On the Mechanism of Endogenous Lipolysis in Rat Heart: A Role of Lysosomes?
Lipolytic activities of rat hearts towards full and partial glycerides were characterized. Our data indicate that the neutral triglyceride lipase (TGase) activity in heparin-preperfused hearts represents the intracellular precursor of vascular lipoprotein lipase (LPL). Upon subcellular fractionation the neutral TGase was recovered in the microsomal and cytosolic fraction. This neutral enzyme is distinct from the lysosomal acid TGase and the microsomal diglyceridase (DGase) and monoglyceridase (MGase) activity. Cycloheximide-induced inhibition of protein synthesis was accompanied by a sharp reduction in heparin-releasable LPL tissue neutral TGase activity, leaving the acid TGase, DGase and MGase activity unchanged. In cycloheximide-treated rat hearts, the basal and glucagon-stimulated release of glycerol was also not changed, ruling out a dominant role of the neutral tissue TGase in TG breakdown in heart. The myocardial lysosomal fraction appeared to be markedly enriched in triglycerides (TGs), while during prolonged perfusion a significant reduction could be observed in lysosomally recovered TGs. We propose that myocardial lipolysis predominantly proceeds by the the action of the lysosomal acid TGase in concert with the microsomal DGase and MGase activity.
KeywordsLipase Activity Partial Glyceride Substrate Fatty Acid Acid Lipase Glycerol Release
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