Identification and Characterization of Muscarinic Cholinergic Receptors in the Isolated Plasma Membranes and Intact Tissue of the Urinary Bladder

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Abstract
The binding characteristics of 3-quinuclidinyl benzilate (QNB) to strips of intact tissue and to isolated plasma membrane fraction (PM) from rabbit urinary bladder were studied. QNB binding to both preparations was of high affinity and low capacity. The equilibrium dissociation constants (KD) for binding to tissue strips and PM were 2.2 and 0.045 nM respectively. Muscarinic antagonists inhibited QNB binding more effectively than agonists. Ca-antagonist D-600, but not nifedipine caused an inhibition of QNB binding to PM. Vanadate, ouabain or N-ethylmelaimide had no significant effect on QNB binding. In contrast to the binding in PM, binding in the intact tissue was reduced by K-depolarization.