Protein kinase C-mediated preconditioning of cardiac myocytes: role of adenosine receptor and K-ATP channel

Activation of the adenosine receptor, protein kinase C (PKC), and the ATP-sensitive potassium (K-ATP) channel is known to induce preconditioning. The objective here was to determine the signaling role of the adenosine receptor, PKC, and the KATP channel and the temporal sequence of activation of these three mediators in preconditioning of cardiac myocytes. Chick embryo ventricular myocytes were used as a myocyte model of preconditioning. Brief hypoxic or adenosine exposure preconditioned the myocytes, and the PKC inhibitors chelerythrine or calphostin C blocked this preconditioning effect, suggesting that PKC is an effector distal to the adenosine receptor in initiating the hypoxia- or adenosine-induced preconditioning. The PKC activator phorbol 12-myristate 13-acetate (PMA), but not the inactive phorbol 4 alpha-phorbol 12,13-didecanoate or 4 alpha-phorbol 12-myristate 13-acetate, could precondition the myocyte; the PMA-induced preconditioning effect was blocked by chelerythrine or calphostin C. Glibenclamide or 5-hydroxydecanoate, when present during a 5-min exposure to PMA or a 90-min hypoxic period, blocked the PMA-induced preconditioning. However, the presence of 8-sulfophenyltheophylline during exposure to PMA failed to block the PMA-induced preconditioning, whereas 8-sulfophenyltheophylline was able to abolish this preconditioning effect when added during the 90-min hypoxic period. The data provide direct evidence that the KATP channel, not the adenosine receptor, is the effector downstream from PKC in initiating PKC-mediated preconditioning. Both the adenosine receptor and KATP channel are required to exert the actual protective effect during the sustained hypoxia.