Spontaneous shape transformation of free-floating lipid membrane nanotubes

Freely floating lipid nanotubes, up to several hundred micrometers long, were found to spontaneously contract in length, and eventually transform into stomatocyte-like structures. This transformation was largely driven by the high curvature energy. The nanotubes equilibrate their membrane leaflet areas, by folding into tubular stomatocyte-like structures without any significant volume change, but require a substantial interleaflet lipid transport rate, estimated to be as high as 0.01–0.001 s−1. The rate of transformation was dependent on the fluorescent membrane stain used, and nanotubes labelled with a water-soluble styryl dye, FM1-43, transformed approximately five-fold faster than nanotubes labelled with the phospholipid conjugated dye Texas Red DHPE.