title: High-affinity [3H]pirenzepine binding to putative M1 muscarinic sites in the neuroblastoma x glioma hybrid cell line (NG 108-15).
abstract: The specific binding of both the non-classical antagonist [3H] pirenzepine ( [3H]PZ) and the classical antagonist [3H](-)quinuclidinyl benzilate ( [3H](-)QNB) was determined in parallel assays of the mouse neuroblastoma x rat glioma hybrid cell line (NG 108-15). Saturation isotherms yielded a Kd = 4.0 nM and Bmax = 27.8 fmoles/mg protein for [3H]PZ and a Kd = 17.2 pM and Bmax = 53.2 fmoles/mg protein for [3H](-)QNB. The inhibition data of pirenzepine vs [3H](-)QNB was best fit to a 2-site binding model revealing both a high affinity pirenzepine site (72%, KH = 10.3 nM) and a low affinity site (28%, KL = 97.5 nM). [3H]PZ competition studies demonstrated stereospecificity, steep inhibition curves for muscarinic antagonists (Hill coefficients close to 1), and a shallow inhibition curve for a muscarinic agonist. These results indicate that muscarinic receptors on NG 108-15 cells may be subclassified (M1/M2) on the basis of the discriminative capability of [3H]PZ.
mesh_terms: D000818:Animals; D001285:Atropine / Q000378:metabolism; D001570:Benzodiazepinones / Q000378:metabolism*; D001667:Binding, Competitive; D002460:Cell Line; D005910:Glioma / Q000378:metabolism*; D006822:Hybrid Cells / Q000378:metabolism*; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism*; D010890:Pirenzepine; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D051381:Rats; D011976:Receptors, Muscarinic / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D001570:Benzodiazepinones; D011976:Receptors, Muscarinic; D010890:Pirenzepine; D011813:Quinuclidinyl Benzilate; D001285:Atropine