Electrophysiological maturation and integration of murine fetal cardiomyocytes after transplantation.

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 alpha-actin promoter were injected into cryoinjured areas and adjacent myocardium of cryoinjured mouse ventricles. Viable short axis tissue slices (thickness, 150 microm) 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. FCMs surrounded by cryoinjured tissue maintain physiological but immature AP properties.

Functional impact of targeted closed-chest transplantation of bone marrow cells in rats with acute myocardial ischemia/reperfusion injury.

Intramyocardial transplantation of bone marrow-derived stem cells is a potential therapeutic option after myocardial infarction (MI). Intramyocardial administration is invasive but allows efficient and targeted stem cell delivery. Aims of this study were validation of minimal-invasive, echo-guided closed-chest cell transplantation (CTx) of mononuclear (MNC) or mesenchymal stem cells (MSC) and quantification of systolic left ventricular function and assessment of contractile reserve with high-resolution reconstructive 3D-echocardiography (r3D-echo) 3 weeks after CTx. Female Fischer344 rats received syngeneic male MNC, MSC, or medium after myocardial ischemia and reperfusion via echo-guided percutaneous injection (open-chest for control). Left ventricular systolic function was measured and dysfunctional myocardium was quantified with r3D-echo. For investigation of contractile reserve and myocardial viability r3D-echo was additionally conducted during low-dose dobutamine 3 weeks after CTx. Cell persistence after echo-guided CTx was quantified via real-time PCR; scar size was measured histologically. Echo-guided percutaneous CTx was feasible in all animals (n = 30) without periprocedural complications. After 3 weeks, 1.4 +/- 1.1% of transplanted MNC and 1.9 +/- 1.2% of MSC were detected. These numbers were comparable to those after open-chest intramyocardial injection of MNC (0.8 +/- 1.1%; n = 8, p = 0.3). In r3D-echo no functional benefit was associated with CTx after MI and reperfusion. All groups (MNC, MSC, and controls) revealed a significant decrease of dysfunctional myocardium and similar contractile reserve during inotropic stimulation.In conclusion, percutaneous echo-guided closed-chest CTx promises to be an effective and safe approach for CTx in small-animal research. However, intramyocardial CTx of MNC or MSC had no influence on systolic function and contractile reserve after reperfused MI.