Mutations of Cys residues in the S5 domain do not prevent oxidation-induced alteration of A653C hERG1 channel gating. (A) G-V relationship for C555A/A653C mutant channels before (V1/2 = −62.6 ± 0.2 mV, k = 9.9 ± 0.2 mV, n = 8) and after 2 mM tbHO2 (V1/2 = −68.1 ± 0.1 mV, k = 10.0 ± 0.1 mV, n = 8). (B) G-V relationship for C566A/A653C channels before (V1/2 = −59.9 ± 0.9 mV, k = 11.2 ± 0.8 mV, n = 5) and after 2 mM tbHO2 (V1/2 = −72.2 ± 2.0 mV, k = 20.6 ± 1.7 mV, n = 5). For both mutant channels, currents shown were elicited at a Vt of −30 mV and Itail was measured at −120 mV. The holding potential was −100 mV.