Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Ion Channel Gating”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources
PubMed1993

Brief-lifetime, fast-inactivating ion channels account for the alpha-bungarotoxin-sensitive nicotinic response in hippocampal neurons.

Single-channel currents underlying the various types of nicotinic receptor-gated whole-cell currents (previously termed IA, IB, II and III) were identified in rat hippocampal neurons. In response to applied acetylcholine (ACh), most of the neurons showed a fast-decaying whole-cell current (type IA) that can be blocked by alpha-bungarotoxin (alpha-BGT). In these neurons, a novel nicotinic receptor channel was found, having a conductance of 73 pS and an open time of 0.12 ms at -80 mV. This channel showed a fast concentration-dependent inactivation that had a time constant of 0.5 ms at 1 mM ACh. A high Ca2+ permeability and the involvement of alpha 7 receptor subunits in the channel structure were suggested.

Acetylcholine↗
PubMed1994

Cobalt accumulation in neurons expressing ionotropic excitatory amino acid receptors in young rat spinal cord: morphology and distribution.

Excitatory amino acids (EAA) acting on N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate receptors play an important role in synaptic transmission in the spinal cord. Quantitative autoradiography and physiological experiments suggest that NMDA receptors are localized mainly in lamina II while kainate and AMPA receptors are found on both dorsal and ventral horn neurons. However the cell types expressing EAA receptors and their laminar distribution is not known. We have used a cobalt uptake method to study the morphology and distribution of spinal cord neurons expressing AMPA, kainate, or NMDA excitatory amino acid receptors in the lumbar enlargement of the rat spinal cord. The technique involved superfusion of hemisected spinal cords of 14 day-old rat pups in vitro with excitatory amino acid receptor ligands in the presence of CoCl2. Cobalt has been shown to enter cells through ligand-gated ion channels in place of Ca2+. Cells which accumulated cobalt ions following activation by ionotropic excitatory amino acid receptors were visualized histochemically. The cobalt uptake generated receptor-specific labeling of cells, as the NMDA receptor antagonist D-(-)-2-amino-(5)-phosphonovaleric acid (D-AP-5) (20 microM) blocked the NMDA, but not kainate-induced cobalt uptake. The kainate-induced cobalt labeling was reduced by the non-selective excitatory amino acid receptor antagonist kynurenic acid (4 mM). Passive opening of the voltage-gated Ca(2+)-channels by KCl (50 mM) did not result in cobalt uptake, indicating that cobalt enters the cells through ligand-gated Ca(2+)-channels. AMPA (500 microM), kainate (500 microM), or NMDA (500 microM) each induced cobalt uptake with characteristic patterns and distributions of neuronal staining. Overall, kainate induced cobalt uptake in the greatest number of neuronal staining. Overall, kainate induced cobalt uptake in the greatest number of neuronal perikarya while NMDA-induced uptake was the lowest. AMPA and kainate, but not NMDA superfusion, resulted in cobalt labeling of glial cells. Our results show that the cobalt uptake technique is a useful way to study the morphology and distribution of cells expressing receptors with ligand-gated Ca2+ channels.

Animals↗
PubMed2003

Identification of gene expression profiles in rat ears with cDNA microarrays.

The physiological processes of hearing implicate thousands of molecules acting in harmony; however, their identities are only partially understood. We used cDNA microarrays containing 1,176 genes to identify >150 genes expressed in rat middle and inner ear tissue. Expressed genes covered several gene families and biological pathways, many of which have previously not been described. Transcription factor genes that were expressed included inhibitors of DNA binding protein (Id). These were localized to the spiral ganglion, organ of Corti and stria vascularis, and they are possibly involved in neurogenesis and angiogenesis. Transcriptional factors that were highly expressed included Gax (homeobox) and I-kappaB, which inhibit cellular proliferation. Their presence suggests that inhibitory programs for cell proliferation are enforced in the ear. Ion channel genes that were expressed included voltage-dependent L-type calcium channels (LTCC) and proton-gated cation channels (PGCC). Genes involved in neurotransmitter production and release included glutamic acid decarboxylase (GAD1). Genes involved in postsynaptic inhibition included neuropeptide Y5 receptors (NPY5) and GAD1. Due to the existence of receptors and/or enzymes involved in their biochemical synthesis, neurotransmitters associated with these might include serotonin, glutamide, acetylcholine, gamma-aminobutyric acid (GABA), neurotensin, and dopamine.

