ANALYSIS OF THE ENDOCYTIC-LYSOSOMAL SYSTEM (VACUOLAR APPARATUS) IN ASTROCYTES DURING PROLIFERATION AND DIFFERENTIATION IN PRIMARY CULTURE

The endocytic-lysosomal system of proliferating and differentiated ast rocytes in primary culture was investigated using a combination of cyt ochemical, immunocytochemical and biochemical procedures. These includ ed impregnation with osmium tetroxide and potassium iodide, phosphotun gstic acid staining, cytochemical demonstration of acid phosphatase an d thiamine pyrophosphatase activities and incorporation of cationized ferritin. The acid phosphatase activity was also analyzed using bioche mical techniques. Our results indicate that while all astrocytes in pr imary culture have a developed endocytic-lysosomal system, this system is different in proliferating cells from that in differentiated astro cytes. Whereas in proliferating astrocytes it appears to be composed m ainly of a variety of vacuoles and vesicles displaying a heterogeneous osmium tetroxide staining pattern, differentiated cells are character ized by the presence of small size vesicles showing an intense reactio n. Both types of astrocyte showed abundant lysosomes, including multiv esicular bodies, which presented an intense phosphatase acid activity. Biochemical analyses demonstrated that this activity increase during the proliferation period, reaching a maximum at 15 days of culture. In corporation of cationized ferritin revealed that lysosomes and endosom es constitute separate systems. Finally, we have also found that the a ctivity of thiamine pyrophosphatase, a marker for the Golgi complex, i ncreases throughout the culture period. These results indicate that as trocytes could play an important role in regulating the macromolecular composition of the extracellular space.