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

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Abstract
Asymmetrical displacement currents (gating current) and Na currents were recorded in intracellularly perfused squid [Loligo forbesi] giant axons with the voltage-clamp method. Inactivation of currents by a long-lasting depolarization to -30 mV and subsequent removal of inactivation were studied at temperatures of 0.5-3.degree. and 8-9.degree. C. The asymmetrical displacement current, recorded with divided pulse procedure, was markedly reduced by a 1.5-800 ms depolarization to -30 mV; a 3 min depolarization led to almost complete blockage. Recovery of asymmetrical displacement current from a 3 min depolarization to -30 mV was slow (20-40% recovery after 50-800 ms at -70 mV and 8-9.degree. C); full recovery from a long-lasting depolarization took several minutes. Recovery of Na current followed a similar time course (20% recovery after 50-800 ms at -70 mV and 8-9.degree. C); the time constant of full recovery was 2-3.5 min. Slow recovery was demonstrated by recording the displacement currents associated with single depolarizing pulses. The asymmetrical displacement current seems to be related to the function of Na gates.