; Majoral, Jean Pierre; Klajnert-Maculewicz, Barbara

2017-05-01

In the last couple of decades, photodynamic therapy emerged as a useful tool in the treatment of basal cell carcinoma. However, it still meets limitations due to unfavorable properties of photosensitizers such as poor solubility or lack of selectivity. Dendrimers, polymers widely studied in biomedical field, may play a role as photosensitizer carriers and improve the efficacy of photodynamic treatment. Here, we describe the evaluation of an electrostatic complex of cationic phosphorus dendrimer and rose bengal in such aspects as singlet oxygen production, cellular uptake, and phototoxicity against three basal cell carcinoma cell lines. Rose bengal-cationic dendrimer complex in molar ratio 5:1 was compared to free rose bengal. Obtained results showed that the singlet oxygen production in aqueous medium was significantly higher for the complex than for free rose bengal. The cellular uptake of the complex was 2-7-fold higher compared to a free photosensitizer. Importantly, rose bengal, rose bengal-dendrimer complex, and dendrimer itself showed no dark toxicity against all three cell lines. Moreover, we observed that phototoxicity of the complex was remarkably enhanced presumably due to high cellular uptake. On the basis of the obtained results, we conclude that rose bengal-cationic dendrimer complex has a potential in photodynamic treatment of basal cell carcinoma.

Phosphorus-31 and carbon-13 nuclear magnetic resonance studies of divalent cation binding to phosphatidylserine membranes. Use of cobalt as a paramagnetic probe

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

McLaughlin, A.C.

1982-01-01

The paramagnetic divalent cation cobalt has large and well-understood effects on NMR signals from ligands bound in the first coordination sphere, i.e., inner-sphere ligands, and the authors have used these effects to identify divalent cation binding sites at the surface of phosphatidylserine membranes. /sup 31/P NMR results show that 13% of the bound cobalt ions are involved in inner-sphere complexes with the phosphodiester group, while /sup 13/C NMR results show that 54% of the bound cobalt ions are involved in unidentate inner sphere complexes with the carboxyl group. No evidence is found for cobalt binding to the carbonyl groups, butmore » proton release studies suggest that 32% of the bound cobalt ions are involved in chelate complexes that contain both the carboxyl and the amine groups. All of the bound cobalt ions can thus be accounted for in terms of inner sphere complexes with the phosphodiester group or the carboxyl group. They suggest that the unidentate inner-sphere complex between cobalt and the carboxyl group of phosphatidylserine and the inner-sphere complex between cobalt and the phosphodiester group of phosphatidylserine provide reasonable models for complexes between alkaline earth cations and phosphatidylserine membranes.« less

Phosphorus-31 and carbon-13 nuclear magnetic resonance studies of divalent cation binding to phosphatidylserine membranes: use of cobalt as a paramagnetic probe

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

McLaughlin, A.C.

1982-09-28

The paramagnetic divalent cation cobalt has large and well-understood effects on NMR signals from ligands bound in the first coordination sphere, i.e., inner-sphere ligands, and we have used these effects to identify divalent cation binding sites at the surface of phosphatidylserine membranes. /sup 31/P NMR results show that 13% of the bound cobalt ions are involved in inner-sphere complexes with the phosphodiester group, while /sup 13/C NMR results show that 54% of the bound cobalt ions are involved in unidentate inner sphere complexes with the carboxyl group. No evidence is found for cobalt binding to the carbonyl groups, but protonmore » release studies suggest that 32% of the bound cobalt ions are involved in chelate complexes that contain both the carboxyl and the amine groups. All (i.e., 13% + 54% + 32% = 99%) of the bound cobalt ions can thus be accounted for in terms of inner sphere complexes with the phosphodiester group or the carboxyl group. We suggest that the unidentate inner-sphere complex between cobalt and the carboxyl group of phosphatidylserine and the inner-sphere complex between cobalt and the phosphodiester group of phosphatidylserine provide reasonable models for complexes between alkaline earth cations and phosphatidylserine membranes.« less

Preparation and in vivo evaluation of cationic elastic liposomes comprising highly skin-permeable growth factors combined with hyaluronic acid for enhanced diabetic wound-healing therapy.

PubMed

Choi, Jeong Uk; Lee, Seong Wook; Pangeni, Rudra; Byun, Youngro; Yoon, In-Soo; Park, Jin Woo

2017-07-15

To enhance the therapeutic effects of exogenous administration of growth factors (GFs) in the treatment of chronic wounds, we constructed GF combinations of highly skin-permeable epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), and platelet-derived growth factor-A (PDGF-A). We genetically conjugated a low-molecular-weight protamine (LMWP) to the N-termini of these GFs to form LMWP-EGF, LMWP-IGF-I, and LMWP-PDGF-A. Subsequently, these molecules were complexed with hyaluronic acid (HA). Combinations of native or LMWP-fused GFs significantly promoted fibroblast proliferation and the synthesis of procollagen, with a magnification of these results observed after the GFs were complexed with HA. The optimal proportions of LMWP-EGF, LMWP-IGF-I, LMWP-PDGF-A, and HA were 1, 1, 0.02, and 200, respectively. After confirming the presence of a synergistic effect, we incorporated the LMWP-fused GFs-HA complex into cationic elastic liposomes (ELs) of 107±0.757nm in diameter and a zeta potential of 56.5±1.13mV. The LMWP-fused GFs had significantly improved skin permeation compared with native GFs. The in vitro wound recovery rate of the LMWP-fused GFs-HA complex was 23% higher than that of cationic ELs composed of LMWP-fused GFs alone. Moreover, the cationic ELs containing the LMWP-fused GFs-HA complex significantly accelerated the wound closure rate in a diabetic mouse model and the wound size was maximally decreased by 65% and 58% compared to cationic ELs loaded with vehicle or native GFs-HA complex, respectively. Thus, topical treatment with cationic ELs loaded with the LMWP-fused GFs-HA complex synergistically enhanced the healing of chronic wounds, exerting both rapid and prolonged effects. We believe that our study makes a significant contribution to the literature, because it demonstrated the potential application of cationic elastic liposomes as topical delivery systems for growth factors (GFs) that have certain limitations in their therapeutic effects (e.g., low percutaneous absorption of GFs at the lesion site and the requirement for various GFs at different healing stages). Topical treatment with cationic elastic liposomes loaded with highly skin-permeable low-molecular-weight protamine (LMWP)-fused GFs-hyaluronic acid (HA) complex synergistically enhanced the healing of diabetic wounds, exerting both rapid and prolonged effects. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A porphyrin complex of Gold(I): (Phosphine)gold(I) azides as cation precursors

PubMed Central

Partyka, David V.; Robilotto, Thomas J.; Zeller, Matthias; Hunter, Allen D.; Gray, Thomas G.

2008-01-01

A silver- and Brönsted acid-free protocol for generating the (tricyclohexylphosphine)gold(I) cation from the corresponding azide complexes is disclosed. The gold(I) cations so liberated are trapped by complexation with octaethylporphyrin. The first structurally authenticated gold(I) porphyrin complex crystallizes with formula C72H112Au2F12N4P2Sb2, space group C2/c, a = 21.388 (4), b = 19.679 (4), c = 19.231 (3) Å; β = 111.030 (3)°. Solution spectroscopic studies indicate that the di-gold complex fragments on dissolution in organic solvents. Approximate density-functional theory calculations find an electrostatic origin for the binding of two gold(I) centers to the unprotonated nitrogen atoms, despite greater orbital density on the porphyrin meso carbons. PMID:18780788

Structural modulation of silver complexes and their distinctive catalytic properties.

PubMed

Zhao, Yue; Chen, Kai; Fan, Jian; Okamura, Taka-aki; Lu, Yi; Luo, Li; Sun, Wei-Yin

2014-02-07

A family of silver(I) complexes, [Ag2(L)2(OOCCF3)2] (1), [Ag(L)0.5(OOCCF3)] (2), [Ag(L)2](OOCCF3)(H2O)2 (3), was obtained by reactions of 4,4'-di(2-oxazolinyl)biphenyl (L) and AgOOCCF3 in different reaction media. Compound 1 has a 1D chain structure with alternative connections between the Ag(I) and L ligand. When the crystal nucleation inductor, pyrazine, was added into the reaction system, complex 2 was isolated with no pyrazine observed in its structure. In 2, the 1D inorganic chains formed by Ag(I) cations and OOCCF3(-) anions were connected by the L ligand to produce a 2D network. When a different inductor, imidazole, was added into the reaction system, 3 with (4,4) topology was synthesized, and again no imidazole was found in 3. When 1-3 were used as catalysts for cycloaddition reactions between imino esters and methyl acrylate, 3 affords the highest yield, in which the particular size of the channels in 3 led to its selective catalytic performance.

TRPs as chemosensors (ROS, RNS, RCS, gasotransmitters).

PubMed

Shimizu, Shunichi; Takahashi, Nobuaki; Mori, Yasuo

2014-01-01

The transient receptor potential (trp) gene superfamily encodes TRP proteins that act as multimodal sensor cation channels for a wide variety of stimuli from outside and inside the cell. Upon chemical or physical stimulation of cells, TRP channels transduce electrical and/or Ca(2+) signals via their cation channel activities. These functional features of TRP channels allow the body to react and adapt to different forms of environmental changes. Indeed, members of one class of TRP channels have emerged as sensors of reactive oxygen species (ROS), reactive nitrogen species (RNS), reactive carbonyl species (RCS), and gaseous messenger molecules including molecular oxygen (O2), hydrogen sulfide (H2S), and carbon dioxide (CO2). Hydrogen peroxide (H2O2), an ROS, triggers the production of ADP-ribose, which binds and activates TRPM2. In addition to TRPM2, TRPC5, TRPV1, and TRPA1 are also activated by H2O2 via modification of cysteine (Cys) free sulfhydryl groups. Nitric oxide (NO), a vasoactive gaseous molecule, regulates TRP channels directly via Cys S-nitrosylation or indirectly via cyclic GMP (cGMP)/protein kinase G (PKG)-dependent phosphorylation. Anoxia induced by O2-glucose deprivation and severe hypoxia activates TRPM7 and TRPC6, respectively, whereas TRPA1 serves as a sensor of mild hypoxia and hyperoxia in vagal and sensory neurons. TRPA1 also detects other gaseous molecules, such as hydrogen sulfide (H2S) and carbon dioxide (CO2). In this review, we highlight our current knowledge of TRP channels as chemosensors for ROS, RNS, RCS, and gaseous molecules and discuss their functional impacts on physiological and pathological events.

Differential Effects of TRPA and TRPV Channels on Behaviors of Caenorhabditis elegans

PubMed Central

Thies, Jennifer; Neutzler, Vanessa; O’Leary, Fidelma; Liu, He

2016-01-01

TRPA and TRPV ion channels are members of the transient receptor potential (TRP) cation channel superfamily, which mediates various sensory transductions. In Caenorhabditis elegans, the TRPV channels are known to affect chemosensation, while the TRPA-1 channel is associated with thermosensation and mechanosensation. We examined thermosensation, chemosensation, and osmosensation in strains lacking TRPA-1 or TRPV channels. We found that TRPV channel knockout worms exhibited similar behavioral deficits associated with thermotaxis as the TRPA-1 channel knockout, suggesting a dual role for TRPV channels. In contrast, chemosensation responses, assessed by both avoidance reversal behavior and NaCl osmosensation, were dependent on TRPV channels but seemed independent of TRPA-1 channel. Our findings suggest that, in addition to TRPA-1 channel, TRPV channels are necessary for thermotaxis and may activate, or modulate, the function of TRPA-1 channels. In contrast, TRPA-1 channels do not have a dual responsibility, as they have no functional role in odorant avoidance or osmosensation. PMID:27168724

Vanilloid receptor-related osmotically activated channel (VR-OAC), a candidate vertebrate osmoreceptor

PubMed Central

Liedtke, Wolfgang; Choe, Yong; Martí-Renom, Marc A.; Bell, Andrea M.; Denis, Charlotte S.; Šali, Andrej; Hudspeth, A. J.; Friedman, Jeffrey M.; Heller, Stefan

2008-01-01

SUMMARY The detection of osmotic stimuli is essential for all organisms, yet few osmoreceptive proteins are known, none of them in vertebrates. By employing a candidate-gene approach based on genes encoding members of the TRP superfamily of ion channels, we cloned cDNAs encoding the vanilloid receptor-related osmotically activated channel (VR-OAC) from the rat, mouse, human, and chicken. This novel cation-selective channel is gated by exposure to hypotonicity within the physiological range. In the central nevous system, the channel is expressed neurons of the circumventricular organs, neurosensory cells responsive to systemic osmotic pressure. The channel also occurs in other neurosensory cells, including inner-ear hair cells, sensory neurons, and Merkel cells. PMID:11081638

Radiopharmaceuticals for imaging the heart

DOEpatents

Green, Mark A.; Tsang, Brenda W.

1994-01-01

Radiopharmaceuticals for imaging myocardial tissues are prepared by forming lipophilic, cationic complexes of radioactive metal ions with metal chelating ligands comprising the Schiff base adducts of triamines and tetraamines with optionally substituted salicylaldehydes. The lipophilic, cationic, radioactive complexes of the invention exhibit high uptake and retention in myocardial tissues. Preferred gallium-68(III) complexes in accordance with this invention can be used to image the heart using positron emission tomography.

Single Nisoldipine-Sensitive Calcium Channels in Smooth Muscle Cells Isolated from Rabbit Mesenteric Artery

NASA Astrophysics Data System (ADS)

Worley, Jennings F.; Deitmer, Joachim W.; Nelson, Mark T.

1986-08-01

Single smooth muscle cells were enzymatically isolated from the rabbit mesenteric artery. At physiological levels of external Ca, these cells were relaxed and contracted on exposure to norepinephrine, caffeine, or high levels of potassium. The patch-clamp technique was used to measure unitary currents through single channels in the isolated cells. Single channels were selective for divalent cations and exhibited two conductance levels, 8 pS and 15 pS. Both types of channels were voltage-dependent, and channel activity occurred at potentials positive to -40 mV. The activity of both channel types was almost completely inhibited by 50 nM nisoldipine. These channels appear to be the pathways for voltage-dependent Ca influx in vascular smooth muscle and may be the targets of the clinically used dihydropyridines.

The cyclic nucleotide gated cation channel AtCNGC10 traffics from the ER via Golgi vesicles to the plasma membrane of Arabidopsis root and leaf cells.

PubMed

Christopher, David A; Borsics, Tamas; Yuen, Christen Y L; Ullmer, Wendy; Andème-Ondzighi, Christine; Andres, Marilou A; Kang, Byung-Ho; Staehelin, L Andrew

2007-09-19

The cyclic nucleotide-gated ion channels (CNGCs) maintain cation homeostasis essential for a wide range of physiological processes in plant cells. However, the precise subcellular locations and trafficking of these membrane proteins are poorly understood. This is further complicated by a general deficiency of information about targeting pathways of membrane proteins in plants. To investigate CNGC trafficking and localization, we have measured Atcngc5 and Atcngc10 expression in roots and leaves, analyzed AtCNGC10-GFP fusions transiently expressed in protoplasts, and conducted immunofluorescence labeling of protoplasts and immunoelectron microscopic analysis of high pressure frozen leaves and roots. AtCNGC10 mRNA and protein levels were 2.5-fold higher in roots than leaves, while AtCNGC5 mRNA and protein levels were nearly equal in these tissues. The AtCNGC10-EGFP fusion was targeted to the plasma membrane in leaf protoplasts, and lightly labeled several intracellular structures. Immunofluorescence microscopy with affinity purified CNGC-specific antisera indicated that AtCNGC5 and AtCNGC10 are present in the plasma membrane of protoplasts. Immunoelectron microscopy demonstrated that AtCNGC10 was associated with the plasma membrane of mesophyll, palisade parenchyma and epidermal cells of leaves, and the meristem, columella and cap cells of roots. AtCNCG10 was also observed in the endoplasmic reticulum and Golgi cisternae and vesicles of 50-150 nm in size. Patch clamp assays of an AtCNGC10-GFP fusion expressed in HEK293 cells measured significant cation currents. AtCNGC5 and AtCNGC10 are plasma membrane proteins. We postulate that AtCNGC10 traffics from the endoplasmic reticulum via the Golgi apparatus and associated vesicles to the plasma membrane. The presence of the cation channel, AtCNGC10, in root cap meristem cells, cell plate, and gravity-sensing columella cells, combined with the previously reported antisense phenotypes of decreased gravitropic and cell enlargement responses, suggest roles of AtCNGC10 in modulating cation balance required for root gravitropism, cell division and growth.

Correction: A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide.

PubMed

Ng, Chee Koon; Wu, Jie; Hor, T S Andy; Luo, He-Kuan

2016-12-22

Correction for 'A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide' by Chee Koon Ng et al., Chem. Commun., 2016, 52, 11842-11845.

Cationic gold(I) axially chiral biaryl bisphosphine complex-catalyzed atropselective synthesis of heterobiaryls

PubMed Central

Shibuya, Tetsuro; Nakamura, Kyosuke

2011-01-01

Summary It has been established that a cationic gold(I)/(R)-DTBM-Segphos or (R)-BINAP complex catalyzes the atropselective intramolecular hydroarylation of alkynes leading to enantioenriched axially chiral 4-aryl-2-quinolinones and 4-arylcoumarins with up to 61% ee. PMID:21915192

Organo-Lewis acid as cocatalyst for cationic homogeneous Ziegler-Natta olefin polymerizations

DOEpatents

Marks, Tobin J.; Chen, You-Xian

2001-01-01

Organo-Lewis acids of the formula BR'R".sub.2 wherein B is boron, R' is fluorinated biphenyl, and R" is a fluorinated phenyl, fluorinated biphenyl, or fluorinated polycyclic fused ring group, and cationic metallocene complexes formed therewith. Such complexes are useful as polymerization catalysts.

Organo-Lewis acid as cocatalyst for cationic homogeneous Ziegler-Natta olefin polymerizations

DOEpatents

Marks, Tobin J.; Chen, You-Xian

2002-01-01

Organo-Lewis acids of the formula BR'R".sub.2 wherein B is boron, R' is fluorinated biphenyl, and R" is a fluorinated phenyl, fluorinated biphenyl, or fluorinated polycyclic fused ring group, and cationic metallocene complexes formed therewith. Such complexes are useful as polymerization catalysts.

Channels Formed by Botulinum, Tetanus, and Diphtheria Toxins in Planar Lipid Bilayers: Relevance to Translocation of Proteins across Membranes

NASA Astrophysics Data System (ADS)

Hoch, David H.; Romero-Mira, Miryam; Ehrlich, Barbara E.; Finkelstein, Alan; Dasgupta, Bibhuti R.; Simpson, Lance L.

1985-03-01

The heavy chains of both botulinum neurotoxin type B and tetanus toxin form channels in planar bilayer membranes. These channels have pH-dependent and voltage-dependent properties that are remarkably similar to those previously described for diphtheria toxin. Selectivity experiments with anions and cations show that the channels formed by the heavy chains of all three toxins are large; thus, these channels could serve as ``tunnel proteins'' for translocation of active peptide fragments. These findings support the hypothesis that the active fragments of botulinum neurotoxin and tetanus toxin, like that of diphtheria toxin, are translocated across the membranes of acidic vesicles.

Novel Gardos channel mutations linked to dehydrated hereditary stomatocytosis (xerocytosis).

PubMed

Andolfo, Immacolata; Russo, Roberta; Manna, Francesco; Shmukler, Boris E; Gambale, Antonella; Vitiello, Giuseppina; De Rosa, Gianluca; Brugnara, Carlo; Alper, Seth L; Snyder, L Michael; Iolascon, Achille

2015-10-01

Dehydrated hereditary stomatocytosis (DHSt) is an autosomal dominant congenital hemolytic anemia with moderate splenomegaly and often compensated hemolysis. Affected red cells are characterized by a nonspecific cation leak of the red cell membrane, reflected in elevated sodium content, decreased potassium content, elevated MCHC and MCV, and decreased osmotic fragility. The majority of symptomatic DHSt cases reported to date have been associated with gain-of-function mutations in the mechanosensitive cation channel gene, PIEZO1. A recent study has identified two families with DHSt associated with a single mutation in the KCNN4 gene encoding the Gardos channel (KCa3.1), the erythroid Ca(2+) -sensitive K(+) channel of intermediate conductance, also expressed in many other cell types. We present here, in the second report of DHSt associated with KCNN4 mutations, two previously undiagnosed DHSt families. Family NA exhibited the same de novo missense mutation as that recently described, suggesting a hot spot codon for DHSt mutations. Family WO carried a novel, inherited missense mutation in the ion transport domain of the channel. The patients' mild hemolytic anemia did not improve post-splenectomy, but splenectomy led to no serious thromboembolic events. We further characterized the expression of KCNN4 in the mutated patients and during erythroid differentiation of CD34+ cells and K562 cells. We also analyzed KCNN4 expression during mouse embryonic development. © 2015 Wiley Periodicals, Inc.

Influence of ionic strength, anions, cations, and natural organic matter on the adsorption of pharmaceuticals to silica.

PubMed

Bui, Tung Xuan; Choi, Heechul

2010-08-01

The adsorption of four wide-use pharmaceuticals (carbamazepine, diclofenac, ibuprofen, and ketoprofen) onto a porous silica was investigated under varied ionic strengths, different anions, divalent cations (Ca(2+) and Mg(2+)), trivalent cations (Al(3+) and Fe(3+)), and natural organic matter (NOM). The experiments demonstrated that at a given pH the adsorption was most affected by ionic strength, trivalent cations, and properties of pharmaceuticals. The increase of ionic strength resulted in an increase in the adsorption of ketoprofen, but a decrease in the adsorption of carbamazepine. Trivalent metal cations made intense increases in the adsorption of three acidic pharmaceuticals, which could be due to the formation of inner-sphere complex of the cations on the surface and/or complexation of the pharmaceuticals with both surface and aqueous metal species. It was found that the adsorption of carbamazepine was not affected by divalent and trivalent cations, whereas the adsorption of diclofenac was solely impacted by the presence of Al(3+). Moreover, divalent cations at low concentration could slightly enhance the adsorption of ibuprofen and ketoprofen, whereas NOM caused a reduction in the adsorption of the tested pharmaceuticals except for diclofenac. These results suggest that ionic strength, divalent cations, trivalent cations, and NOM are notable factors affecting the adsorption of pharmaceuticals and thus the ultimate fate of pharmaceuticals in the aqueous environment. Copyright 2010 Elsevier Ltd. All rights reserved.

Localization of beta and gamma subunits of ENaC in sensory nerve endings in the rat foot pad.

PubMed

Drummond, H A; Abboud, F M; Welsh, M J

2000-11-24

The molecular mechanisms underlying mechanoelectrical transduction and the receptors that detect light touch remain uncertain. Studies in Caenorhabditis elegans suggest that members of the DEG/ENaC cation channel family may be mechanoreceptors. Therefore, we tested the hypothesis that subunits of the mammalian epithelial Na(+) channel (ENaC) family are expressed in touch receptors in rat hairless skin. We detected betaENaC and gammaENaC, but not alphaENaC transcripts in cervical and lumbar dorsal root ganglia (DRG). Using immunofluorescence, we found betaENaC and gammaENaC expressed in medium to large lumbar DRG neurons. Moreover, we detected these two subunits in Merkel cell-neurite complexes, Meissner-like corpuscles, and small lamellated corpuscles, specialized mechanosensory structures of the skin. Within these structures, betaENaC and gammaENaC were localized in the nerve fibers believed to contain the sensors responsive to mechanical stress. Thus beta and gammaENaC subunits are good candidates as components of the molecular sensor that detects touch.

Spacer length controlled lamello-columnar to oblique-columnar mesophase transition in liquid crystalline DNA - discotic cationic lipid complexes

NASA Astrophysics Data System (ADS)

Zhu, Lei; Cui, Li; Miao, Jianjun

2006-03-01

A series of asymmetric triphenylene imidazolium salts with different spacer lengths (C5, C8, and C11) were synthesized and their ionic complexes with double-strand DNA were prepared in aqueous solution. The molecular composition of the complexes was determined by FTIR analysis. The liquid crystalline morphology was characterized by polarized light microscopy, X-ray diffraction (XRD), and transmission electron microscope. 2D XRD results indicated an oblique columnar phase for the complex with a short spacer length of C5, while lamello-columnar phases for those with longer spacer lengths (C8 and C11). Thin film circular dichroism results showed the disappearing of any helical conformation in the DNA in all the complexes. Instead, the complexation between single-strand RNA and discotic cationic lipids did not show columnar morphology; therefore, the columnar liquid crystalline morphology in the DNA-discotic cationic lipid complexes was attributed to the DNA double-strand chain rigidity.

Cooperativity and complexity in the binding of anions and cations to a tetratopic ion-pair host.

PubMed

Howe, Ethan N W; Bhadbhade, Mohan; Thordarson, Pall

2014-05-21

Cooperative interactions play a very important role in both natural and synthetic supramolecular systems. We report here on the cooperative binding properties of a tetratopic ion-pair host 1. This host combines two isophthalamide anion recognition sites with two unusual "half-crown/two carbonyl" cation recognition sites as revealed by the combination of single-crystal X-ray analysis of the free host and the 1:2 host:calcium cation complex, together with two-dimensional NMR and computational studies. By systematically comparing all of the binding data to several possible binding models and focusing on four different variants of the 1:2 binding model, it was in most cases possible to quantify these complex cooperative interactions. The data showed strong negative cooperativity (α = 0.01-0.05) of 1 toward chloride and acetate anions, while for cations the results were more variable. Interestingly, in the competitive (CDCl3/CD3OD (9:1, v/v)) solvent, the addition of calcium cations to the tetratopic ion-pair host 1 allosterically switched "on" chloride binding that is otherwise not present in this solvent system. The insight into the complexity of cooperative interactions revealed in this study of the tetratopic ion-pair host 1 can be used to design better cooperative supramolecular systems for information transfer and catalysis.

Infrared Spectroscopic and Theoretical Study of the HC_nO^+(N=5-12) Cations

NASA Astrophysics Data System (ADS)

Li, Wei; Jin, Jiaye; Wang, Guanjun; Zhou, Mingfei

2017-06-01

Carbon chains and derivatives are highly active species, which are widely existed as reactive intermediates in many chemical processes including atmospheric chemistry, hydrocarbon combustion, as well as interstellar chemistry. The carbon chain cations, HC_nO^+ (n = 5-12) are produced via pulsed laser vaporization of a graphite target in supersonic expansions containing carbon monoxide and hydrogen. The infrared spectra are measured via mass-selected infrared photodissociation spectroscopy of the CO "tagged" [HC_nO.CO] cation complexes in the 1600-3500 \\wn region. The geometries and electronic ground states of these cation complexes are determined by their infrared spectra in conjunction with theoretical calculations. All the HC_nO^+ (n = 5-12) core cations are characterized to be linear carbon chain derivatives terminated by hydrogen and oxygen. The HC_nO^+ cations with odd n have closed-shell singlet ground states with polyyne-like structures, while those with even n have triplet ground states with allene-like structures.

