Membrane Transport of NH3 and NH4+

NH3 和 NH4 的膜传输

• 批准号: 6846627
• 负责人: Nazih Nakhoul
• 金额: $ 26.14万
• 依托单位: TULANE UNIVERSITY OF LOUISIANA
• 依托单位国家: 美国
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-04-01 至 2008-01-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6846627
• 关键词: Xenopus; Xenopus oocyte; acidity /alkalinity; ammonia; biological transport; blood group antigens; fluorescent dye /probe; glycoproteins; intracellular transport; membrane permeability; membrane transport proteins; microelectrodes; molecular cloning; perfusion; protein isoforms; protein structure function; renal tubular transport; tissue /cell culture; voltage /patch clamp; water channel

DESCRIPTION (provided by applicant): Renal production and excretion of NH3/NH4+ play a vital role in acid/base homeostasis and regulation of systemic pH. The classical model of NH3/NH4+ transport proposes that: 1) NH3 crosses cell membranes solely by non-ionic diffusion through the lipid phase of the membrane and 2) NH4+ transport occurs via channels (e.g., K+ channels) or transporters (e.g. Na/K/2CI co-transport or Na-H exchange), mostly as a substitute for K+. Recent studies report new characteristics of NH3/NH4+ transport and regulation that were not previously recognized. A new class of recently cloned membrane proteins, belonging to the Rh antigen family, may function as transporters of NH4+. Other studies indicate that NH3 transport may be facilitated by the presence of water channels (AQP). In addition, NH3 was reported to act as a signaling molecule and recent studies proposed that the Rh proteins may actually be gas channels for NH3 and even CO2. The main objectives of this proposal are to investigate the characteristics of AQPs and Rh glycoproteins with respect to NH3 and NH4+ transport. Specifically we will address the following aims: 1) Transport of NH3 through carrier proteins and the role of AQPs. 2) Characterization of transport properties of Rh glycoproteins. These studies will involve expression of cloned genes (Rh and AQPs) in oocytes to study their transport characteristics. Measurements of intracellular pH and other ions will be obtained by microelectrodes and pH sensitive dyes. Studies will also be conducted on cells in culture and the isolated perfused tubule preparation. Because of the importance of NH3/NH4+ in regulating pH, these studies have significant physiological implications. The possibility that a gas, such as NH3, could be transported through an AQP or another carrier protein, is unique and suggest that its transport could be regulated. NH4+-specific transporters, as Rh glycoproteins may be, have never been described in mammalian cells before. These are new properties of NH3/NH4+ transport that will help explain the role of NH3 and NH4+ in acidosis and their effect on transport of other ions a well.

描述（由申请人提供）：NH3/NH4+的肾脏产生和排泄在酸/碱基稳态中起着至关重要的作用，并调节全身性pH值。 NH3/NH4+转运的经典模型提出：1）NH3仅通过非离子扩散通过膜的脂质相跨越细胞膜，而2）NH4+转运通过通道（例如K+通道）或转运蛋白（例如Na///////// K/2CI共同传输或NA-H交换），主要用作K+的替代品。最近的研究报告说，NH3/NH4+运输和调节的新特征先前未被认可。属于RH抗原家族的新的新的克隆膜蛋白可能是NH4+的转运蛋白。其他研究表明，水道的存在（AQP）可能会促进NH3转运。此外，据报道NH3充当信号分子，最近的研究提出，RH蛋白实际上可能是NH3甚至CO2的气通道。 该提案的主要目标是研究相对于NH3和NH4+转运的AQP和RH糖蛋白的特征。具体而言，我们将解决以下目的：1）NH3通过载体蛋白的运输和AQP的作用。 2）表征RH糖蛋白的转运特性。这些研究将涉及卵母细胞中克隆基因（RH和AQP）的表达以研究其运输特征。细胞内pH和其他离子的测量将通过微电极和pH敏感染料获得。研究还将对培养细胞和分离的灌注小管制剂进行研究。 由于NH3/NH4+在调节pH值中的重要性，这些研究具有显着的生理意义。诸如NH3之类的气体可以通过AQP或其他载体蛋白运输的可能性是独特的，并表明可以调节其运输。 NH4+特异性转运蛋白，作为RH糖蛋白可能是，以前从未在哺乳动物细胞中描述过。这些是NH3/NH4+转运的新特性，它将有助于解释NH3和NH4+在酸中毒中的作用及其对其他离子孔的运输的影响。