Binding, uptake and efflux of 65Zn by isolated human trophoblast cells

The isolated trophoblast from human placenta at term has been used as model for placental transport. Binding to the cells showed to be of low specificity and very limited (less than 10%) in presence of serum. Uptake of zinc was 90% reduced at 4 degrees C and depended on the presence of sulfhydryl groups (as suggested with the inhibition produced by N-ethylmaleimide). There is considerable efflux (50%) of zinc from preloaded cells and the process was enhanced by presence of histidine in the medium. The model proved to be useful in studying the mode of zinc transport. The results indicate that the uptake of zinc by the trophoblast is probably the limiting process in the placental transport of this metal.