Changes in channel voltage dependence during run-down. (A) Families of mean IV currents (n = 8) evoked by 25 ms voltage steps to test potentials between −80 mV and +60 mV at the onset of run-down (0 min) and in 7-min intervals thereafter. They have been normalized to the maximum peak I_Ba at time 0. Inset: Current lost to run-down at the indicated test potentials, determined by subtracting from the normalized current traces recorded at time 0 the corresponding traces recorded after 7 (orange lines), 14 (purple lines), and 21 min (green lines) of run-down. (B) Mean IV relationships measured at the same time points as in A and normalized to the maximum peak current amplitude recorded at time 0 (n = 49). (C) Voltage dependence of activation (right) and prepulse inactivation (left), determined at the same time points as in A (same cells as in B). (D) Time course of changes in the half-activation (V_0.5act) and half-inactivation (V_0.5inact) voltages, determined from single Boltzmann fits to the data in C. (E) Time course of changes in the activation (k_act) and inactivation (k_inact) slope factors, determined from single Boltzmann fits to the data in C. Values are expressed as mean ± SEM.