Effects of cholesterol and cholesteryl ester on dynamic surface tension of dipalmitoyl lecithin

Abstract

The lipid composition of cell membranes, serum lipoproteins, and various subcellular particles determines the lipid-lipid interactions that are in part responsiblefor the architecture, and the physical properties (such as plasticity, viscosity, thermal transitions) of the resulting structures as well as for the biochemical function of the related aqueous surfaces. Cholesterol exists free in cell membranes (1), is carried also free and in the form of cholesteryl esters by serum lipoproteins (2), and is found in both forms in pulmonary lavage, which is obtained by irrigation of the lung with 0.15 M NaCI (3, 4) and is known to affect the surface activity of pulmonary surfactant (5, 6). Also known are the binding of cholesterol to phosphatidyl cholines (lecithins) (7-9) and the influence of cholesteryl esters on the equilibrium force-area curves of lecithin's monomolecular films (10). In this communication, we wish to describe the influence of cholesterol and cholesteryl palmitate on the dynamic force-area curve of dipalmitoyl lecithin at 25 and 37°C in a modified Langmuir trough. A similar study, using adsorbed DPL-cholesterol mixed films by the bubble method has been published recently (6). In our approach we study both adsorbed and spread films, whereby we are able to consider the effect of the physical state of the lipid and of the mode in which the lipid is applied to the interface (3, 5). MATERIALS AND METHODS