Figure 1. Prestin's charge movement is sensitive to initial voltage.

A, gating current (a) in a prestin-transfected TSA201 cell induced by a voltage step (c) to -100 mV from a holding potential of 0 mV. Non-transfected cells did not produce gating currents (b). P/-4 protocol was used with a subtraction holding potential of +50 mV. B, whole-cell C_m determined with dual sinusoidal technique (top panel). The bottom panel shows the voltage protocol. Sinusoids have been removed for visual clarity. Data were obtained from 4 episodes; voltage was stepped to -150 mV with incrementing durations from a holding potential of 0 mV. Five-second intervals at the holding potential were allowed for recovery between episodes. C, capacitance data from B are plotted vs. ramp voltage. Traces are shifted downward (1 pF decrements) for visual clarity. Fits indicate a shift in V_pkcm denoted by • (V_pkcm, Q_max, z and C_lin were, respectively: -87.15 mV, 0.89 pC, 0.66 and 14.7 pF), ▾ (-84.2 mV, 0.91 pC, 0.64 and 15.0 pF), ▪ (-81.5 mV, 0.97 pC, 0.61 and 15.0 pF) and ♦ (-79.8 mV, 0.96 pC, 0.63 and 14.9 pF). The same symbols are used in the inset plot to show the time course of the shift. A single exponential fit gave τ= 116 ms.