KCNE3 sensitivities are lost in the S1 phenylalanine double mutants. (A) Representative current traces of the hKCNQ1 F127L/F130L mutant in the absence (black) and presence of KCNE1 (red) or KCNE3 (blue) are shown. The membrane potential was stepped up from −100 to +60 mV in 20-mV increments. (B) G-V relationships for the human KCNQ1 WT and phenylalanine double mutants in the absence (black) and presence of KCNE1 (red) or KCNE3 (blue). All plots are fitted with the Boltzmann equation except the hKCNQ1 WT with KCNE3, which could not be fitted with it.