TY - JOUR T1 - The Binding of Antagonists to Brain Muscarinic Receptors JF - Molecular Pharmacology JO - Mol Pharmacol SP - 737 LP - 750 VL - 14 IS - 5 AU - E. C. HULME AU - N. J. M. BIRDSALL AU - A. S. V. BURGEN AU - P. MEHTA Y1 - 1978/09/01 UR - http://molpharm.aspetjournals.org/content/14/5/737.abstract N2 - The equilibrium binding of muscarinic antagonists to a crude synaptosome fraction from rat cerebral cortex obeys the simple Langmuir isotherm. The affinity constants measured range from 105 to 1010 M-1 and in all cases agree within a factor of 3 with the corresponding values derived from measurements of anticholinergic potency on smooth muscle. The methodology which must be applied to obtain valid measurements of affinity constants from in vitro studies using radiolabelled ligands is discussed. ACKNOWLEDGMENTS The authors wish to express their thanks to Dr. R. B. Barlow for measurement of the antimuscarinic potency of PrBCh, and for the gift of the following compounds: N-methyl-piperidin-3-yl-phenylacetate methiodide; N-methyl-piperidin-4-yl-phenylacetate methiodide; N-methyl-piperidin-4-yl-diphenylacetate methiodide; N-methyl-quinuclidin-3-yl-phenylacetate; N-methyl-quinuclidin-3-yl-diphenylacetate. ER -