Electrical stimulation induces fiber type-specific translocation of glut4 to t-tubules in rat skeletal muscle. Roy, Denis, Erlingur J[acute]ohannsson, Arend Bonen, and Andr[acute]e Marette. Department of Physiology & Lipid Research Unit, Laval University Hospital Research Center, Ste-Foy, Qu[acute]ebec, G1V 4G2, Canada and Department of Anatomy, Institute of Basic medical Sciences, University of Oslo, POB 1105 Blindern, N-0317 Oslo, Norway and Department of Kinesiology, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
APStracts 4:0130E, 1997.
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 GLUT4 glucose transporters. The aim of the present study was to test the hypothesis that a greater GLUT4 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 sec 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 (RG, type I and IIa fibers) and white (WG, type IIb fibers) gastrocnemius muscle. Resting 2-DG uptake was greater in red RG than WG. Electrical stimulation increased 2-DG uptake over resting values similarly in WG and RG. Fractions enriched with either plasma membranes, transverse tubules, triads or GLUT4-enriched intracellular membranes were isolated from RG and WG using a recently developed subcellular fractionation procedure. Electrical stimulation similarly increased GLUT4 protein content in plasma membranes of RG and WG, whereas it stimulated GLUT4 translocation more (50%) in transverse tubules of WG than in RG. GLUT4 content was not changed in triads of both muscle types. The increments in cell surface GLUT4 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 GLUT4 translocation more in transverse tubules of WG than RG. The physiological implications of this finding for glucose uptake by contracting RG and WG muscles is discussed. 

Received 6 November 1996; accepted in final form 5 June 1997
APS Manuscript Number E559-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 1 July 1997