Size and shape determination of fixed chylomicrons and emulsions with fluid or solid surfaces by three-dimensional...

Chylomicrons and chylomicron-sized emulsions are spherical particles in suspension but their shape and apparent size may be distorted by electron microscopy processing. To assess adsorption to grids, flattening, and shrinkage, chylomicrons and emulsions were fixed with osmium tetroxide and together with polystyrene beads were shadowed with platinum. Vertical profiles projected from particle shadows indicated that the chylomicrons and emulsions were slightly shrunken, slightly truncated, oblate spheroids while the polystyrene beads were spheres. Particle diameters were corrected by assuming that volumes of oblate spheroids on the grid surface were equal to volumes of spheres in the original lipid suspension. Because of the compensating effects of shrinkage (decreases diameter) and flattening (increases diameter) the differences between the means of measured diameters and corrected diameters were less than or equal to 5%.