REGULATION OF RENAL CALCIUM TRANSPORT BY CALCIUM

肾脏过滤并重新吸收大量的钙。远端 曲管是荷尔蒙调节的主要部位。 进程。对其调控机制知之甚少。 然而，钙的运输。存在一种钙敏感受体(CAR)。 在远端小管中，但该受体的作用 未知。汽车的预期作用将是抑制钙离子 高钙血症时的重吸收，导致尿丢失增加 钙离子的含量。我们有初步数据显示，这种车抑制了钙离子的转运 在远端小管细胞培养模型中，这一规定要求 一种蛋白激酶。我们假设钙离子会抑制自身的运输。 通过降低质膜Ca~(2+)-ATPase活性。这 该提案将调查汽车使用的信号转导路径 调节MDCK和DCT细胞的钙转运。具体的 调节钙离子转运所需的分子将被确定 使用特定的药理和显性的这些负性抑制物 信号分子。将使用类似的方法来确定 信号通路是钙离子排出和吸收所必需的。 将确认由CAR激活第二个信使。终于 细胞外钙对磷酸化状态的直接影响， 质膜钙ATPase的表面定位和活性， 究竟是哪种钙离子泵出细胞，将会被确定。预期中的 这些研究的结果是对信号转导的理解 负责调节钙转运的级联反应。这些 研究将有助于确定调节钙的机制。 在远端小管中排泄和重吸收。了解这些 机制将有助于阐明钙的正常生理 以及确定更有效的治疗方法 高钙血症与恶性肿瘤、甲状旁腺功能亢进症等 原因和慢性钙丢失，发生在 骨质疏松症和免疫抑制的结果。

The kidney filters and reabsorbs large amounts of calcium. The distal convoluted tubule is the primary site for hormonal regulation of this process. Relatively little is known about the mechanisms regulating calcium transport, however. A calcium-sensing receptor (CaR) is present in the distal tubule but the role of this receptor has been previously unknown. An expected role for the CaR would be to inhibit Ca2+ reabsorption during hypercalcemia, resulting in increased urinary loss of Ca2+. We have preliminary data that the CaR inhibits Ca2+ transport in a distal tubule cell culture model and that this regulation requires a protein kinase. We hypothesize that Ca2+ inhibits its own transport through decreased activity of the plasma membrane Ca2+ ATPase. This proposal will investigate the signal transduction pathways the CaR uses to regulate Ca2+ transport in MDCK and DCT cells. The specific molecules necessary for regulation of Ca2+ transport will be determined using specific pharmacological and dominant negative inhibitors of these signaling molecules. A similar approach will be used to determine which signaling pathways are necessary for Ca2+ extrusion and uptake. Activation of second messengers by the CaR will be confirmed. Finally the direct effects of extracellular calcium on phosphorylation state, surface localization and activity of the plasma membrane calcium ATPase, which pumps Ca2+ out of the cell, will be determined. The anticipated result of these studies is an understanding of the signal transduction cascade that is responsible for regulation of calcium transport. These studies will help determine the mechanisms that regulate calcium excretion and reabsorption in the distal tubule. Understanding these mechanisms will help elucidate both the normal physiology of calcium homeostasis as well as to determine more effective treatments for hypercalcemia associated with malignancy, hyperparathyroidism and other causes and with the chronic loss of calcium which occurs with osteoporosis and as a result of immunosupression.