Chloride transport across syncytiotrophoblast microvillous membrane of first trimester human placenta

There are significant changes in the activity of some placental transporters between first trimester and term. However, chloride transport has previously been studied only in the term placenta. Therefore, in this study, we investigated chloride transport mechanisms in syncytiotrophoblast microvillous membrane (MVM) vesicles from first trimester human placentas and compared them with those in vesicles from term placentas. Cl-36(-) uptake into MVM vesicles was linear up to 45 s and had reached equilibrium by 1 h for both first trimester and term vesicles. In first trimester MVM at 0 mV, 0.1 mM diisothiocyano-2,2'-disulfonic stilbene (DIDS) blocked 25 +/- 3% (n = 8) of Cl-36(-) uptake at 30 s (initial rate), which was similar to the 30 +/- 7% (n = 6) inhibition by DIDS in term MVM. In the presence of a 25 mV inside-positive electrical potential difference, induced by imposition of a K+, gradient after preincubation with 200 mu M valinomycin, 0.5 mM diphenylamine-2-carboxylate (DPC) significantly blocked 30 +/- 4% of Cl-36(-) uptake at 30 s by first trimester MVM (p < 0.01); 18 +/- 5% (n = 8) of total uptake was inhibited by DPC but not by DIDS. There was a similar 15 +/- 3% (n = 6) component of Cl-36(-) uptake by term MVM, which was inhibited by DPC but not by DIDS. Using Western blotting, it was shown that the anion exchanger-1 protein was expressed in first trimester MVM in quantitatively similar amounts to that in term MVM. This study suggests that there is both an anion exchanger and a DPC-sensitive conductance in MVM of first trimester placenta with activity similar to that of term human placenta.