Stimulatory release of hepatic lipase activity from rat hepatocytes by ruthenium red

Ruthenium Red (RuR; ruthenium oxychloride ammoniated) stimulated the release of hepatic lipase (HTGL) activity from primary cultured rat hepatocytes into medium in a time- and dose-dependent manner. The RuR-stimulated release of HTGL activity was suppressed by tyrosine kinase (TK) inhibitors (ST-638 and biochanin A). The activity of partially purified TK preparation from hepatocytes was found to be increased by incubation with RuR. In addition, treatment of the hepatocytes with H-89, a potent inhibitor of cAMP-dependent protein kinase (PKA), decreased the stimulatory release of HTGL activity by RuR. Moreover, cAMP content in RuR-incubated hepatocytes was rapidly increased, and activation of PKA was observed. The RuR-stimulated release of HTGL activity is also inhibited by uncouplers and glycosylation inhibitors. In addition, incorporation of [3H]leucine into protein was increased in the present of RuR. Under marked inhibition of protein synthesis by cycloheximide, RuR still showed a full effect on the release of HTGL activity. These results suggest that RuR stimulates the release of HTGL activity through mechanisms of action involving TK- and PKA-activating pathways, which require a metabolic energy-sensitive process rather than elevation of enzyme molecule synthesis.