scholarly journals Kinetic analysis of pancuronium interaction with sodium channels in squid axon membranes.

1977 ◽  
Vol 69 (3) ◽  
pp. 293-323 ◽  
Author(s):  
J Z Yeh ◽  
T Narahashi
Keyword(s):  
Membrane Potential ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Rate Constant ◽  
Time Course ◽  
Voltage Dependence ◽  
Sodium Current ◽  
Sodium Concentration ◽  
Internal Concentration ◽  
Sodium Inactivation

The interaction of pancuronium with sodium channels was investigated in squid axons. Sodium current turns on normally but turns off more quickly than the control with pancuronium 0.1-1mM present internally; The sodium tail current associated with repolarization exhibits an initial hook and then decays more slowly than the control. Pancuronium induces inactivation after the sodium inactivation has been removed by internal perfusion of pronase. Such pancuronium-induced sodium inactivation follows a single exponential time course, suggesting first order kinetics which represents the interaction of the pancuronium molecule with the open sodium channel. The rate constant of association k with the binding site is independent of the membrane potential ranging from 0 to 80 mV, but increases with increasing internal concentration of pancuronium. However, the rate constant of dissociation l is independent of internal concentration of pancuronium but decreases with increasing the membrane potential. The voltage dependence of l is not affected by changine external sodium concentration, suggesting a current-independent conductance block, The steady-state block depends on the membrane potential, being more pronounced with increasing depolarization, and is accounted for in terms of the voltage dependence of l. A kinetic model, based on the experimental observations and the assumption on binding kinetics of pancuronium with the open sodium channel, successfully simulates many features of sodium current in the presence of pancuronium.

scholarly journals Tracking S4 movement by gating pore currents in the bacterial sodium channel NaChBac

2014 ◽  
Vol 144 (2) ◽  
pp. 147-157 ◽  
Author(s):  
Tamer M. Gamal El-Din ◽  
Todd Scheuer ◽  
William A. Catterall
Keyword(s):  
Membrane Potential ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Voltage Dependence ◽  
Periodic Paralysis ◽  
Membrane Potentials ◽  
Structural Basis ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Gating Charges

Voltage-gated sodium channels mediate the initiation and propagation of action potentials in excitable cells. Transmembrane segment S4 of voltage-gated sodium channels resides in a gating pore where it senses the membrane potential and controls channel gating. Substitution of individual S4 arginine gating charges (R1–R3) with smaller amino acids allows ionic currents to flow through the mutant gating pore, and these gating pore currents are pathogenic in some skeletal muscle periodic paralysis syndromes. The voltage dependence of gating pore currents provides information about the transmembrane position of the gating charges as S4 moves in response to membrane potential. Here we studied gating pore current in mutants of the homotetrameric bacterial sodium channel NaChBac in which individual arginine gating charges were replaced by cysteine. Gating pore current was observed for each mutant channel, but with different voltage-dependent properties. Mutating the first (R1C) or second (R2C) arginine to cysteine resulted in gating pore current at hyperpolarized membrane potentials, where the channels are in resting states, but not at depolarized potentials, where the channels are activated. Conversely, the R3C gating pore is closed at hyperpolarized membrane potentials and opens with channel activation. Negative conditioning pulses revealed time-dependent deactivation of the R3C gating pore at the most hyperpolarized potentials. Our results show sequential voltage dependence of activation of gating pore current from R1 to R3 and support stepwise outward movement of the substituted cysteines through the narrow portion of the gating pore that is sealed by the arginine side chains in the wild-type channel. This pattern of voltage dependence of gating pore current is consistent with a sliding movement of the S4 helix through the gating pore. Through comparison with high-resolution models of the voltage sensor of bacterial sodium channels, these results shed light on the structural basis for pathogenic gating pore currents in periodic paralysis syndromes.

scholarly journals Effects of Internal Divalent Cations on Voltage-Clamped Squid Axons

1974 ◽  
Vol 63 (6) ◽  
pp. 675-689 ◽  
Author(s):  
Ted Begenisich ◽  
Carl Lynch
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Divalent Cations ◽  
Sodium Current ◽  
Ionic Currents ◽  
Zinc Concentrations ◽  
Sodium Inactivation ◽  
Kinetics Of ◽  
Internal Calcium ◽  
Reversible Reduction

