Voltage-dependence of two components of recovery from inactivation.(A) A log-scale plot of averaged fractional recovery from inactivation following a 5-ms depolarizing voltage step to 0 mV is shown for recovery voltages of −50, −70, −90, and −110 mV, using the protocol illustrated in Fig. 2. Each point shows the mean ± SD (at −50 mV, n = 11 cells; at −70, n = 14; at −90, n = 15; and at −110 mV, n = 13). Lines are the best fit of a two-exponential function to the recovery time course. Each cell was equilibrated at −80 mV for 1 s before the initial inactivating test step to 0 mV. At −110 mV, Af = 0.51 ± 0.01, τf = 3.1 ± 0.2 ms, As = 0.51 ± 0.01, and τs = 83.2 ± 4.7 ms (fitted value and 90% confidence limit); at −90 mV, Af = 0.50 ± 0.01, τf = 7.6 ± 0.5 ms, As = 0.51 ± 0.01, and τs = 215.3 ± 17.1 ms; at −70 mV, Af = 0.36 ± 0.01, τf = 23.1 ± 1.6 ms, As = 0.53 ± 0.13, and τs = 404.9 ± 27.3 ms; for −50 mV, Af = 0.14 ± 0.01, τf = 64.7 ± 5.8 ms, As = 0.05 ± 0.01, and τs = 359.1 ± 110.9 ms. (B) For a different set of cells (10 or 11 cells), fractional recovery was determined at −60, −80, −100, and −120 mV, with solid lines indicating the double exponential fit. At −120 mV, Af = 0.51 ± 0.01, τf = 2.9 ± 0.4 ms, As = 0.52 ± 0.01, and τs = 56.5 ± 0.6 ms; at −100 mV, Af = 0.50 ± 0.01, τf = 6.4 ± 0.6 ms, As = 0.53 ± 0.01, and τs = 162.9 ± 1.8 ms; at −80 mV, Af = 0.45 ± 0.01, τf = 18.4 ± 0.3 ms, As = 0.53 ± 0.01, and τs = 373.5 ± 6.1 ms; at −60 mV, Af = 0.21 ± 0.01, τf = 55.93 ± 1.1 ms, As = 0.34 ± 0.01, and τs = 487.8 ± 7.6 ms. (C) At each recovery voltage, the mean fast and slow time constants (±SD) obtained from fits to individual cells are plotted for each set of cells. These mean values for sets of individual cells agree closely with the fits to the averaged data shown in A and B. (D) The mean amplitude (±SD) of faster and slower recovery components are plotted as a function of voltage along with the sum of the two components. Single Boltzmann fits to each relationship are shown. For the fast component (red circles), Af = 0.51 ± 0.02, V0.5 = −61.8 ± 1.5 mV, and z = 3.2 ± 0.8e; for the slow component (blue circles), As = 0.51 ± 0.01, V0.5 = −57.3 ± 0.87 mV, and z = 6.2 ± 1.9e. For the sum of the two components (black rectangles), V0.5 = −58.6 ± 0.3 mV with z = 3.7 ± 0.2e, agreeing closely with the measurements of fractional availability in Fig. 1 E (green line), V0.5 = −57.7 mV and z = 4.3e.
Figure 3.

Voltage-dependence of two components of recovery from inactivation. (A) A log-scale plot of averaged fractional recovery from inactivation following a 5-ms depolarizing voltage step to 0 mV is shown for recovery voltages of −50, −70, −90, and −110 mV, using the protocol illustrated in Fig. 2. Each point shows the mean ± SD (at −50 mV, n = 11 cells; at −70, n = 14; at −90, n = 15; and at −110 mV, n = 13). Lines are the best fit of a two-exponential function to the recovery time course. Each cell was equilibrated at −80 mV for 1 s before the initial inactivating test step to 0 mV. At −110 mV, Af = 0.51 ± 0.01, τf = 3.1 ± 0.2 ms, As = 0.51 ± 0.01, and τs = 83.2 ± 4.7 ms (fitted value and 90% confidence limit); at −90 mV, Af = 0.50 ± 0.01, τf = 7.6 ± 0.5 ms, As = 0.51 ± 0.01, and τs = 215.3 ± 17.1 ms; at −70 mV, Af = 0.36 ± 0.01, τf = 23.1 ± 1.6 ms, As = 0.53 ± 0.13, and τs = 404.9 ± 27.3 ms; for −50 mV, Af = 0.14 ± 0.01, τf = 64.7 ± 5.8 ms, As = 0.05 ± 0.01, and τs = 359.1 ± 110.9 ms. (B) For a different set of cells (10 or 11 cells), fractional recovery was determined at −60, −80, −100, and −120 mV, with solid lines indicating the double exponential fit. At −120 mV, Af = 0.51 ± 0.01, τf = 2.9 ± 0.4 ms, As = 0.52 ± 0.01, and τs = 56.5 ± 0.6 ms; at −100 mV, Af = 0.50 ± 0.01, τf = 6.4 ± 0.6 ms, As = 0.53 ± 0.01, and τs = 162.9 ± 1.8 ms; at −80 mV, Af = 0.45 ± 0.01, τf = 18.4 ± 0.3 ms, As = 0.53 ± 0.01, and τs = 373.5 ± 6.1 ms; at −60 mV, Af = 0.21 ± 0.01, τf = 55.93 ± 1.1 ms, As = 0.34 ± 0.01, and τs = 487.8 ± 7.6 ms. (C) At each recovery voltage, the mean fast and slow time constants (±SD) obtained from fits to individual cells are plotted for each set of cells. These mean values for sets of individual cells agree closely with the fits to the averaged data shown in A and B. (D) The mean amplitude (±SD) of faster and slower recovery components are plotted as a function of voltage along with the sum of the two components. Single Boltzmann fits to each relationship are shown. For the fast component (red circles), Af = 0.51 ± 0.02, V0.5 = −61.8 ± 1.5 mV, and z = 3.2 ± 0.8e; for the slow component (blue circles), As = 0.51 ± 0.01, V0.5 = −57.3 ± 0.87 mV, and z = 6.2 ± 1.9e. For the sum of the two components (black rectangles), V0.5 = −58.6 ± 0.3 mV with z = 3.7 ± 0.2e, agreeing closely with the measurements of fractional availability in Fig. 1 E (green line), V0.5 = −57.7 mV and z = 4.3e.

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