Recombinant cardiac ATP-sensitive K+ channel subunits confer resistance to chemical hypoxia-reoxygenation injury

Background - Opening of cardiac ATP-sensitive K+ (K-ATP) channels has emerged as a promising but still controversial cardioprotective mechanism. Defining K-ATP channel function at the level of recombinant channel proteins is a necessary step toward further evaluation of the cardioprotective significance of this ion conductance. Methods and Results - K-ATP channel-deficient COS-7 cells were found to be vulnerable to chemical hypoxia-reoxygenation injury that induced significant cytosolic Ca2+ loading (from 97 +/- 3 to 236 +/- 11 nmol/L). In these cells, the potassium channel opener pinacidil (10 mu mol/L) did not prevent Ca2+ loading (from 96 +/- 3 nmol/L before to 233 +/- 12 nmol/L after reoxygenation) or evoked membrane current. Cotransfection with Kir6.2/SUR2A genes, which encode cardiac K-ATP, channel subunits, resulted in a cellular phenotype that, in the presence of pinacidil (10 mu mol/L), expressed K+ current and gained resistance to hypoxia-reoxygenation (Ca2+ concentration from 99 +/- 7 to 127 +/- 11 nmol/L; P > 0.05). Both properties were abolished by the K-ATP channel blocker glyburide (1 mu mol/L). In COS-7 cells transfected with individual channel subunits Kir6.2 or SUR2A, which alone do not form functional cardiac K-ATP channels, pinacidil did not protect against hypoxia-reoxygenation. Conclusions - The fact that transfer of cardiac K-ATP channel subunits protected natively K-ATP channel-deficient cells provides direct evidence that the cardiac K-ATP channel protein complex harbors intrinsic cytoprotective properties. These findings validate the concept that targeting cardiac K-ATP channels should be considered a valuable approach to protect the myocardium against injury.