In vivo survival and function of transplanted rat cardiomyocytes

Recent studies have demonstrated the feasibility of transplanting fetal mouse cardiomyocytes into the hearts of adult syngeneic mice. However, the function of the transplanted cardiomyocytes and their capacity to survive in fibrous connective tissue were not assessed. In the present study, we evaluated the viability and contractility of transplanted fetal and neonatal rat cardiomyocytes in the connective tissue of the adult rat hindlimb. Purified fetal or neonatal rat cardiomyocytes were cultured. These cells contained sarcomeres, formed junctions composed of desmosomes and fascia adherens, and contracted regularly and spontaneously. A fetal or neonatal cardiomyocyte suspension was injected into the subcutaneous tissue of adult rat hindlimbs. Cyclosporin A (5 mg/kg) was administered subcutaneously daily for the 3-month duration of the study, at which time the animals were killed. The transplanted cardiomyocytes formed 'tissue' in vivo that increased in size for the first 2 weeks and remained the same size at the third week. The tissue derived from the transplanted fetal cardiomyocytes contracted spontaneously at a rate of 73 +/- 12 bpm, and that from the neonatal cardiomyocytes contracted at a rate of 43 +/- 21 bpm. The electrocardiogram was similar to that seen in myocardium with an idioventricular rhythm. Histologically, the tissue appeared to be cardiac muscle with sarcomeres. Angiogenesis occurred in the cardiomyocyte graft. In summary, a cell suspension of cultured fetal and neonatal rat cardiomyocytes transplanted into the adult rat hindlimb formed contractile cardiac tissue in the subcutaneous connective tissue.