Synthesis and characterization of two novel chiral-type formate frameworks templated by protonated diethylamine and ammonium cations

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

Mączka, Mirosław, E-mail: m.maczka@int.pan.wroc.pl; Gągor, Anna; Hanuza, Jerzy

2017-01-15

Two novel formate frameworks templated by ammonium and diethylammonium (DEtA{sup +}) cations have been synthesized. Chemical analysis as well as optical, Raman and IR studies showed partial substitution of nickel ions by Cr(III) or Fe(III). X-ray diffraction revealed that these compounds crystallize in the chiral-type structure of P6{sub 3}22 symmetry. The oxygen atoms from formate ligands form octahedral coordination around the metal centers and the octahedra are bridged by the formate groups in the anti-anti mode configuration forming the hexagonal structure with large channels expanding along the c direction. The channels are filled with disordered DEtA{sup +} and NH{sub 4}{supmore » +} ions and they show unusual compression with the c/a ratio of only 0.862 and 0.852 for the iron- and chromium-containing compound, respectively. Magnetic studies revealed that the both compounds order magnetically at low temperatures but the ordering temperature is significantly higher for the iron compound (37 K) compared to the chromium analogue (26 K). - Graphical abstract: Temperature dependence of magnetization M of DEtAFeNi showing magnetic order at 37 K. - Highlights: • Two novel chiral formates of P6{sub 3}22 symmetry were synthesized. • The structures contain strongly compressed hexagonal channels filled with disordered cations. • The obtained compounds exhibit magnetic order at low temperatures. • Raman, IR and absorption spectra prove incorporation of Cr(III) and Fe(III) in the frameworks.« less

Polymeric microchip for the simultaneous determination of anions and cations by hydrodynamic injection using a dual-channel sequential injection microchip electrophoresis system.

PubMed

Gaudry, Adam J; Nai, Yi Heng; Guijt, Rosanne M; Breadmore, Michael C

2014-04-01

A dual-channel sequential injection microchip capillary electrophoresis system with pressure-driven injection is demonstrated for simultaneous separations of anions and cations from a single sample. The poly(methyl methacrylate) (PMMA) microchips feature integral in-plane contactless conductivity detection electrodes. A novel, hydrodynamic "split-injection" method utilizes background electrolyte (BGE) sheathing to gate the sample flows, while control over the injection volume is achieved by balancing hydrodynamic resistances using external hydrodynamic resistors. Injection is realized by a unique flow-through interface, allowing for automated, continuous sampling for sequential injection analysis by microchip electrophoresis. The developed system was very robust, with individual microchips used for up to 2000 analyses with lifetimes limited by irreversible blockages of the microchannels. The unique dual-channel geometry was demonstrated by the simultaneous separation of three cations and three anions in individual microchannels in under 40 s with limits of detection (LODs) ranging from 1.5 to 24 μM. From a series of 100 sequential injections the %RSDs were determined for every fifth run, resulting in %RSDs for migration times that ranged from 0.3 to 0.7 (n = 20) and 2.3 to 4.5 for peak area (n = 20). This system offers low LODs and a high degree of reproducibility and robustness while the hydrodynamic injection eliminates electrokinetic bias during injection, making it attractive for a wide range of rapid, sensitive, and quantitative online analytical applications.

Post-Synthetic Modification of Porphyrin-Encapsulating Metal-Organic Materials by Cooperative Addition of Inorganic Salts to Enhance CO 2/CH 4 Selectivity

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

Zhang, Zhenjie; Gao, Wen-Yang; Wojtas, Lukasz

Keeping MOM: Reaction of biphenyl-3,4',5-tricarboxylate and Cd(NO 3) 2 in the presence of meso-tetra(N-methyl-4-pyridyl)porphine tetratosylate afforded porph@MOM-11, a microporous metal–organic material (MOM) that encapsulates cationic porphyrins and solvent in alternating open channels. Porph@MOM-11 has cation and anion binding sites that facilitate cooperative addition of inorganic salts (such as M +Cl -) in a stoichiometric fashion.

The In-Situ Structure of Cationic Lipid/DNA Complexes in Animal Cells: Applications to Gene Therapy

NASA Astrophysics Data System (ADS)

Lin, Alison J.; Slack, Nelle L.; Idziak, S. H. J.; George, C. X.; Samuel, C. E.; Safinya, C. R.

1997-03-01

Gene therapy has been the focus of many recent investigations. One promising technique is to use cationic lipids as vectors for DNA transfection. However, the exact mechanism of DNA uptake is unknown, due to a lack of knowledge regarding interactions and structures of DNA and cationic lipids. We are developing x-ray and optical microscopy techniques to directly image the temporal and spatial distribution of cationic lipid/DNA complexes (CL-DNA) during the various stages of transfection in mouse L-cells. The structure of these complexes in water have been shown by x-ray studies to consist of alternating lipid bilayers and DNA monolayers.(J. Radler, I. Koltover, T. Salditt, C. R. Safinya, Science (January 1997)) We demonstrate the feasibility of in-situ x-ray diffraction studies of CL-DNA complexes in L-cells. The x-ray data implies that complexes are taken up by endocytosis and DOPE destabilizes the endosomal membrane. Results from optical microscopy studies and X-Gal staining of transfected cells support the x-ray data. Funded in part by NSF grant DMR-9624091, PRF (No. 31352-AC7), Los Alamos CULAR grant No. STB/UC: 96-118.

Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential

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

Tournassat, C.; Tinnacher, R. M.; Grangeon, S.

The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonitemore » edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites (‘spillover’ effect).« less

Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential

DOE PAGES

Tournassat, C.; Tinnacher, R. M.; Grangeon, S.; ...

2017-10-06

The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonitemore » edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites (‘spillover’ effect).« less

ITQ-54: a multi-dimensional extra-large pore zeolite with 20 × 14 × 12-ring channels

DOE PAGES

Jiang, Jiuxing; Yun, Yifeng; Zou, Xiaodong; ...

2015-01-01

A multi-dimensional extra-large pore silicogermanate zeolite, named ITQ-54, has been synthesised by in situ decomposition of the N,N-dicyclohexylisoindolinium cation into the N-cyclohexylisoindolinium cation. Its structure was solved by 3D rotation electron diffraction (RED) from crystals of ca. 1 μm in size. The structure of ITQ-54 contains straight intersecting 20 × 14 × 12-ring channels along the three crystallographic axes and it is one of the few zeolites with extra-large channels in more than one direction. ITQ-54 has a framework density of 11.1 T atoms per 1000 Å 3, which is one of the lowest among the known zeolites. ITQ-54 wasmore » obtained together with GeO 2 as an impurity. A heavy liquid separation method was developed and successfully applied to remove this impurity from the zeolite. ITQ-54 is stable up to 600 °C and exhibits permanent porosity. The structure was further refined using powder X-ray diffraction (PXRD) data for both as-made and calcined samples.« less

RORγt+ cells selectively express redundant cation channels linked to the Golgi apparatus

PubMed Central

Drujont, Lucile; Lemoine, Aurélie; Moreau, Aurélie; Bienvenu, Géraldine; Lancien, Mélanie; Cens, Thierry; Guillot, Flora; Bériou, Gaëlle; Bouchet-Delbos, Laurence; Fehling, Hans Jörg; Chiffoleau, Elise; Nicot, Arnaud B.; Charnet, Pierre; Martin, Jérôme C.; Josien, Régis; Cuturi, Maria Cristina; Louvet, Cédric

2016-01-01

Retinoid-related orphan receptor gamma t (RORγt) is a master transcription factor central to type 17 immunity involving cells such as T helper 17, group 3 innate lymphoid cells or IL-17-producing γδ T cells. Here we show that the intracellular ion channel TMEM176B and its homologue TMEM176A are strongly expressed in these RORγt+ cells. We demonstrate that TMEM176A and B exhibit a similar cation channel activity and mainly colocalise in close proximity to the trans-Golgi network. Strikingly, in the mouse, the loss of Tmem176b is systematically associated with a strong upregulation of Tmem176a. While Tmem176b single-deficiency has no effect on the course of experimental autoimmune encephalomyelitis, T cell or DSS-induced colitis, it significantly reduces imiquimod-induced psoriasis-like skin inflammation. These findings shed light on a potentially novel specific process linked to post-Golgi trafficking for modulating the function of RORγt+ cells and indicate that both homologues should be simultaneously targeted to clearly elucidate the role of this intracellular ion flow. PMID:27009467

Molecular Dynamics Simulations of Voltage-Gated Cation Channels: Insights on Voltage-Sensor Domain Function and Modulation

PubMed Central

Delemotte, Lucie; Klein, Michael L.; Tarek, Mounir

2012-01-01

Since their discovery in the 1950s, the structure and function of voltage-gated cation channels (VGCC) has been largely understood thanks to results stemming from electrophysiology, pharmacology, spectroscopy, and structural biology. Over the past decade, computational methods such as molecular dynamics (MD) simulations have also contributed, providing molecular level information that can be tested against experimental results, thereby allowing the validation of the models and protocols. Importantly, MD can shed light on elements of VGCC function that cannot be easily accessed through “classical” experiments. Here, we review the results of recent MD simulations addressing key questions that pertain to the function and modulation of the VGCC’s voltage-sensor domain (VSD) highlighting: (1) the movement of the S4-helix basic residues during channel activation, articulating how the electrical driving force acts upon them; (2) the nature of the VSD intermediate states on transitioning between open and closed states of the VGCC; and (3) the molecular level effects on the VSD arising from mutations of specific S4 positively charged residues involved in certain genetic diseases. PMID:22654756

Synthetic Nanopores as a Test Case for Ion Channel Theories: The Anomalous Mole Fraction Effect without Single Filing

PubMed Central

Gillespie, Dirk; Boda, Dezső; He, Yan; Apel, Pavel; Siwy, Zuzanna S.

2008-01-01

The predictions of a theory for the anomalous mole fraction effect (AMFE) are tested experimentally with synthetic nanopores in plastic. The negatively charged synthetic nanopores under consideration are highly cation selective and 50 Å in diameter at their smallest point. These pores exhibit an AMFE in mixtures of Ca2+ and monovalent cations. An AMFE occurs when the conductance through a pore is lower in a mixture of salts than in the pure salts at the same concentration. For ion channels, the textbook interpretation of the AMFE is that multiple ions move through the pore in coordinated, single-file motion. However, because the synthetic nanopores are so wide, their AMFE shows that single filing is not necessary for the AMFE. It is shown that the AMFE in the synthetic nanopores is explained by a theory of preferential ion selectivity. The unique properties of the synthetic nanopores allow us to experimentally confirm several predictions of this theory. These same properties make synthetic nanopores an interesting new platform to test theories of ion channel permeation and selectivity in general. PMID:18390596

Radiopharmaceuticals for imaging the heart

DOEpatents

Green, M.A.; Tsang, B.W.

1994-06-28

Radiopharmaceuticals for imaging myocardial tissues are prepared by forming lipophilic, cationic complexes of radioactive metal ions with metal chelating ligands comprising the Schiff base adducts of triamines and tetraamines with optionally substituted salicylaldehydes. The lipophilic, cationic, radioactive complexes of the invention exhibit high uptake and retention in myocardial tissues. Preferred gallium-68(III) complexes in accordance with this invention can be used to image the heart using positron emission tomography. 6 figures.

Gas phase chemistry of N-benzylbenzamides with silver(I) cations: characterization of benzylsilver cation.

PubMed

Sun, Hezhi; Jin, Zhe; Quan, Hong; Sun, Cuirong; Pan, Yuanjiang

2015-03-07

The benzylsilver cation which emerges from the collisional dissociation of silver(I)-N-benzylbenzamide complexes was characterized by deuterium-labeling experiments, theoretical calculations, breakdown curves and substituent effects. The nucleophilic attack of the carbonyl oxygen on an α-hydrogen results in the generation of the benzylsilver cation, which is competitive to the AgH loss with the α-hydrogen.

Redox potential tuning by redox-inactive cations in nature's water oxidizing catalyst and synthetic analogues.

PubMed

Krewald, Vera; Neese, Frank; Pantazis, Dimitrios A

2016-04-28

The redox potential of synthetic oligonuclear transition metal complexes has been shown to correlate with the Lewis acidity of a redox-inactive cation connected to the redox-active transition metals of the cluster via oxo or hydroxo bridges. Such heterometallic clusters are important cofactors in many metalloenzymes, where it is speculated that the redox-inactive constituent ion of the cluster serves to optimize its redox potential for electron transfer or catalysis. A principal example is the oxygen-evolving complex in photosystem II of natural photosynthesis, a Mn4CaO5 cofactor that oxidizes water into dioxygen, protons and electrons. Calcium is critical for catalytic function, but its precise role is not yet established. In analogy to synthetic complexes it has been suggested that Ca(2+) fine-tunes the redox potential of the manganese cluster. Here we evaluate this hypothesis by computing the relative redox potentials of substituted derivatives of the oxygen-evolving complex with the cations Sr(2+), Gd(3+), Cd(2+), Zn(2+), Mg(2+), Sc(3+), Na(+) and Y(3+) for two sequential transitions of its catalytic cycle. The theoretical approach is validated with a series of experimentally well-characterized Mn3AO4 cubane complexes that are structural mimics of the enzymatic cluster. Our results reproduce perfectly the experimentally observed correlation between the redox potential and the Lewis acidities of redox-inactive cations for the synthetic complexes. However, it is conclusively demonstrated that this correlation does not hold for the oxygen evolving complex. In the enzyme the redox potential of the cluster only responds to the charge of the redox-inactive cations and remains otherwise insensitive to their precise identity, precluding redox-tuning of the metal cluster as a primary role for Ca(2+) in biological water oxidation.

Entropy-enthalpy compensation at the single protein level: pH sensing in the bacterial channel OmpF.

PubMed

Alcaraz, Antonio; Queralt-Martín, María; Verdiá-Báguena, Carmina; Aguilella, Vicente M; Mafé, Salvador

2014-12-21

The pH sensing mechanism of the OmpF channel operates via ligand modification: increasing acidity induces the replacement of cations with protons in critical binding sites decreasing the channel conductance. Aside from the change in enthalpy associated with the binding, there is also a change in the microscopic arrangements of ligands, receptors and the surrounding solvent. We show that the pH-modulation of the single channel conduction involves small free energy changes because large enthalpic and entropic contributions change in opposite ways, demonstrating an approximate enthalpy-entropy compensation for different salts and concentrations.

Identification of ML204, a Novel Potent Antagonist That Selectively Modulates Native TRPC4/C5 Ion Channels*

PubMed Central

Miller, Melissa; Shi, Jie; Zhu, Yingmin; Kustov, Maksym; Tian, Jin-bin; Stevens, Amy; Wu, Meng; Xu, Jia; Long, Shunyou; Yang, Pu; Zholos, Alexander V.; Salovich, James M.; Weaver, C. David; Hopkins, Corey R.; Lindsley, Craig W.; McManus, Owen; Li, Min; Zhu, Michael X.

2011-01-01

Transient receptor potential canonical (TRPC) channels are Ca2+-permeable nonselective cation channels implicated in diverse physiological functions, including smooth muscle contractility and synaptic transmission. However, lack of potent selective pharmacological inhibitors for TRPC channels has limited delineation of the roles of these channels in physiological systems. Here we report the identification and characterization of ML204 as a novel, potent, and selective TRPC4 channel inhibitor. A high throughput fluorescent screen of 305,000 compounds of the Molecular Libraries Small Molecule Repository was performed for inhibitors that blocked intracellular Ca2+ rise in response to stimulation of mouse TRPC4β by μ-opioid receptors. ML204 inhibited TRPC4β-mediated intracellular Ca2+ rise with an IC50 value of 0.96 μm and exhibited 19-fold selectivity against muscarinic receptor-coupled TRPC6 channel activation. In whole-cell patch clamp recordings, ML204 blocked TRPC4β currents activated through either μ-opioid receptor stimulation or intracellular dialysis of guanosine 5′-3-O-(thio)triphosphate (GTPγS), suggesting a direct interaction of ML204 with TRPC4 channels rather than any interference with the signal transduction pathways. Selectivity studies showed no appreciable block by 10–20 μm ML204 of TRPV1, TRPV3, TRPA1, and TRPM8, as well as KCNQ2 and native voltage-gated sodium, potassium, and calcium channels in mouse dorsal root ganglion neurons. In isolated guinea pig ileal myocytes, ML204 blocked muscarinic cation currents activated by bath application of carbachol or intracellular infusion of GTPγS, demonstrating its effectiveness on native TRPC4 currents. Therefore, ML204 represents an excellent novel tool for investigation of TRPC4 channel function and may facilitate the development of therapeutics targeted to TRPC4. PMID:21795696

Crystal structures of tris-[1-oxo-pyridine-2-olato(1-)]silicon(IV) chloride chloro-form-d 1 disolvate, tris-[1-oxo-pyridine-2-olato(1-)]silicon(IV) chloride aceto-nitrile unqu-anti-fied solvate, and fac-tris-[1-oxo-pyridine-2-thiol-ato(1-)]silicon(IV) chloride chloro-form-d 1 disolvate.

PubMed

Kraft, Bradley M; Brennessel, William W; Ryan, Amy E; Benjamin, Candace K

2015-12-01

The cations in the title salts, [Si(OPO)3]Cl·2CDCl3, (I), [Si(OPO)3]Cl·xCH3CN, (II), and fac-[Si(OPTO)3]Cl·2CDCl3, (III) (OPO = 1-oxo-2-pyridin-one, C5H4NO2, and OPTO = 1-oxo-2-pyridine-thione, C5H4NOS), have distorted octa-hedral coordination spheres. The first two structures contain the same cation and anion, but different solvents of crystallization led to different solvates and packing arrangements. In structures (I) and (III), the silicon complex cations and chloride anions are well separated, while in (II), there are two C-H⋯Cl distances that fall just within the sum of the van der Waals radii of the C and Cl atoms. The pyridine portions of the OPO ligands in (I) and (II) are modeled as disordered with the planar flips of themselves [(I): 0.574 (15):0.426 (15), 0.696 (15):0.304 (15), and 0.621 (15):0.379 (15); (II): 0.555 (13):0.445 (13), 0.604 (14):0.396 (14) and 0.611 (13):0.389 (13)], demonstrating that both fac and mer isomers are co-crystallized. In (II), highly disordered solvent, located in two independent channels along [100], was unable to be modeled. Reflection contributions from this solvent were fixed and added to the calculated structure factors using the SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] function of program PLATON, which determined there to be 54 electrons in 225 Å(3) accounted for per unit cell (25 electrons in 109 Å(3) in one channel, and 29 electrons in 115 Å(3) in the other). In (I) and (II), all species lie on general positions. In (III), all species are located along crystallographic threefold axes.

Molecular dynamics simulations of electrostatics and hydration distributions around RNA and DNA motifs

NASA Astrophysics Data System (ADS)

Marlowe, Ashley E.; Singh, Abhishek; Semichaevsky, Andrey V.; Yingling, Yaroslava G.

2009-03-01

Nucleic acid nanoparticles can self-assembly through the formation of complementary loop-loop interactions or stem-stem interactions. Presence and concentration of ions can significantly affect the self-assembly process and the stability of the nanostructure. In this presentation we use explicit molecular dynamics simulations to examine the variations in cationic distributions and hydration environment around DNA and RNA helices and loop-loop interactions. Our simulations show that the potassium and sodium ionic distributions are different around RNA and DNA motifs which could be indicative of ion mediated relative stability of loop-loop complexes. Moreover in RNA loop-loop motifs ions are consistently present and exchanged through a distinct electronegative channel. We will also show how we used the specific RNA loop-loop motif to design a RNA hexagonal nanoparticle.

Engineering Fast Ion Conduction and Selective Cation Channels for a High-Rate and High-Voltage Hybrid Aqueous Battery.

PubMed

Liu, Chunyi; Wang, Xusheng; Deng, Wenjun; Li, Chang; Chen, Jitao; Xue, Mianqi; Li, Rui; Pan, Feng

2018-03-14

The rechargeable aqueous metal-ion battery (RAMB) has attracted considerable attention due to its safety, low costs, and environmental friendliness. Yet the poor-performance electrode materials lead to a low feasibility of practical application. A hybrid aqueous battery (HAB) built from electrode materials with selective cation channels could increase the electrode applicability and thus enlarge the application of RAMB. Herein, we construct a high-voltage K-Na HAB based on K 2 FeFe(CN) 6 cathode and carbon-coated NaTi 2 (PO 4 ) 3 (NTP/C) anode. Due to the unique cation selectivity of both materials and ultrafast ion conduction of NTP/C, the hybrid battery delivers a high capacity of 160 mAh g -1 at a 0.5 C rate. Considerable capacity retention of 94.3 % is also obtained after 1000 cycles at even 60 C rate. Meanwhile, high energy density of 69.6 Wh kg -1 based on the total mass of active electrode materials is obtained, which is comparable and even superior to that of the lead acid, Ni/Cd, and Ni/MH batteries. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Response of a benzoxainone derivative linked to monoaza-15-crown-5 with divalent heavy metals.

PubMed

Addleman, R S; Bennett, J; Tweedy, S H; Elshani, S; Wai, C M

1998-08-01

The response of a monoaza-15-crown-5 with an optically active aminobenzoxazinone moiety to divalent cations was investigated. The crown ether was found to undergo a strong emission shift to the blue when complexed with specific divalent metals that have ionic diameters between 1.9-2.4 A. Consequently the photoactive macrocycle is responsive to Mg(2+), Ca(2+), Ba(2+), Sr(2+), Cd(2+), and particularly responsive to Hg(2+)and Pb(2+). Macrocycle emission spectra are shown to be a function of cation concentration. Alkaline metal cations and smaller transition metals ions such as Ni(2+), Co(2+)and Zn(2+)do not cause significant changes in the macrocycle emission spectra. Emission, absorption, and complex stability constants are determined. Mechanisms of cation selectivity and spectral emission shifts are discussed. Challenges involving immobilization of the macrocycle while preserving its spectral response to cations are explored.

Infrared spectroscopic characterization of dehydration and accompanying phase transition behaviors in NAT-topology zeolites

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

Wang, Hsiu-Wen; Bishop, David

2012-01-01

Relative humidity (PH2O, partial pressure of water)-dependent dehydration and accompanying phase transitions in NAT-topology zeolites (natrolite, scolecite, and mesolite) were studied under controlled temperature and known PH2O conditions by in situ diffuse-reflectance infrared Fourier transform spectroscopy and parallel X-ray powder diffraction. Dehydration was characterized by the disappearance of internal H2O vibrational modes. The loss of H2O molecules caused a sequence of structural transitions in which the host framework transformation path was coupled primarily via the thermal motion of guest Na?/Ca2? cations and H2O molecules. The observation of different interactions of H2O molecules and Na?/Ca2? cations with host aluminosilicate frameworks undermore » highand low-PH2O conditions indicated the development of different local strain fields, arising from cation H2O interactions in NAT-type channels. These strain fields influence the Si O/Al O bond strength and tilting angles within and between tetrahedra as the dehydration temperature is approached. The newly observed infrared bands (at 2,139 cm-1 in natrolite, 2,276 cm-1 in scolecite, and 2,176 and 2,259 cm-1 in mesolite) result from strong cation H2O Al Si framework interactions in NAT-type channels, and these bands can be used to evaluate the energetic evolution of Na?/Ca2? cations before and after phase transitions, especially for scolecite and mesolite. The 2,176 and 2,259 cm-1 absorption bands in mesolite also appear to be related to Na?/Ca2? order disorder that occur when mesolite loses its Ow4 H2O molecules.« less

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

Huang, Ching-Shin; Pedersen, Bjørn Panyella; Stokes, David L.

Cellular potassium import systems play a fundamental role in osmoregulation, pH homeostasis and membrane potential in all domains of life. In bacteria, the kdp operon encodes a four-subunit potassium pump that maintains intracellular homeostasis, cell shape and turgor under conditions in which potassium is limiting1. This membrane complex, called KdpFABC, has one channel-like subunit (KdpA) belonging to the superfamily of potassium transporters and another pump-like subunit (KdpB) belonging to the superfamily of P-type ATPases. Although there is considerable structural and functional information about members of both superfamilies, the mechanism by which uphill potassium transport through KdpA is coupled with ATPmore » hydrolysis by KdpB remains poorly understood. Here we report the 2.9 Å X-ray structure of the complete Escherichia coli KdpFABC complex with a potassium ion within the selectivity filter of KdpA and a water molecule at a canonical cation site in the transmembrane domain of KdpB. The structure also reveals two structural elements that appear to mediate the coupling between these two subunits. Specifically, a protein-embedded tunnel runs between these potassium and water sites and a helix controlling the cytoplasmic gate of KdpA is linked to the phosphorylation domain of KdpB. On the basis of these observations, we propose a mechanism that repurposes protein channel architecture for active transport across biomembranes.« less

Evans Blue is not a suitable inhibitor of the epithelial sodium channel δ-subunit.

PubMed

Perniss, Alexander; Wolf, Annemarie; Wichmann, Lukas; Schönberger, Matthias; Althaus, Mike

2015-10-23

The Epithelial Sodium Channel (ENaC) is a heterotrimeric ion channel which can be either formed by assembly of its α-, β- and γ-subunits or, alternatively, its δ-, β- and γ-subunits. The physiological function of αβγ-ENaC is well established, but the function of δβγ-ENaC remains elusive. The azo-dye Evans Blue (EvB) has been routinely used to discriminate between the two channel isoforms by decreasing transmembrane currents and amiloride-sensitive current fractions of δβγ-ENaC expressing Xenopus oocytes. Even though these results could be reproduced, it was found by precipitation experiments and spectroscopic methods that the cationic amiloride and the anionic EvB directly interact in solution, forming a strong complex. Thereby a large amount of pharmacologically available amiloride is removed from physiological buffer solutions and the effective amiloride concentration is reduced. This interaction did not occur in the presence of albumin. In microelectrode recordings, EvB was able to abrogate the block of δβγ-ENaC by amiloride or its derivative benzamil. In sum, EvB reduces amiloride-sensitive ion current fractions in electrophysiological experiments. This is not a result of a specific inhibition of δβγ-ENaC but rather represents a pharmacological artefact. EvB should therefore not be used as an inhibitor of δ-ENaC. Copyright © 2015 Elsevier Inc. All rights reserved.

Ultrahigh-resolution crystal structures of Z-DNA in complex with Mn(2+) and Zn(2+) ions.

