Gating currents were recorded at 11 degrees C in cell-attached and inside-out patches from the innervated membrane of Electrophorus main organ electrocytes. With pipette tip diameters of 3-8 microns, maximal charge measured in patches ranged from 0.74 to 7.19 fC. The general features of the gating currents are similar to those from the squid giant axon. The steady-state voltage dependence of the ON gating charge was characterized by an effective valence of 1.3 +/- 0.4 and a midpoint voltage of -56 +/- 7 mV. The charge vs. voltage relation lies approximately 30 mV negative to the channel open probability curve. The ratio of the time constants of the OFF gating current and the Na current was 2.3 at -120 mV and equal at -80 mV. Charge immobilization and Na current inactivation develop with comparable time courses and have very similar voltage dependences. Between 60 and 80% of the charge is temporarily immobilized by inactivation.

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