The effect of deoxygenation rate on the formation of irreversibly sickled cells

The effects of the deoxygenation rate on the formation of irreversibly sickled cells (ISCs) were investigated by using metabolically replete sickle cells (SS cells). We found that the formation of ISCs required Ca2+ and that the amount formed depended on the rate of deoxygenation. When less dense SS discocytes were deoxygenated slowly by flushing with 95% N2 and 5% CO2 at a rate of 3 mL/min, the percentage of ISCs increased from 5% to 26.5% after 24 hours. In contrast, upon rapid deoxygenation (10, 35 mL/min) ISC formation was reduced significantly. The difference may be related to fact that more sickle-shaped cells were formed upon slow deoxygenation than upon the rapid deoxygenation that resulted in the formation of star-shaped and granulated cells. So-called ISCs were formed more easily from sickle-shaped cells. To express the shape of sickled cells numerically, we calculated the mean maximum cell length (MCL) after cells were incubated under various deoxygenation conditions. The MCL of slowly deoxygenated SS cells after 24 hours of incubation was about twice (20.0 +/- 7.0 micron) that of quickly deoxygenated (35 mL/min) SS cells (12.5 +/- 5.0 microns) (initial MCL, 8.0 +/- 1.0 micron). The decrease in potassium content was greater with slow deoxygenation than with rapid deoxygenation. Because the increase in sodium influx was less than that of potassium efflux under slow deoxygenation, SS cells became more dense than those rapidly deoxygenated. In the absence of Ca2+, morphological changes were the same as in the presence of Ca2+; however, under this condition there was no change in density, and no ISCs were formed regardless of the rate of deoxygenation. These results demonstrate that the number of ISCs formed correlates with the MCL. The length of fibers of sickle hemoglobin may be a determinant of the length of sickled cells. This suggests that membrane stretching plays an important role in cell density and irreversible membrane deformation.