Figure 2.

Frequency-dependent effect of Me5 on macroscopic–current-like Na⁺ currents in a cell-attached patch of rat skeletal muscle fibre. (A) Time course of changes in peak Na⁺ currents induced by 10 μM Me5 added to the bath solution. Na⁺ currents were elicited by depolarizing the patch membrane from a holding potential of −100 mV to −20 mV, at a frequency of 0.3 Hz or 1 Hz as indicated. Peak current amplitudes were measured on each trace, averaged every five consecutive traces and reported as means +s.e.mean as a function of the recording time. The blanks in the time course of Me5 effect correspond to the application of voltage protocols for the measure of I–V and steady-state inactivation relationships, maintaining the 1 Hz or the 0.3 Hz stimulation frequencies. The solid line indicates a typical time course of changes in peak Na⁺ currents recorded in the presence of 10 μM mexiletine. (B) Ensemble average Na⁺ currents constructed from 30 consecutive traces elicited as in (A) (same patch) at stimulation frequencies of 0.3 or 1 Hz, before (control) and after application of 10 μM Me5. (C) Ensemble average Na⁺ currents constructed as in (B), before and after application of 10 μM mexiletine. Only currents elicited at 1 Hz are illustrated.