Fig. 5.

Activation and inactivation ofI_K. In A, the activation ofI_K (after inactivation ofI_A by a prepulse to −20 mV) follows a sigmoid kinetics that is best-fitted by a double-power exponential function (superimposed in the left traces). The membrane was depolarized from a holding potential of −50 mV in 20 mV steps.Traces on the right represent tail currents from the same bouton after membrane repolarization after a 60 msec pulse, and they were well-fitted by a single exponential function with a time constant of 5–6 msec. B,I_K slow inactivation during prolonged depolarization. Two current traces at two different time scales are displayed to illustrate the inactivating nature ofI_K. The delayed current recorded in response to long depolarizing pulses always exhibits a similar profile with a slowly inactivating and a noninactivating component.