Figure 6. Steady-state inactivation of hNav1.4 l443C/A444W mutant channels without and with mexiletien.

Superimposed current traces were evoked by a 5 ms test pulse to +30 mV in the absence (A) or presence (B) of 100 μm mexiletine. Test pulses were preceded by 100 ms conditioning pulses and increased in 5 mV increments between –160 and –15 mV C, peak currents in A and B were measured and normalized with respect to the amplitude with the –160 mV conditioning pulse and plotted against the conditioning voltage. Plots were fitted with the Boltzmann function as described in Fig. 2C. The average midpoint (V_0.5) and slope factor (k) for the control solution (○, n= 11) were –83.6 ± 1.2 mV and 10.6 ± 1.0 mV, respectively, and –88.6 ± 0.7 mV and 11.1 ± 0.6 mV for the cells treated with mexiletine (•, n= 6; dashed line). A second Boltzmann function (V_0.5=–57.2 ± 2.7 mV; k= 4.5 ± 0.2 mV; continuous line) was applied to fit the mexiletine data.