The emerging role of glial cells in modulating neuronal excitability and synaptic strength is a growing field in neuroscience. In recent years, a pivotal role of gliotransmission in homeostatic presynaptic plasticity has been highlighted and glial-derived ATP arises as a key contributor. However, very little is known about the glial non-vesicular ATP-release pathway and how ATP participates in the modulation of synaptic strength. Here, we investigated the functional changes occurring in neurons upon chronic inactivity and the role of the purinergic signaling, connexin43 and pannexin1 hemichannels in this process. By using hippocampal dissociated cultures, we showed that blocking connexin43 and pannexin1 hemichannels decreases the amount of extracellular ATP. Moreover, Ca imaging assays using Fluo-4/AM revealed that blocking connexin43, neuronal P2X7Rs and pannexin1 hemichannels decreases the amount of basal Ca in neurons. A significant impairment in synaptic vesicle pool size was also evidenced under these conditions. Interestingly, rescue experiments where Panx1HCs are blocked showed that the compensatory adjustment of cytosolic Ca was recovered after P2X7Rs activation, suggesting that Panx1 acts downstream P2X7Rs. These changes were accompanied by a modulation of neuronal permeability, as revealed by ethidium bromide uptake experiments. In particular, the permeability of neuronal P2X7Rs and pannexin1 hemichannels is increased upon 24 h of inactivity. Taken together, we have uncovered a role for connexin43-dependent ATP release and neuronal P2X7Rs and pannexin1 hemichannels in the adjustment of presynaptic strength by modulating neuronal permeability, the entrance of Ca into neurons and the size of the recycling pool of synaptic vesicles.

中文翻译：

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胶质细胞 Cx43 半通道、神经元 Panx1 半通道和 P2X7 受体协调突触前稳态可塑性

神经胶质细胞在调节神经元兴奋性和突触强度方面的新兴作用是神经科学中不断发展的领域。近年来，神经胶质细胞传递在稳态突触前可塑性中的关键作用已被强调，神经胶质细胞衍生的 ATP 成为关键贡献者。然而，人们对神经胶质非囊泡 ATP 释放途径以及 ATP 如何参与突触强度的调节知之甚少。在这里，我们研究了神经元在长期不活动时发生的功能变化，以及嘌呤能信号、connexin43 和 pannexin1 半通道在此过程中的作用。通过使用海马分离培养物，我们发现阻断 connexin43 和 pannexin1 半通道会减少细胞外 ATP 的量。此外，使用 Fluo-4/AM 的 Ca 成像测定表明，阻断 connexin43、神经元 P2X7R 和 pannexin1 半通道会减少神经元中基础 Ca 的量。在这些条件下也证明了突触小泡池大小的显着损害。有趣的是，Panx1HCs 被阻断的救援实验表明，P2X7Rs 激活后胞浆 Ca 的代偿性调节得到恢复，这表明 Panx1 作用于 P2X7Rs 下游。正如溴化乙锭摄取实验所揭示的，这些变化伴随着神经元通透性的调节。特别是，神经元 P2X7R 和 pannexin1 半通道的通透性在 24 小时不活动后增加。总之，我们发现了 connexin43 依赖性 ATP 释放以及神经元 P2X7R 和 pannexin1 半通道在通过调节神经元通透性、Ca 进入神经元和突触小泡回收池的大小来调节突触前强度中的作用。