Red Cells Shrink During Sickling

Rapid transformation of discoid hemoglobin SS erythrocytes into grossly distorted sickled forms suggests alteration of surface/volume ratio. We, therefore, examined the effect of deoxygenation on red cell volume. ¹³¹I-labeled albumin was used as a marker of plasma volume in normal (Hb AA), sickle (Hb SS), and sickle-C (Hb SC) blood. Heparinized blood was incubated for 30 min at 37°C in a tonometer under deoxy (90% N₂, 10% CO₂) or oxy (90% O₂, 10% CO₂) atmospheres. Whole blood and plasma concentrations of radioactivity were determined. The hematocrits thus obtained with ¹³¹I-albumin showed that deoxygenation caused: (1) Hb AA cells to swell (mean MCV +4.0 cu µ ± 3.0, p < 0.01), as is predicted by the Bohr effect; (2) Hb SS cells to shrink (mean MCV -9.4 cu µ ± 2.9, p < 0.001); Hb SC cells to shrink (mean MCV -4.1 cu µ ± 0.8, p < 0.02). We also measured size distributions of glutaraldehyde-fixed oxy and deoxy cells using a Coulter Model B counter. This method confirmed the results of the radioalbumin experiments. These results demonstrate loss of cell volume during sickling of intact erythrocytes. Possible mechanisms for this loss include potassium efflux with obligatory water efflux, increased intracellular hydrostatic pressure from deformation of the cell membrane, or loss of intracellular osmotic activity of hemoglobin secondary to polymerization. This dehydration enables the sickled cell to develop more extreme shape distortion without membrane disruption, may facilitate continued hemoglobin polymerization, and may play a role in the formation of "irreversibly" sickled cells.