Dephosphorylation of AMP-activated protein kinase in a postural muscle: A key signaling event on the first day of functional unloading

Abstract

The AMP analog 5-aminoimidazole-4-carboxamide ribofuranoside (AICAR), which acts as an AMP-activated protein kinase (AMPK) activator, was used to study the signal effects of AMPK dephosphorylation. AMPK activation was found to prevent an increase in phosphor-p70S6K after 24 h of gravitational unloading. Pretreatment with AICAR abolished an increase in the expression of the slow myosin pre-mRNA and mature mRNA and myosin heavy chain IIA mRNA in soleus muscle fibers of rats after short-term gravitational unloading. The finding was taken to indicate that a decrease in phosphorylated AMPK under unloading is an important factor in downregulating expression of slow myosin and myosin IIA.