Garcia-Perez A, Burg M B
Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung and Blood Institute, Bethesda, Maryland 20892.
J Membr Biol. 1991 Jan;119(1):1-13. doi: 10.1007/BF01868535.
Kidney cells accumulate organic osmolytes in order to protect themselves from the high concentrations of NaCl and urea in the blood and interstitial fluid of the renal medulla. The renal medullary organic osmolytes are sorbitol, inositol, betaine and GPC. The concentrations of these solutes in renal medullary NaCl and urea concentration, as summarized in Fig. 8 (the putative controlled steps are highlighted). Sorbitol accumulates by synthesis from glucose, catalyzed by aldose reductase. Hypertonicity increases the transcription of the gene that encodes this enzyme. GPC is synthesized from choline, and the amount retained apparently may be controlled by the activity of GPC diesterase, an enzyme that catabolizes GPC. Inositol and betaine are taken up from the medium by sodium-dependent transport, and this transport is increased by hypertonicity. Control of these processes is slow (hours to days), but a decrease in tonicity causes a transient, rapid efflux of the solutes, which prevents the cells from becoming overly distended. Similar strategies are used by all types of cells, including bacteria and those in plants and animals, that can adapt to hyperosmotic stress.
肾细胞积累有机渗透溶质，以保护自身免受肾髓质血液和间质液中高浓度氯化钠和尿素的影响。肾髓质有机渗透溶质包括山梨醇、肌醇、甜菜碱和甘油磷酰胆碱（GPC）。图8总结了这些溶质在肾髓质中的浓度与氯化钠和尿素浓度的关系（突出显示了假定的控制步骤）。山梨醇通过醛糖还原酶催化由葡萄糖合成而积累。高渗性增加了编码该酶的基因的转录。GPC由胆碱合成，其保留量显然可能受GPC二酯酶活性的控制，GPC二酯酶是一种分解GPC的酶。肌醇和甜菜碱通过钠依赖性转运从介质中摄取，这种转运因高渗性而增加。这些过程的控制较慢（数小时至数天），但张力降低会导致溶质短暂、快速外流，从而防止细胞过度膨胀。包括细菌以及植物和动物细胞在内的所有类型的细胞，在适应高渗应激时都采用类似的策略。
