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). Cl-dependent K efflux or K-Cl 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-Cl cotransport followed the sequence: human HbA (1) < rabbit (1.8) < sheep (6.9) < human HbS (9.5) ∼ rat (9.7). Relative diamide concentrations for half maximal activation of K-Cl 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-Cl 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-Cl 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-Cl 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-Cl 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 Cl (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.
The Journal of Membrane Biology – Springer Journals
Published: Feb 1, 1997
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