ENaC regulation by biliary factors

晚期肝病患者常出现液体滞留和电解质紊乱。 部分原因是肾素-血管紧张素-醛固酮系统的激活。醛固酮激活 远端肾单位上皮钠通道(ENaC)增强尿钠、钾的滞留 排泄物。但许多肝病患者体液滞留却没有明显的活跃性。 肾素-血管紧张素-醛固酮系统。肝病患者也经常表现出 血浆胆汁酸升高和高胆红素血症。初步数据显示，特定的胆汁酸 结合胆红素体外激活ENaC，牛磺胆酸激活ENaC 孤立的收集管道。我们建议的中心假设是尿胆汁酸和 可能的结合胆红素直接激活ENaC，促进钠和液体滞留和钾 排泄物。这项提案的目标是确定这种调节是否在体内发生，并 确定其调控的分子机制。初步数据显示尿液来自 酒精性肝炎患者体内活化型胆汁酸和结合型胆汁酸浓度 胆红素足以激活通道，甚至激活通道。我们将决定 酒精性肝炎患者的尿液是否激活实验细胞中的ENaC。我们进一步 假设升高的胆汁因子激活远端肾单位的ENaC，促进Na 蓄积和排钾。我们将在孤立的收集管道中测试这一假设。我们还将 在体内测试这一假说，方法是长期应用胆汁因子并量化 体重、血钾、尿钠和尿钾、血浆醛固酮和全身水分。初步数据 提示牛磺胆酸可促进钠滞留、钾丢失和容量扩张。我们会 通过使用药物阻断ENaC来确定ENaC对观察到的变化的贡献，并通过 利用基因改变增加通道对胆道因素的敏感性或降低ENaC的敏感性 对肾脏钠钾代谢的贡献。实验还将研究分子 胆汁酸对ENaC的调节机制。我们假设激活的胆汁酸相互作用 直接与渠道合作，增强渠道活跃度。我们将使用衍生胆汁酸来检测 通道酸和胆汁酸的直接结合以及关键的化学和生物物理性质 来剖析这种相互作用。关键实验将在多个细胞模型中进行，包括 非洲爪哇卵母细胞、培养的上皮细胞和小鼠的集合管。通过以下方式直接激活ENaC 肝病中胆道因素升高以前从未被研究过，可能与此有关 与肝病相关的容量超载、浮肿和电解质失衡有关。

Patients with advanced liver disease often experience fluid retention and electrolyte disturbances due in part to activation of the renin-angiotensin-aldosterone system. Aldosterone activates the epithelial Na+ channel (ENaC) in the distal nephron, enhancing urinary Na+ retention and K+ excretion. But many liver disease patients experience fluid retention without apparent activation of the renin-angiotensin-aldosterone system. Liver disease patients also frequently exhibit elevated plasma bile acids and hyperbilirubinemia. Preliminary data show that specific bile acids and conjugated bilirubin activate ENaC in vitro and that taurocholic acid activates ENaC in isolated collecting ducts. The central hypothesis of our proposal is that urinary bile acids and possibly conjugated bilirubin directly activate ENaC, promoting Na+ and fluid retention and K+ excretion. The goal of this proposal is to determine whether this regulation occurs in vivo and to determine the molecular mechanism of regulation. Preliminary data suggest that urine from patients with alcoholic hepatitis contains concentrations of activating bile acids and conjugated bilirubin sufficient to activate the channel, and indeed activate the channel. We will determine whether urine from alcoholic hepatitis patients activates ENaC in experimental cells. We further hypothesize that elevated biliary factors activate ENaC in the distal nephron, promoting Na+ retention and K+ excretion. We will test this hypothesis in isolated collecting ducts. We will also test this hypothesis in vivo by chronically administering biliary factors and quantifying changes in weight, blood K+, urinary Na+ and K+, plasma aldosterone, and total body water. Preliminary data suggest that taurocholic acid promotes Na+ retention, K+ loss, and volume expansion. We will determine the contribution of ENaC to observed changes by using drugs to block ENaC, and by using genetic changes to increase the channel's sensitivity to biliary factors or to decrease ENaC's contribution to renal Na+ and K+ handling. Experiments will also investigate the molecular mechanism of ENaC regulation by bile acids. We hypothesize that activating bile acids interact directly with the channel to enhance channel activity. We will use derivatized bile acids to detect direct binding, and key chemical and biophysical properties of the both the channel and bile acids to dissect the interaction. Key experiments will be performed in multiple cell models, including Xenopus oocytes, cultured epithelial cells, and mouse collecting ducts. Direct ENaC activation by biliary factors elevated in liver disease has not been previously investigated, and may contribute to the volume overload, edema, and electrolyte imbalances associated with liver disease.