Receptor occupation, calcium mobilization, and amylase release in pancreatic acini: effect of CCK-JMV-180.
We examined the relationships between receptor occupation, calcium mobilization, and stimulated amylase release for cholecystokinin octapeptide (CCK-8) and for CCK-JMV-180, an analogue of the COOH-terminal heptapeptide of CCK having the structure Boc-Tyr(SO3)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester using dispersed acini from rat pancreas. CCK-8 and CCK-JMV-180 each bind to two classes of CCK receptors: one class has a high affinity for CCK-8 and CCK-JMV-180 and the other class has a low affinity for CCK-8 and CCK-JMV-180. Mobilization of cellular calcium was assessed by measuring cytosolic calcium with a fluorescent indicator and by measuring outflux of radioactive calcium from preloaded cells. In terms of causing an increase in cytosolic calcium or an increase in calcium outflux, CCK-JMV-180 was 50-60% as efficacious as CCK-8. Analysis of the relationship between receptor occupation and calcium mobilization caused by CCK-8 and CCK-JMV-180 in combination indicates that calcium mobilization is caused by occupation of low-affinity CCK receptors. Comparison of the dose-response curve for calcium mobilization and amylase release stimulated by CCK-8 or CCK-JMV-180 indicates that very low concentrations of each peptide stimulate amylase release without causing detectable calcium mobilization. At these very low concentrations, CCK-8 or CCK-JMV-180 do not cause potentiation of amylase release when combined with vasoactive intestinal peptide.
Sato
S
S
Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Stark
H A
HA
Martinez
J
J
Beaven
M A
MA
Jensen
R T
RT
Gardner
J D
JD
D000681:Amylases / Q000378:metabolism*; D000818:Animals; D001572:Benzofurans; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D007700:Kinetics; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011949:Receptors, Cholecystokinin / Q000187:drug effects / Q000378:metabolism*; D012844:Sincalide / Q000031:analogs & derivatives* / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D001572:Benzofurans; D005456:Fluorescent Dyes; D011949:Receptors, Cholecystokinin; C058451:JMV 180; D014660:Vasoactive Intestinal Peptide; D000681:Amylases; D012844:Sincalide; D002118:Calcium; D016257:Fura-2