AJP - Gastrointestinal and Liver Physiology, Vol 259, Issue 5 873-G881, Copyright © 1990 by American Physiological Society
Characterization of cholecystokinin receptors on the sphincter of Oddi
K. L. Cox, T. von Schrenck, T. H. Moran, J. D. Gardner and R. T. Jensen
Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
To characterize directly the ability of cholecystokinin (CCK) to interact
with receptors on the sphincter of Oddi (SO), we measured binding of
125I-labeled Bolton-Hunter-labeled COOH-terminal octapeptide of
cholecystokinin (125I-BH-CCK-8) to tissue sections from the guinea pig SO.
Autoradiography localized binding of 125I-BH-CCK-8 over the SO smooth
muscle layer. Binding was saturable, specific, dependent on time, pH, and
temperature, and was reversible. Binding of 125I-BH-CCK-8 was inhibited by
various CCK receptor agonists with the following potencies: CCK-8 much
greater than des(SO3)CCK-8 much greater than gastrin-17-I and by various
CCK receptor antagonists with the following potencies: L-364,718 greater
than proglumide analogue 10 much greater than
carbobenzoxy-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-NH2 greater than N2,O2'
dibutyryl guanosine 3',5'-cyclic monophosphate. The potencies of agonists
in stimulating and of antagonists in inhibiting CCK-8-stimulated SO
contractions correlated closely with their abilities to inhibit binding of
125I-BH-CCK-8. Analysis of binding of 125I-BH-CCK-8 to SO tissue sections
revealed two classes of CCK binding sites: a high-affinity site
[dissociation constant (Kd) 0.2 nM] and a low-affinity site (Kd 70 nM).
Atropine or tetrodotoxin (TTX) caused a similar rightward shift of the
CCK-8 dose-response curve for stimulation of SO contraction. Comparison of
receptor occupation to CCK-8-induced contraction suggested that CCK-8
occupation of the high-affinity binding site correlated with contraction in
the absence of atropine and the low-affinity CCK binding with contraction
in the presence of atropine or TTX.(ABSTRACT TRUNCATED AT 250 WORDS)
