Muscarinic Agonist-Mediated Heterologous Desensitization in Isolated Ileum Requires Activation of Both Muscarinic M2 and M3 Receptors
- Michael T. Griffin,
- Minoru Matsui1,
- Darakhshanda Shehnaz2,
- Khurram Z. Ansari,
- Makoto M. Taketo3,
- Toshiya Manabe and
- Frederick J. Ehlert
- Department of Physical Sciences, Chapman University, Orange, California (M.T.G.); Laboratory of Biomedical Genetics, Graduate School of Pharmaceutical Sciences, University of Tokyo, Bunkyo-ku, Tokyo, Japan (M.M., M.M.T.); Department of Pharmacology, College of Medicine, University of California, Irvine, Irvine, California (D.S., K.Z.A., F.J.E.); and Division of Neural Network, Department of Basic Medical Sciences, University of Tokyo, Tokyo, Japan (T.M.)
- Address correspondence to:
Dr. Frederick J. Ehlert, Department of Pharmacology, University of California, Irvine, Irvine, California 92697-4625. E-mail: fjehlert{at}uci.edu
Abstract
We investigated the subtypes of the muscarinic receptor mediating short-term heterologous desensitization in the isolated ileum. Treatment of the ileum from C57BL/6 mice with acetylcholine (30 μM) for 20 min caused a subsequent decrease in contractile sensitivity to both prostaglandin F2α (PGF2α) and the muscarinic agonist, oxotremorine-M. This subsensitivity was characterized by 7- and 3-fold increases in the EC50 values of the agonists, respectively, with no significant effect on the maximal response. The subsensitivity to PGF2α was prevented in both M2 and M3 muscarinic receptor knockout mice. Similarly, the subsensitivity to oxotremorine-M was prevented in M2 knockout mice. Acetylcholine-mediated desensitization of histamine-induced contractions in the guinea pig ileum was inhibited by both M2- and M3-selective muscarinic antagonists with high potency, although careful analysis of the data suggested behavior more consistent with an M2 antagonistic profile. Modeling studies showed that the competitive antagonism of response contingent upon activation of two receptor subtypes should exhibit a pharmacological profile similar to that of the least sensitive signaling pathway. Our results demonstrate that muscarinic agonist-mediated short-term heterologous desensitization of intestinal smooth muscle is contingent upon activation of both M2 and M3 muscarinic receptors and that activation of either receptor by itself is insufficient to cause desensitization.
Footnotes
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This work was supported by National Institutes of Health Grant NS30882, by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture (to M.M. and M.M.T.), by Industrial Technology Research Grant Program in 2000 and 2002 from the New Energy and Industrial Technology Development Organization of Japan (to M.M.), and by Grant from Organization for Pharmaceutical Safety and Research, Japan (to M.M.T.).
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DOI: 10.1124/jpet.103.055327.
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ABBREVIATIONS: KO, knockout; 4-DAMP, N,N-dimethyl-4-piperidinyldiphenylacetate; PGF2á, prostaglandin F2á; KRB, Krebs-Ringer bicarbonate; AF-DX 116, [[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido[2,3b][1,4]-benzodiazepine-6-one; CHO, Chinese hamster ovary; NMS, N-methylscopolamine.
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↵1 Current address: Division of Neuronal Network, Department of Basic Medical Sciences, the Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
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↵2 Current address: Banting and Best Department of Medical Research, University of Toronto, Ontario, Canada M5G1L6.
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↵3 Current address: Department of Pharmacology, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
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- Received June 6, 2003.
- Accepted August 22, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
