Objective:To investigate the ability of mesenchymal stem cells differentiated into cardiomyocytes in vivo.Methods:MSCs isolated form rats bilateral tibias were purified

expanded in vitro culture

labeled with DAPI

then injected into the myocardium of the recipients(including acute myocardial infraction and normal rats).The hearts were harvested 2～4 weeks after implantation.Morphology of the differentiated cardiomyocytes was identified using HE stain and electron microscopy.Cardiac-specific antigen was detected using immunohistochemistry.Results:Viable cells labeled with DAPI can be identified in host myocardium at all time points after implantation.Implanted MSCs showed the growth potential in myocardial environments

after 4 weeks

donor cells derived from MSCs demonstrated myogenic differentiation with the expressing of myosin heavy chain.Donor cells demonstrated cardiomyocytes phenotypes with the expressing of cardiac-specific antigen Cx43.Meanwhile

electron microscopy examination demonstrated the existence of intercalated disks between donor cells and host cells.Conclusion:MSCs can differentiate into cardiomyoytes in host myocardial microenvironments.