PROCESS FORMATION IN ASTROCYTES - MODULATION OF CYTOSKELETAL PROTEINS

Studies on primary astrocytes cultured in vitro have shown that proces s formation involves changes in cytoskeletal proteins and release of t ension on the substratum. Actin filament reorganization has previously been found to be the major cytoskeletal change occurring during proce ss formation. These changes are relatively rapid with breakdown of the actin web and release of contacts occur within 15 min. of cyclic AMP treatment. The former is regulated by myosin light chain (MLC) and act in depolymerizing factor (ADF), with MLC involved in the initial relea se of contractile tension and ADF in both initial and longer term acti n breakdown. Our results show that the dephosphorylation of MLC is due to the phosphorylation and inactivation of myosin light chain kinase (MLCK) in response to cyclic AMP. To further study the mechanisms unde rlying the process formation in astrocytes we used endothelin-1 (ET-1) , a vasopeptide which has been shown to inhibit process formation in a strocytes and sodium fluoride which is a general phosphatase inhibitor . We observe an increase in phosphorylation of MLC on inhibition of pr ocess formation. To study the role of adhesion in process formation we used suspension cultures of astrocytes. Our results with the astrocyt es in suspension suggest that the process formation in astrocytes is a dhesion dependent and the changes in ADF and MLC occur only when there is process formation.