Immunohistochemical and functional studies for M3 muscarinic receptors and cyclo-oxygenase-2 expressed in the mouse atrium

N. Harada, K. Ochi, N. Yaosaka, H. Teraoka, T. Hiraga, T. Iwanaga, T. Unno, S. Komori, M. Yamada, T. Kitazawa
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引用次数: 5

Abstract

  1. In mouse atrium, M2 and M3 muscarinic receptors (M2R and M3R) are involved in biphasic (negative and positive) inotropic actions of muscarinic agonists, and the positive inotropic action is reduced by indomethacin. The aim of our study was to determine the localization of M2R, M3R and cyclo-oxygenase (COX) in mouse atrium and to characterize muscarinic receptor-mediated positive inotropy.
  2. M2R immunoreactivity was found only on atrial myocardium, but M3R immunoreactivity was localized on both the myocardium and endocardial endothelium. COX-1 and COX-2 immunoreactivities were identified in both myocardial and endocardial endothelium.
  3. In electrically stimulated left atria, carbachol caused M2R-mediated negative inotropy followed by M3R-mediated positive inotropy. Removal of atrial endothelium reduced the positive inotropy without affecting the negative inotropy, suggesting that stimulation of endothelial M3R mediates the positive inotropy.
  4. N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS398, COX-2 inhibitor) decreased the carbachol-induced positive inotropy; however, 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC560, COX-1 inhibitor), 1-[[4,5-bis(4-methoxyphenyl)-2-thiazolyl]carbonyl]-4-methylpiperazine (FR122047, COX-1 inhibitor) and l-nitroarginine methylester did not affect the inotropic response.
  5. M3R activation caused positive chronotropy in spontaneously beating right atria when M2R-mediated negative chronotropy was suppressed and rate of contraction was low, <350 beats min−1.
  6. Our results indicate that although M3Rs are located on both myocardial cells and endocardial endothelial cells, only endothelial M3Rs mediate positive inotropy in response to muscarinic agonists via activation of COX-2 in the mouse atrium. M3R-mediated positive chronotropy counteracting M2R-mediated negative chronotropy was also demonstrated.
小鼠心房中M3毒蕈碱受体和环氧化酶-2表达的免疫组化和功能研究
小鼠心房中,M2和M3毒蕈碱受体(M2R和M3R)参与毒蕈碱激动剂的双相(负性和正性)肌力作用,吲哚美辛可降低正性肌力作用。本研究的目的是确定小鼠心房中M2R、M3R和环加氧酶(COX)的定位,并表征毒蕈碱受体介导的正性肌力变化。M2R仅在心房心肌有免疫反应,而M3R在心肌和心内膜均有免疫反应。心肌和心内膜均有COX-1和COX-2免疫反应。在电刺激的左心房,carbachol引起m2r介导的负性肌力,然后是m3r介导的正性肌力。去除心房内皮降低了正性肌力,但不影响负性肌力,提示内皮细胞M3R的刺激介导了正性肌力。N-[2-(环己氧基)-4-硝基苯基]-甲磺酰胺(NS398, COX-2抑制剂)降低了碳甾醇诱导的正性肌力;然而,5-(4-氯苯基)-1-(4-甲氧基苯基)-3-三氟甲基吡唑(SC560, COX-1抑制剂)、1-[[4,5-双(4-甲氧基苯基)-2-噻唑基]羰基]-4-甲基哌嗪(FR122047, COX-1抑制剂)和l-硝基精氨酸甲基lester对肌力反应没有影响。M3R激活引起自发搏动右心房的正性时变性,而m2r介导的负性时变性受到抑制,收缩率较低,为350次/ min - 1。我们的研究结果表明,尽管M3Rs位于心肌细胞和心内膜内皮细胞上,但只有内皮细胞的M3Rs通过激活小鼠心房中的COX-2介导毒菌碱激动剂的正性肌力变化。还证实了m3r介导的正性时变性与m2r介导的负性时变性相互抵消。
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