The mechanism by which the mitochondrial ATP-sensitive K+ channel opening and H2O2 inhibit the mitochondrial permeability transition

Myocardial infarction is a manifestation of necrotic cell death as a result of opening of the mitochondrial permeability transition ( MPT). Receptor-mediated cardioprotection is triggered by an intracellular signaling pathway that includes phosphatidylinositol 3-kinase, endothelial nitric-oxide synthase, guanylyl cyclase, protein kinase G ( PKG), and the mitochondrial K-ATP channel ( mitoKATP). In this study, we explored the pathway that links mitoKATP with the MPT. We confirmed previous findings that diazoxide and activators of PKG or protein kinase C ( PKC) inhibited MPT opening. We extended these results and showed that other K+ channel openers as well as the K+ ionophore valinomycin also inhibited MPT opening and that this inhibition required reactive oxygen species. By using isoform-specific peptides, we found that the effects of K-ATP channel openers, PKG, or valinomycin were mediated by a PKC epsilon. Activation of PKC epsilon by phorbol 12-myristate 13-acetate or H2O2 resulted in mitoK(ATP)-independent inhibition of MPT opening, whereas activation of PKC epsilon by PKG or the specific PKC epsilon agonist psi epsilon receptor for activated C kinase caused mitoK(ATP)-dependent inhibition of MPT opening. Exogenous H2O2 inhibited MPT, because of its activation of PKC epsilon, with an IC50 of 0.4 ( +/- 0.1) mu M. On the basis of these results, we propose that two different PKC epsilon pools regulate this signaling pathway, one in association with mitoK(ATP) and the other in association with MPT.