Stimulation by uraemic plasma of frusemide-sensitive sodium efflux in erythrocytes from normal women.

1. Reduced Na+,K+ pump activity has been reported in uraemic erythrocytes, and this has been attributed to the presence of a circulating ouabain-like inhibitor. Since we have previously reported marked suppression of Na+,K+ co-transport activity in erythrocytes from dialysis patients, we have now examined the effect of incubation with uraemic plasma on Na+ efflux through the Na+,K+ pump and the co-transport pathway in normal erythrocytes from both men and women. 2. The results show that Na+ efflux via the Na+,K+ pump is not different between men and women (3.14 +/- 0.14 vs 3.68 +/- 0.18 mmol h-1 litre-1 of cells) and is not inhibited by incubation with uraemic plasma. 3. In contrast, co-transport-mediated Na+ efflux is lower in erythrocytes from normal women when compared with normal men (0.17 +/- 0.02 vs 0.25 +/- 0.05 mmol h-1 litre-1 of cells, P less than 0.001). 4. Moreover, incubation with uraemic plasma causes stimulation of Na+ efflux through the co-transport pathway in erythrocytes of healthy women (0.17 +/- 0.02 vs 0.27 +/- 0.03 mmol h-1 litre-1 of cells, P less than 0.005), but not in erythrocytes of healthy men (0.27 +/- 0.03 vs 0.25 +/- 0.05 mmol h-1 litre-1 of cells). 5. Our data do not support the presence of either a Na+,K+ pump or a co-transport inhibitor in plasma from dialysed uraemic patients. Thus, the suppressed co-transport activity demonstrated in uraemic erythrocytes cannot be attributed to a circulating inhibitor, and may reflect an acquired membrane or transport defect.(ABSTRACT TRUNCATED AT 250 WORDS)