title: Benzilylcholine mustard and spare receptors in guinea pig ileum.
abstract: A comparison was made of muscarinic receptor occupancy by the irreversible antagonist benzilylcholine mustard (BCM) as determined from shifts in the dose-response curve to a muscarinic agonist and from  3H-QNB binding to homogenates of BCM-treated tissue. Major discrepancies were found. A low concentration of BCM (3x10-8M/15 min.) produced a parallel dose-response curve shift corresponding to 98-99% receptor occupancy by BCM, whereas 3H-QNB binding revealed only 48% receptor occupancy. Possible origins of this discrepancy are discussed. High concentrations of BCM (5x10-5M, 15 min.) fail to completely alkylate all 3H-QNB binding sites even though response is completely lost. Although significant (64%) recovery of response occurs after prolonged tissue washing (240 min.) this is not accompanied by an increase in 3H-QNB binding. The small fraction (approximately 5%) of sites inaccessible to BCM and with reduced affinity for 3H-QNB may represent a subpopulation of muscarinic receptors.
mesh_terms: D000818:Animals; D002794:Choline / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism*; D004148:Dioxolanes / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011869:Radioligand Assay; D011950:Receptors, Cholinergic / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*
chemical_list: D004148:Dioxolanes; D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic; C028858:methamilane methiodide; C100238:benzilylcholine mustard; D011813:Quinuclidinyl Benzilate; D002794:Choline