Deoxygenation-induced alterations in sickle cell membrane cholesterol exchange.

Changes in a membrane sterol exchange of sickle red blood cells (SS RBC) induced by deoxygenation were studied using the fluorescent cholesterol analogue dehydroergosterol (DHE). DHE uptake by SS RBC membrane was measured by the incubation of SS RBC with small unilamellar vesicles (SUV) containing DHE. Deoxygenation of SS RBC, but not normal RBC, increased the rate of DHE uptake. DHE membrane content after 5 h of incubation with SUV in the cell-to-SUV ratio of 1:1 (mol lipid) was 16.25 +/- 0.94 and 12.22 +/- 0.85% of total sterol for deoxygenated and oxygenated cells, respectively. Membrane spicules isolated from these deoxygenated SS RBC had three-fold higher DHE content, suggesting that the increased sterol exchange was localized to spicules. When isolated spicules were incubated with DHE-SUV directly, 91 +/- 3% of membrane sterol was rapidly exchanged, in contrast to intact RBC, in which a maximum of 33% of sterol could be exchanged. The results suggest that spicule formation in SS RBC alters membrane cholesterol structure, such that a domain of cholesterol that is normally nonexchangeable becomes readily exchangeable with exogenous sterol.