Properties of binding of lipases to non-parenchymal rat liver cells

The binding of a heparin-releasable acylglycerol hydrolase from rat liver (liver lipase) to non-parenchymal liver cells was studied in vitro. The binding of the partially purified liver lipase to the cells was found to be rapid. Within 1 min 80% of the maximal binding occurred at either 4 or 25 degrees C. The binding capacity of the cells was saturable, with a maximal binding of 46 mU lipase activity per mg cell protein. Albumin did not prevent the binding and neither did glucose, galactose or methyl-alpha-mannoside. Mg2+, but not Ca2+, promoted the binding of the lipase to the cells. The in vitro bound enzyme activity was releasable from the cells by heparin. Both the soluble and bound liver lipase could be completely inhibited by an antibody against liver lipase. Lipoprotein lipase, derived from rat adipose tissue, was also found to bind preferentially to non-parenchymal liver cells. The presented results show that non-parenchymal liver cells contain 10(5) binding sites per cell for heparin-releasable lipases. Lipase secreted from parenchymal cells in vitro was also bound to the non-parenchymal cells. The data suggest that in vivo the liver lipase bound to endothelial liver cells can be derived from parenchymal cells.