Insulin and dexamethasone stimulation of cardiac lipoprotein lipase activity involves the actin-based cytoskeleton

Lipoprotein lipase (LPL) activity in cultured ventricular cardiomyocytes fr om adult rat hearts was stimulated by the combination of insulin (100 nM) a nd dexamethasone (100 nM) during an overnight (16 h) incubation. Wortmannin (100 nM), rapamycin (30 ng/ml) or PD98059 (50 mu M) did not prevent this s timulation, suggesting that phosphatidylinositol 3-kinase, p70 S6 kinase an d the mitogen-activated protein kinase cascade are not involved in transduc ing the hormonal signal. In contrast, cytochalasin D (2 mu M) completely ab olished the stimulatory effect of insulin and dexamethasone on both heparin -releasable LPL and total cellular LPL activities. The potential role of th e actin cytoskeleton in the stimulation of LPL activity by insulin and dexa methasone appears to be distal to the initial signalling events since cytoc halasin D is still effective in preventing the stimulation when added 2h af ter the hormones.