Fig. 4. Immunohistochemical localization of Na⁺/K⁺-ATPase (stained in brown colour) in the Triakis kidney. Sections are counterstained with haematoxylin. (A) Low power micrograph. Large renal corpuscles (RC) are situated between sinus and bundle zones. The anti-Na⁺/K⁺-ATPase antibody stained numerous tubules in both bundle and sinus zones (arrows and arrowheads). (B) Magnified view of five tubular segments in the bundle zone. Intense signal to Na⁺/K⁺-ATPase was detected in the ascending limb of the third loop (arrow) and the convoluted early distal segment of the third loop (arrowheads). Na⁺/K⁺-ATPase was not detected in the collecting tubule (CT). (C) Magnified view of the convoluted early distal segment at the distal end of the bundle zone. (D) Magnified view of the sinus zone. Intense signal was observed in the basolateral membrane of the intermediate segment (arrows). Arrowheads show the proximal II segment of the second loop. Scale bars: A, 500 µm; B, 20 µm; C,D, 100 µm.