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 K-m 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 mu mol 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 mu mol h(-1) l(-1) of cells in uraemia, while K-m values increased from 44 to 94 mu mol/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 mu mol/l, V-max = 353 mu mol h(-1) l(-1) of cells) and y+L (K-m = 17 mu mol/l, V-max = 51.3 mu mol 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.