Uptake of neutral alpha- and beta-amino acids by human proximal tubular cells.
The transport characteristics of amino acids in primary cell cultures from the proximal tubule of human adults (AHKE cells) were examined, using alpha-aminoisobutyric acid (AIB) and beta-alanine as representatives of alpha- and beta-amino acids, respectively. The Na(+)-gradient dependent influx of AIB occurred by a single, saturable transport system, whereas the Na(+)-gradient dependent uptake data for beta-alanine could be described in terms of two-independent transport components as well as one-transport one-leak model with identical kinetic constants for the high-affinity system. Competition experiments revealed that all the neutral amino acids tested reduced the uptake of AIB, whereas there was no effect of taurine, L-aspartic acid, and L-arginine. By contrast, the influx of beta-alanine was only drastically reduced by beta-amino acids, whereas the inhibition by neutral alpha-amino acids was relatively low. Nor did L-arginine and L-aspartic acid affect the uptake of beta-alanine into AHKE cells. Comparison with the results obtained for normal (NHKE) and immortalized (IHKE) embryonic cells suggested an unaltered expression of the types of transport carriers for neutral alpha- and beta-amino acids in the embryonic and AHKE cells. However, the uptake capacity of the above-mentioned transport proteins was relatively smaller in the embryonic kidney compared with the adult human kidney, which may explain, at least partly, the phenomenon of physiologic amino aciduria in neonates.
Jessen
H
H
Department of Medical Biochemistry, University of Aarhus, Denmark.
Røigaard
H
H
Jacobsen
C
C
D000328:Adult; D000596:Amino Acids / Q000378:metabolism; D000621:Aminoisobutyric Acids / Q000378:metabolism*; D001667:Binding, Competitive; D001692:Biological Transport; D002478:Cells, Cultured; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D012964:Sodium / Q000494:pharmacology; D015091:beta-Alanine / Q000378:metabolism*
D000596:Amino Acids; D000621:Aminoisobutyric Acids; D015091:beta-Alanine; C100049:2-aminoisobutyric acid; D012964:Sodium