Renal Physiology of Pendrin

哺乳动物的肾脏有很强的排泄碱性物质的能力。例如，啮齿类动物在饮用水中给予等渗NaHCO 3，尽管有巨大的碱负荷，但只会产生轻度的代谢紊乱。肾脏排泄大量碱性负荷的能力部分通过皮质集合管（CCD）中的活性HCO 3-分泌发生，该分泌由B闰细胞中的顶端阴离子交换介导。虽然顶端阴离子交换功能的特点是在CCD，基因产物，介导这一运输过程中一直存在争议。然而，我们实验室的工作和我们的合作者已经证明，pendrin，阴离子交换剂，定位于大鼠，人类和小鼠的非A插入细胞的顶端膜。此外，我们的实验室已经证明，pendrin介导的HCO 3-在小鼠CCD的分泌。这种转运蛋白是否代表假定的顶端阴离子交换器仍有待充分测试。基因敲除小鼠的发展极大地促进了pendrin在体内的肾脏生理学研究。由于没有pendrin或顶端阴离子交换的特异性抑制剂，因此可以利用基因敲除小鼠作为生物抑制剂，并用于体外测试pendrin在肾脏中的转运特性。此外，使用这些动物进行的平衡研究将使我们能够确定这些pendrin缺陷小鼠是否存在碱性负荷排泄缺陷。因此，本提案将测试pendrin是否代表CCD的假定阴离子交换剂。此外，这些研究将有助于我们了解这种转运蛋白的生理作用。为了回答这些问题，我们的实验室和我们的合作者将采用平衡研究，小管灌注在体外，实时定量RT-PCR，免疫金细胞化学和免疫组织化学研究野生型和pendrin缺陷小鼠。该项目的具体目标是：1。为了确定pendrin在天然肾组织中的转运特性，2.为了确定pendrin是否在代谢性肾病期间在肾脏中上调，3.确定pendrin和4.确定pendrin在肾脏的定位。这些研究将有助于我们了解哺乳动物肾脏如何排泄碱性负荷。

The mammalian kidney has a substantial capacity to excrete an alkaline load. For example, rodents given isotonic NaHCO3 in their drinking water develop only a mild metabolic alkalosis despite this huge base load. The kidney's ability to excrete large alkaline loads occurs in part through active HCO3- secretion in the cortical collecting duct (CCD) mediated by apical anion exchange in the B intercalated cell. While apical anion exchange has been characterized functionally in the CCD, the gene product, which mediates this transport process has remained an area of controversy. However the work of our laboratory and that of our collaborators has demonstrated that pendrin, an anion exchanger, localizes to the apical membrane of non-A intercalated cells in rat, human and mouse. Moreover, our laboratory has demonstrated that pendrin mediates secretion of HCO3- in the mouse CCD. Whether this transporter represents the putative apical anion exchanger remains to be tested fully. Development of knockout mice has greatly facilitated the study of the renal physiology of pendrin in vivo. Because there are no specific inhibitors of either pendrin or apical anion exchange available, knockout mice can be exploited as a biological inhibitor and used to test transport characteristics of pendrin in kidney in vitro. Moreover, balance studies using these animals will allow us to determine if these pendrin-deficient mice have a defect in excretion of an alkaline load. Thus, the present proposal will test if pendrin represents the putative anion exchanger of the CCD. Moreover, these studies will contribute to our understanding of the physiological role of this transporter. To answer these questions our laboratory and that of our collaborators will employ balance studies, tubules perfused in vitro, real-time quantitative RT-PCR, immunogold cytochemistry and immunohistochemistry studies in wild type and pendrin-deficient mice. The Specific Aims of the project are: 1. To determine the transport characteristics of pendrin in native renal tissue, 2. To determine if pendrin is upregulated in kidney during metabolic alkalosis, 3. To determine the renal phenotype of pendrin and 4. To determine the localization of pendrin in kidney. These studies will contribute to our understanding of how the mammalian kidney excretes an alkaline load.