Figure 5. A-type K+ currents.

A, current responses to 200 ms voltage steps to +50 mV from a holding potential of −70 mV (voltage pulse protocol shown in the inset) in the presence of 0.3 μm TTX and 20 mm TEA⁺ before and after the addition of 10 mm 4-aminopyridine. Similar results were seen in 7 cells. B, peak current–voltage relationship of currents after the substraction of the mean sustained current obtained using the experimental set-up shown in Fig. 4A in the presence of TEA⁺ (n = 11). C, voltage dependence of the inactivation time constant, τ_inact, obtained by fitting the declining phase of the current traces (as in Fig. 4A) with a single exponential (n = 5 to12). D, voltage-dependent inactivation was measured by holding the membrane potential for 200 ms at conditioning voltages from −120 to 0 mV (at 10 mV increments) before stepping to −70 mV for 1 ms, +50 mV for 200 ms, and then to −70 mV. The voltage pulse protocol is shown in the inset. Only the current response to the test pulse to +50 mV is shown. E, the peak currents obtained as in D (n = 9) were normalized to the maximum peak current, and plotted against the holding potential applied during the conditioning pulse. The data were fitted with a Boltzmann equation (eqn (1), V_0.5 =−61 ± 2 mV, k = 7.5 ± 0.4 mV, A₂ = 0).