The role of M(2)-muscarinic receptors in mediating contraction of the pig urinary bladder in vitro.
1. In urinary bladder, M(2)-muscarinic receptors predominate, but it is the smaller population of M(3)-receptors which mediate detrusor contraction. This study examines the M(2) : M(3) ratio and the role of M(2)-receptors in contraction of pig urinary bladder. 2. Competition experiments with [(3)H]-QNB determined the ratio of M(2) : M(3). In functional studies, affinity values (pK(B)) for 4-DAMP, darifenacin and methoctramine were calculated. Similar experiments were performed on tissues following selective M(3)-inactivation (incubation with 40 nM 4-DAMP mustard in the presence of 1 microM methoctramine to protect M(2)-receptors), precontraction with 50 mM KCl and relaxation with isoprenaline (30 microM) or forskolin (1 microM). 3. In competition binding, displacement of [(3)H]-QNB by 4-DAMP, darifenacin and methoctramine best fitted a two-site model suggesting a predominant (70 - 80%) population of M(2)-receptors. 4. On normal detrusor in vitro, 4-DAMP and methoctramine caused surmountable antagonism of responses to carbachol with pK(B) values of 9.37+/-0.07 and 6.05+/-0.05 respectively. Darifenacin caused unsurmountable antagonism, the apparent pK(B) value being 8.61+/-0.10. 5. In tissues where the M(3)-receptors had been inactivated and cyclic AMP levels elevated, 4-DAMP and darifenacin were less potent, with apparent pK(B) values of 8.72+/-0.08 and 6.74+/-0.07. In contrast, methoctramine was more potent, the apparent pK(B) value increasing significantly to 6.86+/-0.06. 6. se data suggest that the pig bladder possesses a similar muscarinic receptor population to the human bladder and that the M(3)-receptor subtype mediates contraction of the normal detrusor muscle. However an involvement of M(2)-receptors in contraction can be observed following pharmacological manipulation of the receptor population.
Yamanishi
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Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN.
Chapple
C R
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Yasuda
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Chess-Williams
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R
D000818:Animals; D001572:Benzofurans / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D003959:Diamines / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D010880:Piperidines / Q000378:metabolism / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011869:Radioligand Assay; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D013552:Swine; D014316:Tritium; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*
D001572:Benzofurans; D003959:Diamines; D018727:Muscarinic Antagonists; D010880:Piperidines; D011759:Pyrrolidines; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D014316:Tritium; D011813:Quinuclidinyl Benzilate; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D002217:Carbachol; C101207:darifenacin; C054938:methoctramine