Abstract

κ-Opioid receptor (OR) stimulation with a selective agonist, U50,488H (U50), known to mediate the delayed cardioprotection of metabolic inhibition preconditioning (MIP) against cell injury/death in rat ventricular myocytes, has been shown to act via protein kinase C (PKC). We attempted to identify the PKC isoform(s) that is activated, thus triggering delayed cardioprotection of MIP and pretreatment with 10 μM U50 (U50 pretreatment, UP). Release of lactate dehydrogenase and exclusion of trypan blue by isolated rat ventricular myocytes were used as indices of cell injury and death, respectively. Both MIP and UP induced translocation of PKC-ε, but not other PKC isoforms, -α and -δ, from cytosolic to membrane fractions. This was accompanied by reductions in cell injury/death induced by lethal simulated ischemia. The effects of MIP and UP were attenuated and abolished by 1 μM nor-binaltorphimine, a selective κ-OR antagonist, administered before and during preconditioning/pretreatment, respectively. The effects were mimicked by 10 nM phorbol-12-myristate-13-acetate, a PKC activator, but attenuated by 5 μM chelerythrine, a PKC inhibitor. More importantly, 0.1 μM εV1–2, a selective PKC-ε inhibitor administered before and during MIP/UP, also attenuated the effects of both treatments on cell injury/death and translocation of PKC-ε. On the other hand, 5 μM rottlerin, a selective PKC-δ inhibitor, did not alter the effects of either treatment on injury/death. The results indicate that both MIP and UP activate PKC-ε, leading to delayed cardioprotection in rat ventricular myocytes.