Lipid synthesis in permeabilized cultured rat hepatocytes.

Hepatic lipid synthesis was verified and studied in lysolecithin-permeabilized cultured rat hepatocytes and compared to that of intact liver cells. Triacylglycerol synthesis in permeabilized cells incubated in the presence of glycerol 3-phosphate and long chain fatty acids approached that of intact hepatocytes. Similarly, phosphatidylcholine synthesis in permeable cells incubated in the presence of exogenous CDP-choline was similar to that of intact hepatocytes and at the expense of microsomal neutral lipid synthesis. Phosphatidic acid accumulation in lysolecithin-permeabilized liver cells was remarkably increased as compared to that of intact cells, and its synthesis was mostly accounted for by the activity of mitochondrial glycerol-3-phosphate acyltransferase. Mitochondrial-generated phosphatidate was found to migrate to the endoplasmic reticulum, thus establishing a novel lipid esterification pathway which begins in mitochondrial glycerol 3-phosphate acylation and results in microsomal triacylglycerol and phospholipid synthesis. The free access of permeabilized liver cells to substrates and modulators of lipid synthesis, while maintaining an overall synthetic pattern similar to that of intact hepatocytes, makes them a system of choice for studying hepatic lipid synthesis in general and the microsomal/mitochondrial distribution of fluxes in particular.