PubMed

Drozdzal, Pawel; Gilski, Miroslaw; Kierzek, Ryszard; Lomozik, Lechoslaw; Jaskolski, Mariusz

2013-06-01

X-ray crystal structures of the spermine(4+) form of the Z-DNA duplex with the self-complementary d(CG)3 sequence in complexes with Mn(2+) and Zn(2+) cations have been determined at the ultrahigh resolutions of 0.75 and 0.85 Å, respectively. Stereochemical restraints were only used for the sperminium cation (in both structures) and for nucleotides with dual conformation in the Zn(2+) complex. The Mn(2+) and Zn(2+) cations at the major site, designated M(2+)(1), bind at the N7 position of G6 by direct coordination. The coordination geometry of this site was octahedral, with complete hydration shells. An additional Zn(2+)(2) cation was bis-coordinated in a tetrahedral fashion by the N7 atoms of G10 and G12 from a symmetry-related molecule. The coordination distances of Zn(2+)(1) and Zn(2+)(2) to the O6 atom of the guanine residues were 3.613 (6) and 3.258 (5) Å, respectively. Moreover, a chloride ion was also identified in the coordination sphere of Zn(2+)(2). Alternate conformations were observed in the Z-DNA-Zn(2+) structure not only at internucleotide linkages but also at the terminal C3'-OH group of G12. The conformation of the sperminium chain in the Z-DNA-Mn(2+) complex is similar to the spermine(4+) conformation in analogous Z-DNA-Mg(2+) structures. In the Z-DNA-Zn(2+) complex the sperminium cation is disordered and partially invisible in electron-density maps. In the Z-DNA-Zn(2+) complex the sperminium cation only interacts with the phosphate groups of the Z-DNA molecules, while in the Z-DNA-Mn(2+) structure it forms hydrogen bonds to both the phosphate groups and DNA bases.

Lanthanide-organic complexes based on polyoxometalates: Solvent effect on the luminescence properties

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

Tang Qun; Liu Shuxia, E-mail: liusx@nenu.edu.cn; Liang Dadong

2012-06-15

A series of lanthanide-organic complexes based on polyoxometalates (POMs) [Ln{sub 2}(DNBA){sub 4}(DMF){sub 8}][W{sub 6}O{sub 19}] (Ln=La(1), Ce(2), Sm(3), Eu(4), Gd(5); DNBA=3,5-dinitrobenzoate; DMF=N,N-dimethylformamide) has been synthesized. These complexes consist of [W{sub 6}O{sub 19}]{sup 2-} and dimeric [Ln{sub 2}(DNBA){sub 4}(DMF){sub 8}]{sup 2+} cations. The luminescence properties of 4 are measured in solid state and different solutions, respectively. Notably, the emission intensity increases gradually with the increase of solvent permittivity, and this solvent effect can be directly observed by electrospray mass spectrometry (ESI-MS). The analyses of ESI-MS show that the eight coordinated solvent DMF units of dimeric cation are active. They can movemore » away from dimeric cations and exchange with solvent molecules. Although the POM anions escape from 3D supramolecular network, the dimeric state structure of [Ln{sub 2}(DNBA){sub 4}]{sup 2+} remains unchanged in solution. The conservation of red luminescence is attributed to the maintenance of the aggregated state structures of dimeric cations. - Graphical abstract: 3D POMs-based lanthanide-organic complexes performed the solvent effect on the luminescence property. The origin of such solvent effect can be understood and explained on the basis of the existence of coordinated active sites by the studies of ESI-MS. Highlights: Black-Right-Pointing-Pointer The solvent effect on the luminescence property of POMs-based lanthanide-organic complexes. Black-Right-Pointing-Pointer ESI-MS analyses illuminate the correlation between the structure and luminescence property. Black-Right-Pointing-Pointer The dimeric cations have eight active sites of solvent coordination. Black-Right-Pointing-Pointer The aggregated state structure of dimer cation remains unchanged in solution. Black-Right-Pointing-Pointer Luminescence associating with ESI-MS is a new method for investigating the interaction of complex and solvent.« less

Coordination Chemistry of Alkali and Alkaline-Earth Cations with Macrocyclic Ligands.

ERIC Educational Resources Information Center

Dietrich, Bernard

1985-01-01

Discusses: (l) alkali and alkaline-earth cations in biology (considering naturally occurring lonophores, their X-ray structures, and physiochemical studies); (2) synthetic complexing agents for groups IA and IIA; and (3) ion transport across membranes (examining neutral macrobicyclic ligands as metal cation carriers, transport by anionic carriers,…

Pore size matters for potassium channel conductance

PubMed Central

Moldenhauer, Hans; Pincuntureo, Matías

2016-01-01

Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K+ channels discriminate K+ over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K+ channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K+ channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K+ channels, accounting for their diversity in unitary conductance. PMID:27619418

Redox-mediated regulation of connexin proteins; focus on nitric oxide.

PubMed

García, Isaac E; Sánchez, Helmuth A; Martínez, Agustín D; Retamal, Mauricio A

2018-01-01

Connexins are membrane proteins that form hemichannels and gap junction channels at the plasma membrane. Through these channels connexins participate in autocrine and paracrine intercellular communication. Connexin-based channels are tightly regulated by membrane potential, phosphorylation, pH, redox potential, and divalent cations, among others, and the imbalance of this regulation have been linked to many acquired and genetic diseases. Concerning the redox potential regulation, the nitric oxide (NO) has been described as a modulator of the hemichannels and gap junction channels properties. However, how NO regulates these channels is not well understood. In this mini-review, we summarize the current knowledge about the effects of redox potential focused in NO on the trafficking, formation and functional properties of hemichannels and gap junction channels. Copyright © 2017 Elsevier B.V. All rights reserved.

Electrophoretic extraction of low molecular weight cationic analytes from sodium dodecyl sulfate containing sample matrices for their direct electrospray ionization mass spectrometry.

PubMed

Kinde, Tristan F; Lopez, Thomas D; Dutta, Debashis

2015-03-03

While the use of sodium dodecyl sulfate (SDS) in separation buffers allows efficient analysis of complex mixtures, its presence in the sample matrix is known to severely interfere with the mass-spectrometric characterization of analyte molecules. In this article, we report a microfluidic device that addresses this analytical challenge by enabling inline electrospray ionization mass spectrometry (ESI-MS) of low molecular weight cationic samples prepared in SDS containing matrices. The functionality of this device relies on the continuous extraction of analyte molecules into an SDS-free solvent stream based on the free-flow zone electrophoresis (FFZE) technique prior to their ESI-MS analysis. The reported extraction was accomplished in our current work in a glass channel with microelectrodes fabricated along its sidewalls to realize the desired electric field. Our experiments show that a key challenge to successfully operating such a device is to suppress the electroosmotically driven fluid circulations generated in its extraction channel that otherwise tend to vigorously mix the liquid streams flowing through this duct. A new coating medium, N-(2-triethoxysilylpropyl) formamide, recently demonstrated by our laboratory to nearly eliminate electroosmotic flow in glass microchannels was employed to address this issue. Applying this surface modifier, we were able to efficiently extract two different peptides, human angiotensin I and MRFA, individually from an SDS containing matrix using the FFZE method and detect them at concentrations down to 3.7 and 6.3 μg/mL, respectively, in samples containing as much as 10 mM SDS. Notice that in addition to greatly reducing the amount of SDS entering the MS instrument, the reported approach allows rapid solvent exchange for facilitating efficient analyte ionization desired in ESI-MS analysis.

Generalized Breit-Wigner treatment of molecular transport: Charging effects in a single decanedithiol molecule

NASA Astrophysics Data System (ADS)

Cabrera-Tinoco, Hugo Andres; Moreira, Augusto C. L.; de Melo, Celso P.

2018-05-01

We examine the relative contribution of ballistic and elastic cotunneling mechanisms to the charge transport through a single decanedithiol molecule linked to two terminal clusters of gold atoms. For this, we first introduced a conceptual model that permits a generalization of the Breit-Wigner scattering formalism where the cation, anion, and neutral forms of the molecule can participate with different probabilities of the charge transfer process, but in a simultaneous manner. We used a density functional theory treatment and considered the fixed geometry of each charge state to calculate the corresponding eigenvalues and eigenvectors of the extended system for different values of the external electric field. We have found that for the ballistic transport the HOMO and LUMO of the neutral species play a key role, while the charged states give a negligible contribution. On the other hand, an elastic cotunneling charge transfer can occur whenever a molecular orbital (MO) of the cation or anion species, even if localized in just one side of the molecule-gold clusters complex, has energy close to that of a delocalized MO of the neutral species. Under these conditions, a conduction channel is formed throughout the entire system, in a process that is controlled by the degree of resonance between the MOs involved. Our results indicate that while different charge transfer mechanisms contribute to the overall charge transport, quantum effects such as avoided-crossing situations between relevant frontier MOs can be of special importance. In these specific situations, the interchange of spatial localization of two MOs involved in the crossing can open a new channel of charge transfer that otherwise would not be available.

Direct versus indirect actions of ghrelin on hypothalamic NPY neurons.

PubMed

Hashiguchi, Hiroshi; Sheng, Zhenyu; Routh, Vanessa; Gerzanich, Volodymyr; Simard, J Marc; Bryan, Joseph

2017-01-01

Assess direct versus indirect action(s) of ghrelin on hypothalamic NPY neurons. Electrophysiology was used to measure ion channel activity in NPY-GFP neurons in slice preparations. Ca2+ imaging was used to monitor ghrelin activation of isolated NPY GFP-labeled neurons. Immunohistochemistry was used to localize Trpm4, SUR1 and Kir6.2 in the hypothalamus. Acylated ghrelin depolarized the membrane potential (MP) of NPY-GFP neurons in brain slices. Depolarization resulted from a decreased input resistance (IR) in ~70% of neurons (15/22) or an increased IR in the remainder (7/22), consistent with the opening or closing of ion channels, respectively. Although tetrodotoxin (TTX) blockade of presynaptic action potentials reduced ghrelin-induced changes in MP and IR, ghrelin still significantly depolarized the MP and decreased IR in TTX-treated neurons, suggesting that ghrelin directly opens cation channel(s) in NPY neurons. In isolated NPY-GFP neurons, ghrelin produced a sustained rise of [Ca2+]c, with an EC50 ~110 pM. Pharmacologic studies confirmed that the direct action of ghrelin was through occupation of the growth hormone secretagogue receptor, GHS-R, and demonstrated the importance of the adenylate cyclase/cAMP/protein kinase A (PKA) and phospholipase C/inositol triphosphate (PLC/IP3) pathways as activators of 5' AMP-activated protein kinase (AMPK). Activation of isolated neurons was not affected by CNQX or TTX, but reducing [Na+]o suppressed activation, suggesting a role for Na+-permeable cation channels. SUR1 and two channel partners, Kir6.2 and Trpm4, were identified immunologically in NPY-GFP neurons in situ. The actions of SUR1 and Trpm4 modulators were informative: like ghrelin, diazoxide, a SUR1 agonist, elevated [Ca2+]c and glibenclamide, a SUR1 antagonist, partially suppressed ghrelin action, while 9-phenanthrol and flufenamic acid, selective Trpm4 antagonists, blocked ghrelin actions on isolated neurons. Ghrelin activation was unaffected by nifedipine and ω-conotoxin, inhibitors of L- and N-type Ca2+ channels, respectively, while Ni2+, mibefradil, and TTA-P2 completely or partially inhibited ghrelin action, implicating T-type Ca2+ channels. Activation was also sensitive to a spider toxin, SNX-482, at concentrations selective for R-type Ca2+ channels. Nanomolar concentrations of GABA markedly inhibited ghrelin-activation of isolated NPY-GFP neurons, consistent with chronic suppression of ghrelin action in vivo. NPY neurons express all the molecular machinery needed to respond directly to ghrelin. Consistent with recent studies, ghrelin stimulates presynaptic inputs that activate NPY-GFP neurons in situ. Ghrelin can also directly activate a depolarizing conductance. Results with isolated NPY-GFP neurons suggest the ghrelin-activated, depolarizing current is a Na+ conductance with the pharmacologic properties of SUR1/Trpm4 non-selective cation channels. In the isolated neuron model, the opening of SUR1/Trpm4 channels activates T- and SNX482-sensitive R-type voltage dependent Ca2+ channels, which could contribute to NPY neuronal activity in situ.

Voltage activation and hysteresis of the non-selective voltage-dependent channel in the intact human red cell.

PubMed

Bennekou, Poul; Barksmann, Trine L; Jensen, Lars R; Kristensen, Berit I; Christophersen, Palle

2004-05-01

Suspension of intact human red cells in media with low chloride and sodium concentrations (isotonic sucrose substitution) results in strongly inside positive membrane potentials, which activate the voltage-dependent non-selective cation (NSVDC) channel. By systematic variation of the initial Nernst potentials for chloride (degree of ion substitution) as well as the chloride conductance (block by NS1652), and by exploiting the interplay between the Ca(2+)-permeable NSVDC channel, the Ca(2+)-activated K+ channel (the Gárdos channel) and the Ca(2+)-pump, a graded activation of the NSVDC channel was achieved. Under these conditions, it was shown that the NSVDC channels exist in two states of activation depending on the initial conditions for the activation. The hysteretic behaviour, which in patch clamp experiments has been found for the individual channel unit, is thus retained at the cellular level and can be demonstrated with red cells in suspension.

Novel role for the transient potential receptor melastatin 4 channel in guinea pig detrusor smooth muscle physiology

PubMed Central

Smith, Amy C.; Hristov, Kiril L.; Cheng, Qiuping; Xin, Wenkuan; Parajuli, Shankar P.; Earley, Scott; Malysz, John

2013-01-01

Members of the transient receptor potential (TRP) channel superfamily, including the Ca2+-activated monovalent cation-selective TRP melastatin 4 (TRPM4) channel, have been recently identified in the urinary bladder. However, their expression and function at the level of detrusor smooth muscle (DSM) remain largely unexplored. In this study, for the first time we investigated the role of TRPM4 channels in guinea pig DSM excitation-contraction coupling using a multidisciplinary approach encompassing protein detection, electrophysiology, live-cell Ca2+ imaging, DSM contractility, and 9-phenanthrol, a recently characterized selective inhibitor of the TRPM4 channel. Western blot and immunocytochemistry experiments demonstrated the expression of the TRPM4 channel in whole DSM tissue and freshly isolated DSM cells with specific localization on the plasma membrane. Perforated whole cell patch-clamp recordings and real-time Ca2+ imaging experiments with fura 2-AM, both using freshly isolated DSM cells, revealed that 9-phenanthrol (30 μM) significantly reduced the cation current and decreased intracellular Ca2+ levels. 9-Phenanthrol (0.1–30 μM) significantly inhibited spontaneous, 0.1 μM carbachol-induced, 20 mM KCl-induced, and nerve-evoked contractions in guinea pig DSM-isolated strips with IC50 values of 1–7 μM and 70–80% maximum inhibition. 9-Phenanthrol also reduced nerve-evoked contraction amplitude induced by continuous repetitive electrical field stimulation of 10-Hz frequency and shifted the frequency-response curve (0.5–50 Hz) relative to the control. Collectively, our data demonstrate the novel finding that TRPM4 channels are expressed in guinea pig DSM and reveal their critical role in the regulation of guinea pig DSM excitation-contraction coupling. PMID:23302778

Impact of Dendrimer Terminal Group Chemistry on Blockage of the Anthrax Toxin Channel: A Single Molecule Study.

PubMed

Yamini, Goli; Kalu, Nnanya; Nestorovich, Ekaterina M

2016-11-15

Nearly all the cationic molecules tested so far have been shown to reversibly block K⁺ current through the cation-selective PA 63 channels of anthrax toxin in a wide nM-mM range of effective concentrations. A significant increase in channel-blocking activity of the cationic compounds was achieved when multiple copies of positively charged ligands were covalently linked to multivalent scaffolds, such as cyclodextrins and dendrimers. Even though multivalent binding can be strong when the individual bonds are relatively weak, for drug discovery purposes we often strive to design multivalent compounds with high individual functional group affinity toward the respective binding site on a multivalent target. Keeping this requirement in mind, here we perform a single-channel/single-molecule study to investigate kinetic parameters of anthrax toxin PA 63 channel blockage by second-generation (G2) poly(amido amine) (PAMAM) dendrimers functionalized with different surface ligands, including G2-NH₂, G2-OH, G2-succinamate, and G2-COONa. We found that the previously reported difference in IC 50 values of the G2-OH/PA 63 and G2-NH₂/PA 63 binding was determined by both on- and off-rates of the reversible dendrimer/channel binding reaction. In 1 M KCl, we observed a decrease of about three folds in k o n and a decrease of only about ten times in t r e s with G2-OH compared to G2-NH₂. At the same time for both blockers, k o n and t r e s increased dramatically with transmembrane voltage increase. PAMAM dendrimers functionalized with negatively charged succinamate, but not carboxyl surface groups, still had some residual activity in inhibiting the anthrax toxin channels. At 100 mV, the on-rate of the G2-succinamate binding was comparable with that of G2-OH but showed weaker voltage dependence when compared to G2-OH and G2-NH₂. The residence time of G2-succinamate in the channel exhibited opposite voltage dependence compared to G2-OH and G2-NH₂, increasing with the cis -negative voltage increase. We also describe kinetics of the PA 63 ion current modulation by two different types of the "imperfect" PAMAM dendrimers, the mixed-surface G2 75% OH 25% NH₂ dendrimer and G3-NH₂ dendron. At low voltages, both "imperfect" dendrimers show similar rate constants but significantly weaker voltage sensitivity when compared with the intact G2-NH₂ PAMAM dendrimer.

Impact of Dendrimer Terminal Group Chemistry on Blockage of the Anthrax Toxin Channel: A Single Molecule Study

PubMed Central

Yamini, Goli; Kalu, Nnanya; Nestorovich, Ekaterina M.

2016-01-01

Nearly all the cationic molecules tested so far have been shown to reversibly block K+ current through the cation-selective PA63 channels of anthrax toxin in a wide nM–mM range of effective concentrations. A significant increase in channel-blocking activity of the cationic compounds was achieved when multiple copies of positively charged ligands were covalently linked to multivalent scaffolds, such as cyclodextrins and dendrimers. Even though multivalent binding can be strong when the individual bonds are relatively weak, for drug discovery purposes we often strive to design multivalent compounds with high individual functional group affinity toward the respective binding site on a multivalent target. Keeping this requirement in mind, here we perform a single-channel/single-molecule study to investigate kinetic parameters of anthrax toxin PA63 channel blockage by second-generation (G2) poly(amido amine) (PAMAM) dendrimers functionalized with different surface ligands, including G2-NH2, G2-OH, G2-succinamate, and G2-COONa. We found that the previously reported difference in IC50 values of the G2-OH/PA63 and G2-NH2/PA63 binding was determined by both on- and off-rates of the reversible dendrimer/channel binding reaction. In 1 M KCl, we observed a decrease of about three folds in kon and a decrease of only about ten times in tres with G2-OH compared to G2-NH2. At the same time for both blockers, kon and tres increased dramatically with transmembrane voltage increase. PAMAM dendrimers functionalized with negatively charged succinamate, but not carboxyl surface groups, still had some residual activity in inhibiting the anthrax toxin channels. At 100 mV, the on-rate of the G2-succinamate binding was comparable with that of G2-OH but showed weaker voltage dependence when compared to G2-OH and G2-NH2. The residence time of G2-succinamate in the channel exhibited opposite voltage dependence compared to G2-OH and G2-NH2, increasing with the cis-negative voltage increase. We also describe kinetics of the PA63 ion current modulation by two different types of the “imperfect” PAMAM dendrimers, the mixed-surface G2 75% OH 25% NH2 dendrimer and G3-NH2 dendron. At low voltages, both “imperfect” dendrimers show similar rate constants but significantly weaker voltage sensitivity when compared with the intact G2-NH2 PAMAM dendrimer. PMID:27854272

Competitive fragmentation pathways of acetic acid dimer explored by synchrotron VUV photoionization mass spectrometry and electronic structure calculations.

PubMed

Guan, Jiwen; Hu, Yongjun; Zou, Hao; Cao, Lanlan; Liu, Fuyi; Shan, Xiaobin; Sheng, Liusi

2012-09-28

In present study, photoionization and dissociation of acetic acid dimers have been studied with the synchrotron vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. Besides the intense signal corresponding to protonated cluster ions (CH(3)COOH)(n)·H(+), the feature related to the fragment ions (CH(3)COOH)H(+)·COO (105 amu) via β-carbon-carbon bond cleavage is observed. By scanning photoionization efficiency spectra, appearance energies of the fragments (CH(3)COOH)·H(+) and (CH(3)COOH)H(+)·COO are obtained. With the aid of theoretical calculations, seven fragmentation channels of acetic acid dimer cations were discussed, where five cation isomers of acetic acid dimer are involved. While four of them are found to generate the protonated species, only one of them can dissociate into a C-C bond cleavage product (CH(3)COOH)H(+)·COO. After surmounting the methyl hydrogen-transfer barrier 10.84 ± 0.05 eV, the opening of dissociative channel to produce ions (CH(3)COOH)(+) becomes the most competitive path. When photon energy increases to 12.4 eV, we also found dimer cations can be fragmented and generate new cations (CH(3)COOH)·CH(3)CO(+). Kinetics, thermodynamics, and entropy factors for these competitive dissociation pathways are discussed. The present report provides a clear picture of the photoionization and dissociation processes of the acetic acid dimer in the range of the photon energy 9-15 eV.

Altered sexual and social behaviors in trp2 mutant mice

PubMed Central

Leypold, Bradley G.; Yu, C. Ron; Leinders-Zufall, Trese; Kim, Michelle M.; Zufall, Frank; Axel, Richard

2002-01-01

We have used gene targeting to generate mice with a homozygous deficiency in trp2, a cation channel expressed in the vomeronasal organ (VNO). Trp2 mutant animals reveal a striking reduction in the electrophysiological response to pheromones in the VNO, suggesting that trp2 plays a central role in mediating the pheromone response. These mutants therefore afford the opportunity to examine the role of the VNO in the generation of innate sexual and social behaviors in mice. Trp2 mutant males and nursing females are docile and fail to initiate aggressive attacks on intruder males. Male–female sexual behavior appears normal, but trp2 mutant males also vigorously mount other males. These results suggest that the cation channel trp2 is required in the VNO to detect male-specific pheromones that elicit aggressive behaviors and dictate the choice of sexual partners. PMID:11972034

Behavior of cesium and thallium cations inside a calixarene cavity as probed by nuclear spin relaxation. Evidence of cation-pi interactions in water.

PubMed

Cuc, Diana; Bouguet-Bonnet, Sabine; Morel-Desrosiers, Nicole; Morel, Jean-Pierre; Mutzenhardt, Pierre; Canet, Daniel

2009-08-06

We have studied the complexes formed between the p-sulfonatocalix[4]arene and cesium or thallium metal cation, first by carbon-13 longitudinal relaxation of the calixarene molecule at two values of the magnetic field B(0). From the longitudinal relaxation times of an aromatic carbon directly bonded to a proton, thus subjected essentially to the dipolar interaction with that proton, we could obtain the correlation time describing the reorientation of the CH bond. The rest of this study has demonstrated that it is also the correlation time describing the tumbling of the whole calixarene assembly. From three non-proton-bearing carbons of the aromatic cycles (thus subjected to the chemical shift anisotropy and dipolar mechanisms), we have been able to determine the variation of the chemical shift anisotropy when going from the free to the complex form of the calixarene. These variations not only provide the location of the cation inside the calixarene cavity but also constitute a direct experimental proof of the cation-pi interactions. These results are complemented by cesium and thallium relaxation measurements performed again at two values of the magnetic field B(0). An estimation of the mean distance between the cation and the calixarene protons could be obtained. These measurements have also revealed an important chemical shift anisotropy of thallium upon complexation.

The interplay of ion crosslinking, free ion content, and polymer mobility in PEO-based single-ion conductors

NASA Astrophysics Data System (ADS)

Lin, Kan-Ju; Maranas, Janna

2010-03-01

We use molecular dynamics simulation to study ion clustering and dynamics in ion containing polymers. This PEO based single-ion conducting ionomer serves as a model system for understanding cation transport in solid state polymer electrolytes (SPEs). Although small-angle x-ray scattering does not show an ionomer peak, we observer various cation-anion complexes in the simulation, suggesting ionomer backbones are crosslinked through ion complexes. These crosslinks reduce the adjacent PEO mobility resulting in a symmetric mobility gradient along the PEO chain. We vary the cation-anion interaction in the simulation to observe the interplay of cation-anion association, polymer mobility and cation motion. Cation-anion association controls the number of free ions, which is important in ionic conductivity when these materials are used as SPEs. Polymer mobility controls how fast the free ions are able to move through the SPE. High conductivity requires both a high free ion content and fast polymer motion. To understand the connection between the two, we ``tune'' the force field in order to manipulate the free ion content and observe the influence on PEO dynamics.

Infrared multiple photon dissociation spectroscopy of group I and group II metal complexes with Boc-hydroxylamine.

PubMed

Dain, Ryan P; Gresham, Gary; Groenewold, Gary S; Steill, Jeffrey D; Oomens, Jos; Van Stipdonk, Michael J

2013-08-30

Hydroxamates are essential growth factors for some microbes, acting primarily as siderophores that solubilize iron for transport into a cell. Here we determined the intrinsic structure of 1:1 complexes between Boc-protected hydroxylamine and group I ([M(L)](+)) and group II ([M(L-H)](+)) cations, where M and L are the cation and ligand, respectively, which are convenient models for the functional unit of hydroxamate siderphores. The relevant complex ions were generated by electrospray ionization (ESI) and isolated and stored in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Infrared spectra of the isolated complexes were collected by monitoring (infrared) photodissociation yield as a function of photon energy. Experimental spectra were then compared to those predicted by density functional theory (DFT) calculations. The infrared multiple photon dissociation (IRMPD) spectra collected are in good agreement with those predicted to be lowest-energy by DFT. The spectra for the group I complexes contain six resolved absorptions that can be attributed to amide I and II type and hydroxylamine N-OH vibrations. Similar absorptions are observed for the group II cation complexes, with shifts of the amide I and amide II vibrations due to the change in structure with deprotonation of the hydroxylamine group. IRMPD spectroscopy unequivocally shows that the intrinsic binding mode for the group I cations involves the O atoms of the amide carbonyl and hydroxylamine groups of Boc-hydroxylamine. A similar binding mode is preferred for the group II cations, except that in this case the metal ion is coordinated by the O atom of the deprotonated hydroxylamine group. Copyright © 2013 John Wiley & Sons, Ltd.

