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Adrian Gericke, Veronique G. A. Mayer, Andreas Steege, Andreas Patzak, Ulrike Neumann, Franz H. Grus, Stephanie C. Joachim, Lars Choritz, Jürgen Wess, Norbert Pfeiffer; Cholinergic Responses of Ophthalmic Arteries in M3 and M5 Muscarinic Acetylcholine Receptor Knockout Mice. Invest. Ophthalmol. Vis. Sci. 2009;50(10):4822-4827. doi: 10.1167/iovs.09-3600.
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purpose. To determine the functional role of M3 and M5 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 M3 and M5 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 M1, M3, and M5 receptors were higher than those of M2 and M4 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 M3 or M5 receptor did not affect responses to nonmuscarinic vasodilators such as bradykinin or nitroprusside.
conclusions. These findings provide the first evidence that M3 receptors are critically involved in cholinergic regulation of diameter in murine ophthalmic arteries.
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