The mammalian brain consists of 80% water, which is continuously shifted between different compartments and cellular structures by mechanisms that are, to a large extent, unresolved. Aquaporin 4 (AQP4) is abundantly expressed in glia and ependymal cells of the mammalian brain and has been proposed to act as a gatekeeper for brain water dynamics, predominantly based on studies utilizing AQP4‐deficient mice. However, these mice have a range of secondary effects due to the gene deletion. An efficient and selective AQP4 inhibitor has thus been sorely needed to validate the results obtained in the AQP4^−/− mice to quantify the contribution of AQP4 to brain fluid dynamics. In AQP4‐expressing Xenopus laevis oocytes monitored by a high‐resolution volume recording system, we here demonstrate that the compound TGN‐020 is such a selective AQP4 inhibitor. TGN‐020 targets the tested species of AQP4 with an IC₅₀ of ~3.5 μM, but displays no inhibitory effect on the other AQPs (AQP1‐AQP9). With this tool, we employed rat hippocampal slices and ion‐sensitive microelectrodes to determine the role of AQP4 in glia cell swelling following neuronal activity. TGN‐020‐mediated inhibition of AQP4 did not prevent stimulus‐induced extracellular space shrinkage, nor did it slow clearance of the activity‐evoked K⁺ transient. These data, obtained with a verified isoform‐selective AQP4 inhibitor, indicate that AQP4 is not required for the astrocytic contribution to the K⁺ clearance or the associated extracellular space shrinkage.

中文翻译：

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活动诱发的 K+ 瞬变和相关神经胶质细胞肿胀的清除独立于 AQP4：使用异构体选择性 AQP4 抑制剂的研究。

哺乳动物的大脑由 80% 的水组成，通过在很大程度上尚未解决的机制在不同的隔室和细胞结构之间不断转移。水通道蛋白 4 (AQP4) 在哺乳动物大脑的神经胶质细胞和室管膜细胞中大量表达，并且已被提议作为脑水动力学的看门人，主要基于利用 AQP4 缺陷小鼠的研究。然而，由于基因缺失，这些小鼠会产生一系列副作用。因此，迫切需要一种有效且选择性的 AQP4 抑制剂来验证在 AQP4 ^-/-小鼠中获得的结果，以量化 AQP4 对脑液动力学的贡献。在表达 AQP4 的非洲爪蟾中通过高分辨率体积记录系统监测卵母细胞，我们在此证明了化合物 TGN-020 是一种选择性 AQP4 抑制剂。TGN-020 靶向 AQP4 的测试物种，IC ₅₀约为 3.5 μM，但对其他 AQP (AQP1-AQP9) 没有抑制作用。使用该工具，我们使用大鼠海马切片和离子敏感微电极来确定 AQP4 在神经元活动后胶质细胞肿胀中的作用。TGN-020 介导的 AQP4 抑制不能阻止刺激诱导的细胞外空间收缩，也不能减缓活动诱发的 K ⁺瞬态的清除。这些数据是用经过验证的同种型选择性 AQP4 抑制剂获得的，表明 AQP4 不是星形胶质细胞对 K ^{+的贡献所必需的。}清除或相关的细胞外空间收缩。