Electron microscopy studies on the pinocytosis activity of Ehrlich ascites tumor cells in monolayer culture]

During the phase of exponential growth ferritin was added to the culture medium of monolayer cell cultures from the Ehrlich ascites tumor in order to observe the pinocytosis phenomenon in these cells by means of electron microscopy. After a phase of adsorption, the ferritin arrived in vesicles and vacuoles of the cytoplasm - probably by ligature of coat invaginations. Within larger-sized vesicles, which might have been formed by fusion of smaller ones, less electron-dense ferritin-free internal compartments are resulting possibly from interaction with primary lysosomes; this is interpreted as a sign of interior digestive phenomena. Sometimes, this internal compartment was coated with a structure similar to a membrane. In the further course, concentration of the electron-dense zones containing ferritin occurred in the marginal zone of the vacuoles. Some vacuoles comprised two or three of the less electron-dense compartments. Vacuoles containing ferritin were also observed comprising residual membranes. The formation of these transition stages to residual bodies is regarded as an interaction and fusion of heterophagocytic or autophagocytic vacuoles with primary lysosomes.