Adult rat cardiomyocytes in culture A model system to study the plasticity of the differentiated cardiac phenotype at the molecular and cellular levels

Adult rat cardiomyocytes (ARCs) in long-term culture, which show a distinct adaptive flexibility, are presented as a system to study cardiac cell hypertrophy in vitro. In the first 1-2 weeks after isolation, ARCs undergo a process of de- and redifferentiation during which the cell morphology is remodeled and the myofibrillar apparatus is restructured, accompanied by a cell enlargement. The growing cells spread and eventually establish new cell-cell contacts, which display newly formed intercalated discs; synchronous cell beating is resumed in the resulting tissuelike sheet. During myofibrillogenesis, the early fetal program of gene expression is reactivated for several genes, as is observed during hemodynamic overload hypertrophy. The cells resume hormonal activity and express atrial natriuretic factor (ANF); the expression pattern of ANF is also reminiscent of that seen in hypertrophy. In cells grown in a medium conditioned by 12-day ARCs, though, myofibrillogenesis is accelerated and accompanied by a downregulation of ANF. In a creatine-deficient medium, on the other hand, the ARCs display giant mitochondria with paracrystalline inclusions imitating a situation found, for example, in mitochondrial myopathies.