Gastrin13 and the C-terminal octapeptide of cholecystokinin are differently coupled to G-proteins in guinea-pig brain membranes.
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.(ABSTRACT TRUNCATED AT 250 WORDS)
Lallement
J C
JC
Faculté de Pharmacie, CNRS, Montpellier, France.
Galleyrand
J C
JC
Lima-Leite
A C
AC
Fulcrand
P
P
Martinez
J
J
D000818:Animals; D001570:Benzodiazepinones / Q000378:metabolism; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D020109:Devazepide; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005755:Gastrins / Q000737:chemistry / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism*; D010671:Phenylurea Compounds; D012844:Sincalide / Q000378:metabolism*
C089482:3-(3-iodo-4-hydroxyphenyl)propionyl(Leu(15))gastrin-(5-17); D001570:Benzodiazepinones; D005755:Gastrins; D010446:Peptide Fragments; D010671:Phenylurea Compounds; C058121:L 365260; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D020109:Devazepide; D012844:Sincalide