Gating currents in th intact crayfish giant axon.

Both single-sweep and signal-averaged asymmetry current are measured from intact crayfish axons after ionic currents are blocked with tetrodotoxin and 4-aminopyridine. The ON asymmetry charge saturates at about 0 mV and no ON charge movement is detectable at voltages negative to -140 mV. The areas of ON and OFF asymmetry charge are equal for short depolarizations but the ratio QOFF/QON decreases for longer depolarizing pulses. Sodium and asymmetry current magnitudes can be changed in parallel by lowering the hold potential or by imposing conditioning prepulses. Our results are consistent with the concept that asymmetry current in generated by movement of trapped charge in association with Na channel gating.