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How renal cells handle urea [Review]

机译：肾细胞如何处理尿素[评论]

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摘要

The urine concentration process requires an osmolality gradient along the renal cortico-medullary axis, with highest values in the renal papilla, NaCl and urea are the major solutes in the renal inner medulla, concentrations of urea up to 500-600 mM are found in the rat renal papilla. Urea can diffuse across cell membranes and contributes to balance intracellular and extracellular osmotic equilibrium. However, urea has perturbing effects on enzyme activity, and in concentrations above 300 mM is toxic for renal cultured cells. There is increasing evidence that urea can induce cellular responses distinct from those due to NaCl and other non-permeable solutes, including upregulation of immediate-early genes (IEGs). Urea transport by epithelial and endothelial cells is important for intra-medullary urea recycling and preservation of high urea concentration in the inner medulla, Transcellular movement of urea in cells expressing urea transporters may influence intracellular levels of this solute and modulate urea-induced signaling pathways. Regulation of urea transporters expression and activity can therefore be viewed as one aspect of cellular adaptation to urea. We have identified tonicity-responsive transcription as one mechanism regulating expression of the urea transporter UT-A. The shortterm and long-term effects of variable extracellular urea concentration on the function of renal cells remain still unclear. Copyright (C) 2000 S. Karger AG. Basel. [References: 43]
机译：尿液浓缩过程需要沿肾皮质-髓质轴的渗透压梯度，肾乳头中的最高值是NaCl和尿素，是肾内髓质中的主要溶质，尿液中的尿素浓度高达500-600 mM。大鼠肾乳头。尿素可以在细胞膜上扩散，并有助于平衡细胞内和细胞外的渗透平衡。然而，尿素对酶活性具有干扰作用，并且浓度高于300 mM对肾培养细胞有毒。越来越多的证据表明，尿素可以诱导不同于NaCl和其他不可渗透溶质的细胞反应，包括立即早期基因（IEG）的上调。上皮细胞和内皮细胞的尿素运输对于髓内尿素的回收和内髓质中高尿素浓度的保存很重要。尿素在表达尿素转运蛋白的细胞中的跨细胞运动可能影响该溶质的细胞内水平并调节尿素诱导的信号通路。因此，尿素转运蛋白表达和活性的调节可被视为细胞对尿素适应的一方面。我们已经确定张力调节转录为调节尿素转运蛋白UT-A表达的一种机制。可变的细胞外尿素浓度对肾细胞功能的短期和长期影响仍然不清楚。版权所有（C）2000 S. Karger AG。巴塞尔[参考：43]

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