Logarithmic Domain Growth in Ternary Mixture Lipid Multilayer Systems

Abstract

Cholesterol, one essential constituent of cell membrane, is shown to perform an important function as to maintaining the membrane integrity and fluidity. However, the role of cholesterol in mixed membrane phase behavior is still not completely understood. In our study of model membrane multilayer systems consisting of 1:1 DPPC/DOPC with 0∼30% Cholesterol, we have studied the kinetics of domain growth as a function of time. Both the DOPC rich domains and DPPC rich domains grow vertically via interlayer registry, and also laterally as domains coarsen. X-ray diffraction measurements reveal two different time scales of domain growth: fast growth at small time scale of minutes, and slow growth at large time scale which exhibits a logarithmic growth law for the single domain volume. AFM measurements were also performed to demonstrate the initial fast growth of the domains in real-time hydrated condition. The logarithmic growth occurs at different time scales for different cholesterol concentrations. This logarithmic growth law may indicate that the barriers to domain growth increase linearly with the domain size [1,2]. Our detailed analysis of domain lipid structure from electron density profiles with different cholesterol concentrations, and comparison of the growth law time constants should shed new light on the effects of cholesterol on membrane domains.[1] J.D. Shore, M. Holzer, and J.P. Sethna, Phys. Rev. B 46, 11376 (1992).[2] Z.W. Lai, G.F. Mazenko, and O.T. Valls, Phys. Rev. B 37, 9481 (1988).