Percolation and diffusion in three-component lipid bilayers: effect of cholesterol on an equimolar mixture of two phosphatidylcholines.
The lateral diffusion of a phospholipid probe is studied in bilayers of binary mixtures of dimyristoylphosphatidylcholine (DMPC)/cholesterol and distearoylphosphatidylcholine (DSPC)/cholesterol and in the ternary system DMPC/DSPC/cholesterol using fluorescence recovery after photobleaching. An approximate phase diagram for the ternary system, as a function of temperature and cholesterol concentration, was obtained using differential scanning calorimetry and the phase diagrams of the binary systems. This phase diagram is similar to those of the phospholipid/cholesterol binary mixtures. In bilayers where solid and liquid phases coexist, the diffusion results are interpreted in terms of phase percolation. The size of the liquid-phase domains is estimated using percolation theory. In the ternary system, addition of cholesterol up to approximately 20 mol% shifts the percolation threshold to lower area fractions of liquid, but the size of the liquid-phase domains does not change. Above approximately 20 mol% cholesterol, the liquid phase is always connected. The size of solid-phase domains clusters is estimated using a model recently developed (Almeida, P.F.F., W.L.C. Vaz, and T.E. Thompson. 1992. Biochemistry. 31:7198-7210). For cholesterol concentrations up to 20 mol%, the size of solid-phase domain units does not change. Beyond 20 mol%, cholesterol causes the size of the solid units to decrease.
Almeida
P F
PF
Department of Biochemistry, University of Virginia School of Medicine, Charlottesville 22908.
Vaz
W L
WL
Thompson
T E
TE
D055592:Biophysical Phenomena; D001703:Biophysics; D002784:Cholesterol / Q000737:chemistry*; D004058:Diffusion; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008956:Models, Chemical; D015335:Molecular Probes; D010713:Phosphatidylcholines / Q000737:chemistry*; D010777:Photochemistry; D013816:Thermodynamics
D008051:Lipid Bilayers; D015335:Molecular Probes; D010713:Phosphatidylcholines; D002784:Cholesterol; C010942:1,2-distearoyllecithin; D004134:Dimyristoylphosphatidylcholine