Gating currents of the cloned delayed-rectifier K+ channel DRK1.

Gating currents of the cloned delayed-rectifier K+ channel DRK1 expressed in Xenopus oocytes were measured with the open-oocyte Vaseline-gap voltage-clamp technique. DRK1 gating charge had the following salient properties: (i) gating-charge amplitude correlated positively with size of the expressed ionic K+ currents; (ii) the time integral of ON and OFF gating currents was similar, indicating charge conservation and lack of charge immobilization; (iii) the gating-charge activation curve was shallower and had a half-activation potential 15 mV more negative than the activation curve for K+ conductance; (iv) effective valence for the gating current was about two electronic charges per gating subunit; (v) for large depolarizations (to > 0 mV) prominent rising phases were observed during the ON and OFF gating charge, which appeared as shoulders in unsubtracted traces; (vi) for small depolarizing pulses (to < 0 mV) ionic-current activation and deactivation had time constants similar to ON and OFF gating-current decay, respectively; (vii) negative prepulses made more prominent the ON rising phase and delayed ionic and gating currents. The results are consistent with a model for K+ channel activation that has an early slow and/or weakly voltage-dependent transition between early closed states followed by more voltage-dependent transitions between later closed states and a final voltage-independent closed-open transition.