LOCALIZATION AND PROPERTIES OF MEMBRANE ADENOSINE TRIPHOSPHATASES IN THE GUINEA-PIG PLACENTA

The distribution and properties of cytochemically demonstrable phosphatases in the near-term guinea-pig placenta were examined using a Sr capture technique for Na+, K+-ATPase and a lead capture technique for Mg2+-ATPase. Localizations with the Sr technique in the presence of an alkaline phosphatase inhibitor were mainly on the syncytiotrophoblast plasma membranes. The reaction was K+-dependent and ouabain-sensitive. Reaction product using the lead capture method was found on both trophoblast and endothelial cell plasma membranes and was independent of Mg2+ and insensitive to p-hydroxymercuribenzoate, an inhibitor of membrane ATPases. A very large proportion of this reaction could be blocked by an alkaline phosphatase inhibitor. The Sr capture technique gave a reliable localization for Na+, K+-ATPase. The lead capture method mainly demonstrated alkaline phosphatase, and does not offer a useful approach to specific ATPase studies in this particular system.