Lorenz, Eva

Background—Opening of cardiac ATP-sensitive K+(KATP) channels has emerged as a promising but still controversial cardioprotective mechanism. Defining KATPchannel 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—KATPchannel–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 withKir6.2/SUR2Agenes, which encode cardiac KATPchannel 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 KATPchannel blocker glyburide (1 μmol/L). In COS-7 cells transfected with individual channel subunitsKir6.2orSUR2A, which alone do not form functional cardiac KATPchannels, pinacidil did not protect against hypoxia-reoxygenation.Conclusions—The fact that transfer of cardiac KATPchannel subunits protected natively KATPchannel–deficient cells provides direct evidence that the cardiac KATPchannel protein complex harbors intrinsic cytoprotective properties. These findings validate the concept that targeting cardiac KATPchannels should be considered a valuable approach to protect the myocardium against injury.