Gastrin13 and the C-terminal octapeptide of cholecystokinin are differently coupled to G-proteins in guinea-pig brain membranes

• Published in: European journal of pharmacology Vol. 267; no. 3; pp. 297 - 305
• Main Authors: Lallement, J C, Galleyrand, J C, Lima-Leite, A C, Fulcrand, P, Martinez, J
• Format: Journal Article
• Language: English
• Published: Netherlands 17.05.1994
• Subjects: Animals; Benzodiazepinones - metabolism; Binding Sites; Brain - metabolism; Devazepide; Gastrins - chemistry; Gastrins - metabolism; GTP-Binding Proteins - metabolism; Guanosine 5'-O-(3-Thiotriphosphate) - pharmacology; Guinea Pigs; In Vitro Techniques; Male; Peptide Fragments - metabolism; Phenylurea Compounds; Sincalide - metabolism
• ISSN: 0014-2999

In the course of our study concerning gastrin and cholecystokinin (CCK) receptors, we synthesized and characterized a labelled gastrin ligand, [125I]BH[Leu15]gastrin-(5-17) (3-(3-[125I]iodo-4-hydroxyphenyl)propionyl[Leu15]gastrin-(5-17)). On isolated canine fundic mucosal cells and human Jurkat lymphoblastic cell line, known to express CCKB/gastrin receptors, the binding experiments performed indicate that [125I]BH[Leu15]gastrin-(5-17) provides a convenient biologically active ligand for cholecystokinin/gastrin receptor studies. We showed in this study that, on guinea-pig brain membranes known to possess CCKB and CCKA receptors, [125I]BH[Leu15]gastrin-(5-17) binds to a single class of high-affinity binding sites in a saturable and specific manner. [125I]BH[Leu15]gastrin-(5-17) interacts with guinea-pig brain membranes with a maximal binding capacity that is about three-fold lower than that of [125I]BHCCK8 (CCK8, the C-terminal octapeptide of cholecystokinin). The apparent affinities of CCK analogues and selective CCK receptor antagonists L-365,260 and MK-329 for the sites labelled by both probes were in accordance with a CCKB-like profile. Association-dissociation kinetics of [125I]BH[Leu15]gastrin-(5-17) and [125I]BHCCK8 were performed and compared. They showed that [125I]BHCCK8 equilibrated more slowly than [125I]BH[Leu15]gastrin-(5-17). The effects of pH, monovalent and divalent cations on binding of both probes were investigated. The results obtained did not indicate strong differences between [125I]BH[Leu15]gastrin-(5-17) and [125I]BHCCK8 binding. Binding experiments in the presence of stable analogues of GTP showed a different behavior between [125I]BH[Leu15]gastrin-(5-17) and [125I]BHCCK8. GTP gamma S strongly decreased [125I]BH[Leu15]gastrin-(5-17) binding whereas it weakly affected [125I]BHCCK8 binding.