Effect of the KCNQ1-S277L mutation on KCNQ1 current. (A) Whole-cell current traces of KCNQ1 (Q1) channels, with patch protocol in inset. WT and S277L channels were transiently expressed in CHO cells either alone, or in a 50/50 ratio. For the 50/50 expression, trace is enlarged for clarity. (B) Current density. n = 5, ***P < 0.001. (C) Normalized voltage-dependent activation curves. Curves were fitted using a Boltzmann function. Vh for KCNQ1-WT = −26.0 ± 1.4 mV, KCNQ1-WT/KCNQ1-S277L = −15.0 ± 4.1 mV. n = 5, P < 0.05. (D) Rates of activation measured as half-max rise time. n = 5, ***P < 0.001.