A Bout Of Local Heat Stress Activates Protein Synthesis Signaling In Rat Skeletal Muscle

Abstract

PURPOSE: It has been reported that heat stress enhanced muscle hypertrophy. However, it still unclear about protein synthesis signaling activated by a bout of local heat stress. Therefore, the purpose of this study was to reveal changes of protein synthesis signaling following a bout of local heat stress. METHODS: Male Wistar rats (15 wk-old) were used in this study. Under anesthesia with pentobarbital sodium (50 mg/kg), a leg was immersed in a hot water (43°C) for 30 min. The other leg was served as a control one. Muscle temperature was recorded by a needle thermometer. The soleus and plantaris muscles in both legs were removed at 0, 30 or 60 min after the heat stress. Phospho- and total-Akt, mTOR, p70S6K and 4E-BP1 protein expressions in the muscles were determined by Western blotting technique. RESULTS: Muscle temperature of the heat-stressed leg was gradually increased to 41.8±0.3°C. In the heat-stressed plantaris muscle, phosphorylated Akt and p70S6K levels were increased at 0 and 30 min after heat stress, and phosphorylation of mTOR was increased at 30 min after the heat stress. The ratio of phosphorylated to total Akt, mTOR and p70S6K increased at 0, 30 and 60 min after the heat stress. In the heat-stressed soleus muscle, the phospho to total ratio of Akt showed no change, but that of mTOR and p70S6K tended to increase at 30 min after the heat stress. There was no change in the phospho to total ratio of 4E-BP1 in both plantaris and soleus muscles CONCLUSIONS: These results show that a bout of local heat stress activated protein synthesis signaling mediated by Akt/mTOR pathway and its downstream targets p70S6K, and the activation was occurred within 60 min after heat stress. It is concluded that protein synthesis signaling pathway were activated at the early phase after local heat stress.