Freeze-replica study of lipid droplets in the Ito cells of rat liver.

The structure of lipid droplets in the Ito cells was studied by the freeze-replica method in vitamin A-treated rats. Most lipid droplets were fractured in planes through their lipid contents. Some of them were surrounded by a membrane structure that had intramembranous particles (IMP), which were more numerous on the protoplasmic face than the exoplasmic face. Those with the membrane containing IMP correspond to the membrane-bounded lipid droplets (lipid droplets surrounded by lysosomes) seen in the electron microscopic observation of conventional thin section preparations. There were no lipid droplets showing concave or convex multilayered structures in the Ito cells from properly fixed livers. Since these multilayered structures were observed only in the materials fixed by immersion with glutaraldehyde or fixed 40 minutes after the death of animals, it is likely that they represent an artifact, showing an autolytic change, caused by poor fixation or postmortem change.