Metabolism Regulates the Spontaneous Firing of Substantia Nigra Pars Reticulata Neurons via KATP and Nonselective Cation Channels

PubMed Central

Lutas, Andrew; Birnbaumer, Lutz

2014-01-01

Neurons use glucose to fuel glycolysis and provide substrates for mitochondrial respiration, but neurons can also use alternative fuels that bypass glycolysis and feed directly into mitochondria. To determine whether neuronal pacemaking depends on active glucose metabolism, we switched the metabolic fuel from glucose to alternative fuels, lactate or β-hydroxybutyrate, while monitoring the spontaneous firing of GABAergic neurons in mouse substantia nigra pars reticulata (SNr) brain slices. We found that alternative fuels, in the absence of glucose, sustained SNr spontaneous firing at basal rates, but glycolysis may still be supported by glycogen in the absence of glucose. To prevent any glycogen-fueled glycolysis, we directly inhibited glycolysis using either 2-deoxyglucose or iodoacetic acid. Inhibiting glycolysis in the presence of alternative fuels lowered SNr firing to a slower sustained firing rate. Surprisingly, we found that the decrease in SNr firing was not mediated by ATP-sensitive potassium (KATP) channel activity, but if we lowered the perfusion flow rate or omitted the alternative fuel, KATP channels were activated and could silence SNr firing. The KATP-independent slowing of SNr firing that occurred with glycolytic inhibition in the presence of alternative fuels was consistent with a decrease in a nonselective cationic conductance. Although mitochondrial metabolism alone can prevent severe energy deprivation and KATP channel activation in SNr neurons, active glucose metabolism appears important for keeping open a class of ion channels that is crucial for the high spontaneous firing rate of SNr neurons. PMID:25471572

Wall to membrane linkers, stretch activated channels, and the detection of tension, voltage, temperature, auxin, and pH

NASA Technical Reports Server (NTRS)

Pickard, B. G.

1992-01-01

Introduction. The higher plant is a heterogeneous, mechanically prestressed structure continually subject to shifting forces. When a cell grows in a plant at gravitropic equilibrium, it must create localized maxima of shear in walls of neighboring cells. Such mechanical stress and strain are likely detected in a variety of ways. However, tension-sensitive ion channels are of particular interest because it appears that they are elaborately evolved for sensory function. We hypothesize that 1) the patchy patterns of high shear are focused via wall-to-membrane linkers onto the plasma membrane, where 2) they are translated by mechanosensory cation channels into corresponding patterns of high cytosolic Ca2+, which 3) initiate local enhancement of wall expansion. Further, we hypothesize that the local promotion of enhancement is achieved at least in part by local intensification of auxin transport across the plasma membrane. By implication, when an organ is asymmetrically pressed, rubbed, or bent or when it is displaced in the gravitational field, the net asymmetry of shear stress occurring across the organ would lead to asymmetric redistribution of auxin and corrective asymmetric growth. We shall describe a representative mechanosensitive Ca(2+) -selective cation channel (MCaC) with susceptibilities to xenobiotics implicating it as a force transducer in thigmo- and gravitropism. Then, we shall consider whether a putative wall-to-membrane linker (WML) could be a key feature of the molecular architecture permitting the stress distributed in the wall system to be focused on the channels.

Metal adsorption onto bacterial surfaces: development of a predictive approach

NASA Astrophysics Data System (ADS)

Fein, Jeremy B.; Martin, Aaron M.; Wightman, Peter G.

2001-12-01

Aqueous metal cation adsorption onto bacterial surfaces can be successfully modeled by means of a surface complexation approach. However, relatively few stability constants for metal-bacterial surface complexes have been measured. In order to determine the bacterial adsorption behavior of cations that have not been studied in the laboratory, predictive techniques are required that enable estimation of the stability constants of bacterial surface complexes. In this study, we use a linear free-energy approach to compare previously measured stability constants for Bacillus subtilis metal-carboxyl surface complexes with aqueous metal-organic acid anion stability constants. The organic acids that we consider are acetic, oxalic, citric, and tiron. We add to this limited data set by conducting metal adsorption experiments onto Bacillus subtilis, determining bacterial surface stability constants for Co, Nd, Ni, Sr, and Zn. The adsorption behavior of each of the metals studied here was described well by considering metal-carboxyl bacterial surface complexation only, except for the Zn adsorption behavior, which required carboxyl and phosphoryl complexation to obtain a suitable fit to the data. The best correlation between bacterial carboxyl surface complexes and aqueous organic acid anion stability constants was obtained by means of metal-acetate aqueous complexes, with a linear correlation coefficient of 0.97. This correlation applies only to unhydrolyzed aqueous cations and only to carboxyl binding of those cations, and it does not predict the binding behavior under conditions where metal binding to other bacterial surface site types occurs. However, the relationship derived in this study permits estimation of the carboxyl site adsorption behavior of a wide range of aqueous metal cations for which there is an absence of experimental data. This technique, coupled with the observation of similar adsorption behaviors across bacterial species (Yee and Fein, 2001), enables estimation of the effects of bacterial adsorption on metal mobilities for a large number of environmental and geologic applications.

Studies on the interactions between purified bovine caseins and alkaline-earth-metalions

PubMed Central

Dickson, I. R.; Perkins, D. J.

1971-01-01

1. Alkaline-earth-metal cations at low concentrations form soluble complexes with bovine caseins. The relative order of binding capacities is: Mg2+>Ca2+>Ba2+>Sr2+. 2. The cations interact with both free ionized carboxyl groups of aspartic acid and glutamic acid and with monoester phosphate groups covalently bound to serine and threonine; at low concentrations of the cations interactions are predominantly with the phosphate groups. 3. The order of binding capacities for purified components of the casein complex is: αs1-casein>β-casein>κ-casein. PMID:5166590

Structure of 1:1 complex of 1-naphthylmethyl ester of monensin A with sodium perchlorate studied by X-ray, FT-IR and ab initio methods

NASA Astrophysics Data System (ADS)

Huczyński, Adam; Janczak, Jan; Brzezinski, Bogumil

2012-12-01

A new crystalline complex formed between 1-naphthylmethyl ester of the naturally occurring antibiotic - monensin A (MON8) with sodium perchlorate has been obtained and studied using X-ray crystallography and FT-IR spectroscopy. The X-ray data of the complex show that MON8 forms a pseudo-cyclic structure stabilised by one weak intramolecular hydrogen bond and the sodium cation co-ordinated by two oxygen atoms of hydroxyl groups and four etheric oxygen atoms in the hydrophilic sphere. Within this structure the oxygen atoms of the ester groups are not involved in the coordination of sodium cation. In contrast to the solid state structure of the complex, in acetonitrile solution an equilibrium between two structures, in which the oxygen atom of the carbonyl ester group is either involved or not involved in the complexation of the sodium cation, is found. In acetonitrile this equilibrium is shifted towards the latter structure i.e. the structure existing in the solid state. The gas-phase structure of [MON8sbnd Na]+ cation as shown the ab initio MO calculations is comparable with the crystal one. Three-dimensional molecular electrostatic potential calculated for the neutral MON8 and [MON8sbnd Na]+ molecules is helpful for understanding the structural aspects of the sodium complex formation.

Energy-resolved collision-induced dissociation studies of 1,10-phenanthroline complexes of the late first-row divalent transition metal cations: determination of the third sequential binding energies.

PubMed

Nose, Holliness; Chen, Yu; Rodgers, M T

2013-05-23

The third sequential binding energies of the late first-row divalent transition metal cations to 1,10-phenanthroline (Phen) are determined by energy-resolved collision-induced dissociation (CID) techniques using a guided ion beam tandem mass spectrometer. Five late first-row transition metal cations in their +2 oxidation states are examined including: Fe(2+), Co(2+), Ni(2+), Cu(2+), and Zn(2+). The kinetic energy dependent CID cross sections for loss of an intact Phen ligand from the M(2+)(Phen)3 complexes are modeled to obtain 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of the internal energy of the complexes, multiple ion-neutral collisions, and unimolecular decay rates. Electronic structure theory calculations at the B3LYP, BHandHLYP, and M06 levels of theory are employed to determine the structures and theoretical estimates for the first, second, and third sequential BDEs of the M(2+)(Phen)x complexes. B3LYP was found to deliver results that are most consistent with the measured values. Periodic trends in the binding of these complexes are examined and compared to the analogous complexes to the late first-row monovalent transition metal cations, Co(+), Ni(+), Cu(+), and Zn(+), previously investigated.

Substance P Activates Ca2+-Permeable Nonselective Cation Channels through a Phosphatidylcholine-Specific Phospholipase C Signaling Pathway in nNOS-Expressing GABAergic Neurons in Visual Cortex.

PubMed

Endo, Toshiaki; Yanagawa, Yuchio; Komatsu, Yukio

2016-02-01

To understand the functions of the neocortex, it is essential to characterize the properties of neurons constituting cortical circuits. Here, we focused on a distinct group of GABAergic neurons that are defined by a specific colocalization of intense labeling for both neuronal nitric oxide synthase (nNOS) and substance P (SP) receptor [neurokinin 1 (NK1) receptors]. We investigated the mechanisms of the SP actions on these neurons in visual cortical slices obtained from young glutamate decarboxylase 67-green fluorescent protein knock-in mice. Bath application of SP induced a nonselective cation current leading to depolarization that was inhibited by the NK1 antagonists in nNOS-immunopositive neurons. Ruthenium red and La(3+), transient receptor potential (TRP) channel blockers, suppressed the SP-induced current. The SP-induced current was mediated by G proteins and suppressed by D609, an inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC), but not by inhibitors of phosphatidylinositol-specific PLC, adenylate cyclase or Src tyrosine kinases. Ca(2+) imaging experiments under voltage clamp showed that SP induced a rise in intracellular Ca(2+) that was abolished by removal of extracellular Ca(2+) but not by depletion of intracellular Ca(2+) stores. These results suggest that SP regulates nNOS neurons by activating TRP-like Ca(2+)-permeable nonselective cation channels through a PC-PLC-dependent signaling pathway. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

A mutation in the extracellular domain of the α7 nAChR reduces calcium permeability.

PubMed

Colón-Sáez, José O; Yakel, Jerrel L

2014-08-01

The α7 neuronal nicotinic acetylcholine receptor (nAChR) displays the highest calcium permeability among the different subtypes of nAChRs expressed in the mammalian brain and can impact cellular events including neurotransmitter release, second messenger cascades, cell survival, and apoptosis. The selectivity for cations in nAChRs is thought to be achieved in part by anionic residues which are located on either side of the channel mouth and increase relative cationic concentration. Mutagenesis studies have improved our understanding of the role of the second transmembrane domain and the intracellular loop of the channel in ion selectivity. However, little is known about the influence that the extracellular domain (ECD) plays in ion permeation. In the α7 nAChR, it has been found that the ECD contains a ring of ten aspartates (two per subunit) that is believed to face the lumen of the pore and could attract cations for permeation. Using mutagenesis and a combination of electrophysiology and imaging techniques, we tested the possible involvement of these aspartate residues in the calcium permeability of the rat α7 nAChR. We found that one of these residues (the aspartate at position 44) appears to be essential since mutating it to alanine resulted in a decrease in amplitude for both whole cell and single-channel responses and in the complete disappearance of detectable calcium changes in most cells, which indicates that the ECD of the α7 nAChR plays a key role in calcium permeation.

A mutation in the extracellular domain of the α7 nAChR reduces calcium permeability

PubMed Central

Colón-Sáez, José O.

2013-01-01

The α7 neuronal nicotinic acetylcholine receptor (nAChR) displays the highest calcium permeability among the different subtypes of nAChRs expressed in the mammalian brain and can impact cellular events including neurotransmitter release, second messenger cascades, cell survival, and apoptosis. The selectivity for cations in nAChRs is thought to be achieved in part by anionic residues which are located on either side of the channel mouth and increase relative cationic concentration. Mutagenesis studies have improved our understanding of the role of the second transmembrane domain and the intracellular loop of the channel in ion selectivity. However, little is known about the influence that the extracellular domain (ECD) plays in ion permeation. In the α7 nAChR, it has been found that the ECD contains a ring of ten aspartates (two per subunit) that is believed to face the lumen of the pore and could attract cations for permeation. Using mutagenesis and a combination of electrophysiology and imaging techniques, we tested the possible involvement of these aspartate residues in the calcium permeability of the rat α7 nAChR. We found that one of these residues (the aspartate at position 44) appears to be essential since mutating it to alanine resulted in a decrease in amplitude for both whole cell and single-channel responses and in the complete disappearance of detectable calcium changes in most cells, which indicates that the ECD of the α7 nAChR plays a key role in calcium permeation. PMID:24177919

Expression and distribution of the transient receptor potential cationic channel ankyrin 1 (TRPA1) in the human vagina.

PubMed

Ückert, S; Sonnenberg, J E; Albrecht, K; Kuczyk, M A; Hedlund, P

2015-01-01

The transient receptor potential cationic channel type A1 (TRPA1), belonging to a superfamily of cationic membrane channels, has been suggested to act as mechano- and pain sensor and, thus, to play a role in neurotransmission in the human body, including the urogenital tract. While the expression of TRPA1 has been investigated in a variety of tissues, up until today, no study has addressed the expression and distribution in the female genital tract. The present study aimed to investigate the expression and distribution of TRPA1 protein in human vaginal tissue. Reverse transcriptase PCR (RT-PCR) was applied in order to identify messenger ribonuleic acid specifically encoding for TRPA/A1. The distribution of TRPA1 in relation to the neuronal nitric oxide synthase (nNOS) and the signaling peptide calcitonin gene-related peptide (CGRP) was examined by means of immunohistochemical methods (double-antibody technique, laser fluorescence microscopy). RT-PCR analysis revealed the expression of mRNA encoding sequences specific for TRPA in the vaginal wall and epithelium. Immunostaining related to TRPA1 was observed in the basal epithelium and in slender varicose nerve fibers transversing the subepithelial and stromal space of the vaginal sections. In addition, these fibers presented immunoreactivity specific for nNOS or CGRP. The smooth musculature of the vaginal wall and small vessels interspersing the tissue did not present signals related to TRPA1. The findings indicate that TRPA1 might be involved in afferent neurotransmission in the vagina and work synergistically together with the nitric oxide/cyclic guanosine monophosphate pathway.

CNT loading into cationic cholesterol suspensions show improved DNA binding and serum stability and ability to internalize into cancer cells

NASA Astrophysics Data System (ADS)

Chhikara, Bhupender S.; Misra, Santosh K.; Bhattacharya, Santanu

2012-02-01

Methods which disperse single-walled carbon nanotubes (SWNTs) in water as ‘debundled’, while maintaining their unique physical properties are highly useful. We present here a family of cationic cholesterol compounds (Chol+) {Cholest-5en-3β-oxyethyl pyridinium bromide (Chol-PB+), Cholest-5en-3β-oxyethyl N-methyl pyrrolidinium bromide (Chol-MPB+), Cholest-5en-3β-oxyethyl N-methyl morpholinium bromide (Chol-MMB+) and Cholest-5en-3β-oxyethyl diazabicyclo octanium bromide (Chol-DOB+)}. Each of these could be easily dispersed in water. The resulting cationic cholesterol (Chol+) suspensions solubilized single-walled carbon nanotubes (SWCNTs) by the non-specific physical adsorption of Chol+ to form stable, transparent, dark aqueous suspensions at room temperature. Electron microscopy reveals the existence of highly segregated CNTs in these samples. Zeta potential measurements showed an increase in potential of cationic cholesterol aggregates on addition of CNTs. The CNT-Chol+ suspensions were capable of forming stable complexes with genes (DNA) efficiently. The release of double-helical DNA from such CNT-Chol+ complexes could be induced upon the addition of anionic micellar solution of SDS. Furthermore, the CNT-based DNA complexes containing cationic cholesterol aggregates showed higher stability in fetal bovine serum media at physiological conditions. Confocal studies confirm that CNT-Chol+ formulations adhere to HeLa cell surfaces and get internalized more efficiently than the cationic cholesterol suspensions alone (devoid of any CNTs). These cationic cholesterol-CNT suspensions therefore appear to be a promising system for further use in biological applications.

Natural Indices for the Chemical Hardness/Softness of Metal Cations and Ligands

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

Xu, Huifang; Xu, David C.; Wang, Yifeng

Quantitative understanding of reactivity and stability for a chemical species is fundamental to chemistry. The concept has undergone many changes and additions throughout the history of chemistry, stemming from the ideas such as Lewis acids and bases. For a given complexing ligand (Lewis base) and a group of isovalent metal cations (Lewis acids), the stability constants of metal–ligand (ML) complexes can simply correlate to the known properties of metal ions [ionic radii (r Mn+), Gibbs free energy of formation (ΔG° f,Mn+), and solvation energy (ΔG° s,Mn+)] by 2.303RT log K ML = (α* MLΔG° f,Mn+ – β* MLr Mn+ +more » γ* MLΔG° s,Mn+ – δ* ML), where the coefficients (α* ML, β* ML, γ* ML, and intercept δ* ML) are determined by fitting the equation to the existing experimental data. Coefficients β* ML and γ* ML have the same sign and are in a linear relationship through the origin. Gibbs free energies of formation of cations (ΔG° f,Mn+) are found to be natural indices for the softness or hardness of metal cations, with positive values corresponding to soft acids and negative values to hard acids. The coefficient α* ML is an index for the softness or hardness of a complexing ligand. Proton (H +) with the softness index of zero is a unique acid that has strong interactions with both soft and hard bases. The stability energy resulting from the acid–base interactions is determined by the term α* MLΔG° f,Mn+; a positive product of α* ML and ΔG° f,Mn+ indicates that the acid–base interaction between the metal cation and the complexing ligand stabilizes the complex. The terms β* MLr Mn+ and γ* MLΔG° s,Mn+, which are related to ionic radii of metal cations, represent the steric and solvation effects of the cations. The new softness indices proposed here will help to understand the interactions of ligands (Lewis bases) with metal cations (Lewis acids) and provide guidelines for engineering materials with desired chemical reactivity and selectivity. As a result, the new correlation can also enhance our ability for predicting the speciation, mobility, and toxicity of heavy metals in the earth environments and biological systems.« less

Natural Indices for the Chemical Hardness/Softness of Metal Cations and Ligands

DOE PAGES

Xu, Huifang; Xu, David C.; Wang, Yifeng

2017-10-26

Quantitative understanding of reactivity and stability for a chemical species is fundamental to chemistry. The concept has undergone many changes and additions throughout the history of chemistry, stemming from the ideas such as Lewis acids and bases. For a given complexing ligand (Lewis base) and a group of isovalent metal cations (Lewis acids), the stability constants of metal–ligand (ML) complexes can simply correlate to the known properties of metal ions [ionic radii (r Mn+), Gibbs free energy of formation (ΔG° f,Mn+), and solvation energy (ΔG° s,Mn+)] by 2.303RT log K ML = (α* MLΔG° f,Mn+ – β* MLr Mn+ +more » γ* MLΔG° s,Mn+ – δ* ML), where the coefficients (α* ML, β* ML, γ* ML, and intercept δ* ML) are determined by fitting the equation to the existing experimental data. Coefficients β* ML and γ* ML have the same sign and are in a linear relationship through the origin. Gibbs free energies of formation of cations (ΔG° f,Mn+) are found to be natural indices for the softness or hardness of metal cations, with positive values corresponding to soft acids and negative values to hard acids. The coefficient α* ML is an index for the softness or hardness of a complexing ligand. Proton (H +) with the softness index of zero is a unique acid that has strong interactions with both soft and hard bases. The stability energy resulting from the acid–base interactions is determined by the term α* MLΔG° f,Mn+; a positive product of α* ML and ΔG° f,Mn+ indicates that the acid–base interaction between the metal cation and the complexing ligand stabilizes the complex. The terms β* MLr Mn+ and γ* MLΔG° s,Mn+, which are related to ionic radii of metal cations, represent the steric and solvation effects of the cations. The new softness indices proposed here will help to understand the interactions of ligands (Lewis bases) with metal cations (Lewis acids) and provide guidelines for engineering materials with desired chemical reactivity and selectivity. As a result, the new correlation can also enhance our ability for predicting the speciation, mobility, and toxicity of heavy metals in the earth environments and biological systems.« less

TRP ion channels in thermosensation, thermoregulation and metabolism

PubMed Central

Wang, Hong; Siemens, Jan

2015-01-01

In humans, the TRP superfamily of cation channels includes 27 related molecules that respond to a remarkable variety of chemical and physical stimuli. While physiological roles for many TRP channels remain unknown, over the past years several have been shown to function as molecular sensors in organisms ranging from yeast to humans. In particular, TRP channels are now known to constitute important components of sensory systems, where they participate in the detection or transduction of osmotic, mechanical, thermal, or chemosensory stimuli. We here summarize our current understanding of the role individual members of this versatile receptor family play in thermosensation and thermoregulation, and also touch upon their immerging role in metabolic control. PMID:27227022

[The nature of pacemaker activity].

PubMed

Kabakov, A Iu

1991-01-01

A general equation of the membrane resting potential (RP) has been derived for closed cell membrane (CM) model. It is shown that Na,K-ATPase of cardiomyocytes is in the antielectrogenic phase. A hypothesis is proposed: a pacemaker cell is an excitable cell, which has RP corresponding to the given activity of Na,K-ATPase and non-activated cationic conductivities of CM higher than the activation threshold of Na-channels. The equation of the equipotential levels of the membrane RP on the surface of the cationic conductivities has been derived. It is shown that the substances (e. g. neuromediator) that change the membrane cation permeability are able to depolarize or to hyperpolarize CM. The direction of polarization is dependent on the state of the cell electrogenic system. The following factors promote the hyperpolarizing effect of the magnifying cation permeability substances: 1) high activity of Na,K-ATPase, 2) low background cation permeability of CM (among their number the integrity of CM) and 3) high ratio of the potassium permeability alteration in respect to that of sodium which is evoked by the substance (delta gK/delta gNa).

Anion channels in the sea urchin sperm plasma membrane.

PubMed

Morales, E; de la Torre, L; Moy, G W; Vacquier, V D; Darszon, A

1993-10-01

Ionic fluxes in sea urchin sperm plasma membrane regulate cell motility and the acrosome reaction (AR). Although cationic channels mediate some of the ionic movements, little is known about anion channels in these cells. The fusion of sperm plasma membranes into lipid bilayers allowed identification of a 150 pS anion channel. This anion channel was enriched from detergent-solubilized sperm plasma membranes using a wheat germ agglutinin Sepharose column. Vesicles formed from this preparation were fused into black lipid membranes (BLM), yielding single channel anion-selective activity with the properties of those found in the sperm membranes. The following anion selectivity sequence was found: NO3- > CNS- > Br- > Cl-. This anion channel has a high open probability at the holding potentials tested, it is partially blocked by 4,4'-diisothiocyano-2,2'-stilbendisulfonic acid (DIDS), and it often displays substates. The sperm AR was also inhibited by DIDS.

Distinct properties of Ca2+–calmodulin binding to N- and C-terminal regulatory regions of the TRPV1 channel

PubMed Central

Lau, Sze-Yi; Procko, Erik

2012-01-01

Transient receptor potential (TRP) vanilloid 1 (TRPV1) is a molecular pain receptor belonging to the TRP superfamily of nonselective cation channels. As a polymodal receptor, TRPV1 responds to heat and a wide range of chemical stimuli. The influx of calcium after channel activation serves as a negative feedback mechanism leading to TRPV1 desensitization. The cellular calcium sensor calmodulin (CaM) likely participates in the desensitization of TRPV1. Two CaM-binding sites are identified in TRPV1: the N-terminal ankyrin repeat domain (ARD) and a short distal C-terminal (CT) segment. Here, we present the crystal structure of calcium-bound CaM (Ca2+–CaM) in complex with the TRPV1-CT segment, determined to 1.95-Å resolution. The two lobes of Ca2+–CaM wrap around a helical TRPV1-CT segment in an antiparallel orientation, and two hydrophobic anchors, W787 and L796, contact the C-lobe and N-lobe of Ca2+–CaM, respectively. This structure is similar to canonical Ca2+–CaM-peptide complexes, although TRPV1 contains no classical CaM recognition sequence motif. Using structural and mutational studies, we established the TRPV1 C terminus as a high affinity Ca2+–CaM-binding site in both the isolated TRPV1 C terminus and in full-length TRPV1. Although a ternary complex of CaM, TRPV1-ARD, and TRPV1-CT had previously been postulated, we found no biochemical evidence of such a complex. In electrophysiology studies, mutation of the Ca2+–CaM-binding site on TRPV1-ARD abolished desensitization in response to repeated application of capsaicin, whereas mutation of the Ca2+–CaM-binding site in TRPV1-CT led to a more subtle phenotype of slowed and reduced TRPV1 desensitization. In summary, our results show that the TRPV1-ARD is an important mediator of TRPV1 desensitization, whereas TRPV1-CT has higher affinity for CaM and is likely involved in separate regulatory mechanisms. PMID:23109716

Distinct properties of Ca 2+-calmodulin binding to N- and C-terminal regulatory regions of the TRPV1 channel

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

Lau, Sze-Yi; Procko, Erik; Gaudet, Rachelle

2012-11-01

Transient receptor potential (TRP) vanilloid 1 (TRPV1) is a molecular pain receptor belonging to the TRP superfamily of nonselective cation channels. As a polymodal receptor, TRPV1 responds to heat and a wide range of chemical stimuli. The influx of calcium after channel activation serves as a negative feedback mechanism leading to TRPV1 desensitization. The cellular calcium sensor calmodulin (CaM) likely participates in the desensitization of TRPV1. Two CaM-binding sites are identified in TRPV1: the N-terminal ankyrin repeat domain (ARD) and a short distal C-terminal (CT) segment. Here, we present the crystal structure of calcium-bound CaM (Ca 2+–CaM) in complex withmore » the TRPV1-CT segment, determined to 1.95-Å resolution. The two lobes of Ca 2+–CaM wrap around a helical TRPV1-CT segment in an antiparallel orientation, and two hydrophobic anchors, W787 and L796, contact the C-lobe and N-lobe of Ca 2+–CaM, respectively. This structure is similar to canonical Ca 2+–CaM-peptide complexes, although TRPV1 contains no classical CaM recognition sequence motif. Using structural and mutational studies, we established the TRPV1 C terminus as a high affinity Ca 2+–CaM-binding site in both the isolated TRPV1 C terminus and in full-length TRPV1. Although a ternary complex of CaM, TRPV1-ARD, and TRPV1-CT had previously been postulated, we found no biochemical evidence of such a complex. In electrophysiology studies, mutation of the Ca 2+–CaM-binding site on TRPV1-ARD abolished desensitization in response to repeated application of capsaicin, whereas mutation of the Ca 2+–CaM-binding site in TRPV1-CT led to a more subtle phenotype of slowed and reduced TRPV1 desensitization. In summary, our results show that the TRPV1-ARD is an important mediator of TRPV1 desensitization, whereas TRPV1-CT has higher affinity for CaM and is likely involved in separate regulatory mechanisms.« less

Mechanism of host-guest complexation by cucurbituril.

