Protein kinase Cε mediates salutary effects on electrical coupling induced by ischemic preconditioning

Background: Ischemic preconditioning delays the onset of electrical uncoupling and prevents loss of the primary ventricular gap junction protein connexin 43 (Cx43) from gap junctions during subsequent ischemia. Objective: To test the hypothesis that these effects are mediated by protein kinase C epsilon (PKCε), we studied isolated Langendorff-perfused hearts from mice with homozygous germline deletion of PKCε (PKCε-KO). Methods: Cx43 phosphorylation and distribution were measured by quantitative immunoblotting and confocal microscopy. Changes in electrical coupling were monitored using the 4-electrode technique to measure whole-tissue resistivity. Results: The amount of Cx43 located in gap junctions, measured by confocal microscopy under basal conditions, was significantly greater in PKCε-KO hearts compared with wild-type, but total Cx43 content measured by immunoblotting was not different. These unanticipated results indicate that PKCε regulates subcellular distribution of Cx43 under normal conditions. Preconditioning prevented loss of Cx43 from gap junctions during ischemia in wild-type but not PKCε-KO hearts. Specific activation of PKCε, but not PKCδ, also prevented ischemia-induced loss of Cx43 from gap junctions. Preconditioning delayed the onset of uncoupling in wild-type but hastened uncoupling in PKCε-KO hearts. Cx43 phosphorylation at the PKC site Ser368 increased 5-fold after ischemia in wild-type hearts, and surprisingly, by nearly 10-fold in PKCε-KO hearts. Preconditioning prevented phosphorylation of Cx43 in gap junction plaques at Ser368 in wild-type but not PKCε-KO hearts. Conclusion: Taken together, these results indicate that PKCε plays a critical role in preconditioning to preserve Cx43 signal in gap junctions and delay electrical uncoupling during ischemia.