CONTROL OF EPITHELIAL NA+ TRANSPORT BY APICAL NA+ ENTRY

在肾上皮细胞中，钠离子的载体转运是一个两步过程。 首先，钠进入发生通过阿米洛利可阻断的离子通道 位于钠转运细胞的顶膜。 第二、 钠通过基底外侧膜主动转运出细胞 Na+/K+-ATP酶。 这两个过程的净效应， 串联，是钠从管腔的矢量运输 室到基底外侧室。 之前的数据显示 顶端Na+进入的速率调节这些细胞的活性， 转运蛋白 因此，nA+重吸收能力的远端 肾单位节段响应于增加的负荷而增加， 减少，以减少负载。 这种形式的管制是 对盐平衡的许多临床重要作用负责， 包括维持肾小球-肾小管平衡， 利尿剂抵抗现象，后结构的发展 利尿和下游肾小管萎缩的发生， 肾小球疾病 此外，控制肾钠排泄 参与多种疾病状态的发病机制， 高血压、肾病综合征和充血性心力衰竭。 目前，Na+进入速率调节 Na+转运体活性知之甚少。 拟议的研究 将在分子水平上使用一种表征良好的 收集管上皮细胞模型，A6细胞系生长在 多孔载体 发表的细胞培养模型的初步数据 表明Na+进入的阻断导致了 调节顶端Na+通道和基底外侧 Na+/K+-ATP酶。 此外，刺激applical Na+ uptake， 调节这两种途径。 最近cDNA编码三种蛋白质， α、β和γ EnaC（上皮Na+通道），已被 识别和克隆。 所有的活性电导低， 钠选择性，阿米洛利敏感性上皮钠通道 皮质集合管可以通过这些通道蛋白来解释。 这些蛋白质的同源物已在A6细胞中描述， XeNaC（Xenopus Na+ channel）。 使用抗体 和北方印迹探针的XeNaC通道，和α和 Na+/K+-ATP酶的β亚基，顶端Na+进入的影响 对转录、翻译和翻译后调节的影响 将描述这些转运蛋白。

In kidney epithelial, vectorial sodium transport is a two step process. First, sodium entry occurs trough amiloride-blockable ion channels located in the apical membrane of sodium transporting cells. Second, the sodium is active transported out of the cells via a basolateral Na+/K+-ATPase. The net effect of these two processes, which occur in series, is the vectorial transport of sodium from the luminal compartment to the basolateral compartment. Previous data suggest that the rate of apical Na+ entry regulates the activity of these transporter proteins. Thus, the nA+ reabsorptive capacity of distal nephron segments increases in response to increased load and decreases in espouse to decreased load. This form of regulation is responsible from many clinically important effects on salt balance, including the maintenance of glomerular-tubular balance, the phenomenon of diuretic resistance, the development of post-obstructure diuresis and the occurrence of downstream tubular atrophy in glomerular disease. Moreover, the control of renal sodium excretion is involved in the pathogenesis of diverse disease states such as hypertension, nephrotic syndrome, and congestive heart failure. Currently, the mechanisms by which the rate of na+ entry regulates Na+ transporter activity are poorly understood. The proposed studies will address this issue at a molecular level using a well characterized model of collecting duct epithelial cells, the A6 cell line grown on porous supports. Published preliminary data in t his cell culture model demonstrates that blockage of Na+ entry result in striking on regulation of both the apical Na+ channel and the basolateral Na+/K+-ATPase. In addition, stimulation of aplical Na+ etry up- regulates both pathways. Recently cDNA encoding for three proteins, alpha, beta, and gamma EnaC (epithelial Na+ channel), has been identified and cloned. All of the activity of low conductance, highly sodium selective, amiloride-sensitive epithelial sodium channel from cortical collecting duct can be accounted for by these channel proteins. Homologues of these proteins have been described in A6 cells and have been termed XeNaC (Xenopus Na+ channel). Using antibody and northern blot probes to the XeNaC channel, and to the alpha and beta subunits of the Na+/K+-ATPase, the effect of apical Na+ entry on the transcriptional, translational and post-translational regulation of these transporter proteins will be described.