Voltage dependence of steady-state and instantaneous current decline. (A) Mean steady-state (IV) currents (n = 6) recorded at the indicated test potentials before (black lines) and after 5 min of run-down (orange lines). To allow for comparison of the relative change at different test potentials, they have been normalized to the peak current amplitude observed at each voltage before run-down. (B) Mean instantaneous (IIV) currents recorded from the same cells as in A before (black lines) and after 5 min of run-down (orange lines). To allow for comparison of the relative change at different test potentials, they have been normalized as in A. (C) Comparison of steady-state IV (squares) and IIV (circles) relationships, determined immediately after complete run-up (open symbols) and after 5 min of run-down (orange symbols; same cells as in A and B). (D) Voltage dependence of the fraction of IV (squares) and IIV (circles) current remaining after 5 min of run-down, determined as the ratio between current amplitudes after 5 min of run-down and current amplitudes at time 0 (same cells as in A–C). (E) Mean changes over time in the fraction of IIV current recorded at −20 mV (open circles with dotted line) and +20 mV (black circles with solid line) and in the slope conductance (g_IIV) between −80 and 0 mV (same cells as in A–D). (F) Mean changes over time in the fraction of IV current recorded at −20 mV (open squares with dotted line) and +20 mV (black squares with solid line) and in the maximum slope conductance (g_IV) determined from IV relationships (same cells as in A–E). Values are expressed as mean ± SEM.