Charge-conserving mutations in S4 modulate hERG voltage-dependent gating. (A) Typical current traces recorded from S4 mutant channels in response to the voltage protocols shown (insets). Note the change in scale for K538R. Arrows indicate the zero current level. (B) Comparison of the mean G-V relationships for WT hERG and the mutant channels shown in A. Lines represent fits of the data to a Boltzmann function. n values and Boltzmann parameters are summarized in Table 1. (C) Plot of τ_act values for WT hERG and the S4 mutant channels against the electrochemical potential for activation. The envelope of tails protocol described in Fig. 3 A was used to measure τ_act values over a range of voltages that depended on the V_1/2 of the G-V curve for each mutant. (D) Comparison of τ_deact values for WT hERG and the S4 mutant channels. τ_deact was measured using the deactivation protocol described in Fig. 3 B, with a variable voltage range to accommodate the different shifts in the G-V curves caused by each mutant. For B–D, data points represent mean ± SEM (error bars). Similar to Fig. 3, electrochemical potential energies for WT hERG calculated using ΔG₀ values derived from G-V curves obtained using both 2- and 10-s pulse durations are presented.