Effects of variation in duration of inactivation step on relative amplitudes of fast and slow components.(A–D) Paired depolarizing pulses to +0 mV from a −80-mV holding potential were used to examine the time course of recovery from inactivation with inactivation pulse durations of 5, 25, 250, and 500 ms duration. All traces are from the same cell, with colored traces showing recovery durations preceding the second pulse indicated on each panel. (E) Mean fractional recovery (16 cells for 5, 25, 100, and 250 ms, and 10 cells for 500 ms) following the indicated inactivation durations are plotted as a function of recovery duration, with each set of points fit by a double exponential recovery function. Errors bars in E and F are SD. For 5 ms inactivation, Af = 0.44 ± 0.01, τf = 16.2 ± 1.12 ms, As = 0.57 ± 0.01, and τs = 359.4 ± 21.3 ms; for 25 ms, Af = 0.41 ± 0.01, τf = 19.4 ± 1.5 ms, As = 0.60 ± 0.01, and τs = 389.9 ± 22.2 ms; for 100 ms, Af = 0.36 ± 0.01, τf = 22.7 ± 1.8 ms, As = 0.63 ± 0.01, and τs = 404.6 ± 20.3 ms; for 250 ms, Af = 0.32 ± 0.02, τf = 27.9 ± 3.1 ms, As = 0.68 ± 0.02, and τs = 430.3 ± 24.7 ms; for 500 ms, Af = 0.26 ± 0.01, τf = 31.1 ± 3.5 ms, As = 0.73 ± 0.01, and τs = 432.3 ± 18.9 ms. (F) Recovery was examined in another set of four cells for 5, 500, and 1,000 ms inactivation durations at 0 mV, again with double exponential fits overlaid. For 5 ms, Af = 0.40 ± 0.01, τf = 16.4 ± 1.4 ms, As = 0.60 ± 0.01, and τs = 364.9 ± 22.6 ms; for 500 ms, Af = 0.26 ± 0.02, τf = 34.6 ± 3.4 ms, As = 0.71 ± 0.01, and τs = 476.1 ± 23.1 ms; for 1,000 ms, Af = 0.24 ± 0.02, τf = 44.5 ± 5.9 ms, As = 0.73 ± 0.02, and τs = 509.2 ± 28.9 ms. (G) The Af and As components are plotted as a function of recovery duration. In this case, the Af and As values from each individual cell in E were averaged to determine the mean ± SD. Filled circles correspond to cells tested sequentially with 5, 25, 100, 250, and 500 ms inactivation durations. Filled diamonds correspond to cells tested in the sequence of 500, 250, 100, 25, and 5 ms. Open circles correspond to four cells tested with 5, 500, and 1,000 ms durations in both forward and reverse orders. Solid lines correspond to single exponential fits to the temporal changes in each amplitude component. Changes in Af occur with a time constant of 248.0 ± 126.0 ms, while As changes with a time constant of 219.0 ± 205.1 ms. Af, As, τf, and τs values measured at 5 and 25 ms were not statistically different. (H) The time constants for fast and slow recovery monitored at −80 mV following inactivation steps for different durations to 0 mV are plotted, illustrating a slow prolongation of both τf and τs with inactivation duration. Errors bars are SD.
Figure 4.

Effects of variation in duration of inactivation step on relative amplitudes of fast and slow components. (A–D) Paired depolarizing pulses to +0 mV from a −80-mV holding potential were used to examine the time course of recovery from inactivation with inactivation pulse durations of 5, 25, 250, and 500 ms duration. All traces are from the same cell, with colored traces showing recovery durations preceding the second pulse indicated on each panel. (E) Mean fractional recovery (16 cells for 5, 25, 100, and 250 ms, and 10 cells for 500 ms) following the indicated inactivation durations are plotted as a function of recovery duration, with each set of points fit by a double exponential recovery function. Errors bars in E and F are SD. For 5 ms inactivation, Af = 0.44 ± 0.01, τf = 16.2 ± 1.12 ms, As = 0.57 ± 0.01, and τs = 359.4 ± 21.3 ms; for 25 ms, Af = 0.41 ± 0.01, τf = 19.4 ± 1.5 ms, As = 0.60 ± 0.01, and τs = 389.9 ± 22.2 ms; for 100 ms, Af = 0.36 ± 0.01, τf = 22.7 ± 1.8 ms, As = 0.63 ± 0.01, and τs = 404.6 ± 20.3 ms; for 250 ms, Af = 0.32 ± 0.02, τf = 27.9 ± 3.1 ms, As = 0.68 ± 0.02, and τs = 430.3 ± 24.7 ms; for 500 ms, Af = 0.26 ± 0.01, τf = 31.1 ± 3.5 ms, As = 0.73 ± 0.01, and τs = 432.3 ± 18.9 ms. (F) Recovery was examined in another set of four cells for 5, 500, and 1,000 ms inactivation durations at 0 mV, again with double exponential fits overlaid. For 5 ms, Af = 0.40 ± 0.01, τf = 16.4 ± 1.4 ms, As = 0.60 ± 0.01, and τs = 364.9 ± 22.6 ms; for 500 ms, Af = 0.26 ± 0.02, τf = 34.6 ± 3.4 ms, As = 0.71 ± 0.01, and τs = 476.1 ± 23.1 ms; for 1,000 ms, Af = 0.24 ± 0.02, τf = 44.5 ± 5.9 ms, As = 0.73 ± 0.02, and τs = 509.2 ± 28.9 ms. (G) The Af and As components are plotted as a function of recovery duration. In this case, the Af and As values from each individual cell in E were averaged to determine the mean ± SD. Filled circles correspond to cells tested sequentially with 5, 25, 100, 250, and 500 ms inactivation durations. Filled diamonds correspond to cells tested in the sequence of 500, 250, 100, 25, and 5 ms. Open circles correspond to four cells tested with 5, 500, and 1,000 ms durations in both forward and reverse orders. Solid lines correspond to single exponential fits to the temporal changes in each amplitude component. Changes in Af occur with a time constant of 248.0 ± 126.0 ms, while As changes with a time constant of 219.0 ± 205.1 ms. Af, As, τf, and τs values measured at 5 and 25 ms were not statistically different. (H) The time constants for fast and slow recovery monitored at −80 mV following inactivation steps for different durations to 0 mV are plotted, illustrating a slow prolongation of both τf and τs with inactivation duration. Errors bars are SD.

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