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), meausured 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 significant 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).
- membrane transport
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