Glucose transport and cell surface glut4 protein in skeletal muscle
of the obese zucker rat.
Etgen, Garret J., Cindy M. Wilson, J[stod]orgen Jensen, Samuel W.
Cushman, and John L. Ivy.
Exercise Physiology and Metabolism Laboratory, Department of
Kinesiology, University of Texas at Austin 78712, and the
Experimental Diabetes, Metabolism, and Nutrition Section, DB/NIDDK
National Institutes of Health, Bethesda, MD 20892-1420
APStracts 3:0064E, 1996.
3-O-methyl-D-glucose transport and 2-N-4-(l-azi-2,2,2
-trifluoroethyl)benzoyl-1,3-bis-(D-mannos-4-yloxy)-2-propylamine (ATB
-BMPA) labelled cell surface GLUT4 protein were assessed in fast-
(epitrochlearis) and slow-twitch (soleus) muscles of lean and obese
(fa/fa) Zucker rats. Glucose transport and cell surface GLUT4 protein
were similar in both epitrochlearis and soleus of lean and obese rats
in the absence of insulin. In contrast, insulin-stimulated glucose
transport rates were significantly higher for lean than obese in both
soleus (0.74 +/- 0.05 [mu]mol/g/10 min vs. 0.40 +/- 0.02 [mu]mol/g/10
min) and epitrochlearis (0.51 +/- 0.05 [mu]mol/g/10 min vs. 0.17 +/-
0.02 [mu]mol/g/10 min) 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 GLUT4
protein. Muscle contraction elicited similar increases in glucose
transport in lean and obese rats, with the effect being more
pronounced in fast- (0.70 +/- 0.07 and 0.77 +/- 0.04 [mu]mol/g/10 min
for obese and lean, respectively) than slow-twitch muscle (0.36 +/-
0.03 and 0.40 +/- 0.02 [mu]mol/g/10 min for obese and lean,
respectively). The contraction-induced changes in glucose transport
directly corresponded with the observed changes in cell surface GLUT4
protein. The combination of contraction and insulin had an additive
effect on glucose transport and cell surface GLUT4 protein in soleus
of lean rats, and a synergistic effect on these parameters in soleus
of obese rats. In contrast, the combined effects of contraction and
insulin on glucose transport and cell surface GLUT4 protein were not
greater than the effect of contraction alone in epitrochlearis
muscles of either lean or obese rats. Thus, under all conditions, in
both normal and insulin resistant, fast- and slow-twitch muscle,
glucose transport rates were directly related to cell surface GLUT4
protein concentrations. Therefore, it is suggested that the reduced
insulin-stimulated glucose transport capacity in muscle of the obese
Zucker rat results directly from an inability to effectively enhance
cell surface GLUT4 protein.
Received 23 January 1996; accepted in final form 8 March 1996.
APS Manuscript Number E39-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96