title: ASC system activity is altered by development of cell polarity in trophoblast from human placenta.
abstract: Pathways of neutral amino acid uptake were investigated in vitro during differentiation of primary cultures of trophoblast isolated from full-term human placentas and a clone (b30) of the BeWo cell line. Inhibition of initial alanine (0.1 microM) uptake by 2-(methylamino)isobutyric acid and unlabeled alanine revealed two Na(+)-dependent systems and one Na(+)-independent transporter. Characterization of these transporters, by selective inhibition, suggested system A, ASC, and L-like transporters. Concomitant with formation of microvillous membrane and syncytium, system ASC activity decreased from 16.1 +/- 2.8 pmol.mg DNA-1.min-1 at 24 h to 2.4 +/- 1.1 pmol.mg DNA-1.min-1 at 72 h. Na(+)-independent alanine uptake increased from 6.0 +/- 2.0 to 12.9 +/- 0.9 pmol.mg DNA-1.min-1 at 24 and 72 h, respectively. Similarly, alpha-(methylamino)isobutyric acid-insensitive, Na(+)-dependent activity in b30 cells (100 microM alanine) decreased from 6.5 +/- 1.6 to 1.2 +/- 1.2 nmol.mg DNA-1.min-1 for control and forskolin-treated cells, respectively. We conclude that membrane specialization accompanying fusion and differentiation of the cytotrophoblast to form syncytiotrophoblast results in a polarization of neutral amino acid transport systems.
authors.affiliation: Edward Mallinckrodt Department of Pediatrics, Washington University School of Medicine, St. Louis Children's Hospital, Missouri 63110.
authors.forename: T C
authors.initials: TC
authors.lastname: Furesz
authors.forename: C H
authors.initials: CH
authors.lastname: Smith
authors.forename: A J
authors.initials: AJ
authors.lastname: Moe
mesh_terms: D000409:Alanine / Q000493:pharmacokinetics*; D001692:Biological Transport; D016764:Cell Polarity; D016922:Cellular Senescence; D005576:Colforsin / Q000494:pharmacology; D015726:Giant Cells / Q000378:metabolism; D006801:Humans; D008871:Microvilli / Q000378:metabolism; D010920:Placenta; D012964:Sodium / Q000493:pharmacokinetics; D013997:Time Factors; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism* / Q000502:physiology*; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: D005576:Colforsin; D012964:Sodium; D000409:Alanine