Temperature dependence of gating current in myelinated nerve fibers

Summary

Asymmetrical displacement currents and Na currents of single myelinated nerve fibers ofXenopus laevis were studied in the temperature range from 5 to 24°C. The time constant of the on-response atE=4 mV,τ _on, was strongly temperature dependent, whereas the amount of displaced charge atE=39 mV, Q_on, was only slightly temperature dependent. The mean Q₁₀ forτ ^-1_on was 2.54, the mean Q₁₀ for Q_on was 1.07. The time constant of charge immobilization,τ _i , atE=4 mV varied significantly (α=0.001) with temperature. The mean Q₁₀ forτ ^-1 _i 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°C. The Q_off/Q_on ratio forE=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 Q_on (E) curves to more negative potentials by 0.51 mVK ⁻¹, but shiftedP _Na (E) curves andh _∞ (E) curves to more positive potentials by 0.43 and 0.57 mV K⁻¹, respectively.h _∞ (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.