Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskie gory 1/12, Moscow, 119991, Russia.
Department of Physiology, Russian National Research Medical University, Ostrovitjanova 1, Moscow, 117997, Russia.
Purinergic Signal. 2018 Dec;14(4):459-469. doi: 10.1007/s11302-018-9630-7. Epub 2018 Oct 25.
P2X7 receptors are present in presynaptic membranes of motor synapses, but their regulatory role in modulation of neurotransmitter release remains poorly understood. P2X7 receptors may interact with pannexin 1 channels to form a purinergic signaling unit. The potential mechanism of P2X7 receptor-dependent modulation of acetylcholine (ACh) release was investigated by recording miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) in neuromuscular junctions of wild-type (WT) and pannexin 1 knockout (Panx1) mice. Modulation of P2X7 receptors with the selective inhibitor A740003 or the selective agonist BzATP did not alter the parameters of either spontaneous or evoked ACh release in WT mice. In Panx1 mice, BzATP-induced activation of P2X7 receptors resulted in a uniformly increased quantal content of EPPs during a short stimulation train. This effect was accompanied by an increase in the size of the readily releasable pool, while the release probability did not change. Inhibition of calmodulin by W-7 or of calcium/calmodulin-dependent kinase II (CaMKII) by KN-93 completely prevented the potentiating effect of BzATP on the EPP quantal content. The blockade of L-type calcium channels also prevented BzATP action on evoked synaptic activity. Thus, the activation of presynaptic P2X7 receptors in mice lacking pannexin 1 resulted in enhanced evoked ACh release. Such enhanced release was provoked by triggering the calmodulin- and CaMKII-dependent signaling pathway, followed by activation of presynaptic L-type calcium channels. We suggest that in WT mice, this pathway is downregulated due to pannexin 1-dependent tonic activation of inhibitory presynaptic purinergic receptors, which overcomes P2X7-mediated effects.
P2X7 受体存在于运动突触的突触前膜中，但它们在调节神经递质释放中的调节作用仍知之甚少。P2X7 受体可能与连接蛋白 1 通道相互作用形成嘌呤能信号单元。通过记录野生型 (WT) 和连接蛋白 1 敲除 (Panx1) 小鼠神经肌肉接头的微小终板电位 (MEPPs) 和诱发终板电位 (EPPs)，研究了 P2X7 受体依赖性调节乙酰胆碱 (ACh) 释放的潜在机制。用选择性抑制剂 A740003 或选择性激动剂 BzATP 调节 P2X7 受体，不会改变 WT 小鼠自发或诱发 ACh 释放的参数。在 Panx1 小鼠中，BzATP 诱导的 P2X7 受体激活导致在短刺激过程中 EPP 的量子含量均匀增加。这种效应伴随着易释放池大小的增加，而释放概率没有变化。钙调蛋白抑制剂 W-7 或钙调蛋白依赖性激酶 II (CaMKII) 抑制剂 KN-93 完全阻止了 BzATP 对 EPP 量子含量的增强作用。L 型钙通道的阻断也阻止了 BzATP 对诱发突触活动的作用。因此，在缺乏连接蛋白 1 的小鼠中，激活突触前 P2X7 受体导致诱发的 ACh 释放增强。这种增强的释放是通过触发钙调蛋白和 CaMKII 依赖性信号通路引起的，随后激活突触前 L 型钙通道。我们认为，在 WT 小鼠中，由于连接蛋白 1 依赖性抑制性突触前嘌呤能受体的紧张性激活，该途径被下调，从而克服了 P2X7 介导的作用。
