| The purpose of this investigation was to examine differences under resting conditions (baseline) and after a bout of resistance exercise, in the total amount and the activation (phosphorylation) of the p42/44 MAPK signaling cascade proteins (ERK 1/2, p90RSK, and MNK 1) in young and old men. Eight young (22 +/- 1 yr) and eight old (79 +/- 3 yr) men underwent a resting muscle biopsy of the vastus lateralis, then a knee extensor resistance exercise session (29 contractions at ∼70% of max), followed by a post-exercise biopsy. The total protein expression and phosphorylation state for ERK 1/2, p90RSK, and MNK 1 was determined by Western immunoblot analysis. Total protein expression of ERK 1/2 and MNK I were not different between the young and old, before and after exercise. The resistance exercise bout caused an increase in phosphorylation of the ERK 1/2, p90RSK, and MNK 1 proteins (73, 95, and 61%, respectively; P < 0.05) in the young men. Conversely, the older men showed a decrease in ERK 1/2, p90RSK, and MNKI phosphorylation (-48, -62, and -37%, respectively; P < 0.05) after the exercise bout (versus old pre). Although, the old men displayed higher pre-exercise phosphorylation of these proteins versus young pre-exercise (131, 248, and 74%, respectively; P < 0.05). This investigation is the first to provide evidence that MAPK signaling pathways differentially respond under resting and exercise conditions in skeletal muscle of young and old men. These findings may have implications for other processes (e.g. transcription and translation) involved in skeletal muscle type and growth, when examining the changes occurring with aging muscle before and after resistance exercise/training. |
