Reduced Plasma-Membrane Calcium ATPase Activity and Extracellular Acidification Trigger Presynaptic Homeostatic Potentiation at the Mouse Neuromuscular Junction
Reduced Plasma-Membrane Calcium ATPase Activity and Extracellular Acidification Trigger Presynaptic Homeostatic Potentiation at the Mouse Neuromuscular Junction
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DOI：
10.1016/j.neuroscience.2023.09.014
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发表时间：
2023-10-10
期刊：
影响因子：
3.3
通讯作者：
Lindgren，Clark A.
中科院分区：
文献类型：
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作者：
Imomnazarov，Khondamir;Torrence，Sarah E.;Lindgren，Clark A.
在脊椎动物神经肌肉接头（NMJ），突触前稳态增强（PHP）是指在阻断烟碱乙酰胆碱受体（nAChR）后神经递质释放的增加，其恢复突触传递的强度。突触前末梢丧失突触后感受性的机制仍然知之甚少。先前在小鼠NMJ的研究表明，细胞外质子可能作为一种逆行信号，通过激活酸敏感离子通道（ASIC）触发神经递质输出（通过量子含量，QC测量）的上调。我们进一步研究了PHP在活体小鼠肌肉制备中的pH依赖性。我们观察到，用HEPES增加灌注盐水的缓冲能力消除了PHP，并且将盐水从pH 7.4酸化至pH 7.2-7.1增加了QC，证明了细胞外酸化对于PHP的必要性和充分性。然后，我们试图揭示nAChR的阻断如何导致pH降低。质膜钙ATP酶（PMCA）是一种钙-质子逆向转运蛋白，它以钙依赖的方式使神经传递后的突触间隙碱化。我们假设，由于nAChR阻断减少突触后钙离子进入，它也减少了碱性活性的PMCA，从而导致酸中毒，ASIC激活，QC上调。根据这一假设，我们发现，药理学抑制PMCA与羧肌球蛋白诱导QC上调，这种效果需要功能ASIC。我们还证明，肌肉预处理与羧肌球蛋白不能产生PHP。这些发现表明，PMCA活性降低通过激活小鼠NMJ处的ASIC引起突触前稳态增强。
At the vertebrate neuromuscular junction (NMJ), presynaptic homeostatic potentiation (PHP) refers to an increase in neurotransmitter release that restores the strength of synaptic transmission following a blockade of nicotinic acetylcholine receptors (nAChRs). Mechanisms informing the presynaptic terminal of the loss of postsynaptic receptivity remain poorly understood. Previous research at the mouse NMJ suggests that extracellular protons may function as a retrograde signal that triggers an upregulation of neurotransmitter output (measured by quantal content, QC) through the activation of acid-sensing ion channels (ASICs). We further investigated the pH-dependency of PHP in anex-vivomouse muscle preparation. We observed that increasing the buffering capacity of the perfusion saline with HEPES abolishes PHP and that acidifying the saline from pH 7.4 to pH 7.2–7.1 increases QC, demonstrating the necessity and sufficiency of extracellular acidification for PHP. We then sought to uncover how the blockade of nAChRs leads to the pH decrease. Plasma-membrane calcium ATPase (PMCA), a calcium-proton antiporter, is known to alkalize the synaptic cleft following neurotransmission in a calcium-dependent manner. We hypothesize that since nAChR blockade reduces postsynaptic calcium entry, it also reduces the alkalizing activity of the PMCA, thereby causing acidosis, ASIC activation, and QC upregulation. In line with this hypothesis, we found that pharmacological inhibition of the PMCA with carboxyeosin induces QC upregulation and that this effect requires functional ASICs. We also demonstrated that muscles pre-treated with carboxyeosin fail to generate PHP. These findings suggest that reduced PMCA activity causes presynaptic homeostatic potentiation by activating ASICs at the mouse NMJ.