Figure 5.

The steady-state activation curve for resurgent Na⁺ currents in the WT and the p.V781I and p.A1737T mutant channels. (A) The cells were held at −120 mV for approximately 30 ms, and then subjected to various 10 ms depolarizing prepulse sampling between −100 and +180 mV range with stepwise 10 mV increments for about 50 ms. Repolarization pulses evoked the resurgent Na⁺ currents at −60 mV for approximately 150 ms. We obtained sample sweeps from the WT and the p.V781I and p.A1737T mutant Na_v1.4 channels. The blue traces demonstrate that inactivated currents in the p.V781I and p.A1737T mutant channels were slower than those in the WT channels. (B) The steady-state activation curves of the transient (fitted lines in Figure 1B replotted for comparison) and resurgent Na⁺ currents. The resurgent Na⁺ activation curve for each cell was obtained by fitting the data with a Boltzmann function. (C,D) The population data (n = 8) for Vh and q. The mean values were 33.4 ± 0.8 mV and 30.6 ± 0.8 for the WT channel, respectively. Those for the p.V781I mutant channel were 22.5 ± 0.7 mV (n = 8; * p < 0.05) and 44.4 ± 0.9 (n = 8; * p < 0.05), and those for the p.A1737T mutant channel were 38.27 ± 0.8 mV (n = 8; * p < 0.05) and 33.9 ± 0.9.