Protein Kinase G Transmits the Cardioprotective Signal From Cytosol to Mitochondria

Abstract

Ischemic and pharmacological preconditioning can be triggered by an intracellular signaling pathway in which G i -coupled surface receptors activate a cascade including phosphatidylinositol 3-kinase, endothelial nitric oxide synthase, guanylyl cyclase, and protein kinase G (PKG). Activated PKG opens mitochondrial K ATP channels (mitoK ATP ) which increase production of reactive oxygen species. Steps between PKG and mitoK ATP opening are unknown. We describe effects of adding purified PKG and cGMP on K + transport in isolated mitochondria. Light scattering and respiration measurements indicate PKG induces opening of mitoK ATP similar to K ATP channel openers like diazoxide and cromakalim in heart, liver, and brain mitochondria. This effect was blocked by mitoK ATP inhibitors 5-hydroxydecanoate, tetraphenylphosphonium, and glibenclamide, PKG-selective inhibitor KT5823, and protein kinase C (PKC) inhibitors chelerythrine, Ro318220, and PKC-ε peptide antagonist εV 1-2 . MitoK ATP are opened by the PKC activator 12-phorbol 13-myristate acetate. We conclude PKG is the terminal cytosolic component of the trigger pathway; it transmits the cardioprotective signal from cytosol to inner mitochondrial membrane by a pathway that includes PKC-ε.