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This Article Full Text Full Text (PDF) All Versions of this Article: 293/6/E1622    most recent 00113.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lai, Y.-C. Articles by Jensen, J. Search for Related Content PubMed PubMed Citation Articles by Lai, Y.-C. Articles by Jensen, J.

Glycogen content and contraction regulate glycogen synthase phosphorylation and affinity for UDP-glucose in rat skeletal muscles

¹Department of Physiology, National Institute of Occupational Health, ²The Norwegian University of Sport and Physical Education, Oslo, Norway; and ³Laboratory of Exercise Biochemistry, Taipei Physical Education College, Taipei, Republic of China

Submitted 19 February 2007 ; accepted in final form 11 September 2007

Glycogen content and contraction strongly regulate glycogen synthase (GS) activity, and the aim of the present study was to explore their effects and interaction on GS phosphorylation and kinetic properties. Glycogen content in rat epitrochlearis muscles was manipulated in vivo. After manipulation, incubated muscles with normal glycogen [NG; 210.9 ± 7.1 mmol/kg dry weight (dw)], low glycogen (LG; 108.1 ± 4.5 mmol/ kg dw), and high glycogen (HG; 482.7 ± 42.1 mmol/kg dw) were contracted or rested before the studies of GS kinetic properties and GS phosphorylation (using phospho-specific antibodies). LG decreased and HG increased GS K_m for UDP-glucose (LG: 0.27 ± 0.02 < NG: 0.71 ± 0.06 < HG: 1.11 ± 0.12 mM; P < 0.001). In addition, GS fractional activity inversely correlated with glycogen content (R = –0.70; P < 0.001; n = 44). Contraction decreased K_m for UDP-glucose (LG: 0.14 ± 0.01 = NG: 0.16 ± 0.01 < HG: 0.33 ± 0.03 mM; P < 0.001) and increased GS fractional activity, and these effects were observed independently of glycogen content. In rested muscles, GS Ser⁶⁴¹ and Ser⁷ phosphorylation was decreased in LG and increased in HG compared with NG. GSK-3β Ser⁹ and AMPK Thr¹⁷² phosphorylation was not modulated by glycogen content in rested muscles. Contraction decreased phosphorylation of GS Ser⁶⁴¹ at all glycogen contents. However, contraction increased GS Ser⁷ phosphorylation even though GS was strongly activated. In conclusion, glycogen content regulates GS affinity for UDP-glucose and low affinity for UDP-glucose in muscles with high glycogen content may reduce glycogen accumulation. Contraction increases GS affinity for UDP-glucose independently of glycogen content and creates a unique phosphorylation pattern.

uridine diphosphate; adenosine monophosphate kinase; glycogen synthase kinase-3; acetyl-coenzyme A carboxylase; enzyme kinetic