Molecular Pharmacology, Vol 10, 861-867, Copyright © 1974 by the American Society for Pharmacology and Experimental Therapeutics

Muscarinic Cholinergic Receptor Binding in the Longitudinal Muscle of the Guinea Pig Ileum with [³H]Quinuclidinyl Benzilate

¹ Department of Pharmacology and Experimental Therapeutics and Department of Psychiatry and the Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

The binding of [³H]quinuclidinyl benzilate (QNB) to homogenates of the longitudinal muscle of guinea pig ileum appears to represent an almost exclusive interaction with muscarinic cholinergic receptor sites. [³H]QNB binds to particulate matter in these preparations in a saturable fashion with respect to [³H]QNB. A variety of muscarinic antagonists and agonists inhibit specific [³H]QNB binding in parallel with their estimated affinity for muscarinic receptors in the guinea pig ileum, based on pharmacological procedures. Numerous nicotinic cholinergic and noncholinergic drugs have negligible affinity for [³H]QNB binding sites. The dissociation constant of the QNB-receptor complex estimated from saturation experiments with [³H]QNB and from inhibition experiments with QNB is about 0.3-0.5 nM at 25°. The bimolecular rate constant of association (4 x 10⁸ M^-1 min^-1) and dissociation (1.2 x 10^-2 min^-1) were estimated at 35° and indicate a dissociation constant of 0.03 nM. The maximal specific binding of [³H]QNB indicates a concentration of receptors of about 190 pmoles/g of tissue. Specific [³H]QNB binding can also be demonstrated in guinea pig spleen, heart, and lung, but not in guinea pig diaphragm, kidney, or liver.

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ACKNOWLEDGMENT The authors express their appreciation to David Greenberg and James Clark for their excellent assistance.

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				References PsychiatryOnline CME, May 1, 2007; 2007(1): 2 - 2. [Full Text]