[Alkaline phosphatase activity in the placental labyrinth of the cat and problems of specific localization of transport adenosine triphosphatase. An ultrastructural study (author's transl)].

The ultrastructural localizations of alkaline phosphatase (ALPase) and of Na+-K+-dependent adenosine triphosphatase (Na+-K+-ATPase) were studied in the placental labyrinth of the cat during the last days of gestation. ALPase activity could be detected in the syncytiotrophoblast but was absent from maternal tissues. Enzyme activity was observed only along plasma membranes of microvilli and absorption tubules on the maternal surface of the syncytium and also on the podocytes-like cytoplasmic processes of the fetal face. The localization of the Na+-K+-ATPase activity as obtained with the method of Ernst was identical with that of ALPase. This activity was not very ouabaine sensitive or K+ dependent, but was almost completely inhibited by levamisole. The strong ALPase activity of the syncytiotrophoblast does not allow a specific detection of Na+-K+-ATPase. However, the localization of these enzymes activities on syncytiotrophoblast surfaces directly related to fetal and maternal capillaries could suggest that these surfaces are associated with transport mechanisms of the trophoblast.