Animals↗
PubMed1999

Enhancement of GABA-activated current by muscarine in rat dorsal root ganglion neurons.

The modulation of GABA-gated ion channel responses to GABA, pentobarbital and diazepam by muscarine was studied in freshly isolated rat dorsal root ganglion neurons using a whole-cell patch-clamp technique. Muscarine enhanced current activated by 5 microM GABA dose-dependently with an EC50 of 40 +/- 2 microM. This potentiation was not blocked by pirenzepine, gallamine and atropine, the specific and non-specific muscarinic receptor antagonists. Muscarine shifted the GABA dose-response curve to the left, with the GABA EC50 decreased from 45 +/- 2 to 13 +/- 2 microM. The maximal response to GABA was suppressed to 89.3 +/- 4.6% as compared with the control (100%) by 80 microM muscarine. Muscarine potentiated GABA (1-100 microM)-activated current in a voltage-independent manner. Muscarine shifted the dose-response curve for pentobarbital enhancement of GABA-activated current to the left, and the enhancement of GABA-activated current by muscarine was additive to that of pentobarbital over all pentobarbital concentrations. Muscarine shifted the dose-response curve for diazepam (1-100 nM) enhancement of GABA-activated current to the left. However, muscarine attenuated the facilitatory effect of saturating concentrations of diazepam (> 100 nM). The potentiating effect of muscarine was blocked by 1 nM ethyl-beta-carboline-3-carboxylate, the inverse agonist of benzodiazepine receptors. These results suggest that GABA-gated ion channel responses to GABA and pentobarbital were potentiated by muscarine and the binding site(s) for muscarine might be related to those for diazepam.

Acetylcholine↗
PubMed2002

Two tarantula peptides inhibit activation of multiple sodium channels.

Two peptides, ProTx-I and ProTx-II, from the venom of the tarantula Thrixopelma pruriens, have been isolated and characterized. These peptides were purified on the basis of their ability to reversibly inhibit the tetrodotoxin-resistant Na channel, Na(V) 1.8, and are shown to belong to the inhibitory cystine knot (ICK) family of peptide toxins interacting with voltage-gated ion channels. The family has several hallmarks: cystine bridge connectivity, mechanism of channel inhibition, and promiscuity across channels within and across channel families. The cystine bridge connectivity of ProTx-II is very similar to that of other members of this family, i.e., C(2) to C(16), C(9) to C(21), and C(15) to C(25). These peptides are the first high-affinity ligands for tetrodotoxin-resistant peripheral nerve Na(V) channels, but also inhibit other Na(V) channels (IC(50)'s < 100 nM). ProTx-I and ProTx-II shift the voltage dependence of activation of Na(V) 1.5 to more positive voltages, similar to other gating-modifier ICK family members. ProTx-I also shifts the voltage dependence of activation of Ca(V) 3.1 (alpha(1G), T-type, IC(50) = 50 nM) without affecting the voltage dependence of inactivation. To enable further structural and functional studies, synthetic ProTx-II was made; it adopts the same structure and has the same functional properties as the native peptide. Synthetic ProTx-I was also made and exhibits the same potency as the native peptide. Synthetic ProTx-I, but not ProTx-II, also inhibits K(V) 2.1 channels with 10-fold less potency than its potency on Na(V) channels. These peptides represent novel tools for exploring the gating mechanisms of several Na(V) and Ca(V) channels.

Amino Acid Sequence↗
PubMed1991

Ion channel formation by synthetic transmembrane segments of the inhibitory glycine receptor--a model study.

