Intracellular signaling specificity in skeletal muscle in response to different modes of exercise.

The aim of this study was to understand better the specific signaling events resulting from different modes of exercise. Three different exercise protocols were employed based on their well-characterized, long-term training effects on either muscle hypertrophy or endurance phenotypes. Rats were subjected to a single bout of either a high-frequency electrical stimulation, a low-frequency electrical stimulation, or a running exercise protocol. Postexercise intracellular signaling was analyzed in the tibialis anterior and soleus muscles at 0, 3, and 6 h. A prolonged increase in p70(S6k) and a transient increase in protein kinase B phosphorylation were only observed in response to a growth-inducing stimulus (e.g., tibialis anterior in high-frequency electrical stimulation). In contrast, extracellular regulated kinase and 38-kDa stress-activated protein kinase were activated in response to all forms of exercise at 0 h, but only extracellular regulated kinase phosphorylation was found significantly elevated at 6 h after running exercise. These results demonstrate that different exercise protocols resulted in the selective activation of specific intracellular signaling pathways, which may determine the specific adaptations induced by different forms of exercise.