Metabolic and mitogenic signal transduction in human skeletal muscle after intense cycling exercise

We determined whether mitogen‐activated protein kinase (MAPK) and 5′‐AMP‐activated protein kinase (AMPK) signalling cascades are activated in response to intense exercise in skeletal muscle from six highly trained cyclists (peak O2 uptake (V̇O2,peak) 5.14 ± 0.1 l min−1) and four control subjects (V̇O2,peak 3.8 ± 0.1 l min−1) matched for age and body mass. Trained subjects completed eight 5 min bouts of cycling at ≈85% of V̇O2,peak with 60 s recovery between work bouts. Control subjects performed four 5 min work bouts commencing at the same relative, but a lower absolute intensity, with a comparable rest interval. Vastus lateralis muscle biopsies were taken at rest and immediately after exercise. Extracellular regulated kinase (ERK1/2), p38 MAPK, histone H3, AMPK and acetyl CoA‐carboxylase (ACC) phosphorylation was determined by immunoblot analysis using phosphospecific antibodies. Activity of mitogen and stress‐activated kinase 1 (MSK1; a substrate of ERK1/2 and p38 MAPK) and α1 and α2 subunits of AMPK were determined by immune complex assay. ERK1/2 and p38 MAPK phosphorylation and MSK1 activity increased (P < 0.05) after exercise 2.6‐, 2.1‐ and 2.0‐fold, respectively, in control subjects and 1.5‐, 1.6‐ and 1.4‐fold, respectively, in trained subjects. Phosphorylation of histone H3, a substrate of MSK1, increased (P < 0.05) ≈1.8‐fold in both control and trained subject. AMPKα2 activity increased (P < 0.05) after exercise 4.2‐ and 2.3‐fold in control and trained subjects, respectively, whereas AMPKα1 activity was not altered. Exercise increased ACC phosphorylation (P < 0.05) 1.9‐ and 2.8‐fold in control and trained subjects. In conclusion, intense cycling exercise in subjects with a prolonged history of endurance training increases MAPK signalling to the downstream targets MSK1 and histone H3 and isoform‐specific AMPK signalling to ACC. Importantly, exercise‐induced signalling responses were greater in untrained men, even at the same relative exercise intensity, suggesting muscle from previously well‐trained individuals requires a greater stimulus to activate signal transduction via these pathways.