Mechanisms of arsenic transport in kidney & bladder

基于生理的动力学模型越来越多地被纳入到毒物暴露风险的评估中，包括砷在内的金属的动力学行为模型的开发已经被积极地研究了几年。几年来，人们一直在积极研究开发包括砷在内的金属动力学行为模型的合理方法。开发复杂的动力学模型，如砷所需的动力学模型(具有它可以采取的几种化学形式)的合理方法包括首先建立模型的最基本组件，在此基础上可以建立更高水平的相互作用。暴露靶组织的细胞首先要求毒物穿过细胞膜进入细胞内中毒部位。紧随其后的是出口化学上不同形式的毒物，然后这些毒物可以作为遥远地点的底物。因此，了解砷通过靶组织细胞膜的途径和速率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。目前的建议有两个主要目的，即阐明两个组织/器官系统的细胞内主要的砷运输过程，这两个组织/器官系统在体内消除砷的过程中发挥核心作用：肾脏(重点是近端小管)和膀胱(这是砷致癌的重要目标)。本提案中概述的研究将首次确定主要形式的砷进入和离开肾脏细胞的方式。具体地说，我们将定义As(III)、As(V)、甲基砷酸和二甲基砷酸的细胞转运机制，并确定它们在每个测试组织中的转运动力学。我们将检验这一普遍假设，即几种砷物种与细胞内谷胱甘肽的相互作用对细胞输出砷产生深远影响，从而影响其他靶细胞接触的砷物种的性质。我们还将测试这一新的假设，即内吞作用在进入和暴露于膀胱细胞中的砷的数量上起着重要的作用。我们的方法包括比较从完整组织获得的效果与获得的单个克隆运输蛋白的效果。后一种系统将允许对单一转运体的性质进行重点检查，而前者提供了评估一系列过程的综合活动如何影响砷的细胞净转运的唯一手段。这些数据将为这些组织中总砷通量的运输过程提供一种手段。可以预期，这些结果将为正在进行的努力提供必要的改进，以开发生物系统中砷行为的基于生理的动力学模型。

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.