Slow recovery of sodium current and 'gating current' from inactivation

1. Asymmetrical displacement currents ('gating currents') and Na currents have been recorded in intracellularly perfused squid giant axons with the voltage-clamp method. Inactivation of the currents by a long-lasting depolarization to -30 mV and subsequent removal of inactivation have been studied at temperatures of 0-5-3 degrees and 8-9 degrees C. 2. The asymmetrical displacement current, recorded with the divided pulse procedure, was markedly reduced by a 1-5-800 msec depolarization to -30 mV; a 3 min depolarization led to almost complete blockage. 3. Recovery of the asymmetrical displacement current from a 3 min depolarization to -30 mV was slow (20-40% recovery after 50-800 msec at -70 mV and 8-9 degrees C); full recovery from a long-lasting depolarization took several minutes. 4. Recovery of the Na current followed a similar time course (20% recovery after 50-800 msec at -70 mV and 8-9 degrees C); the time constant of full recovery was 2-3-5 min. 5. Slow recovery was also demonstrated by recording the displacement currents associated with single depolarizing pulses. 6. The results are consistent with the idea that the asymmetrical displacement current is related to the function of the Na gates.