Mechanisms of arsenic transport in kidney & bladder

基于生理学的动力学模型越来越多地被纳入毒物暴露风险的评估中，几年来一直在积极研究开发包括砷在内的金属的动力学行为模型。一种合理的方法来发展模型的金属，包括砷的动力学行为，已经积极地研究了几年。建立一个复杂的动力学模型的合理方法，比如砷（它可以有几种化学形式）需要首先建立模型的最基本组成部分，在此基础上可以建立更高层次的相互作用。对靶组织细胞的暴露首先要求毒物穿过细胞膜到达中毒的细胞内部位。随后可以出口化学上不同形式的毒物，然后作为远距离地点的底物。因此，砷通过靶组织细胞膜的途径和速率的知识必须被认为是发展和最终校准和验证砷行为的生理动力学模型的基本要素。本提案有两个主要目的，即阐明在消除体内砷的两个组织/器官系统的细胞内的主要砷运输过程：肾脏（重点是近端小管）和膀胱（这是砷致癌性的重要目标）。本提案概述的研究将首次确定，主要形式的砷是如何进入和离开肾脏细胞的。本提案概述的研究将首次确定，主要形式的砷是如何进入和离开肾脏和膀胱细胞的。具体来说，我们将定义As(III), As(V)，甲基larsonic acid和二甲基larsinic acid的细胞运输机制，并确定它们在每个测试组织中的运输动力学。我们将检验这样一个一般假设，即几种砷与细胞内谷胱甘肽的相互作用对砷从细胞中输出产生深远影响，从而影响其他靶细胞所暴露的砷的性质。我们还将测试新的假设，即内吞作用在膀胱细胞进入和暴露于砷中起定量重要作用。我们的方法包括比较完整组织获得的效果与获得单个克隆转运蛋白的效果。后一种系统将允许对单个转运体的特性进行重点检查，前者提供了评估一套过程的综合活性如何影响砷的净细胞运输的唯一手段。这些数据将为砷在这些组织中的总通量的运输过程提供一种手段。这些结果有望为正在进行的开发砷在生物系统中行为的基于生理的动力学模型提供所需的改进。

Physiologically-based kinetic models are increasingly being incorporated into the assessment of risk arising from exposure to toxicants, and development of models on the kinetic behavior of metals, including arsenic, has been actively investigated for several years. A rational approach to the development of models on the kinetic behavior of metals, including arsenic, has been actively investigated for several years. A rational approach to the development of a complex kinetic model such as that required for arsenic (with the several chemical forms that it can take) involves establishing the most fundamental components of the model first, upon which higher levels of interaction can be built. Exposure of the cells of target tissues requires first that the toxicant cross cell membranes to access intracellular sites of intoxication. This can be followed by export of chemically different forms of the toxicant which can then serve as substrate for distant sites. Consequently, knowledge of the pathways and rates of arsenic flux across target tissue cell membranes must be considered a fundamental element in the development and ultimate calibration and validation of a physiological kinetic model of arsenic behavior. The present proposal has two principal aims, namely the elucidation of the major arsenic transport processes within cells of two tissue/organ systems which play central roles in the elimination of arsenic from the body: the kidney (with an emphasis on the proximal tubule), and the urinary bladder (which is an important target of arsenic carcinogenicity). The studies outlined in this proposal will determine, for the first time, how the major forms of arsenic enter and leave cells of the kidney studies outlined in this proposal will determine, for the first time, how the major forms of arsenic enter and leave cells of the kidney and bladder. Specifically, we will define the mechanisms of cellular transport of As(III), As(V), methylarsonic acid and dimethylarsinic acid, and determine the kinetics of their transport in each test tissue. We will test the general hypothesis that interactions of several arsenic species with intracellular glutathione exerts a profound effect on the export of arsenic from cells and therefore, influences the nature of the arsenic species to which other target cells are exposed. We will also test the novel hypothesis that endocytosis plays a quantitatively significant role in the entry and exposure to arsenic in bladder cells. Our approach involves comparison of effects obtained with intact tissues with those obtained single cloned transport proteins. The latter system will permit a well- focused examination of the properties of single transporters, with the former provides the only means to assess how the integrate activity of a suite of processes influences net cellular transport of arsenic. These data will provide a means for transport processes on overall arsenic flux in these tissues. These results can be expected to provide needed refinements to ongoing efforts to develop a physiologically-based kinetic model for the behavior of arsenic in biological systems.