title: M(3) muscarinic acetylcholine receptor plays a critical role in parasympathetic control of salivation in mice.
abstract: The M(1) and M(3) subtypes are the major muscarinic acetylcholine receptors in the salivary gland and M(3) is reported to be more abundant. However, despite initial reports of salivation abnormalities in M(3)-knockout (M(3)KO) mice, it is still unclear which subtype is functionally relevant in physiological salivation. In the present study, salivary secretory function was examined using mice lacking specific subtype(s) of muscarinic receptor. The carbachol-induced [Ca(2+)](i) increase was markedly impaired in submandibular gland cells from M(3)KO mice and completely absent in those from M(1)/M(3)KO mice. This demonstrates that M(3) and M(1) play major and minor roles, respectively, in the cholinergically induced [Ca(2+)](i) increase. Two-dimensional Ca(2+)-imaging analysis revealed the patchy distribution of M(1) in submandibular gland acini, in contrast to the ubiquitous distribution of M(3). In vivo administration of a high dose of pilocarpine (10 mg kg(-1), s.c.) to M(3)KO mice caused salivation comparable to that in wild-type mice, while no salivation was induced in M(1)/M(3)KO mice, indicating that salivation in M(3)KO mice is caused by an M(1)-mediated [Ca(2+)](i) increase. In contrast, a lower dose of pilocarpine (1 mg kg(-1), s.c.) failed to induce salivation in M(3)KO mice, but induced abundant salivation in wild-type mice, indicating that M(3)-mediated salivation has a lower threshold than M(1)-mediated salivation. In addition, M(3)KO mice, but not M(1)KO mice, had difficulty in eating dry food, as shown by frequent drinking during feeding, suggesting that salivation during eating is mediated by M(3) and that M(1) plays no practical role in it. These results show that the M(3) subtype is essential for parasympathetic control of salivation and a reasonable target for the drug treatment and gene therapy of xerostomia, including Sjögren's syndrome.
authors.affiliation: Calcium Oscillation Project, Japan Science and Technology Agency, Tokyo, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nakamura
authors.forename: Minoru
authors.initials: M
authors.lastname: Matsui
authors.forename: Keiko
authors.initials: K
authors.lastname: Uchida
authors.forename: Akira
authors.initials: A
authors.lastname: Futatsugi
authors.forename: Shinji
authors.initials: S
authors.lastname: Kusakawa
authors.forename: Nagisa
authors.initials: N
authors.lastname: Matsumoto
authors.forename: Kyoko
authors.initials: K
authors.lastname: Nakamura
authors.forename: Toshiya
authors.initials: T
authors.lastname: Manabe
authors.forename: Makoto M
authors.initials: MM
authors.lastname: Taketo
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mikoshiba
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004327:Drinking Behavior; D005247:Feeding Behavior; D005260:Female; D051379:Mice; D018345:Mice, Knockout; D018721:Muscarinic Agonists / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010862:Pilocarpine / Q000494:pharmacology; D043587:Receptor, Muscarinic M3 / Q000235:genetics / Q000502:physiology*; D012469:Salivary Glands / Q000166:cytology / Q000294:innervation / Q000502:physiology*; D012472:Salivation / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D018679:Cholinergic Agonists; D018721:Muscarinic Agonists; D043587:Receptor, Muscarinic M3; D010862:Pilocarpine; D002217:Carbachol; D002118:Calcium