INACTIVATION-RESISTANT CHANNELS UNDERLYING THE PERSISTENT SODIUM CURRENT IN RAT VENTRICULAR MYOCYTES

Single-channel sodium currents that could be blocked with TTX were eli cited by depolarizing voltage pulses in either cell-attached or inside -out patches from rat ventricular myocytes. A transient burst of chann els was followed by late-opening (persistent) channels with low open p robability. Conditioning depolarizing pre-pulses that inactivated tran sient channels and 'chattering' late-opening channels had no effect on persistent channels. The open probability of persistent channels reac hed a maximum at more negative potentials than transient channels. Bet ween -70 mV and -40 mV, the average open time of persistent channels i ncreased, whereas the average open time of transient channels did not change significantly, so the open times of the two channels diverged a s the potential became more positive. The conductance of transient and persistent channels was similar, and the conductance of both kinds of channel increased at more depolarized potentials.