Genetic Models for Disorders of Acid-Base Transport

描述（由申请人提供）：我们的目的是了解跨上皮离子转运中碳酸氢盐和质子转运蛋白的功能和偶联模式。HCO 3和H通过碳酸酐酶活性由H2 O和CO2产生，并通过Na/H交换剂（NHE 1 -4）、Cl/HCO交换剂（AE 1 -4、PAT 1、NH 4）、Na-HCO 3共转运蛋白（NBCe 1、NBCe 2）、H、K-ATP酶等与其他离子的转运偶联。在偶联系统中，它们介导胃酸分泌;维持肠内腔内容物的流动性和pH值;恢复结肠中的离子和水;并控制肾脏的酸碱、电解质和液体排泄。为了研究这些问题，我们正在利用各种酸碱转运蛋白基因消融的小鼠。在目的1中，将通过检验以下假设来分析胃中HCl分泌和壁细胞（PC）活力维持的机制：AE 2是平衡HCl分泌的主要基底外侧Cl/HCO 3交换器; AE 2与基底外侧NHE 4 Na/ H交换器偶联以进行体积负荷; NHE 4和NHE 2是PC活力所需的;并且CLIC细胞内Cl通道是酸分泌所必需的。目的2将检验以下假设，即在涉及偶联Cl/HCO的肠道中顶端NaCl吸收的减少（PAT 1，PAT 2）和Na/H（NHE 3）交换可纠正囊性纤维化（CF）时肠腔流动性和pH的紊乱，减轻CF肠道疾病的严重程度;并且基底外侧AE 2与顶端NHE 3和/或结肠H，K-ATP酶一起介导肠道中Na-HCO 3和K-HCO 3的吸收。目的3将检验以下假设：NBCe 1和AE 4 Cl/HCO交换器（各自为肾脏不同节段中偶联系统的组成部分）有助于Na-HCO吸收; NBCe 2介导集合管中独特的Na-HCO分泌功能;结肠H，K-ATP酶有助于集合管中的K-HCO 3吸收。这些研究将扩大我们的耦合模式，使这些转运介导的吸收和分泌功能的理解。它们与胃食管反流和涉及酸分泌的其他疾病、食管炎、囊性纤维化肠病以及从由胃肠道和其他疾病引起的全身性酸碱、电解质和液体体积稳态紊乱中恢复的肾脏机制具有临床相关性。 公共卫生相关性：该项目的目标是了解蛋白质的功能和相互作用，这些蛋白质在胃肠道和肾脏中跨细胞膜转运酸（质子）和碱（碳酸氢盐）。为此，我们正在分析这些蛋白质发生突变的小鼠模型。这些研究将扩大我们对这些转运蛋白在吸收和分泌功能中的作用的理解，并与胃食管反流病、食管炎、囊性纤维化肠病和胃肠道和其他疾病引起的酸碱、电解质和液体体积稳态紊乱的肾脏恢复机制具有临床相关性。

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.