We have studied the effects of internally applied divalent cations on the ionic currents of voltage-clamped squid giant axons. Internal concentrations of calcium up to 10 mM have little, if any, effect on the time-course, voltage dependence, or magnitude of the ionic currents. This is inconsistent with the notion that an increase in the internal calcium concentration produced by an inward calcium movement with the action potential triggers sodium inactivation or potassium activation. Low internal zinc concentrations (∼1 mM) selectively and reversibly slow the kinetics of the potassium current and reduce peak sodium current by about 40% with little effect on the voltage dependence of the ionic currents. Higher concentrations (∼10 mM) produce a considerable (ca. 90%) nonspecific reversible reduction of the ionic currents. Large hyperpolarizing conditioning pulses reduce the zinc effect. Internal zinc also reversibly depolarizes the axon by 20–30 mV. The effects of internal cobalt, cadmium, and nickel are qualitatively similar to those of zinc: only calcium among the cations tested is without effect.

scholarly journals Interaction of n-alkylguanidines with the sodium channels of squid axon membrane.

1980 ◽  
Vol 76 (3) ◽  
pp. 315-335 ◽  
Author(s):  
G E Kirsch ◽  
J Z Yeh ◽  
J M Farley ◽  
T Narahashi
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Sodium Current ◽  
Time Dependent ◽  
Squid Axon ◽  
Axon Membrane ◽  
Inactivation Mechanism ◽  
Hydrophobic Binding ◽  
Sodium Inactivation ◽  
Guanidino Group

The effects of n-alkylguanidine derivatives on sodium channel conductance were measured in voltage clamped, internally perfused squid giant axons. After destruction of the sodium inactivation mechanism by internal pronase treatment, internal application of n-amylguanidine (0.5 mM) or n-octylguanidine (0.03 mM) caused a time-dependent block of sodium channels. No time-dependent block was observed with shorter chain derivatives. No change in the rising phase of sodium current was seen and the block of steady-state sodium current was independent of the membrane potential. In axons with intact sodium inactivation, an apparent facilitation of inactivation was observed after application of either n-amylguanidine or n-octylguanidine. These results can be explained by a model in which alkylguanidines enter and occlude open sodium channels from inside the membrane with voltage-independent rate constants. Alkylguanidine block bears a close resemblance to natural sodium inactivation. This might be explained by the fact that alkylguanidines are related to arginine, which has a guanidino group and is thought to be an essential amino acid in the molecular mechanism of sodium inactivation. A strong correlation between alkyl chain length and blocking potency was found, suggesting that a hydrophobic binding site exists near the inner mouth of the sodium channel.

scholarly journals Kinetic Analysis of Block of Open Sodium Channels by a Peptide Containing the Isoleucine, Phenylalanine, and Methionine (IFM) Motif from the Inactivation Gate

1998 ◽  
Vol 111 (1) ◽  
pp. 75-82 ◽  
Author(s):  
Galen Eaholtz ◽  
William N. Zagotta ◽  
William A. Catterall
Keyword(s):  
Electric Field ◽  
Sodium Channel ◽  
Kinetic Analysis ◽  
Sodium Channels ◽  
Rate Constant ◽  
Voltage Dependence ◽  
Bimolecular Reaction ◽  
Voltage Dependent ◽  
Kinetics Of ◽  
The Brain

We analyzed the kinetics of interaction between the peptide KIFMK, containing the isoleucine, phen-ylalanine, and methionine (IFM) motif from the inactivation gate, and the brain type IIA sodium channels with a mutation that disrupts inactivation (F1489Q). The on-rate constant was concentration dependent, consistent with a bimolecular reaction with open sodium channels, while the off rates were unaffected by changes in the KIFMK concentration. The apparent Kd was ∼33 μM at 0 mV. The on rates were voltage dependent, supporting the hypothesis that one or both of the charges in KIFMK enter the membrane electric field. The voltage dependence of block was consistent with the equivalent movement of ∼0.6 electronic charges across the membrane. In contrast, the off rates were voltage independent. The results are consistent with the hypothesis that the KIFMK peptide enters the pore of the open sodium channel from the intracellular side and blocks it.

scholarly journals Removal of sodium channel inactivation in squid giant axons by n-bromoacetamide.

