Caveolin, GLUT4 and insulin receptor protein content in human arm and leg muscles

Recent evidence suggests that insulin sensitivity is relatively better preserved in arm muscle than in leg muscle in both healthy controls and type 2 DM, based on measurements of basal and insulin-mediated glucose clearance performed simultaneously in the two sets of muscles. It has also been reported that glucose uptake rates are higher in arm compared to leg muscles in the fasted state during normo-insulinaemia. However, the mechanism(s) for this are unknown. Currently, no information is available on the content of glucose transport proteins between arm and leg muscles. Therefore, we compared four proteins, Caveolin-1 (Cav-1), Caveolin-3 (Cav-3), GLUT4, and IR-beta, each of which plays an important role in regulating glucose transport between arm and leg muscles using muscle samples that were obtained from the deltoid (DEL) and vastus lateralis (VAS) of 14 male college pentathlon athletes before and after two swimming trials performed over 100 and 1,500 m. In the present study, we have shown the levels of Cav-1, -3, GLUT4, and IR-beta measured together for the first time in human arm and leg muscles. There was no difference in the levels of these proteins between arm and leg muscles. Cav-3, GLUT4, and IR-beta were unchanged from the resting levels after both exercise trials in DEL, while Cav-1 was increased (17%) at the end of the longer swim trial. In contrast, all measurements of Cav-1, -3, GLUT4, and IR-beta after the 1,500 m swim trial in VAS were increased, by 120, 46, 123, and 60%, respectively. These data imply that there was no functional difference in glucose transport capacity between arm and leg muscles in highly trained pentathlon athletes in the resting state. Although Cav-3, GLUT4, and IR-beta were unchanged from the resting levels at the end of both exercise trials in DEL, all measures, including Cav-1, increased after the 1,500 m swim trial in VAS.