Regulation of GLUT4 protein expression and glycogen storage after prolonged exercise

The purpose of this study was to determine the lime course of GLUT4 protein accumulation following an exercise-carbohydrate supplementation regimen, a nd to evaluate the effect of this regimen on GLUT4 mRNA regulation. Rats we re exercised by swimming and intubated with 1 mL of a 50% glucose solution immediately post-exercise. Exercise significantly reduced muscle glycogen b y 50%. By 1.5 h of recovery, muscle glycogen was normalized, but continued to increase above the control level during the next 16 h. A faster and larg er repletion of glycogen occurred in the fast-twitch red compared with the fast-twitch white muscle during the 16 h of recovery. GLUT4 protein concent ration in fast-twitch red muscle was significantly increased above control by 1.5 h of recovery, and progressively increased throughout the recovery p eriod. Fast-twitch white muscle demonstrated a similar trend, but the incre ase in GLUT4 protein did not reach significance until 5 h of recovery. Fast -twitch red muscle GLUT4 mRNA was increased by 53% above control immediatel y post-exercise, but returned to the control level by 1.5 h of recovery. GL UT4 mRNA associated with polysomes, however, increased significantly during this time and remained elevated for a minimum of 5 h. The results suggest that the increased GLUT4 protein expression following a regimen of exercise -carbohydrate supplementation occurs sufficiently fast to contribute to the resynthesis of muscle glycogen, and is controlled by both pre-translationa l and translational mechanisms.