Cholinergic responses of ophthalmic arteries in M3 and M5 muscarinic acetylcholine receptor knockout mice.
OBJECTIVE
To determine the functional role of M(3) and M(5) muscarinic acetylcholine receptor subtypes in ophthalmic arteries using gene-targeted mice.


METHODS
Muscarinic receptor gene expression was quantified in murine ophthalmic arteries using real-time PCR. To test the functional relevance of M(3) and M(5) receptors, ophthalmic arteries from mice deficient in either subtype (M3R(-/-), M5R(-/-), respectively) and wild-type controls were isolated, cannulated with micropipettes, and pressurized. Changes in luminal vessel diameter in response to muscarinic and nonmuscarinic receptor agonists were measured by video microscopy.


RESULTS
With the use of real-time PCR, all five muscarinic receptor subtypes were detected in ophthalmic arteries. However, mRNA levels of M(1), M(3), and M(5) receptors were higher than those of M(2) and M(4) receptors. In functional studies, after preconstriction with phenylephrine, acetylcholine and carbachol produced concentration-dependent dilations of ophthalmic arteries that were similar in M5R(-/-) and wild-type mice. Strikingly, cholinergic dilation of ophthalmic arteries was almost completely abolished in M3R(-/-) mice. Deletion of either M(3) or M(5) receptor did not affect responses to nonmuscarinic vasodilators such as bradykinin or nitroprusside.


CONCLUSIONS
These findings provide the first evidence that M(3) receptors are critically involved in cholinergic regulation of diameter in murine ophthalmic arteries.
Gericke
Adrian
A
Department of Ophthalmology, Universitätsmedizin der Johannes Gutenberg-Universität Mainz, Mainz, Germany. adrian.gericke@gmx.net
Mayer
Veronique G A
VG
Steege
Andreas
A
Patzak
Andreas
A
Neumann
Ulrike
U
Grus
Franz H
FH
Joachim
Stephanie C
SC
Choritz
Lars
L
Wess
Jürgen
J
Pfeiffer
Norbert
N
D000109:Acetylcholine / Q000494:pharmacology*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D018678:Cholinergic Agents / Q000494:pharmacology*; D015870:Gene Expression; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009599:Nitroprusside / Q000494:pharmacology; D009880:Ophthalmic Artery / Q000187:drug effects / Q000502:physiology*; D010656:Phenylephrine / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D043587:Receptor, Muscarinic M3 / Q000502:physiology*; D043642:Receptor, Muscarinic M5 / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014664:Vasodilation / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology; D014741:Video Recording
D000316:Adrenergic alpha-Agonists; D018678:Cholinergic Agents; D012333:RNA, Messenger; D043587:Receptor, Muscarinic M3; D043642:Receptor, Muscarinic M5; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine; D002217:Carbachol; D000109:Acetylcholine; D001920:Bradykinin