PubMed

Márquez, César; Hudgins, Robert R; Nau, Werner M

2004-05-12

The factors affecting host-guest complexation between the molecular container compound cucurbit[6]uril (CB6) and various guests in aqueous solution are studied, and a detailed complexation mechanism in the presence of cations is derived. The formation of the supramolecular complex is studied in detail for cyclohexylmethylammonium ion as guest. The kinetics and thermodynamics of complexation is monitored by NMR as a function of temperature, salt concentration, and cation size. The binding constants and the ingression rate constants decrease with increasing salt concentration and cation-binding constant, in agreement with a competitive binding of the ammonium site of the guest and the metal cation with the ureido carbonyl portals of CB6. Studies as a function of guest size indicate that the effective container volume of the CB6 cavity is approximately 105 A(3). It is suggested that larger guests are excluded for two reasons: a high activation barrier for ingression imposed by the tight CB6 portals and a destabilization of the complex due to steric repulsion inside. For example, in the case of the nearly spherical azoalkane homologues 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH, volume ca. 96 A(3)) and 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO, volume ca. 110 A(3)), the former forms the CB6 complex promptly with a sizable binding constant (1300 M(-1)), while the latter does not form a complex even after several months at optimized complexation conditions. Molecular mechanics calculations are performed for several CB6/guest complexes. A qualitative agreement is found between experimental and calculated activation energies for ingression as a function of both guest size and state of protonation. The potential role of constrictive binding by CB6 is discussed.

Bumetanide hyperpolarizes Madin-Darby canine kidney cells and enhances cellular gentamicin uptake via elevating cytosolic Ca2+ thus facilitating intermediate conductance Ca2+-activated potassium channels

PubMed Central

Wang, Tian; Yang, Yu-qin; Karasawa, Takatoshi; Wang, Qi; Phillips, Amanda; Guan, Bing-Cai; Ma, Ke-Tao; Jiang, Meiyan; Xie, Ding-Hua; Steyger, Peter S.; Jiang, Zhi-Gen

2012-01-01

Loop diuretics such as bumetanide and furosemide enhance aminoglycoside ototoxicity when co-administered to patients and animal models. The underlying mechanism(s) is poorly understood. We investigated the effect of these diuretics on cellular uptake of aminoglycosides, using Texas Red-tagged gentamicin (GTTR), and intracellular/whole-cell recordings of Madin-Darby Canine kidney (MDCK) cells. We found that bumetanide and furosemide concentration-dependently enhanced cytoplasmic GTTR fluorescence by ~60%. This enhancement was suppressed by La3+, a non-selective cation channel (NSCC) blocker, and by K+ channel blockers Ba2+ and clotrimazole, but not by tetraethylammonium (TEA), 4-aminopyridine (4-AP) or glipizide, nor by Cl− channel blockers diphenylamine-2-carboxylic acid (DPC), niflumic acid (NFA), and CFTRinh-172. Bumetanide and furosemide hyperpolarized MDCK cells by ~14 mV, increased whole-cell I/V slope conductance; the bumetanide-induced net current I/V showed a reversal potential (Vr) ~−80 mV. Bumetanide-induced hyperpolarization and I/V change was suppressed by Ba2+ or clotrimazole, and absent in elevated [Ca2+]i, but not affected by apamin, 4-AP, TEA, glipizide, DPC, NFA or CFTRinh-172. Bumetanide and furosemide stimulated a surge of Fluo-4-indicated cytosolic Ca2+. Ba2+ and clotrimazole alone depolarized cells by ~18 mV and reduced I/V slope with a net current Vr near −85 mV, and reduced GTTR uptake by ~20%. La3+ alone hyperpolarized the cells by ~−14 mV, reduced the I/V slope with a net current Vr near −10 mV, and inhibited GTTR uptake by ~50%. In the presence of La3+, bumetanide caused negligible potential or I/V change. We conclude that NSCCs constitute a major cell entry pathway for cationic aminoglycosides; bumetanide enhances aminoglycoside uptake by hyperpolarizing cells that increases cation influx driving force; and bumetanide-induced hyperpolarization is caused by elevating the intracellular Ca2+ and thus a facilitation of the intermediate conductance Ca2+-activated K+ channels. PMID:23109177

Bumetanide hyperpolarizes madin-darby canine kidney cells and enhances cellular gentamicin uptake by elevating cytosolic Ca(2+) thus facilitating intermediate conductance Ca(2+)--activated potassium channels.

PubMed

Wang, Tian; Yang, Yu-Qin; Karasawa, Takatoshi; Wang, Qi; Phillips, Amanda; Guan, Bing-Cai; Ma, Ke-Tao; Jiang, Meiyan; Xie, Ding-Hua; Steyger, Peter S; Jiang, Zhi-Gen

2013-04-01

Loop diuretics such as bumetanide and furosemide enhance aminoglycoside ototoxicity when co-administered to patients and animal models. The underlying mechanism(s) is poorly understood. We investigated the effect of these diuretics on cellular uptake of aminoglycosides, using Texas Red-tagged gentamicin (GTTR), and intracellular/whole-cell recordings of Madin-Darby canine kidney (MDCK) cells. We found that bumetanide and furosemide dose-dependently enhanced cytoplasmic GTTR fluorescence by ~60 %. This enhancement was suppressed by La(3+), a non-selective cation channel (NSCC) blocker, and by K(+) channel blockers Ba(2+) and clotrimazole, but not by tetraethylammonium (TEA), 4-aminopyridine (4-AP) or glipizide, nor by Cl(-) channel blockers diphenylamine-2-carboxylic acid (DPC), niflumic acid (NFA), and CFTRinh-172. Bumetanide and furosemide hyperpolarized MDCK cells by ~14 mV, increased whole-cell I/V slope conductance; the bumetanide-induced net current I/V showed a reversal potential (V r) ~-80 mV. Bumetanide-induced hyperpolarization and I/V change was suppressed by Ba(2+) or clotrimazole, and absent in elevated [Ca(2+)]i, but was not affected by apamin, 4-AP, TEA, glipizide, DPC, NFA, or CFTRinh-172. Bumetanide and furosemide stimulated a surge of Fluo-4-indicated cytosolic Ca(2+). Ba(2+) and clotrimazole alone depolarized cells by ~18 mV and reduced I/V slope with a net current V r near -85 mV, and reduced GTTR uptake by ~20 %. La(3+) alone hyperpolarized the cells by ~-14 mV, reduced the I/V slope with a net current V r near -10 mV, and inhibited GTTR uptake by ~50 %. In the presence of La(3+), bumetanide-caused negligible change in potential or I/V. We conclude that NSCCs constitute a major cell entry pathway for cationic aminoglycosides; bumetanide enhances aminoglycoside uptake by hyperpolarizing cells that increases the cation influx driving force; and bumetanide-induced hyperpolarization is caused by elevating intracellular Ca(2+) and thus facilitating activation of the intermediate conductance Ca(2+)-activated K(+) channels.

Electronic structure of the [MNH2]+ (M = Sc-Cu) complexes.

PubMed

Hendrickx, Marc F A; Clima, Sergiu

2006-11-23

B3LYP geometry optimizations for the [MNH2]+ complexes of the first-row transition metal cations (Sc+-Cu+) were performed. Without any exception the ground states of these unsaturated amide complexes were calculated to possess planar geometries. CASPT2 binding energies that were corrected for zero-point energies and including relativistic effects show a qualitative trend across the series that closely resembles the experimental observations. The electronic structures for the complexes of the early and middle transition metal cations (Sc+-Co+) differ from the electronic structures derived for the complexes of the late transition metal cations (Ni+ and Cu+). For the former complexes the relative higher position of the 3d orbitals above the singly occupied 2p(pi) HOMO of the uncoordinated NH2 induces an electron transfer from the 3d shell to 2p(pi). The stabilization of the 3d orbitals from the left to the right along the first-row transition metal series causes these orbitals to become situated below the HOMO of the NH2 ligand for Ni+ and Cu+, preventing a transfer from occurring in the [MNH2]+ complexes of these metal cations. Analysis of the low-lying states of the amide complexes revealed a rather unique characteristic of their electronic structures that was found across the entire series. Rather exceptionally for the whole of chemistry, pi-type interactions were calculated to be stronger than the corresponding sigma-type interactions. The origin of this extraordinary behavior can be ascribed to the low-lying sp2 lone pair orbital of the NH2 ligand with respect to the 3d level.

Structure-activity relationship of carbamate-linked cationic lipids bearing hydroxyethyl headgroup for gene delivery.

PubMed

Zhi, Defu; Zhang, Shubiao; Qureshi, Farooq; Zhao, Yinan; Cui, Shaohui; Wang, Bing; Chen, Huiying; Yang, Baoling; Zhao, Defeng

2013-12-01

A novel series of carbamate-linked cationic lipids containing hydroxyl headgroup were synthesized and included in formulations for transfection assays. The DNA-lipid complexes were characterized for their ability to bind DNA, their size, ζ-potential and cytotoxicity. Compared with our previously reported cationic transfection lipid DDCDMA lacking the hydroxyl group and the commercially available, these cationic liposomes exhibited relatively higher transfection efficiency. Copyright © 2013 Elsevier B.V. All rights reserved.

A uniquely adaptable pore is consistent with NALCN being an ion sensor

PubMed Central

Senatore, Adriano; Spafford, J. David

2013-01-01

NALCN is an intriguing, orphan ion channel among the 4x6TM family of related voltage-gated cation channels, sharing a common architecture of four homologous domains consisting of six transmembrane helices, separated by three cytoplasmic linkers and delimited by N and C-terminal ends. NALCN is one of the shortest 4x6TM family members, lacking much of the variation that provides the diverse palate of gating features, and tissue specific adaptations of sodium and calcium channels. NALCN’s most distinctive feature is that that it possesses a highly adaptable pore with a calcium-like EEEE selectivity filter in radially symmetrical animals and a more sodium-like EEKE or EKEE selectivity filter in bilaterally symmetrical animals including vertebrates. Two lineages of animals evolved alternative calcium-like EEEE and sodium-like EEKE / EKEE pores, spliced to regulate NALCN functions in differing cellular environments, such as muscle (heart and skeletal) and secretory tissue (brain and glands), respectively. A highly adaptable pore in an otherwise conserved ion channel in the 4x6TM channel family is not consistent with a role for NALCN in directly gating a significant ion conductance that can be either sodium ions or calcium ions. NALCN was proposed to be an expressible Gd3+-sensitive, NMDG+-impermeant, non-selective and ohmic leak conductance in HEK-293T cells, but we were unable to distinguish these reported currents from leaky patch currents (ILP) in control HEK-293T cells. We suggest that NALCN functions as a sensor for the much larger UNC80/UNC79 complex, in a manner consistent with the coupling mechanism known for other weakly or non-conducting 4x6TM channel sensor proteins such as Nax or Cav1.1. We propose that NALCN serves as a variable sensor that responds to calcium or sodium ion flux, depending on whether the total cellular current density is generated more from calcium-selective or sodium-selective channels. PMID:23442378

A uniquely adaptable pore is consistent with NALCN being an ion sensor.

PubMed

Senatore, Adriano; Spafford, J David

2013-01-01

NALCN is an intriguing, orphan ion channel among the 4x6TM family of related voltage-gated cation channels, sharing a common architecture of four homologous domains consisting of six transmembrane helices, separated by three cytoplasmic linkers and delimited by N and C-terminal ends. NALCN is one of the shortest 4x6TM family members, lacking much of the variation that provides the diverse palate of gating features, and tissue specific adaptations of sodium and calcium channels. NALCN's most distinctive feature is that that it possesses a highly adaptable pore with a calcium-like EEEE selectivity filter in radially symmetrical animals and a more sodium-like EEKE or EKEE selectivity filter in bilaterally symmetrical animals including vertebrates. Two lineages of animals evolved alternative calcium-like EEEE and sodium-like EEKE / EKEE pores, spliced to regulate NALCN functions in differing cellular environments, such as muscle (heart and skeletal) and secretory tissue (brain and glands), respectively. A highly adaptable pore in an otherwise conserved ion channel in the 4x6TM channel family is not consistent with a role for NALCN in directly gating a significant ion conductance that can be either sodium ions or calcium ions. NALCN was proposed to be an expressible Gd ( 3+) -sensitive, NMDG (+) -impermeant, non-selective and ohmic leak conductance in HEK-293T cells, but we were unable to distinguish these reported currents from leaky patch currents (ILP) in control HEK-293T cells. We suggest that NALCN functions as a sensor for the much larger UNC80/UNC79 complex, in a manner consistent with the coupling mechanism known for other weakly or non-conducting 4x6TM channel sensor proteins such as Nax or Cav 1.1. We propose that NALCN serves as a variable sensor that responds to calcium or sodium ion flux, depending on whether the total cellular current density is generated more from calcium-selective or sodium-selective channels.

Synthesis, activity, and structure--activity relationship studies of novel cationic lipids for DNA transfer.

PubMed

Byk, G; Dubertret, C; Escriou, V; Frederic, M; Jaslin, G; Rangara, R; Pitard, B; Crouzet, J; Wils, P; Schwartz, B; Scherman, D

1998-01-15

We have designed and synthesized original cationic lipids for gene delivery. A synthetic method on solid support allowed easy access to unsymmetrically monofunctionalized polyamine building blocks of variable geometries. These polyamine building blocks were introduced into cationic lipids. To optimize the transfection efficiency in the novel series, we have carried out structure-activity relationship studies by introduction of variable-length lipids, of variable-length linkers between lipid and cationic moiety, and of substituted linkers. We introduce the concept of using the linkers within cationic lipids molecules as carriers of side groups harboring various functionalities (side chain entity), as assessed by the introduction of a library composed of cationic entities, additional lipid chains, targeting groups, and finally the molecular probes rhodamine and biotin for cellular traffic studies. The transfection activity of the products was assayed in vitro on Hela carcinoma, on NIH3T3, and on CV1 fibroblasts and in vivo on the Lewis Lung carcinoma model. Products from the series displayed high transfection activities. Results indicated that the introduction of a targeting side chain moiety into the cationic lipid is permitted. A primary physicochemical characterization of the DNA/lipid complexes was demonstrated with this leading compound. Selected products from the series are currently being developed for preclinical studies, and the labeled lipopolyamines can be used to study the intracellular traffic of DNA/cationic lipid complexes.

Spiropyran-Isoquinoline Dyad as a Dual Chemosensor for Co(II) and In(III) Detection.

PubMed

Kho, Yong-Min; Shin, Eun Ju

2017-09-19

Spiropyran derivatives have been studied as light-regulated chemosensors for a variety of metal cations and anions, but there is little research on chemosensors that simultaneously detect multiple metal cations. In this study, a spiropyran derivative with isoquinoline, SP-IQ , was prepared and it functions investigated as a light-regulated sensor for both Co 2+ and In 3+ cations. A colorless nonfluorescent SP-IQ converts to a pink-colored fluorescent MC-IQ by UV irradiation or standing in the dark, and MC-IQ returns to SP-IQ with visible light. Upon UV irradiation with the Co 2+ cation for 7 min, the stronger absorption at 540 nm and the similar fluorescence intensity at 640 nm are observed, compared to when no metal cation is added, due to the formation of a Co 2+ complex with pink color and pink fluorescence. When placed in the dark with the In 3+ cation for 7 h, the colorless solution of SP-IQ changes to the In 3+ complex with yellow color and pink fluorescence, which shows strong absorption at 410 nm and strong fluorescence at 640 nm. Selective detection of the Co 2+ cation with UV irradiation and the In 3+ cation in the dark could be possible with SP-IQ by both absorption and fluorescence spectroscopy or by the naked eye.

Method of separating and recovering uranium and related cations from spent Purex-type systems

DOEpatents

Mailen, J.C.; Tallent, O.K.

1987-02-25

A process for separating uranium and related cations from a spent Purex-type solvent extraction system which contains degradation complexes of tributylphosphate wherein the system is subjected to an ion-exchange process prior to a sodium carbonate scrubbing step. A further embodiment comprises recovery of the separated uranium and related cations. 5 figs.

Isolation of homoleptic platinum oxyanionic complexes with doubly protonated diazacrown cation

NASA Astrophysics Data System (ADS)

Vasilchenko, Danila; Tkachev, Sergey; Baidina, Iraida; Romanenko, Galina; Korenev, Sergey

2017-02-01

Doubly protonated diazacrown ether cation (1,4,10,13-tetraoxa-7,16-diazoniacyclooctadecane DCH22+) was used for the efficient isolation of the homoleptic platinum complexes [Pt(NO3)6]2- and [Pt(C2O4)2]2- to crystalline solid phases from solutions containing mixtures of related platinum complexes. DCH22+ molecules in nitric acid solution were shown to prevent the condensation of mononuclear [Pt(H2O)n(NO3)6-n]n-2 species.

Furfural: The Unimolecular Dissociative Photoionization Mechanism of the Simplest Furanic Aldehyde.

PubMed

Winfough, Matthew; Voronova, Krisztina; Muller, Giel; Laguisma, Gabrielle; Sztáray, Bálint; Bodi, Andras; Meloni, Giovanni

2017-05-11

The unimolecular dissociation reactions of energy-selected furfural cations have been studied by imaging photoelectron photoion coincidence spectroscopy at the vacuum-ultraviolet (VUV) beamline of the Swiss Light Source. In the photon energy range of 10.9-14.5 eV, furfural ions decay by numerous fragmentation channels. Modeling the breakdown diagram yielded the 0 K appearance energies of 10.95 ± 0.10, 11.16, and 12.03 eV for the c-C 4 H 3 O-CO + (m/z = 95), c-C 4 H 4 O + (m/z = 68), and c-C 3 H 3 + (m/z = 39) fragment ions, respectively, formed by parallel dissociation channels. An internal conversion from the A″ to the A' electronic state via a conical intersection takes place along the reaction coordinate in the case of the H-loss channel (c-C 4 H 3 O-CO + formation). Quantum chemical calculations and experimental results confirmed a fast conversion to the A' state and that the rate-determining step is a tight transition state on the potential energy surface. Appearance energies were also derived for the sequential dissociation products from the furan cation, c-C 4 H 4 O + , for the formation of CH 2 CO + (m/z = 42), C 3 H 4 + (m/z = 40), and CHO + (m/z = 29) at 12.81, 12.80, and 13.34 eV, respectively. Statistical rate theory modeling of the breakdown diagram can also be used to predict the fractional ion abundances and thermal shifts in mass spectrometric pyrolysis studies to help assigning the m/z channels either to ionization of the neutrals or to dissociative ionization processes, with potential use for combustion diagnostics. The cationic geometry optimizations yielded functional-dependent spurious DFT minima and a deviating planar MP2 optimized geometry, which are briefly discussed.

Structures of the dehydrogenation products of methane activation by 5d transition metal cations revisited: Deuterium labeling and rotational contours

NASA Astrophysics Data System (ADS)

Owen, Cameron J.; Boles, Georgia C.; Chernyy, Valeriy; Bakker, Joost M.; Armentrout, P. B.

2018-01-01

A previous infrared multiple photon dissociation (IRMPD) action spectroscopy and density functional theory (DFT) study explored the structures of the [M,C,2H]+ products formed by dehydrogenation of methane by four, gas-phase 5d transition metal cations (M+ = Ta+, W+, Ir+, and Pt+). Complicating the analysis of these spectra for Ir and Pt was observation of an extra band in both spectra, not readily identified as a fundamental vibration. In an attempt to validate the assignment of these additional peaks, the present work examines the gas phase [M,C,2D]+ products of the same four metal ions formed by reaction with perdeuterated methane (CD4). As before, metal cations are formed in a laser ablation source and react with methane pulsed into a reaction channel downstream, and the resulting products are spectroscopically characterized through photofragmentation using the free-electron laser for intracavity experiments in the 350-1800 cm-1 range. Photofragmentation was monitored by the loss of D for [Ta,C,2D]+ and [W,C,2D]+ and of D2 in the case of [Pt,C,2D]+ and [Ir,C,2D]+. Comparison of the experimental spectra and DFT calculated spectra leads to structural assignments for all [M,C,2H/2D]+ systems that are consistent with previous identifications and allows a full description of the systematic spectroscopic shifts observed for deuterium labeling of these complexes, some of the smallest systems to be studied using IRMPD action spectroscopy. Further, full rotational contours are simulated for each vibrational band and explain several observations in the present spectra, such as doublet structures in several bands as well as the observed linewidths. The prominent extra bands in the [Pt,C,2D/2H]+ spectra appear to be most consistent with an overtone of the out-of-plane bending vibration of the metal carbene cation structure.

Growth and Filling Regularities of Filamentary Channels in Non-Metallic Inorganic Coatings Under Anodic Oxidation of Valve Metals. Mathematical Modeling

NASA Astrophysics Data System (ADS)

Mamaev, A. I.; Mamaeva, V. A.; Kolenchin, N. F.; Chubenko, A. K.; Kovalskaya, Ya. B.; Dolgova, Yu. N.; Beletskaya, E. Yu.

2015-12-01

Theoretical models are developed for growth and filling processes in filamentary channels of nanostructured non-metallic coatings produced by anodizing and microplasma oxidation. Graphical concentration distributions are obtained for channel-reacting anions, cations, and sparingly soluble reaction products depending on the time of electric current transmission and the length of the filamentary channel. Graphical distributions of the front moving velocity for the sparingly soluble compound are presented. The resulting model representation increases the understanding of the anodic process nature and can be used for a description and prediction of porous anodic film growth and filling. It is shown that the character of the filamentary channel growth and filling causes a variety of processes determining the textured metal - nonmetallic inorganic coating phase boundary formation.

Rational redesign of a cation···π···π stacking at cardiovascular Fbw7-Skp1 complex interface and its application for deriving self-inhibitory peptides to disrupt the complex interaction.

PubMed

Zhou, Jing; Wang, Yao-Sheng

2017-09-26

The Fbw7-Skp1 complex is an essential component in the formation and development of the mammalian cardiovascular system; the complex interaction is mediated through binding of Skp1 C-terminal peptide (qGlu-peptide) to the F-box domain of Fbw7. By visually examining the crystal structure, we identified a typical cation ···π···π stacking system at the complex interface, which is formed by the Trp1159 residue of qGlu-peptide with the Lys2299 and His2359 residues of Fbw7 F-box domain. Both hybrid quantum mechanics/molecular mechanics (QM/MM) analysis of the real domain-peptide complex and electron-correlation ab initio calculation of the stacking system model suggested that the cation···π···π plays an important role in stabilizing the complex; substitution of peptide Trp1159 residue with aromatic Phe and Tyr would not cause a considerable effect on the configuration and energetics of cation···π···π stacking system, whereas His substitution seems to largely destabilize the system. Subsequently, the qGlu-peptide was stripped from the full-length Skp1 protein to define a so-called self-inhibitory peptide, which may rebind to the domain-peptide complex interface and thus disrupt the complex interaction. Fluorescence polarization (FP) assays revealed that the Trp1159Phe and Trp1159Tyr variants have a comparable or higher affinity (K d  = 41 and 62 μM) than the wild-type qGlu-peptide (K d  = 56 μM), while the Trp1159His mutation would largely impair the binding potency of qGlu-peptide to Fbw7 F-box domain (K d  = 280 μM), confirming that the cation···π···π confers both affinity and specificity to the domain-peptide recognition, which can be reshaped by rational molecular design of the nonbonded interaction system. Graphical abstract Stereoview of the complex structure of Fbw7 with Skp1 (PDB: 2ovp), where the Trp1159 residue of Skp1 qGlu-peptide can form a cation···π···π stacking system with the Lys2299 and His2359 residues of Fbw7 F-box domain.

State-dependent block of CNG channels by dequalinium.

PubMed

Rosenbaum, Tamara; Gordon-Shaag, Ariela; Islas, León D; Cooper, Jeremy; Munari, Mika; Gordon, Sharona E

2004-03-01

Cyclic nucleotide-gated (CNG) ion channels are nonselective cation channels with a high permeability for Ca(2+). Not surprisingly, they are blocked by a number of Ca(2+) channel blockers including tetracaine, pimozide, and diltiazem. We studied the effects of dequalinium, an extracellular blocker of the small conductance Ca(2+)-activated K(+) channel. We previously noted that dequalinium is a high-affinity blocker of CNGA1 channels from the intracellular side, with little or no state dependence at 0 mV. Here we examined block by dequalinium at a broad range of voltages in both CNGA1 and CNGA2 channels. We found that dequalinium block was mildly state dependent for both channels, with the affinity for closed channels 3-5 times higher than that for open channels. Mutations in the S4-S5 linker did not alter the affinity of open channels for dequalinium, but increased the affinity of closed channels by 10-20-fold. The state-specific effect of these mutations raises the question of whether/how the S4-S5 linker alters the binding of a blocker within the ion permeation pathway.

Retinal Cyclic Nucleotide-Gated Channels: From Pathophysiology to Therapy.

PubMed

Michalakis, Stylianos; Becirovic, Elvir; Biel, Martin

2018-03-07

The first step in vision is the absorption of photons by the photopigments in cone and rod photoreceptors. After initial amplification within the phototransduction cascade the signal is translated into an electrical signal by the action of cyclic nucleotide-gated (CNG) channels. CNG channels are ligand-gated ion channels that are activated by the binding of cyclic guanosine monophosphate (cGMP) or cyclic adenosine monophosphate (cAMP). Retinal CNG channels transduce changes in intracellular concentrations of cGMP into changes of the membrane potential and the Ca 2+ concentration. Structurally, the CNG channels belong to the superfamily of pore-loop cation channels and share a common gross structure with hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and voltage-gated potassium channels (KCN). In this review, we provide an overview on the molecular properties of CNG channels and describe their physiological role in the phototransduction pathways. We also discuss insights into the pathophysiological role of CNG channel proteins that have emerged from the analysis of CNG channel-deficient animal models and human CNG channelopathies. Finally, we summarize recent gene therapy activities and provide an outlook for future clinical application.

Retinal Cyclic Nucleotide-Gated Channels: From Pathophysiology to Therapy

PubMed Central

Biel, Martin

2018-01-01

The first step in vision is the absorption of photons by the photopigments in cone and rod photoreceptors. After initial amplification within the phototransduction cascade the signal is translated into an electrical signal by the action of cyclic nucleotide-gated (CNG) channels. CNG channels are ligand-gated ion channels that are activated by the binding of cyclic guanosine monophosphate (cGMP) or cyclic adenosine monophosphate (cAMP). Retinal CNG channels transduce changes in intracellular concentrations of cGMP into changes of the membrane potential and the Ca2+ concentration. Structurally, the CNG channels belong to the superfamily of pore-loop cation channels and share a common gross structure with hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and voltage-gated potassium channels (KCN). In this review, we provide an overview on the molecular properties of CNG channels and describe their physiological role in the phototransduction pathways. We also discuss insights into the pathophysiological role of CNG channel proteins that have emerged from the analysis of CNG channel-deficient animal models and human CNG channelopathies. Finally, we summarize recent gene therapy activities and provide an outlook for future clinical application. PMID:29518895

Involvement of plasma membrane-located calmodulin in the response decay of cyclic nucleotide-gated cation channel of cultured carrot cells.

