Developmental analyses of the cardiac conduction system and cardiomyocytic functions in the rats with congenital cardiac anomalies

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Bis-diamine induces congenital heart defects in embryos when administered to pregnant rats. Histological analyses of the developing cardiac conduction system were performed in this animal model and the normal control rat embryos using whole embryo culture. Bis-diamine disturbed the conduction tissue development through overall poor myocardial growth. We investigated developmental changes of the physiological characteristics in the neonatal mouse myocardial cells isolated using chunk method or from Langendorff perfusion method. All the isolated cells exhibited elongated spindle-shaped appearance and a conduction tissue cell could not be distinguished from a myocardial cell or a fibroblast. Whole-cell patch-clamp experiments clearly showed the developmental changes in electrophysiological characteristics of the myocardial cells including the decrease in the inward rectifier K^+current and depolarization of resting membrane potential.