Transport of large neutral amino acids into BeWo cells.
BeWo choriocarcinoma cells were cultured onto solid microcarrier beads, packed into columns and superfused. Unidirectional influx of l -phenylalanine (l -phe) and l -leucine (l -leu) across the microvillous border of the cells was studied using a rapid paired-tracer dilution technique. Influx of l -phe and l -leu comprised both saturable and non-saturable components. K(m)values for l -phe and l -leu were 0.57+/-0.01 m m and 0.05+/-0.01 m m, respectively, with V(max)values of 120.4+/-0.5 nmol/mg/min and 41. 7+/-0.2 nmol/mg/min. Non-saturable uptake components were 29.0+/-0.1 nmol/mg/m m and 37.9+/-0.1 nmol/mg/min/m m respectively. l -leu uptake was found to be sodium-independent. The uptake of l -[(3)H]phe was strongly inhibited (90-100 per cent) by unlabelled l -phe, d -phe, l -leu or 2-aminoendobicyclo-[2,2, 1]-heptane-2-carboxylic acid (BCH) but not by l -arginine (l -arg) or methyl alpha-aminoisobutric acid (Me-AIB). Pre-incubation of Bewo cultures for 24 h in the presence of an additional 1.2 m ml -phe (simulating maternal phenylketonuria) significantly reduced both the K(m)and V(max)components of l -phe influx. l -arg (2 m m) had no effect on l -leu influx whereas 2 m ml -phe completely inhibited saturable l -leu influx. These data suggest that the microvillous border of differentiated BeWo cells transport large neutral amino acids predominantly via system L rather than by B(0) or y(+)L transporters.
Department of Maternal and Fetal Medicine, Imperial College School of Medicine, Chelsea and Westminster Hospital, London, UK. b.eaton@ic.ac.uk
B M
BM
Eaton
S R
SR
Sooranna
D000328:Adult; D000596:Amino Acids / Q000502:physiology; D000598:Amino Acids, Cyclic; D000621:Aminoisobutyric Acids / Q000494:pharmacology; D001120:Arginine / Q000494:pharmacology; D001692:Biological Transport; D002822:Choriocarcinoma / Q000378:metabolism*; D005260:Female; D006801:Humans; D007930:Leucine / Q000493:pharmacokinetics*; D008871:Microvilli / Q000378:metabolism; D010649:Phenylalanine / Q000493:pharmacokinetics* / Q000494:pharmacology; D011247:Pregnancy; D012964:Sodium / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000596:Amino Acids; D000598:Amino Acids, Cyclic; D000621:Aminoisobutyric Acids; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; C017911:2-(methylamino)isobutyric acid; D010649:Phenylalanine; D001120:Arginine; D012964:Sodium; D007930:Leucine