1. Transport of l-arginine was investigated under zero- trans conditions in human erythrocytes from healthy donors and patients with heart failure. 2. Saturable influx of l-arginine was mediated by the classical cationic amino acid transport systems y + and y + L. 3. The V max for l-arginine transport via system y + increased from 292 to 490 μmol h −-1 l −-1 of cells in heart failure. 4. With system y + inhibited by N -ethylmaleimide (0.2 mmol/l), the V max for the transport of l-arginine via system y + L was unaffected in erythrocytes from patients with heart failure. 5. The inhibition of l-arginine and l-leucine influx by N G -monomethyl-l-arginine was similar in erythrocytes from control and heart failure patients. 6. Plasma l-arginine levels were reduced in patients with heart failure (59 μmol/l) compared with controls (125 μmol/l). Plasma from patients with heart failure also contained the endogenous l-arginine analogue N G -monomethyl-l-arginine, which was undetectable in plasma from controls. 7. Intracellular concentrations of l-arginine and N G -monomethyl-l-arginine were significantly elevated in erythrocytes from patients with heart failure compared with controls, consistent with an increased transport capacity for l-arginine and N G -monomethyl-l-arginine. 8. The present study provides the first evidence that system y + mediates the increased transport of l-arginine in human erythrocytes from patients with chronic heart failure. These findings are similar to our previous results obtained in patients with chronic renal failure. Since both pathologies seem to present with an increased synthesis of nitric oxide, studies of l-arginine transport in erythrocytes may provide a valuable paradigm to study abnormalities of the l-arginine-nitric oxide signalling pathway.

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 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, V max = 353 μmol h −1 l −1 of cells) and y+L ( K m = 17 μmol/l, V max = 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.

1. Erythrocyte choline transport was studied in 10 haemodialysis patients immediately before and after a haemodialysis session and in 10 control subjects. Choline uptake was measured in erythrocytes from normal and uraemic patients after washing in vitro and subsequent incubation in autologous plasma. Amines present in uraemic plasma were examined for their effect on choline transport in normal erythrocytes. 2. NMR spectroscopy was used to measure choline, trimethylamine and dimethylamine in erythrocyte extracts from nine control subjects, 32 subjects with renal impairment and nine samples from haemodialysis patients. 3. The increased choline influx in uraemic erythrocytes is significantly decreased by prior haemodialysis (mean V max pre-dialysis 146±20 μmol h −1 I −1 , postdialysis 113±13 μ/mol h–1 I −1 ( P < 0.005). After in vitro washing there is a fall in V max , and no longer any significant difference between pre- and post-dialysis samples. There remains a significant difference in the erythrocyte choline V max between samples from patients with chronic renal failure and from normal subjects ( P < 0.005). 4. Human plasma was found to contain factors capable of increasing choline uptake. Trimethylamine and dimethylamine were found to inhibit choline uptake. Trimethylamine and trimethylamine- N -oxide transstimulated choline efflux, but the major transport substrate present in erythrocyte extracts from all groups was choline, which was higher in those with renal impairment (71 ± 10 μmol/l) than in haemodialysis patients (47 ± 10 μmol/l) and control subjects with normal renal function (40 ± 9 μmol/l). 5. Our data suggest that erythrocyte choline transport is increased in uraemia as a consequence of increased transporter number or activity, rather than the presence of intracellular substrate.

1. Erythrocyte choline transport has been studied in nine patients on maintenance haemodialysis for chronic renal failure, six patients on continuous ambulatory peritoneal dialysis, 31 patients with renal transplants and in nine normal control subjects. 2. The mean maximum rate of choline influx ( V max. , measured at an extracellular choline concentration of 250 μmol/l) was 66.7 ( sd 14.1) μmol h −1 l −1 cells in patients on haemodialysis, 87.8 ( sd 18.5) μmol h −1 l −1 cells in patients on continuous ambulatory peritoneal dialysis and 30.5 ( sd 4.9) μmol h −1 l −1 cells in control subjects. The increase in choline flux in patients on haemodialysis and patients on continuous ambulatory peritoneal dialysis compared with control subjects was highly significant ( P < 0.001). 3. Renal transplant patients showed variable values for the V max. of choline influx (range 17.7-71.7 μmol h −1 l −1 cells). The values showed a signifcant negative correlation with creatinine clearance and this correlation correctly extrapolated to the maximum choline flux in normal subjects and in patients on dialysis. 4. The kinetics of choline transport have been studied in erythrocytes of patients on haemodialysis and control subjects in ‘zero-trans’ conditions after depletion of intracellular choline. The mean V max. in these conditions was 38.4 ( sd 4.6) μmol h −1 l −1 cells in patients on haemodialysis compared with 14.2 ( sd 3.7) μmol h −1 l −1 cells in control subjects. The mean K m under ‘zero-trans’ conditions was 19.4 ( sd 2.4) μmol/l in patients on haemodialysis and 7.4 ( sd 1.4) μmol/l in control subjects. These differences were significant ( P < 0.001).

1. The initial rate of l -lysine influx into erythrocytes from 13 patients with chronic renal failure has been measured using 14 C-labelled lysine. Ten patients were on maintenance haemodialysis and three had never been dialysed. The results are compared with data obtained from 12 normal individuals. 2. The rate of lysine influx into washed cells from buffered saline containing 0.02–0.5 mmol of l -lysine/l has been calculated. The results can be fitted with a model in which influx has a single saturable component obeying Michaelis–Menten kinetics, and a linear non-saturable component. 3. In uraemic erythrocytes the saturable component had a mean V max. of 0.762 mmol h −1 litre −1 of cells ( n = 13, sem 0.072) and a mean K m of 68.2 μmol/l ( sem 5.7). These values in normal erythrocytes were 0.566 mmol h −1 litre −1 of cells ( n = 12, sem 0.033) and 70.5 μmol/l ( sem 4.1), respectively. The mean apparent diffusion constant ( K D ) for the linear component of influx was 0.224 h −1 ( sem 0.039) in uraemic cells and 0.178 h −1 ( sem 0.028) in normals. 4. The 35% increase in mean V max. seen in uraemic erythrocytes was statistically significant ( P = 0.02). A similar increase in V max. in uraemic cells compared with controls was seen in erythrocytes which were studied in zero-trans conditions after depletion of intracellular amino acids. The mean values of K m and K D were not significantly different in uraemia. The origins of this increased membrane transport capacity for lysine in uraemia are discussed.

1. Radioisotopic cation transport studies are described in a family whose erythrocytes had previously been found to show an abnormal net efflux of potassium when cooled to room temperature. This net efflux effect, which was inherited as an autosomal dominant trait, was associated with a few target cells on the blood film and a mild compensated haemolytic state. 2. Measurements of intracellular electrolyte concentrations, cell water and of Na + and K + transport rates across the membrane at 37°C were consistent with a diagnosis of mild hereditary xerocytosis. 3. Studies of cation transport in the temperature range 20–37°C revealed that the fluxes attributable to the Na + -K + pump showed a temperature dependence comparable with that in normal cells, but that the ouabain plus loop-diuretic insensitive fluxes of K + , which probably represent the ‘passive diffusional leak’ to K + , were less sensitive to temperature than normal over the range 20–37°C. These findings were held to account for the net efflux effect previously reported.