1. Transport of l-arginine and the nitric oxide synthase inhibitors NG-monomethyl-l-arginine and NG-nitro-l-arginine was investigated in human erythrocytes from healthy donors and uraemic patients on haemodialysis.
2. Although Km values for total l-arginine influx were not significantly different in erythrocytes freshly isolated from controls or uraemic patients, uraemia was associated with an increase in the Vmax for transport (826 compared with 1176 μmol h−1 l−1 of cells) which was reduced to control values after dialysis.
3. Saturable influx of l-arginine was mediated by the classical cationic amino acid transport system y+ and system y+L, known to transport cationic and neutral amino acids with higher affinity.
4. Under zero-trans conditions, the Vmax for l-arginine transport via system y+ increased from 271 to 700 μmol h−1 l−1 of cells in uraemia, while Km values increased from 44 to 94 μmol/l. Dialysis had no significant effect on the kinetic parameters altered by uraemia.
5. Under zero-trans conditions, and with system y+ inhibited by N-ethylmaleimide (0.2 mmol/l), transport of l-arginine via system y+L was unaffected by uraemia.
6. Saturable influx of NG-monomethyl-l-arginine was also mediated by systems y+ (Km = 56 μmol/l, Vmax = 353 μmol h−1 l−1 of cells) and y+L (Km = 17 μmol/l, Vmax = 51.3 μmol h−1 l−1 of cells) and, as with l-arginine, uraemia increased the transport capacity for NG-monomethyl-l-arginine.
7. Influx of the neutral nitric oxide synthase inhibitor NG-nitro-l-arginine was not readily saturable.
8. Intracellular concentrations of l-arginine and NG-monomethyl-l-arginine were significantly increased in erythrocytes from uraemic patients when compared with controls, consistent with an increased transport capacity for l-arginine and NG-monomethyl-l-arginine.
9. The present study provides evidence that system y+ mediates the increased transport of l-arginine and NG-monomethyl-l-arginine in human erythrocytes from patients with chronic renal failure. Our findings may have implications for the activity of the l-arginine—nitric oxide signalling pathway in vascular endothelial and smooth-muscle cells in uraemia.