Calcium-dependence of somatostatin binding to receptors

Binding of 125I-[Tyr11] somatostatin (S14) and 125I-[Tyr1]S14 has been studied in pancreatic acini and cerebral cortex. Ca2+-dependence of somatostatin binding to receptors was observed only with the highly non degradable iodinated analog 125I-[Tyr11] somatostatin but not with 125I-[Tyr1] somatostatin. The inhibitory activity of S14 on secretin-stimulated cAMP cellular content was decreased when Ca2+ concentration in the medium was reduced to 30 nM, indicating that the Ca2+ dependence of somatostatin binding to receptors is also present with the native peptide.