[Reaction of lymphatic heart muscle in the adult grass frog to autotransplantation. Electron microscopic and electron microscopic autoradiographic studies].

Cellular and subcellular responses, related to destruction, survival and regeneration of striated muscle fibers in the autografted intact lymph heart of the adult frog, were examined by electron microscopy and electron microscopical autoradiography. It has been shown that a small number of myofibers in the grafted lymph heart wall undergo an irreversible degeneration. Numerous myofibers retain their almost normal ultrastructure up to the end of the 1st posttransplantation week and later. However, a considerable part of surviving muscle fibers exhibited various degrees of reversible degenerative changes. Prominent morphological features of activation, related to the nuclear and cytoplasmic ultrastructural reorganization, were revealed in these reversibly degenerated myofibers since the middle of the second week after autotransplantation. It is shown that some myonuclei of these reactive fibers are able to synthesize DNA. No mitoses were observed in myonuclei. The number of satellite cells (normally approximately 11%) doubled by the end of the 3rd week of posttransplantation. Evidence was provided for the formation of some myotubes in the interstitium outside the basal membrane of the original muscle fibers. Cellular sources of regeneration are discussed in addition to peculiar reaction of lymph heart muscle fibers to free grafting.