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. 2012 Nov;140(5):481–493. doi: 10.1085/jgp.201210817

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© 2012 Labro et al.

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Figure 2. — Slowing in I_gOFF and I_deac kinetics of Shaker channels with prolonged depolarization. (A) Deactivating I_gOFF currents upon different depolarization times at 20 mV. To avoid nonspecific effects or depletion effects, the pulse protocols were ran in random order, and, in the case of the represented currents, the protocol with a 10-s prepulse (bottom traces) was recorded before the 100-ms trace (top traces). (bottom) A superposition of I_gOFF at different voltages upon 100-ms (black) and 10-s depolarizations (red). Note that I_gOFF slows down and the total charge becomes more spread out when depolarizations are prolonged. (B) Ionic current deactivation after 100 ms (top traces) and 5 s (bottom traces) at 20 mV. (bottom) A superposition of scaled currents at −80 and −50 mV upon 100-ms (black) and 5-s (red) depolarizations. (C) I_gOFF was fitted with a double exponential function, and the weighted time constants ± SEM are represented (n = 6). Note the gradual increase of the time constants with prolonged depolarization times. (D) Development of the ionic deactivation I_deac weighted time constant as a function of depolarization time, displaying, like I_gOFF, a gradual slowing with prolonged depolarizations. (E, top) The weighted I_gOFF time constant at −50 mV plotted as a function of depolarization time clearly displaying two slowing processes. The fit with a double exponential function yielded a fast τ_f of 8.5 ± 1.0 ms and a slow τ_s of 1,100 ± 100 ms (n = 6). (bottom) The behavior of I_deac kinetics at −50 mV showing a similar biphasic slowing process with a τ_f of 4.8 ± 0.6 ms and a τ_s of 670 ± 90 ms (n = 5). Error bars represent SEM.