Temperature dependence of gating current in myelinated nerve fibers.
Asymmetrical displacement currents and Na currents of single myelinated nerve fibers of Xenopus laevis were studied in the temperature range from 5 to 24 degrees C. The time constant of the on-response at E = 4 mV, tau on, was strongly temperature dependent, whereas the amount of displaced charge at E = 39 mV, Qon, was only slightly temperature dependent. The mean Q10 for tau on-1 was 2.54, the mean Q10 for Qon was 1.07. The time constant of charge immobilization, tau i, at E = 4 mV varied significantly (alpha = 0.001) with temperature. The mean Q10 for tau i-1 was 2.71 +/- 0.38. The time constants of immobilization of gating charge and of fast inactivation of Na permeability were similar in the temperature range from 6 to 22 degrees C. The Qoff/Qon ratio for E = 4 mV pulses of 0.5 msec duration decreased with increasing temperature. The temperature dependence of the time constant of the off-response could not be described by a single Q10 value, since the Q10 depended on the duration of the test pulse. Increasing temperature shifted Qon (E) curves to more negative potentials by 0.51 mV K-1, but shifted PNa (E) curves and h infinity (E) curves to more positive potentials by 0.43 and 0.57 mV K-1, respectively. h infinity (E = -70 mV) increased monotonously with increasing temperature. The present data indicate that considerable entropy changes may occur when the Na channel molecule passes from closed through open to inactivated states.
Jonas
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P
Physiologisches Institut der Justus-Liebig-Universität Giessen, Federal Republic of Germany.
D000703:Analog-Digital Conversion; D000818:Animals; D002463:Cell Membrane Permeability; D015640:Ion Channel Gating; D008564:Membrane Potentials; D009431:Neural Conduction; D011487:Protein Conformation; D011901:Ranvier's Nodes / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors; D014982:Xenopus laevis
D015222:Sodium Channels