Increased lysine transport capacity in erythrocytes from patients with chronic renal failure

1. The initial rate of l-lysine influx into erythrocytes from 13 patients with chronic renal failure has been measured using ¹⁴C-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.