Fig. 3.

Instantaneous I–V relationship of EXP-2. A, EXP-2 channels were activated and inactivated by 1 sec prepulses to 20 mV and then allowed to recover from inactivation at −80 mV for 40 msec. After recovery from inactivation, the instantaneous current through open channels was determined for the beginning of 1 sec test pulses applied in 10 mV increments ranging from −120 to 60 mV. The arrow points to current decline attributable to rapid channel inactivation at −60 mV. No outward currents could be detected at positive potentials. B,HERG channels show little inactivation at negative potentials and outward current at positive potentials (arrow at 60 mV).C,I–V relationship for EXP-2 at different extracellular KCl concentrations, ranging from 2 to 100 mm (same oocyte). Inward currents are only detectable at voltages more negative than E_K, indicating the potassium selectivity of EXP-2. D,Uninjected control oocytes show no EXP-2-like currents. The same pulse protocol was used for experiments presented in A,B, and D.