Ca-ATPase of Human Syncytiotrophoblast Basal Plasma Membranes

Abstract

In the present work, a Mg 2+ -dependent, Ca 2+ -stimulated ATPase activity was determined and characterized in purified preparations of syncytiotrophoblast basal (fetal facing) plasma membranes, and its characteristics were compared to those of the active Ca 2+ -transport already demonstrated in this tissue. Similar to the active Ca 2+ transport, the Ca-ATPase is Mg 2+ -dependent, is stimulated by calmodulin, and is inhibited by vanadate. The K m for Ca 2+ activation is 0.25 ± 0.02µM, a value near to that described for calcium active transport in this tissue. Consequently, the Ca-ATPase activity of human syncytiotrophoblast basal plasma membrane described in this paper could be responsible for the active extrusion of calcium from the syncytiotrophoblast toward the fetal circulation.