title: Volume-activated amino acid efflux from term human placental tissue: stimulation of efflux via a pathway sensitive to anion transport inhibitors.
abstract: The effect of a hyposmotic challenge and hence cell-swelling upon the efflux of a variety of solutes from isolated human placental tissue has been examined. A hyposmotic shock increased the fractional release of taurine, the most abundant free amino acid in placental tissue, via a pathway sensitive to niflumic acid, DIDS (4,4'-Diisothiocyanatostilbene-2',2'-disulphonic acid,) NPPB (5-Nitro-2(3-phenylpropylamino)benzoic acid) and DIOA (R(+)[2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden -5-y) oxy] acetic acid). In contrast, tamoxifen was without effect. The cell-swelling induced efflux of taurine was attenuated (40 per cent) by replacing external Cl- with NO3-. The efflux of glutamic acid was also markedly increased by a hyposmotic challenge. Niflumic acid inhibited both basal and volume-activated glutamic acid efflux. A hyposmotic shock also increased alpha-aminoisobutyric acid efflux but not that of 3-O-methylglucose and SO4(2)-. The results suggest that the human placenta can respond to cell-swelling by releasing organic osmolytes such as amino acids via a pathway which is sensitive to anion transport inhibitors. However, it appears that the volume-activated amino acid transport system is independent from the placental anion-exchange pathways. The efflux of these compounds may act with K+ and Cl- efflux to effect a regulatory volume decrease in placental tissue. In addition, volume-activated transport may play a role in transplacental amino acid transfer.
authors.affiliation: Hannah Research Institute, Ayr, Scotland, UK.
authors.forename: D B
authors.initials: DB
authors.lastname: Shennan
authors.forename: S A
authors.initials: SA
authors.lastname: McNeillie
mesh_terms: D019325:3-O-Methylglucose; D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000378:metabolism; D000838:Anions / Q000378:metabolism; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D008757:Methylglucosides / Q000378:metabolism; D009997:Osmotic Pressure; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D013268:Stimulation, Chemical; D013431:Sulfates / Q000378:metabolism; D013654:Taurine / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000621:Aminoisobutyric Acids; D000838:Anions; D008757:Methylglucosides; D013431:Sulfates; D019325:3-O-Methylglucose; C100049:2-aminoisobutyric acid; D013654:Taurine; D018698:Glutamic Acid