Prazosin-stimulated release of hepatic triacylglyceride lipase from primary cultured rat hepatocytes is involved in the regulation of cAMP-dependent protein kinase through activation of the Ca(2+)/calmodulin-dependent protein kinase-II.

BACKGROUND: Prazosin is an α1 adrenoceptor antagonist used in pharmacotherapy for the treatment of hypertension. Prazosin alters lipid metabolism in vivo, but the involved mechanism is not fully understood. In this study, we investigated the mechanism underlying the alteration of lipid metabolism. We show that the prazosin-stimulated release of hepatic triacylglyceride lipase (HTGL) from primary cultured rat hepatocytes involved Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II) activation.

METHODS: Primary cultured rat hepatocytes were incubated with prazosin and other agents. The hepatocytes were used in the CaMK-II and protein kinase A (PKA) activity assay. The supernatant was used in the HTGL activity assay and western blotting.

RESULTS: Prazosin-stimulated HTGL release was suppressed by the inositol triphosphate receptor inhibitor xestospongin C and by the calmodulin inhibitor trifluoperazine but not by the protein kinase C inhibitor chelerythrine chloride or a diacylglycerol kinase inhibitor (R59949). Furthermore, the calmodulin-dependent protein kinase II (CaMK-II) activity in prazosin-treated hepatocytes increased in a time- and dose-dependent manner. The cAMP-dependent PKA activity of prazosin-stimulated hepatocytes was suppressed by a phospholipase C (PLC) inhibitor (U-73122), trifluoperazine, and a CaMK-II inhibitor (KN-93).

CONCLUSIONS: These results suggested that prazosin-stimulated HTGL release from hepatocytes was caused by activation of PKA associated with stimulation of CaMK-II activity through a signal cascade from PLC.