Wortmannin inhibits both insulin- and contraction-stimulated glucose uptake and transport in rat skeletal muscle

Jørgen F. P. Wojtaszewski, Bo F. Hansen, Birgitte Ursø, and Erik A. Richter Copenhagen Muscle Research Centre, August Krogh Institute, University of Copenhagen, DK-2100 Copenhagen; Hagedorn Research Center, Gentofte, DK-2820 Copenhagen; and Diabetes Research, Novo Nordisk, DK-2880 Bagsvaerd, Denmark Received 22 February 1996; accepted in final form 13 May 1996. Wojtaszewski, Jørgen F. P., Bo F. Hansen, Birgitte Ursø, and Erik A. Richter. Wortmannin inhibits both insulin- and contraction-stimulated glucose uptake and transport in rat skeletal muscle. J. Appl. Physiol. 81(4): 1501-1509, 1996. The role of phosphatidylinositol (PI) 3-kinase for insulin- and contraction-stimulated muscle glucose transport was investigated in rat skeletal muscle perfused with a cell-free perfusate. The insulin receptor substrate-1-associated PI 3-kinase activity was increased sixfold upon insulin stimulation but was unaffected by contractions. In addition, the insulin-stimulated PI 3-kinase activity and muscle glucose uptake and transport in individual muscles were dose-dependently inhibited by wortmannin with one-half maximal inhibition values of ~10 nM and total inhibition at 1 µM. This concentration of wortmannin also decreased the contraction-stimulated glucose transport and uptake by ~30-70% without confounding effects on contractility or on muscle ATP and phosphocreatine concentrations. At higher concentrations (3 and 10 µM), wortmannin completely blocked the contraction-stimulated glucose uptake but also decreased the contractility. In conclusion, inhibition of PI 3-kinase with wortmannin in skeletal muscle coincides with inhibition of insulin-stimulated glucose uptake and transport. Furthermore, in contrast to recent findings in incubated muscle, wortmannin also inhibited contraction-stimulated glucose uptake and transport. The inhibitory effect of wortmannin on contraction-stimulated glucose uptake may be independent of PI 3-kinase activity or due to inhibition of a subfraction of PI 3-kinase with low sensitivity to wortmannin. hindlimb; signaling; phosphatidylinositol 3-kinase 0161-7567/96 $5.00 Copyright © 1996 the American Physiological Society