Dynamic Domains in Lipid Membranes near a Miscibility Critical Point

Abstract

Micron‐scale liquid domains appear in membranes containing at least three lipid types (lipids with high melting temperature, lipids with low melting temperature, and cholesterol or a similar sterol) as long as the membrane is at a temperature below a miscibility transition. When the transition occurs at a critical point, distinctive phenomena occur. Just below the critical temperature, the edges of domains fluctuate. Just above the critical point, domains are replaced by submicron fluctuations. We find that the size of the largest fluctuations (the correlation length) and their lipid composition (the order parameter) scale in a way that is consistent with predictions from a reductionist physical model (the two‐dimensional Ising model) (Honerkamp‐Smith et al. BJ 2008). Other researchers have found that complex mixtures of lipids and proteins derived from cell membranes in GPMVs (giant plasma membrane vesicles) exhibit the same critical behavior (Veatch et al. ACS Chem. Biol. 2008). Recently, we became interested in how long composition fluctuations persist in lipid membranes. We measured the effective dynamic critical exponent relating the decay time of membrane composition fluctuations to the wavenumber (an inverse length). We find that at temperatures far from the critical point, the exponent is 2, as expected from diffusion. As the temperature approaches the critical point, the exponent increases