Effects of pressure on the phase transition of bilayers in liposomes. Influence of cholesterol and alpha-tocopherol.

The effects of pressure on the gel-to-liquid crystalline phase transition temperature of dimyristoylphosphatidylcholine (DMPC) bilayers containing cholesterol, alpha-tocopherol, and alpha-tocopheryl acetate were studied by fluorescence depolarization. The transition temperature of cholesterol mixtures (greater than 7.5 mol%) was lower than that of 100% DMPC at atmospheric pressure, but it became higher than the latter on increase in pressure. The thermodynamic parameters of the transition (delta V, delta S, delta H) were estimated and the functions of cholesterol and alpha-tocopherols in the bilayers are discussed.