Molecular Mechanisms of Proximal Tubule Ion Transport

说明（申请人提供）：本提案为延续性提案 一个长期的研究项目，旨在识别和表征 离子交换剂介导近端的酸碱和NaCl运输 小管在近端小管中，主要的顶膜途径 Na ~+的吸收和H ~+的分泌是Na ~+-H ~+交换。Cl-跨膜吸收 该肾单位节段顶膜由几种不同的 C1-碱交换过程，包括CL-甲酸盐交换。C1-草酸盐 交换和Cl- -OH-交换。在过去的项目期间，我们使用了 各种实验方法来证明NHE 3是同种型 主要负责近端膜Na+-H+交换 小管此外，我们已经产生并使用抗NHE 3单克隆抗体 发现NHE 3结构的意想不到的方面，包括其 与二肽基肽酶IV的寡聚复合物中的缔合，以及 C-末端亲水性“胞质”结构域内的表位是 实际上是外质的在下一个项目期间，我们将继续研究， 定义结构的这两个新方面的功能后果 NHE3。在相关的研究中，我们已经完成了一个新成员的克隆， 在肾脏中表达的NHE基因家族。我们建议描述 这种新的NHE亚型的功能特性，并确定它是否是 在近端小管和/或其它肾单位节段中表达。最后我们 已经鉴定了一种新的阴离子转运蛋白， 近端小管细胞膜上的C1-甲酸盐交换（CFEX）。我们 计划更详细地描述CFEX的功能特性，并将 寻求确定可能负责顶端的其他转运蛋白 Cl--近端小管中的碱交换。总体而言，拟议的研究 应该能加深对Na+、HCO 3-和Cl-的机制的理解， 肾脏中的运输，这与由以下原因引起的临床疾病相关 肾脏酸碱平衡的改变（例如，肾结石、骨质疏松症）和 NaCl运输（例如，高血压、充血性心力衰竭）。

DESCRIPTION (provided by applicant): The present proposal is for continuation of a long-standing research program directed at identifying and characterizing the ion exchangers mediating acid-base and NaC1 transport in the proximal tubule. In the proximal tubule, the principal apical membrane pathway for absorption of Na+ and secretion of H+ is Na+-H+ exchange. Cl- absorption across the apical membrane in this nephron segment occurs by several different C1--base exchange processes including CL--formate exchange. C1--oxalate exchange and Cl- -OH- exchange. During the past project period we have used a variety of experimental approaches to demonstrate that NHE3 is the isoform principally responsible for apical membrane Na+-H+ exchange in the proximal tubule. In addition, we have generated and used anti-NHE3 monoclonal antibodies to discover unexpected aspects of the structure of NHE3 including its association in oligomeric complexes with dipeptidyl peptidase IV, and the fact that epitopes within the C-terminal hydrophilic "cytoplasmic" domain are actually exoplasmic. In the next project period we will pursue studies to define the functional consequences of these two novel aspects of the structure of NHE3. In related studies, we have completed the cloning of a new member of the NHE gene family that is expressed in the kidney. We propose to characterize the functional properties of this new NHE isoform and determine whether it is expressed in the proximal tubule and/or other nephron segments. Finally, we have identified a novel anion transporter that is expressed on the apical membrane of proximal tubule cells and mediates C1--formate exchange (CFEX). We plan to characterize the functional properties of CFEX in more detail and will seek to identify additional transporters that may be responsible for apical Cl--base exchange in the proximal tubule. Taken together, the proposed studies should enhance understanding of the mechanisms of Na+, HCO3-- and CI-- transport in the kidney, which is relevant to clinical disorders caused by alterations in renal acid-base balance (eg. nephrolithiasis, osteoporosis) and NaC1 transport (eg. hypertension, congestive heart failure).