Effects of Zn²⁺ on macroscopic activation, deactivation, and inactivation kinetics. (A) Activation (right) and deactivation (left) time-constants, determined from exponential fits to I-V or II-V currents carried by 4 mM free Ca²⁺ and recorded before (black squares), during (orange circles), and after (gray diamonds) application of 5.4 µM free Zn²⁺ at pH = 7.4. Note that deactivation time-constants reflect a weighted τ comprising fast and intermediate components of tail-current decay. (B) Inactivation time constants determined from exponential fits to II-V current decay at the indicated test potentials in the absence (black squares) and presence (orange circles) of 5.4 µM Zn²⁺ (same cells as in A). (C) Contribution of deactivation (open symbols) and inactivation (filled symbols) to total II-V current decay in the absence (black squares) and presence (orange circles) of 5.4 µM Zn²⁺ (same cells as in A and B). (D) Inactivation time constants, determined from exponential fits to the decaying phase of currents recorded during 400-ms voltage steps to the indicated test potentials before (open squares), during (orange circles), and after (gray squares) application of 5.4 µM Zn²⁺.