EFFECT OF CROSS-REINNERVATION ON THE EXPRESSION OF GLUT-4 AND GLUT-1 IN SLOW AND FAST RAT MUSCLES

We determined whether the twitch-velocity phenotype or the metabolic p henotype of a muscle influences the content of GLUT-4 and GLUT-1 prote ins. The soleus (Sol) and extensor digitorum longus (EDL) muscles were cross-reinnervated (X-Sol, X-EDL). After 3 mo the X-EDL had become en riched in slow-twitch oxidative (SO) fibers (70.5% SO) compared with i ts control (3.8% SO), whereas the X-Sol became enriched in fast-twitch oxidative-glycolytic (FOG) fibers (78.6% FOG) compared with its contr ol (10% FOG). Thus the twitch phenotype of X-Sol shifted to fast-twitc h muscle, whereas X-EDL shifted to a slow-twitch muscle. In the X-EDL, the oxidative nature of the X-EDL was increased to 97% oxidative fibe rs compared with 43% oxidative fibers in the normal EDL. In the Sol th e oxidative nature of the X-Sol was retained at 100%. GLUT-4 content w as increased 1.6-fold in the X-EDL (P < 0.05) but was not changed in t he X-Sol (P > 0.05). GLUT-1 content was increased fourfold in X-EDL bu t was not altered in the X-Sol. We conclude that GLUT-4 and GLUT-1 con tent in muscle is related to the oxidative phenotype of the muscle rat her than the twitch-velocity phenotype.