Diadenosine tetraphosphate (AP4A) mimics cardioprotective effect of ischemic preconditioning in the rat heart:: contribution of KATP channel and PKC

Diadenosine tetraphosphate (AP4A) administration is reported to mimic the effect of ischemic preconditioning (PC) via purine 2y receptors (P2yR) and adenosine receptors. This study was designed to test the contributions of the ATP-sensitive potassium channel (K-ATP channel) and protein kinase C (PKC), two of the main regulator in PC, to the effect of AP4A. Isolated buffer-perfused rat hearts were subjected to 20 min of global ischemia (37 degrees C) and 20 min of reperfusion. Three cycles of 1-min ischemia and 3-min reperfusion induced PC. Chemicals were administrated for 2 min before 20 min of ischemia. AP4A (10 mu M) administration was as effective as PC in improving the recovery of post-ischemic contractile function and reducing creatine kinase leakage after reperfusion, whereas adenosine (10 and 100 mu M) have not effect. AP4A had not effect on reperfusion-induced arrhythmia, whereas PC significantly prevented it. These effects of AP4A and PC were reversed by co-administration of glibenclimade (K-ATP channel blocker, 100 mu M) and GF109203X (PKC inhibitor, 10 mu M); the effects of AP4A but not PC were reversed by co-administration of reactive blue (P2yR antagonist, 13 nM). AP4A appears to activate the K-ATP channel and PKC via P2yR mimic the effects of PC in part. The role of P2yR indicated that trigger mechanism of the effect of PC and AP4A administration might differ in rat hearts.