OSMOREGULATION OF GPC-CHOLINE PHOSPHODIESTERASE IN MDCK CELLS - DIFFERENT EFFECTS OF UREA AND NACL
OSMOREGULATION OF GPC-CHOLINE PHOSPHODIESTERASE IN MDCK CELLS - DIFFERENT EFFECTS OF UREA AND NACL
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DOI：
10.1152/ajpcell.1995.269.1.c35
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发表时间：
1995-07-01
影响因子：
5.5
通讯作者：
BURG, MB
中科院分区：
文献类型：
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作者：
KWON, ED;ZABLOCKI, K;BURG, MB
有机渗压剂甘油磷酸胆碱（GPC）在肾细胞中蓄积，以响应高浓度的NaCl或尿素，尽管这些溶质对细胞功能和体积的影响非常不同。总之，高水平的这些溶质通过抑制其酶降解增加Madin-Darby犬肾细胞中的GPC量。本研究测试NaCl和尿素的影响，分别对GPC的积累和降解。开发了一种通过测量[H-3]GPC（通过低渗休克脉冲进入细胞）的初始消失速率和GPC在细胞中的比活性来确定GPC降解的绝对速率的技术。GPC在细胞中的质量是通过另一种新开发的方法，一种灵敏的荧光分析来测量的。我们发现，暴露于高氯化钠或尿素降低细胞GPC降解的绝对速率约一半，在第一个20.5小时。GPC降解的减少伴随着GPC活性的相应降低：胆碱磷酸二酯酶（GPC：PDE; EC 3.1.4.2），一种催化GPC降解的酶。在暴露于高渗透压2小时的细胞中，GPC：PDE的活性下降福尔斯> 50%。仅用高尿素抑制持续7天。相比之下，单独使用高NaCl，GPC：PDE活性恢复到对照。值增加7天，此时GPC的合成增加，说明持续的GPC积累。总的来说，这些数据表明，响应于高NaCl或尿素的GPC积累最初通过抑制其降解而发生，但是NaCl对降解的影响不同，因为它是瞬时的，而尿素是持续的。
The organic osmolyte, glycerophosphocholine (GPC), accumulates in renal cells in response to high concentrations of either NaCl or urea, despite the very different effects of these solutes on cell function and volume. Together, high levels of these solutes increase GPC amount in Madin-Darby canine kidney cells by inhibiting its enzymatic degradation. The present study tests the effects of NaCl and urea, individually, on GPC accumulation and its degradation. A technique was developed to determine the absolute rate of GPC degradation by measuring the initial rate of disappearance of [H-3]GPC (pulsed into the cells by hypotonic shock) and the specific activity of GPC in the cells. The mass of GPC in the cells was measured by another newly developed method, a sensitive chemiluminescent assay. We find that exposure to high NaCl or urea decreases the absolute rate of cellular GPC degradation by approximately one-half during the first 20.5 h. Reductions in GPC degradation are accompanied by commensurate decreases in the activity of GPC:choline phosphodiesterase (GPC:PDE; EC 3.1.4.2), an enzyme that catalyzes degradation of GPC. Activity of GPC:PDE falls > 50% in cells exposed for 2 h to high osmolality. Inhibition is sustained for 7 days with high urea alone. In contrast, with high NaCl alone, GPC:PDE activity reverts to control. values by 7 days, by which time synthesis of GPC is increased, accounting for sustained GPC accumulation. Collectively, these data suggest that GPC accumulation in response to either high NaCl or urea occurs initially by inhibition of its degradation but that the effect of NaCl on degradation differs, in that it is transient, while that of urea is sustained.