Muscarinic receptor subtypes mediating Ca(2+) sensitization of intestinal smooth muscle contraction: Studies with receptor knockout mice
2010
Suguro, M., Gifu Univ. (Japan). Faculty of Applied Biological Sciences | Matsuyama, H. | Tanahashi, Y. | Unno, T. | Kitazawa, T. | Yamada, M. | Komori, S.
In the present study, we have characterized muscarinic receptor subtypes that mediate carbachol-induced Casup(2+) sensitization of contraction in intestinal smooth muscle, using mutant mice lacking Msub(2) or Msub(3) muscarinic receptors or both receptor subtypes. In alpha-toxin-permeabilized muscle strips from wild-type (WT) mice, isometric tension responses to Casup(2+) applied cumulatively (pCa 7.0-5.0) were increased when the muscarinic agonist carbachol (100 microM) was added to the medium, as judged from shifts of pCa-tension curves in both 50% effective concentration (ECsub(50)) and maximum response (Esub(max)) of pCa-tension curve. In preparations from Msub(2)-knockout (KO) mice, pCa-tension curves were also shifted by carbachol (100 microM), and the extents of the ECsub(50) and Esub(max) changes resembled those observed in preparations from WT mice. In preparations from Msub(3)-KO or Msub(2)/Msub(3)-double KO mice, however, no significant changes in pCa-tension curves were obtained after carbachol application. The Gsub(q/II)-type G-protein inhibitor YM-254890 (1 microM) completely blocked the Casup(2+) sensitization of contraction induced by carbachol in Msub(2)-KO or WT preparations. The results strongly support the idea that the muscarinic activation of Casup(2+) sensitization in intestinal smooth muscles is mediated by the Msub(3) muscarinic receptor coupled to Gsub(q/II)-type G-proteins, without any significant involvement of the other muscarinic receptor subtypes including Msub(2).
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