title: Secretin binding sites coupled with adenylate cyclase in rat fundic membranes.
abstract: Specific binding sites for secretin have been identified in rat fundic membranes, using 125I-secretin. The binding was saturable, reversible, time and temperature dependent. Optimal pH for binding was around 7-7.5. Scatchard plots were compatible with the existence of 2 classes of receptors; the first class with a high affinity for secretin (apparent Kd of 4 x 10(-10) M) and a low binding capacity (150 fmol per mg membrane protein, i.e., 4,500 high affinity sites/cell) and a class of receptors with a lower affinity (Kd of 3 x 10(-9) M) and a higher binding capacity (580 fmol per mg membrane protein i.e., 17,400 sites/cell). Glucagon, gastric inhibitory polypeptide and somatostatin had no-effect on secretin binding. In contrast, VIP inhibited 125I-secretin binding and stimulated adenylate cyclase activity, in both cases at a 200-times lower potency than secretin (ID50 and Ka = 2 x 10(-7) M VIP). The properties of these secretin receptors strongly support the concept that secretin acts as a regulatory peptide on the rat gastric epithelium.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D005748:Gastric Fundus / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D011964:Receptors, Gastrointestinal Hormone; D012633:Secretin / Q000378:metabolism* / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
chemical_list: D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D011964:Receptors, Gastrointestinal Hormone; C029937:secretin receptor; D012633:Secretin; D014660:Vasoactive Intestinal Peptide; D000262:Adenylyl Cyclases