The inhibitory glycine receptor (GlyR) of rat spinal cord contains an intrinsic transmembrane channel mediating agonist-gated anion flux. Here, synthetic peptides modelled after the predicted transmembrane domains M2 and M4 of its ligand-binding subunit were incorporated into lipid vesicle membranes and black lipid bilayers to analyze their channel forming capabilities. Both types of peptides prohibited the establishment of, or dissipated, preexisting transmembrane potentials in the vesicle system. Incorporation of peptide M2 into the black lipid bilayer elicited randomly gated single channel events with various conductance states and life-times. Peptide M4 increased the conductance of the bilayer without producing single channels. Exchange of the terminal arginine residues of peptide M2 by glutamate resulted in a significant shift towards cation selectivity of the respective channels as compared to peptide M2. In conclusion, the peptide channels observed differed significantly from native GlyR in both conductivity and ion-selectivity indicating that individual synthetic transmembrane segments are not sufficient to mimic a channel protein composed of subunits with multiple transmembrane segments.

Amino Acid Sequence↗
PubMed2006

Role of ion channels in acute and chronic responses of the pulmonary vasculature to hypoxia.

Localized alveolar hypoxia causes constriction of the small resistance pulmonary arteries, thus diverting the desaturated, mixed-venous blood to better ventilated areas of the lung. Although modulated by endothelial vasoactive substances, the constrictor response to hypoxia is intrinsic to the smooth muscle cell. Ion channels are important elements in two of the three components of the response. Hypoxia inhibits several potassium channels (voltage-gated and TASK), leading to membrane depolarization and calcium entry through L-type channels. It also causes release of calcium from the sarcoplasmic reticulum, with consequent repletion through store-operated calcium channels. Finally, the effect of the rise in cytosolic calcium is amplified by enhanced calcium sensitivity of the actin/myosin interaction, achieved by the hypoxia-induced increase in Rho-kinase activity. The change in oxygen tension that stimulates these three "executive" components is signaled by a change in the redox status of the smooth muscle cell and probably by downstream changes in G-proteins. Ion channels also play a critical role in the vascular remodeling that results in chronic hypoxic pulmonary hypertension, seen when all the pulmonary vascular bed is hypoxic, at high altitude and in patients with chronic lung diseases. The same inhibition of potassium channels and influx of calcium results in high cytosolic levels of potassium and calcium. These, respectively, lead to inhibition of apoptosis and an increase in cellular proliferation. A better understanding of the pathophysiology of hypoxic pulmonary vasoconstriction and vascular remodeling will enable the design of better treatments for hypoxic and other forms of pulmonary hypertension.

Adaptation, Physiological↗
PubMed1999

Cyclic GMP-gated channel and peripherin/rds-rom-1 complex of rod cells.

The cGMP-gated channel and the peripherin/rds-rom-1 complex are two oligomeric membrane proteins that play key roles in the structure and function of photoreceptor outer segments. The channel is localized on the plasma membrane where it controls the flow of Na+ and Ca2+ into the outer segment in response to light-induced changes in cGMP. The rod channel consists of two homologous subunits, designated alpha and beta, which assemble into a heterotetrameric complex. Both subunits contain a core structural unit consisting of six transmembrane segments, a pore region and a cGMP binding domain. The alpha subunit is the dominant functional subunit since it forms a functional channel by itself. The beta subunit does not assemble into a functional channel by itself, but modulates the activity of the channel. The peripherin/rds-rom-1 complex is localized along the rim region of disk membranes where it plays a crucial role in disk morphogenesis. This complex consists of two peripherin/rds and two rom-1 subunits that interact non-covalently to form a heterotetramer. Peripherin/rds is the dominant subunit since, in the absence of rom-1, it self-assembles into a homotetramer that effectively supports outer segment disk formation and structure. Rom-1 on its own does not initiate outer segment formation. Instead, it plays a minor role in fine tuning disk structure. Recently, peripherin/rds-containing tetramers have been shown to form disulfide-mediated higher-order oligomers. This novel oligomerization is suggested to play a central role in outer segment disk formation.

