Adult mammalian cardiac muscle cells in culture.

Adult rat cardiac muscle cells were isolated from the ventricle by a retrograde perfusion technique through the aorta (Nag and Zak, 1979). These single, isolated cardiac muscle cells were cultured for 4 weeks. Throughout the culture period, a small number of muscle cells retained their cylindrical shape, while the rest exhibited alterations in shape and size assuming a flattened body of irregular shape with pseudopodia-like processes and thereby resembling embryonic/neonatal cardiac muscle cells in culture. Transmission electron microscopy revealed that the cylindrical muscle cells contained compactly arranged myofibrils and cellular organelles, similar to those of freshly isolated and in vivo cells. A few irregularly shaped cardiac muscle cells were similar to the cylindrical cells in their internal structural organization. Most of the irregular cells exhibited less myofibrillar content than that of the freshly dissociated and in vivo cells. Myofibrils in the irregular cells were widely spaced and myofilament of some of the myofibrils were loosely bunched. In addition, scattered patches of myofibrils and free myofilaments were observed in many of these cells. The internal structural organization of these irregularly shaped cardiac muscle cells closely resembled the embryonic and neonatal cardiac muscle cells in vitro and in vivo. Most of the muscle cells in culture continued to contract spontaneously, and electron microscope studies clearly indicated that they underwent dedifferentiation. Autoradiography studies demonstrated that the cylindrical and irregularly shaped cardiac muscle cells underwent DNA synthesis and cell division in culture.