Biochemical evidence for somatostatin receptors in murine neuroblastoma clone N1E-115

Abstract

Radioligand binding and functional assays were employed to demonstrate the existence of somatostatin receptors in the murine neuroblastoma clone N1E-115. Saturation experiments with [ 125I][Tyr 11]somatostatin-14 indicated the presence of a single class of binding sites in membranes prepared from N1E-115 cells (K d = 83 pM; B max = 21 000 receptors/cell). Somatostatin-14, somatostatin-28 and L363586 (cyclo(N-Me-ALA-TYR-D-TRP-LYS-VAL-PHE)) all displaced the 125I-ligand monophasically in N1E-115 cells (K i values were 28, 82 and 34 pM, respectively), which contrasted with the binding heterogeneity apparent with L363586 in rat brain membranes. The binding of [ 125I][Tyr 11]somatostatin-14 was reduced by GppNHp, indicating that N1E-115 somatostatin receptors interacted with guanine nucleotide binding protein(s). Somatostatin agonists decreased by 30–50% the levels of [ 3H]cyclic AMP induced in intact cells by forskolin, prostaglandin E 1, or vasoactive intestinal polypeptide. The EC 50 values for inhibition of the [ 3H]cyclic AMP response to PGE 1 by L363586, somatostatin-14, and somatostatin-28 were 0.24, 0.63 and 1.0 nM, respectively. Pertussis toxin treatment of N1E-115 cells reduced both binding to the receptor and the functional response to somatastatin-14. These data suggest that a single class of somatostatin receptors in N1E-115 cells are linked to the inhibition of adenylate cyclase through a G i protein.