EXPRESSION OF THE INSULIN-REGULATABLE TRANSPORTER GLUT-4 IN MUSCLE IS INFLUENCED BY NEUROGENIC FACTORS

To investigate whether the expression of GLUT-4 is influenced by neurogenic factor(s) released from the nerve to the muscle, we measured GLUT-4 at different time points after sectioning the sciatic nerve at different locations in two groups of rats. Specifically, GLUT-4 was measured at 12, 24, and 48 h after severing the sciatic nerve. In one group of animals the muscles were left either with a short nerve stump attached to the muscle, or, in another group of animals, a long nerve stump remained attached to the muscle. In both groups of animals the contralateral limb served as a control. We examined GLUT-4 in the red (RG) and white gastrocnemius (WG), since the RG is highly responsive to denervation and the WG is quite resistant to denervation [L. A. Megeney, P. D. Neufer, G. L. Dohm, M. H. Tan, C. A. Blewtt, G. C. B. Elder, and A. Bonen. Am. J. Physiol. 264 (Endocrinol. Metab. 27): E583-E593, 1993]. In the long nerve stump WG no change in GLUT-4 was observed at 12, 24, or 48 h after denervation (P > 0.05). In the short nerve stump WG, changes were not evident at 12 and 24 h (P > 0.05), but by 48 h a significant decrement (-12.7 +/- 6.7%) was observed (P < 0.05). GLUT-4 changes were only evident 48 h after denervation (-19.8 +/- 4.5%; P < 0.05) in the long nerve stump RG. In contrast, in the short nerve stump RG, changes occurred much more rapidly; already 24 h after denervation a large decrease in GLUT-4 (-35.5 +/- 6.7%) had occurred (P < 0.05, which did not change during the next 24 h. Given that GLUT-4 decrements occurred more rapidly in denervated muscles with a short nerve stump than in those with a long nerve stump, our studies suggest that neurogenic factor(s) released from the nerve influences GLUT-4 expression.