Instituto Teófilo Hernando, IIS Hospital Universitario de la Princesa, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain.
Eur J Neurosci. 2011 Jan;33(1):69-81. doi: 10.1111/j.1460-9568.2010.07475.x. Epub 2010 Nov 23.
We investigated the effects of muscarinic acetylcholine receptor (mAChR) activation on GABAergic synaptic transmission in rat hippocampal neurons. Current-clamp recordings revealed that methacholine produced membrane depolarization and action potential firing. Methacholine augmented the bicuculline-sensitive and GABA(A) -mediated frequency of spontaneous inhibitory postsynaptic currents (sIPSCs); the action of methacholine had a slow onset and longer duration. The increase in methacholine-evoked sIPSCs was completely inhibited by atropine and was insensitive to glutamatergic receptor blockers. Interestingly, methacholine action was not inhibited by intracellular perfusion with GDP-β-S, suggesting that muscarinic effects on membrane excitability and sIPSC frequency are mainly presynaptic. McN-A-343 and pirenzepine, selective agonist and antagonist of the m1 mAChR subtype, respectively, neither enhanced sIPSCs nor inhibited the methacholine effect. However, the m3-m5 mAChR antagonist 4-DAMP, and the m2-m4 mAChR antagonist himbacine inhibited the methacholine effect. U73122, an IP(3) production inhibitor, and 2APB, an IP(3) receptor blocker, drastically decreased the methacholine effect. Recording of miniature events revealed that besides the effect exerted by methacholine on membrane firing properties and sIPSC frequency, muscarinic receptors also enhanced the frequency of mIPSCs with no effect on their amplitude, possibly modulating the molecular machinery subserving vesicle docking and fusion and suggesting a tight colocalization at the active zone of the presynaptic terminals. These data strongly suggest that by activating presynaptic m2, m3, m4 and m5 mAChRs, methacholine can increase membrane excitability and enhance efficiency in the GABA release machinery, perhaps through a mechanism involving the release of calcium from the endoplasmic reticulum.
我们研究了毒蕈碱乙酰胆碱受体（mAChR）激活对大鼠海马神经元 GABA 能突触传递的影响。电流钳记录显示，毛果芸香碱产生膜去极化和动作电位发放。毛果芸香碱增强了育亨宾敏感和 GABA(A)介导的自发性抑制性突触后电流（sIPSCs）频率；毛果芸香碱的作用具有缓慢的起始和较长的持续时间。毒蕈碱激动剂毛果芸香碱引起的 sIPSCs 增加完全被阿托品抑制，并且对谷氨酸能受体阻断剂不敏感。有趣的是，毛果芸香碱的作用不受细胞内 GDP-β-S 灌流的抑制，表明 mAChR 对膜兴奋性和 sIPSC 频率的影响主要是突触前的。 McN-A-343 和 pirenzepine 分别是 m1 mAChR 亚型的选择性激动剂和拮抗剂，它们既不增强 sIPSCs，也不抑制毛果芸香碱的作用。然而，m3-m5 mAChR 拮抗剂 4-DAMP 和 m2-m4 mAChR 拮抗剂 himbacine 抑制了毛果芸香碱的作用。IP(3) 产生抑制剂 U73122 和 IP(3) 受体阻断剂 2APB 大大降低了毛果芸香碱的作用。微小事件的记录表明，除了毛果芸香碱对膜发放特性和 sIPSC 频率的作用外，毒蕈碱受体还增强了 mIPSCs 的频率，而对其幅度没有影响，这可能调节了囊泡停泊和融合的分子机制，并提示在突触前末梢的活性区存在紧密的共定位。这些数据强烈表明，通过激活突触前 m2、m3、m4 和 m5 mAChR，毛果芸香碱可以增加膜兴奋性，并增强 GABA 释放机制的效率，这可能涉及内质网钙的释放。
