Fig. 5. Identification of the nephron segment immunoreactive to the cloned urea transporter (UT) using antibody raised against the C-terminal peptide of UT. (A) Immunoreactive tubules in the bundle zone representing the straight portion (arrowhead) and the convoluted portion (arrows) of the collecting tubule. (B) Immunoreactive tubules (arrows) are connected directly to the collecting duct (CD) in the bundle zone. (C) Magnified view showing the connection between the immunoreactive tubule (arrow) and the collecting duct (CD). (D) Schematic drawing of the course of a single nephron and of the segment expressing the UT. UT was expressed only in the collecting tubule, the final segment in the bundle zone, in the kidney of Triakis scyllia. Each nephron makes four turns (1-4) and traverses repeatedly between the sinus zone (SZ) and the bundle zone (BZ). The resulting five tubular segments in the bundle zone are enclosed in a peritubular sheath. RC, renal corpuscle. Scale bars: A,B, 100 µm; C, 20 µm.