1978 ◽  
Vol 71 (3) ◽  
pp. 227-247 ◽  
Author(s):  
G S Oxford ◽  
C H Wu ◽  
T Narahashi
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Single Channel ◽  
Sodium Current ◽  
Complete Removal ◽  
Specific Protein ◽  
Peptide Bonds ◽  
Voltage Dependent ◽  
Inactivation Gating ◽  
Sodium Inactivation

The group-specific protein reagents, N-bromacetamide (NBA) and N-bromosuccinimide (NBS), modify sodium channel gating when perfused inside squid axons. The normal fast inactivation of sodium channels is irreversibly destroyed by 1 mM NBA or NBS near neutral pH. NBA apparently exhibits an all-or-none destruction of the inactivation process at the single channel level in a manner similar to internal perfusion of Pronase. Despite the complete removal of inactivation by NBA, the voltage-dependent activation of sodium channels remains unaltered as determined by (a) sodium current turn-on kinetics, (b) sodium tail current kinetics, (c) voltage dependence of steady-state activation, and (d) sensitivity of sodium channels to external calcium concentration. NBA and NBS, which can cleave peptide bonds only at tryptophan, tyrosine, or histidine residues and can oxidize sulfur-containing amino acids, were directly compared with regard to effects on sodium inactivation to several other reagents exhibiting overlapping protein reactivity spectra. N-acetylimidazole, a tyrosine-specific reagent, was the only other compound examined capable of partially mimicking NBA. Our results are consistent with recent models of sodium inactivation and support the involvement of a tyrosine residue in the inactivation gating structure of the sodium channel.

Kinetics of Change in Spike Height During Anodal Polarization of Isolated Single Nerve Fibers

1956 ◽  
Vol 187 (3) ◽  
pp. 549-557 ◽  
Author(s):  
Gordon M. Schoepfle
Keyword(s):  
Membrane Potential ◽  
Time Course ◽  
Sodium Current ◽  
Nerve Fibers ◽  
Time Dependent ◽  
Peak Time ◽  
Axon Membrane ◽  
Membrane Hyperpolarization ◽  
Anodal Polarization ◽  
Sodium Inactivation

The time dependent change in magnitude of the nodal action potential was analyzed as a function of time and of change in membrane potential during brief intervals of anodal polarization. The time course of this function involves an exponential term whose time constant decreases to a limiting value as extent of membrane hyperpolarization is progressively increased. While the time course of change in spike height cannot be correlated with any change in membrane potential induced by the polarization, the kinetics suggest that the sodium inactivation mechanism of Hodgkin and Huxley is sufficient to account for the results obtained. Brief direct current pulses elicit changes of membrane potential during activity which indicate that an augmented change in resistance of the hyperpolarized node is sufficient to account for the time dependent increase in spike height. These findings are consistent with the Hodgkin-Huxley scheme in that hyperpolarization of the squid axon membrane at constant membrane potential inhibits ‘sodium inactivation’ thereby allowing sodium conductance and sodium current to attain greater than normal values at peak time of activity. It is concluded that no change in emf of the membrane need be postulated in order to account for the time dependent increase in spike height during hyperpolarization of normal or depressed nodes.

scholarly journals Voltage dependence of intramembrane charge movement and conductance activation of batrachotoxin-modified sodium channels in frog node of Ranvier.

1983 ◽  
Vol 81 (6) ◽  
pp. 829-844 ◽  
Author(s):  
J M Dubois ◽  
M F Schneider ◽  
B I Khodorov
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Voltage Dependence ◽  
Sodium Current ◽  
Node Of Ranvier ◽  
Charge Movement ◽  
Gating Charge ◽  
Before And After ◽  
Intramembrane Charge Movement ◽  
The Individual

Sodium current and sodium channel intramembrane gating charge movement (Q) were monitored in voltage-clamped frog node of Ranvier after modification of all sodium channels by batrachotoxin (BTX). BTX caused an approximately threefold increase in steepness of the Q vs. voltage relationship and a 50-mV negative shift in its midpoint. The maximum amount of intramembrane charge was virtually identical before and after BTX treatment. BTX treatment eliminated the charge immobilization observed in untreated nodes after relatively long depolarizing pulses and slowed the rate of OFF charge movement after a pulse. After BTX treatment, the voltage dependence of charge movement was the same as the steady-state voltage dependence of sodium conductance activation. The observations are consistent with the hypothesis that BTX induces an aggregation of the charged gating particles associated with each channel and causes them to move as a unit having approximately three times the average valence of the individual particles. Movement of this single aggregated unit would open the BTX-modified sodium channel.

