TEMPERATURE DEPENDENCE OF THE SODIUM CHANNEL GATING KINETICS IN THE NODE OF RANVIER

¹ Department of Biophysics, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ

Temperature dependence of the Na⁺ channel gating kinetics was measured from the ionic and charge displacement currents in the node of Ranvier of Xenopus laevis. m³h kinetics was applied, assuming a delay, t, in the activation process. The rate constants for the m- and h-process showed Arrhenius temperature-dependence with Q₁₀ of 2·34 and 2·9 respectively, while t exhibited non-Arrhenius temperature-dependence. Q₁₀ for [unknown]P_Na, measured as 1·6, was smaller than for the rate constants and similar to that for a diffusion process. A negative shift and decrease in voltage sensitivity of the steady-state curves, h and m, occurred with decreasing temperature. The maximum time constant obtained from a single exponential fit to the displacement currents during the pulse for times greater than 90 µs exhibited Q₁₀ of 2·01, which lies between that for [unknown]P_Na and that for _m.

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