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Rapid Report |
1 Copenhagen Muscle Research Centre, Institute of Exercise and Sport Sciences, Department of Human Physiology, Copenhagen University, Universitetsparken 13, Copenhagen, Denmark, 2100
2 Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland, UK
3 Department of Biochemistry & Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver BC V6T 1Z3, Canada
4 Hormone and Metabolic Research Unit, Christian de Duve Institute of Cellular Pathology, University of Louvain Medical School, Avenue Hippocrate 75, ICP-UCL 7529, B-1200 Brussels, Belgium
Protein synthesis in skeletal muscle is known to decrease during contractions but the underlying regulatory mechanisms are unknown. Here, the effect of exercise on skeletal muscle eukaryotic elongation factor 2 (eEF2) phosphorylation, a key component in protein translation machinery, was examined. Eight healthy men exercised on a cycle ergometer at a workload eliciting 
67% peak pulmonary oxygen consumption 
with skeletal muscle biopsies taken from the vastus lateralis muscle at rest as well as after 1, 10, 30, 60 and 90 min of exercise. In response to exercise, there was a rapid (i.e. < 1 min) 5- to 7-fold increase in eEF2 phosphorylation at Thr56 that was sustained for 90 min of continuous exercise. The in vitro activity of skeletal muscle eEF2 kinase was not altered by exercise indicating that the increased activity of eEF2 kinase to eEF2 is not mediated by covalent mechanisms. In support of this, the increase in AMPK activity was temporally unrelated to eEF2 phosphorylation. However, skeletal muscle eEF2 kinase was potently activated by Ca2+–calmodulin in vitro, suggesting that the higher eEF2 phosphorylation in working skeletal muscle is mediated by allosteric activation of eEF2 kinase by Ca2+ signalling via calmodulin. Given that eEF2 phosphorylation inhibits eEF2 activity and mRNA translation, these findings suggest that the inhibition of protein synthesis in contracting skeletal muscle is due to the Ca2+-induced stimulation of eEF2 kinase.
(Received 23 August 2005;
accepted after revision 3 October 2005;
first published online 6 October 2005)
Corresponding author A. J. Rose: Copenhagen Muscle Research Centre, Institute of Exercise and Sport Sciences, Department of Human Physiology, Copenhagen University, Universitetsparken 13, Copenhagen, Denmark, 2100. Email: arose{at}ifi.ku.dk
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