THE EFFECTS OF MUSCLE-CONTRACTION AND INSULIN ON GLUCOSE-TRANSPORTER TRANSLOCATION IN RAT SKELETAL-MUSCLE

The effect of electrically induced muscle contraction, insulin (10 m-u nits/ml) and electrically-induced muscle contraction in the presence o f insulin on insulin-regulatable glucose-transporter (GLUT-4) protein distribution was studied in female Sprague-Dawley rats during hindlimb perfusion. Plasma-membrane cytochalasin B binding increased similar t o 2-fold, whereas GLUT-4 protein concentration increased similar to 1. 5-fold above control with contractions, insulin, or insulin + contract ion. Microsomal-membrane cytochalasin B binding and GLUT-4 protein con centration decreased by approx. 30% with insulin or insulin + contract ion, but did not significantly decrease with contraction alone. The ra te of muscle glucose uptake was assessed by determining the rate of 2- deoxy[H-3]glucose accumulation in the soleus, plantaris, and red and w hite portions of the gastrocnemius. Both contraction and insulin incre ased glucose uptake significantly and to the same degree in the muscle s examined. Insulin + contraction increased glucose uptake above that of insulin or contraction alone, but this effect was only statisticall y significant in the soleus, plantaris and white gastrocnemius. The co mbined effects of insulin + contraction of glucose uptake were not ful ly additive in any of the muscles investigated. These results suggest that (1) insulin and muscle contraction are mobilizing two separate po ols of GLUT-4 protein, and (2) the increase in skeletal-muscle glucose uptake due to insulin + contraction is not due to an increase in plas ma-membrane GLUT-4 protein concentration above that observed for insul in or contraction alone.