Release of Lipoprotein Lipase Activity from Isolated Fat Cells

Addition of heparin to isolated fat cells incubated at 23° resulted in a 3-fold increase in release of lipoprotein lipase activity into the incubation medium. This increase in medium lipoprotein lipase activity was not due to enhancement or stabilization of lipase activity present in the medium. The maximum increase in lipoprotein lipase activity was obtained on addition of 0.1 unit of heparin per ml to the cells. The heparin-stimulated release of lipoprotein lipase was almost completely inhibited by the metabolic inhibitors, sodium cyanide and Antimycin-A. When protein synthesis was blocked with cycloheximide, and heparin added to the incubation medium, neither the release of lipoprotein lipase activity nor the intracellular enzyme activity was affected for 120 min. At the end of this 120-min incubation there was approximately 5 times as much lipoprotein lipase activity in the medium as in the cells initially. These studies suggest that intracellular lipoprotein lipase undergoes activation in association with heparin-stimulated release from fat cells.