Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA.
Department of Biology, Stanford University, Stanford, CA.
J Gen Physiol. 2021 Apr 5;153(4). doi: 10.1085/jgp.202012655.
The degenerin channels, epithelial sodium channels, and acid-sensing ion channels (DEG/ENaC/ASICs) play important roles in sensing mechanical stimuli, regulating salt homeostasis, and responding to acidification in the nervous system. They have two transmembrane domains separated by a large extracellular domain and are believed to assemble as homomeric or heteromeric trimers. Based on studies of selected family members, these channels are assumed to form nonvoltage-gated and sodium-selective channels sensitive to the anti-hypertensive drug amiloride. They are also emerging as a target of nonsteroidal anti-inflammatory drugs (NSAIDs). Caenorhabditis elegans has more than two dozen genes encoding DEG/ENaC/ASIC subunits, providing an excellent opportunity to examine variations in drug sensitivity. Here, we analyze a subset of the C. elegans DEG/ENaC/ASIC proteins to test the hypothesis that individual family members vary not only in their ability to form homomeric channels but also in their drug sensitivity. We selected a panel of C. elegans DEG/ENaC/ASICs that are coexpressed in mechanosensory neurons and expressed gain-of-function or d mutants in Xenopus laevis oocytes. We found that only DEGT‑1d, UNC‑8d, and MEC‑4d formed homomeric channels and that, unlike MEC‑4d and UNC‑8d, DEGT‑1d channels were insensitive to amiloride and its analogues. As reported for rat ASIC1a, NSAIDs inhibit DEGT‑1d and UNC‑8d channels. Unexpectedly, MEC‑4d was strongly potentiated by NSAIDs, an effect that was decreased by mutations in the putative NSAID-binding site in the extracellular domain. Collectively, these findings reveal that not all DEG/ENaC/ASIC channels are amiloride-sensitive and that NSAIDs can both inhibit and potentiate these channels.
退化阳离子通道、上皮钠离子通道和酸敏离子通道（DEG/ENaC/ASICs）在感知机械刺激、调节盐稳态以及对神经系统酸化作出反应方面发挥着重要作用。它们具有两个跨膜结构域，由一个大的细胞外结构域隔开，被认为可以组装成同源或异源三聚体。基于对选定家族成员的研究，这些通道被认为形成非电压门控且对抗高血压药物氨氯地平敏感的钠离子选择性通道。它们也正在成为非甾体抗炎药（NSAIDs）的靶点。秀丽隐杆线虫拥有二十多个编码 DEG/ENaC/ASIC 亚基的基因，为研究药物敏感性的变化提供了极好的机会。在这里，我们分析了秀丽隐杆线虫 DEG/ENaC/ASIC 蛋白的一个子集，以检验这样一个假说，即各个家族成员不仅在形成同源通道的能力上存在差异，而且在药物敏感性上也存在差异。我们选择了一组在机械感觉神经元中共表达的秀丽隐杆线虫 DEG/ENaC/ASIC 蛋白，并在非洲爪蟾卵母细胞中表达了它们的功能获得或突变体。我们发现只有 DEGT-1d、UNC-8d 和 MEC-4d 形成同源通道，并且与 MEC-4d 和 UNC-8d 不同，DEGT-1d 通道对氨氯地平和其类似物不敏感。与大鼠 ASIC1a 的报道一致，非甾体抗炎药抑制 DEGT-1d 和 UNC-8d 通道。出乎意料的是，MEC-4d 被非甾体抗炎药强烈增强，而在细胞外结构域中假定的非甾体抗炎药结合位点的突变则降低了这种增强作用。总的来说，这些发现表明并非所有的 DEG/ENaC/ASIC 通道对氨氯地平敏感，而且非甾体抗炎药既能抑制又能增强这些通道。
