Fig. 2. Inactivation of HERG wild-type (wt) and HERG Y652A currents. (  A ) Representative current traces of HERG wt and HERG Y652A showing the steady state inactivation. Note that the current for HERG Y652A does not approach the steady state level after hyperpolarization. (  B ) Uncorrected curves for the voltage dependence of steady state inactivation. Tail currents were normalized to the maximum (I^tail/I^max). (  C ) An instantaneous activation protocol was used to determine the inactivation time constants at different test potentials. (  D ) Voltage dependence of inactivation time constants (τ^inact). The differences between HERG wt and HERG Y652A were highly significant (  P < 0.01, tested by analysis of variance).