Absence of slowing of tail current deactivation is not strongly diagnostic among different versions of closed-channel block models. (A) Simulated tail currents were generated with Scheme 1a at −200 mV in the absence of blocker and then with effective 1×, 2×, and 10× increments of [blocker] (50, 100, and 500 kf) for both 4 µM Ca²⁺ (1) and 300 µM Ca²⁺ (2). At each concentration, sets of simulated traces show net current for 1,000 channels (left) and normalized tail currents (right). The trace in red highlights the normalized tail current in the absence of blocker. (B) Simulated tail currents are shown for Scheme 2a under the same conditions as in A. Note that for the highest [blocker] producing an almost 90% reduction in tail current amplitude, there is a noticeable unblocking hook, although changes in the time constant of deactivation are minimal. (C) Simulated tail currents are shown for Scheme 2b (z_c = 0 e). There is minimal tail current prolongation and any unblocking hook is reduced compared with Scheme 2a. (D) Tail currents were simulated for a Scheme 2b′ model with parameters based on Fig. 4 F. (E) Tail currents were simulated with Scheme 3a. (F) Tail currents were generated with Scheme 3b. (G) Tail currents were simulated with Scheme 3b′ with parameters from the fit of the GV curve in Fig. 4 G.