A study of the membrane transport of aminoacids in erythrocytes from patients on haemodialysis

The initial rates of aminoacid influx to erythro cytes from nine patients on maintenence haemodialysis and from nine normal controls have been studied using radiolabelled L-serine, glycine, L-tryptophan and Lleucine. L-serine uptake had an Na-dependent component fitted by Michaelis-Menten kinetics (ASC system) and a non-saturable Na-independent component. In erythrocytes from haemodialysis patients L-serine uptake via the ASC system had a mean (SEM) V_max of 233 (33) μmol/l cells per h, compared to a mean V_max in controls of 353 (21) μmol/l cells per h. The mean K_m for L-serine uptake was 105 (11) μM in haemodialysis erythrocytes and 160 (12) μM in controls. These reductions in V_max and K_m for ASC in haemodialysis erythrocytes were significant (2P<0.02). Glycine uptake had a Michaelis-Menten-type chloride-dependent component (gly system), and a chloride-independent non-saturable component. The mean K_m for glycine influx via the gly system was 26.3 (2.3) μM in haemodialysis erythrocytes, and 34 (3.1) μM in normals (2P<0.02). The V_max for the uptake of glycine by the gly system did not differ significantly between haemodialysis and control erythrocytes. The initial influx rates of L-tryptophan via the T system and of L-leucine via the L system did not vary between control and haemodialysis erythrocytes. It is suggested that abnormalities of the ASC and gly membrane transport systems may contributeto the altered interorgan transport of aminoacids found in renal disease.