Pharmacological characterization of muscarinic receptors in mouse isolated urinary bladder smooth muscle

1 The pharmacological characteristics of muscarinic receptors in the male mice urinary bladder smooth muscle were studied. 2 (+)-Cis-dioxolane, oxotremorine-M, acetylcholine, carbachol and pilocarpine induced concentration-dependent contractions of the urinary bladder smooth muscle (pEC(50)=6.6 +/-0.1, 6.9 +/-0.1, 6.7 +/-0.1, 5.8 +/-0.1 and 5.8 +/-0. 1, E-Max=3.2 +/-0.8 g, 2.7 +/-0.4 g, 1.0 +/-0.1 g, 2.7 +/-0.3 and 0.9 +/-0.2 g, respectively, n=4). These contractions were competitively antagonized by a range of muscarinic receptor antagonists (pK(B) values): atropine (9.22 +/-0.09), pirenzepine (6.85 +/-0.08), 4-DAMP (8.42 +/-0.14), methoctramine (5.96 +/-0.05), p-F-HHSiD (7.48 +/-0.09), tolterodine (8.89 +/-0.13), AQRA 741 (7.04 +/-0.12), s-secoverine (8.21 +/-0.09), zamifenacin (8.30 +/-0.17) and darifenacin (8.70 +/-0.09). 3 In this tissue, the pK(B) values correlated most favourably with pK(i) values for these compounds at human recombinant muscarinic M-3 receptors. A significant correlation was also noted at human recombinant muscarinic m5 receptors given the poor discriminative ability of ligands between M-3 and m5 receptors. 4 In recontraction studies, in which the muscarinic M-3 receptor population was decreased, and conditions optimized to study M-2 receptor activation, methoctramine exhibited an affinity estimate consistent with muscarinic M-3 receptors (pK(B)=6.23 +/-0.14; pA(2)=6.16 +/-0.03). 5 Overall, these data study suggest that muscarinic M-3 receptors are the predominant, if not the exclusive, subtype mediating contractile responses to muscarinic agonists in male mouse urinary bladder smooth muscle.