Mechanisms of arsenic transport in kidney & bladder

以生理学为基础的动力学模型正越来越多地被纳入对接触毒物所产生的风险的评估中，几年来，人们一直在积极研究包括砷在内的金属的动力学行为模型的开发。几年来，人们一直在积极研究一种合理的方法来建立包括砷在内的金属的动力学行为模型。一个合理的方法来开发一个复杂的动力学模型，如砷所需的（与几种化学形式，它可以采取）涉及建立模型的最基本的组件，在此基础上可以建立更高水平的相互作用。靶组织细胞的暴露首先需要毒物穿过细胞膜到达中毒的细胞内位点。这可以通过输出化学上不同形式的毒物，然后可以作为远距离站点的底物。因此，知识的途径和速率的砷通量穿过靶组织细胞膜必须被认为是一个基本要素的发展和最终的校准和验证的生理动力学模型的砷行为。本提案有两个主要目的，即阐明在体内消除砷的两个组织/器官系统细胞内的主要砷转运过程：肾脏（重点是近端小管）和膀胱（这是砷致癌性的重要靶点）。本提案中概述的研究将首次确定砷的主要形式如何进入和离开肾脏细胞。具体而言，我们将定义As（III），As（V），甲基胂酸和二甲基胂酸的细胞转运机制，并确定其在每个测试组织中的转运动力学。我们将测试的一般假设，即几种砷物种与细胞内谷胱甘肽的相互作用产生了深远的影响，砷从细胞的出口，因此，影响其他靶细胞暴露的砷物种的性质。我们还将测试新的假设，内吞作用起着定量的重要作用，在进入和暴露于砷在膀胱细胞。我们的方法包括比较与完整组织获得的效果与那些获得单克隆转运蛋白。后一种系统将允许对单个转运蛋白的性质进行重点检查，而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转运的唯一手段。这些数据将提供一种手段，运输过程中的整体砷通量在这些组织。这些结果可以预期提供所需的改进正在进行的努力，以开发一个基于生理的动力学模型的砷在生物系统中的行为。

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.