Lateral phase separation in mixtures of lipids and cholesterol

¹ Department of Chemistry, Faculty of Science, Tokyo Metropolitan University Tokyo 192-0397, Japan
² School of Physics and Astronomy, University of Leeds - Leeds LS2 9JT, UK
³ School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University - Ramat Aviv 69978, Tel Aviv, Israel

Corresponding author: komura@comp.metro-u.ac.jp

Received: 10 February 2004
Accepted: 5 May 2004

Abstract

In an effort to understand “rafts” in biological membranes, we propose phenomenological models for saturated and unsaturated lipid mixtures, and lipid-cholesterol mixtures. We consider simple couplings between the local composition and internal membrane structure, and their influence on transitions between liquid and gel membrane phases. Assuming that the gel transition temperature of the saturated lipid is shifted by the presence of the unsaturated lipid, and that cholesterol acts as an external field on the chain melting transition, a variety of phase diagrams are obtained. The phase diagrams for binary mixtures of saturated/unsaturated lipids and lipid/cholesterol are in semi-quantitative agreement with the experiments. Our results also apply to regions in the ternary phase diagram of lipid/lipid/cholesterol systems.