CHANGES IN LIPID-COMPOSITION AND FLUIDITY OF HUMAN PLACENTAL BASAL MEMBRANE AND MODULATION OF BILAYER PROTEIN FUNCTIONS WITH PROGRESS OF GESTATION

Human placental syncytiotrophoblast basal membrane plays an important role in transfer of nutrients from the mother to the growing fetus all throughout gestation. The membrane lipid composition together with th e bilayer fluidity is found to be the major index in modulation of the se transport processes. In the present study, the effects of changing lipid composition on the placental basal membrane fluidity and the mod ulating influence of the latter on membrane enzyme and transport funct ions with progress of gestation,were investigated. Steady-state fluore scence analysis using 1,6-diphenyl-1,3,5 hexatriene as the probe, indi cated a decrease in fluorescence anisotropy of both labeled native mem brane vesicles and liposomes prepared from lipids extracted from the b asal membrane vesicles, signifying increased bilayer fluidity with pro gress of gestation. This in turn, was successfully correlated to the l owering of cholesterol content and enhanced phospholipid concentration with a steady decrease in cholesterol/phospholipid ratio during place ntal development. Enhanced Na+-K+-ATPase activity and steady-state glu cose uptake across basal membrane with gestational progress suggested modulation of membrane protein functions by the fluidity, which was fu rther corroborated by the increased bilayer fluidity and enzyme activi ty in benzyl alcohol treated basal membrane in each gestational age gr oup.