Skeletal muscle signaling associated with impaired glucose tolerance in spinal cord-injured men and the effects of contractile activity

Academic Article

Abstract

  • Yarar-Fisher C, Bickel CS, Windham ST, McLain AB, Bamman MM. Skeletal muscle signaling associated with impaired glucose tolerance in spinal cord-injured men and the effects of contractile activity. J Appl Physiol 115: 756-764, 2013. First published June 13, 2013; doi:10.1152/japplphysiol.00122. 2013.-The mechanisms underlying poor glucose tolerance in persons with spinal cord injury (SCI), along with its improvement after several weeks of neuromuscular electrical stimulation-induced resistance exercise (NMES-RE) training, remain unclear, but presumably involve the affected skeletal musculature. We, therefore, investigated skeletal muscle signaling pathways associated with glucose transporter 4 (GLUT-4) translocation at rest and shortly after a single bout of NMES-RE in SCI (n = 12) vs. able-bodied (AB, n = 12) men. Subjects completed an oral glucose tolerance test during visit 1 and ∼90 NMES-RE isometric contractions of the quadriceps during visit 2. Muscle biopsies were collected before, and 10 and 60 min after, NMES-RE. We assessed transcript levels of GLUT-4 by quantitative PCR and protein levels of GLUT-4 and phosphorylated- and total AMP-activated protein kinase (AMPK)-α, CaMKII, Akt, and AS160 by immunoblotting. Impaired glucose tolerance in SCI was confirmed by higher (P < 0.05) plasma glucose concentrations than AB at all time points after glucose ingestion, despite equivalent insulin responses to the glucose load. GLUT-4 protein content was lower (P < 0.05) in SCI vs. AB at baseline. Main group effects revealed higher phosphorylation in SCI of AMPK-α, CaMKII, and Akt (P < 0.05), and Akt phosphorylation increased robustly (P < 0.05) following NMES-RE in SCI only. In SCI, low skeletal muscle GLUT-4 protein concentration may, in part, explain poor glucose tolerance, whereas heightened phosphorylation of relevant signaling proteins (AMPK-α, CaMKII) suggests a compensatory effort. Finally, it is encouraging to find (based on Akt) that SCI muscle remains both sensitive and responsive to mechanical loading (NMES-RE) even ∼22 yr after injury. Copyright © 2013 the American Physiological Society.
  • Digital Object Identifier (doi)

    Author List

  • Yarar-Fisher C; Bickel CS; Windham ST; McLain AB; Bamman MM
  • Start Page

  • 756
  • End Page

  • 764
  • Volume

  • 115
  • Issue

  • 5