Collecting duct endothelin and sodium homeostasis

集合管（CD）内皮素系统已成为肾脏钠排泄的重要调节因子 和全身血压（BP）。CD衍生的内皮素-1（ET-1）发挥了可能是 至少部分是由于CD上皮Na通道（ENaC）的抑制。CD衍生的ET-1在以下方面是重要的： 介导对细胞外液容量（ECFV）扩张的利钠反应并控制动脉血压; CD ET-1系统的缺陷可能导致高血压。虽然CD ET的一般生物学 虽然这一制度已经建立，但关于这一制度如何运作仍有许多未知之处。特别是， 急需研究的关键组成部分是：1）确定ET-1是否以及如何抑制CD Na转运; 2)确定ECFV状态如何与CD ET-1产生相关联。根据初步数据， 拟议的研究将解决以下假设：ECFV扩张增加小管液体流速 通过CD。增加的流量通过多囊蛋白-1和-2增加细胞内Ca浓度[Ca 2 +]。 增加的CD [Ca 2 +]诱导引起ET-1基因转录激活的信号通路。这 增加CD ET-1的产生和分泌，导致最可能的ETB受体的自分泌激活 （ETRB），但也可能是ETA受体（ETRA）。ET-1结合通过降低通道开放概率（Po）和可能的顶端通道数（N）导致ENaC抑制。对Po的影响至少部分是由于c-src/MAPK途径的激活。该项目的具体目标包括： 目标1。检验流动刺激CD ET-1产生的假设，以及这种作用是由 激活特定的细胞信号通路、顺式作用元件和反式激活因子。 因此，我们将：a）确定流动对CD ET-1产生的影响;和B）确定将流动和细胞内Ca偶联到ET-1基因转录的细胞信号传导途径、顺式作用元件和反式激活因子。 目标2.检验ET-1调节CD中ENaC的假设，以及支持这种调节的特定细胞和分子机制。因此，我们将：a）确定ET-1是否调节天然分离的CD细胞中的ENaC Po; B）鉴定参与调节天然CD细胞中的ENaC的特异性ET受体，并阐明将该受体偶联至通道的细胞信号传导途径; c）确定ET-1调节CD ENaC在肾Na处理的生理控制中的重要性，并使用基因靶向小鼠探测破坏该调节的病理生理学后果;和d）确定ET-1调节ENaC功能的分子机制，包括鉴定ENaC中使通道能够响应ET-1的特定残基/区域。

The collecting duct (CD) endothelin system has emerged as an important regulator of renal Na excretion and systemic blood pressure (BP). CD-derived endothelin-1 (ET-1) exerts a hypotensive effect that is likely due, at least partly, to inhibition of the CD epithelial Na channel (ENaC). CD-derived ET-1 is important in mediating the natriuretic response to extracellular fluid volume (ECFV) expansion and controlling arterial BP; defects in the CD ET-1 system may contribute to hypertension. While the general biology of the CD ET system has been established, there remains much unknown about how this system functions. In particular, key components in critical need of study are: 1) determination if and how ET-1 inhibits CD Na transport; and 2) determination how ECFV status is coupled to CD ET-1 production. Based on preliminary data, the proposed studies will address the following hypotheses; ECFV expansion increases tubule fluid fiow rate through the CD. Increased fiow increases intracellular Ca concentration [Ca2+] through polycystins-1 and -2. Increased CD [Ca2+] induces signaling pathways causing transcriptional activation of the ET-1 gene. This increases CD ET-1 production and secretion resulting in autocrine activation of most likely the ETB receptor (ETRB), but also possibly the ETA receptor (ETRA). ET-1 binding leads to inhibition of the ENaC through reduction of channel open probability (Po) and possibly apical channel number (N). The effect on Po is due, at least partly, to activation of the c-src/MAPK pathway. The specific aims for this project include: Aim 1. Test the hypothesis that fiow stimulates CD ET-1 production, and that this effect is exerted by activation of specific cellular signaling pathways, cis-acting elements and trans-activating factors. Accordingly, we will: a) determine the effects of flow on CD ET-1 production; and b) determine the cellular signaling pathways, cis-acting elements and trans-activating factors coupling flow and intracellular Ca to ET-1 gene transcription. Aim 2. Test the hypothesis that ET-1 regulates ENaC in the CD, and that specific cellular and molecular mechanisms underpin this regulation. Accordingly, we will: a) determine if ET-1 regulates ENaC Po in native isolated CD cells; b) identify the specific ET receptor involved in regulating ENaC in native CD cells and elucidate the cellular signaling pathway coupling this receptor to the channel; c) define the importance of ET-1 regulation of CD ENaC in physiologic control of renal Na handling, and probe pathophysiological consequences of disrupting this regulation using gene targeted mice; and d) define the molecular mechanisms by which ET-1 modulates ENaC function, including identifying the specific residues/regions of ENaC that enable the channel to respond to ET-1.