Electrical stimulation induces fiber type-specific translocation of GLUT-4 to T tubules in skeletal muscle

Am J Physiol. 1997 Oct;273(4):E688-94. doi: 10.1152/ajpendo.1997.273.4.E688.

Abstract

Insulin and contraction independently stimulate glucose transport in skeletal muscle. Whereas insulin activates glucose transport more in muscles composed of type I and IIa fibers, electrical stimulation increases glucose transport at least as much in type IIb fiber-enriched muscles despite the fact that the latter fiber type contains less GLUT-4 glucose transporters. The aim of the present study was to test the hypothesis that a greater GLUT-4 translocation to the cell surface may underlie the higher contraction-stimulated glucose transport in type IIb myofibers. Leg muscles from rats were stimulated in situ at 100 Hz (200 ms) each 2 s via the sciatic nerve over a period of 20 min while the contralateral leg was kept at rest. Muscle 2-[3H]deoxy-D-glucose uptake (2-DG) was measured in separated red gastrocnemius (RG, type I and IIa fibers) and white gastrocnemius (WG, type IIb fibers) muscles. Resting 2-DG uptake was greater in RG than WG. Electrical stimulation increased 2-DG uptake over resting values similarly in WG and RG. Fractions enriched with either plasma membranes, transverse (T) tubules, triads, or GLUT-4-enriched intracellular membranes were isolated from RG and WG using a recently developed subcellular fractionation procedure. Electrical stimulation similarly increased GLUT-4 protein content in plasma membranes of RG and WG, whereas it stimulated GLUT-4 translocation more (approximately 50%) in T tubules of WG than in RG. GLUT-4 content was not changed in triads of both muscle types. The increments in cell surface GLUT-4 protein levels were paralleled by significant reductions in the amount of the transporter in the intracellular membrane fractions of both muscle types (by 60% in RG and 56% in WG). It is concluded that electrically induced contraction stimulates GLUT-4 translocation more in T tubules of WG than RG. The physiological implications of this finding for glucose uptake by contracting RG and WG muscles is discussed.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biomarkers
  • Cell Membrane / physiology
  • Deoxyglucose / metabolism
  • Electric Stimulation
  • Glucose Transporter Type 4
  • Glycogen / metabolism
  • Lactates / metabolism
  • Male
  • Monosaccharide Transport Proteins / metabolism*
  • Muscle Fibers, Fast-Twitch / physiology*
  • Muscle Fibers, Slow-Twitch / physiology*
  • Muscle Proteins*
  • Muscle, Skeletal / innervation
  • Muscle, Skeletal / physiology*
  • Rats
  • Rats, Wistar
  • Sciatic Nerve / physiology

Substances

  • Biomarkers
  • Glucose Transporter Type 4
  • Lactates
  • Monosaccharide Transport Proteins
  • Muscle Proteins
  • Slc2a4 protein, rat
  • Glycogen
  • Deoxyglucose