PATHOPHYSIOLOGY OF HYPERCALCIURIA

本课题的目的是探讨高蛋白摄入引起的高脂血症的病理生理基础 高钙尿症上皮细胞钙通道（ECaC 1）存在于远端的顶膜 肾曲小管（DCT）的钙代谢，在维持整体钙稳态中起重要作用。我们的初步研究结果表明，高钙尿症与高蛋白摄入量，至少部分是由酸抑制ECaC 1介导的钙重吸收DCT。在具体目标1中，我们将研究ECaC 1酸抑制的分子机制。用于ECaC 1的酸调节的“pH传感器”的可能候选者将通过定点突变来突变。 诱变将通过全细胞膜片钳记录检查野生型和突变型通道的活性。膜磷脂，磷脂酰肌醇4，5-二磷酸（PIP 2）具有 最近作为一种独特的通道功能调节剂出现。在具体目标2中，我们将研究PIP 2对ECaC 1通道的调节强调了以下机制的假设： 前列腺素E_2可抑制高蛋白摄入引起的高钙尿症。在具体目标3中，我们将证实管腔酸化抑制远曲小管（DCT）中的Ca 2+重吸收。在体微灌流大鼠DCT，以检查管腔pH值对Ca 2+重吸收的影响。这些研究将有助于了解高钙尿症的机制，不仅在高膳食蛋白摄入量，而且在慢性代谢性酸中毒的条件下。

The goal of this project is investigate pathophysiological basis of high protein intake-induced hypercalciuria. Epithelial Ca 2+ channels (ECaC1) are present in the apical membrane of the distal convoluted tubule (DCT) of kidney and play an important role in the maintenance of overall calcium homeostasis. Our preliminary results indicate that hypercalciuria associated with a high protein intake is, at least partly, caused by acid inhibition of ECaC1-mediated Ca 2+ reabsorption in DCT. In Specific Aim 1, we will examine the molecular mechanism of acid inhibition of ECaC1. Likely candidates of "pH sensor" for acid regulation of ECaC1 will be mutated by site-directed mutagenesis. The activity of wild type and mutant channels will be examined by whole-cell patch-clamp recording. Membrane phospholipid, phosphatidylinositol 4,5-bisphosphate (PIP2) has recently emerged as a unique regulator of channel function. In Specific Aim 2, we will examine the hypothesis that PIP2 regulation of ECaC1 channel underlines the mechanism by which prostaglandin E2 worsens the high protein intake-induced hypercalciuria. In Specific Aim 3, we will confirm that luminal acidification inhibits Ca 2+ reabsorption in the distal convoluted tubules (DCT). In vivo microperfusion of rat DCT will be performed to examine the effect of luminal pH on Ca 2+ reabsorption. These studies will help understand the mechanism of hypercalciuria, not only during high dietary protein intake but also under conditions of chronic metabolic acidosis.