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

Lipoprotein lipase (LPL) activity in cultured ventricular cardiomyocytes from adult rat hearts was stimulated by the combination of insulin (100 nM) and 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 stimulation, suggesting that phosphatidylinositol 3-kinase, p70 S6 kinase and the mitogen-activated protein kinase cascade are not involved in transducing the hormonal signal. In contrast, cytochalasin D (2 mu M) completely abolished the stimulatory effect of insulin and dexamethasone on both heparin-releasable LPL and total cellular LPL activities. The potential role of the actin cytoskeleton in the stimulation of LPL activity by insulin and dexamethasone appears to be distal to the initial signalling events since cytochalasin D is still effective in preventing the stimulation when added 2h after the hormones.