title: Specific high affinity binding sites for somatostatin-28 on pancreatic beta-cells: differences with brain somatostatin receptors.
abstract: Saturable and high affinity binding sites have been obtained for an iodinated somatostatin-28 (SS-28) analog, [Leu8,D-Trp22,125I-Tyr25] SS-28, in a membrane preparation from hamster insulinoma, mainly composed of pancreatic beta-cells. Specific binding is maximal after 1 hour incubation at 22C and represents 65% of the total binding. KD for [Leu8,D-Trp22,Tyr25] SS-28 is 0.25 nM with the number of sites corresponding to 68 fmol/mg protein. The KD for SS-28 (1nM) is more than 5 times lower than that for SS-14. SS-28 analogs, such as [D-Trp22] SS-28 and analogs which selectively inhibit insulin release in vivo (Des-Asn5[D-Trp8,D-Ser13] SS-14 and Des-Asn19[D-Trp22,D-Ser27] SS-28), are the most potent compounds in this assay. C-terminal replacement of L-cysteine by D-cysteine reduces the apparent affinity of SS analogs. Unrelated peptides and the inactive analog Des-Trp8-SS-14 have no affinity for insulinoma binding sites. There are differences between the insulinoma SS binding sites and those monitored under similar conditions from rat cerebral cortex. In cerebral cortex, SS-14 and SS-28 have similar affinity for the binding sites, and the insulin selective analogs are less potent than SS-14. It is concluded that pancreatic beta-cells, as well as brain, possess high affinity binding sites for SS, but that they differ in some of their pharmacological properties.
mesh_terms: D007516:Adenoma, Islet Cell / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane; D006224:Cricetinae; D005260:Female; D007340:Insulinoma / Q000378:metabolism*; D007700:Kinetics; D009374:Neoplasms, Experimental / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017481:Receptors, Somatostatin; D013004:Somatostatin / Q000378:metabolism*; D053561:Somatostatin-28
chemical_list: D011498:Protein Precursors; D011956:Receptors, Cell Surface; D017481:Receptors, Somatostatin; C032532:somatostatin-28 receptor; D013004:Somatostatin; D053561:Somatostatin-28