Molecular Mechanisms of Proximal Tubule Ion Transport

描述(由申请人提供)：本提案将继续 一项长期的研究计划，旨在识别和表征 离子交换器介导酸碱和NaC_1在近端的转运 小管。在近端小管中，主要的根尖膜通路 Na+的吸收和H+的分泌是Na+-H+交换。氯离子吸收范围 肾单位段的顶膜由几种不同的 C_1-碱交换过程，包括CL-甲酸盐交换。1-草酸 交换和Cl--OH-交换。在过去的项目期间，我们使用了 证明NHE3是异构体的各种实验方法 主要负责近端根尖膜的Na+-H+交换 小管。此外，我们还制备并使用了抗NHE3的单抗 发现NHE3结构的意想不到的方面，包括它的 寡聚体与二肽基肽酶IV的结合及其事实 C末端亲水性“细胞质”结构域中的表位是 实际上是外质。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。我们建议将其描述为 这种新的NHE异构体的功能性质并确定它是否是 表达于近端肾小管和/或其他肾单位节段。最后，我们 已经确定了一种表达在顶端的新型阴离子转运蛋白 近端小管细胞膜，并介导甲酸交换(CFEX)。我们 计划更详细地描述CFEX的功能特性，并将 寻求确定可能导致心尖部疾病的其他转运蛋白 近端肾小管CL--碱基交换。总而言之，拟议的研究 应加强对Na+、HCO3-和CI-机理的认识 肾脏中的转运，这与由 肾脏酸碱平衡的改变(例如。肾结石、骨质疏松症)和 氯化钠运输(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).