AJP - Endocrinology and Metabolism, Vol 271, Issue 2 E294-E301, Copyright © 1996 by American Physiological Society
Glucose transport and cell surface GLUT-4 protein in skeletal muscle of the obese Zucker rat
G. J. Etgen Jr, C. M. Wilson, J. Jensen, S. W. Cushman and J. L. Ivy
Department of Kinesiology, University of Texas at Austin 78712, USA.
The relationship between 3-O-methyl-D-glucose transport and
2-N-4-(1-azi-2,2,2-trifluoroethyl)-benzoyl-1,
3-bis-(D-mannos-4-yloxy)-2-propylamine (ATB-BMPA)-labeled cell surface
GLUT-4 protein was assessed in fast-twitch (epitrochlearis) and slow-twitch
(soleus) muscles of lean and obese (fa/fa) Zucker rats. In the absence of
insulin, glucose transport as well as cell surface GLUT-4 protein was
similar in both epitrochlearis and soleus muscles of lean and obese rats.
In contrast, insulin-stimulated glucose transport rates were significantly
higher for lean than obese rats in both soleus (0.74 +/- 0.05 vs. 0.40 +/-
0.02 mumol.g-1.10 min-1) and epitrochlearis (0.51 +/- 0.05 vs. 0.17 +/-
0.02 mumol.g-1.10 min-1) muscles. The ability of insulin to enhance glucose
transport in fast- and slow-twitch muscles from both lean and obese rats
corresponded directly with changes in cell surface GLUT-4 protein. Muscle
contraction elicited similar increases in glucose transport in lean and
obese rats, with the effect being more pronounced in fast-twitch (0.70 +/-
0.07 and 0.77 +/- 0.04 mumol.g-1.10 min-1 for obese and lean, respectively)
than in slow-twitch muscle (0.36 +/- 0.03 and 0.40 +/- 0.02 mumol.g-1.10
min-1 for obese and lean, respectively). The contraction-induced changes in
glucose transport directly corresponded with the observed changes in cell
surface GLUT-4 protein. Thus the reduced glucose transport response to
insulin in skeletal muscle of the obese Zucker rat appears to result
directly from an inability to effectively enhance cell surface GLUT-4
protein.
