噻嗪类药物引起的低钙尿症伴有肾脏中钙离子转运蛋白表达的降低。
Thiazide-induced hypocalciuria is accompanied by a decreased expression of Ca2+ transport proteins in kidney.
作者信息
Nijenhuis Tom, Hoenderop Joost G J, Loffing Johannes, van der Kemp Annemiete W C M, van Os Carel H, Bindels René J M
机构信息
Department of Cell Physiology, Nijmegen Center for Molecular Life Sciences, University Medical Center Nijmegen, Nijmegen, The Netherlands.
出版信息
Kidney Int. 2003 Aug;64(2):555-64. doi: 10.1046/j.1523-1755.2003.00128.x.
INTRODUCTION
Thiazide diuretics have the unique characteristic of increasing renal Na+ excretion, while decreasing Ca2+ excretion. However, the molecular mechanism responsible for this thiazide-induced hypocalciuria remains unclear. The present study investigates the effect of thiazides on the expression of the proteins involved in active Ca2+ transport as well as the role of extracellular volume (ECV) status.
METHODS
Hydrochlorothiazide (HCTZ), 12 mg/24 hours, was administered during 7 days to Wistar rats by osmotic minipumps. In addition, ECV contraction was either prevented by Na+ repletion or induced by a low-salt diet. Expression levels of the proteins involved in active Ca2+ transport [i.e., epithelial Ca2+ channel (TRPV5/ECaC1), calbindin-D28K, Na+/Ca2+ exchanger (NCX1)], as well as the thiazide-sensitive Na+ Cl- cotransporter (NCC) were determined by real-time quantitative polymerase chain reaction (PCR) and semiquantitative immunohistochemistry.
RESULTS
HCTZ significantly reduced urinary Ca2+ excretion (22%+/- 5% relative to controls). Hematocrit was significantly increased, confirming ECV contraction. In addition, Na+ depletion virtually abolished Ca2+ excretion (8%+/- 1%), while Na+ repletion during HCTZ treatment prevented both ECV contraction and hypocalciuria. HCTZ significantly decreased mRNA expression of TRPV5 (71%+/- 6%), calbindin-D28K (53%+/- 6%), NCX1 (51%+/- 8%) and NCC (50%+/- 11%), regardless of ECV status or calciuresis. Immunohistochemistry revealed reduced TRPV5 (43%+/- 2%), calbindin-D28K (59%+/- 1%) and NCC (56%+/- 4%) abundance. Furthermore, during HCTZ treatment, the subset of tubules coexpressing NCC and calbindin-D28K was significantly reduced (43%+/- 5%) and a disturbed cellular localization of NCC was observed.
CONCLUSION
These data suggest that ECV contraction is a critical determinant of the thiazide-induced hypocalciuria, which is accompanied by a decreased expression of Ca2+ transport proteins.
引言
噻嗪类利尿剂具有独特的特性，即增加肾脏钠排泄，同时减少钙排泄。然而，噻嗪类药物引起低钙尿症的分子机制仍不清楚。本研究探讨了噻嗪类药物对参与活性钙转运的蛋白质表达的影响以及细胞外液量（ECV）状态的作用。
方法
通过渗透微型泵向Wistar大鼠连续7天给予12mg/24小时的氢氯噻嗪（HCTZ）。此外，通过补充钠预防ECV收缩或通过低盐饮食诱导ECV收缩。通过实时定量聚合酶链反应（PCR）和半定量免疫组织化学测定参与活性钙转运的蛋白质[即上皮钙通道（TRPV5/ECaC1）、钙结合蛋白-D28K、钠/钙交换器（NCX1）]以及噻嗪类敏感的钠氯共转运体（NCC）的表达水平。
结果
HCTZ显著降低尿钙排泄（相对于对照组降低22%±5%）。血细胞比容显著增加，证实了ECV收缩。此外，钠耗竭几乎消除了钙排泄（8%±1%），而HCTZ治疗期间补充钠可预防ECV收缩和低钙尿症。无论ECV状态或钙尿症如何，HCTZ均显著降低TRPV5（71%±6%）、钙结合蛋白-D28K（53%±6%）、NCX1（51%±8%）和NCC（50%±11%）的mRNA表达。免疫组织化学显示TRPV5（43%±2%）、钙结合蛋白-D28K（59%±1%）和NCC（56%±4%）丰度降低。此外，在HCTZ治疗期间，共表达NCC和钙结合蛋白-D28K的肾小管亚群显著减少（43%±5%），并且观察到NCC的细胞定位紊乱。
结论
这些数据表明，ECV收缩是噻嗪类药物引起低钙尿症的关键决定因素，同时伴有钙转运蛋白表达降低。
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