"Regulation of bombesin receptors on pancreatic acini by cholecystokini" by M. Younes, S. A. Wank et al.
 

Regulation of bombesin receptors on pancreatic acini by cholecystokinin

Document Type

Journal Article

Publication Date

1-1-1989

Journal

American Journal of Physiology - Gastrointestinal and Liver Physiology

Volume

256

Issue

2

Abstract

When guinea pig pancreatic acini are first incubated with the COOH-terminal octapeptide of cholecystokinin (CCK-8), washed, and then reincubated with 125I-[Tyr4]bombesin (125I-[Tyr4]BN) there is a significant decrease in binding of 125I-[Tyr4]BN compared with that observed with pancreatic acini that have been first incubated with no additions. The CCK-8-induced decrease in binding is maximal after 90 min of first incubation is abolished by reducing the temperature of the first incubation from 37 to 4°C or by adding L364,718 to the first incubation and cannot be reproduced by first incubating acini with A23187, 8-bromoadenosine 3',5'-cyclic monophosphate (8Br-cAMP), 8-bromoguanosine 3',5'-cyclic monophosphate (8Br-cGMP), or 12-O-tetradecanoylphorbol 13-acetate. 125I-[Tyr4]BN interacts with a single class of receptors on pancreatic acini, and first incubating acini with CCK-8 decreases the affinity of BN receptors for BN with no change in the maximal binding capacity. CCK-8 does not alter the rate at which bound 125I-[Tyr4]BN dissociates from pancreatic acini; therefore, CCK-8 must alter the rate at which the radiolabeled BN analogue associates with its receptor. Pancreatic acini possess two classes of CCK receptors: one has a high affinity for CCK-8; the other has a low affinity for CCK-8. The dose-response curve for CCK-8-induced inhibition of binding of 125I-[Tyr4]BN appears to reflect occupation of low-affinity CCK receptors by CCK-8. Finally, although first incubating acini with CCK-8 reduces the affinity of BN receptors for BN, it reduces the maximal response for BN-stimulated enzyme secretion with no detectable shift in the dose-response curve for BN-stimulated enzyme secretion. Thus the effect of CCK-8 on the affinity of the BN receptor can be dissociated from the effect of CCK-8 on BN-stimulated enzyme secretion.

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