PubMed

Kurosaki, F; Kaburaki, H; Nishi, A

1994-03-07

Increase in cytoplasmic cyclic AMP concentration stimulates Ca2+ influx through the cyclic AMP-gated cation channel in the plasma membrane of cultured carrot cells. However, the Ca2+ current terminated after a few minutes even in the presence of high concentrations of cyclic AMP indicating that hydrolysis of the nucleotide is not responsible for stop of the Ca2+ influx. Cyclic AMP evoked discharge of Ca2+ from inside-out sealed vesicles of carrot plasma membrane, and it was strongly inhibited when the suspension of the vesicles was supplemented with 1 microM of free Ca2+, while Ca2+ lower than 0.1 microM did not affect the Ca(2+)-release. The Ca2+ flux across plasma membrane was restored from this Ca(2+)-induced inhibition by the addition of calmodulin inhibitors or anti-calmodulin. These results suggest that Ca2+ influx initiated by the increase in intracellular cAMP in cultured carrot cells is terminated when the cytosolic Ca2+ concentration reaches the excitatory level in the cells, and calmodulin located in the plasma membrane plays an important role in the response decay of the cyclic nucleotide-gated Ca2+ channel.

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

Chibani, Siwar, E-mail: siwar.chibani@univ-lorraine.fr; Chebbi, Mouheb; Badawi, Michael, E-mail: michael.badawi@univ-lorraine.fr

The potential use of some cation-exchanged mordenite (H{sup +}, Na{sup +}, Cu{sup +}, and Ag{sup +}) as a selective adsorbent for volatile iodine species (ICH{sub 3} and I{sub 2}), which can be released during a nuclear accident together with a steam carrier gas, is investigated using density functional theory. It is found that in the case of Cu-MOR and Ag-MOR, the absolute values of interaction energies of ICH{sub 3} and I{sub 2} are higher than that of water which indicates that these forms of zeolite could be suitable for selective adsorption of iodine species. In contrast, the H-MOR and Na-MORmore » are found to be unsuitable for this purpose. A systematic investigation of all adsorption sites allowed us to analyze the structural effects affecting the adsorption behavior. For the Ag-MOR and Cu-MOR zeolites, the iodine compounds are adsorbed preferentially in the large channel of mordenite (main channel) while water prefers the small channel or the side pocket where it forms stronger hydrogen bonds. The factors governing the interaction energies between the cationic sites and the different molecules are analyzed and the important role of van der Waals interactions in these systems is highlighted.« less

Inhibition of cation channel function at the nicotinic acethylcholine receptor from Torpedo: Agonist self-inhibition and anesthetic drugs

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

Forman, S.A.

1989-01-01

Modulation of the nicotinic acethylcholine receptor from Torpedo by cholinergic agonists, local anesthetics, and n-alkanols was studied using {sup 86}Rb{sup +} flux studies in sealed native Torpedo electroplaque membrane vesicles. Reliable concentration-response and kinetic data were obtained using manual ten sec filtration assays in vesicles partially blocked with alpha-bungarotoxin to remove spare receptors and quenched-flow assays to assess initial {sup 86}Rb{sup +} flux rates or the rate of drug-induced receptor inactivation. Concentration response relationships for the agonists acetylcholine, carbamylcholine, suberyldicholine, phenyltrimethylammonium, and (-)-nicotine are all bell-shape due to stimulation of cation channel opening at low concentrations and inhibition of channelsmore » at higher concentrations. The rate of agonist-induced fast desensitization (k{sub d}) increases with (acetylcholine) in parallel with channel activation, suggesting that desensitization proceeds from the open state and/or states in rapid equilibrium with it. At self-inhibitory acetylcholine concentrations, a new rapid inactivation (rate = k{sub f}) is observed before fast desensitization. The rate and extent of rapid inactivation is compatible with bimolecular association between acethylcholine and inhibitory site with K{sub B} = 40 mM.« less

Ground and Excited-Electronic-State Dissociations of Hydrogen-Rich and Hydrogen-Deficient Tyrosine Peptide Cation Radicals

NASA Astrophysics Data System (ADS)

Viglino, Emilie; Lai, Cheuk Kuen; Mu, Xiaoyan; Chu, Ivan K.; Tureček, František

2016-09-01

We report a comprehensive study of collision-induced dissociation (CID) and near-UV photodissociation (UVPD) of a series of tyrosine-containing peptide cation radicals of the hydrogen-rich and hydrogen-deficient types. Stable, long-lived, hydrogen-rich peptide cation radicals, such as [AAAYR + 2H]+● and several of its sequence and homology variants, were generated by electron transfer dissociation (ETD) of peptide-crown-ether complexes, and their CID-MS3 dissociations were found to be dramatically different from those upon ETD of the respective peptide dications. All of the hydrogen-rich peptide cation radicals contained major (77%-94%) fractions of species having radical chromophores created by ETD that underwent photodissociation at 355 nm. Analysis of the CID and UVPD spectra pointed to arginine guanidinium radicals as the major components of the hydrogen-rich peptide cation radical population. Hydrogen-deficient peptide cation radicals were generated by intramolecular electron transfer in CuII(2,2 ':6 ',2 ″-terpyridine) complexes and shown to contain chromophores absorbing at 355 nm and undergoing photodissociation. The CID and UVPD spectra showed major differences in fragmentation for [AAAYR]+● that diminished as the Tyr residue was moved along the peptide chain. UVPD was found to be superior to CID in localizing Cα-radical positions in peptide cation radical intermediates.

Cation effects on phosphatidic acid monolayers at various pH conditions.

PubMed

Zhang, Ting; Cathcart, Matthew G; Vidalis, Andrew S; Allen, Heather C

2016-10-01

The impact of pH and cations on phase behavior, stability, and surface morphology for dipalmitoylphosphatidic acid (DPPA) monolayers was investigated. At pH<10, DPPA monolayers on water are predominantly populated by neutral species and display the highest packing density. Cations are found to expand and stabilize the monolayer in the following order of increasing magnitude at pH 5.6: Na + >K + ∼Mg 2+ >Ca 2+ . Additionally, cation complexation is tied to the pH and protonation state of DPPA, which are the primary factors controlling the monolayer surface behavior. The binding affinity of cations to the headgroup and thus deprotonation capability of the cation, ranked in the order of Ca 2+ >Mg 2+ >Na + >K + , is found to be well explained by the law of matching water affinities. Nucleation of surface 3D lipid structures is observed from Ca 2+ , Mg 2+ , and Na + , but not from K + , consistent with the lowest binding affinity of K + . Unraveling cation and pH effects on DPPA monolayers is useful in further understanding the surface properties of complex systems such as organic-coated marine aerosols where organic films are directly influenced by the pH and ionic composition of the underlying aqueous phase. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Characterization of Beta-leptinotarsin-h and the Effects of Calcium Flux Antagonists on its Activity

DTIC Science & Technology

2005-04-07

A alone. a IP3R, IP3 receptor ; LO, ligand -operated; RyR, ryanodine receptor ; SERCA, sarcoplasmic reticulum endoplasmic reticulum Ca 2C ATPase; SO...observation eliminated non-selective cation channels such as nicotinic, glutamatergic, purinergic P2X , and serotoni- nergic 5-HT3 ligand -operated Ca 2C...nicardipine, nifedipine, SNX-482) was inhibitory. Selective inhibitors of ligand -operated, store-operated, and transduction-operated channels were also not

Atomistic Modeling of Ion Conduction through the Voltage-Sensing Domain of the Shaker K+ Ion Channel.

PubMed

Wood, Mona L; Freites, J Alfredo; Tombola, Francesco; Tobias, Douglas J

2017-04-20

Voltage-sensing domains (VSDs) sense changes in the membrane electrostatic potential and, through conformational changes, regulate a specific function. The VSDs of wild-type voltage-dependent K + , Na + , and Ca 2+ channels do not conduct ions, but they can become ion-permeable through pathological mutations in the VSD. Relatively little is known about the underlying mechanisms of conduction through VSDs. The most detailed studies have been performed on Shaker K + channel variants in which ion conduction through the VSD is manifested in electrophysiology experiments as a voltage-dependent inward current, the so-called omega current, which appears when the VSDs are in their resting state conformation. Only monovalent cations appear to permeate the Shaker VSD via a pathway that is believed to be, at least in part, the same as that followed by the S4 basic side chains during voltage-dependent activation. We performed μs-time scale atomistic molecular dynamics simulations of a cation-conducting variant of the Shaker VSD under applied electric fields in an experimentally validated resting-state conformation, embedded in a lipid bilayer surrounded by solutions containing guanidinium chloride or potassium chloride. Our simulations provide insights into the Shaker VSD permeation pathway, the protein-ion interactions that control permeation kinetics, and the mechanism of voltage-dependent activation of voltage-gated ion channels.

Impact of Hyperpolarization-activated, Cyclic Nucleotide-gated Cation Channel Type 2 for the Xenon-mediated Anesthetic Effect: Evidence from In Vitro and In Vivo Experiments.

PubMed

Mattusch, Corinna; Kratzer, Stephan; Buerge, Martina; Kreuzer, Matthias; Engel, Tatiana; Kopp, Claudia; Biel, Martin; Hammelmann, Verena; Ying, Shui-Wang; Goldstein, Peter A; Kochs, Eberhard; Haseneder, Rainer; Rammes, Gerhard

2015-05-01

The thalamus is thought to be crucially involved in the anesthetic state. Here, we investigated the effect of the inhaled anesthetic xenon on stimulus-evoked thalamocortical network activity and on excitability of thalamocortical neurons. Because hyperpolarization-activated, cyclic nucleotide-gated cation (HCN) channels are key regulators of neuronal excitability in the thalamus, the effect of xenon on HCN channels was examined. The effects of xenon on thalamocortical network activity were investigated in acutely prepared brain slices from adult wild-type and HCN2 knockout mice by means of voltage-sensitive dye imaging. The influence of xenon on single-cell excitability in brain slices was investigated using the whole-cell patch-clamp technique. Effects of xenon on HCN channels were verified in human embryonic kidney cells expressing HCN2 channels. Xenon concentration-dependently diminished thalamocortical signal propagation. In neurons, xenon reduced HCN channel-mediated Ih current amplitude by 33.4 ± 12.2% (at -133 mV; n = 7; P = 0.041) and caused a left-shift in the voltage of half-maximum activation (V1/2) from -98.8 ± 1.6 to -108.0 ± 4.2 mV (n = 8; P = 0.035). Similar effects were seen in human embryonic kidney cells. The impairment of HCN channel function was negligible when intracellular cyclic adenosine monophosphate level was increased. Using HCN2 mice, we could demonstrate that xenon did neither attenuate in vitro thalamocortical signal propagation nor did it show sedating effects in vivo. Here, we clearly showed that xenon impairs HCN2 channel function, and this impairment is dependent on intracellular cyclic adenosine monophosphate levels. We provide evidence that this effect reduces thalamocortical signal propagation and probably contributes to the hypnotic properties of xenon.

Emerging mechanistic targets in lung injury induced by combustion-generated particles.

EPA Science Inventory

ABSTRACT The mechanism for biological effect following pulmonary exposure to combustion-generated particles is incompletely defined. Transient receptor potential (TRP) cation channels were identified as “particle sensors” in that their activation was coupled with the initiation ...

Accurate prediction of cation-π interaction energy using substituent effects.

PubMed

Sayyed, Fareed Bhasha; Suresh, Cherumuttathu H

2012-06-14

Substituent effects on cation-π interactions have been quantified using a variety of Φ-X···M(+) complexes where Φ, X, and M(+) are the π-system, substituent, and cation, respectively. The cation-π interaction energy, E(M(+)), showed a strong linear correlation with the molecular electrostatic potential (MESP) based measure of the substituent effect, ΔV(min) (the difference between the MESP minimum (V(min)) on the π-region of a substituted system and the corresponding unsubstituted system). This linear relationship is E(M(+)) = C(M(+))(ΔV(min)) + E(M(+))' where C(M(+)) is the reaction constant and E(M(+))' is the cation-π interaction energy of the unsubstituted complex. This relationship is similar to the Hammett equation and its first term yields the substituent contribution of the cation-π interaction energy. Further, a linear correlation between C(M(+))() and E(M(+))()' has been established, which facilitates the prediction of C(M(+)) for unknown cations. Thus, a prediction of E(M(+)) for any Φ-X···M(+) complex is achieved by knowing the values of E(M(+))' and ΔV(min). The generality of the equation is tested for a variety of cations (Li(+), Na(+), K(+), Mg(+), BeCl(+), MgCl(+), CaCl(+), TiCl(3)(+), CrCl(2)(+), NiCl(+), Cu(+), ZnCl(+), NH(4)(+), CH(3)NH(3)(+), N(CH(3))(4)(+), C(NH(2))(3)(+)), substituents (N(CH(3))(2), NH(2), OCH(3), CH(3), OH, H, SCH(3), SH, CCH, F, Cl, COOH, CHO, CF(3), CN, NO(2)), and a large number of π-systems. The tested systems also include multiple substituted π-systems, viz. ethylene, acetylene, hexa-1,3,5-triene, benzene, naphthalene, indole, pyrrole, phenylalanine, tryptophan, tyrosine, azulene, pyrene, [6]-cyclacene, and corannulene and found that E(M)(+) follows the additivity of substituent effects. Further, the substituent effects on cationic sandwich complexes of the type C(6)H(6)···M(+)···C(6)H(5)X have been assessed and found that E(M(+)) can be predicted with 97.7% accuracy using the values of E(M(+))' and ΔV(min). All the Φ-X···M(+) systems showed good agreement between the calculated and predicted E(M(+))() values, suggesting that the ΔV(min) approach to substituent effect is accurate and useful for predicting the interactive behavior of substituted π-systems with cations.

Peroxisomal Pex11 is a pore-forming protein homologous to TRPM channels.

PubMed

Mindthoff, Sabrina; Grunau, Silke; Steinfort, Laura L; Girzalsky, Wolfgang; Hiltunen, J Kalervo; Erdmann, Ralf; Antonenkov, Vasily D

2016-02-01

More than 30 proteins (Pex proteins) are known to participate in the biogenesis of peroxisomes-ubiquitous oxidative organelles involved in lipid and ROS metabolism. The Pex11 family of homologous proteins is responsible for division and proliferation of peroxisomes. We show that yeast Pex11 is a pore-forming protein sharing sequence similarity with TRPM cation-selective channels. The Pex11 channel with a conductance of Λ=4.1 nS in 1.0M KCl is moderately cation-selective (PK(+)/PCl(-)=1.85) and resistant to voltage-dependent closing. The estimated size of the channel's pore (r~0.6 nm) supports the notion that Pex11 conducts solutes with molecular mass below 300-400 Da. We localized the channel's selectivity determining sequence. Overexpression of Pex11 resulted in acceleration of fatty acids β-oxidation in intact cells but not in the corresponding lysates. The β-oxidation was affected in cells by expression of the Pex11 protein carrying point mutations in the selectivity determining sequence. These data suggest that the Pex11-dependent transmembrane traffic of metabolites may be a rate-limiting step in the β-oxidation of fatty acids. This conclusion was corroborated by analysis of the rate of β-oxidation in yeast strains expressing Pex11 with mutations mimicking constitutively phosphorylated (S165D, S167D) or unphosphorylated (S165A, S167A) protein. The results suggest that phosphorylation of Pex11 is a mechanism that can control the peroxisomal β-oxidation rate. Our results disclose an unexpected function of Pex11 as a non-selective channel responsible for transfer of metabolites across peroxisomal membrane. The data indicate that peroxins may be involved in peroxisomal metabolic processes in addition to their role in peroxisome biogenesis. Copyright © 2015 Elsevier B.V. All rights reserved.

Mefloquine inhibits voltage dependent Nav1.4 channel by overlapping the local anaesthetic binding site.

PubMed

Paiz-Candia, Bertin; Islas, Angel A; Sánchez-Solano, Alfredo; Mancilla-Simbro, Claudia; Scior, Thomas; Millan-PerezPeña, Lourdes; Salinas-Stefanon, Eduardo M

2017-02-05

Mefloquine constitutes a multitarget antimalaric that inhibits cation currents. However, the effect and the binding site of this compound on Na + channels is unknown. To address the mechanism of action of mefloquine, we employed two-electrode voltage clamp recordings on Xenopus laevis oocytes, site-directed mutagenesis of the rat Na + channel, and a combined in silico approach using Molecular Dynamics and docking protocols. We found that mefloquine: i) inhibited Na v 1.4 currents (IC 50 =60μM), ii) significantly delayed fast inactivation but did not affect recovery from inactivation, iii) markedly the shifted steady-state inactivation curve to more hyperpolarized potentials. The presence of the β1 subunit significantly reduced mefloquine potency, but the drug induced a significant frequency-independent rundown upon repetitive depolarisations. Computational and experimental results indicate that mefloquine overlaps the local anaesthetic binding site by docking at a hydrophobic cavity between domains DIII and DIV that communicates the local anaesthetic binding site with the selectivity filter. This is supported by the fact that mefloquine potency significantly decreased on mutant Na v 1.4 channel F1579A and significantly increased on K1237S channels. In silico this compound docked above F1579 forming stable π-π interactions with this residue. We provide structure-activity insights into how cationic amphiphilic compounds may exert inhibitory effects by docking between the local anaesthetic binding site and the selectivity filter of a mammalian Na + channel. Our proposed synergistic cycle of experimental and computational studies may be useful for elucidating binding sites of other drugs, thereby saving in vitro and in silico resources. Copyright © 2016 Elsevier B.V. All rights reserved.

Englerin A Agonizes the TRPC4/C5 Cation Channels to Inhibit Tumor Cell Line Proliferation

PubMed Central

Carson, Cheryl; Raman, Pichai; Tullai, Jennifer; Xu, Lei; Henault, Martin; Thomas, Emily; Yeola, Sarita; Lao, Jianmin; McPate, Mark; Verkuyl, J. Martin; Marsh, George; Sarber, Jason; Amaral, Adam; Bailey, Scott; Lubicka, Danuta; Pham, Helen; Miranda, Nicolette; Ding, Jian; Tang, Hai-Ming; Ju, Haisong; Tranter, Pamela; Ji, Nan; Krastel, Philipp; Jain, Rishi K.; Schumacher, Andrew M.; Loureiro, Joseph J.; George, Elizabeth; Berellini, Giuliano; Ross, Nathan T.; Bushell, Simon M.; Erdemli, Gül; Solomon, Jonathan M.

2015-01-01

Englerin A is a structurally unique natural product reported to selectively inhibit growth of renal cell carcinoma cell lines. A large scale phenotypic cell profiling experiment (CLiP) of englerin A on ¬over 500 well characterized cancer cell lines showed that englerin A inhibits growth of a subset of tumor cell lines from many lineages, not just renal cell carcinomas. Expression of the TRPC4 cation channel was the cell line feature that best correlated with sensitivity to englerin A, suggesting the hypothesis that TRPC4 is the efficacy target for englerin A. Genetic experiments demonstrate that TRPC4 expression is both necessary and sufficient for englerin A induced growth inhibition. Englerin A induces calcium influx and membrane depolarization in cells expressing high levels of TRPC4 or its close ortholog TRPC5. Electrophysiology experiments confirmed that englerin A is a TRPC4 agonist. Both the englerin A induced current and the englerin A induced growth inhibition can be blocked by the TRPC4/C5 inhibitor ML204. These experiments confirm that activation of TRPC4/C5 channels inhibits tumor cell line proliferation and confirms the TRPC4 target hypothesis generated by the cell line profiling. In selectivity assays englerin A weakly inhibits TRPA1, TRPV3/V4, and TRPM8 which suggests that englerin A may bind a common feature of TRP ion channels. In vivo experiments show that englerin A is lethal in rodents near doses needed to activate the TRPC4 channel. This toxicity suggests that englerin A itself is probably unsuitable for further drug development. However, since englerin A can be synthesized in the laboratory, it may be a useful chemical starting point to identify novel modulators of other TRP family channels. PMID:26098886

Evidence for the functional involvement of members of the TRP channel family in the uptake of Na(+) and NH4 (+) by the ruminal epithelium.

PubMed

Rosendahl, Julia; Braun, Hannah S; Schrapers, Katharina T; Martens, Holger; Stumpff, Friederike

2016-08-01

Large quantities of protein are degraded in the fermentative parts of the gut to ammonia, which is absorbed, detoxified to urea, and excreted, leading to formation of nitrogenous compounds such as N2O that are associated with global warming. In ruminants, channel-mediated uptake of NH4 (+) from the rumen predominates. The molecular identity of these channels remains to be clarified. Ruminal cells and epithelia from cows and sheep were investigated using patch clamp, Ussing chamber, microelectrode techniques, and qPCR. In patch clamp experiments, bovine ruminal epithelial cells expressed a conductance for NH4 (+) that could be blocked in a voltage-dependent manner by divalent cations. In the native epithelium, NH4 (+) depolarized the apical potential, acidified the cytosol and induced a rise in short-circuit current (I sc) that persisted after the removal of Na(+), was blocked by verapamil, enhanced by the removal of divalent cations, and was sensitive to certain transient receptor potential (TRP) channel modulators. Menthol or thymol stimulated the I sc in Na(+) or NH4 (+) containing solutions in a dose-dependent manner and modulated transepithelial Ca(2+) fluxes. On the level of messenger RNA (mRNA), ovine and bovine ruminal epithelium expressed TRPA1, TRPV3, TRPV4, TRPM6, and TRPM7, with any expression of TRPV6 marginal. No bands were detected for TRPV1, TRPV5, or TRPM8. Functional and molecular biological data suggest that the transport of NH4 (+), Na(+), and Ca(2+) across the rumen involves TRP channels, with TRPV3 and TRPA1 emerging as prime candidate genes. TRP channels may also contribute to the transport of NH4 (+) across other epithelia.

Direct versus indirect actions of ghrelin on hypothalamic NPY neurons

PubMed Central

Sheng, Zhenyu; Routh, Vanessa; Gerzanich, Volodymyr; Simard, J. Marc; Bryan, Joseph

2017-01-01

Objectives Assess direct versus indirect action(s) of ghrelin on hypothalamic NPY neurons. Materials and methods Electrophysiology was used to measure ion channel activity in NPY-GFP neurons in slice preparations. Ca2+ imaging was used to monitor ghrelin activation of isolated NPY GFP-labeled neurons. Immunohistochemistry was used to localize Trpm4, SUR1 and Kir6.2 in the hypothalamus. Results Acylated ghrelin depolarized the membrane potential (MP) of NPY-GFP neurons in brain slices. Depolarization resulted from a decreased input resistance (IR) in ~70% of neurons (15/22) or an increased IR in the remainder (7/22), consistent with the opening or closing of ion channels, respectively. Although tetrodotoxin (TTX) blockade of presynaptic action potentials reduced ghrelin-induced changes in MP and IR, ghrelin still significantly depolarized the MP and decreased IR in TTX-treated neurons, suggesting that ghrelin directly opens cation channel(s) in NPY neurons. In isolated NPY-GFP neurons, ghrelin produced a sustained rise of [Ca2+]c, with an EC50 ~110 pM. Pharmacologic studies confirmed that the direct action of ghrelin was through occupation of the growth hormone secretagogue receptor, GHS-R, and demonstrated the importance of the adenylate cyclase/cAMP/protein kinase A (PKA) and phospholipase C/inositol triphosphate (PLC/IP3) pathways as activators of 5' AMP-activated protein kinase (AMPK). Activation of isolated neurons was not affected by CNQX or TTX, but reducing [Na+]o suppressed activation, suggesting a role for Na+-permeable cation channels. SUR1 and two channel partners, Kir6.2 and Trpm4, were identified immunologically in NPY-GFP neurons in situ. The actions of SUR1 and Trpm4 modulators were informative: like ghrelin, diazoxide, a SUR1 agonist, elevated [Ca2+]c and glibenclamide, a SUR1 antagonist, partially suppressed ghrelin action, while 9-phenanthrol and flufenamic acid, selective Trpm4 antagonists, blocked ghrelin actions on isolated neurons. Ghrelin activation was unaffected by nifedipine and ω-conotoxin, inhibitors of L- and N-type Ca2+ channels, respectively, while Ni2+, mibefradil, and TTA-P2 completely or partially inhibited ghrelin action, implicating T-type Ca2+ channels. Activation was also sensitive to a spider toxin, SNX-482, at concentrations selective for R-type Ca2+ channels. Nanomolar concentrations of GABA markedly inhibited ghrelin-activation of isolated NPY-GFP neurons, consistent with chronic suppression of ghrelin action in vivo. Conclusions NPY neurons express all the molecular machinery needed to respond directly to ghrelin. Consistent with recent studies, ghrelin stimulates presynaptic inputs that activate NPY-GFP neurons in situ. Ghrelin can also directly activate a depolarizing conductance. Results with isolated NPY-GFP neurons suggest the ghrelin-activated, depolarizing current is a Na+ conductance with the pharmacologic properties of SUR1/Trpm4 non-selective cation channels. In the isolated neuron model, the opening of SUR1/Trpm4 channels activates T- and SNX482-sensitive R-type voltage dependent Ca2+ channels, which could contribute to NPY neuronal activity in situ. PMID:28877214

A comprehensive study of the complexation of alkali metal cations by lower rim calix[4]arene amide derivatives.

PubMed

Horvat, Gordan; Frkanec, Leo; Cindro, Nikola; Tomišić, Vladislav

2017-09-13

The complexation of alkali metal cations by lower rim N,N-dihexylacetamide (L1) and newly synthesized N-hexyl-N-methylacetamide (L2) calix[4]arene tertiary-amide derivatives was thoroughly studied at 25 °C in acetonitrile (MeCN), benzonitrile (PhCN), and methanol (MeOH) by means of direct and competitive microcalorimetric titrations, and UV and 1 H NMR spectroscopies. In addition, by measuring the ligands' solubilities, the solution (transfer) Gibbs energies of the ligands and their alkali metal complexes were obtained. The inclusion of solvent molecules in the free and complexed calixarene hydrophobic cavities was also investigated. Computational (classical molecular dynamics) investigations of the studied systems were also carried out. The obtained results were compared with those previously obtained by studying the complexation ability of an N-hexylacetamidecalix[4]arene secondary-amide derivative (L3). The stability constants of 1 : 1 complexes were determined in all solvents used (the values obtained by different methods being in excellent agreement), as were the corresponding complexation enthalpies and entropies. Almost all of the examined reactions were enthalpically controlled. The most striking exceptions were reactions of Li + with both ligands in methanol, for which the entropic contribution to the reaction Gibbs energy was substantial due the entropically favourable desolvation of the smallest lithium cation. The thermodynamic stabilities of the complexes were quite solvent dependent (the stability decreased in the solvent order: MeCN > PhCN ≫ MeOH), which could be accounted for by considering the differences in the solvation of the ligand and free and complexed alkali metal cations in the solvents used. Comparison of the stability constants of the ligand L1 and L2 complexes clearly revealed that the higher electron-donating ability of the hexyl with respect to the methyl group is of considerable importance in determining the equilibria of the complexation reactions. Additionally, the quite strong influence of intramolecular hydrogen bond formation in compound L3 (not present in ligands L1 and L2) and that of the inclusion of solvent molecules in the calixarene hydrophobic cone were shown to be of great importance in determining the thermodynamic stability of the calixarene-cation complexes. The experimental results were fully supported by those obtained by MD simulations.

