Effect of lidocaine on the energetics of the domain III voltage sensor. (A) Time course of voltage-dependent fluorescence signals from domain III of WT and a couple of representative mutant sodium channels. Fluorescence traces were obtained before and after 10-mM lidocaine application by pulsing to a test potential (ranging from +50 to −210 mV) for 20 ms, with a prepulse to −120 mV for 20 ms. Each trace represents an average of 10 trials with an interval of 1 s between each pulse. The scale bars are provided as insets, and the percentage fluorescence changes (ΔF/F) are on the y axis. (B) Steady-state F-V curves before (filled symbols) and after (open symbols) 10-mM lidocaine application. The lines represent the best fits of the averaged data to a single Boltzmann function. The error bars represent the average ± SEM for each data point. (C) Summary of shifts in F-V curves of WT and various mutants upon the application of lidocaine. ΔV_1/2 was obtained as: ΔV_1/2 = V_{1/2(after lidocaine)} − V_{1/2(before lidocaine)}. Each bar represents mean ± SEM of at least three independent oocyte measurements. The gray dashed line represents the shift in F-V curves of WT. To test whether these differences were statistically significant, a one-way ANOVA test was used, followed by a post-hoc Dunnett’s test. *, P < 0.001; #, P < 0.05.