Correlation of the fast component of Kv1.2 fluorescence quenching with gating charge movement. (A) Representative gating currents for Kv1.2 WT, recorded from transiently transfected tsA201 cells. Data were recorded from 12-ms pulses from −80 to 60 mV at 10-mV increments; only every third voltage is shown here for clarity. (B) Overlay of the mean normalized charge-voltage (Q-V) relationship with the fast F-V relationship from Fig. 5 C. The Q-V relationship V_1/2 and k values were −31.5 ± 2.0 mV and 11.5 ± 0.6 mV, respectively. (C) Superposition of fluorescence (gray) and cumulative gating charge (black) versus time in Kv1.2 channels. Data are shown for a range of depolarizations from −50 to 60 mV, as labeled, for the initial 8 ms of depolarization in the case of the fluorescence data and are normalized to the respective maximum values. The fluorescence quenching at this potential is inverted to more closely compare with the gating charge data. (D) Mean time constants of the integrated gating charge movement compared with the fast fluorescence quenching of A291C. Gating charge data were fit to a double exponential function, and the mean ± SEM data (n = 10–15) of the fast (closed squares) and slow (open squares) components were plotted as a function of voltage. Time constants for the fast quenching event (open circles) are as plotted in Fig. 5 B.