Cyclic GMP↗
PubMed2000

Spontaneous gating of olfactory cyclic-nucleotide-gated channels.

In vertebrates, cilia on the olfactory receptor neurons have a high density of cyclic-nucleotide-gated (CNG) channels. During transduction of odorous stimuli, cyclic AMP is formed. cAMP gates the CNG channels and this initiates the neuronal depolarization. Here it is shown that the ciliary CNG channels also open spontaneously. In the absence of odorants and second messengers, olfactory cilia have a small basal conductance to cations. Part of this conductance is similar to the cAMP-activated conductance in its sensitivity to channel inhibitors and divalent cations. The basal conductance may help to stabilize the neuronal membrane potential while limiting the sensitivity of odorant detection.

1-Methyl-3-isobutylxanthine↗
PubMed1994

Dendritic attenuation of synaptic potentials and currents: the role of passive membrane properties.

The dendritic trees of neurons are structurally and functionally complex integrative units receiving thousands of synaptic inputs that have excitatory and inhibitory, fast and slow, and electrical and biochemical effects. The pattern of activation of these synaptic inputs determines if the neuron will fire an action potential at any given point in time and how it will respond to similar inputs in the future. Two critical factors affect the integrative function of dendrites: the distribution of voltage-gated ion channels in the dendritic tree and the passive electrical properties, or 'electrotonic structure', upon which these active channels are superimposed. The authors review recent data from patch-clamp recordings that provide new estimates of the passive membrane properties of hippocampal neurons, and show, with examples, how these properties affect the shaping and attenuation of synaptic potentials as they propagate in the dendrites, as well as how they affect the measurement of current from synapses located in the dendrites. Voltage-gated channels might influence the measurement of 'passive' membrane properties and, reciprocally, passive membrane properties might affect the activation of voltage-gated channels in dendrites.

Animals↗
PubMed2006

Interaction between prostaglandin E2 and l-cis-diltiazem, a specific blocker of cyclic nucleotide gated channels in bovine aortic endothelial cells.

Prostaglandins are known to transduce their signals via 7 transmembrane prostanoid receptors, which typically signal through coupling to G proteins and downstream second messenger molecules and protein kinase activation. Recently we have shown that cyclic nucleotides affect prostaglandins binding to bovine aortic endothelial cells independent of protein kinases. Here we show that incubation of bovine aortic endothelial cells with permeable analogs of cAMP or cGMP leads to a rapid and reversible reduction in PGE(2) binding to the cells. Since cyclic nucleotides are known modulators of cyclic nucleotide gated channels, we examined the effect of a specific cyclic nucleotide gated channel blocker l-cis-diltiazem on prostaglandin E(2) (PGE(2)) binding to bovine aortic endothelial cells. L-cis-diltiazem is shown to displace PGE(2) binding to bovine aortic endothelial cells in a dose dependent manner. In addition the effect of PGE(2) and l-cis-diltiazem on thapsigargin induced calcium elevation in the cells was compared. Both agents reduced in bovine aortic endothelial cells the thapsigargin induced calcium elevation by about half. PGE(2) also retarded the time course of the response to thapsigargin. Simultaneous treatment of the cells with both PGE(2) and l-cis-diltiazem did not yield an inhibitory effect beyond that observed with l-cis-diltiazem alone. Together our data point at the cyclic nucleotide gated channels as a feasible candidate for association with the PGE(2) binding site in bovine aortic endothelial cells.

Animals↗
PubMed1989

Primary structure and functional expression from complementary DNA of the rod photoreceptor cyclic GMP-gated channel.

The complete amino-acid sequence of the cyclic GMP-gated channel from bovine retinal rod photoreceptors, deduced by cloning and sequencing its complementary DNA, shows that the protein contains several putative transmembrane segments, followed by a region that is similar to the cyclic GMP-binding domains of cyclic GMP-dependent protein kinase. Expression of the complementary DNA produces cyclic GMP-gated channel activity in Xenopus oocytes.

