Lateral distribution of cholesterol in membranes probed by means of a pyrene-labelled cholesterol: effects of acyl chain unsaturation.
The lateral distribution of cholesterol in membranes in the fluid state was investigated by studying the variation of the molar absorption coefficient of pyrene-labelled cholesterol (Py-chol) vs. its concentration in vesicles made of phosphatidylcholine, with variable acyl chain unsaturations. Absorption measurements indicated non-ideal mixing of Py-chol in unsaturated lipids, a process mainly controlled by the cholesterol moiety of the probe. Similar abilities of cholesterol and Py-chol in perturbing the phase properties of pure saturated phosphatidylcholine were observed by DSC experiments. Immiscibility of sterols was corroborated by fluorescence polarization measurements, which indicated a weaker ordering effect of cholesterol in unsaturated membranes. The sizes and the quantities of sterol oligomers formed were calculated. A model for the lateral distribution of cholesterol in membranes is proposed and is applied to known cholesterol/phosphatidylcholine phase diagrams. Finally, the results are discussed with regard to recent models of biological membrane organization, (i.e. rafts).
Lagane
B
B
Institut de Pharmacologie et de Biologie Structurale du CNRS, 205 route de Narbonne, 31077 cedex 4, Toulouse, France.
Mazères
S
S
Le Grimellec
C
C
Cézanne
L
L
Lopez
A
A
D002152:Calorimetry, Differential Scanning; D002784:Cholesterol / Q000737:chemistry*; D016231:Fluorescence Polarization Immunoassay; D007202:Indicators and Reagents; D008055:Lipids / Q000737:chemistry; D008567:Membranes, Artificial; D008956:Models, Chemical; D017711:Nonlinear Dynamics; D013056:Spectrophotometry, Ultraviolet
D007202:Indicators and Reagents; D008055:Lipids; D008567:Membranes, Artificial; D002784:Cholesterol