ANTISICKLING EFFECTS OF 2,3-DIPHOSPHOGLYCERATE DEPLETION

Elevation of 2,3-bisphosphoglycerate (2,3-DPG) in sickle erythrocytes (SS RBCs) and concomitant acidification of the cell interior promote p olymerization by decreasing the solubility (c(sat)) of deoxyhemoglobin S. The antisickling effect of 2,3-DPG depletion was evaluated after a ctivation of the 2,3-DPG phosphatase activity of bisphosphoglycerate m utase by glycolate-2-phosphate, leading to rapid loss of intracellular 2,3-DPG. To ensure its maximal reduction in a physiologic medium, iso smotic CO2/bicarbonate-buffered saline, pH 7.0, was used. Substitution of K+ for Na+ as the major extracellular cation suppressed K:Cl cotra nsport, prevented cell shrinkage, and allowed demonstration of the ful l antisickling effect of 2,3-DPG depletion. The modest effect on solub ility per seof removing intraerythrocytic 2,3-DPG (Delta c(sat) = 1.6 g/dL) was amplified into a much larger antisickling effect by interact ion with three other cellular variables affecting solubility and polym er content (intracellular pH, O-2 saturation, and mean cell hemoglobin concentration). Acting in concert, these four antisickling effects (t hree solubilizing, one osmotic) reduced polymer fraction of glycolate- treated SS RBCs by 32% to 63%, with a concomitant decrease in sickling of 46% to 95% at the nominal pO(2) of the microcirculation (20 mm Hg) . A decrement in sickling of this magnitude should significantly ameli orate the vasoocclusive severity of sickle cell disease. (C) 1995 by T he American Society of Hematology.