Further studies on the erythrocyte uptake of lead in vitro in amyotrophic lateral sclerosis (ALS) patients and controls. Abnormal erythrocyte fragility in ALS.

Following our earlier observations on increased plasma concentrations of lead in amyotrophic lateral sclerosis (ALS), the erythrocyte uptake of lead from plasma has been studied in vitro. Whole-blood from ALS patients and controls was incubated after the addition of lead (0.6 mumol/l whole-blood) and plasma lead concentrations were repeatedly determined. Incubation was continued until haemolysis developed. Fairly stable plasma lead concentrations were established at, on the average, 0.5-0.6 mumol/l after 10-30 min and persisted throughout the incubation with no significant difference between ALS- and control samples. Unexpectedly, it was also observed that haemolysis occurred significantly earlier in the ALS- than in the control samples. Plateau levels in plasma lead concentration of the same order as in the present experiments have been observed both in ALS- and control samples in previous experiments with the same technique, where the lead dose added was twice as high, and these plateau levels were about 10 times higher than those observed in vivo in ALS patients and controls. It is therefore suggested that the final plasma lead concentrations in vivo is established by factors other than the erythrocyte uptake and it is improbable that the differences between ALS patients and controls in plasma lead concentration are associated with differences in the degree of lead uptake by the red cells. The increased plasma lead concentrations in ALS patients may instead be caused by increased fragility of the erythrocytes, as manifested by the earlier occurrence of haemolysis in the present experiments. The observation of increased red cell fragility is, however, also of interest as a possible manifestation of a generalized membrane defect.