Abstract:
It has been shown that skeletal muscle 5'-AMP-activated protein kinase (AMPK) phosphorylation and/or activity is more greatly elevated in response to resistance exercise or loading in aged rats, and that eukaryotic elongation factor 2 (eEF2) is more phosphorylated with increased AMPK phosphorylation and/or activity, thereby potentially decreasing the hypertrophic response of translation elongation with age. Increased AMPK phosphorylation has also been shown to occur in old compared to young humans following an acute resistance exercise bout. Thus, we hypothesized that AMPK phosphorylation, AMPK activity, and eEF2 phosphorylation would be greater in the vastus lateralis muscles of old compared to young men and women within the two hours after an acute bout of resisted leg extensions. Subjects (N=6/age group) performed an acute bout of leg extension resistance exercise consisting of 3 working sets. Muscle biopsies were obtained pre-exercise (Pre-Ex), immediately post-exercise (0P), one hour post-exercise (1P), and two hours post-exercise (2P). Phosphorylation of AMPK, acetyl-CoA carboxylase (ACC; a measure of AMPK activity), and eEF2 were analyzed by western blot. There were no differences in AMPK phosphorylation between age groups or over time, while ACC phosphorylation was significantly (P<0.05) increased at 0P and 1P compared to Pre-Ex for both age groups. The percent change in phospho-ACC from Pre-Ex was significantly higher in old compared to young subjects at all post-exercise timepoints. eEF2 phosphorylation was significantly elevated at 0P, and significantly lower at 1P and 2P, regardless of age group. Furthermore, total eEF2 was significantly elevated at 1P and 2P regardless of age group. These findings suggest that AMPK activity may be increased more in old compared to young subjects immediately following an acute bout of resistance exercise. This could lead to lower downstream translational signaling in older humans following resistance exercise, although eEF2 may not be a translational signaling protein affected by this phenomenon.
