Abstract:

Objective The renal distal convoluted tubule (DCT) is the last segment of the nephron. The study on the demarcation, as well as the spatial course and relationship between the DCT and its adjacent tubules, may lay an important structural basis for understanding the mechanism on the morphogenesis of the connection between the collecting duct and the nephrons, and contribute to the understanding on the regulation mechanism of water and salt metabolism in the DCT. The aim of this study is to visualize the course of the mouse distal convoluted tubules with the aid of the three-dimensional reconstruction technology based on the consecutive renal tissue sections. Methods Three C57/BL/6 J mice were fixed via perfusion and embedded in Epon 812. Tissue blocks were cut perpendicularly to the longitudinal axis of the kidney. A total of 720 consecutive sections with a thickness of 2.5 μm were obtained from the renal capsule to the outer stripe of the renal outer medulla. After image recordings and alignment, distal convoluted tubules from 90 nephrons were traced with the custommade computer program. Based on the recorded data, the courses and the spatial arrangement of the DCT were visualized, and the length was also measured.
Results The DCT commenced downstream from the macula densa at an average length of 40-180 μm. The shape of the cell of DCT changed abruptly from simple cubical to high columnar, and the cell nucleus was located near the apical membrane of the cell. The DCT surrounded their parent glomerulus which were located at cortical labyrinth. Virtually, the DCT did not intermingle and each tubule occupied its own separate territory in the cortex. The end of the DCT gradually transited to the connecting tubules whose cells turned short and the nuclei were not limited to the apical membrane. Usually, the DCT of superficial nephron returned and made coils on the way to touch the capsule just for one time. The length of distal convoluted tubule was 500-900 μm. Conclusion Because of the short and convoluted length, the DCT occupied a relatively small and independent space, which may facilitate precise regulation by hormone along the segment.

Key words: Distal convoluted tubules, Spatial course, Three-dimensional reconstruction, Mouse