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Am J Physiol Gastrointest Liver Physiol 257: G402-G408, 1989;
0193-1857/89 $5.00
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AJP - Gastrointestinal and Liver Physiology, Vol 257, Issue 3 402-G408, Copyright © 1989 by American Physiological Society

ARTICLES

Carbachol-induced down-regulation of high-affinity receptors for vasoactive intestinal peptide

M. Murakami, R. Vinayek, R. T. Jensen and J. D. Gardner
Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.

When dispersed acini from guinea pig pancreas are first incubated with carbachol, the subsequent binding of 125I-vasoactive intestinal peptide (VIP) is inhibited during a second incubation. This inhibitory action of carbachol on binding of 125I-VIP depends on time, temperature, and the concentration of carbachol in the first incubation and can be blocked by atropine. First incubating acini with A23187, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), cholecystokinin octapeptide, bombesin, or 12-O-tetradecanoylphorbol-13-acetate does not alter binding of 125I-VIP. Adding EGTA to the first incubation medium abolishes the effect of carbachol on binding of 125I-VIP. In control acini or acini first incubated with carbachol, approximately half of the bound 125I-VIP can be stripped by acetic acid. 125I-VIP interacts with two distinct classes of receptors on pancreatic acini. One has a high affinity for VIP (Kd, 1 nM); the other has a low affinity for VIP (Kd, 2 microM). First incubating acini with carbachol decreases the number but not the affinity of high-affinity VIP receptors with no change in the number or affinity of low-affinity VIP receptors. Pancreatic acini possess two classes of muscarinic cholinergic receptors: one has a high affinity (Kd, 4 microM) and the other has a low affinity (Kd, 698 microM) for carbachol. The dose-response curve for carbachol-induced inhibition of binding of 125I-VIP and that for occupation of low-affinity muscarinic cholinergic receptors by carbachol are similar.(ABSTRACT TRUNCATED AT 250 WORDS)


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 Am. J. Physiol. Gastrointest. Liver Physiol.Home page
T. Akiyama, Y. Hirohata, Y. Okabayashi, I. Imoto, and M. Otsuki
Supramaximal CCK and CCh concentrations abolish VIP potentiation by inhibiting adenylyl cyclase activity
Am J Physiol Gastrointest Liver Physiol, November 1, 1998; 275(5): G1202 - G1208.
[Abstract] [Full Text] [PDF]


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