[Cytochemical study of the electronmicroscopical localization of Ca++ATPase activity in the human trophoblast]

Ca++ATPase is one of the most important regulatory systems that maintain the intracellular Ca++ concentration, which is essential to many cellular functions. The presence of Ca++ATPase in the human placenta has been speculated on biochemical grounds, but direct histochemical evidence has been lacking. Therefore, ultracytochemical localization of Ca++ATPase on trophoblastic cells of the human placenta was investigated by using the lead citrate method. Strong Ca++ATPase activity on the microvillous membrane and weak activity on the basal plasma membrane of the syncytiotrophoblast were observed. This distribution of Ca++ATPase was in good agreement with biochemical speculations. These results suggested that the syncytiotrophoblast might play an important role in the Ca++ metabolism in the human placenta.