In vivo demonstration of M3 muscarinic receptor subtype selectivity of darifenacin in mice.
A novel muscarinic receptor antagonist, darifenacin, inhibited specific binding of [N-methyl-(3)H]scopolamine ([(3)H]NMS) in the mouse bladder, submaxillary gland and heart in a concentration-dependent manner. The inhibitory effect was most potent in the submaxillary gland, followed by the bladder and heart. In addition, darifenacin inhibited specific [(3)H]NMS binding in the membranes of CHO-K1 cell lines expressing muscarinic M(2) and M(3) receptor subtypes, and the potency was significantly (22-fold) greater at the M(3) than at the M(2) subtype. At 0.5 to 12 h after oral administration of darifenacin, a significant increase in K(d) values for specific [(3)H]NMS binding was seen in the bladder, submaxillary gland and lung of mice, compared with control values. Also, there was a sustained decrease in the B(max) values in the submaxillary gland. These data suggest that muscarinic receptor binding of oral darifenacin is rapid in onset and of a long duration. On the other hand, oral darifenacin exerted only temporary or little binding of muscarinic receptors in the heart and colon. Pilocarpine-induced salivary secretion in mice was continuously suppressed by oral darifenacin. The time-course of suppression coincided well with that for the muscarinic receptor binding in the submaxillary gland. The antagonistic effect of darifenacin against the dose-response curves for pilocarpine appeared to be insurmountable. In conclusion, the present study has shown that oral darifenacin may exert a pronounced and long-lasting binding of muscarinic receptors in tissues expressing the M(3) subtype.
Yamada
Shizuo
S
Department of Pharmacokinetics and Pharmacodynamics, University of Shizuoka, Shizuoka 422-8526, Japan. yamada@ys.7.u-shizuoka-ken.ac.jp
Maruyama
Shuji
S
Takagi
Yukiko
Y
Uchida
Shinya
S
Oki
Tomomi
T
D000284:Administration, Oral; D000818:Animals; D001572:Benzofurans / Q000494:pharmacology*; D001667:Binding, Competitive; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D008168:Lung / Q000378:metabolism; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D010862:Pilocarpine / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology*; D043585:Receptor, Muscarinic M2 / Q000096:biosynthesis; D043587:Receptor, Muscarinic M3 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D012463:Saliva / Q000378:metabolism; D013363:Submandibular Gland / Q000378:metabolism; D013997:Time Factors; D001743:Urinary Bladder / Q000378:metabolism
D001572:Benzofurans; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D011759:Pyrrolidines; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D010862:Pilocarpine; C101207:darifenacin