Lateral diffusion cholesterol, effect

Shin, Y. K., and Freed, J. H. (1989), Dynamic imaging of lateral diffusion by electron spin resonance and study of rotational dynamics in model membranes. Effect of cholesterol, Biophys. J., 55, 537-550. 

The above estimates are for fluid-like systems. In gel-like systems with features of frozen order, the time scales are much longer. For example, the lateral diffusion coefficient in a gel-like one-component membrane is about 10 -10 cm /s (43), whereas in a fluid membrane it is usually 10 cm /s. In a similar maimer, the diffusion of matter inside lipid droplets is a much slower process compared with lipid interfaces caused by entanglement effects, as the situation is largely similar to a polymer melt. This effect is the case inside LDL. It has been estimated that the diffusion coefficient for cholesterol esters inside LDL particles is roughly 10 cm /s (44) and is intermediate to diffusion in fluid- and gel-like membranes. 

The effect of cholesterol on lateral diffusion has also been studied. Rubenstein and co-workers [50] have found that the lateral diffusion of a fluorescent labelled phosphoUpid, phosphatidyl-iV-(4-nitrobenzo-2-oxa-l, 3-diazole)ethanolamine, exhibited an abrupt change in its lateral diffusion coefficient at 20 mole% cholesterol in a binary mixture of cholesterol and dimyristoylglycerophosphochoUne. Two explanations for this behaviour have been proposed based on the existence of ordered microscopic domains characterised by ripples or strips of solid phase interspread with the more fluid domains of the phosphoUpid-cholesterol complex [51-53]. Such a structure would form barriers to free lateral diffusion. An alternative... 

A. Filippov, G. Oradd, G. Lindblom, The effect of cholesterol on the lateral diffusion of phospholipids in oriented bilayers, Biophys. J., 2003, 84, 3079-3086. 

Incorporation of cholesterol into model membranes increase the order parameter of the hydrocarbon chains but leaves the lipid lateral diffusion almost unaffected (12). Therefore it can be concluded that the effect of cholesterol on the packing properties of the bilayers is more important than its influence on lipid bilayer dynamics. 

Fluidity in membranes is an easily visualized phenomenon and is a term which is widely used. However, it can be misleading. For example, it is commonly assumed (and stated) that making membrane lipids more saturated or adding cholesterol makes a membrane less fluid. The assumption is that such alterations will reduce the speed of movement of lipids. However, introduction of cholesterol into phosphatidylcholine model membranes has no effect on lateral movement and may actually increase rotational diffusion rates. What cholesterol and increased saturation do is to increase the order in the hydrocarbon matrix and this is what can be measured easily by NMR or ESR order parameters. 

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