AJP - Endocrinology and Metabolism, Vol 272, Issue 5 E864-E869, Copyright © 1997 by American Physiological Society
Exercise training reverses insulin resistance in muscle by enhanced recruitment of GLUT-4 to the cell surface
G. J. Etgen Jr, J. Jensen, C. M. Wilson, D. G. Hunt, S. W. Cushman and J. L. Ivy
Department of Kinesiology, University of Texas at Austin 78712, USA.
The effects of exercise training on cell surface GLUT-4 in skeletal muscle
of the obese (fa/fa) Zucker rat were investigated using the impermeant
glucose transporter photoaffinity reagent
2-N-4-(1-azi-2,2,2-trifluoroethyl)-benzoyl-1,3-bis-
(D-mannos-4-yloxy)-2-propylamine (ATB-BMPA). In the absence of insulin,
3-O-methyl-D-glucose transport activity was no different in either
fast-twitch (epitrochlearis) or slow-twitch (soleus) muscles of trained and
sedentary obese rats. Likewise, basal ATB-BMPA-labeled GLUT-4 was not
altered in these muscles with training. In contrast, the trained group
exhibited significantly greater insulin-stimulated (2 mU/ml) glucose
transport activity in epitrochlearis muscles than the sedentary group (0.53
+/- 0.03 vs. 0.18 +/- 0.03 mumol.g-1 x 10 min-1 for trained and sedentary,
respectively), which was paralleled by a significant enhancement of
insulin-stimulated cell surface GLUT-4 (5.33 +/- 0.20 vs. 1.57 +/- 0.14
disintegrations.min-1.mg-1 for trained and sedentary, respectively).
Exercise training, however, did not alter insulin-stimulated glucose
transport activity or cell surface GLUT-4 in soleus muscles. Finally,
exercise training did not alter the ability of muscle contraction to
elevate glucose transport activity or cell surface GLUT-4 in either
epitrochlearis or soleus muscles of the obese rat. These results indicate
that training improves insulin-stimulated glucose transport in muscle of
the obese Zucker rat by increasing GLUT-4 content and by altering the
normal intracellular distribution of these transporters such that they are
now capable of migrating to the cell surface in response to the insulin
stimulus.
