Human placental syncytiotrophoblast expresses two pharmacologically distinguishable types of Na super(+)-H super(+) exchangers, NHE-1 in the maternal-facing (brush border) membrane and NHE-2 in the fetal-facing (basal) membrane

We investigated whether highly purified preparations of basal (fetal-facing) membrane isolated from normal term human placentas possess Na super(+)-H super(+) exchanger activity. Uptake of Na super(+) into basal membrane vesicles was stimulated many-fold by an outwardly directed H super(+) gradient. This H super(+)-gradient-dependent uptake was inhibitable by amiloride and its analogues. Na super(+) uptake in these vesicles did not occur via a Na super(+) channel, as it was not influenced by changes in membrane potential and, in addition, was inhibited by benzamil only at high micromolar concentrations. The data demonstrate that the basal membrane Na super(+)-H super(+) exchanger is distinct from the brush border membrane Na super(+)-H super(+) exchanger.