Mitosis in Adult Newt Ventricle

Two recent electron microscope studies have demonstrated mitosis in embryonic cardiac fibers . In the chick (3) and the rat (8), both myofibrils and mitotic chromosomes were seen within the same cells. In the normal adult heart, however, cardiac fibers do not usually undergo cell division (2, 7) . The ability of adult cardiac fibers to divide after injury has been a matter of controversy (reviews 4, 9) . A number of studies at the light microscope level have indicated that newborn rat heart (6) and adult frog (7) and rat (1) cardiac muscle can respond to injury by undergoing DNA synthesis and mitosis. However, in light micrographs, it is difficult to identify with certainty the cell type of these mitotic cells. The present electron microscope study demonstrates that mitotic cells in a wounded area of the newt heart do possess characteristics of a cardiac fiber .