Th. Reynolds et al., EFFECTS OF EXERCISE TRAINING ON GLUCOSE-TRANSPORT AND CELL-SURFACE GLUT-4 IN ISOLATED RAT EPITROCHLEARIS MUSCLE, American journal of physiology: endocrinology and metabolism, 35(2), 1997, pp. 320-325
The effects of exercise training on maximal glucose transport activity
and cell surface GLUT-4 were examined in rat epitrochlearis muscle. F
ive days of swim training (2 x 3 h/day) produce a significant increase
in citrate synthase activity (24.5 +/- 0.6 vs. 20.1 +/- 0.7 mu mol .
min(-1) . g(-1)), GLUT-4 content (22.9 +/- 0.8 vs. 17.4 +/- 0.4% GLUT-
4 standard), and glycogen levels (54.3 +/- 9.4 vs. 28.6 +/- 9.4 mu mol
/g). Maximally, insulin-stimulated glucose transport activity and cell
surface GLUT-4 are increased by 55 (1.50 +/- 0.11 vs. 0.97 +/- 0.10 m
u mol . ml(-1) . 20 min(-1)) and 48% [12.0 +/- 0.8 vs. 8.1 +/- 0.9 dis
integrations . min(-1) (dpm) . mg(-1)], respectively, in exercise-trai
ned epitrochlearis muscles. In contrast, hypoxia-stimulated glucose tr
ansport activity and cell surface GLUT-4 are reduced by 38 (0.78 +/- 0
.08 vs. 1.25 +/- 0.14 mu mol . ml(-1) . 20 min(-1)) and 40% (5.7 +/- 0
.9 vs. 9.4 +/- 1.2 dpm/mg), respectively, in exercise-trained epitroch
learis muscles. These results demonstrate that changes in insulin- and
hypoxia-stimulated glucose transport activity after exercise training
are fully accounted for by the appearance of cell surface GLUT-4 and
support the concept of two intracellular pools of GLUT-4. Finally, we
propose that high levels of muscle glycogen with exercise training may
contribute to the decrease in hypoxia-stimulated glucose transport ac
tivity.