Simulated Zn²⁺ effects on macroscopic activation, deactivation, and inactivation kinetics. (A) Activation (right) and deactivation (left) time constants, determined by exponential fits to the rising phase of simulated I-V currents or the decaying phase of simulated II-V currents, with the free Zn²⁺ concentration set to 0 (black squares) or 5.4 µM (orange circles). (B) Inactivation time constants determined from exponential fits to the decay of simulated II-V currents at depolarized test potentials, with the free Zn²⁺ concentration set to 0 (black squares) or 5.4 µM (orange circles). (C) Contribution of deactivation (open symbols) and inactivation (filled symbols) to total decay of simulated II-V currents, with the free Zn²⁺ concentration set to 0 (black squares) or 5.4 µM (orange circles). (D) Inactivation time constants, determined by fitting a single exponential function with variable offset to the decaying phase of simulated currents evoked by 400-ms voltage steps to the indicated test potentials, with the free Zn²⁺ concentration set to 0 (open squares) or 5.4 µM (orange circles).