title: Muscarinic acetylcholine receptor subtype 4 is essential for cholinergic stimulation of duodenal bicarbonate secretion in mice - relationship to D cell/somatostatin.
abstract: We investigated the roles of muscarinic (M) acetylcholine receptor subtype in the cholinergic stimulation of duodenal HCO3(-) secretion using knockout (KO) mice. Wild-type and M1-M5 KO C57BL/6J mice were used. The duodenal mucosa was mounted on an Ussing chamber, and HCO3(-) secretion was measured at pH 7.0 using a pH-stat method in vitro. Carbachol (CCh) or other agents were added to the serosal side. CCh dose-dependently stimulated HCO3(-) secretion in wild-type mice, and this effect was completely inhibited in the presence of atropine. The HCO3(-) response to CCh in wild-type mice was also inhibited by pirenzepine (M1 antagonist), 4DAMP (M3 antagonist), and tropicamide (M4 antagonist), but not by methoctramine (M2 antagonist). CCh stimulated HCO3(-) secretion in M2 and M5 KO animals as effectively as in WT mice; however, this stimulatory effect was significantly attenuated in M1, M3, and M4 KO mice. The decrease observed in the CCh-stimulated HCO3(-) response in M4 KO mice was reversed by the co-application of CYN154806, a somatostatin receptor type 2 (SST2) antagonist. Octreotide (a somatostatin analogue) decreased the basal and CCh-stimulated secretion of HCO3(-) in wild-type mice. The co-localized expression of somatostatin and M4 receptors was confirmed immunohistologically in the duodenum. We concluded that the duodenal HCO3(-) response to CCh was directly mediated by M1/M3 receptors and indirectly modified by M4 receptors. The activation of M4 receptors was assumed to inhibit the release of somatostatin from D cells and potentiate the HCO3(-) response by removing the negative influence of somatostatin via the activation of SST2 receptors.
authors.affiliation: Division of Pathological Sciences, Department of Pharmacology and Experimental Therapeutics, Kyoto Pharmaceutical University, Yamashina, Kyoto, Japan. takeuchi@mb.kyoto-phu.ac.jp.|General Incorporated Association, Kyoto Research Center for Gastrointestinal Diseases, Karasuma-Oike, Kyoto, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Takeuchi
authors.affiliation: Division of Pathological Sciences, Department of Pharmacology and Experimental Therapeutics, Kyoto Pharmaceutical University, Yamashina, Kyoto, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kita
authors.affiliation: Division of Pathological Sciences, Department of Pharmacology and Experimental Therapeutics, Kyoto Pharmaceutical University, Yamashina, Kyoto, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Division of Pathological Sciences, Department of Pharmacology and Experimental Therapeutics, Kyoto Pharmaceutical University, Yamashina, Kyoto, Japan.
authors.forename: E
authors.initials: E
authors.lastname: Aihara
authors.affiliation: Division of Pathological Sciences, Department of Pharmacology and Experimental Therapeutics, Kyoto Pharmaceutical University, Yamashina, Kyoto, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Hayashi
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004386:Duodenum / Q000378:metabolism*; D015870:Gene Expression; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018727:Muscarinic Antagonists / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000235:genetics / Q000502:physiology*; D017481:Receptors, Somatostatin / Q000378:metabolism; D013004:Somatostatin / Q000378:metabolism; D019864:Somatostatin-Secreting Cells / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D018679:Cholinergic Agonists; D018727:Muscarinic Antagonists; D012333:RNA, Messenger; D011976:Receptors, Muscarinic; D017481:Receptors, Somatostatin; C570769:somatostatin receptor 2, mouse; D013004:Somatostatin; D002217:Carbachol