scholarly journals A comparison of sodium currents in rat and frog myelinated nerve: normal and modified sodium inactivation.

1987 ◽  
Vol 382 (1) ◽  
pp. 175-191 ◽  
Author(s):  
B Neumcke ◽  
J R Schwarz ◽  
R Stämpfli
Keyword(s):  
Sodium Currents ◽  
Myelinated Nerve ◽  
Sodium Inactivation

scholarly journals Pharmacological Modifications of the Sodium Channels of Frog Nerve

1968 ◽  
Vol 51 (2) ◽  
pp. 199-219 ◽  
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.

scholarly journals The Inhibition of Sodium Currents in Myelinated Nerve by Quaternary Derivatives of Lidocaine

1973 ◽  
Vol 62 (1) ◽  
pp. 37-57 ◽  
Author(s):  
Gary R. Strichartz
Keyword(s):  
Sodium Channels ◽  
Voltage Dependence ◽  
Nerve Fibers ◽  
Sodium Currents ◽  
Myelinated Nerve ◽  
Variable Voltage ◽  
Electrical Gradient ◽  
A Site ◽  
Derivatives Of ◽  
Tonic Phase

The inhibition of sodium currents by quaternary derivatives of lidocaine was studied in single myelinated nerve fibers. Membrane currents were diminished little by external quaternary lidocaine (QX). QX present in the axoplasm (<0.5 mM) inhibited sodium currents by more than 90%. Inhibition occurred as the sum of a constant, tonic phase and a variable, voltage-sensitive phase. The voltage-sensitive inhibition was favored by the application of membrane potential patterns which produce large depolarizations when sodium channels are open. Voltage-sensitive inhibition could be reversed by small depolarizations which opened sodium channels. One explanation of this observation is that QX molecules enter open sodium channels from the axoplasmic side and bind within the channels. The voltage dependence of the inhibition by QX suggests that the drug binds at a site which is about halfway down the electrical gradient from inside to outside of the sodium channel.

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