MECHANISMS OF CHLORIDE TRANSPORT ACROSS THE SYNCYTIOTROPHOBLAST BASALMEMBRANE IN THE HUMAN PLACENTA

Chloride transport mechanisms in isolated plasma membrane vesicles wer e studied to characterize pathways far transcellular transport of chlo ride. Microvillous membrane (MVM) and basal membranes (BM) vesicles we re isolated from term placentae. Western blot analysis of the anion ex changer isoform 1 (AE1) demonstrated that the density of AE1 was 12-fo ld higher on the MVM compared to the BM. At 30 sec, the Cl- uptake in the absence of a potential difference (p.d.) was 457.3 +/- 69.7 and 11 1.0 +/- 29.1 pmol/mg protein in MVM and BM, respectively (mean +/- SEM , n=6). Choride transport pathways were characterized using diisothioc yano-2'2-disulphonic stilbene. (DIDS, 0.1 mM) and diphenylamine-2-carb oxylate (DPC, 0.5 mM) in the absence or presence of inside positive me mbrane potentials. Anion exchange (DIDS-sensitive uptake at zero mV) w as found in the MVM only. Both MVM and BR;I showed increased chloride uptake in the presence of inside positive potentials, suggesting the p resence of chloride conductance pathways. The chloride uptake with a 2 5-mV inside positive p.d. could be inhibited by both DIDS and DPC in M VM and BM. However greater potentials (50 mV) showed no significant in hibition by DIDS or DPC in BM. In conclusion, the anion exchanger is u nlikely to contribute significantly to chloride fluxes across BM. The data also suggest the presence of Cl- conductance pathways in both the MVM and BM which are sensitive to both DIDS and DPC. (C) 1998 W. B. S aunders Company Ltd.