Protein kinase C isoform-dependent modulation of ATP-sensitive K+ channels during reoxygenation in guinea-pig ventricular myocytes.

Abstract

ATP-sensitive K+ (KATP) channels activated by glucose-free anoxia close immediately upon reoxygenation in single guinea-pig ventricular myocytes, while KATP channels open persistently during reperfusion in coronary-perfused guinea-pig ventricular myocardium. To investigate the reasons behind this discrepancy, we investigated whether protein kinase C (PKC) modulates the opening of KATP channels during anoxia-reoxygenation and ischaemia-reperfusion. Exposure of guinea-pig ventricular cells to glucose-free anoxia shortened the action potential duration at 90% repolarisation (APD90) and evoked the glibenclamide-sensitive robust outward current (IK,ATP). Subsequent reoxygenation caused an immediate prolongation of APD90 and a decrease in IK,ATP within approximately 20 s. When the novel (Ca2+-independent) PKC was activated by applying 1,2-dioctanoyl-sn-glycerol (1,2DOG, 20 M) with EGTA (20 mM) in the pipette, the APD90 restored gradually after reoxygenation and the extent of recovery was appoximately 80% of the pre-anoxic value. Moreover, IK,ATP decreased slowly and remained opened for up to approximately 4 min after reoxygenation. These results suggest persistent opening of KATP channels during reoxygenation. The persistent activation of KATP channels was augmented when both novel and conventional (Ca2+-dependent) isoforms of PKC were activated by applying 1,2DOG without EGTA in the pipette. In coronary-perfused right ventricular myocardium, APD90 remained shortened for up to approximately 30 min of reperfusion. The gradual restoration of APD90 after ischaemia-reperfusion was facilitated by the KATP channel blocker glibenclamide and by the potent PKC inhibitor chelerythrine. Our results provide the first evidence that PKC activation contributes to the persistent opening of KATP channels during reoxygenation and reperfusion. We also conclude that both novel and conventional PKC isoforms co-operatively modulate the opening of KATP channels during the early phase of reoxygenation.