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 h uman erythrocytes from healthy donors and uraemic patients on haemodia lysis. 2. Although K-m values for total L-arginine influx were not sig nificantly different in erythrocytes freshly isolated from controls or uraemic patients, uraemia was associated with an increase in the V-ma x for transport (826 compared with 1176 mu mol h(-1) l(-1) of cells) w hich was reduced to control values after dialysis. 3. Saturable influx of L-arginine was mediated by the classical cationic amino acid trans port 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 70 0 mu mol h(-1) l(-1) of cells in uraemia, while K-m values increased f rom 44 to 94 mu mol/l. Dialysis had no significant effect on the kinet ic parameters altered by uraemia. 5. Under zero-trans conditions, and with system y+ inhibited by N-ethylmaleimide (0.2 mmol/l), transport o f L-arginine via system y+L was unaffected by uraemia, 6. Saturable in flux 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-monomethy l-L-arginine. 7. Influx of the neutral nitric oxide synthase inhibitor N-G-nitro-L-arginine was not readily saturable, 8. Intracellular conc entrations of L-arginine and N-G-monomethyl-L-arginine were significan tly increased in erythrocytes from uraemic patients when compared with controls, consistent with an increased transport capacity for L-argin ine and N-G-monomethyl-L-arginine. 9. The present study provides evide nce that system y+ mediates the increased transport of L-arginine and N-G-monomethyl-L-arginine in human erythrocytes from patients with chr onic renal failure, Our findings may have implications for the activit y of the L-arginine-nitric oxide signalling pathway in vascular endoth elial and smooth-muscle cells in uraemia.