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 μmol/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 μmol/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 μmol/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.