title: Comparison of folic acid uptake characteristics by human placental choriocarcinoma cells at acidic and physiological pH.
abstract: The aim of this work was to characterize the placental uptake of folic acid from the maternal circulation. Using 2 human trophoblast cell lines (BeWo and JAR), we verified that uptake of 3H-folic acid was pH-dependent, increasing significantly with decreasing extracellular pH. In BeWo cells, uptake of 3H-folic acid at pH 5.5 was (i) Na+-independent; (ii) inhibited by folic acid, 5-methyltetrahydrofolate (5-MTHF), and methotrexate (MTX); (iii) inhibited by the anion transport inhibitors 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 4-acetamido-4'-isothiocyano-2,2'-disulfonic acid stilbene (SITS); (iv) inhibited by the proton ionophore carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP); (v) not inhibited by blockers of receptor-mediated endocytosis (cytochalasin D and monensin); (vi) trans-inhibited by MTX and folic acid; and (vii) not affected by an anti-reduced folate transporter-1 (RFC) antibody. At pH 7.5, uptake of 3H-folic acid was (i) Na+-independent; (ii) inhibited by folic acid and MTX, but not by 5-MTHF; (iii) inhibited by SITS, but not by DIDS; (iv) not affected by FCCP; (v) inhibited by monensin (but not by cytochalasin D); (vi) trans-inhibited by folic acid (but not by MTX); and (vii) inhibited by an anti-RFC antibody. In conclusion, in BeWo cells, both RFC and receptor-mediated endocytosis seem to be involved in 3H-folic acid uptake at pH 7.5, whereas at pH 5.5, RFC and (or) a low pH-operating transporter distinct from RFC are involved.
authors.affiliation: Department of Biochemistry (U38/FCT), Faculty of Medicine, University of Porto, Porto 4200-319, Portugal.
authors.forename: Elisa
authors.initials: E
authors.lastname: Keating
authors.forename: Clara
authors.initials: C
authors.lastname: Lemos
authors.forename: Isabel
authors.initials: I
authors.lastname: Azevedo
authors.forename: Fátima
authors.initials: F
authors.lastname: Martel
mesh_terms: D001692:Biological Transport / Q000502:physiology; D045744:Cell Line, Tumor; D002822:Choriocarcinoma / Q000378:metabolism*; D005260:Female; D005492:Folic Acid / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000502:physiology; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D014594:Uterine Neoplasms / Q000378:metabolism*
chemical_list: D005492:Folic Acid