Enhanced insulin action on glucose transport and insulin signaling in 7-day unweighted rat soleus muscle

Matthew P. O'Keefe, Felipe R. Perez, Julie A. Sloniger, Marc E. Tischler, Erik J. Henriksen

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Hindlimb suspension (HS), a model of simulated weightlessness, enhances insulin action on glucose transport in unweighted rat soleus muscle. In the present study, we tested the hypothesis that these changes in glucose transport in 3- and 7-day HS soleus of juvenile, female Sprague-Dawley rats were due to increased functionality of insulin signaling factors, including insulin receptor (IR), IR substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3-kinase), and Akt. Insulin-stimulated (2 mU/ml) glucose transport was significantly (P < 0.05) enhanced in 3- and 7-day HS soleus by 59 and 113%, respectively, compared with weight-bearing controls. Insulin-stimulated tyrosine phosphorylation of IR and Ser473 phosphorylation of Akt was not altered by unweighting. Despite decreased (34 and 64%) IRS-1 protein in 3- and 7-day HS soleus, absolute insulin-stimulated tyrosine phosphorylation of IRS-1 was not diminished, indicating relative increases in IRS-1 phosphorylation of 62 and 184%, respectively. In the 7-day HS soleus, this was accompanied by increased (47%) insulin-stimulated IRS-1 associated with the p85 subunit of PI3-kinase. Interestingly, the enhanced insulin-stimulated glucose transport in the unweighted soleus was not completely inhibited (89-92%) by wortmannin, a PI3-kinase inhibitor. Finally, protein expression and activation of p38 MAPK, a stress-activated serine/threonine kinase associated with insulin resistance, was decreased by 32 and 18% in 7-day HS soleus. These results indicate that the increased insulin action on glucose transport in the 7-day unweighted soleus is associated with increased insulin signaling through IRS-1 and PI3-kinase and decreased p38 MAPK protein expression. However, PI3-kinase-independent mechanisms must also play a small role in this adaptive response to HS.

Original languageEnglish (US)
Pages (from-to)63-71
Number of pages9
JournalJournal of Applied Physiology
Issue number1
StatePublished - Jul 2004


  • Insulin receptor substrate-1
  • Phosphatidylinositol-3-kinase
  • Simulated weightlessness
  • Unweighted soleus
  • p38 mitogen-activated protein kinase

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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