Relative entry into slow and fast recovery pathways is voltage-independent above −10 mV. (A) The standard paired pulse protocol was employed with a 25-ms inactivation depolarization (pulse 1, P1) to voltages from −10 mV to +30 mV, with recovery intervals (at −80 mV) from 1 ms to 3 s, followed by a final 5-ms test step (pulse 2, P2) to the initial inactivation voltage. Traces show currents evoked during P1 on the left for a given voltage, and then during P2 on the right. From top to bottom, traces reflect inactivation voltages of −10, 10, and +30 mV. Green, red, and blue traces show currents following recovery intervals of 20, 100, and 500 ms, respectively. Over this range of voltage, activation of Nav conductance is near maximum (Fig. 1 C). (B) Averaged recoveries following inactivation at the indicated voltages (−10 mV, n = 12 cells; 10 mV, n = 13 cells; +30 mV, n = 11 cells). Colored symbols and error bars show mean ± SD with lines reflecting best fits of a double exponential with the following parameters. Following inactivation at −10 mV, Af = 0.33 ± 0.01, τf = 23.1 ± 1.3 ms, As = 0.67 ± 0.01, and τs = 372.4 ± 14.1 ms; at +10 mV, Af = 0.42 ± 0.02, τf = 20.0 ± 1.1 ms, As = 0.58 ± 0.01, and τs = 376.1 ± 20.2 ms; and at +30 mV, Af = 0.42 ± 0.01, τf = 19.4 ± 1.0 ms, As = 0.58 ± 0.01, and τs = 361.4 ± 19.2 ms. Note that the points for recovery at +10 mV are largely obscured by those for recovery at +30 mV. (C) Mean values (±SD) for the amplitudes of the fast (open black circles, Af) and slow (filled black circles, As) recovery components determined from fits to recovery from at least 11 cells at each voltage are plotted as a function of different inactivation voltages. The red line corresponds to the Nav G/V curve from Fig. 1 C. (D) Mean values (±SD) for fast and slow recovery time constants (τf and τs) for the same set of cells are plotted as a function of the inactivation voltage.