EFFECT OF THE ADDITION OF CERAMIDE TO DIOLEOYLPHOSPHATIDYLCHOLINE VESICLES - AN ESR AND SEM STUDY

Electron spin resonance spectroscopy of doxylstearic acids with the paramagnetic unit inserted in the 5, 6, 7, 9, 12, and 16 carbon position was used to analyze the dynamic and structural features of dioleoylphosphatidylcholine (DOPC) vesicles in the presence and in the absence of ceramide (CER) and as a function of temperature. The sizes and the homogeneity of these lipid aggregates were checked by electron microscopy and turbidimetry. The order parameter, as calculated from the ESR line shapes, indicated that near room temperature the vesicles had a relatively high orientational organization from the polar surface down to the system of the double bonds of the oleoyl residues of DOPC, whereas the double-layer region beyond the double bond was increasingly fluid. At temperatures lower than the gel-liquid crystal phase transition of CER, T(c), the presence of the sphingolipid did not alter significantly the motional properties of the hydrocarbon chains. At T greater-than-or equal-to T(c), the addition of CER affected only the lipid layer region from the surface down to the oleoyl double bonds with resulting increased fluidity. The double-bond region acted therefore as a boundary for the effect of CER. No definitive evidence of lipid interdigitation was given by the results reported in this work.