Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas, USA.
J Physiol. 2022 Nov;600(21):4695-4711. doi: 10.1113/JP283318. Epub 2022 Sep 23.
Bile acids, originally known to emulsify dietary lipids, are now established signalling molecules that regulate physiological processes. Signalling targets several proteins that include the ion channels involved in regulating intestinal motility and bile viscosity. Studies show that bile acids regulate the epithelial sodium channel (ENaC) in cultured cell models and heterologous expression systems. ENaC plays both local and systemic roles in regulating extracellular fluids. Here we investigated whether bile acids regulate ENaC expressed in native tissues. We found that taurocholic acid and taurohyodeoxycholic acid regulated ENaC in both the distal nephron and distal colon. We also tested the hypothesis that regulation occurs through direct binding. Using photoaffinity labelling, we found evidence for specific binding to both the β and γ subunits of the channel. In functional experiments, we found that the α subunit was sufficient for regulation. We also found that regulation by at least one bile acid was voltage-sensitive, suggesting that one binding site may be closely associated with the pore-forming helices of the channel. Our data provide evidence that bile acids regulate ENaC by binding to multiple sites to influence the open probability of the channel. KEY POINTS: Recent studies have shown that bile acids regulate the epithelial sodium channel (ENaC) in vitro. Here we investigated whether bile acids regulate ENaC in native tissues and whether bile acids directly bind the channel. We found that bile acids regulate ENaC expressed in the mouse cortical collecting duct and mouse colon by modulating open probability. Photoaffinity labelling experiments showed specific binding to the β and γ subunits of the channel, while channels comprising only α subunits were sensitive to taurocholic acid in functional experiments using Xenopus oocytes. Taurocholic acid regulation of ENaC was voltage-dependent, providing evidence for binding to pore-forming helices. Our data indicate that bile acids are ENaC regulatory effectors that may have a role in the physiology and pathophysiology of several systems.
胆汁酸最初被认为可以乳化膳食脂质，现在已被确定为调节生理过程的信号分子。信号靶标包括几种参与调节肠道蠕动和胆汁粘度的离子通道的蛋白质。研究表明，胆汁酸在培养细胞模型和异源表达系统中调节上皮钠离子通道（ENaC）。ENaC 在调节细胞外液中发挥局部和全身作用。在这里，我们研究了胆汁酸是否调节天然组织中表达的 ENaC。我们发现牛磺胆酸和牛磺脱氧胆酸调节远曲小管和远段结肠中的 ENaC。我们还测试了通过直接结合进行调节的假设。使用光亲和标记，我们发现了与通道的β和γ亚基都有特异性结合的证据。在功能实验中，我们发现α亚基足以进行调节。我们还发现，至少一种胆汁酸的调节是电压敏感的，这表明一个结合位点可能与通道的形成孔螺旋密切相关。我们的数据提供了证据，表明胆汁酸通过与多个结合位点结合来调节 ENaC，从而影响通道的开放概率。关键点：最近的研究表明，胆汁酸在体外调节上皮钠离子通道（ENaC）。在这里，我们研究了胆汁酸是否在天然组织中调节 ENaC 以及胆汁酸是否直接与通道结合。我们发现，胆汁酸通过调节开放概率来调节小鼠皮质集合管和结肠中表达的 ENaC。光亲和标记实验显示与通道的β和γ亚基特异性结合，而仅由α亚基组成的通道在使用非洲爪蟾卵母细胞的功能实验中对牛磺胆酸敏感。ENaC 的牛磺胆酸调节是电压依赖性的，为结合到形成孔螺旋提供了证据。我们的数据表明，胆汁酸是 ENaC 的调节效应物，可能在几个系统的生理学和病理生理学中发挥作用。
