Oxidative Activation of K-Cl Cotransport by Diamide in Erythrocytes from Humans with Red Cell Disorders,and from Several Other Mammalian Species |
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Authors: | NC Adragna PK Lauf |
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Institution: | (1) Departments of Pharmacology & Toxicology, and Physiology & Biophysics, Wright State University School of Medicine, Dayton, Ohio 45401-0927, USA, US |
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Abstract: | 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.
Received: 5 June 1996/Revised: 4 October 1996 |
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Keywords: | : K-Cl cotransport — Erythrocytes — Oxidation — Diamide — Red cell disorders — Sickle cell anemia — Mammalian species |
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