Recombinant Cardiac ATP-Sensitive K + Channel Subunits Confer Resistance To Chemical Hypoxia-Reoxygenation Injury

Abstract

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 Ca ²⁺ loading (from 97±3 to 236±11 nmol/L). In these cells, the potassium channel opener pinacidil (10 μmol/L) did not prevent Ca ²⁺ 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 (Ca ²⁺ 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.