Roles of tyrosine kinase and protein kinase C in infarct size limitation by repetitive ischemic preconditioning in the rat

In this study, we examined the possibility that infarct-size limitation by repetitive preconditioning (PC) is achieved by activation of both protein k inase C (PKC) and tyrosine kinase. In addition, we assessed whether such ki nase activation is triggered by angiotensin II type 1 (AT(1)) and alpha(1)- adrenergic receptors and whether sarcolemmal and mitochondrial adenosine tr iphosphate (ATP)-sensitive potassium (K-ATP) channels play roles as effecte rs of cardioprotection in the rat. Under pentobarbital anesthesia, myocardi al infarction was induced by 20-min coronary occlusion and 3-h reperfusion in the rat. Infarct size was determined by tetrazolium and expressed as a p ercentage of area at risk (%IS/AR). PC with one cycle of 5-min ischemia/5-m in reperfusion before 20-min ischemia significantly reduced %IS/AR from the control value of 49.4 +/- 2.0 to 35.4 +/- 2.8, and repetitive PC with two cycles of 5-min ischemia/5-min reperfusion further limited %IS/AR to 3.2 +/ - 0.9. Infarct-size limitation by single-cycle PC was completely abolished by a PKC inhibitor, staurosporine (100 mu g/kg; %IS/ AR, 45.7 +/- 5.0). In contrast, the cardioprotection by repetitive PC was only partially blocked by staurosporine (%IS/AR, 19.8 +/- 2.4), another PKC inhibitor, polymyxin B (5 mg/kg; %IS/AR, 16.2 +/- 3.1), or a tyrosine kinase inhibitor, genistein (5 mg/kg; %IS/AR, 21.8 +/- 1.4). However, a combined injection of genistei n and staurosporine additively inhibited protection of repetitive PC (%IS/A R, 36.4 +/- 1.7). Staurosporine, polymyxin B, or genistein alone did not mo dify %IS/AR in nonpreconditioned rat hearts. Infarct-size limitation by rep etitive PC was not attenuated by pretreatment with a selective AT(1)-recept or blocker (CV11974, 10 mg/kg), prazosin (0.6 mg/kg; %IS/AR, 6.4 +/- 3.2 an d 1.6 +/- 0.5, respectively). A selective blocker of mitochondrial K-ATP ch annels, 5-hydroxydecanoate (3 mg/kg), completely abolished the cardioprotec tive effect (%IS/AR, 50.8 +/- 3.5), but HMR1883 (3 mg/kg), a selective bloc ker of sarcolemmal K-ATP channels, failed to inhibit the preconditioning ef fect (%IS/AR, 4.4 +/- 0.7). These findings suggest that repetition of PC pr ovokes activation of both PKC and tyrosine kinase, leading to enhanced anti infarct tolerance by opening of mitochondrial but not sarcolemmal K-ATP cha nnels. It is unlikely that activation of either AT(1) or alpha(1)-adrenergi c receptor alone is crucial to trigger preconditioning.