GLUT 4 and insulin receptor binding and kinase activity in trained human muscle.

Abstract

1. Physical training enhances sensitivity and responsiveness of insulin‐mediated glucose uptake in human muscle. This study examines if this effect of physical training is due to increased insulin receptor function or increased total concentration of insulin‐recruitable glucose transporter protein (GLUT 4). 2. Seven healthy young subjects carried out single leg bicycle training for 10 weeks at 70% of one leg maximal oxygen uptake (VO2,max). Subsequently biopsies were taken from the vastus lateralis muscle of both legs. 3. Single leg VO2,max increased for the trained leg (46 +/‐ 3 to 52 +/‐ 2 ml min‐1 kg‐1 (means +/‐ S.E.M., P < 0.05), and cytochrome c oxidase activity was higher in this compared to the untrained leg (2.0 +/‐ 0.1 vs. 1.4 +/‐ 0.1 nmol s‐1 (mg muscle)‐1, P < 0.05). Insulin binding as well as basal‐ and insulin‐stimulated receptor kinase activity did not differ between trained and untrained muscle. The concentration of GLUT 4 protein was higher in the former (14.9 +/‐ 1.9 vs. 11.6 +/‐ 1.0 arbitrary units (micrograms protein)‐1 in crude membranes, P < 0.05). The training‐induced increase in GLUT 4 (26 +/‐ 11%) matched a previously reported increase in maximum insulin‐stimulated leg glucose uptake (25 +/‐ 7%) in the same subjects, and individual values of the two variables correlated (correlation coefficient (r) = 0.84, P < 0.05). 4. In conclusion, in human muscle training induces a local contraction‐dependent increase in GLUT 4 protein, which enhances the effect of insulin on glucose uptake. On the other hand, insulin receptor function in muscle is unlikely to be affected by training.