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Effect of short‐term training on GLUT‐4 mRNA and protein expression in human skeletal muscle

Six untrained, male subjects (23 ± 1 years old, 84 ± 5 kg, V̇O2peak= 3.7 ± 0.8 l min−1) exercised for 60 min at 75 ± 1%V̇O2peak on 7 consecutive days. Muscle samples were obtained before the start of cycle exercise training and 24 h after the first and seventh exercise sessions and analysed for citrate synthase activity, glycogen and glucose transporter 4 (GLUT‐4) mRNA and protein expression. Exercise training increased (P < 0.05) citrate synthase by ∼20% and muscle glycogen concentration by ∼40%. GLUT‐4 mRNA levels 24 h after the first and seventh exercise sessions were similar to those measured before the start of exercise training. In contrast, GLUT‐4 protein expression was increased after 7 days of exercise training (12.4 ± 1.5 versus 3.4 ± 1.0 arbitray units (a.u.), P < 0.05) and although it tended to be higher 24 h after the first exercise session (6.0 ± 3.0 versus 3.4 ± 1.0 a.u.), this was not significantly different (P= 0.09). These results support the suggestion that the adaptive increase in skeletal muscle GLUT‐4 protein expression with short‐term exercise training arises from the repeated, transient increases in GLUT‐gene transcription following each exercise bout leading to a gradual accumulation of GLUT‐4 protein, despite GLUT‐4 mRNA returning to basal levels between exercise stimuli.