Influence of exercise intensity on ERK/MAP kinase signalling in human skeletal muscle

The mitogen-activated protein (MAP) kinase pathways have been highlighted a s a possible link between exercise and adaptive changes in skeletal muscle In this study, the effect of exercise intensity on the activation of the ER K/MAP kinase pathway was investigated in human skeletal muscle. One-leg exe rcise at low (40%, maximal oxygen consumption, VO2max, for 30 min) and high (75% VO2max for 30 min) intensity resulted in 11.5+/-8. 1-fold and 39.7+/- 6.3-fold (mean +/-SEM) increases in ERK1/2 phosphorylation (P<0.001), respe ctively. The phosphorylation of MEK1/2, the upstream kinase of ERK1/2, incr eased with exercise intensity (P<0.05) to 2.5+/-0.9 and 4.8+/-1.1 times the basal level at the low and high intensity, respectively. The statistical a nalysis revealed a systematic difference between basal, low and high intens ity exercise levels for both kinases. There was no change in the phosphoryl ation of either kinase in the non-exercised leg. The phosphorylation of the transcription factor cyclic AMP response clement binding protein (CREB), a possible downstream target of the ERK/MAP kinase signalling pathway, was u naffected by exercise. The phosphorylation of ERK1/2 was significantly high er in purified freeze-dried compared to crude wet muscle after exercise, wh ereas the opposite pattern was observed for CREB. In conclusion, phosphoryl ation of ERK1/2 and MEK1/2 increases in an exercise intensity-dependent man ner in human skeletal muscle and this seems to originate in the muscle fibr es themselves.