Fig. 5. Immunohistochemical localization of the urea transporter (UT; stained brown) in the kidney of Bufo using affinity-purified Bufo UT antibody. (A) Immunoreactivity was detected on the apical cell membrane of epithelia in the early distal tubules, located in the ventral zone (boxed) of the kidney. (B) Higher magnification of the immunoreactive apical cell membrane in the early distal tubules. (C,D) In adjacent sections, no UT immunoreactivity was detected in the late distal tubule and collecting duct where H⁺-ATPase was expressed. (E,F) Diagrams showing the distribution of UT and H⁺-ATPase in the renal nephron, indicated by red asterisk in each scheme, respectively. Arrowheads in C and D, early distal tubule (ED); arrows in C and D, late distal tubule (LD). Ad, adrenal gland; G, glomerulus; P, proximal tubule. Scale bars, (A,C,D) 100 µm; (B) 20 µm.