Effect of the KCNQ1-S277L mutation on IKs current. (A) Whole-cell current traces of KCNQ1/KCNE1 channels. Patch protocol same as in Fig. 3. WT and S277L channels were transiently expressed in CHO cells either alone, or in a 50/50 ratio, and also with KCNE1. 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/KCNE1 = 9.8 ± 4.5 mV, KCNQ1-WT/KCNQ1-S277L/KCNE1 = 0.6 ± 12.0 mV. n = 5, P not significant. (D) Rates of activation, measured as half-max rise time. n = 5, ***P < 0.001.