Inactivation of the Sodium Current in Myxicola Giant Axons

Experiments were conducted on Myxicola giant axons to determine if the sodium activation and inactivation processes are coupled or independent. The main experimental approach was to examine the effects of changing test pulses on steady-state inactivation curves. Arguments were presented to show that in the presence of a residual uncompensated series resistance the interpretation of the results depends critically on the manner of conducting the experiment. Analytical and numerical calculations were presented to show that as long as test pulses are confined to an approximately linear negative conductance region of the sodium current-voltage characteristic, unambiguous interpretations can be made. When examined in the manner of Hodgkin and Huxley, inactivation in Myxicola is quantitatively similar to that described by the h variable in squid axons. However, when test pulses were increased along the linear negative region of the sodium current-voltage characteristic, steady-state inactivation curves translate to the right along the voltage axis. The shift in the inactivation curve is a linear function of the ratio of the sodium, conductance of the test pulses, showing a 5.8 mv shift for a twofold increase in conductance. An independent line of evidence indicated that the early rate of development of inactivation is a function of the rise of the sodium conductance.

Download Full-text

Quantitative Description of Sodium and Potassium Currents and Computed Action Potentials in Myxicola Giant Axons

The Journal of General Physiology ◽

10.1085/jgp.61.3.361 ◽

1973 ◽

Vol 61 (3) ◽

pp. 361-384 ◽

Cited By ~ 48

Author(s):

L. Goldman ◽

C. L. Schauf

Keyword(s):

Action Potentials ◽

Initial Conditions ◽

Sodium Current ◽

Quantitative Description ◽

Potassium Conductance ◽

Giant Axons ◽

Sodium Conductance ◽

Potassium Conductances ◽

The Right ◽

Sodium And Potassium

All analysis of the sodium and potassium conductances of Myxicola giant axons was made in terms of the Hodgkin-Huxley m, n, and h variables. The potassium conductance is proportional to n2. In the presence of conditioning hyperpolarization, the delayed current translates to the right along the time axis. When this effect was about saturated, the potassium conductance was proportional to n3. The sodium conductance was described by assuming it proportional to m3h. There is a range of potentials for which τh and h∞ values fitted to the decay of the sodium conductance may be compared to those determined from the effects of conditioning pulses. τh values determined by the two methods do not agree. A comparison of h∞ values determined by the two methods indicated that the inactivation of the sodium current is not governed by the Hodgkin-Huxley h variable. Computer simulations show that action potentials, threshold, and subthreshold behavior could be accounted for without reference to data on the effects of initial conditions. However, recovery phenomena (refractoriness, repetitive discharges) could be accounted for only by reference to such data. It was concluded that the sodium conductance is not governed by the product of two independent first order variables.

Download Full-text

Ionic currents in vertebrate myelinated nerve at hyperbaric pressure

AJP Cell Physiology ◽

10.1152/ajpcell.1984.246.1.c84 ◽

1984 ◽

Vol 246 (1) ◽

pp. C84-C90 ◽

Cited By ~ 16

Author(s):

J. J. Kendig

Keyword(s):

Steady State ◽

Sodium Current ◽

Ionic Currents ◽

Base Line ◽

Myelinated Nerve ◽

Hyperbaric Pressure ◽

Voltage Curve ◽

Current Voltage ◽

Voltage Dependent ◽

Steady State Inactivation

To establish a base line for a study of anesthetic-pressure antagonism in axons, voltage-clamped nodes of Ranvier from amphibian sciatic nerve were subjected to pressures of 1-100 atm. Over the time of compression, there was usually an irreversible decrease in peak inward sodium current, but there was no change in peak outward sodium current or in the current-voltage relationship. The steady-state inactivation-voltage curve was shifted 5-15 mV in the depolarizing direction at 70-100 atm. The rate of rise of the sodium current was slowed, as was the time constant of inactivation (tau h). Increase in tau h was markedly voltage dependent, suggesting a selective effect of pressure on beta h, the rate constant governing development of the inactive state. The rate of development of steady-state outward potassium current was also decreased, without significant change in maximum current. The effects of pressure are qualitatively similar to, but different in detail from, those reported in squid axon and different in some details from the effects of cooling in this preparation. None of the effects can presently be related to the high-pressure nervous syndrome.

Download Full-text

Дифференциальные уравнения для восстановления производной безгистерезисной нелинейной вольт-амперной характеристики полупроводниковой структуры

Физика и техника полупроводников ◽

10.21883/ftp.2019.01.46997.8881 ◽

2019 ◽

Vol 53 (1) ◽

pp. 111

Author(s):

Н.Д. Кузьмичев ◽

М.А. Васютин

Keyword(s):

Differential Equations ◽

Direct Current ◽

Numerical Solutions ◽

Voltage Characteristic ◽

Semiconductor Structure ◽

Current Voltage Characteristic ◽

Right Hand ◽

Current Voltage ◽

Harmonic Voltage ◽

The Right

AbstractA sequence of inhomogeneous differential equations for reconstructing the derivative of the nonlinear current–voltage characteristic is studied. The right-hand side of these equations is the experimentally determined dependence of the first-harmonic voltage on direct current. Such voltage arises, e.g., at the output of a nonlinear semiconductor structure simultaneously exposed to alternating and direct current. Based on numerical solutions of differential equations, the developed technique is applied to reconstruct the derivative of the current–voltage characteristic of two antiparallel connected p – n junctions.

Download Full-text