Oxidative activation of K-Cl cotransport by diamide in erythrocytes from humans with red cell disorders, and from several other mammalian species

Red blood cells (RBCs) from different mammalian species were investigated for the presence of diamide-induced oxidative activation of K-Cl cotransport reported to be present in sheep but absent in human RBCs. K efflux was measured in RBCs from human with hemoglobin (Hb) A or S, glucose-phosphate dehydrogenase (G6PDH) and a cytoskeletal deficiency, and from rat, mouse and rabbit. RBCs were incubated with diamide (0-1.0 mM) in K-free Cl or NO3 media of variable osmolalities (200-450 mOsM). CI-dependent K efflux or K-CI cotransport (estimated as the difference between K efflux rate constants in Cl and NO3) was activated by diamide in a sigmoidal fashion. Relative maximum K-CI cotransport followed the sequence: human HbA (1) < rabbit (1.8) < sheep (6.9) < human HbS (9.5) similar to rat (9.7). Relative diamide concentrations for half maximal activation of K-CI cotransport followed the sequence: sheep (1.9) > human Hb A (1) > rabbit (0.75) > human HbS and rat (0.67). Cell swelling in 200 mOsM doubled K-CI cotransport in diamide, both in human HbA and S cells but reduced that in rat RBCs. In contrast, cell shrinkage at 450 mOsM obliterated K-CI cotransport in human HbA and S but not in rat RBCs. Human RBCs with G6PDH and a cytoskeleton deficiency behaved like HbA RBCs. In mouse RBCs, diamide-activated K-CI cotransport was 30% higher in isotonic than in hypotonic medium. In human HbA and S, and in low or high K sheep RBCs fractionated by Percoll density gradient, diamide increased the activity of K-Cl cotransport, an effect inversely correlated with cell density. Analysis of pooled data reveals that K-CI cotransport accounted for about 80% of all K flux in Cl. There was a statistically significant correlation between K-Cl cotransport and K efflux in CI (P < 0.00001) and in NO3 (P < 0.00001). In conclusion, a diamide-activated K-Cl cotransport was present in human RBCs and in all other mammalian RBCs tested, with a large inter-, and for human and sheep, intraspecies variability for its maximum activity.