Differentiation of cardiomyocytes in floating embryoid bodies is comparable to fetal cardiomyocytes

Embryonic stem cells will cluster and differentiate into embryoid bodies, w hich can develop spontaneous rhythmic contractions. From these embryoid bod ies, cardiomyocytes can be isolated based on density by a discontinuous Per coll gradient. These cardiomyocytes differentiate into ventricular myocytes , which is demonstrated by the expression of the ventricular specific isofo rm of the myosin light chain 2 gene, In this study the functional expressio n of ion channels was compared between fetal cardiomyocytes (in vivo) and s tem cell derived cardiomyocytes (in vitro). Sodium and calcium currents tog ether with transient potassium currents could be detected in early developm ental stages (<day 14) both in vivo and in vitro. In the early stages, we f ound a limited number of cells expressing I-Kr and virtual absence of I-Ks. The characteristics and distribution of currents are similar in both cell types. The current characteristics were identical for ventricular compared to atrial or undifferentiated stem cell derived cardiomyocytes, despite dif ferences in expression of regulatory myosin light chain proteins. The myocy te differentiation was verified in a limited number of cardiomyocytes follo wing the patch clamp proccdure by immunocytochemistry. (C) 2000 Academic Pr ess.