Amino acid residues in the pore region of KCNQ1 have a large impact on the KCNE1 modulation. (A) V_1/2 without (light gray bars) and with (dark gray bars) KCNE1 for point mutants of the ciQ1hQ1(S5P) chimera and Ci-KCNQ1 are plotted. Asterisks indicate the significant increase in the level of V_1/2 with KCNE1 compared with those of ciQ1hQ1(S5P) or Ci-KCNQ1 with KCNE1 (Dunnett’s test). The locations of the mutations are indicated by yellow stars in the inset. (B) Representative current traces for the A191G/I258V double mutant of ciQ1hQ1(S5P) in the absence (left) and presence (right) of KCNE1. The membrane potential was stepped up from −100 to +40 mV in 10-mV increments for KCNE1-less current and from −100 to +60 mV in 20-mV increments for KCNE1 current. (C) G-V relationships for the point mutants in the absence (closed circles) and presence (open circles) of KCNE1.