S4 mutations to glutamate restore E1R current. (A) Currents were recorded from double mutations shown using the voltage protocol as in Fig. 1 B. Scale, 6 µA. (B) Peak current amplitudes in A were averaged for each mutation. Error bars represent standard error of the means. (C) Current from E1R paired with S4 residues mutated to glutamate coexpressed with KCNE1. Scale, 20 µA. (D) Peak current amplitudes in C were averaged for each mutant. Error bars represent standard error of the means.