Mode shift of ionic current in S631A hERG. (A) Example traces recorded in response to the protocols shown to measure the voltage-dependent equilibria of activation (i) and deactivation (ii) of ionic current in inactivation-deficient S631A hERG channels. Insets are expansions of the highlighted regions. (B) Summary of the voltage-dependent equilibria of activation and deactivation. Solid lines are fits of the Boltzmann equation to activation data, whereas broken lines are fits of the Boltzmann equation to the deactivation data. Neither the V_0.5 values for activation (−20.32 ± 0.5 mV and −21.7 ± 0.7 mV for wild type and S631A, respectively, SEM; n ≥ 5) nor deactivation (−54.9 ± 1.6 mV and −50.72 ± 0.9 mV for wild type and S631A, respectively, SEM; n = 4) were significantly different from wild type (Student’s t test, P < 0.05).