POLARITY OF PROCESSES WITH GOLGI-APPARATUS IN A SUBPOPULATION OF TYPE-I ASTROCYTES

The Golgi apparatus-complex (GA), is a key organelle involved in sever al posttranslational modifications of polypeptides destined for lysoso mes, plasma membranes and secretion. As reported from this laboratory, certain astrocytes in rat brain contain cisternae of the GA not only in perikarya, but also in processes. In order to further investigate w hich type of astrocytes contain GA in processes we conducted the prese nt study using primary cultures of rat astrocytes and organelle specif ic antibodies against the GA and the rough endoplasmic reticulum (RER) . While the perikarya of all cells contained elements of the GA, only a single process of a subset of type I astrocytes, negative to antibod ies A2B5 and HNK-1, contained GA. In contrast, elements of the RER wer e found within perikarya and all processes. In order to confirm that t he immunostained structures in processes indeed represent the GA, we e xposed cultures to Brefeldin A (BFA), a secretion blocker which disper ses the GA and redistributes it to the RER. We observed that BFA disru pted the GA of both perikarya and processes. However, astrocytes were resistant to prolonged incubations with BFA, while a similar treatment killed cultured fibroblasts and PC-12 cells. Furthermore, in astrocyt es exposed to BFA for several days, the delicate network of glial fibr illary acidic protein (GFAP), was replaced by large perinuclear masses of the protein. These observations demonstrate that a subset of type I astrocytes have a single process with elements of the GA. We suggest that this specialization of the GA may be related to yet unrecognized secretory or protein processing functions of these cells. The resista nce of astrocytes to BFA and the striking changes in their cytoskeleto n induced by the drug, may contribute to studies on the mechanism(s) o f action of BFA.