Gating currents in the node of Ranvier: voltage and time dependence

1975 ◽  
Vol 270 (908) ◽  
pp. 483-492 ◽  
Keyword(s):  
Membrane Potential ◽  
Time Constant ◽  
Time Course ◽  
Voltage Dependence ◽  
Sudden Change ◽  
Node Of Ranvier ◽  
Ionic Currents ◽  
Gating Currents ◽  
Myelinated Nerve ◽  
Sodium Conductance

Like the axolemma of the giant nerve fibre of the squid, the nodal membrane of frog myelinated nerve fibres after blocking transmembrane ionic currents exhibits asymmetrical displacement currents during and after hyperpolarizing and depolarizing voltage clamp pulses of equal size. The steady-state distribution of charges as a function of membrane potential is consistent with Boltzmann’s law (midpoint potential —33.7 mV; saturation value 17200 charges/(μm 2 ). The time course of the asymmetry current and the voltage dependence of its time constant are consistent with the notion that due to a sudden change in membrane potential the charges undergo a first order transition between two configurations. Size and voltage dependence of the time constant are similar to those of the activation of the sodium conductance assuming m 2 h kinetics, The results suggest the presence of ten times more sodium channels (5000/μm2) in the node of Ranvier than in the squid giant axon with similar sodium conductance per channel (2-3 pS),

scholarly journals Analysis of sodium current fluctuations in the cut-open squid giant axon.

1984 ◽  
Vol 83 (2) ◽  
pp. 133-142 ◽  
Author(s):  
I Llano ◽  
F Bezanilla
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Sodium Current ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Statistical Techniques ◽  
Current Fluctuations ◽  
Small Populations ◽  
Squid Axon ◽  
Single Sodium Channel

Patch pipettes were used to record the current arising from small populations of sodium channels in voltage-clamped cut-open squid axons. The current fluctuations associated with the time-variant sodium conductance were analyzed with nonstationary statistical techniques in order to obtain an estimate for the conductance of a single sodium channel. The results presented support the notion that the open sodium channel in the squid axon has only one value of conductance, 3.5 pS.

scholarly journals GS-967 and Eleclazine Block Sodium Channels in Human Induced Pluripotent Stem Cell-derived Cardiomyocytes

2020 ◽  
Author(s):  
Franck Potet ◽  
Defne E. Egecioglu ◽  
Paul W. Burridge ◽  
Alfred L. George
Keyword(s):  
Stem Cell ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Pluripotent Stem Cell ◽  
Sodium Current ◽  
Induced Pluripotent Stem Cell ◽  
Slow Inactivation ◽  
Molecular Pharmacology ◽  
Recovery From Inactivation ◽  
Induced Pluripotent

ABSTRACTGS-967 and eleclazine (GS-6615) are novel sodium channel inhibitors exhibiting antiarrhythmic effects in various in vitro and in vivo models. The antiarrhythmic mechanism has been attributed to preferential suppression of late sodium current (INaL). Here, we took advantage of a throughput automated electrophysiology platform (SyncroPatch 768PE) to investigate the molecular pharmacology of GS-967 and eleclazine on peak sodium current (INaP) recorded from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes. We compared GS-967 and eleclazine to the antiarrhythmic drug lidocaine, the prototype INaL inhibitor ranolazine, and the slow inactivation enhancing drug lacosamide. In human induced pluripotent stem cell-derived cardiomyocytes, GS-967 and eleclazine caused a reduction of INaP in a frequency-dependent manner consistent with use-dependent block (UDB). GS-967 and eleclazine had similar efficacy but evoked more potent UDB of INaP (IC50=0.07 and 0.6 μM, respectively) than ranolazine (7.8 μM), lidocaine (133.5 μM) and lacosamide (158.5 μM). In addition, GS-967 and eleclazine exerted more potent effects on slow inactivation and recovery from inactivation compared to the other sodium channel blocking drugs we tested. The greater UDB potency of GS-967 and eleclazine was attributed to the significantly higher association rates (KON) and moderate unbinding rate (KOFF) of these two compounds with sodium channels. We propose that substantial UDB contributes to the observed antiarrhythmic efficacy of GS-967 and eleclazine.SIGNIFICANCE STATEMENTWe investigated the molecular pharmacology of GS-967 and eleclazine on sodium channels in human induced pluripotent stem cell derived cardiomyocytes using a high throughput automated electrophysiology platform. Sodium channel inhibition by GS-967 and eleclazine has unique features including accelerating the onset of slow inactivation and impairing recovery from inactivation. These effects combined with rapid binding and moderate unbinding kinetics explain potent use-dependent block, which we propose contributes to their observed antiarrhythmic efficacy.

Sign in / Sign up

Export Citation Format

Share Document