Yancey P H, Burg M B
Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
Am J Physiol. 1990 Jan;258(1 Pt 2):R198-204. doi: 10.1152/ajpregu.1990.258.1.R198.
Urea and methylamines, such as betaine, are among the major organic osmotic effectors accumulated by organisms under hyperosmotic (high NaCl) stress; the mammalian renal medulla also accumulates such compounds in antidiuresis. Studies on isolated proteins show that urea generally destabilizes protein structure, whereas methylamines are generally stabilizers capable of offsetting the effects of urea. The counteracting-osmolytes hypothesis predicts that cells exposed to high urea concentrations require methylamines for optimal function. In this study, urea, betaine, and other solutes (NaCl, glycerol, sorbitol) were added to growth medium of cultured mammalian cells under conditions in which most solutes entered the cells. For two renal [Madin-Darby canine kidney (MDCK) and PAP-HT25] and one nonrenal (Chinese hamster ovary) cell line, urea (greater than 100 mM) or betaine (greater than 50-100 mM) alone inhibited cell growth and survival, measured as colony-forming efficiency. However, the addition of betaine (up to 120 mM) to media with urea (50-300 mM) greatly increased colony-forming efficiency above that with urea alone. A similar, although less marked effect, was seen on colony sizes with MDCK cells. These results support the counteracting-osmolytes hypothesis.
尿素和甲胺类物质，如甜菜碱，是生物体在高渗（高氯化钠）应激下积累的主要有机渗透效应物；哺乳动物肾髓质在抗利尿过程中也会积累此类化合物。对分离出的蛋白质的研究表明，尿素通常会使蛋白质结构不稳定，而甲胺类物质通常是能够抵消尿素作用的稳定剂。抗渗透压溶质假说预测，暴露于高尿素浓度下的细胞需要甲胺类物质才能实现最佳功能。在本研究中，在大多数溶质进入细胞的条件下，将尿素、甜菜碱和其他溶质（氯化钠、甘油、山梨醇）添加到培养的哺乳动物细胞的生长培养基中。对于两种肾细胞系[麦迪逊-达比犬肾（MDCK）细胞系和PAP-HT25细胞系]和一种非肾细胞系（中国仓鼠卵巢细胞系），单独的尿素（大于100 mM）或甜菜碱（大于50 - 100 mM）会抑制细胞生长和存活，以集落形成效率来衡量。然而，在含有尿素（50 - 300 mM）的培养基中添加甜菜碱（高达120 mM），会使集落形成效率比单独使用尿素时大幅提高。在MDCK细胞的集落大小方面也观察到了类似但不太明显的效果。这些结果支持了抗渗透压溶质假说。
