Rate of deoxygenation modulates rheologic behavior of sickle red blood cells at a given mean corpuscular hemoglobin concentration

Although the mean corpuscular hemoglobin concentration (MCHC) plays a domin ant role in the theologic behavior of deoxygenated density-defined sickle r ed blood cells (SS RBCs), previous studies have not explored the relationsh ip between the rate of deoxygenation and the bulk viscosity of SS RBCs at a given MCHC. In the present study, we have subjected density defined SS cla sses (i.e., medium-density SS4 and dense SS5 discocytes) to varying deoxyge nation rates. This approach has allowed us to minimize the effects of SS RB C heterogeneity and investigate the effect of deoxygenation rates at a give n MCHC. The results show that the percentages of granular cells, classic si ckle cells and holly leaf forms in deoxygenated samples are significantly i nfluenced by the rate of deoxygenation and the MCHC of a given discocyte su bpopulation. increasing the deoxygenation rate using high K+ medium (pH 6.8 ), results in a greater percentage of granular cells in SS4 suspensions, ac companied by a pronounced increase in the bulk viscosity of these cells com pared with gradually deoxygenated samples (mainly classic sickle cells and holly leaf forms). The effect of MCHC becomes apparent when SS5 dense cells are subjected to varying deoxygenation rates. At a given deoxygenation rat e, SS5 dense discocytes show a greater increase in the percentage of granul ar cells than that observed for SS4 RBCs. Also, at a given deoxygenation ra te, SS5 suspensions exhibit a higher viscosity than SS4 suspensions with fa st deoxygenation resulting in maximal increase in viscosity. Although MCHC is the main determinant of SS RBC rheologic behavior, these studies demonst rate for the first time that at a given MCHC, the rate of deoxygenation (he nce HbS polymerization rates) further modulates the theologic behavior of S S RBCs. Thus, both MCHC and the deoxygenation rate may contribute to microc irculatory flow behavior of SS RBCs.