Amino Acid Sequence↗
PubMed1996

Rat hippocampal neurons express genes for both rod retinal and olfactory cyclic nucleotide-gated channels: novel targets for cAMP/cGMP function.

Cyclic nucleotide-gated (CNG) channels are Ca(2+)-permeable, nonspecific cation channels that can be activated through direct interaction with cAMP and/or cGMP. Recent electrophysiological evidence for these channels in cultured hippocampal neurons prompted us to investigate the expression of CNG channel genes in hippocampus. PCR amplification detected the expression of transcripts for subunit 1 of both the rod photoreceptor (RCNGC1) and the olfactory receptor cell (OCNGC1) subtype of CNG channel in adult rat hippocampus. In situ hybridization detected expression of both channel subtypes in most principal neurons, including pyramidal cells of the CA1 through CA3 regions and granule cells of the dentate gyrus. From the hybridization patterns, we conclude that the two genes are colocalized in individual neurons. Comparison of the patterns of expression of type 1 cGMP-dependent protein kinase and the CNG channels suggests that hippocampal neurons can respond to changes in cGMP levels with both rapid changes in CNG channel activity and slower changes induced by phosphorylation. Future models of hippocampal function should include CNG channels and their effects on both electrical responses and intracellular Ca2+ levels.

Animals↗
PubMed1996

Families of ion channels with two hydrophobic segments.

The family of epithelial sodium channels and nematode degenerins has expanded recently to include a member found only in brain, and another that functions in molluscs as a ligand-gated channel. A new gene family of mammalian ATP-gated channels has been discovered; one of its seven members plays a role in the lysis of macrophages. The mechanosensitive channel of bacteria has emerged as the simplest form of a channel protein subunit with two hydrophobic domains.

Amino Acid Sequence↗
PubMed2000

Probing the role of a conserved M1 proline residue in 5-hydroxytryptamine(3) receptor gating.

A conserved proline residue is found in the first transmembrane domain (M1) of every subunit in the ligand-gated ion channel superfamily. The position of this proline between the N-terminal extracellular agonist binding and the second transmembrane (M2) channel lining domains in the primary sequence suggests its possible involvement in the gating of the receptor. Replacing this proline with alanine, glycine, or leucine in the 5-hydroxytryptamine (5-HT)(3A) homomeric receptors expressed in Xenopus laevis oocytes resulted in the absence of 5-HT-induced whole-cell currents, although there were normal levels of specific surface [(3)H]granisetron ([(3)H]BRL-43694) binding sites. To determine what properties of the conserved proline are critical for the function of the channel, two imino acids and an alpha-hydroxy acid were incorporated at the proline position using the nonsense suppression method. trans-3-Methyl-proline, pipecolic acid, and leucic acid were able to replace the conserved proline to produce active channels with EC(50) values similar to that for the wild-type receptor. These trends are preserved in the heteromeric receptors consisting of 5-HT(3A) and 5-HT(3B) subunits in oocytes. The prominent common feature among these residues and proline is the lack of hydrogen bond donor activity, potentially resulting in a flexible secondary structure in the M1 region. Thus, lack of hydrogen bond donor activity may be a key element in channel gating and may explain the high degree of conservation of this M1 proline.

Animals↗
PubMed2001

Anesthetics and ion channels: molecular models and sites of action.

The mechanisms of general anesthesia in the central nervous system are finally yielding to molecular examination. As a result of research during the past several decades, a group of ligand-gated ion channels have emerged as plausible targets for general anesthetics. Molecular biology techniques have greatly accelerated attempts to classify ligand-gated ion channel sensitivity to general anesthetics, and have identified the sites of receptor subunits critical for anesthetic modulation using chimeric and mutated receptors. The experimental data have facilitated the construction of tenable molecular models for anesthetic binding sites, which in turn allows structural predictions to be tested. In vivo significance of a putative anesthetic target can now be examined by targeted gene manipulations in mice. In this review, we summarize from a molecular perspective recent advances in our understanding of mechanisms of action of general anesthetics on ligand-gated ion channels.

