Myslivecek Jaromir, Klein Martin, Novakova Martina, Ricny Jan
Institute of Physiology, 1st Faculty of Medicine, Charles University, Albertov 5, 12800, Prague, Czech Republic.
Naunyn Schmiedebergs Arch Pharmacol. 2008 Jul;378(1):103-16. doi: 10.1007/s00210-008-0285-8. Epub 2008 Apr 29.
Mammal heart tissue has long been assumed to be the exclusive domain of the M(2) subtype of muscarinic receptor, but data supporting the presence of other subtypes also exist. We have tested the hypothesis that muscarinic receptors other than the M(2) subtype are present in the heart as minor populations. We used several approaches: a set of competition binding experiments with pirenzepine, AFDX-116, 4-DAMP, PD 102807, p-F-HHSiD, AQ-RA 741, DAU 5884, methoctramine and tripinamide, blockage of M(1) muscarinic receptors using MT7 toxin, subtype-specific immunoprecipitation experiments and determination of phospholipase C activity. We also attempted to block M(1)-M(4) receptors using co-treatment with MT7 and AQ-RA 741. Our results show that only the M(2) subtype is present in the atria. In the ventricles, however, we were able to determine that 20% (on average) of the muscarinic receptors were subtypes other than M(2), with the majority of these belonging to the M(1) subtype. We were also able to detect a marginal fraction (6 +/- 2%) of receptors that, based on other findings, belong mainly to the M(5) muscarinic receptors. Co-treatment with MT7 and AQ-RA 741 was not a suitable tool for blocking of M(1)-M(4) receptors and can not therefore be used as a method for M(5) muscarinic receptor detection in substitution to crude venom. These results provide further evidence of the expression of the M(1) muscarinic receptor subtype in the rat heart and also show that the heart contains at least one other, albeit minor, muscarinic receptor population, which most likely belongs to the M(5) muscarinic receptors but not to that of the M(3) receptors.
长期以来,人们一直认为哺乳动物心脏组织是毒蕈碱受体M(2)亚型的专属领域,但也有数据支持其他亚型的存在。我们测试了这样一个假设,即除M(2)亚型外的其他毒蕈碱受体以少量群体的形式存在于心脏中。我们采用了几种方法:用哌仑西平、AFDX - 116、4 - DAMP、PD 102807、p - F - HHSiD、AQ - RA 741、DAU 5884、甲溴东莨菪碱和曲吡那敏进行一系列竞争结合实验,使用MT7毒素阻断M(1)毒蕈碱受体,进行亚型特异性免疫沉淀实验以及测定磷脂酶C活性。我们还尝试通过联合使用MT7和AQ - RA 741来阻断M(1) - M(4)受体。我们的结果表明,心房中仅存在M(2)亚型。然而,在心室中,我们能够确定平均20%的毒蕈碱受体是M(2)以外的亚型,其中大多数属于M(1)亚型。我们还能够检测到一小部分(6±2%)受体,根据其他研究结果,这些受体主要属于M(5)毒蕈碱受体。联合使用MT7和AQ - RA 741并非阻断M(1) - M(4)受体的合适工具,因此不能用作替代粗毒液检测M(5)毒蕈碱受体的方法。这些结果进一步证明了M(1)毒蕈碱受体亚型在大鼠心脏中的表达,并且还表明心脏中至少存在另一种(尽管数量较少)毒蕈碱受体群体,其很可能属于M(5)毒蕈碱受体而非M(3)受体。