Sodium inactivation mechanism modulates QX-314 block of sodium channels in squid axons

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.

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Removal of sodium inactivation and block of sodium channels by chloramine-T in crayfish and squid giant axons

Biophysical Journal ◽

10.1016/s0006-3495(87)83203-4 ◽

1987 ◽

Vol 52 (2) ◽

pp. 155-163 ◽

Cited By ~ 22

Author(s):

J.M. Huang ◽

J. Tanguy ◽

J.Z. Yeh

Keyword(s):

Sodium Channels ◽

Giant Axons ◽

Sodium Inactivation ◽

Chloramine T

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Pharmacological Modifications of the Sodium Channels of Frog Nerve

The Journal of General Physiology ◽

10.1085/jgp.51.2.199 ◽

1968 ◽

Vol 51 (2) ◽

pp. 199-219 ◽

Cited By ~ 308

Author(s):

Bertil Hille

Keyword(s):

Sodium Channels ◽

Nerve Fibers ◽

Myelinated Nerve ◽

Apparent Dissociation Constant ◽

Specific Change ◽

Myelinated Nerve Fibers ◽

Sodium Activation ◽

Sodium Inactivation ◽

Na Ions ◽

Ionic Forms

Voltage clamp measurements on myelinated nerve fibers show that tetrodotoxin, saxitoxin, and DDT specifically affect the sodium channels of the membrane. Tetrodotoxin and saxitoxin render the sodium channels impermeable to Na ions and to Li ions and probably prevent the opening of individual sodium channels when one toxin molecule binds to a channel. The apparent dissociation constant of the inhibitory complex is about 1 nM for the cationic forms of both toxins. The zwitter ionic forms are much less potent. On the other hand, DDT causes a fraction of the sodium channels that open during a depolarization to remain open for a longer time than is normal. The effect cannot be described as a specific change in sodium inactivation or as a specific change in sodium activation, for both processes continue to govern the opening of the sodium channels and neither process is able to close the channels. The effects of DDT are very similar to those of veratrine.

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

The Journal of General Physiology ◽

10.1085/jgp.71.3.227 ◽

1978 ◽

Vol 71 (3) ◽

pp. 227-247 ◽

Cited By ~ 83

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.

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

The Journal of General Physiology ◽

10.1085/jgp.69.3.293 ◽

1977 ◽

Vol 69 (3) ◽

pp. 293-323 ◽

Cited By ~ 71

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.

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Molecular dissection of multiphase inactivation of the bacterial sodium channel NaVAb

The Journal of General Physiology ◽

10.1085/jgp.201711884 ◽

2018 ◽

Vol 151 (2) ◽

pp. 174-185 ◽

Cited By ~ 6

Author(s):

Tamer M. Gamal El-Din ◽

Michael J. Lenaeus ◽

Karthik Ramanadane ◽

Ning Zheng ◽

William A. Catterall

Keyword(s):

Sodium Channel ◽

Sodium Channels ◽

Conformational Changes ◽

Protein Interactions ◽

Early Phase ◽

Molecular Volume ◽

Slow Inactivation ◽

Dependent Inactivation ◽

Voltage Dependent ◽

Inactivation Mechanism

Homotetrameric bacterial voltage-gated sodium channels share major biophysical features with their more complex eukaryotic counterparts, including a slow-inactivation mechanism that reduces ion-conductance activity during prolonged depolarization through conformational changes in the pore. The bacterial sodium channel NaVAb activates at very negative membrane potentials and inactivates through a multiphase slow-inactivation mechanism. Early voltage-dependent inactivation during one depolarization is followed by late use-dependent inactivation during repetitive depolarization. Mutations that change the molecular volume of Thr206 in the pore-lining S6 segment can enhance or strongly block early voltage-dependent inactivation, suggesting that this residue serves as a molecular hub controlling the coupling of activation to inactivation. In contrast, truncation of the C-terminal tail enhances the early phase of inactivation yet completely blocks late use-dependent inactivation. Determination of the structure of a C-terminal tail truncation mutant and molecular modeling of conformational changes at Thr206 and the S6 activation gate led to a two-step model of these gating processes. First, bending of the S6 segment, local protein interactions dependent on the size of Thr206, and exchange of hydrogen-bonding partners at the level of Thr206 trigger pore opening followed by the early phase of voltage-dependent inactivation. Thereafter, conformational changes in the C-terminal tail lead to late use-dependent inactivation. These results have important implications for the sequence of conformational changes that lead to multiphase inactivation of NaVAb and other sodium channels.

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Effects of strychnine on the sodium conductance of the frog node of Ranvier.

The Journal of General Physiology ◽

10.1085/jgp.69.6.915 ◽

1977 ◽

Vol 69 (6) ◽

pp. 915-926 ◽

Cited By ~ 48

Author(s):

B I Shapiro

Keyword(s):

Sodium Channels ◽

Node Of Ranvier ◽

Scorpion Venom ◽

Time Dependent ◽

Channel Block ◽

Approach To Equilibrium ◽

Sodium Conductance ◽

Quaternary Derivative ◽

Tetraethylammonium Ion ◽

Sodium Inactivation

Strychnine blocks sodium conductance in the frog node of Ranvier. This block was studied by reducing and slowing sodium inactivation with scorpion venom. The block is voltage and time dependent. The more positive the axoplasm the greater the block and the faster the approach to equilibrium. Some evidence is presented suggesting that only open channels can be blocked. The block is reduced by raising external sodium or lithium but not impermeant cations. A quaternary derivative of strychnine was synthesized and found to have the same action only when applied intracellularly. We conclude that strychnine blocks sodium channels by a mechanism analogous to that by which it blocks potassium channels. The potassium channel block had previously been found to be identical to that by tetraethylammonium ion derivatives. In addition, strychnine resembles procaine and its derivatives in both its structure and the mechanism of sodium channel block.

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