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AS160 phosphorylation is associated with activation of ₂₂₁- but not ₂₂₃-AMPK trimeric complex in skeletal muscle during exercise in humans

Department of Human Physiology, Institute of Exercise and Sport Sciences, Copenhagen Muscle Research Centre, University of Copenhagen, Copenhagen, Denmark

Submitted 31 July 2006 ; accepted in final form 31 October 2006

We investigated time- and intensity-dependent effects of exercise on phosphorylation of Akt substrate of 160 kDa (AS160) in human skeletal muscle. Subjects performed cycle exercise for 90 min (67% O_{2 peak}, n = 8), 20 min (80% O_{2 peak}, n = 11), 2 min (110% of peak work rate, n = 9), or 30 s (maximal sprint, n = 10). Muscle biopsies were obtained before, during, and after exercise. In trial 1, AS160 phosphorylation increased at 60 min (60%, P = 0.06) and further at 90 min of exercise (120%, P < 0.05). ₂₂₃-AMP-activated protein kinase (AMPK) activity increased significantly to a steady-state level after 30 min, whereas ₂₂₁-AMPK activity increased after 60 min of exercise with a further significant increase after 90 min. ₂₂₁-AMPK activity and AS160 phosphorylation correlated positively (r² = 0.55). In exercise trials 2, 3, and 4, ₂₂₃-AMPK activity but neither AS160 phosphorylation nor ₂₂₁-AMPK activity increased. Akt Ser⁴⁷³ phosphorylation was unchanged in all trials, whereas Akt Thr³⁰⁸ phosphorylation increased significantly in trial 3 and 4 only. These results show that AS160 is phosphorylated in a time-dependent manner during moderate-intensity exercise and suggest that ₂₂₁- but not ₂₂₃-AMPK may act in a pathway responsible for exercise-induced AS160 phosphorylation. Furthermore, we show that AMPK complexes in skeletal muscle are activated differently depending on exercise intensity and duration.

Akt; Akt substrate of 160 kilodaltons; adenosine 5'-monophosphate-activated protein kinase

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