Morel F, Hus-Citharel A, Levillain O
Laboratoire de Physiologie Cellulaire, Collège de France, Paris.
Kidney Int. 1996 Jun;49(6):1608-10. doi: 10.1038/ki.1996.233.
By using an in vitro single tubule micromethod of high specificity, in four different species of mammals it has been observed that (a) arginine synthesis from citrulline (arginine synthase activity, E.C. 6.3.4.5 and E.C. 4.3.2.1) is restricted to the early portions of proximal convoluted tubules, whereas (b) urea production from arginine (arginase activity, E.C. 3.5.3.1.) is present mainly in the cortical (CPST) and even more in the outer medullary (OSPST) portions of straight proximal tubules. The data suggest that (a) in early PCT cells, the citrulline reabsorbed from glomerular filtrate is converted into arginine, which in turn crosses peritubular cell membranes together with reabsorbed arginine, and (b) the urea formed in CPST and OSPST cells might passively diffuse into the luminal fluid entering Henle's loops. Such urea secretion might contribute to sustain the process of urea recycling in kidney medulla and thereby participate in the mechanism of urine concentration.
通过使用一种具有高特异性的体外单肾小管微方法，在四种不同的哺乳动物物种中观察到：(a) 从瓜氨酸合成精氨酸（精氨酸合酶活性，酶编号6.3.4.5和4.3.2.1）仅限于近端曲管的起始部分，而(b) 从精氨酸产生尿素（精氨酸酶活性，酶编号3.5.3.1）主要存在于近端直小管的皮质部（CPST），在外髓部（OSPST）中含量更高。数据表明：(a) 在近端曲管起始段细胞中，从肾小球滤液中重吸收的瓜氨酸转化为精氨酸，精氨酸继而与重吸收的精氨酸一起穿过肾小管周围细胞膜，以及(b) 在CPST和OSPST细胞中形成的尿素可能被动扩散到进入髓袢的管腔液中。这种尿素分泌可能有助于维持肾髓质中的尿素循环过程，从而参与尿液浓缩机制。
