STRUCTURE AND REGULATION OF EPITHELIAL SODIUM CHANNELS

阿米洛利敏感的上皮钠通道(ENaC)发挥着中枢作用 在维持钠的动态平衡方面，它构成了主要的 钠在致密上皮(如远端)重吸收的途径 尼龙。钠通道在维持心脏功能中的重要作用 这一发现强调了细胞外体积和血压 人类基因的突变，要么是活跃的通道导致 高血压(利德尔综合征)，或相反，降低 导致盐耗和低血容量状态的通道 (假性醛固酮减少症)。阐明了正常情况下 调节ENaC的功能和表达对 对生理性和非生理性的血容量维持的认识 病理情况。这项工作的长期目标是 了解通道功能和调节的分子机制。 该提案的具体目标是：1)确定功能 使用所形成的通道所表现出的属性差异的域 按ab和ag亚单位计算。将执行功能域映射 利用b和g亚基之间产生的嵌合体；2)阐明 醛固酮介导ENaC磷酸化的机制。 醛固酮通过增加钠离子的丰度来增加钠的通透性 钠通道和激活预先存在的通道。然而， 介导通道激活的机制(S)仍不清楚。 我们认为，醛固酮诱导的磷酸化是 激活预先存在的渠道的机制；3)了解 泛素化对ENaC表达的调节我们将研究 泛素化参与血浆内吞作用的假说 细胞膜和细胞内通道的降解。 注射的非洲爪哇卵母细胞和转基因细胞将提供 野生型和突变型通道的表达系统 检查功能属性、表达水平、细胞 渠道生物合成和降解的分布和速率。 实验的设计是为了检查活性和性质 通过电生理学技术。频道合唱团将 采用双微电极电压钳和单电极进行研究 使用膜片钳技术的通道。生化，免疫学， 并将应用分子生物学方法来检查这种状态 通道的磷酸化和泛素化。这些研究 将确定钠通道中的重要功能区域，以及 是首次探索了两种新的调节机制的功能 和钠通道的表达。

The amiloride-sensitive epithelial sodium channel (ENaC) plays a central role in the maintenance of sodium homeostasis, it constitutes the main pathway for reabsorption of sodium in tight epithelia such as the distal nephron. The importance of the sodium channel in the maintenance of extracellular volume and blood pressure is underscored by the finding of mutations in the human genes that either active channels leading to hypertension (Liddle's syndrome), or conversely, decrease activity of channels leading to salt-wasting and hypovolemic states (pseudohypoaldosteronism). Elucidation of the mechanisms that normally regulate the function and expression of ENaC is of major importance for the understanding of blood volume maintenance in physiological and pathological conditions. The long term objectives of this work are to understand the molecular mechanisms of channel function and regulation. The specific goals of this proposal are: 1) to identify functional domains using the differences in properties exhibited by channels formed by ab and ag subunits. Mapping of functional domains will be performed using chimeras generated between the b and g subunits; 2) to elucidate the mechanics by which aldosterone mediates phosphorylation of ENaC. Aldosterone increase sodium permeability by increasing the abundance of sodium channels and by activating pre-existing channels. However, the mechanism(s) that mediate the activation of channels is still unknown. We propose that aldosterone induced phosphorylation is one of the mechanisms that activates pre-existing channels; 3) to understand the regulation of expression of ENaC by ubiquitination. We will examine the hypothesis that ubiquitination participates in endocytosis at the plasma membrane and in degradation of channels in intracellular compartments. Injected Xenopus oocytes and transfected cells will provide the expression systems for wild-type and mutant channels in which we will examine the functional properties, levels of expression, cellular distribution and rates of biosynthesis and degradation of channels. Experiments are designed to examine the activity and properties of channels by electrophysiologycal techniques. Ensembles of channels will be studied using the two micro-electrode voltage clamp and single channels using the patch-clamp technique. Biochemical, immunological, and molecular biological approaches will be applied to examine the state of phosphorylation and ubiquitination of the channel. These studies will identify important functional domains in the sodium channel, and are the first to explore two novel regulatory mechanisms of the function and expression of sodium channels.