Evidence for a direct reticulocyte origin of dense red cells in sickle cell anemia.
To explore our hypothesis of a direct reticulocyte origin of irreversibly sickled cells (ISCs), we fractionated light, reticulocyte-rich, and discocyte-rich sickle anemia red cells on Stractan gradients, and examined the effects of deoxygenation-induced sickling, external Ca2+, acidification, and replacing external Na+ by impermeant N-methyl-D-glucamine (NMG+). Sickling permeabilized light reticulocyte-rich cells to cations (Na+, K+, and Ca2+) more than discocytes; without external Ca2+, Na+ influx matched K+ efflux, with stable cell volume; with Ca2+, many light, low hemoglobin (Hb) F reticulocytes dehydrated rapidly (preventable by quinine, a Ca2(+)-dependent K+ channel inhibitor). Acidification of oxygenated discocytes (high mean Hb F) and reticulocyte-rich fractions yielded denser, reticulocyte-enriched cells with lower Hb F (as in light reticulocyte or dense ISC-rich fractions). Light cells shrank when NMG+ replaced Na+, supporting predictions of a Na(+)-dependent volume control system. Demonstration of sickling-induced, Ca2(+)-dependent dehydration of Hb F-free reticulocytes, and conservation of acid-stimulated K:Cl cotransport among low Hb F, reticulocyte-enriched cells in discocyte fractions support the hypothesis. Ancillary new findings included heparin stimulation of sickling-induced Na+ and K+ permeabilizations, and Ca2+ inhibition of the Na+ leak.
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
R M
RM
Bookchin
O E
OE
Ortiz
V L
VL
Lew
D000755:Anemia, Sickle Cell / Q000097:blood* / Q000378:metabolism; D001834:Body Water / Q000378:metabolism; D002118:Calcium / Q000097:blood / Q000494:pharmacology; D002463:Cell Membrane Permeability; D004912:Erythrocytes / Q000378:metabolism*; D005319:Fetal Hemoglobin / Q000032:analysis; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D011188:Potassium / Q000097:blood; D011803:Quinine / Q000494:pharmacology; D012156:Reticulocytes / Q000378:metabolism*; D012964:Sodium / Q000097:blood
D006493:Heparin; D005319:Fetal Hemoglobin; D012964:Sodium; D011803:Quinine; D011188:Potassium; D002118:Calcium