Recovery from charge immobilization in sodium channels of the frog node of Ranvier.

The gating current off-response of the frog node of Ranvier shows a fast and a slow phase, reflecting presumably charges moving back into the resting position and charges returning from immobilization. The paper describes measurements of the time constant of the slow component, tau off2, at different potentials at 20 or 17 degrees C. The time constant tau off2 decreased markedly when the potential to which the fibre was repolarized at the end of the test pulses was decreased from -100 to -145 mV. tau off2 was compared with tau re gat and tau re Na, the time constants of the recovery of gating current and peak sodium current from the effect of a depolarizing conditioning pulse. The three time constants were equal at -145 mV, but somewhat different at -100 to -130 mV, the sequence being tau re gat greater than tau off2 greater than tau re Na. The inequality tau re gat greater than tau off2 was small and statistically not significant. It does not seem to be due to contamination of the charge movement with ionic currents because a) the Qoff/Qon ratio was near 1.0 at -100 to -120 mV, b) partial replacement of internal CsCl by KCl did not significantly alter tau off2 or Qoff/Qon, c) tau off2 was independent of pulse size. The small inequality tau re gat greater than tau off2 suggests that charges which have returned from immobilization are not immediately available for displacement. The inequality tau re gat greater than tau re Na was larger and statistically significant at -100 and -110 mV.(ABSTRACT TRUNCATED AT 250 WORDS)