Time course of GLUT4 and AMPK protein expression in human skeletal muscle during one month of physical training

Endurance training elicits profound adaptations of skeletal muscle, including increased expression of several proteins. The 5'-AMP activated protein kinase (AMPK) may be one of these, considering the fact that acute exercise increases AMPK activity. Eight young (26+/-1 year) lean, healthy males endurance trained one leg (while the other leg remained resting) on an ergometer bicycle for 30 min/day for four weeks (workload corresponding to similar to70% of maximal oxygen uptake). Muscle biopsies were obtained similar to18 h after the previous training session. On day eight GLUT4 protein expression was 36% higher in trained (T) compared with untrained (UT) (P<0.05), but no further increase was seen at day 14 and 30 despite continuously increasing absolute workloads. Expression of AMPKalpha(2) and actin did not change with training. In contrast, expression of AMPKalpha(1) was 27% higher in T vs. UT muscle (P<0.05) (measured only on day 30). Conclusions: GLUT4 protein expression increases substantially after seven days of endurance training with no further increase with prolonged training at progressively increasing workloads. AMPKalpha(1) and alpha(2) behave differently in their expression in response to endurance training. AMPKalpha(1) protein content is increased after one month of training, while no change in AMPKalpha(2) and actin expression was detected over the time course of the training period .