CHLORIDE TRANSPORT ACROSS SYNCYTIOTROPHOBLAST MICROVILLOUS MEMBRANE OF FIRST-TRIMESTER HUMAN PLACENTA

There are significant changes in the activity of some placental transp orters between first trimester and term. However, chloride transport h as previously been studied only in the term placenta. Therefore, in th is study, we investigated chloride transport mechanisms in syncytiotro phoblast microvillous membrane (MVM) vesicles from first trimester hum an placentas and compared them with those in vesicles from term placen tas. Cl-36(-) uptake into MVM vesicles was linear up to 45 s and had r eached 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 b y DIDS in term MVM. In the presence of a 25 mV inside-positive electri cal potential difference, induced by imposition of a K+, gradient afte r preincubation with 200 mu M valinomycin, 0.5 mM diphenylamine-2-carb oxylate (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 uptak e 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 quan titatively similar amounts to that in term MVM. This study suggests th at 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.