Three-dimensional structure of lipid vesicles embedded in vitreous ice and investigated by automated electron tomography.

Automated electron tomography is shown to be a suitable means to visualize the shape of phospholipid vesicles embedded in vitrified ice. With a slow-scan charge-coupled device camera as a recording device, the cumulative electron dose needed to record a data set of 60 projections at a magnification of 20,000X can be kept as low as 15 e-/A2 (or 1500 electrons/nm2). The membrane of the three-dimensionally reconstructed vesicles is clearly visible in two-dimensional sections through the three-dimensionally reconstructed volume. Some edges indicating a polygonal shape of the vesicles, frozen from the gel phase, are also clearly recognized. Because of the presently limited tilt angle range (+/- 60 degrees), the upper and lower "caps" of the vesicles (representing about 35% of the surface of the ellipsoidal particles) remain invisible in the three-dimensional reconstruction.