Patch recordings from the electrocytes of Electrophorus: Na channel gating currents

Abstract

Gating currents were recorded at 11°C in cell-attached and inside-out patches from the innervated membrane of Electrophorus main organ electrocytes. With pipette tip diameters of 3-8 μm, 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 ∼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.