Effects of deoxygenation on active and passive Ca2+ transport and on the cytoplasmic Ca2+ levels of sickle cell anemia red cells.
Elevated [Ca2+]i in deoxygenated sickle cell anemia (SS) red cells (RBCs) could trigger a major dehydration pathway via the Ca(2+)-sensitive K+ channel. But apart from an increase in calcium permeability, the effects of deoxygenation on the Ca2+ metabolism of sickle cells have not been previously documented. With the application of 45Ca(2+)-tracer flux methods and the combined use of the ionophore A23187, Co2+ ions, and intracellular incorporation of the Ca2+ chelator benz-2, in density-fractionated SS RBCs, we show here for the first time that upon deoxygenation, the mean [Ca2+]i level of SS discocytes was significantly increased, two- to threefold, from a normal range of 9.4 to 11.4 nM in the oxygenated cells, to a range of 21.8 to 31.7 nM in the deoxygenated cells, closer to K+ channel activatory levels. Unlike normal RBCs, deoxygenated SS RBCs showed a two- to fourfold increase in pump-leak Ca2+ turnover. Deoxygenation of the SS RBCs reduced their Ca2+ pump Vmax, more so in reticulocyte- and discocyte-rich than in dense cell fractions, and decreased their cytoplasmic Ca2+ buffering. Analysis of these results suggests that both increased Ca2+ influx and reduced Ca2+ pump extrusion contribute to the [Ca2+]i elevation.
Etzion
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Z
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
Tiffert
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Bookchin
R M
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Lew
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VL
D000755:Anemia, Sickle Cell / Q000378:metabolism*; D001692:Biological Transport; D001693:Biological Transport, Active; D002021:Buffers; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D015687:Cell Hypoxia; D003035:Cobalt / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism*; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008956:Models, Chemical; D012156:Reticulocytes / Q000378:metabolism
D002021:Buffers; D007477:Ions; D000001:Calcimycin; D003035:Cobalt; D000252:Calcium-Transporting ATPases; D002118:Calcium