[Histogenesis of muscle tissue in the developing lymph hearts of Rana temporaria larvae and younglings. A study by electron microscopic and electron microscopic autoradiographic methods].

Using 3HT electron microscope autoradiography, the ultrastructure of muscle fibers and the capacity of 3HT-incorporation into the nuclei of these fibers and the adjacent cells were studied in the developing lymph hearts of larvae and yearlings of R. temporaria. The presence of myofilaments arranged in sarcomeres of prominent disks Z, I, A, H and M line, and of the well developed sarcoplasmic reticulum may serve a good evidence of a high level of myofibrillar differentiation both in larvae and in yearlings. Myosatellite cells were found in the close contact with muscle fibers at all the investigated stages of the lymph heart development. 4 hours after 3HT administration to larvae, only mononuclear cells deprived of myofibers were seen labeled. The labeled myonuclei were observed in the experiments with double 3HT injections to larvae and with the fixation following 24 hours after the last 3HT administration. These data evidence that, according to the ratio of differentiation and reproduction, the histogenesis of the lymph heart muscle tissues of larvae and yearlings of R. temporaria corresponds to the myogenesis of cross striated skeletal muscles of vertebrates.