Binding of somatostatin to guinea-pig pancreatic membranes: regulation by ions.
Somatostatin receptors were characterized on guinea-pig pancreatic acini membranes using 125I-[Tyr11] somatostatin 14 as a radioligand. In 0.1 mM Ca2+ buffer the binding was saturable and slowly reversible, exhibiting a single class of high affinity binding sites (KD = 0.15 +/- 0.03 nM) with a maximal binding capacity (B max) of 178 +/- 18 fmol/mg protein. In 30 nM) free Ca2+ buffer, the binding was highly reversible. Affinity and B max were decreased by about 2-fold. Ca2+ exhibited an EC50 of 2.4 +/- 0.9 microM to potentiate the binding of somatostatin. Na+, but not K+, inhibited the binding: Bmax was decreased with no change in affinity. Somatostatin analogs inhibited the binding of 125I-[Tyr11] somatostatin 14. The relative potencies were: somatostatin 14 greater than somatostatin 28 = [Nle8]somatostatin 28 greater than [D Tryp8, D Cys14]somatostatin 14.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D006168:Guinea Pigs; D007700:Kinetics; D010179:Pancreas / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D017481:Receptors, Somatostatin; D012964:Sodium / Q000494:pharmacology; D013004:Somatostatin / Q000378:metabolism*
D011956:Receptors, Cell Surface; D017481:Receptors, Somatostatin; D013004:Somatostatin; D012964:Sodium; D011188:Potassium; D002118:Calcium