ИСТИНА

It is well known that resistance exercise results in shift of protein balance toward anabolic response in skeletal muscles (Phillips et al., 2010). Increase in protein synthesis rate particularly is due to activation of key regulator of translation initiation and elongation – mTORC1 (Proud, 2007). Crucial role of mTORC1 in adaptation of a muscle to resistance exercise is confirmed by the experiments with its specific inhibitors (Bodine et al., 2001; Goodman et al., 2011). It was shown that exercise-induced signaling events depend on fitness level: acute resistance exercise after training period could results in less pronounced effect on mTORC1 signalling in comparison with that after first exposure (Ogasawara et al., 2013; Phillips et al., 1999). Thus in present study we compared the effects of single resistance exercise on signalling involved in regulation of protein synthesis in skeletal muscle of trained and untrained subjects. The study was approved by the Human Ethics Committee of the Institute of Biomedical Problems (Moscow, Russia). Eight untrained subjects and eight powerlifters were involved in the experiment. They visited the laboratory three times separated by at least three days: familiarization visit, visit when their maximal voluntary contraction (MVC) was examined, and experimental session. In experimental day the subjects performed one leg press exercise with load corresponding to 65% of MVC. Venous blood samples were taken before, immediately after and 15 min after the exercise for evaluation of lactate and hormones level. Biopsy samples from m. vastus lateralis were taken before, 1, 5, 10 hours after the exercise. mRNA expression level and phosphorylated protein content were evaluated using q-PCR and Western blot, accordingly. All data are presented as median and interquartile range, statistical analisis has been performed using Wilcoxon matched pairs signed-rank test or Fisher criterion. The level of significance was set at P < 0.05. Absolute and specific strength (ratio of MVC to volume of m. quadriceps femoris) of one leg extensors were 1.54 and 1.21 times higher in powerlifters accordingly compared with untrained persons. There was significant correlation between muscle volume and MVC. Basal testosterone and cortisol levels were not different between the groups, whereas the increase in testosterone level after exercise was observed in untrained subjects only. The phosphorylation level of mTORC1 downstream kinase p70S6k (site) was increased in both trained and untrained groups after exercise. On the other hand the phosphorylation level of another target of mTORC1 - 4EBP1 had just a tendency to increase after exercise only in trained group. The phosphorylation level of mechano dependent site of p70S6k (421/424) was increased in both groups. The phosphorylation level of elongation factor 2 (eEF2) was significantly decreased in trained group and had a tendency to decrease in untrained group. The phosphorylation level of mitogen activated proteinkinase Erk1/2 was increased in both groups. The phosphorylation level of FOXO1, a key regulator of ubiquitin-ligase genes expression, was decreased only in trained group. Thus the strength exercise results in activation of kinases regulating translation initiation and elongation. When exercise intensity is equalized by relative level these molecular events do not differ between trained and untrained skeletal muscles.