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1 Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
2 Department of Kinesiology, Faculty of Physical Education, K.U. Leuven, Leuven, Belgium
3 Diabetes Biology, Novo Nordisk, Bagsvaerd, Denmark
4 Department of Human Physiology, Institute of Exercise and Sports Sciences, University of Copenhagen, Copenhagen, Denmark
* To whom correspondence should be addressed. E-mail: fthong{at}sympatico.ca.
We have examined the effects of insulin on p38 mitogen-activated protein kinase (MAPK) phosphorylation in human skeletal muscle, and the effects of prior exercise hereon. Seven men performed 1h one-legged knee extensor exercise 3h before the initiation of a 100-min euglycemic-hyperinsulinemic (600 pmol/l) clamp. Glucose uptake across the legs was measured with the leg balance technique, and muscle biopsies were obtained from the rested and exercised vastus lateralis before and during insulin infusion. Net glucose uptake during the clamp was ~ 50% higher (p<0.05) in the exercised than the rested leg. Insulin induced a modest sustained 1.2- and 1.3-fold increase (p<0.05) in p38 MAPK phosphorylation in the rested and exercised legs, respectively. However, p38 phosphorylation was ~ 50% higher (p<0.05) in the exercised compared to the rested leg before and during insulin infusion. We conclude that a physiological concentration of insulin causes modest but sustained activation of the p38 MAPK pathway in human skeletal muscle. Furthermore, the stimulatory effect of exercise on p38 phosphorylation is persistent for at least 3h after exercise and remains evident during subsequent insulin stimulation. Because p38 MAPK has been suggested to play a necessary role in activation of GLUT4 at the cell surface, the present data may suggest a putative role of p38 MAPK in the increased insulin sensitivity of skeletal muscle following exercise.
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