ESR studies on the effect of cholesterol on chlorpromazine interaction with saturated and unsaturated liposome membranes Original Research Article

In this study, the effects of chlorpromazine (CPZ) on lipid order and motion in saturated (DMPC, DMPG) and unsaturated (SOPC) liposome membranes were investigated by electron spin resonance (ESR) spin labeling technique. We have shown that above the main phase transition temperature of membrane lipids (TM), CPZ slightly increases lipid order in membranes without cholesterol, whereas below TM it has a strong opposite effect. Addition of 30 mol% of cholesterol into DMPC and SOPC membranes changes significantly the CPZ effects both above and below TM. Additionally, above TM, the ordering effect of CPZ on pure SOPC membrane is stronger at pH 7.4 than at pH 9.0, whereas below TM, as well as in the presence of cholesterol, pH does not seem to play a role in CPZ effect on both membranes. Because of the strong influence of membrane composition on CPZ effect on membranes, the use of cholesterol as a marker of CPZ photosensitized reactions has been discussed.