Electrophysiological Maturation and Integration of Murine Fetal Cardiomyocytes After Transplantation

Abstract

Abstract-In the present study, we investigated the electrophysiological maturation and integration of immature cardiomyocytes after transplantation; maturation and integration are essential to achieve the cardiac regeneration. Murine fetal cardiomyocytes (FCMs) (d12.5-d15.5) expressing enhanced green fluorescent protein under the control of the ␣-actin promoter were injected into cryoinjured areas and adjacent myocardium of cryoinjured mouse ventricles. Viable short axis tissue slices (thickness, 150 m) of the ventricles were prepared 5 to 6 days after transplantation. Glass microelectrodes were used for measurements of action potentials in transplanted FCMs and host cardiomyocytes within the slices. Stimulation at frequencies of up to 10 Hz was performed via a unipolar electrode placed in viable host tissue. Transplanted FCMs could be distinguished clearly from host tissue by their green fluorescence and their electrophysiological properties: maximal upstroke velocity (V max ) was significantly lower and action potential duration at 50% repolarization (APD 50 ) was significantly longer compared with values of adult cardiomyocytes. Transplanted FCMs surrounded by cryoinjured tissue showed spontaneous electrical and contractile activity, which was in no case synchronous with host tissue. V max and APD 50 of these nonintegrated cells matched values of cultivated dissociated FCMs. In contrast, 82% of transplanted FCMs surrounded by viable host tissue were electrically integrated; ie, electrical and contractile activity was synchronous with host tissue and these cells had more mature action potential parameters (significantly higher V max and shorter APD 50 ) compared with nonintegrated FCMs. In conclusion, electrophysiological maturation and integration of transplanted FCMs depend on an embedment in viable host myocardium. Key Words: cardiac electrophysiology Ⅲ cardiomyoplasty Ⅲ coupling Ⅲ heart slices Ⅲ maturation A cute myocardial infarction and chronic heart failure are among the most frequent causes of morbidity and mortality in Western countries. In the course of physiological reparation processes, cardiomyocytes lost because of myocardial infarction are replaced by scar tissue, leading to an impaired cardiac function and remodeling of the remaining myocardium. Despite advances in the conventional therapy, this loss of functional myocardium remains irreversible. Thus, there is a strong need for a novel therapeutic approach aiming at a regeneration of cardiomyocytes: cardiac cell therapy.Cardiomyocytes derived from embryonic stem cells (ESCCMs) are promising candidates for cell therapy via an exogenic replacement of lost cardiomyocytes, because their cardiac phenotype, including cardiac specific protein expression as well as typical cardiac electrophysiological properties, is undoubted. 1 Clinical studies using ESC-CMs have not been performed, because, first, techniques enabling the production and selection of sufficient cell numbers must be developed and potential risks and immunological issues must be investi...

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