title: Identification of the muscarinic acetylcholine receptor subtype mediating cholinergic vasodilation in murine retinal arterioles.
abstract: OBJECTIVE
  To identify the muscarinic acetylcholine receptor subtype that mediates cholinergic vasodilation in murine retinal arterioles.
  
  
  METHODS
  Muscarinic receptor gene expression was determined in murine retinal arterioles using real-time PCR. To assess the functional relevance of muscarinic receptors for mediating vascular responses, retinal vascular preparations from muscarinic receptor-deficient mice were studied in vitro. Changes in luminal arteriole diameter in response to muscarinic and nonmuscarinic vasoactive substances were measured by video microscopy.
  
  
  RESULTS
  Only mRNA for the M(3) receptor was detected in retinal arterioles. Thus, M(3) receptor-deficient mice (M3R(-/-)) and respective wild-type controls were used for functional studies. Acetylcholine concentration-dependently dilated retinal arterioles from wild-type mice. In contrast, vasodilation to acetylcholine was almost completely abolished in retinal arterioles from M3R(-/-) mice, whereas responses to the nitric oxide (NO) donor nitroprusside were retained. Carbachol, an acetylcholinesterase-resistant analog of acetylcholine, also evoked dilation in retinal arterioles from wild-type, but not from M3R(-/-), mice. Vasodilation responses from wild-type mice to acetylcholine were negligible after incubation with the non-subtype-selective muscarinic receptor blocker atropine or the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester, and were even reversed to contraction after endothelial damage with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate.
  
  
  CONCLUSIONS
  These findings provide evidence that endothelial M(3) receptors mediate cholinergic vasodilation in murine retinal arterioles via activation of NO synthase.
authors.affiliation: Department of Ophthalmology, University Medical Center, Johannes Gutenberg University Mainz, Mainz, Germany. adrian.gericke@gmx.net
authors.forename: Adrian
authors.initials: A
authors.lastname: Gericke
authors.forename: Jan J
authors.initials: JJ
authors.lastname: Sniatecki
authors.forename: Evgeny
authors.initials: E
authors.lastname: Goloborodko
authors.forename: Andreas
authors.initials: A
authors.lastname: Steege
authors.forename: Olga
authors.initials: O
authors.lastname: Zavaritskaya
authors.forename: Jan M
authors.initials: JM
authors.lastname: Vetter
authors.forename: Franz H
authors.initials: FH
authors.lastname: Grus
authors.forename: Andreas
authors.initials: A
authors.lastname: Patzak
authors.forename: Jürgen
authors.initials: J
authors.lastname: Wess
authors.forename: Norbert
authors.initials: N
authors.lastname: Pfeiffer
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology; D005260:Female; D015870:Gene Expression / Q000502:physiology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D009599:Nitroprusside / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D043587:Receptor, Muscarinic M3 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D012161:Retinal Artery / Q000502:physiology*; D014664:Vasodilation / Q000502:physiology*; D014741:Video Recording
chemical_list: D012333:RNA, Messenger; D043587:Receptor, Muscarinic M3; D009599:Nitroprusside; D002217:Carbachol; D052250:Nitric Oxide Synthase Type III; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester