摘要OBJECTIVE In this study we explored the role of Epac1-Rap1 pathway in the acute myocardial ischemia/reperfusion injury (MIRI) in vitro and in vivo. METHODS An acute myocardial ischemia/reperfusion injury model was established by the ligation of left anterior descending coronary. Myocardial architecture, fibers and apoptosis was evaluated by the Masson trichrome staining, Sirius red staining and TUNEL assay.H9c2 cells were subjected to hypoxia for 5 h followed by 1-h reoxygen-ation in vitro.Cell viability was measured by MTT assay and cellular injury was evaluated by measuring the release of lactate dehydrogenase (LDH). Western blot, real-time PCR and immunofluorescence were used to detect the expressions of Epac1 and relative downstream molecules.RESULTS Myocardial IR-induced cardiac apoptosis and accumulation of Epac1 and Rap1 in rat IR injury model.Direct Epac activation by 8-CPT(8-(4-chlorophenylthio)-2′-O-methyl-cAMP)exacerbated cardiomyocyte death and dysfunction following hypoxia-reoxygenation(H/R),selective activation of Epac in response to H/R was evident which enriched for cytosolic/membrane proteins and mRNA. Harmacological inhibitor of Epac (ESI-09)significantly ameliorated myocardial injury with the decline of Epac expression.Epac inhibitor and agonist studies also implicated the effect of Rap1, which is downstream of Epac in this pathway. The expression of Rap1 elevated when activated by Epac agonist and was blocked by Epac inhibitor. The same result was true for myocyte CaMK-II and intracellular calcium ions activation.Moreover,ESI-09 also increased ERK1/2 phosphorylation. CONCLUSION Our study reveal that Epac1/Rap1 signaling pathway is involved in the pathogenesis of myocardial I/R injury in rats,which provides evidence on the development of therapeutic strategies target this pathway for myocardial I/R injury.