Lipolytic activities of freshly isolated rat liver parenchymal cells.

By using a specific collagenase preparation preserving lipolytic enzymes, we could isolate intact rat liver cells with monoester lipase (MEL) and, for the first time, substantial amounts of endogenous neutral triester lipase (TEL) activities assayable as cell-bound enzymes. TEL and MEL activities were found exclusively in parenchymal cells. Virtually all TEL was located on plasma membrane from which it was rapidly released at 37 degrees C in the absence of any additive. MEL was distributed almost equally inside the cell and in the membrane, to which it was firmly attached. Infusion of heparin to the whole animal before liver exposure decreased by 80% the TEL content of parenchymal cells (a property typical of hepatic lipase) whilst MEL was unchanged. These results question the concept that heparin-releasable hepatic lipase acts at the surface of endothelial liver cells and further suggest that TEL and MEL refer to distinct catalytic entities.