Characterization of Lipid Membrane Assembly and Physical Properties by Studying Lipid Nanotube Radii

Lipid membrane structures are essential within living cells, especially in inter/intra-cellular communication. Artificial lipid membrane systems, such as vesicles, are used to model biological processes and to investigate membrane properties and behavior.

We developed a novel approach to determine lipid nanotube radii (Fig. 1). These radii have a critical dimension below the diffraction limit of confocal microscopy, but are essential for modeling and understanding of highly curved membrane compartments of living cells. The nanotube radii are directly related to fundamental properties of lipid material and lipid self assembly. Therefore radial measurement is sensitive to changes in lipid composition, like insertion of sterols, or to membrane interactions with solutes, for example sodium ions (Fig. 2). Method is also useful to characterize lamellarity of vesicles. Figure 3 illustrates change in one, two and three bilayer nanotubes radii with increase of cholesterol content.

Figure 1 Determination of a nanotube radius with membrane displacement analysis.

Figure 2 Nanotube radius change with lipid composition or upon membrane interaction with solutes.

Figure 3 Nanotube radii dependence upon cholesterol concentration for 1 (•), 2 (×), and 3 (°) lamellar nanotubes, indicating measurable compositional changes.