title: Role of the M3 muscarinic acetylcholine receptor subtype in murine ophthalmic arteries after endothelial removal.
abstract: OBJECTIVE
  We tested the hypothesis that the M3 muscarinic acetylcholine receptor subtype mediates cholinergic responses in murine ophthalmic arteries after endothelial removal.
  
  
  METHODS
  Muscarinic receptor gene expression was determined in ophthalmic arteries with intact and with removed endothelium using real-time PCR. To examine the role of the M3 receptor in mediating vascular responses, ophthalmic arteries from M3 receptor-deficient mice (M3R(-/-)) and respective wild-type controls were studied in vitro. Functional studies were performed in nonpreconstricted arteries with either intact or removed endothelium using video microscopy.
  
  
  RESULTS
  In endothelium-intact ophthalmic arteries, mRNA for all five muscarinic receptor subtypes was detected, but M3 receptor mRNA was most abundant. In endothelium-removed ophthalmic arteries, M1, M2, and M3 receptors displayed similar mRNA expression levels, which were higher than those for M4 and M5 receptors. In functional studies, acetylcholine evoked vasoconstriction in endothelium-removed arteries from wild-type mice that was virtually abolished after incubation with the muscarinic receptor blocker atropine, indicative of the involvement of muscarinic receptors. In concentration-response experiments, acetylcholine and carbachol concentration-dependently constricted endothelium-removed ophthalmic arteries from wild-type mice, but produced only negligible responses in arteries from M3R(-/-) mice. In contrast, acetylcholine concentration-dependently dilated ophthalmic arteries with intact endothelium from wild-type mice, but not from M3R(-/-) mice. Responses to the nitric oxide donor nitroprusside and to KCl did not differ between ophthalmic arteries from wild-type and M3R(-/-) mice, neither in endothelium-intact nor in endothelium-removed arteries.
  
  
  CONCLUSIONS
  These findings provide evidence that in murine ophthalmic arteries the muscarinic M3 receptor subtype mediates cholinergic endothelium-dependent vasodilation and endothelium-independent vasoconstriction.
authors.affiliation: Department of Ophthalmology, University Medical Center, Johannes Gutenberg University Mainz, Mainz, Germany.
authors.forename: Adrian
authors.initials: A
authors.lastname: Gericke
authors.forename: Andreas
authors.initials: A
authors.lastname: Steege
authors.forename: Caroline
authors.initials: C
authors.lastname: Manicam
authors.forename: Tobias
authors.initials: T
authors.lastname: Böhmer
authors.forename: Jürgen
authors.initials: J
authors.lastname: Wess
authors.forename: Norbert
authors.initials: N
authors.lastname: Pfeiffer
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000601:surgery; D005786:Gene Expression Regulation; D051379:Mice; D018345:Mice, Knockout; D009880:Ophthalmic Artery / Q000378:metabolism* / Q000503:physiopathology / Q000601:surgery; D012333:RNA, Messenger / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D043587:Receptor, Muscarinic M3 / Q000096:biosynthesis / Q000235:genetics*; D012164:Retinal Diseases / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D014661:Vasoconstriction
chemical_list: D012333:RNA, Messenger; D043587:Receptor, Muscarinic M3
keywords: acetylcholine; mice; muscarinic receptors; ophthalmic arteries; vasoconstriction