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

The pharmacological characteristics of muscarinic receptors in the male mice urinary bladder smooth muscle were studied. (+)‐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 (p K 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), AQ‐RA 741 (7.04±0.12), s‐secoverine (8.21±0.09), zamifenacin (8.30±0.17) and darifenacin (8.70±0.09). In this tissue, the p K B values correlated most favourably with p K 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. 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 (p K B =6.23±0.14; pA 2 =6.16±0.03). 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.British Journal of Pharmacology (2001) 133 , 1035–1040; doi: 10.1038/sj.bjp.0704165