Kinetics of Q_OFF. (A) Gating currents elicited under control conditions. Top panel is a plot of gating currents in response to voltage pulse protocol shown in the middle panel. Bottom panel shows the first integral of Ig_OFF traces depicted in top panel. (B) Gating currents, pulse protocol, and integration of currents are shown for the same oocyte after bath application of 30 mM Cd²⁺. (C) Plot of total Q_OFF versus pulse duration determined before (filled squares) and after treatment of an oocyte with Cd²⁺ (open circles). Smooth curves are best fits for single-exponential function (τ = 29 ms for control; τ = 100 ms for Cd²⁺). (D) Plot of Q_Cd-out in the presence of 30 µM Cd²⁺ versus pulse duration. Data for pulse durations >70 ms (filled circles) were fitted with a single-exponential function (τ = 95 ms). Thus, after accounting for a delay caused by overlap of the faster rising phase of Ig_OFF for short pulse durations, the time course of the development of Q_Cd-out matches that of Q_OFF.