Formation of light irreversibly sickled cells during deoxygenation-oxygenation cycles

Changes in density, morphology, and monovalent cation content of sickle (SS) cells caused by repetitive sickling were investigated in vitro with a device by which red cells can be exposed to cycles of deoxygenation and oxygenation (d-o cycles). Experiments were done using the discocyte-rich, less dense fractions of SS cells. When such cells were subjected to d-o cycles in the presence of 2 mmol/L Ca2+, most became dense within 4 hours. The density of these cells was slightly lower than usual for irreversibly sickled cells (ISCs), and because they reverted to the discoidal shape after oxygenation, they were not considered ISCs. However, on further d-o incubation, they did assume the morphology and density typical of ISCs. After an additional incubation (20 hours), most cells decreased in density, became very fragile, and hemolyzed easily. Such light ISCs could also be formed from freshly prepared dense cells on d-o incubation. Once light ISCs were formed, they did not reconvert to dense cells on further incubation. It should be noted that light ISCs created in vitro tended to aggregate much more easily than ordinary (heavy) ISCs did, suggesting that the membrane of these cells may be very adhesive.