Oxygen transport in thin layers of packed sickle erythrocytes

A diffusion cell was used to examine the effect of HbS polymerization on the oxygen effective diffusivity, Deff, in packed sickle erythrocytes compared to that in packed normal erythrocytes at 25 degrees. In increasing PO2 experiments, the samples were fully oxygen saturated after a very brief transient. In decreasing PO2 experiments, the average oxygen tension decreased progressively over the time course of the experiment. At full oxygen saturation, Deff in the packed sickle erythrocyte samples was not significantly different from that in normal erythrocytes and was in agreement with prior workers' measurements of unfacilitated oxygen diffusion. Deff measured in the decreasing PO2 experiments on packed sickle erythrocytes was significantly different from that in normal erythrocytes. As the average oxygen tension decreased, Deff in packed normal erythrocytes increased to a maximum of 40% over its unfacilitated value and then decreased. In contrast, in sickle erythrocytes which contained over 90% HbS, as PO2 decreased, Deff increased only slightly and then decreased dramatically. The results of decreasing PO2 experiments on sickle erythrocytes containing significant amounts of other hemoglobins (HbF, HbC) were different from those of both the normal erythrocytes and sickle erythrocytes with dominant HbS fraction, showing the effect of hemoglobin composition on effective diffusivity. These results demonstrate a dramatic effect of HbS polymerization on the resistance to oxygen transport in sickle erythrocytes.