Grunewald R W, Reisse C H, Müller G A
Abteilung Nephrologie and Rheumatologie, Universitätsklinik Göttingen, Germany.
Kidney Int. 1998 Jul;54(1):152-9. doi: 10.1046/j.1523-1755.1998.00980.x.
The thick ascending limb of Henle's loop (TALH) is thought to be involved in the regulation of the renal urea gradient.
We have characterized the uptake of urea (oil density centrifugation and 2-compartment-culture) and volume regulation (impedance measurement) in highly differentiated cells derived from rabbit outer medulla.
TALH cells exposed to 600 mOsm/liter (300 mM urea) shrunk to 72 +/- 5% of the isoosmotic volume. Due to a regulatory volume increase (RVI), the cell volume was almost completely regained at 92 +/- 6% after five minutes. The uptake of 14C-urea in the presence of urea concentrations up to 600 mM did not show any saturation. In the presence of phloretin the urea uptake decreased to 69 +/- 14%. The transport was sodium and chloride independent. Changing the membrane potential caused an increase of regulatory volume increase and urea uptake. Hyperosmolarity induced by sucrose (300 mM) and NaCl (150 mM) caused a decrease of urea uptake to 70 +/- 14% and 53 +/- 11%, respectively. The permeability coefficient (P) in a two compartment culture was P = 1.7 . 10(-6) +/- 0.39.10(-6) cm/second, suggesting a relatively low permeability.
Due to the low permeability, it seems impossible to achieve a physiologically significant participation of the TALH in the urea circulation within the nephron. However, the results of this study provides significant hints about the existence of a specific urea transport mechanism that enables the cell to adapt rapidly to different osmolarities.
髓袢升支粗段（TALH）被认为参与肾尿素梯度的调节。
我们已对源自兔外髓的高度分化细胞中的尿素摄取（油密度离心和双室培养）及体积调节（阻抗测量）进行了特性描述。
暴露于600 mOsm/升（300 mM尿素）的TALH细胞收缩至等渗体积的72±5%。由于调节性容积增加（RVI），五分钟后细胞体积几乎完全恢复至92±6%。在尿素浓度高达600 mM的情况下，14C-尿素的摄取未显示任何饱和现象。在根皮素存在的情况下，尿素摄取降至69±14%。该转运不依赖钠和氯。改变膜电位会导致调节性容积增加和尿素摄取增加。由蔗糖（300 mM）和氯化钠（150 mM）诱导的高渗分别导致尿素摄取降至70±14%和53±11%。双室培养中的通透系数（P）为P = 1.7. 10(-6)±0.39.10(-6)厘米/秒，表明通透性相对较低。
由于通透性较低，TALH在肾单位内尿素循环中实现生理上显著的参与似乎不太可能。然而，本研究结果为一种特定尿素转运机制的存在提供了重要线索，该机制使细胞能够快速适应不同的渗透压。
