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J Appl Physiol 102: 1007-1013, 2007. First published November 22, 2006; doi:10.1152/japplphysiol.01034.2006
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Effect of acute activation of 5'-AMP-activated protein kinase on glycogen regulation in isolated rat skeletal muscle

¹Department of Medicine and Clinical Science, Graduate School of Medicine, ²Laboratory of Nutrition Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, and ³Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan

Submitted 15 September 2006 ; accepted in final form 19 November 2006

5'-AMP-activated protein kinase (AMPK) has been implicated in glycogen metabolism in skeletal muscle. However, the physiological relevance of increased AMPK activity during exercise has not been fully clarified. This study was performed to determine the direct effects of acute AMPK activation on muscle glycogen regulation. For this purpose, we used an isolated rat muscle preparation and pharmacologically activated AMPK with 5-aminoimidazole-4-carboxamide-1--D-ribonucleoside (AICAR). Tetanic contraction in vitro markedly activated the ₁- and ₂-isoforms of AMPK, with a corresponding increase in the rate of 3-O-methylglucose uptake. Incubation with AICAR elicited similar enhancement of AMPK activity and 3-O-methylglucose uptake in rat epitrochlearis muscle. In contrast, whereas contraction stimulated glycogen synthase (GS), AICAR treatment decreased GS activity. Insulin-stimulated GS activity also decreased after AICAR treatment. Whereas contraction activated glycogen phosphorylase (GP), AICAR did not alter GP activity. The muscle glycogen content decreased in response to contraction but was unchanged by AICAR. Lactate release was markedly increased when muscles were stimulated with AICAR in buffer containing glucose, indicating that the glucose taken up into the muscle was catabolized via glycolysis. Our results suggest that AMPK does not mediate contraction-stimulated glycogen synthesis or glycogenolysis in skeletal muscle and also that acute AMPK activation leads to an increased glycolytic flux by antagonizing contraction-stimulated glycogen synthesis.

contraction; glycogen synthase; glycogen phosphorylase; epitrochlearis muscle; glycolysis