Somatostatin binding to a fresh rat astrocyte-enriched suspension

Since there are conflicting reports regarding the effects of somatostatin (SS) on cyclic AMP levels in astrocytes derived from rat cerebral cortex and, to date, the SS binding to mature astrocytes is unknown, the present study has determined SS binding and its effect on cyclic AMP accumulation in a fresh astrocyte-rich suspension from rat cerebral cortex. 125I-Tyr11-SS binding was inhibited by SS in a dose-dependent manner. The Scatchard analysis of binding data was linear and yielded a dissociation constant of 0.95 +/- 0.15 nM with a maximal binding capacity of 122 +/- 13 fmol/mg protein. Vasoactive intestinal peptide (VIP) stimulated cyclic AMP accumulation up to 2.3 times above the basal levels whereas SS had no effect. This effect at any of the VIP concentrations. Likewise, SS did not inhibit the stimulation of cyclic AMP accumulation provoked by other effectors such as isoproterenol and forskolin. In view of our results and those of other authors, SS receptor localized in astrocytes must be able to couple with signal transduction systems other than adenylate cyclase, in order to carry out its biological actions in the cell.