CALCIUM RECEPTOR SIGNALING OF P450 ARACHIDONIC ACID METABOLITES

本计划项目的项目#3中要探索的假设是 细胞色素P450（P450）花生四烯酸（AA）代谢物提供了一种 细胞外钙/多价阳离子的主要信号系统- G蛋白偶联受体（CaSR）在哺乳动物的肾脏。遗传 对人类和实验动物的生理学研究表明， CaSR不仅对细胞外钙依赖性 调节甲状旁腺激素形成甲状旁腺，而且还用于 肾脏正常处理二价矿物质。CaSR表示为 哺乳动物肾脏肾单位的许多上皮节段，特别是在 形成最初近端小管的细胞的尿液面和 亨利氏袢升段血间质面 称为厚上升翼（TAL）。由于盐的运输过程中， 近端小管和TAL都参与调节二价 矿物质离子的排泄，这些肾单位段中的CaSR的激活， 预期调节尿中钙和镁的流失。调制 这些节段中CaSR的转运过程也改变了肾脏 盐和水的排泄，有助于确保钙 镁可以排出体外，降低肾结石的可能性 形成或肾钙质沉着。具体地说，钙激活的 TAL中的CaSR功能与内源性“袢”利尿剂相同， 一种机制可以解释膳食钙摄入的有益作用 在实验室动物和人身上观察到的血压。 分子、生物化学和生理学方法，我们将：a） 鉴定参与CaSR信号传导的特异性P450基因， 肾小管上皮细胞; B）定义特异性P450 omega/omega-1 通过激活CaSR产生的AA代谢物; c）鉴定 CaSR-P450信号传导途径的酶组分;和 CaSR作用对盐运移过程的生理效应。结果 这些研究应该明确CaSR在肾脏调节中的作用， 二价矿物质平衡和盐和水平衡。

The hypothesis to be explored in Project #3 of this Program Project is that cytochrome P450 (P450) arachidonic acid (AA) metabolites provide a major signaling system for the extracellular calcium/polyvalent cation- sensing G protein-coupled receptor (CaSR) in the mammalian kidney. Genetic and physiological studies in man and laboratory animals have demonstrated that the CaSR is crucial not only for the extracellular calcium-dependent regulation of parathyroid hormone form parathyroid glands, but also for normal divalent mineral handling by the kidney. The CaSR is expressed in many epithelial segments of the mammalian kidney nephron, particularly at the urinary face of cells forming the initial proximal tubule and at the blood-interstitial face of the ascending segment of the loop of Henle called the thick ascending limb (TAL). Since salt transport processes in both the proximal tubule and TAL are involved in regulated divalent mineral ion excretion, activation of the CaSR in these nephron segments is expected to modulate calcium and magnesium loss in the urine. Modulation of transport processes by the CaSR in these segments also alter the kidney excretion of salt and water, processes that help to ensure that calcium and magnesium can be excreted with a reduced likelihood for kidney stone formation or nephrocalcinosis. Specifically, calcium activation of the CaSR in the TAL functions as in endogenous "loop" diuretic, and this mechanism may account for the beneficial effect of dietary calcium intake on blood pressure seen in laboratory animals and man. Using a combination of molecular, biochemical and physiological approaches, we will: a) identify the specific P450 gene(s) involved in CaSR signaling in the kidney tubule epithelial cells; b) define the specific P450 omega/omega-1 AA metabolites generated by activation of the CaSR; c) identify the enzymatic components of the CaSR-P450 signaling pathway; and d) define the physiological effects of CaSR action on salt transport process. Results of these studies should define roles for the CaSR in the renal regulation of divalent mineral homeostasis and salt and water balance.