Molecular simulation of the adsorption of methane in Engelhard titanosilicate frameworks.

PubMed

Pillai, Renjith S; Gomes, José R B; Jorge, Miguel

2014-07-01

Molecular simulations were carried out to elucidate the influence of structural heterogeneity and of the presence of extra-framework cations and water molecules on the adsorption of methane in Engelhard titanosilicates, ETS-10 and ETS-4. The simulations employed three different modeling approaches, (i) with fixed cations and water at their single crystal positions, (ii) with fixed cations and water at their optimized positions, and (iii) with mobile extra-framework cations and water molecules. Simulations employing the final two approaches provided a more realistic description of adsorption in these materials, and showed that at least some cations and water molecules are displaced from the crystallographic positions obtained from single crystal data. Upon methane adsorption in the case of ETS-10, the cations move to the large rings, while in the case of ETS-4, the water molecules and cations migrate to more available space in the larger 12-membered ring channels for better accommodation of the methane molecules. For ETS-4, we also considered adsorption in all possible pure polymorph structures and then combined these to provide an estimate of adsorption in a real ETS-4 sample. By comparing simulated adsorption isotherms to experimental data, we were able to show that both the mobility of extra-framework species and the structural heterogeneity should be taken into account for realistic predictions of adsorption in titanosilicate materials.

Polyamines control of cation transport across plant membranes: implications for ion homeostasis and abiotic stress signaling.

PubMed

Pottosin, Igor; Shabala, Sergey

2014-01-01

Polyamines are unique polycationic metabolites, controlling a variety of vital functions in plants, including growth and stress responses. Over the last two decades a bulk of data was accumulated providing explicit evidence that polyamines play an essential role in regulating plant membrane transport. The most straightforward example is a blockage of the two major vacuolar cation channels, namely slow (SV) and fast (FV) activating ones, by the micromolar concentrations of polyamines. This effect is direct and fully reversible, with a potency descending in a sequence Spm(4+) > Spd(3+) > Put(2+). On the contrary, effects of polyamines on the plasma membrane (PM) cation and K(+)-selective channels are hardly dependent on polyamine species, display a relatively low affinity, and are likely to be indirect. Polyamines also affect vacuolar and PM H(+) pumps and Ca(2+) pump of the PM. On the other hand, catabolization of polyamines generates H2O2 and other reactive oxygen species (ROS), including hydroxyl radicals. Export of polyamines to the apoplast and their oxidation there by available amine oxidases results in the induction of a novel ion conductance and confers Ca(2+) influx across the PM. This mechanism, initially established for plant responses to pathogen attack (including a hypersensitive response), has been recently shown to mediate plant responses to a variety of abiotic stresses. In this review we summarize the effects of polyamines and their catabolites on cation transport in plants and discuss the implications of these effects for ion homeostasis, signaling, and plant adaptive responses to environment.

Polyamines control of cation transport across plant membranes: implications for ion homeostasis and abiotic stress signaling

PubMed Central

Pottosin, Igor; Shabala, Sergey

2014-01-01

Polyamines are unique polycationic metabolites, controlling a variety of vital functions in plants, including growth and stress responses. Over the last two decades a bulk of data was accumulated providing explicit evidence that polyamines play an essential role in regulating plant membrane transport. The most straightforward example is a blockage of the two major vacuolar cation channels, namely slow (SV) and fast (FV) activating ones, by the micromolar concentrations of polyamines. This effect is direct and fully reversible, with a potency descending in a sequence Spm4+ > Spd3+ > Put2+. On the contrary, effects of polyamines on the plasma membrane (PM) cation and K+-selective channels are hardly dependent on polyamine species, display a relatively low affinity, and are likely to be indirect. Polyamines also affect vacuolar and PM H+ pumps and Ca2+ pump of the PM. On the other hand, catabolization of polyamines generates H2O2 and other reactive oxygen species (ROS), including hydroxyl radicals. Export of polyamines to the apoplast and their oxidation there by available amine oxidases results in the induction of a novel ion conductance and confers Ca2+ influx across the PM. This mechanism, initially established for plant responses to pathogen attack (including a hypersensitive response), has been recently shown to mediate plant responses to a variety of abiotic stresses. In this review we summarize the effects of polyamines and their catabolites on cation transport in plants and discuss the implications of these effects for ion homeostasis, signaling, and plant adaptive responses to environment. PMID:24795739

Optical absorption, electron spin resonance, and electron spin echo studies of the photoionization of tetramethylbenzidine in cationic and anionic synthetic vesicles: comparison with analogous micellar systems

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

Li, A.S.W.; Kevan, L.

1983-09-07

The photoionization of N,N,N',N'-tetramethylbenzidine (TMB) in dihexadecylphosphate anionic vesicles and in dioctadecyldimethylammonium chloride cationic vesicles has been studied by optical absorption and electron spin resonance in liquid and frozen solutions. The TMB cation has been observed to be stabilized in both types of vesicles. The photoionization efficiency is about twofold greater in the cationic vesicles compared to the anionic vesicles. Shifts in the optical absorption maximum between micellar and vesicle solutions indicate that TMB is in a less polar environment in the vesicle systems. Electron spin echo modulation spectrometry has been used to detect TMB cation-water interactions that are foundmore » to be weaker than in previously studied micellar solutions. This is consistent with the optical absorption results and with an asymmetric solubilization site for TMB and TMB/sup +/ within the vesicular structure. A new absorption in the photoionized vesicles is assigned to a nonparamagnetic diamine-diimine charge-transfer complex between two TMB cations in the same vesicle. This complex is not formed in micellar systems. 5 figures.« less

Kinetics studies of the reactions of main fourth-period monocations (Ga+, Ge+, As+, and Se+) with methyl fluoride.

PubMed

Barrientos, Carmen; Rayón, Víctor Manuel; Largo, Antonio; Sordo, José Ángel; Redondo, Pilar

2013-08-22

Thermodynamics and kinetics theoretical studies on the gas-phase reactions of fluoromethane with main fourth-period monocations (Ga(+), Ge(+), As(+), and Se(+)) have been carried out. Density functional theory (in particular mPW1K functional) was employed in the description of the potential energy surfaces, and refinement of the energies were done at the CCSD(T) level. The reaction rate constants were estimated using variational/conventional microcanonical transition state theory. From a thermodynamic viewpoint, the fluorine abstraction product is predicted for Ga(+) and Ge(+), whereas for As(+) and Se(+) the elimination product, MCH2(+) (M = As, Se) + HF, is the preferred one. Nevertheless, the most favorable channel for the reactions of CH3F with Ga(+) and Se(+) cations present a net activation barrier. In the case of Ga(+), the reaction proceeds via an addition channel forming the adduct complex, CH3FGa(+), whereas for Se(+) no reaction is found, in agreement with the experiments. The predicted reaction rate constants are in reasonable good agreement with the experimental values available. Apart from the harpoon-like mechanism, our results suggest that an oxidative addition mechanism seems to play a relevant role.

GABA(C) receptors: a molecular view.

PubMed

Enz, R

2001-08-01

In the central nervous system inhibitory neurotransmission is primarily achieved through activation of receptors for gamma-aminobutyric acid (GABA). Three types of GABA receptors have been identified on the basis of their pharmacological and electrophysiological properties. The predominant type, termed GABA(A), and a recently identified GABA(C) type, form ligand-gated chloride channels, whereas GABA(B) receptors activate separate cation channels via G proteins. Based on their homology to nicotinic acetylcholine receptors, GABA(C) receptors are believed to be oligomeric protein complexes composed of five subunits in a pentameric arrangement. To date up to five different GABA(C) receptors subunits have been identified in various species. Recent studies have shed new light on the biological characteristics of GABA(C) receptors, including the chromosomal localization of its subunit genes and resulting links to deseases, the cloning of new splice variants, the identification of GABA(C) receptor-associated proteins, the identification of domains involved in subunit assembly, and finally structure/function studies examining functional consequences of introduced mutations. This review summarizes recent data in view of the molecular structure of GABA(C) receptors and presents new insights into the biological function of this protein in the retina.

MK-801, but not drugs acting at strychnine-insensitive glycine receptors, attenuate methamphetamine nigrostriatal toxicity.

PubMed

Layer, R T; Bland, L R; Skolnick, P

1993-10-15

Repeated administration of methamphetamine (METH) results in damage to nigrostriatal dopaminergic neurons. Both competitive N-methyl-D-aspartate (NMDA) receptor antagonists and use-dependent cation channel blockers attenuate METH-induced damage. The objectives of the present study were to examine whether comparable reductions in METH-induced damage could be obtained by compounds acting at strychnine-insensitive glycine receptors on the NMDA receptor complex. Four injections of METH (5 mg/kg i.p.) resulted in a approximately 70.9% depletion of striatal dopamine (DA) and approximately 62.7% depletion of dihydroxyphenylacetic acid (DOPAC) content, respectively. A significant protection against METH-induced DA and DOPAC depletion was afforded by the use-dependent channel blocker, MK-801. The competitive glycine antagonist 7-chlorokynurenic acid (7-Cl-KA), the low efficacy glycine partial agonist (+)-3-amino-1-hydroxy-2-pyrrolidone ((+)-HA-966), and the high efficacy partial glycine agonist 1-aminocyclopropane-carboxylic acid (ACPC) were ineffective against METH-induced toxicity despite their abilities to attenuate glutamate-induced neurotoxicity under both in vivo and in vitro conditions. These results indicate that glycinergic ligands do not possess the same broad neuroprotective spectrum as other classes of NMDA antagonists.

Structure and dynamics of cationic membrane peptides and proteins: Insights from solid-state NMR

PubMed Central

Hong, Mei; Su, Yongchao

2011-01-01

Many membrane peptides and protein domains contain functionally important cationic Arg and Lys residues, whose insertion into the hydrophobic interior of the lipid bilayer encounters significant energy barriers. To understand how these cationic molecules overcome the free energy barrier to insert into the lipid membrane, we have used solid-state NMR spectroscopy to determine the membrane-bound topology of these peptides. A versatile array of solid-state NMR experiments now readily yields the conformation, dynamics, orientation, depth of insertion, and site-specific protein–lipid interactions of these molecules. We summarize key findings of several Arg-rich membrane peptides, including β-sheet antimicrobial peptides, unstructured cell-penetrating peptides, and the voltage-sensing helix of voltage-gated potassium channels. Our results indicate the central role of guanidinium-phosphate and guanidinium-water interactions in dictating the structural topology of these cationic molecules in the lipid membrane, which in turn account for the mechanisms of this functionally diverse class of membrane peptides. PMID:21344534

Calix[4]arene-bis(t-octylbenzo-18-crown-6) as an extraordinarily effective macrocyclic receptor for the univalent thallium cation

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

Makrlik, Emanuel; Toman, Petr; Vanura, Petr

2013-01-01

From extraction experiments and -activity measurements, the exchange extraction constant corresponding to the equilibrium Tl+ (aq) + 1 Cs+ (org) 1 Tl+ (org) + Cs+ (aq) taking place in the two-phase water phenyltrifluoromethyl sulfone (abbrev. FS 13) system (1 = calix[4]arene-bis(t-octylbenzo-18-crown-6); aq = aqueous phase, org = FS 13 phase) was evaluated as log Kex (Tl+, 1 Cs+) = 1.7 0.1. Further, the extraordinarily high stability constant of the 1 Tl+ complex in FS 13 saturated with water was calculated for a temperature of 25 C: log org(1 Tl+) = 13.1 0.2. Finally, by using quantum mechanical DFT calculations, themore » most probable structure of the cationic complex species 1 Tl+ was derived. In the resulting 1 Tl+ complex, the central cation Tl+ is bound by eight bond interactions to six oxygen atoms from the respective 18-crown-6 moiety and to two carbons of the corresponding two benzene rings of the parent receptor 1 via cation interaction.« less

Novel thioarsenates {[Mn(2,2'-bipy)2(SCN)][Mn(2,2'-bipy)](As(V)S4)}2 and {[Mn(2,2'-bipy)2(SCN)]2[As(III)2(S2)2S2]}: introducing an anionic second ligand to modify MnII complex cations of 2,2'-bipyridine.

PubMed

Liu, Guang-Ning; Guo, Guo-Cong; Wang, Ming-Sheng; Huang, Jin-Shun

2014-03-14

Two novel manganese thioarsenates, {[Mn(2,2'-bipy)2(SCN)][Mn(2,2'-bipy)](As(V)S4)}2 (1, 2,2'-bipy = 2,2'-bipyridine) and {[Mn(2,2'-bipy)2(SCN)]2[As(III)2(S2)2S2]} (2), containing thiocyanate-modified Mn-2,2'-bipy complex cations were synthesized. They feature two terminal [Mn(2,2'-bipy)2(SCN)](+) complex cations bridged by a polyanion {[Mn(2,2'-bipy)]2(As(V)S4)2}(2-) for 1 and a cyclic thioarsenate anion (As(III)2S6)(2-) for 2. In 2, the [As(III)2(S2)2S2](2-) anion can be described as two (As(III)S3)(3-) trigonal-pyramids interlinked through S-S bonds. The method to obtain new metal complex cations shown here, introducing an anionic second ligand to modify the number of coordination sites and the charges of the metal complex cations simultaneously, is different from the traditional methods, varying either the TM center or the organic ligand or employing mixed neutral organic ligands, and may open up a new route for preparing novel chalcogenidometalates. Compounds 1 and 2 exhibit wide optical gaps of 2.20 and 2.67 eV, respectively, and photoluminescence with the emission maxima occurring around 440 nm. Magnetic measurements show the presence of antiferromagnetic interactions between Mn(II) centers in the two compounds.

Identification of a unique Ca2+-binding site in rat acid-sensing ion channel 3.

PubMed

Zuo, Zhicheng; Smith, Rachel N; Chen, Zhenglan; Agharkar, Amruta S; Snell, Heather D; Huang, Renqi; Liu, Jin; Gonzales, Eric B

2018-05-25

Acid-sensing ion channels (ASICs) evolved to sense changes in extracellular acidity with the divalent cation calcium (Ca 2+ ) as an allosteric modulator and channel blocker. The channel-blocking activity is most apparent in ASIC3, as removing Ca 2+ results in channel opening, with the site's location remaining unresolved. Here we show that a ring of rat ASIC3 (rASIC3) glutamates (Glu435), located above the channel gate, modulates proton sensitivity and contributes to the formation of the elusive Ca 2+ block site. Mutation of this residue to glycine, the equivalent residue in chicken ASIC1, diminished the rASIC3 Ca 2+ block effect. Atomistic molecular dynamic simulations corroborate the involvement of this acidic residue in forming a high-affinity Ca 2+ site atop the channel pore. Furthermore, the reported observations provide clarity for past controversies regarding ASIC channel gating. Our findings enhance understanding of ASIC gating mechanisms and provide structural and energetic insights into this unique calcium-binding site.

Structure of the full-length TRPV2 channel by cryo-EM

NASA Astrophysics Data System (ADS)

Huynh, Kevin W.; Cohen, Matthew R.; Jiang, Jiansen; Samanta, Amrita; Lodowski, David T.; Zhou, Z. Hong; Moiseenkova-Bell, Vera Y.

2016-03-01

Transient receptor potential (TRP) proteins form a superfamily Ca2+-permeable cation channels regulated by a range of chemical and physical stimuli. Structural analysis of a `minimal' TRP vanilloid subtype 1 (TRPV1) elucidated a mechanism of channel activation by agonists through changes in its outer pore region. Though homologous to TRPV1, other TRPV channels (TRPV2-6) are insensitive to TRPV1 activators including heat and vanilloids. To further understand the structural basis of TRPV channel function, we determined the structure of full-length TRPV2 at ~5 Å resolution by cryo-electron microscopy. Like TRPV1, TRPV2 contains two constrictions, one each in the pore-forming upper and lower gates. The agonist-free full-length TRPV2 has wider upper and lower gates compared with closed and agonist-activated TRPV1. We propose these newly revealed TRPV2 structural features contribute to diversity of TRPV channels.

Structure of the full-length TRPV2 channel by cryo-EM

PubMed Central

Huynh, Kevin W.; Cohen, Matthew R.; Jiang, Jiansen; Samanta, Amrita; Lodowski, David T.; Zhou, Z. Hong; Moiseenkova-Bell, Vera Y.

2016-01-01

Transient receptor potential (TRP) proteins form a superfamily Ca2+-permeable cation channels regulated by a range of chemical and physical stimuli. Structural analysis of a ‘minimal' TRP vanilloid subtype 1 (TRPV1) elucidated a mechanism of channel activation by agonists through changes in its outer pore region. Though homologous to TRPV1, other TRPV channels (TRPV2–6) are insensitive to TRPV1 activators including heat and vanilloids. To further understand the structural basis of TRPV channel function, we determined the structure of full-length TRPV2 at ∼5 Å resolution by cryo-electron microscopy. Like TRPV1, TRPV2 contains two constrictions, one each in the pore-forming upper and lower gates. The agonist-free full-length TRPV2 has wider upper and lower gates compared with closed and agonist-activated TRPV1. We propose these newly revealed TRPV2 structural features contribute to diversity of TRPV channels. PMID:27021073

Structure of the full-length TRPV2 channel by cryo-EM.

PubMed

Huynh, Kevin W; Cohen, Matthew R; Jiang, Jiansen; Samanta, Amrita; Lodowski, David T; Zhou, Z Hong; Moiseenkova-Bell, Vera Y

2016-03-29

Transient receptor potential (TRP) proteins form a superfamily Ca(2+)-permeable cation channels regulated by a range of chemical and physical stimuli. Structural analysis of a 'minimal' TRP vanilloid subtype 1 (TRPV1) elucidated a mechanism of channel activation by agonists through changes in its outer pore region. Though homologous to TRPV1, other TRPV channels (TRPV2-6) are insensitive to TRPV1 activators including heat and vanilloids. To further understand the structural basis of TRPV channel function, we determined the structure of full-length TRPV2 at ∼5 Å resolution by cryo-electron microscopy. Like TRPV1, TRPV2 contains two constrictions, one each in the pore-forming upper and lower gates. The agonist-free full-length TRPV2 has wider upper and lower gates compared with closed and agonist-activated TRPV1. We propose these newly revealed TRPV2 structural features contribute to diversity of TRPV channels.

Transport across the outer membrane porin of mycolic acid containing actinomycetales: Nocardia farcinica.

PubMed

Singh, Pratik Raj; Bajaj, Harsha; Benz, Roland; Winterhalter, Mathias; Mahendran, Kozhinjampara R

2015-02-01

The role of the outer-membrane channel from a mycolic acid containing Gram-positive bacteria Nocardia farcinica, which forms a hydrophilic pathway across the cell wall, was characterized. Single channel electrophysiology measurements and liposome swelling assays revealed the permeation of hydrophilic solutes including sugars, amino acids and antibiotics. The cation selective N. farcinica channel exhibited strong interaction with the positively charged antibiotics; amikacin and kanamycin, and surprisingly also with the negatively charged ertapenem. Voltage dependent kinetics of amikacin and kanamycin interactions were studied to distinguish binding from translocation. Moreover, the importance of charged residues inside the channel was investigated using mutational studies that revealed rate limiting interactions during the permeation. Copyright © 2014 Elsevier B.V. All rights reserved.

Requirement for tyrosine phosphatase during serotonergic neuromodulation by protein kinase C.

PubMed

Catarsi, S; Drapeau, P

1997-08-01

Tyrosine kinases and phosphatases are abundant in the nervous system, where they signal cellular differentiation, mediate the responses to growth factors, and direct neurite outgrowth during development. Tyrosine phosphorylation can also alter ion channel activity, but its physiological significance remains unclear. In an identified leech mechanosensory neuron, the ubiquitous neuromodulator serotonin increases the activity of a cation channel by activating protein kinase C (PKC), resulting in membrane depolarization and modulation of the receptive field properties. We observed that the effects on isolated neurons and channels were blocked by inhibiting tyrosine phosphatases. Serotonergic stimulation of PKC thus activates a tyrosine phosphatase activity associated with the channels, which reverses their constitutive inhibition by tyrosine phosphorylation, representing a novel form of neuromodulation.

A common pathway for charge transport through voltage-sensing domains.

PubMed

Chanda, Baron; Bezanilla, Francisco

2008-02-07

Voltage-gated ion channels derive their voltage sensitivity from the movement of specific charged residues in response to a change in transmembrane potential. Several studies on mechanisms of voltage sensing in ion channels support the idea that these gating charges move through a well-defined permeation pathway. This gating pathway in a voltage-gated ion channel can also be mutated to transport free cations, including protons. The recent discovery of proton channels with sequence homology to the voltage-sensing domains suggests that evolution has perhaps exploited the same gating pathway to generate a bona fide voltage-dependent proton transporter. Here we will discuss implications of these findings on the mechanisms underlying charge (and ion) transport by voltage-sensing domains.

Magnesium Excretion in C. elegans Requires the Activity of the GTL-2 TRPM Channel

PubMed Central

Teramoto, Takayuki; Sternick, Laura A.; Kage-Nakadai, Eriko; Sajjadi, Shirine; Siembida, Jakub; Mitani, Shohei; Iwasaki, Kouichi; Lambie, Eric J.

2010-01-01

Systemic magnesium homeostasis in mammals is primarily governed by the activities of the TRPM6 and TRPM7 cation channels, which mediate both uptake by the intestinal epithelial cells and reabsorption by the distal convoluted tubule cells in the kidney. In the nematode, C. elegans, intestinal magnesium uptake is dependent on the activities of the TRPM channel proteins, GON-2 and GTL-1. In this paper we provide evidence that another member of the TRPM protein family, GTL-2, acts within the C. elegans excretory cell to mediate the excretion of excess magnesium. Thus, the activity of GTL-2 balances the activities of the paralogous TRPM channel proteins, GON-2 and GTL-1. PMID:20221407

Integrating Security into the Curriculum

DTIC Science & Technology

1998-12-01

predicate calculus, discrete math , and finite-state machine the- ory. In addition to applying standard mathematical foundations to constructing hardware and...models, specifi- cations, and the use of formal methods for verification and covert channel analysis. The means for analysis is based on discrete math , information

Metabolism regulates the spontaneous firing of substantia nigra pars reticulata neurons via KATP and nonselective cation channels.

PubMed

Lutas, Andrew; Birnbaumer, Lutz; Yellen, Gary

2014-12-03

Neurons use glucose to fuel glycolysis and provide substrates for mitochondrial respiration, but neurons can also use alternative fuels that bypass glycolysis and feed directly into mitochondria. To determine whether neuronal pacemaking depends on active glucose metabolism, we switched the metabolic fuel from glucose to alternative fuels, lactate or β-hydroxybutyrate, while monitoring the spontaneous firing of GABAergic neurons in mouse substantia nigra pars reticulata (SNr) brain slices. We found that alternative fuels, in the absence of glucose, sustained SNr spontaneous firing at basal rates, but glycolysis may still be supported by glycogen in the absence of glucose. To prevent any glycogen-fueled glycolysis, we directly inhibited glycolysis using either 2-deoxyglucose or iodoacetic acid. Inhibiting glycolysis in the presence of alternative fuels lowered SNr firing to a slower sustained firing rate. Surprisingly, we found that the decrease in SNr firing was not mediated by ATP-sensitive potassium (KATP) channel activity, but if we lowered the perfusion flow rate or omitted the alternative fuel, KATP channels were activated and could silence SNr firing. The KATP-independent slowing of SNr firing that occurred with glycolytic inhibition in the presence of alternative fuels was consistent with a decrease in a nonselective cationic conductance. Although mitochondrial metabolism alone can prevent severe energy deprivation and KATP channel activation in SNr neurons, active glucose metabolism appears important for keeping open a class of ion channels that is crucial for the high spontaneous firing rate of SNr neurons. Copyright © 2014 the authors 0270-6474/14/3416336-12$15.00/0.

Atomistic Detailed Mechanism and Weak Cation-Conducting Activity of HIV-1 Vpu Revealed by Free Energy Calculations

PubMed Central

Padhi, Siladitya; Burri, Raghunadha Reddy; Jameel, Shahid; Priyakumar, U. Deva

2014-01-01

The viral protein U (Vpu) encoded by HIV-1 has been shown to assist in the detachment of virion particles from infected cells. Vpu forms cation-specific ion channels in host cells, and has been proposed as a potential drug target. An understanding of the mechanism of ion transport through Vpu is desirable, but remains limited because of the unavailability of an experimental structure of the channel. Using a structure of the pentameric form of Vpu – modeled and validated based on available experimental data – umbrella sampling molecular dynamics simulations (cumulative simulation time of more than 0.4 µs) were employed to elucidate the energetics and the molecular mechanism of ion transport in Vpu. Free energy profiles corresponding to the permeation of Na+ and K+ were found to be similar to each other indicating lack of ion selection, consistent with previous experimental studies. The Ser23 residue is shown to enhance ion transport via two mechanisms: creating a weak binding site, and increasing the effective hydrophilic length of the channel, both of which have previously been hypothesized in experiments. A two-dimensional free energy landscape has been computed to model multiple ion permeation, based on which a mechanism for ion conduction is proposed. It is shown that only one ion can pass through the channel at a time. This, along with a stretch of hydrophobic residues in the transmembrane domain of Vpu, explains the slow kinetics of ion conduction. The results are consistent with previous conductance studies that showed Vpu to be a weakly conducting ion channel. PMID:25392993

The permeability of endplate channels to monovalent and divalent metal cations

PubMed Central

1980-01-01

The relative permeability of endplate channels to monovalent and divalent metal ions was determined from reversal potentials. Thallium is the most permeant ion with a permeability ratio relative to Na+ of 2.5. The selectivity among alkali metals is weak with a sequence, Cs+ greater than Rb+ greater than K+ greater than Na+ greater than Li+, and permeability ratios of 1.4, 1.3, 1.1, 1.0, and 0.9. The selectivity among divalent ions is also weak, with a sequence for alkaline earths of Mg++ greater than Ca++ greater than Ba++ greater than Sr++. The transition metal ions Mn++, Co++, Ni++, Zn++, and Cd++ are also permeant. Permeability ratios for divalent ions decreased as the concentration of divalent ion was increased in a manner consistent with the negative surface potential theory of Lewis (1979 J. Physiol. (Lond.). 286: 417--445). With 20 mM XCl2 and 85.5 mM glucosamine.HCl in the external solution, the apparent permeability ratios for the alkaline earth cations (X++) are in the range 0.18--0.25. Alkali metal ions see the endplate channel as a water-filled, neutral pore without high-field-strength sites inside. Their permeability sequence is the same as their aqueous mobility sequence. Divalent ions, however, have a permeability sequence almost opposite from their mobility sequence and must experience some interaction with groups in the channel. In addition, the concentrations of monovalent and divalent ions are increased near the channel mouth by a weak negative surface potential. PMID:6247423

Redox regulation of epithelial sodium channels examined in alveolar type 1 and 2 cells patch-clamped in lung slice tissue.

