Predominant α2/β2/γ3 AMPK activation during exercise in human skeletal muscle

5'AMP-activated protein kinase (AMPK) is a key regulator of cellular metabolism and is regulated in muscle during exercise. We have previously established that only three of 12 possible AMPK α/β/γ-heterotrimers are present in human skeletal muscle. Previous studies describe discrepancies between total AMPK activity and regulation of its target acetyl-CoA-carboxylase (ACC)β. Also, exercise training decreases expression of the regulatory γ3 AMPK subunit and attenuates α2 AMPK activity during exercise. We hypothesize that these observations reflect a differential regulation of the AMPK heterotrimers. We provide evidence here that only the α2/β2/γ3 subunit is phosphorylated and activated during high-intensity exercise in vivo . The activity associated with the remaining two AMPK heterotrimers, α1/β2/γ1 and α2/β2/γ1, is either unchanged (20 min, 80% maximal oxygen uptake     ) or decreased (30 or 120 s sprint-exercise). The differential activity of the heterotrimers leads to a total α-AMPK activity, that is decreased (30 s trial), unchanged (120 s trial) and increased (20 min trial). AMPK activity associated with the α2/β2/γ3 heterotrimer was strongly correlated to γ3-associated α-Thr-172 AMPK phosphorylation ( r ²= 0.84, P < 0.001) and to ACCβ Ser-221 phosphorylation ( r ²= 0.65, P < 0.001). These data single out the α2/β2/γ3 heterotrimer as an important actor in exercise-regulated AMPK signalling in human skeletal muscle, probably mediating phosphorylation of ACCβ.