title: The colon-selective spasmolytic otilonium bromide inhibits muscarinic M(3) receptor-coupled calcium signals in isolated human colonic crypts.
abstract: 1. Otilonium bromide (OB) is a smooth muscle relaxant used in the treatment of irritable bowel syndrome. Otilonium bromide has been shown to interfere with the mobilization of calcium in intestinal smooth muscle, but the effects on other intestinal tissues have not been investigated. We identified the muscarinic receptor subtype coupled to calcium signals in colonic crypt derived from the human colonic epithelium and evaluated the inhibitory effects of OB. 2. Calcium signals were monitored by fluorescence imaging of isolated human colonic crypts and Chinese hamster ovary cells stably expressing the cloned human muscarinic M(3) receptor subtype (CHO-M(3)). Colonic crypt receptor expression was investigated by pharmacological and immunohistochemical techniques. 3. The secretagogue acetylcholine (ACh) stimulated calcium mobilization from intracellular calcium stores at the base of human colonic crypts with an EC(50) of 14 micro M. The muscarinic receptor antagonists 4-DAMP, AF-DX 384, pirenzepine and methroctamine inhibited the ACh-induced calcium signal with the following respective IC(50) (pK(b)) values: 0.78 nM (9.1), 69 nM (7.2), 128 nM (7.1), and 2510 nM (5.8). 4. Immunohistochemical analyses of muscarinic receptor expression demonstrated the presence of M(3) receptor subtype expression at the crypt-base. 5. Otilonium bromide inhibited the generation of ACh-induced calcium signals in a dose dependent manner (IC(50)=880 nM). 6. In CHO-M(3) cells, OB inhibited calcium signals induced by ACh, but not ATP. In addition, OB did not inhibit histamine-induced colonic crypt calcium signals. 7. The present studies have demonstrated that OB inhibited M(3) receptor-coupled calcium signals in human colonic crypts and CHO-M(3) cells, but not those induced by stimulation of other endogenous receptor types. We propose that the M(3) receptor-coupled calcium signalling pathway is directly targeted by OB at the level of the colonic epithelium, suggestive of an anti-secretory action in IBS patients suffering with diarrhoea.
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich, UK.
authors.forename: Susanne
authors.initials: S
authors.lastname: Lindqvist
authors.forename: James
authors.initials: J
authors.lastname: Hernon
authors.forename: Paul
authors.initials: P
authors.lastname: Sharp
authors.forename: Neil
authors.initials: N
authors.lastname: Johns
authors.forename: Sarah
authors.initials: S
authors.lastname: Addison
authors.forename: Mark
authors.initials: M
authors.lastname: Watson
authors.forename: Richard
authors.initials: R
authors.lastname: Tighe
authors.forename: Shaun
authors.initials: S
authors.lastname: Greer
authors.forename: Jean
authors.initials: J
authors.lastname: Mackay
authors.forename: Michael
authors.initials: M
authors.lastname: Rhodes
authors.forename: Michael
authors.initials: M
authors.lastname: Lewis
authors.forename: William
authors.initials: W
authors.lastname: Stebbings
authors.forename: Chris
authors.initials: C
authors.lastname: Speakman
authors.forename: Stefano
authors.initials: S
authors.lastname: Evangelista
authors.forename: Ian
authors.initials: I
authors.lastname: Johnson
authors.forename: Mark
authors.initials: M
authors.lastname: Williams
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D003106:Colon / Q000187:drug effects* / Q000378:metabolism; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D006801:Humans; D066298:In Vitro Techniques; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D010276:Parasympatholytics / Q000494:pharmacology*; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D018727:Muscarinic Antagonists; D010276:Parasympatholytics; D010880:Piperidines; D000644:Quaternary Ammonium Compounds; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D014665:Vasodilator Agents; C065959:AFDX 384; C013934:octylonium; D010890:Pirenzepine; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D000109:Acetylcholine; D002118:Calcium