The binding of [3H] quinuclidinyl benzilate (QNB) to homogenates of the longitudinal muscle of guineapig 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 guineapig 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 to 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 guineapig spleen, heart, and lung, but not in guineapig diaphragm, kidney, or liver.
|Original language||English (US)|
|Number of pages||7|
|State||Published - Jan 1 1974|
ASJC Scopus subject areas
- Molecular Medicine