Haddad A, Bennett G, Leblond C P
Am J Anat. 1977 Feb;148(2):241-73. doi: 10.1002/aja.1001480205.
The formation and turnover of the glycoproteins of the plasma membrane have been investigated by quantitative radioautography in the kidney tubules of young rats and adult mice killed at various time intervals after an intravenous injection of 3H-fucose. In young (40 g) rats killed five to ten minutes after the injection, radioautographs of distal tubule cells show that the Golgi apparatus contained about 85% of the cell label. By 30 hours, only 8% of the label remained in this organnele, whereas 67% was in the plasma membrane, indicating that most of the label had migrated from Golgi apparatus to this membrane. Similarly, in proximal tubule cells, about 82% of the label was initially in the Golgi apparatus, but less than 2% remained at 30 hours, at which time 78% was in the plasma membrane. In the latter cells, the apical tubules and vacuoles became heavily labeled before the apical microvilli did and, therefore, may be involved in the transit of label from the Golgi apparatus to the microvillous membrane. The results are interpreted to mean that, in kidney tubule cells, the Golgi apparatus is the site of a continuous incorporation of fucose into glycoproteins and that these migrate to the plasma membrane. In fully formed cells, such a conclusion would imply a continuous turnover of plasma membrane glycoproteins. However, in the rapidly growing kidney of young rats many new cells are added daily, the growth of which might involve net addition as well as turnover of glycoproteins. Accordingly, the experiment has been repeated in adult mice, in which the cells are assumed to be fully formed. Furthermore, since turnover implies eventual decrease of incorporated label, some of the animals have been killed at longer intervals, up to 27 days after injection. In these adult mice, as in young rats, prompt Golgi uptake and subsequent migration of label to the plasma membrane were observed in distal and proximal tubules cells. With time the label content of the plasma membrane decreased gradually, and by 27 days had virtually disappeared. From grain counts, it is concluded that the mean half-life of glycoproteins in the apical membrane of distal tubule cells is about two days, whereas in both the apical and basal membranes of proximal tubule cells, it is slightly over three days.
静脉注射³H-岩藻糖后，在不同时间间隔处死幼年大鼠和成年小鼠，通过定量放射自显影技术研究了肾小管质膜糖蛋白的形成和更新。注射后5至10分钟处死的幼年（40克）大鼠，远曲小管细胞的放射自显影片显示，高尔基体含有约85%的细胞标记。到30小时时，该细胞器中仅留存8%的标记，而67%在质膜中，这表明大部分标记已从高尔基体迁移至该膜。同样，在近端小管细胞中，约82%的标记最初在高尔基体中，但30小时时留存不到2%，此时78%在质膜中。在后者细胞中，顶端小管和液泡在顶端微绒毛之前就被大量标记，因此可能参与了标记从高尔基体向微绒毛膜的转运。结果表明，在肾小管细胞中，高尔基体是岩藻糖持续掺入糖蛋白的部位，且这些糖蛋白会迁移至质膜。在完全成熟的细胞中，这一结论意味着质膜糖蛋白的持续更新。然而，在幼年大鼠快速生长的肾脏中，每天会添加许多新细胞，其生长可能涉及糖蛋白的净添加以及更新。因此，在成年小鼠中重复了该实验，假定成年小鼠的细胞已完全成熟。此外，由于更新意味着掺入标记最终会减少，一些动物在注射后更长时间间隔处死，最长达27天。在这些成年小鼠中，与幼年大鼠一样，在远曲小管和近端小管细胞中观察到高尔基体迅速摄取标记，随后标记迁移至质膜。随着时间推移，质膜中的标记含量逐渐降低，到27天时几乎消失。根据颗粒计数得出结论，远曲小管细胞顶端膜中糖蛋白的平均半衰期约为两天，而在近端小管细胞的顶端和基底膜中，半衰期略超过三天。
