Liver parenchymal cells differ from the fat‐storing cells in their lipid composition

The neutral lipid and phospholipid compositions of purified sinusoidal (fat‐storing, endothelial and Kupffer) cells, parenchymal cells and liver homogenates were determined by thin layer chromatography. In addition, the retinoid content of the same purified cell populations was determined by high performance liquid chromatography. From each cell type, both a lipid droplet fraction and a pellet fraction (containing the majority of the remaining cell organelles) were prepared by differential centrifugation. Electron microscopic analysis showed that lipid droplets isolated from fat‐storing cells were larger (up to 8 μm) than those isolated from parenchymal cells (up to 2.5 μm). Moreover, the parenchymal lipid droplets seemed to be surrounded by a membranous structure, while the fat‐storing lipid droplets seemed not to be. Both fat‐storing and parenchymal cells contained high concentrations of neutral lipids, 57.9 μg and 71.0 μg/106 cells, respectively, while endothelial and Kupffer cells contained only 8.6 μg and 13.8 μg/106 cells of neutral lipids, respectively. Sixty‐five percent of fat‐storing cell lipid droplet fractions comprised esters of retinol and cholesterol. This combined ester fraction contained mainly retinyl esters. In addition, considerable quantities (20%) of triglycerides were present. Parenchymal cell lipid droplet fractions comprised triglycerides (62%) and cholesteryl esters (up to 30%). The pellet fractions prepared from all four cell types consisted mainly of cholesterol (41–67%) and free fatt acids (20–28%). The phospholipid content was much higher in parenchymal cells than in the sinusoidal liver cell types. The relative proportions of the four major phospholipid classes were comparable in all liver cell types analyzed. It is concluded that parenchymal cell lipid droplets comprised mainly triglycerides and cholesteryl esters, which is in agreement with the function of parenchymal cells in lipid metabolism. Fat‐storing cell lipid droplets consisted of retinyl esters and triglycerides, which correlates well with their function in retionid storage and metabolism.