Distinct myoprotective roles of cardiac sarcolemmal and mitochondrial K ATP channels during metabolic inhibition and recovery

The protective roles of sarcolemmal (sarc) and mitochondrial (mito)K ATP channels are un‐clear despite their apparent importance to ischemic preconditioning. We examined these roles by monitoring intracellular calcium ([Ca] int ), using fura‐2 and fluo‐3, in enzymatically isolated rat right ventricular myocytes. Myocyte mortality, estimated using a trypan blue assay, changed approximately in parallel with changes in [Ca] int . Chemically induced hypoxia (CIH), induced by application of cyanide and 2‐deoxy‐glucose, caused a steady rise in [Ca] int . Calcium increased more rapidly on ‘reoxygenation’ by return to control solutions. The protein kinase C (PKC) activator PMA abolished both phases of calcium increase. The mito K ATP channel‐selective blocker 5‐hydroxydecanoate partially prevented the PMA‐induced protection during CIH, but not during reoxygenation. In contrast, HMR 1098, a sarc K ATP channel‐selective blocker, abolished protection only during the reoxygenation. Adenosine (A 1 ) receptor activation prevented or reduced increases in [Ca] int and improved cell viability via a PKC and mito / sarc K ATP channel‐dependent mechanism. PKC‐dependent protection against cytoplasmic calcium increases was also observed in a human cell line (tsA201) transiently expressing sarc K ATP channels. Protection was abolished only during the reoxygenation phase by the amino acid substitution (T180A) in the pore‐forming Kir6.2 subunit, a mutation previously shown to prevent PKC‐dependent modulation. Our data suggest that sarc and mito K ATP channel populations play distinct protective roles, triggered by PKC and/or adenosine, during chemically induced hypoxia/reoxygenation.—Light, P. E., Kanji, H. D., Manning Fox, J. E., French, R. J. Distinct myoprotective roles of cardiac sarcolem‐mal and mitochondrial K ATP channels during metabolic inhibition and recovery. FASEB J. 15, 2586–2594 (2001)