Calcium‐Independent, Tyrosine Phosphorylation‐Dependent Effects of Serum on the Morphology of Cultured Neurohypophysial Astrocytes

Abstract

Activation of adenylate cyclase induces cultured neurohypophysial astrocytes (pituicytes) to change from a protoplasmic, nonstellate form to a stellate form. Stellation is inhibited and reversed (destellation) by serum. The objective of the present studies was to examine the roles of Ca2+ and tyrosine phosphorylation in mediating these morphological changes. The effects of forskolin (to induce stellation) and serum (to inhibit and reverse stellation) were not affected by replacement of Ca2+ with Co2+ in the medium or by treatment of cultures with thapsigargin. However, genistein, a specific inhibitor of tyrosine kinase(s), significantly reduced the effect of serum on forskolin-induced stellation. Also, dephostatin, a specific inhibitor of tyrosine phosphatase, inhibited forskolin-induced stellation. In contrast, genistein did not have a dramatic effect on serum-induced destellation. The data demonstrate that morphological changes exhibited by cultured pituicytes are independent of Ca2+ but may be modulated by the activity of tyrosine kinase(s) and phosphatase(s).

Ca2+ mobilization mediated by transient receptor potential canonical 3 is associated with thrombin‐induced morphological changes in 1321N1 human astrocytoma cells

“…Previous studies have shown that thrombin‐stimulated morphological change is a primary result of the G 12/13 ‐mediated MLC phosphorylation that leads to actin rearrangement (Majumdar et al, 1998). In addition, a previous study by Seasholtz et al (2004) revealed modulation of cell rounding by the G i/o and G q/11 pathways. In the case of thrombin‐induced morphological changes, these authors mentioned the weak coupling between cell rounding and the G i/o pathway and the potent link between cell rounding and the G q/11 pathway involving PLC activation and PIP 2 breakdown.…”

“…Therefore, we postulate that bidirectional regulation might allow the cells to rapidly accommodate their elastic morphology. In the view of Ca 2+ dynamics, previous studies indicated that extensions of astrocytic protrusions (stellation) induced by dibutyryl cyclic AMP, forskolin, or amyloid beta peptide were independent of extracellular Ca 2+ (Ramsell and Cobbett, 2000; Abe and Saito, 2001), implying that bidirectional motions can be distinguished by their dependence on Ca 2+ entry. Thus, TRPC3 might contribute to the mechanism of thrombin‐induced advancing retraction rather than retraction‐induced counter‐reextension in astrocytoma cells.…”