Nitric oxide synthesis requires activity of the cationic and neutral amino acid transport system y+L in human umbilical vein endothelium

Exp Physiol. 2003 Nov;88(6):699-710. doi: 10.1113/eph8802647.

Abstract

L-arginine transport is mediated by the cationic/neutral amino acid transport system y+L and cationic amino acid transporters y+/CATs in human umbilical vein endothelial cells (HUVECs). System y+/CATs activity may be rate-limiting for nitric oxide (NO) synthesis, but no reports have demonstrated system y+L involvement in NO synthesis in endothelium. We investigated the role of system y+L in NO synthesis in HUVECs. Transport of 1.5 microM L-arginine was inhibited (P < 0.05) by L-lysine (K(i), 1.4 micro M), L-leucine (K(i), 1.8 micro M) and L-phenylalanine (K(i), 4.1 microM), but was unaltered (P > 0.05) by L-alanine or L-cysteine. The system y+/CATs inhibitor, N-ethylmaleimide (NEM), did not alter 1.5 microM L-arginine transport, but inhibited (92 +/- 3 %) 100 microM L-arginine transport. L-arginine transport in the presence of NEM was saturable (V(max), 0.37 +/- 0.02 pmol (microg protein)(-1) min(-1); K(m), 1.5 +/- 0.3 microM) and competitively inhibited by L-leucine in the presence of Na+ (V(max), 0.49 +/- 0.06 pmol (microg protein)(-1) min(-1); K(m), 6.5 +/- 0.9 microM). HUVECs express SLC3A2/4F2hc, SLC7A7/4F2-lc2 and SLC7A6/4F2-lc3 genes encoding for the high-affinity transport system y+L. N(G)-Nitro-L-arginine methyl ester and L-leucine, but not NEM, inhibited NO synthesis in medium containing 1.5 microM L-arginine. Cells exposed to 25 mM D-glucose (24 h) exhibited reduced system y+L activity (V(max), 0.15 +/- 0.008 pmol (microg protein)(-1) min(-1); K(m), 1.4 +/- 0.3 microM) and NO synthesis. However, 25 mM D-glucose increased NO synthesis and L-arginine transport via system y+. Thus, L-arginine transport through system y+L plays a role in NO synthesis, which could be a determining factor in pathological conditions where the endothelial L-arginine-NO pathway is altered, such as in diabetes mellitus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Transport System y+L / metabolism*
  • Amino Acid Transport Systems, Basic / metabolism
  • Amino Acid Transport Systems, Neutral / metabolism
  • Arginine / pharmacokinetics*
  • Biological Transport, Active / physiology
  • Cells, Cultured
  • Endothelium, Vascular / metabolism*
  • Humans
  • Kinetics
  • Nitric Oxide / biosynthesis*
  • Umbilical Veins / metabolism*

Substances

  • Amino Acid Transport System y+L
  • Amino Acid Transport Systems, Basic
  • Amino Acid Transport Systems, Neutral
  • Nitric Oxide
  • Arginine