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phosphorylation and potentiates the feeding-induced stimulation of p70S6k1 and rpS6 in young men
1 Department of Kinesiology, McMaster University, Hamilton, Canada
2 Neuromuscular Disease Unit, Departments of Pediatrics and Medicine, McMaster University, Hamilton, Canada
* To whom correspondence should be addressed. E-mail: phillis{at}mcmaster.ca.
We investigated the effect of resistance exercise and feeding on the activation of signaling proteins of translation initiation. Nine young men (23.7±0.41 yr; BMI = 25.5±1.0 kg/m2; mean ± SEM) were tested twice after they performed a strenuous bout of unilateral resistance exercise, such that their contralateral leg acted as a non-exercised comparator, in either the fasted and fed (1000kJ q90min [3 doses]: 10g protein, 41g carbohydrate, 4g fat) states. Muscle biopsies were obtained 6h post-exercise from both legs resulting in four experimental conditions: rest-fasted, rest-fed, exercise-fasted, and exercise-fed. Feeding increased PKB/Akt (Ser473) phosphorylation (P<0.05) while exercise increased the phosphorylation of Akt and the downstream 70-kDa S6 protein kinase (p70S6k1, Thr389) and ribosomal protein S6 (rpS6, Ser235/236, Ser240/244; all P<0.05). The combination of resistance exercise and feeding increased the phosphorylation of p70S6k1 (Thr389) and rpS6 (Ser240/244) above exercise alone (P<0.05). Exercise also reduced phosphorylation of the catalytic epsilon subunit of eukaryotic initiation factor 2B (eIF2B
, Ser540; P<0.05). Mammalian target of rapamycin (mTOR, Ser2448), glycogen synthase kinase-3
(GSK-3
, Ser9), and focal adhesion kinase (FAK, Tyr576/577) phosphorylation were unaffected by either feeding or resistance exercise (all P>0.14). In summary, feeding resulted in phosphorylation of Akt while resistance exercise stimulated phosphorylation of Akt, p70S6k1, rpS6, and dephosphorylation eIF2B
with a synergistic effect of feeding and exercise on p70S6k1 and its downstream target rpS6. We conclude that resistance exercise potentiates the effect of feeding on the phosphorylation and presumably activation of critical proteins involved in the regulation of muscle protein synthesis in young men.
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