Expression of hormone-sensitive lipase and its regulation by adrenaline inskeletal muscle

The enzymic regulation of triacylglycerol breakdown in skeletal muscle is p oorly understood, Western blotting of muscle fibres isolated by collagenase treatment or after freeze-drying demonstrated the presence of immunoreacti ve hormone-sensitive lipase (HSL), with the concentrations in soleus and di aphragm being more than four times the concentrations in extensor digitorum longus and epitrochlearis muscles. Neutral lipase activity determined unde r conditions optimal for HSL varied directly with immunoreactivity. Express ed relative to triacylglycerol content, neutral lipase activity in soleus m uscle was about 10 times that in epididymal adipose tissue. In incubated so leus muscle, both neutral lipase activity against triacylglycerol (but not against a diacylglycerol analogue) and glycogen phosphorylase activity incr eased in response to adrenaline (epinephrine). The lipase activation was co mpletely inhibited by anti-HSL antibody and by propranolol. The effect of a drenaline could be mimicked by incubation of crude supernatant from control muscle with the catalytic subunit of cAMP-dependent protein kinase, while no effect of the kinase subunit was seen with supernatant from adrenaline-t reated muscle. The results indicate that HSL is present in skeletal muscle and is stimulated by adrenaline via beta-adrenergic activation of cAMP-depe ndent protein kinase. The concentration of HSL is higher in oxidative than in glycolytic muscle, and the enzyme is activated in parallel with glycogen phosphorylase.