Department of Cell and Systems Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan.
J Pharmacol Sci. 2011;117(4):253-64. doi: 10.1254/jphs.11125fp. Epub 2011 Nov 18.
The muscarinic receptor is known to be involved in the acetylcholine (ACh)-induced secretion of catecholamines in the adrenal medullary (AM) cells of various mammals. The muscarinic receptor subtype involved and its physiological role, however, have not been elucidated yet. Thus, we investigated these issues in acutely isolated rat AM cells and perfused rat adrenal medulla. The RT-PCR analysis revealed the presence of M(2), M(3), M(4), and M(5) mRNAs. Immunocytochemistry with specific antibodies showed that M(5)-like immunoreactivities (IRs) were detected at half the cell membrane area, which was much larger than that with M(3)- or M(4)-like IRs. Muscarine produced inward currents in a dose-dependent manner. Pilocarpine, McN-A-343, and oxotremorine were less efficient than muscarine; and RS-86, which has no action on the M(5) receptor, produced no current. Electrical stimulation of nerve fibers produced a frequency-dependent increase in the Ca(2+) signal in perfused adrenal medullae. Muscarinic receptors were found to be involved in neuronal transmission in AM cells in the presence of a cholinesterase inhibitor, which suppresses ACh degradation. We concluded that the M(5) receptor is the major muscarinic receptor subtype in rat AM cells and may be involved in neuronal transmission under conditions where ACh spills over the synapse.
毒蕈碱型乙酰胆碱受体（Muscarinic Acetylcholine Receptor，mAChR）已知参与各种哺乳动物肾上腺髓质（Adrenal Medulla，AM）细胞中乙酰胆碱（Acetylcholine，ACh）诱导儿茶酚胺的分泌。然而，涉及的毒蕈碱型乙酰胆碱受体亚型及其生理作用尚未阐明。因此，我们在急性分离的大鼠 AM 细胞和灌流的大鼠肾上腺髓质中研究了这些问题。RT-PCR 分析显示存在 M(2)、M(3)、M(4) 和 M(5)mRNA。用特异性抗体进行免疫细胞化学显示，M(5)-样免疫反应性（Immunoreactivity，IR）检测到的细胞膜面积为一半，明显大于 M(3)-或 M(4)-样 IR。毒蕈碱以剂量依赖性方式产生内向电流。毛果芸香碱、 McN-A-343 和 Oxotremorine 的效率低于毒蕈碱；而对 M(5)受体无作用的 RS-86 则没有电流产生。刺激神经纤维产生的频率依赖性增加，在灌流的肾上腺髓质中增加 Ca(2+)信号。在存在胆碱酯酶抑制剂的情况下，发现毒蕈碱受体参与 AM 细胞中的神经元传递，该抑制剂抑制 ACh 的降解。我们得出结论，M(5)受体是大鼠 AM 细胞中主要的毒蕈碱型乙酰胆碱受体亚型，并且可能在 ACh 溢出突触的情况下参与神经元传递。
