MORE TETANIC CONTRACTIONS ARE REQUIRED FOR ACTIVATING GLUCOSE-TRANSPORT MAXIMALLY IN TRAINED MUSCLE

Exercise training increases contraction-stimulated maximal glucose tra nsport and muscle glycogen level in skeletal muscle. However, there is a possibility that more muscle contractions are required to maximally activate glucose transport in trained than in untrained muscle, becau se increased glycogen level after training may inhibit glucose transpo rt. Therefore, the purpose of this study was to investigate the relati onship between the increase in glucose transport and the number of tet anic contractions in trained and untrained muscle. Male rats swam 2 h/ day for 15 days. In untrained epitrochlearis muscle, resting glycogen was 26.6 mu mol glucose/g muscle. Ten, 10-s-long tetani at a rate of 1 contraction/min decreased glycogen level to 15.4 mu mol glucose/g mus cle and maximally increased 8-deoxy-D-glucose (2-DG) transport. Traini ng increased contraction-stimulated maximal 2-DG transport (+71%; P < 0.01), GLUT-4 protein content (+78%; P < 0.01), and resting glycogen l evel (to 39.3 mu mol glucose/g muscle; P < 0.01) on the next day after the training ended, although this training effect might be due, at le ast in part, to last bout of exercise. In trained muscle, 20 tetani we re necessary to maximally activate glucose transport. Twenty tetani de creased muscle glycogen to a lower level than 10 tetani (18.9 vs. 24.0 mu mol glucose/g muscle; P < 0.01). Contraction-stimulated 2-DG trans port was negatively correlated with postcontraction muscle glycogen le vel in trained (r = -0.60; P < 0.01) and untrained muscle (r = -0.57; P < 0.01).