The obligate role of protein kinase C in mediating clinically accessible cardiac preconditioning

Background. Cardiac preconditioning is an adaptation of cardiomyocytes that promotes tolerance to a subsequent ischemic insult. Adenosine receptor signaling is proposed as a mediator of preconditioning, but its mechanism of protection remains unknown. We hypothesized that protection against hypoxia-reoxygenation (H/R) injury could be conferred in a rat ventricle by adenosine-mediated protein kinase C (PKC) activation and that adenosine-mediated cardioprotection could be extended to human ventricular muscle. Methods, Isolated mt and human ventricular muscle (VM) strips were subjected to 30 minutes of hypoxia and 60 minutes of reoxygenation (H/R control). The VM was pretreated with 125 mu mol/L adenosine, an adenosine antagonist ((p-Sulfophenyl) theophylline [SPT] 50 mu mol/L) and adenosine (adenosine + SPT), or with a PKC inhibitor (chelerythrine, 10 mu mol/L) and adenosine (adenosine + chelerythrine) before H/R. Developed force (DF) and tissue creatine kinase (CK) activity were assessed at end reoxygenation. Human trabeculae were obtained from diseased explanted hearts at cardiac transplantation and were also subjected to H/R injury. Human VM was pretreated with adenosine (125 mu mol/L) before H/R injury. Results are expressed as mean +/- standard error of mean. Results. In the rat, adenosine pretreatment conferred protection of DF against H/R injury (adenosine, 62 % +/- 6%; H/R control, 21% +/- 2 %, p < 0.05). Adenosine + SPT or adenosine + chelerythrine eliminated the functional recovery conferred by adenosine. This recovery of contractile function was associated with greater tissue CK activity (adenosine, 415 +/- 40 units/gm; H/R control, 78 +/- 13 units/gm, p < 0.05). The protective effects of adenosine against H/R were present In the human ventricle and with recovery of DF in adenosine (66% + 5%) and H/R control (24 % +/- 4 %), p < 0.05. Conclusions, Adenosine, a clinically accessible agonist, induces protection against H/R injury through a PKC-mediated mechanism in the rat ventricle. Fu?ther, the protection conferred by adenosine against H/R extends to the human ventricle.