Dehydration of mature and immature sickle red blood cells during fast oxygenation/deoxygenation cycles: role of KCl cotransport and extracellular calcium

Sickle red blood cells (RBC) become dehydrated as a consequence of potassiu m loss. This process depends at least partly on deoxygenation and may be in fluenced by the presence of oxygenation/deoxygenation cycles and the freque ncy of cycling. In this study, sickle RBC were subjected to approximately 1 80 oxygenation/deoxygenation cycles during 4 hours to evaluate RBC dehydrat ion with cycle periods more similar to in vivo cycles than those in previou s studies, A continuous-flow, steady-state apparatus circulated a dilute RB C suspension through gas-permeable silicone tubing with segments that were exposed to either nitrogen or ambient oxygen. The percentage of sickling an d partial pressure of oxygen were measured by means of sampling ports in th e deoxygenation and oxygenation regions. The density increase (dehydration) of young (transferrin receptor-positive) and mature (transferrin receptor- negative) RBC and the requirements for calcium and chloride were evaluated. Density increase correlated with the percentage of sickled cells at the de oxygenation sampling port and was observed only in the presence of calcium, thereby implicating the calcium-dependent potassium channel (Gardos pathwa y). Density Increase was not dependent on the presence of chloride, making it unlikely that KCI cotransport was an important pathway under these condi tions, (C) 2000 by The American Society of Hematology.