Phospholipid vesicle stability and temporal variations in acyl chain organization

• Phospholipid vesicles do not change in size following extrusion.
• Cholesterol alters the size of extruded vesicles.
• Lipid acyl chains in vesicles anneal over hours.
• Re-extrusion of vesicles decreases annealing-induced order.

We report on our investigation of the long-term dimensional stability and acyl chain organization of unilamellar vesicles containing 1,2-dimyristoyl-sn-phosphatidylcholine (DMPC) and DMPC with cholesterol. Vesicles of 100% DMPC, 80% DMPC/20% cholesterol and 70% DMPC/30% cholesterol, formed by extrusion in aqueous buffer solution (pH 8) were shown to remain dimensionally stable for periods in excess of 600 h by dynamic light scattering (DLS) measurements. The rotational diffusion dynamics of perylene confined in the vesicle acyl chain region revealed structural evolution that was dependent on vesicle composition. Re-extrusion of the vesicles caused no changes in the average diameter or size distribution, but did give rise to diminished organization in the lipid acyl chain region for DMPC vesicles. Cholesterol-containing vesicles exhibited somewhat less pronounced change in organization on re-extrusion, suggesting a structurally mediating role for cholesterol.

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