CRYO-TRANSMISSION ELECTRON-MICROSCOPY OF A SUPERSTRUCTURE OF FLUID DIOLEOYLPHOSPHATIDYLCHOLINE (DOPC) MEMBRANES

Using cryo-transmission electron microscopy, we have obtained abundant and reproducible evidence for a superstructure of dioleoylphosphatidy lcholine (DOPC) bilayers. Dispersions of vesicles were prepared by gen tle shaking of a 2% suspension of DOPC in water followed in part by ex trusion through a porous technical membrane. Sampling and cryofixation took place at various times within 3 weeks after the preparation. Fro m the micrographs we infer that the small fraction of vesicles enclosi ng one another develop passages (connections) between the bilayers. In contrast, the superstructure is basically a feature of disconnected m embranes. Among its modifications are isolated membrane bends or folds and a grainy membrane texture with a minimal grain spacing of 4-6 nm. In the extruded dispersions the passages and the superstructure seem to be formed mostly within the first day. The fraction of smooth and u nilamellar vesicles is large at all times and in all dispersions.