Department of Integrative Biology

We previously showed inhibition of K(ir)2 inward rectifier K+ channels expressed in Xenopus oocytes by the mitochondrial agents carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and sodium azide. Mutagenesis studies suggested that FCCP may act via phosphatidylinositol 4,5-bisphosphate (PIP2) depletion. This mechanism could be reversible in intact cells but not in excised membrane patches which preclude PIP2 regeneration. This prediction was tested by investigating the reversibility of the inhibition of K(ir)2.2 by FCCP in intact cells and excised patches. We also investigated the effect of FCCP on K(ir)2.2 expressed in human embryonic kidney (HEK) cells. K(ir)2.2 current, expressed in Xenopus oocytes, increased in inside-out patches from FCCP-treated and untreated oocytes. The fraction of total current that increased was 0.79 +/- 0.05 in control and 0.89 +/- 0.03 in 10 mu M FCCP-treated (P > .05). Following "run-up," K(ir)2.2 current was re-inhibited by "cramming" inside-out patches into oocytes. Therefore, run-up reflected not reversal of inhibition by FCCP, but washout of an endogenous inhibitor. K(ir)2.2 current recovered in intact oocytes within 26.5 h of FCCP removal. Injection of oocytes with 0.1 U apyrase completely depleted ATP (P