Renal Physiology of Pendrin

哺乳动物的肾脏有很大的排泄碱性负荷的能力。例如，啮齿类动物在其饮用水中给予等渗NaHCO3，尽管有巨大的碱负荷，但只会发生轻度代谢性碱中毒。肾脏排泄大量碱性负荷的能力部分是通过B插层细胞顶端阴离子交换介导的皮质收集管（CCD）中活跃的HCO3-分泌来实现的。虽然顶端阴离子交换在CCD中的功能已经被表征，但介导这一转运过程的基因产物仍然是一个有争议的领域。然而，我们的实验室和我们的合作者的工作已经证明，pendrin，阴离子交换剂，定位于大鼠，人类和小鼠的非a嵌入细胞的顶膜。此外，我们的实验室已经证明penddrin介导小鼠CCD中HCO3-的分泌。这种转运体是否代表假定的顶端阴离子交换剂仍有待充分测试。基因敲除小鼠的建立，极大地促进了penddrin体内肾生理的研究。由于没有特定的penddrin或根尖阴离子交换抑制剂可用，敲除小鼠可以作为一种生物抑制剂，并用于测试penddrin在体外肾脏中的运输特性。此外，利用这些动物进行的平衡研究将使我们能够确定这些penddrin缺乏的小鼠在排泄碱性负荷方面是否存在缺陷。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体的生理作用。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、体外小管灌注、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pendin缺陷小鼠。该项目的具体目标是：1。为了确定penddrin在天然肾组织中的转运特性，为了确定代谢性碱中毒期间肾脏中的penddrin是否上调。目的：确定pendrin和4的肾表型。目的：确定肾内潘度素的定位。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.