Fig. 2. State-dependent block of sodium channels by 10 μm prenylamine. The pulse protocol is shown in the inset. Conditioning prepulses (10 s each) ranging in amplitude from −180 to −50 mV were applied. After a 100-ms interval at −140 mV, Na⁺currents were evoked by the delivery of the test pulse to +30 mV. Currents were normalized to the control currents obtained with a prepulse to −180 mV. (A ) Representative tracings for a drug concentration of 10 μm are shown for the resting state (conditioning prepulse potential [Epp]=−150 mV) and for the inactivated state (Epp =−60 mV). (B ) Normalized Na⁺current in the absence (control) or presence of prenylamine and bupivacaine at a concentration of 10 μm was plotted against conditioning prepulse potential. Data were fitted well with a Boltzmann function (1/[1+exp((V^0.5−V)/K^E)]). The average V^0.5value (50% availabilities) and K^Evalue (a slope factor) for the fitted Boltzmann functions were −56.1 ± 9.4 and 5.4 ± 4.4 mV for the control, −80.7 ± 0.5 and 8.2 ± 0.4 mV for bupivacaine, and −103.7 ± 0.4 and 5.9 ± 0.3 mV for prenylamine.