Carbachol-Induced Down-Regulation of Receptors for Pancreatic Secretagogues

Abstract

Pancreatic acini possess a high affinity class of cholinergic receptors and a low affinity class of cholinergic receptors. Carbachol occupation of high affinity cholinergic receptors produces a reduction in binding of [³H]N-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 a reduction 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.