Roles of Cx43-associated protein kinases in suppression of gap junction-mediated chemical coupling by ischemic preconditioning.

Ischemic preconditioning (PC) suppresses chemical coupling of cardiomyocytes via gap junctions (GJs) during ischemia, which is an adjunct mechanism of protection. The aim of this study was to characterize roles of protein kinases in PC-induced GJ modulation. In isolated rat hearts, ventricular tissues were sampled before and after ischemia with or without PC, and intercalated disc-rich fractions were separated for immunoprecipitation and immunoblotting. Levels of protein kinase C (PKC)-epsilon, p38mitogen-activated protein kinase (MAPK)-alpha, and Src coimmunoprecipitated with connexin-43 (Cx43) were increased after ischemia, whereas p38MAPKbeta was not detected in the Cx43 immunoprecipitates. PC did not modify the level of Cx43-Src complex after ischemia. However, PC enhanced Cx43-PKCepsilon complex formation, which was abolished by PKCepsilon translocation inhibitory peptide (TIP). In contrast, PC reduced Cx43-p38MAPKalpha complex level and p38MAPK activity in the Cx43 immunoprecipitates after ischemia. The effect of PC on Cx43-p38MAPKalpha interaction was mimicked by SB-203580, a p38MAPK inhibitor. PC reduced permeability of GJs to Lucifer yellow in the myocardium at 25 min after ischemia, and this effect was abolished by PKCepsilon-TIP. SB-203580 increased the GJ permeability at 15 min after ischemia compared with that in untreated controls, but the difference became insignificant 25 min after ischemia. In conclusion, PC has distinct effects on interaction of GJ Cx43 with PKCepsilon, p38MAPKalpha, and Src during ischemia. Suppression of GJ permeability during ischemia by PC is primarily achieved by enhanced interaction of Cx43 with PKCepsilon, which overwhelms the counterbalancing effect of reduced Cx43-p38MAPKalpha interaction.