Sulfate transport in brush border membrane vesicles prepared from human placental syncytiotrophoblast.

Isolated brush-border membrane vesicles prepared from human placenta are known to transport amino acids via a Na+-dependent mechanism akin to that found in gut and kidney vesicle preparations. We studied sulfate transport in placental vesicles and failed to identify any Na+-dependent uptake mechanism. Rather, uptake is a non-electrogenic process that is trans-stimulated by outwardly directed anion flux which is independent of cation. If anion exchange is tightly coupled in vivo, the net transfer of sulfate from mother to the growing fetus may be driven by the continuous flux of bicarbonate in the opposite direction.