Intramitochondrial signaling:: interactions among mitoKATP, PKCε, ROS, and MPT

Activation of protein kinase C epsilon (PKC epsilon), opening of mitochondrial ATP-sensitive K+ channels (mitoK(ATP)), and increased mitochondrial reactive oxygen species (ROS) are key events in the signaling that underlies cardioprotection. We showed previously that mitoK(ATP) is opened by activation of a mitochondrial PKC epsilon, designated PKC epsilon 1, that is closely associated with mitoK(ATP). mitoK(ATP) opening then causes an increase in ROS production by complex I of the respiratory chain. This ROS activates a second pool of PKC epsilon, designated PKC epsilon 2, which inhibits the mitochondrial permeability transition (MPT). In the present study, we measured mitoK(ATP)-dependent changes in mitochondrial matrix volume to further investigate the relationships among PKC epsilon, mitoK(ATP), ROS, and MPT. We present evidence that 1) mitoK(ATP) can be opened by H2O2 and nitric oxide (NO) and that these effects are mediated by PKC epsilon 1 and not by direct actions on mitoKATP, 2) superoxide has no effect on mitoKATP opening, 3) exogenous H2O2 or NO also inhibits MPT opening, and both compounds do so independently of mitoK(ATP) activity via activation of PKC epsilon e2, 4) mitoK(ATP) opening induced by PKG, phorbol ester, or diazoxide is not mediated by ROS, and 5) mitoK(ATP)-generated ROS activates PKC epsilon 1 and induces phosphorylation-dependent mitoK(ATP) opening in vitro and in vivo. Thus mitoK(ATP)-dependent mitoK(ATP) opening constitutes a positive feedback loop capable of maintaining the channel open after the stimulus is no longer present. This feedback pathway may be responsible for the lasting protective effect of preconditioning, colloquially known as the memory effect.