Implication of ATP and sodium in arachidonic acid incorporation by placental syncytiotrophoblast brush border and basal plasma membranes in the human

The human placental syncytiotrophoblast is the main site of exchange of nut rients and minerals between the mother and her fetus. In order to character ize the placental transport of some fatty acids, we studied the incorporati on of arachidonic acid, a fetal primordial fatty acid, in purified bipolar syncytiotrophoblast brush border (BBM) and basal plasma membranes (BPM) fro m human placenta. The basal arachidonic acid incorporation in BBM and BPM w as time dependent and reached maximal values of 0.75 +/- 0.10 and 0.48 +/- 0.18 pmol/mg protein, respectively, after 2.5 min. The presence of adenosin e triphosphate (ATP) (3 mM) increases significantly the maximal incorporati on of arachidonic acid by sixfold (4.75 +/- 0.35 pmol/mg) and ninefold (4.4 0 +/- 0.84 pmol/mg) in BBM and BPM, respectively. Moreover, an increase in the arachidonic acid incorporation was also obtained in the presence of sod ium where the values achieved 7.68 +/- 0.98 (10 x) and 6.53 pmol/mg (13.6 x ) for BBM and BPM, respectively. We also showed that the combination of bot h Na+ and ATP increases significantly the maximal incorporation of arachido nic acid in BPM to 7.89 +/- 0.15 pmol/mg protein, while in BBM it did not m odify its incorporation (8.18 +/- 0.25 pmol/mg protein), as compared to the presence of sodium alone. Our results demonstrate that arachidonic acid is incorporated by both placental syncytiotrophoblast membranes, and is ATP a nd sodium-linked. However, different mechanisms seem to be involved in this fatty acid incorporation through BBM and BPM, since the presence of Na+ or ATP increased it, while the association of these two elements increased it only in BPM. We also demonstrated by osmolarity experiments that both memb ranes bind arachidonic acid, potentially involving one or more fatty acids binding proteins. (C) 2000 Harcourt Publishers Ltd.