Glucose transporter expression in skeletal muscle of endurance-trained individuals

Two recently identified glucose transporters, GLUT8 and GLUT12, are expressed in human skeletal muscle and may be involved in insulin-mediated sugar transport. Purpose: The purpose of this study was to measure GLUT8 and GLUT12 mRNA levels in endurance-trained versus sedentary individuals in an effort to determine the effect of repeated days of contractile activity on gene expression. Methods: GLUT 4, 8, and 12 mRNA were measured in biopsies from the vastus lateralis using quantitative real-time PCR in endurance-trained (N = 16, age = 22.0 ± 0.9 yr, V̇O_2max (L·min^-1) = 4.13 ± 0.25) and sedentary (N = 15, age = 21.3 ± 0.8 yr, V̇O_2max (L·min^-1) = 3.21 ± 0.24) subjects. Results: GLUT12 mRNA was lower (40 ± 14%, P < 0.05) in the exercise-trained compared with the sedentary subjects. There was no difference between groups in GLUT8 mRNA content. mRNA of the insulin-sensitive glucose transporter (GLUT4) was 78 ± 27% (P < 0.05) higher in skeletal muscle from endurance-trained compared with sedentary individuals. Conclusion: These findings suggest an isoform-specific effect on the mRNA of the glucose transporters in human skeletal muscle with repeated days of contractile activity.