Lateral diffusion in the liquid phases of dimyristoylphosphatidylcholine/cholesterol lipid bilayers: a free volume analysis

Abstract

The technique of fluorescence recovery after photobleaching is used to perform an extensive study of the lateral diffusion of a phospholipid probe in the binary mixture dimyristoylphosphatidylcholine/cholesterol, above the melting temperature of the phospholipid. In the regions of the phase diagram where a single liquid phase exists, diffusion can be quantitatively described by free volume theory, using a modified Macedo-Litovitz hybrid equation. In the liquid-liquid immiscibility region, the temperature dependence of the diffusion coefficient is in excellent agreement with current theories of generalized diffusivities in composite two-phase media. A consistent interpretation of the diffusion data can be provided based essentially on the idea that the primary effect of cholesterol addition to the bilayer is to occupy free volume. On this basis, a general interpretation of the phase behavior of this mixture is also proposed.

The effects of cholesterol and β-sitosterol on the structure of saturated diacylphosphatidylcholine bilayers

“…3 show that 33 mol% cholesterol suppresses both the pretransition and the main phase transition. This is in accordance with cholesterol-DPPC (Vist and Davis 1990) and cholesterol-DMPC (Almeida et al 1992) phase diagrams, according to which the systems studied are in a broad range of temperatures in the liquid-ordered phase L o in the presence of more than approximately 25 mol% cholesterol. The decrease of d was 0.21 ± 0.01 nm when the temperature was increased from 20 to 50°C (Fig.…”

Aggregatibacter actinomycetemcomitans Leukotoxin Utilizes a Cholesterol Recognition/Amino Acid Consensus Site for Membrane Association

“…The liposomes were composed of DMPC with 0, 20, 40, or 60% cholesterol (or ergosterol). At room temperature, DMPC with 0% cholesterol exists in a nonraft-like state (liquid disordered); at 40 and 60% cholesterol, DMPC exists in a raft-like state (liquid ordered); and at 20% cholesterol, both phases coexist (27,28).…”

“…2, the difference between panels E and J indicates that the strong affinity of LtxA to sterol-containing membranes is specific for cholesterol. Membranes composed of DMPC and cholesterol are known to phase separate into cholesterol-poor (liquid-disordered) and cholesterol-rich (liquid-ordered) regions, depending on the temperature and cholesterol composition of the system (28). The liquid-ordered phase is often used as a model of lipid rafts because of their similar compositions (rich in cholesterol and saturated lipids, poor in unsaturated lipids).…”

Effect of tetracaine on DMPC and DMPC+cholesterol biomembrane models: Liposomes and monolayers

“…The existence of two superimposed peaks that tend to merge as the number of heating/cooling scans increases, suggests domains with different CHOL contents [40,41]. According to the literature, at low temperatures, the mixture of DMPC with 30 mol% CHOL is mainly in a liquid ordered phase, l 0 , coexisting with a small amount of solid-gel phase [42]. At higher temperatures, the solid phase disappears and, between  30-37ºC, part of the liquid ordered phase gives rise to a liquid disordered phase, l d .…”

“…The obtained results point to the initial presence of two phases that merge in one phase, probably the l 0 phase. The broad and small enthalpic peak at  30ºC may be related with the transition from l 0 to the l d phase [42].…”