CHARACTERIZATION OF SPECIFIC CALCITONIN-GENE-RELATED PEPTIDE RECEPTORS PRESENT IN HAMSTER PANCREATIC BETA-CELLS

Calcitonin gene-related peptide (CGRP) shares about 46% and 20% amino acid sequence homology with islet amyloid polypeptide (IAPP) and salmon calcitonin (sCT). We investigated whether these related peptides could cross-react with the specific binding of I-125-[His]hCGRP I to the CGRP receptor in hamster insulinoma cell membranes. A rapid dissociation of membrane bound I-125- [His]hCGRP I could be induced in the presence of 1 mu M chicken CGRP (cCGRP). The specific I-125-[His]hCGRP I binding was inhibited by the related peptides and their half-maximal inhibitory concentrations (IC50) were: cCGRP (0.1 nM), rat CGRP I and human CGRP I and II (1.0-2.0 nM), fragment of hCGRP I (8-37) (150 nM), human IAPP (440 nM). The non-amidated form of hIAPP; human diabetes-associated peptide (hDAP) did not inhibit the binding of I-125-[His]hCGRP I and sCT was only effective at a high concentration (I mu M). Binding of I-125-[His]hCGRP I was dose dependently inhibited by guanosine-5'-O-(3-thiotriphosphate) or (GTP gamma S) and a 70% reduction of binding was obtained with 0.1 mM GTP gamma S. The IC50 value of cCGRP (0.1 nM) was increased 100-fold in the presence of O.l mM GTP gamma S. Human CGRP I and cCGRP at 2.5 gamma M did not stimulate the activity of hamster insulinoma cell membranes adenylate cyclase, while glucagon (1 mu M) induced a 2-fold increase. Thus, specific CGRP receptors present in hamster beta cells are associated with G protein (s) and IAPP can interact with these receptors. These results and the observation that cCGRP and hCGRP I did not influence adenylate cyclase activity provide further evidence for CGRP receptor subtypes.