Genetic Models for Disorders of Acid-Base Transport

描述（由申请人提供）：我们的目标是了解碳酸氢盐和质子转运体在上皮离子转运中的功能和耦合模式。HCO3和H由H2 O和CO2通过碳酸酐酶活性产生，并通过Na/H交换体（NHE1-4）、Cl/HCO交换体（AE1-4、PAT1、DRA）、Na- HCO3共转运体（NBCe1、NBCe2）、H、K-ATPases等与其他离子的转运偶联。在耦合系统中，它们介导胃酸分泌；维持肠内内容物的流动性和pH值；回收结肠内的离子和水分；控制酸碱、电解质和肾脏排出的液体。为了研究这些问题，我们利用基因消融多种酸碱转运体的小鼠。在Aim 1中，通过验证AE2是平衡HCl分泌的主要基底外侧Cl/HCO3交换剂的假设，将分析胃中HCl分泌和维持壁细胞（PC）活力的机制；AE2与基底侧NHE4 Na/ H交换器耦合进行体积加载；NHE4和NHE2是PC生存所必需的；酸分泌需要CLIC细胞内Cl通道。目的2将验证以下假设：肠道根尖NaCl吸收的减少，涉及Cl/HCO （PAT1， DRA）和Na/H （NHE3）交换的耦合，可以纠正囊性纤维化（CF）的管腔流动性和pH的扰动，并减轻CF肠道疾病的严重程度；基底侧AE2与根尖NHE3和/或结肠H、k - atp酶一起介导肠道对Na-HCO3和K-HCO3的吸收。目的3将测试NBCe1和AE4 Cl/HCO交换器的假设，它们都是肾脏不同部分耦合系统的组成部分，有助于Na-HCO吸收；NBCe2介导了集管内独特的Na-HCO分泌功能；结肠H， k - atp酶有助于K-HCO3在收集管中的吸收。这些研究将扩大我们对允许这些转运体介导吸收和分泌功能的耦合模式的理解。与胃食管反流及其他涉及胃酸分泌的疾病有临床相关性；类腹泻;囊性纤维化肠病；从胃肠道疾病和其他疾病引起的全身酸碱、电解质和液体容量平衡紊乱中恢复的肾脏机制。

DESCRIPTION (provided by applicant): Our objective is to understand the functions and coupling modes of bicarbonate and proton transporters in transepithelial ion transport. HCO 3 and H are generated from H2 O and CO2 via carbonic anhydrase activity and coupled to transport of other ions by Na/H exchangers (NHE1-4), Cl/HCO exchangers (AE1-4, PAT1, DRA), Na- HCO3 cotransporters (NBCe1, NBCe2), H,K-ATPases, and others. In coupled systems, they mediate gastric acid secretion; maintain fluidity and pH of lumenal contents in intestine; recover ions and water in colon; and control acid-base, electrolyte, and fluid excretion by the kidney. To study these issues, we are utilizing mice with genetic ablation of various acid-base transporters. In Aim 1, the mechanisms of HCl secretion in stomach and maintenance of parietal cell (PC) viability will be analyzed by testing the hypotheses that AE2 is the major basolateral Cl/HCO3 exchanger that balances HCl secretion; that AE2 is coupled with the basolateral NHE4 Na/ H exchanger for volume loading; that NHE4 and NHE2 are required for PC viability; and that CLIC intracellular Cl channels are required for acid secretion. Aim 2 will test the hypotheses that reductions in apical NaCl absorption in the intestinal tract involving coupled Cl/HCO (PAT1, DRA) and Na/H (NHE3) exchange can correct perturbations of lumenal fluidity and pH in Cystic Fibrosis (CF) and lessen the severity of CF intestinal disease; and that basolateral AE2 in concert with apical NHE3 and/or colonic H,K-ATPase mediates Na-HCO3 and K-HCO3 absorption in the intestinal tract. Aim 3 will test the hypotheses that NBCe1 and the AE4 Cl/HCO exchanger, each a component of coupled systems in different segments of the kidney, contribute to Na-HCO absorption; that NBCe2 mediates a unique Na-HCO secretory function in the collecting duct; and that the colonic H,K-ATPase contributes to K-HCO3 absorption in the collecting duct. These studies will expand our understanding of the coupling modes that allow these transporters to mediate both absorptive and secretory functions. They have clinical relevance to gastroesophageal reflux and other diseases involving acid secretion; diarrheas; cystic fibrosis intestinal disease; and renal mechanisms for recovery from disorders of systemic acid-base, electrolyte, and fluid-volume homeostasis caused by gastrointestinal and other diseases. PUBLIC HEALTH RELEVANCE: The goal of this project is to understand the functions and interactions of proteins that transport acid (protons) and base (bicarbonate) across cell membranes in the gastrointestinal tract and kidney. To do this we are analyzing mouse models in which these proteins have been mutated. These studies will expand our understanding of the role of these transporters in absorptive and secretory functions, and have clinical relevance to gastroesophageal reflux disease; diarrheas; cystic fibrosis intestinal disease; and renal mechanisms for recovery from disorders of acid-base, electrolyte, and fluid-volume homeostasis caused by gastrointestinal and other diseases.