AJP - Gastrointestinal and Liver Physiology, Vol 239, Issue 3 204-G209, Copyright © 1980 by American Physiological Society
Isolated parietal cells: [3H]QNB binding to putative cholinergic receptors
R. Ecknauer, W. J. Thompson, L. R. Johnson and G. C. Rosenfeld
The tritiated muscarinic cholinergic antagonist quinuclidinyl benzilate,
[3H]QNB, was used as a direct probe for the detection and characterization
of muscarinic cholinergic receptors associated with the particulate
fraction of isolated and purified rat gastric muscosal parietal cells.
Specific binding is saturable (Bmax = 55 fmol/mg protein, KD = 0.78 nM),
shows a single population of binding sites, and has appropriate
pharmacological specificity. Nanomolar concentrations of muscarinic
cholinergic antagonists, such as atropine and scopolamine, inhibit [3H]QNB
binding by 50%, whereas micromolar concentrations are needed for agonists,
such as acetylcholine, oxotremorine, and carbamylcholine. Binding is also
stereoselective as shown by the more than 1,000-fold difference in
inhibitory potencies of the stereoisomers of benzetimide. Noncholinergic
agents, including pentagastrin, histamine, and the H2-receptor antagonists
cimetidine and metiamide, have little or no effect on [3H]QNB binding at
concentrations of 100 microM. These data support the existence of specific
parietal cell muscarinic cholinergic receptors with which the secretagogue
acetylcholine may directly interact to initiate gastric acid secretion.
