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

Yu Chiang Lai, Jorid Thrane Stuenæs, Chia Hua Kuo, Jørgen Jensen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


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 Km 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 Km 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 AMPKα 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.

Original languageEnglish
Pages (from-to)E1622-E1629
Number of pages8
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number6
Publication statusPublished - 1 Dec 2007


  • Acetyl-coenzyme A carboxylase
  • Adenosine monophosphate kinase
  • Enzyme kinetic
  • Glycogen synthase kinase-3
  • Uridine diphosphate

ASJC Scopus subject areas

  • Physiology
  • Endocrinology
  • Biochemistry


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