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 $\text{in}\text{vivo}$, the net transfer of sulfate from mother to the growing fetus may be driven by the continuous flux of bicarbonate in the opposite direction.