CORE--ELECTROPHYSIOLOGY CORE

本核心的目的是为研究上皮ca2 +通道（ECaC）和组分I、III和IV中的电致钠/二羧酸盐共转运体（NaDC-1）提供支持。ECaC通道存在于肠的顶端膜和肾脏的远端弯曲小管（DCT）中，并作为这些部位的跨细胞ca2 +运输的门卫。ECaC是许多调节胃肠道和肾脏ca2 +吸收的激素的主要靶点，如甲状旁腺激素、维生素D等(1)。最近，Bindels博士(2)和Hediger博士的研究小组（3,4）分别分离出了ECaC及其亚型的cdna。我们也从Dr. Bindels（本核心的顾问）那里分离出了兔ECaC1的cDNA，并获得了小鼠ECaC2的cDNA。近端小管中的NaDC-1重新吸收过滤过的克雷布斯循环中间体，并在调节尿中柠檬酸盐浓度中起重要作用(5)。低尿柠檬酸盐是肾结石形成的重要危险因素。在成分一中，我们将检验蛋白质产物与吸收性高钙尿症（AH）相关的假设

The purpose of this core is to provide support for studies on epithelial Ca 2+ channels (ECaC) and the electrogenic sodium/dicarboxylate co-transporter (NaDC-1) in components I, III, and IV. ECaC channels are present in the apical membrane of intestine and the distal convoluted tubule (DCT) of kidney and serve as gatekeepers for transcellular Ca 2+ transport in these sites. ECaC is a major target for many hormones that regulate gastrointestinal and kidney Ca 2+ absorption, such as parathyroid hormone, vitamin D, etc (1). cDNAs for ECaC and its isoforms have recently been isolated by Dr. Bindels' (2) and Dr. Hediger's groups (3, 4) independently. We have also isolated cDNA for rabbit ECaC1 and obtained cDNA for mouse ECaC2 from Dr. Bindels (consultant for this core) NaDC-1 in the proximal tubules reabsorbs filtered Krebs cycle intermediates and plays an important role in the regulation of urinary citrate concentrations (5). Low urinary citrate is an important risk factor for formation of kidney stone. In component I, we will test the hypothesis that protein product of an absorptive hypercalciuria (AH)-related gene, AH-related adenylate cyclase (AHRAC), regulates ECaC channel activity. In component III project 1, we will investigate the role of intracellular vs extracellular pH in the regulation of the electrogenic NaDC-1 (6). In component III project 2, we will test the hypothesis that acid inhibition of ECaCl-mediated Ca 2+ reabsorption in DCT contributes to the hypercalciuria induced by a high dietary protein intake and the hypothesis that membrane phospholipid, phosphatidylinositol 4,5-bisphosphate (PIP2) regulates ECaC1 channel activity. In component IV, we will test the hypothesis that down-regulation of calbindin-D28k by estrogen lack (in addition to the downregulation of ECaC) is important for renal calcium. leak and examine the molecular mechanism by which calbindin- D28k regulates Ca 2+ reabsorption through ECaC.