Novel mechanisms to ATP‐dependent glucose uptake in skeletal muscle cells

Abstract

Contraction and insulin stimulate glucose influx into muscle, and contraction further sensitizes muscle to insulin. Insulin signals via α,β class I phosphatidylinositol 3‐kinase (PI3Kα,β) to Akt, but contraction signals remain elusive. Interestingly, ATP is released by contracting muscle, and it was recently reported that extracellular ATP can act auto/paracrinely on muscle cells. Our aim was to investigate if ATP induces glucose uptake in muscle cells and promotes insulin action.Rat primary myotubes transiently transfected with GLUT4myc and L6 myoblasts stably expressing GLUT4myc were exposed to 9s 6V electric stimulation (ES); insulin (100 nM, 5 min) or ATP (100 uM, 5min). Uptake of the fluorescent hexose 2NBDG was assayed in real time. Surface GLUT4 was measured by anti‐myc antibodies in fixed, unpermeabilizad cells. Phosphorylation of Akt and its target AS160 was detected with site‐specific antibodies.ES, insulin and ATP each stimulated glucose uptake, GLUT4 translocation, Akt and AS160 phosphorylation. ATP added prior to insulin increased glucose uptake beyond insulin's effect. Inhibitors of Akt (AktVIII), PI3Kα–γ (LY294002), PI3Kγ (AS605240) or dominant‐negative PI3Kγ and Akt inhibited the ATP‐effect. In sum, ES or ATP promote glucose uptake via GLUT4, and ATP adds to insulin action. These effects may be mediated by PI3‐Kγ and Akt and contribute to glucose uptake during muscle activity.Support: FONDAP 15010006, AT‐24100067, CIHR‐MT12601.