REGULATION OF RENAL CALCIUM TRANSPORT BY CALCIUM

肾脏过滤和重吸收大量的钙。 远侧 曲小管是激素调节这一过程的主要场所。 过程 相对而言，人们对调节 钙的运输。 存在钙敏感受体（CaR） 但这种受体的作用以前一直是 未知 CaR的预期作用是抑制Ca 2 + 高钙血症期间的重吸收，导致尿丢失增加 的Ca 2+。 我们有初步数据表明CaR抑制Ca 2+转运 在远端小管细胞培养模型中， 蛋白激酶。 我们假设Ca 2+抑制其自身的运输， 通过降低细胞膜Ca ~（2+）ATP酶的活性。 这 该提案将研究CaR使用的信号转导途径 调节MDCK和DCT细胞的Ca ~（2+）转运。 具体 将确定调节Ca 2+转运所必需的分子 使用这些的特定药理学和显性负抑制剂， 信号分子 类似的方法将用于确定 信号传导途径对于Ca 2+的挤出和摄取是必需的。 将确认CaR激活第二信使。 最后 细胞外钙离子对磷酸化状态的直接影响， 质膜钙ATP酶的表面定位和活性， 将Ca 2+泵出细胞。 预期 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， 在远端小管中的排泄和重吸收。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， 与恶性肿瘤、甲状旁腺功能亢进和其他相关高钙血症 导致和与慢性损失的钙，发生与 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.