PubMed

Helms, My N; Jain, Lucky; Self, Julie L; Eaton, Douglas C

2008-08-15

The alveolar surface of the lung is lined by alveolar type 1 (AT1) and type 2 (AT2) cells. Using single channel patch clamp analysis in lung slice preparations, we are able to uniquely study AT1 and AT2 cells separately from intact lung. We report for the first time the Na+ transport properties of type 2 cells accessed in live lung tissue (as we have done in type 1 cells). Type 2 cells in lung tissue slices express both highly selective cation and nonselective cation channels with average conductances of 8.8 +/- 3.2 and 22.5 +/- 6.3 picosiemens, respectively. Anion channels with 10-picosiemen conductance are also present in the apical membrane of type 2 cells. Our lung slice studies importantly verify the use of cultured cell model systems commonly used in lung epithelial sodium channel (ENaC) studies. Furthermore, we identify novel functional differences between the cells that make up the alveolar epithelium. One important difference is that exposure to the nitric oxide (NO) donor, PAPA-NONOate (1.5 microm), significantly decreases average ENaC NPo in type 2 cells (from 1.38 +/- 0.26 to 0.82 +/- 0.16; p < 0.05 and n = 18) but failed to alter ENaC activity in alveolar type 1 cells. Elevating endogenous superoxide (O2.) levels with Ethiolat, a superoxide dismutase inhibitor, prevented NO inhibition of ENaC activity in type 2 cells, supporting the novel hypothesis that O2. and NO signaling plays an important role in maintaining lung fluid balance.

External protons destabilize the activated voltage sensor in hERG channels.

PubMed

Shi, Yu Patrick; Cheng, Yen May; Van Slyke, Aaron C; Claydon, Tom W

2014-03-01

Extracellular acidosis shifts hERG channel activation to more depolarized potentials and accelerates channel deactivation; however, the mechanisms underlying these effects are unclear. External divalent cations, e.g., Ca(2+) and Cd(2+), mimic these effects and coordinate within a metal ion binding pocket composed of three acidic residues in hERG: D456 and D460 in S2 and D509 in S3. A common mechanism may underlie divalent cation and proton effects on hERG gating. Using two-electrode voltage clamp, we show proton sensitivity of hERG channel activation (pKa = 5.6), but not deactivation, was greatly reduced in the presence of Cd(2+) (0.1 mM), suggesting a common binding site for the Cd(2+) and proton effect on activation and separable effects of protons on activation and deactivation. Mutational analysis confirmed that D509 plays a critical role in the pH dependence of activation, as shown previously, and that cooperative actions involving D456 and D460 are also required. Importantly, neutralization of all three acidic residues abolished the proton-induced shift of activation, suggesting that the metal ion binding pocket alone accounts for the effects of protons on hERG channel activation. Voltage-clamp fluorimetry measurements demonstrated that protons shifted the voltage dependence of S4 movement to more depolarized potentials. The data indicate a site and mechanism of action for protons on hERG activation gating; protonation of D456, D460 and D509 disrupts interactions between these residues and S4 gating charges to destabilize the activated configuration of S4.

Chemistry in acetone complexes of metal dications: a remarkable ethylene production pathway.

PubMed

Wu, Jianhua; Liu, Dan; Zhou, Jian-Ge; Hagelberg, Frank; Park, Sung Soo; Shvartsburg, Alexandre A

2007-06-07

Electrospray ionization can generate microsolvated multiply charged metal ions for various metals and ligands, allowing exploration of chemistry within such clusters. The finite size of these systems permits comparing experimental results with accurate calculations, creating a natural laboratory to research ion solvation. Mass spectrometry has provided much insight into the stability and dissociation of ligated metal cations. While solvated singly charged ions tend to shrink by ligand evaporation, solvated polycations below a certain size exhibit charge reduction and/or ligand fragmentation due to organometallic reactions. Here we investigate the acetone complexes of representative divalent metals (Ca, Mn, Co, Ni, and Cu), comparing the results of collision-induced dissociation with the predictions of density functional theory. As for other solvated dications, channels involving proton or electron transfer compete with ligand loss and become dominant for smaller complexes. The heterolytic C-C bond cleavage is common, like in DMSO and acetonitrile complexes. Of primary interest is the unanticipated neutral ethylene loss, found for all metals studied except Cu and particularly intense for Ca and Mn. We focus on understanding that process in the context of competing dissociation pathways, as a function of metal identity and number of ligands. According to first-principles modeling, ethylene elimination proceeds along a complex path involving two intermediates. These results suggest that chemistry in microsolvated multiply charged ions may still hold major surprises.

Radiation creation of cation defects in alkali halide crystals: Review and today's concept (Review Article)

NASA Astrophysics Data System (ADS)

Lushchik, A.; Lushchik, Ch.; Vasil'chenko, E.; Popov, A. I.

2018-04-01

Irradiation of alkali halide crystals creates pairs of Frenkel defects both in anion and cation sublattices. However, the particular nonimpact creation mechanisms (related to the decay of different electronic excitations) of cation Frenkel pairs are still unclear. At helium temperatures, there is yet no direct evidences of the creation of stable (long-lived) elemental cation defects. On the other hand, a number of complex structural defects containing cation vacancies and/or interstitials, were detected after irradiation of alkali halides at higher temperatures. Besides already proved mechanism related to the association of H and VK centers into trihalide molecules, the following possibilities of cation interstitial-vacancy pair creation are analyzed as well: (i) a direct decay of cation or anion excitons, (ii) the transformation of anion Frenkel pairs, formed at the decay of anion excitons or e-h recombination, into cation ones.

Modulation of pyridinium cationic lipid-DNA complex properties by pyridinium gemini surfactants and its impact on lipoplex transfection properties

PubMed Central

Sharma, Vishnu Dutt; Lees, Julia; Hoffman, Nicholas E.; Brailoiu, Eugen; Madesh, Muniswamy; Wunder, Stephanie L.; Ilies, Marc A.

2014-01-01

The study presents the effects of blending a cationic gemini surfactant into cationic lipid bilayers and its impact towards plasmid DNA compaction and delivery process. Using nanoDSC, dynamic light scattering, zeta potential and electrophoretic mobility measurements, together with transfection (2D- and 3D-) and viability assays, we identified the main physicochemical parameters of the lipid bilayers, liposomes and lipoplexes that are affected by the gemini surfactant addition. We also correlated the cationic bilayer composition with the dynamics of the DNA compaction process, and with transfection efficiency, cytotoxicity and internalization mechanism of the resultant nucleic acid complexes. We found that blending of gemini surfactant into the cationic bilayers fluidized the supramolecular assemblies, reduced the amount of positive charge required to fully compact the plasmid DNA and, in certain cases, changed the internalization mechanism of the lipoplexes. Transfection efficiency of select ternary lipoplexes derived from cationic gemini surfactants and lipids was several times superior to transfection efficiency of corresponding binary lipoplexes, also surpassing standard transfection systems. The overall impact of gemini surfactants into the formation and dynamic of cationic bilayers was found to depend heavily on the presence of co-lipids, their nature and amount present into lipoplexes. The study confirmed the possibility of combining the specific properties of pyridinium gemini surfactants and cationic lipids synergistically for obtaining efficient synthetic transfection systems with negligible cytotoxicity useful for therapeutic gene delivery. PMID:24377350

Electron Transfer Dissociation: Effects of Cation Charge State on Product Partitioning in Ion/Ion Electron Transfer to Multiply Protonated Polypeptides

PubMed Central

Liu, Jian; McLuckey, Scott A.

2012-01-01

The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentation of backbone bonds versus fragmentation of side chains, was measured quantitatively as a function of peptide charge state to allow insights to be drawn about the fundamental aspects of ion/ion reactions that lead to ETD. The ET channel increases relative to the PT channel, ETD increases relative to ET,noD, and fragmentation at backbone bonds increases relative to side-chain cleavages as cation charge state increases. The increase in ET versus PT with charge state is consistent with a Landau-Zener based curve-crossing model. An optimum charge state for ET is predicted by the model for the ground state-to-ground state reaction. However, when the population of excited product ion states is considered, it is possible that a decrease in ET efficiency as charge state increases will not be observed due to the possibility of the population of excited electronic states of the products. Several factors can contribute to the increase in ETD versus ET,noD and backbone cleavage versus side-chain losses. These factors include an increase in reaction exothermicity and charge state dependent differences in precursor and product ion structures, stabilities, and sites of protonation. PMID:23264749

Muscarinic receptor-mediated excitation of rat intracardiac ganglion neurons.

PubMed

Hirayama, Michiko; Ogata, Masanori; Kawamata, Tomoyuki; Ishibashi, Hitoshi

2015-08-01

Modulation of the membrane excitability of rat parasympathetic intracardiac ganglion neurons by muscarinic receptors was studied using an amphotericin B-perforated patch-clamp recording configuration. Activation of muscarinic receptors by oxotremorine-M (OxoM) depolarized the membrane, accompanied by repetitive action potentials. OxoM evoked inward currents under voltage-clamp conditions at a holding potential of -60 mV. Removal of extracellular Ca(2+) markedly increased the OxoM-induced current (IOxoM). The inward IOxoM in the absence of extracellular Ca(2+) was fully inhibited by removal of extracellular Na(+), indicating the involvement of non-selective cation channels. The IOxoM was inhibited by organic cation channel antagonists including SKF-96365 and ML-204. The IOxoM was antagonized by muscarinic receptor antagonists with the following potency: 4-DAMP > pirenzepine = darifenacin > methoctramine. Muscarinic toxin 7 (MT-7), a highly selective inhibitor for M1 receptor, produced partial inhibition of the IOxoM. In the presence of MT-7, concentration-inhibition curve of the M3-preferring antagonist darifenacin was shifted to the left. These results suggest the contribution of M1 and M3 receptors to the OxoM response. The IOxoM was inhibited by U-73122, a phospholipase C inhibitor. The membrane-permeable IP3 receptor blocker xestospongin C also inhibited the IOxoM. Furthermore, pretreatment with thapsigargin and BAPTA-AM inhibited the IOxoM, while KN-62, a blocker of Ca(2+)/calmodulin-dependent protein kinase II, had no effect. These results suggest that the activation mechanism involves a PLC pathway, release of Ca(2+) from intracellular Ca(2+) stores and calmodulin. The cation channels activated by muscarinic receptors may play an important role in neuronal membrane depolarization in rat intracardiac ganglion neurons. Copyright © 2015 Elsevier Ltd. All rights reserved.

The Minimal Pharmacophore for Silent Agonism of the α7 Nicotinic Acetylcholine Receptor

PubMed Central

Chojnacka, Kinga; Horenstein, Nicole A.

2014-01-01

The minimum pharmacophore for activation of the human α7 nicotinic acetylcholine receptor (nAChR) is the tetramethylammonium cation. Previous work demonstrated that larger quaternary ammonium compounds, such as diethyldimethylammonium or 1-methyl quinuclidine, were α7-selective partial agonists, but additional increase in the size of the ammonium cation or the quinuclidine N-alkyl group by a single carbon to an N-ethyl group led to a loss of efficacy for ion channel activation. We report that although such compounds are ineffective at inducing the normal channel open state, they nonetheless regulate the induction of specific conformational states normally considered downstream of channel activation. We synthesized several panels of quaternary ammonium nAChR ligands that systematically varied the size of the substituents bonded to the central positively charged nitrogen atom. In these molecular series, we found a correlation between the molecular volume of the ligand and/or charge density, and the receptor’s preferred distribution among conformational states including the closed state, the active state, a nonconducting state that could be converted to an activated state by a positive allosteric modulator (PAM), and a PAM-insensitive nonconducting state. We hypothesize that the changes of molecular volume of an agonist’s cationic core subtly impact interactions at the subunit interface constituting the orthosteric binding site in such a way as to regulate the probability of conversions among the conformational states. We define a new minimal pharmacophore for the class of compounds we have termed “silent agonists,” which are able to induce allosteric modulator-dependent activation but not the normal activated state. PMID:24990939

In-membrane micro fuel cell

DOEpatents

Omosebi, Ayokunle; Besser, Ronald

2016-09-06

An in-membrane micro fuel cell comprises an electrically-insulating membrane that is permissive to the flow of cations, such as protons, and a pair of electrodes deposited on channels formed in the membrane. The channels are arranged as conduits for fluids, and define a membrane ridge between the channels. The electrodes are porous and include catalysts for promoting the liberation of a proton and an electron from a chemical species and/or or the recombination of a proton and an electron with a chemical specie. The fuel cell may be provided a biosensor, an electrochemical sensor, a microfluidic device, or other microscale devices fabricated in the fuel cell membrane.

TRPV4 channels: physiological and pathological role in cardiovascular system.

PubMed

Randhawa, Puneet Kaur; Jaggi, Amteshwar Singh

2015-11-01

TRPV4 channels are non-selective cation channels permeable to Ca(2+), Na(+), and Mg(2+) ions. Recently, TRPV4 channels have received considerable attention as these channels are widely expressed in the cardiovascular system including endothelial cells, cardiac fibroblasts, vascular smooth muscles, and peri-vascular nerves. Therefore, these channels possibly play a pivotal role in the maintenance of cardiovascular homeostasis. TRPV4 channels critically regulate flow-induced arteriogenesis, TGF-β1-induced differentiation of cardiac fibroblasts into myofibroblasts, and heart failure-induced pulmonary edema. These channels also mediate hypoxia-induced increase in proliferation and migration of pulmonary artery smooth muscle cells and progression of pulmonary hypertension. These channels also maintain flow-induced vasodilation and preserve vascular function by directly activating Ca(2+)-dependent KCa channels. Furthermore, these may also induce vasodilation and maintain blood pressure indirectly by evoking the release of NO, CGRP, and substance P. The present review discusses the evidences and the potential mechanisms implicated in diverse responses including arteriogenesis, cardiac remodeling, congestive heart failure-induced pulmonary edema, pulmonary hypertension, flow-induced dilation, regulation of blood pressure, and hypoxic preconditioning.

High temperature sensitivity is intrinsic to voltage-gated potassium channels

PubMed Central

Yang, Fan; Zheng, Jie

2014-01-01

Temperature-sensitive transient receptor potential (TRP) ion channels are members of the large tetrameric cation channels superfamily but are considered to be uniquely sensitive to heat, which has been presumed to be due to the existence of an unidentified temperature-sensing domain. Here we report that the homologous voltage-gated potassium (Kv) channels also exhibit high temperature sensitivity comparable to that of TRPV1, which is detectable under specific conditions when the voltage sensor is functionally decoupled from the activation gate through either intrinsic mechanisms or mutations. Interestingly, mutations could tune Shaker channel to be either heat-activated or heat-deactivated. Therefore, high temperature sensitivity is intrinsic to both TRP and Kv channels. Our findings suggest important physiological roles of heat-induced variation in Kv channel activities. Mechanistically our findings indicate that temperature-sensing TRP channels may not contain a specialized heat-sensor domain; instead, non-obligatory allosteric gating permits the intrinsic heat sensitivity to drive channel activation, allowing temperature-sensitive TRP channels to function as polymodal nociceptors. DOI: http://dx.doi.org/10.7554/eLife.03255.001 PMID:25030910

Protonation of a lanthanum phosphide-alkyl occurs at the P-La not the C-La bond: isolation of a cationic lanthanum alkyl complex.

PubMed

Izod, Keith; Liddle, Stephen T; Clegg, William

2004-08-07

Protonation of the heteroleptic, cyclometalated lanthanum phosphide complex [((Me3Si)2CH)(C6H4-2-CH2NMe2)P]La(THF)[P(C6H4-2-CH2NMe2)(CH(SiMe3)(SiMe2CH2))] with [Et3NH][BPh4] yields the cationic alkyllanthanum complex [(THF)4La[P(C6H4-2-CH2NMe2)(CH(SiMe3)(SiMe2CH2))

The styryl dye FM1-43 suppresses odorant responses in a subset of olfactory neurons by blocking cyclic nucleotide-gated (CNG) channels.

PubMed

Breunig, Esther; Kludt, Eugen; Czesnik, Dirk; Schild, Detlev

2011-08-12

Many olfactory receptor neurons use a cAMP-dependent transduction mechanism to transduce odorants into depolarizations. This signaling cascade is characterized by a sequence of two currents: a cation current through cyclic nucleotide-gated channels followed by a chloride current through calcium-activated chloride channels. To date, it is not possible to interfere with these generator channels under physiological conditions with potent and specific blockers. In this study we identified the styryl dye FM1-43 as a potent blocker of native olfactory cyclic nucleotide-gated channels. Furthermore, we characterized this substance to stain olfactory receptor neurons that are endowed with cAMP-dependent transduction. This allows optical differentiation and pharmacological interference with olfactory receptor neurons at the level of the signal transduction.

Phosphorus dendrimers and photodynamic therapy. Spectroscopic studies on two dendrimer-photosensitizer complexes: Cationic phosphorus dendrimer with rose bengal and anionic phosphorus dendrimer with methylene blue.

PubMed

Dabrzalska, Monika; Zablocka, Maria; Mignani, Serge; Majoral, Jean Pierre; Klajnert-Maculewicz, Barbara

2015-08-15

Dendrimers due to their unique architecture may play an important role in drug delivery systems including chemotherapy, gene therapy and recently, photodynamic therapy as well. We investigated two dendrimer-photosensitizer systems in context of potential use of these systems in photodynamic therapy. The mixtures of an anionic phosphorus dendrimer of the second generation and methylene blue were studied by UV-vis spectroscopy while that of a cationic phosphorus dendrimer (third generation) and rose bengal were investigated by spectrofluorimetric methods. Spectroscopic analysis of these two systems revealed the formation of dendrimer-photosensitizer complexes via electrostatic interactions as well as π stacking. The stoichiometry of the rose bengal-cationic dendrimer complex was estimated to be 7:1 and 9:1 for the methylene blue-anionic dendrimer complex. The results suggest that these polyanionic or polycationic phosphorus dendrimers can be promising candidates as carriers in photodynamic therapy. Copyright © 2015 Elsevier B.V. All rights reserved.

Direct Imaging of Gene-Carrier Complexes in Animal Cells

NASA Astrophysics Data System (ADS)

Lin, Alison J.; Slack, Nelle L.; Ahmad, Ayesha; Matsumoto, Brian; Safinya, Cyrus R.

1998-03-01

Cationic lipids are promising gene carriers for DNA transfection. Establishing the correlations between structures of cationic lipid/DNA complexes (CL-DNA) and pathways of transfection will greatly aid us in achieving the optimal CL-DNA transfections. Our first step is to determine the uptake mechanism of DNA by studying the interactions and structures of DNA and cationic lipids. X-ray diffraction shows that the CL-DNA undergoes structural phase transitions from lamellar( J. Raedler, I. Koltover, T. Salditt, C. R. Safinya, Science 275, 810 (1997).) to inverted hexagonal self-assemblies as we change the lipid composition. X-ray diffraction and optical microscopy techniques are used to directly image the progress of the CL-DNA in mouse L-cells and unravel the complex structure in-situ. Fluorescence and confocal optical microscopy techniques allow us to monitor the interactions between the complexes and different organelles in the cell cytoplasm. Current results indicate that once inside cells, complexes containing DOPE follow a different pathway from those containing DOPC. This research is funded by NSF-DMR-9624091, PRF-31352-AC7, and Los Alamos-STB/UC:96-108.

Control of cerium oxidation state through metal complex secondary structures

DOE PAGES

Levin, Jessica R.; Dorfner, Walter L.; Carroll, Patrick J.; ...

2015-08-11

A series of alkali metal cerium diphenylhydrazido complexes, M x(py) y[Ce(PhNNPh) 4], M = Li, Na, and K, x = 4 (Li and Na) or 5 (K), and y = 4 (Li), 8 (Na), or 7 (K), were synthesized to probe how a secondary coordination sphere would modulate electronic structures at a cerium cation. The resulting electronic structures of the heterobimetallic cerium diphenylhydrazido complexes were found to be strongly dependent on the identity of the alkali metal cations. When M = Li + or Na +, the cerium(III) starting material was oxidized with concomitant reduction of 1,2-diphenylhydrazine to aniline. Reductionmore » of 1,2-diphenylhydrazine was not observed when M = K +, and the complex remained in the cerium(III) oxidation state. Oxidation of the cerium(III) diphenylhydrazido complex to the Ce( IV) diphenylhydrazido one was achieved through a simple cation exchange reaction of the alkali metals. As a result, UV-Vis spectroscopy, FTIR spectroscopy, electrochemistry, magnetic susceptibility, and DFT studies were used to probe the oxidation state and the electronic changes that occurred at the metal centre.« less

Mechanism of drug-induced gingival overgrowth revisited: a unifying hypothesis

PubMed Central

Brown, RS; Arany, PR

2015-01-01

Drug-induced gingival overgrowth (DIGO) is a disfiguring side effect of anti-convulsants, calcineurin inhibitors, and calcium channel blocking agents. A unifying hypothesis has been constructed which begins with cation flux inhibition induced by all three of these drug categories. Decreased cation influx of folic acid active transport within gingival fibroblasts leads to decreased cellular folate uptake, which in turn leads to changes in matrix metalloproteinases metabolism and the failure to activate collagenase. Decreased availability of activated collagenase results in decreased degradation of accumulated connective tissue which presents as DIGO. Studies supporting this hypothesis are discussed. PMID:24893951

pH-Sensitive self-propelled motion of oil droplets in the presence of cationic surfactants containing hydrolyzable ester linkages.

PubMed

Banno, Taisuke; Kuroha, Rie; Toyota, Taro

2012-01-17

Self-propelled oil droplets in a nonequilibrium system have drawn much attention as both a primitive type of inanimate chemical machinery and a dynamic model of the origin of life. Here, to create the pH-sensitive self-propelled motion of oil droplets, we synthesized cationic surfactants containing hydrolyzable ester linkages. We found that n-heptyloxybenzaldehyde oil droplets were self-propelled in the presence of ester-containing cationic surfactant. In basic solution prepared with sodium hydroxide, oil droplets moved as molecular aggregates formed on their surface. Moreover, the self-propelled motion in the presence of the hydrolyzable cationic surfactant lasted longer than that in the presence of nonhydrolyzable cationic surfactant. This is probably due to the production of a fatty acid by the hydrolysis of the ester-containing cationic surfactant and the subsequent neutralization of the fatty acid with sodium hydroxide. A complex surfactant was formed in the aqueous solution because of the cation and anion combination. Because such complex formation can induce both a decrease in the interfacial tension of the oil droplet and self-assembly with n-heptyloxybenzaldehyde and lauric acid in the aqueous dispersion, the prolonged movement of the oil droplet may be explained by the increase in heterogeneity of the interfacial tension of the oil droplet triggered by the hydrolysis of the ester-containing surfactant. © 2011 American Chemical Society

Effects of Zinc Gluconate and 2 Other Divalent Cationic Compounds on Olfactory Function in Mice

PubMed Central

Duncan-Lewis, Christopher A; Lukman, Roy L; Banks, Robert K

2011-01-01

Intranasal application of zinc gluconate has commonly been used to treat the common cold. The safety of this treatment, however, has come into question recently. In addition to a United States recall of a homeopathic product that contains zinc gluconate, abundant literature reports cytotoxic effects of zinc on the olfactory epithelium. Additional research suggests that divalent cations (such as zinc) can block ion channels that facilitate the transduction of odors into electrical signals on the olfactory epithelium. The purpose of the current study was 2-fold: to confirm whether zinc gluconate causes anosmia and to reveal whether any other divalent cationic compounds produce a similar effect. Groups of mice underwent a buried food-pellet test to gauge olfactory function and then were nasally irrigated with 1 of 3 divalent cationic compounds. When tested after treatment, mice irrigated with zinc gluconate and copper gluconate experienced a marked increase in food-finding time, indicating that they had lost their ability to smell a hidden food source. Control mice irrigated with saline had a significantly lower increase in times. These results confirm that zinc gluconate can cause anosmia and reveal that multiple divalent cations can negatively affect olfaction. PMID:22330252

Modulation of slow inactivation in human cardiac Kv1.5 channels by extra- and intracellular permeant cations

PubMed Central

Fedida, David; Maruoka, Neil D; Lin, Shunping

1999-01-01

The properties and regulation of slow inactivation by intracellular and extracellular cations in the human heart K+ channel hKv1.5 have been investigated. Extensive NH2- and COOH-terminal deletions outside the central core of transmembrane domains did not affect the degree of inactivation. The voltage dependence of steady-state inactivation curves of hKv1.5 channels was unchanged in Rb+ and Cs+, compared with K+, but biexponential inactivation over 10 s was reduced from ∼100% of peak current in Na+ to ∼65% in K+, ∼50% in Rb+ and ∼30% in Cs+. This occurred as a result of a decrease in both fast and slow components of inactivation, with little change in inactivation time constants. Changes in extracellular cation species and concentration (5-300 mM) had only small effects on the rates of inactivation and recovery from inactivation (τrecovery∼1 s). Mutation of residues at a putative regulatory site at R487 in the outer pore mouth did not affect slow inactivation or recovery from inactivation of hKv1.5, although sensitivity to extracellular TEA was conferred. Symmetrical reduction of both intra- and extracellular cation concentrations accelerated and augmented both components of inactivation of K+ (Kd = 34.7 mM) and Cs+ (Kd = 20.5 mM) currents. These effects could be quantitatively accounted for by unilateral reduction of intracellular K+ (Ki+) (Kd = 43.4 mM) or Csi+ with constant 135 mM external ion concentrations. We conclude that inactivation and recovery from inactivation in hKv1.5 were not typically C-type in nature. However, the ion species dependence of inactivation was still closely coupled to ion permeation through the pore. Intracellular ion modulatory actions were more potent than extracellular actions, although still of relatively low affinity. These results suggest the presence of ion binding sites capable of regulating inactivation located on both intracellular and extracellular sides of the pore selectivity filter. PMID:10050000