Deoxygenation-induced cation fluxes in sickle cells. IV. Modulation by external calcium.
Net cation movements were measured in low-density sickle red blood cells (SS RBC) in the presence and absence of oxygen. External Ca2+ (Ca2+o) partially inhibited deoxygenation-induced fluxes of both Na+ and K+. Deoxygenation-induced Na+ influx was reduced by 2 mM Ca2+o to 0.71 +/- 0.04 (SE) of its value in Ca(2+)-free solutions, whereas this ratio was 0.90 +/- 0.05 for K+ efflux (P < 0.01 by paired t-test). Because Ca2+o inhibited Na+ influx more than K+ efflux, net cation loss in deoxygenated SS RBC was higher in the presence of Ca2+o. In separate experiments, Ca2+o reduced deoxygenation-induced Na+ influx to 0.66 +/- 0.03 of its Ca(2+)-free value compared with 0.77 +/- 0.03 for Rb+ influx (P < 0.001), indicating relative selectivity of this effect for Na+ over Rb+. However, this effect is not specific for Ca2+ because other divalent cations also inhibited deoxygenation-induced Na+ and K+ fluxes. Under the conditions of these experiments, no evidence for K+ channel activation was found, indicating that K+ loss measured in deoxygenated SS RBC was mediated by the deoxygenation-induced pathway. These studies show that in the presence of Ca2+o deoxygenation-induced Na+ influx and K+ efflux are unbalanced. This pathway can, therefore, mediate cation loss and contribute directly to cellular dehydration in SS RBC.
Joiner
C H
CH
Department of Pediatrics, University of Cincinnati College of Medicine, Children's Hospital Medical Center, Ohio, USA.
Jiang
M
M
Franco
R S
RS
D002118:Calcium / Q000494:pharmacology*; D002412:Cations / Q000097:blood*; D002413:Cations, Divalent / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D010100:Oxygen / Q000097:blood*; D011188:Potassium / Q000097:blood; D012805:Sickle Cell Trait / Q000097:blood* / Q000473:pathology; D012964:Sodium / Q000097:blood
D002412:Cations; D002413:Cations, Divalent; D012964:Sodium; D011188:Potassium; D010100:Oxygen; D002118:Calcium