Anesthetics↗
PubMed2001

A (beta)-strand in the (gamma)2 subunit lines the benzodiazepine binding site of the GABA A receptor: structural rearrangements detected during channel gating.

Benzodiazepines (BZDs) exert their effects in the CNS by binding to a modulatory site on GABA(A) receptors. Individual amino acids have been implicated in BZD recognition and modulation of the GABA(A) receptor, but the secondary structure of the amino acids contributing to the BZD binding site has not been elucidated. In this report we used the substituted cysteine accessibility method to understand the structural dynamics of a region of the GABA(A) receptor implicated in BZD binding, gamma(2)Y72-gamma(2)Y83. Each residue within this region was mutated to cysteine and expressed with wild-type alpha(1) and beta(2) subunits in Xenopus oocytes. Methanethiosulfonate (MTS) reagents were used to modify covalently the engineered cysteines, and the subsequent effects on BZD modulation of the receptor were monitored functionally by two-electrode voltage clamp. We identified an alternating pattern of accessibility to sulfhydryl modification, indicating that the region gamma(2)T73-gamma(2)T81 adopts a beta-strand conformation. By monitoring the ability of BZD ligands to impede the covalent modification of accessible cysteines, we also identified two residues within this region, gamma(2)A79 and gamma(2)T81, that line the BZD binding site. Sulfhydryl modification of gamma(2)A79C or gamma(2)T81C allosterically shifts the GABA EC(50) of the receptor, suggesting that certain MTS compounds may act as tethered agonists at the BZD binding site. Last, we present structural evidence that a portion of the BZD binding site undergoes a conformational change in response to GABA binding and channel gating (opening and desensitization). These data represent an important step in understanding allosteric communication in ligand-gated ion channels.

Allosteric Regulation↗
PubMed2003

Glycosylation affects rat Kv1.1 potassium channel gating by a combined surface potential and cooperative subunit interaction mechanism.

The effect of glycosylation on Kv1.l potassium channel function was investigated in mammalian cells stably transfected with Kv1.l or Kv1.1N207Q. Macroscopic current analysis showed that both channels were expressed but Kv1.1N207Q, which was not glycosylated, displayed functional differences compared with wild-type, including slowed activation kinetics, a positively shifted V 1/2, a shallower slope for the conductance versus voltage relationship, slowed C-type inactivation kinetics, and a reduced extent of and recovery from C-type inactivation. Kv1. 1N207Q activation properties were also less sensitive to divalent cations compared with those of Kv1.l. These effects were largely due to the lack of trans-Golgi added sugars, such as galactose and sialic acid, to the N207 carbohydrate tree. No apparent change in ionic current deactivation kinetics was detected inKv1.1N207Q compared with wild-type. Our data, coupled with modelling, suggested that removal of the N207 carbohydrate tree had two major effects. The first effect slowed the concerted channel transition from the last dosed state to the open state without changing the voltage dependence of its kinetics. This effect contributed to the G-V curve depolarization shift and together with the lower sensitivity to divalent cations suggested that the carbohydrate tree and its negatively charged sialic acids affected the negative surface charge density on the channel's extracellular face that was sensed by the activation gating machinery. The second effect reduced a cooperativity factor that slowed the transition from the open state to the dosed state without changing its voltage dependence. This effect accounted for the shallower G-V slope, and contributed to the depolarized G-V shift, and together with the inactivation changes it suggested that the carbohydrate tree also affected channel conformations. Thus N-glycosylation, and particularly terminal sialylation, affected Kv1.l gating properties both by altering the surface potential sensed by the channel's activation gating machinery and by modifying conformational changes regulating cooperative subunit interactions during activation and inactivation. Differences in glycosylation pattern among closely related channels may contribute to their functional differences and affect their physiological roles.

Amino Acid Sequence↗