Localization and activity of Na⁺, K⁺ ‐ATPase in the ductuli efferentes of the rat

The Na⁺, K⁺ ‐ATPase enzyme through its p‐nitrophenyl phosphatase activity was localized in the ductuli efferentes of rats. Enzymatic activity was demonstrated along the cytoplasmic side of the plasmalemma of the ductular epithelial cells. The most intense deposition of reaction products was found on the plasmalemma delimiting the lower lateral and basal regions of the cells. The plasma membranes forming the microvilli, apical junctional complexes were devoid of reaction product while the midlateral membranes showed a weak reaction. The enzyme reaction was potassium‐dependent and was abolished by addition of 10 mM ouabain to the incubation media. Enzyme activity decreased significantly from proximal to distal regions of the ductules (8,101.47 ± 274.53, 6,658.95 ± 269.53 and 4,668.10 ± 575.41 pmoles p‐nitrophenol/mm/h, respectively in initial, conus vasculosus and terminal zones). A unified model for water absorption is proposed in the efferent ductules based upon this data and that of others.© Willey‐Liss, Inc.