Carbachol desensitizes pancreatic enzyme secretion by downregulation of receptors.
First incubating guinea pig pancreatic acini with carbachol reduced the subsequent stimulation of amylase release caused by carbachol, cholecystokinin octapeptide (CCK-8), and bombesin but not that caused by vasoactive intestinal peptide, substance P, 8-bromoadenosine 3',5'-cyclic monophosphate, A23187, or 12-O-tetradecanoylphorbol-13-acetate. Carbachol also reduced the subsequent binding of N-[3H]methylscopolamine, 125I-CCK-8, and 125I-[Tyr4]bombesin. Pancreatic acini possess a high-affinity class of cholinergic receptors and a low-affinity cholinergic receptors appears to produce the reduction in carbachol-stimulated amylase release and binding of N-[3H]methylscopolamine. First incubating acini with carbachol caused a complete loss of high-affinity cholinergic receptors with no change in the number or affinity of low-affinity cholinergic receptors. Carbachol occupation of low-affinity cholinergic receptors appears to produce the reduction in CCK-8- and bombesin-stimulated amylase release and in binding of 125I-CCK-8 and 125I-[Tyr4]bombesin. Acini possess two classes of CCK receptors. One class has a high affinity for CCK-8; the other class has a low affinity for CCK-8. First incubating acini with carbachol caused a 60% decrease in the number of high-affinity CCK receptors with no change in the number of low-affinity receptors or the affinities of either class of receptors for CCK-8. Acini possess a single class of bombesin receptors, and first incubating acini with carbachol caused a 40% decrease in the number of bombesin receptors with no change in their affinity for bombesin. 12-O-tetradecanoyl phorbol-13-acetate reproduced the action of carbachol on binding of N-[3H]methylscopolamine and 125I-CCK-8 but not on binding of 125I-[Tyr4]bombesin, suggesting that carbachol activation of protein kinase C may in some way mediate the effect of carbachol on receptors for carbachol and those for CCK but not that on receptors for bombesin.
Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
R
R
Vinayek
M
M
Murakami
C M
CM
Sharp
R T
RT
Jensen
J D
JD
Gardner
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000681:Amylases / Q000378:metabolism*; D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology*; D003513:Cycloheximide / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D010179:Pancreas / Q000187:drug effects / Q000201:enzymology*; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012844:Sincalide / Q000494:pharmacology; D013373:Substance P / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D011956:Receptors, Cell Surface; D015124:8-Bromo Cyclic Adenosine Monophosphate; D013373:Substance P; D014660:Vasoactive Intestinal Peptide; D000001:Calcimycin; D002217:Carbachol; D003513:Cycloheximide; D000681:Amylases; D012844:Sincalide; D013755:Tetradecanoylphorbol Acetate; D001839:Bombesin