Transport of l-Arginine and the Nitric Oxide Inhibitor N^G-Monomethyl-l-Arginine in Human Erythrocytes in Chronic Renal Failure

1. Transport of l-arginine and the nitric oxide synthase inhibitors N^G-monomethyl-l-arginine and N^G-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 V_max 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 V_max for l-arginine transport via system y+ increased from 271 to 700 μmol h⁻¹ l⁻¹ of cells in uraemia, while K_m 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 N^G-monomethyl-l-arginine was also mediated by systems y+ (K_m = 56 μmol/l, Vmax = 353 μmol h⁻¹ l⁻¹ of cells) and y+L (K_m = 17 μmol/l, Vmax = 51.3 μmol h⁻¹ l⁻¹ of cells) and, as with l-arginine, uraemia increased the transport capacity for N^G-monomethyl-l-arginine.

7. Influx of the neutral nitric oxide synthase inhibitor N^G-nitro-l-arginine was not readily saturable.

8. Intracellular concentrations of l-arginine and N^G-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 N^G-monomethyl-l-arginine.

9. The present study provides evidence that system y+ mediates the increased transport of l-arginine and N^G-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.