Condensed complexes of cholesterol and phospholipids

There is overwhelming evidence that lipid bilayer regions of animal cell membranes are in a liquid state. Quantitative models of these bilayer regions must then be models of liquids. These liquids are highly non-ideal. For example, it has been known for more than 75 years that mixtures of cholesterol and certain phospholipids undergo an area contraction or condensation in lipid monolayers at the air-water interface. In the past 3 years, a thermodynamic model of "condensed complexes" has been proposed to account for this non-ideal behavior. Here we give an overview of the model, its relation to other models, and to modem views of the properties of animal cell membranes. (C) 2003 Elsevier Science B.V. All rights reserved.