AUTORADIOGRAPHIC AND ELECTRON-MICROSCOPIC STUDIES OF MINCED CARDIAC-MUSCLE REGENERATION IN THE ADULT NEWT, NOTOPHTHALMUS-VIRIDESCENS

The regenerative response of minced cardiac muscle grafts in the adult newt was studied using autoradiography and EM. About 1/16-1/8 of the newt ventricle was amputated, minced and returned to the wounded ventricle. At 5 days after grafting no reorganization of graft muscle pieces was apparent and there was degeneration of much of the muscle graft. A smaller population of 5-day myocytes had euchromatic nuclei and intact sarcolemma. In 10- and 16-day grafts, continuity between ventricular and graft lumina was established and coalescence of graft pieces was apparent. Ultrastructurally, 10- and 16-day graft myocytes had fewer myofibrils and increased amounts of rough endoplasmic reticulum, polyribosomes, Golgi complexes and dense bodies when compared to uninjured ventricular myocytes. The peak of proliferative activity of graft cells was seen at 16 days. EM autoradiography showed breakdown of myofibrillar structure in labeled myocytes; in myocytes in the later stages of mitosis only scattered myofilaments and no Z bands were present. By 30 days, grafts appeared as an integrated structure composed primarily of cardiac muscle. Myocytes of 30-day grafts were observed in various stages of myofibrillogenesis and contained numerous 10-nm filaments. The 70-day graft myocytes had numerous well-organized myofibrils and intercellular junctions similar to those in uninjured ventricular myocytes.