Adrenaline-mediated glycogen phosphorylase activation is enhanced in rat soleus muscle with increased glycogen content

The effect of glycogen content on the activation of glycogen phosphorylase during adrenaline stimulation was investigated in soleus muscles from Wista r rats. Furthermore, adrenergic activation of glycogen phosphorylase in the slow-twitch oxidative soleus muscle was compared to the fast-twitch glycol ytic epitrochlearis muscle. The glycogen content was 96.4 +/- 4.4 mmol (kg dw)(-1) in soleus muscles. Three hours of incubation with 10 mU/ml of insul in (and 5.5 mM glucose) increased the glycogen content to 182.2 +/- 5.9 mmo l (kg dw)(-1) which is similar to that of epitrochlearis muscles (175.7 +/- 6.9 mmol (kg dw)(-1)). Total phosphorylase activity in soleus was independ ent of glycogen content. Adrenaline (10(-6) M) transformed about 20% and 35 % (P < 0.01) of glycogen phosphorylase to the a form in soleus with normal and high glycogen content, respectively. In epitrochlearis, adrenaline stim ulation transformed about 80% of glycogen phosphorylase to the a form. Glyc ogen synthase activation was reduced to low level in soleus muscles with bo th normal and high glycogen content. In conclusion, adrenaline-mediated gly cogen phosphorylase activation is enhanced in rat soleus muscles with incre ased glycogen content. Glycogen phosphorylase activation during adrenaline stimulation was much higher in epitrochlearis than in soleus muscles with a similar content of glycogen. (C) 1999 Elsevier Science B.V. All rights res erved.