Cytoplasmic effects of X-irradiation on cultured cells 2. Alterations in lysosomes, plasma membrane, Golgi apparatus, and related structures.

Topoinhibited human glia cells in vitro were exposed to X-radiation generated by an 8-MeV linear accelerator at a dose of 20,000 rad. Transmission electron microscopy of irradiated cells at intervals varying between 30 min. and 5 days following irradiation revealed alterations mainly in the plasma membrane and the lysosomal vacuome. Increased ruffling of plasma membranes, augmented endocytosis and extensive intracellular autophagy developed within 24 hours after irradiation. The implications of the plasma membrane alterations are discussed, and a tentative model covering possible mechanism involved in the development of autophagic vacuoles is presented. The possibility is entertained that alternative mechanism may be operative during the formation of the autophagic vacuole in irradiated glia cells. The origin of the isolation membrane appears to be (a) preexisting lysosomes; and (b) flattened vacuolar cytoplasmic elements.