Muscarinic receptors in isolated urinary bladder smooth muscle from different mouse strains

Abstract

1. The pharmacological characteristics of muscarinic receptors in male and female mouse urinary bladder smooth muscle from different strains (C57Bl/6, 129/SvJ and hybrid backcross N1F2) were studied. 2. (+)-Cis-dioxolane, oxotremorine-M, acetylcholine, carbachol and pilocarpine induced concentration-dependent contractions of the urinary bladder smooth muscle (range for pEC(50)=6.4-6.6, 6.2-6.7, 6.2-6.4, 5.4-6.0 and 0.0-5.1, T(max)=1.9-4.7 g, 1.3-3.4 g, 1.0-3.0 g, 1.4-2.4 and 0.0-0.3 g, respectively, n=4-6 depending on the gender and the strain). In females, these contractions were competitively antagonized by a range of muscarinic receptor antagonists (pK(B) value range, depending on the strain): atropine (8.0-8.9), pirenzepine (6.1-6.4), 4-DAMP (7.6-8.4), methoctramine (5.6-6.1), p-F-HHSiD (7.5-7.7), zamifenacin (7.7-8.4) and darifenacin (8.2-8.7). 3. 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)=6.26+/-0.08, pA(2)=6.31+/-0.07; pK(B)=6.09+/-0.22, pA(2)=6.08+/-0.01 for female inbred strain 129/SvJ and hybrid backcross N1F2, respectively) or intermediate between the one expected for this compound at M(2) and M(3) receptors, (pK(B)=6.66+/-0.08, pA(2)=7.00+/-0.27 for female inbred strain C57BL/6). 4. These data study suggest that muscarinic M(3) receptors are the predominant, if not the exclusive, subtype mediating contractile responses to muscarinic agonists in female mouse urinary bladder smooth muscle, with strain differences.

Figure 1

Effects of muscarinic agonists on female C57B1/6 mouse urinary bladder smooth muscle. Contractile effects were expressed as percentages of the maximum response of the control curve. The values shown are mean±s.e.mean, n=4 animals.

Figure 2

Correlation between the functional affinities (pK_B values) of muscarinic antagonists at muscarinic receptor in female mouse isolated urinary bladder smooth muscle and binding affinities (pK_i values) at human recombinant muscarinic receptors (m₁–m₅; a–e respectively). The binding data were taken from Dörje et al., 1991; Eglen et al., 1997; Hegde et al., 1997; Nilvebrant et al., 1996. The broken line is the line of identity (x=y) while the solid line is the correlation plot (the inserts give the correlation factors (r) and the sum of squares values (ssq)).

Figure 3

Recontraction experiments in female N1F2 mouse urinary bladder smooth muscle: effect of methoctramine on the recontractile concentration-effect to (+)-cis-dioxolane obtained after elevation of adenylyl cyclase activity following preferential alkylation of muscarinic M₃ receptors (n=4). (a) Time control; (b) +0.3 μM methoctramine; (c) +1.0 μM methoctramine; (d) +3.0 μM methoctramine.