Phosphorylation of Ser535 on eIF2Bϵ may be Important for Elevations in Muscle Protein Synthesis After Resistance Exercise in Rats

Abstract

1256 Purpose: Rates of skeletal muscle protein synthesis are consistently reported to be elevated after an acute bout of resistance exercise, however the mechanisms responsible for this response remain unclear. Methods: Several potential regulators of the initiation of mRNA translation, a key rate-controlling step in protein synthesis, were examined in gastrocnemius muscle of rats 16 hr after moderate intensity resistance exercise. Results: Rates of protein synthesis were elevated after exercise, but at the time point examined no change was observed in phosphorylation of glycogen synthase kinase-3β, phosphorylation of Thr389 on p70S6K, or the phosphorylation pattern for total p70S6K. In contrast, the phosphorylation state of eIF2α on Ser 51 and eIF2Bε on Ser535 was reduced in exercised animals compared to sedentary control animals. Conclusions: These results suggest that phosphorylation of initiation factors that affect eIF2B activity (eIF2Bε and eIF2α) changes with resistance exercise in a manner compatible with an anabolic state.