Cyclodextrin-catalyzed extraction of fluorescent sterols from monolayer membranes and small unilamellar vesicles

This study examined the kinetics of sterol desorption from monolayer and sm all unilamellar vesicle membranes to 2-hydroxypropyl-beta-cyclodextrin. The sterols used include cholesterol, dehydroergosterol (ergosta-5,7,9,(11),22 -tetraen-3 beta-ol) and cholestatrienol (cholesta-5,7,9,(11)-trien-3 beta-o l). Desorption rates of dehydroergosterol and cholestatrienol from pure ste rol monolayers were faster (3.3-4.6-fold) than the rate measured for choles terol. In mixed monolayers (sterol: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosp hocholine 30:70 mol%), both dehydroergosterol and cholestatrienol desorbed faster than cholesterol, clearly indicating a difference in interfacial beh avior of these sterols. In vesicle membranes desorption of dehydroergostero l was slower than desorption of cholestatrienol, and both rates were marked ly affected by the phospholipid composition. Desorption of sterols was slow er from sphingomyelin as compared to phosphatidylcholine vesicles. Desorpti on of fluorescent sterols was also faster from vesicles prepared by ethanol -injection as compared to extruded vesicles. The results of this study sugg est that dehydroergosterol and cholestatrienol differ from cholesterol in t heir membrane behavior, therefore care should be exercised when experimenta l data derived with these probes are interpreted. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.