title: Evidence for muscarinic cholinergic receptors in dog portal vein: binding of [3H]quinuclidinyl benzilate.
abstract: Muscarinic cholinergic receptor sites in dog portal veins were analyzed directly using [3H]quinuclidinyl benzilate (QNB) as a ligand. Specific [3H]QNB binding to crude membrane preparations from the isolated veins was saturable, reversible and of high affinity (KD = 15.5 +/- 2.8 pM) with a Bmax of 110 +/- 14.7 fmol/mg protein. Scatchard and Hill plot analyses of the data indicated one class of binding sites. From kinetic analysis of the data, association and dissociation rate constants of 1.91 X 10(9) M-1 min-1 and 0.016 min-1, respectively, were calculated. The dissociation constant calculated from the equation KD = K-1/K+1 was 8.3 pM, such being in good agreement with the Scatchard estimate of KD (15.5 pM). Specific binding of [3H]QNB was displaced by muscarinic agents. Nicotinic cholinergic agents, alpha-bungarotoxin, nicotine and hexamethonium, were ineffective in displacing [3H]QNB binding at 10 microM. Our findings provide direct evidence for the existence of muscarinic cholinergic receptors in dog portal veins.
mesh_terms: D000818:Animals; D004285:Dogs; D005260:Female; D007700:Kinetics; D008297:Male; D011169:Portal Vein / Q000378:metabolism*; D011812:Quinuclidines / Q000378:metabolism*; D011813:Quinuclidinyl Benzilate / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D013379:Substrate Specificity; D013997:Time Factors
chemical_list: D011812:Quinuclidines; D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate