Protein kinase G transmits the cardioprotective signal from cytosol to mitochondria

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 ( mitoKATP) 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-epsilon peptide antagonist epsilon V1-2. 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-epsilon.