Nc. Adragna et Pk. Lauf, OXIDATIVE ACTIVATION OF K-CL COTRANSPORT BY DIAMIDE IN ERYTHROCYTES FROM HUMANS WITH RED-CELL DISORDERS, AND FROM SEVERAL OTHER MAMMALIAN-SPECIES, The Journal of membrane biology, 155(3), 1997, pp. 207-217
Red blood cells (RBCs) from different mammalian species were investiga
ted for the presence of diamide-induced oxidative activation of K-Cl c
otransport 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, g
lucose-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 differe
nce between K efflux rate constants in Cl and NO3) was activated by di
amide in a sigmoidal fashion. Relative maximum K-CI cotransport follow
ed the sequence: human HbA (1) < rabbit (1.8) < sheep (6.9) < human Hb
S (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 hum
an HbA and S cells but reduced that in rat RBCs. In contrast, cell shr
inkage 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 cotranspo
rt was 30% higher in isotonic than in hypotonic medium. In human HbA a
nd S, and in low or high K sheep RBCs fractionated by Percoll density
gradient, diamide increased the activity of K-Cl cotransport, an effec
t inversely correlated with cell density. Analysis of pooled data reve
als that K-CI cotransport accounted for about 80% of all K flux in Cl.
There was a statistically significant correlation between K-Cl cotran
sport and K efflux in CI (P < 0.00001) and in NO3 (P < 0.00001). In co
nclusion, a diamide-activated K-Cl cotransport was present in human RB
Cs and in all other mammalian RBCs tested, with a large inter-, and fo
r human and sheep, intraspecies variability for its maximum activity.