Fig. 4.

Inward rectification is caused by ultrafast inactivation. The cut-open oocyte technique was used to study fast inactivation. EXP-2 channels were activated and inactivated by 1 sec prepulses to 20 mV from a holding potential at −80 mV and then allowed to recover from inactivation for 20 msec at −120 mV. To determine the instantaneous current, the voltage was then stepped in 20 mV increments to different potentials from −120 to 60 mV. The arrowpoints to current decline attributable to rapid channel inactivation.A, With 2.5 mm KCl in the bath, the current reversed direction at approximately −60 mV. B, In 100 mm KCl, outward and inward currents are larger, and the current reversed direction at ∼0 mV. C,I–V relationship in 2.5 and 100 mmextracellular KCl solution (same oocyte).