Reduced insulin-stimulated glucose transport in denervated muscle is associated with impaired Akt-alpha activation

Insulin signaling was examined in muscle made insulin resistant by short-term (24-h) denervation. Insulin-stimulated glucose transport in vitro was reduced by 28% (P < 0.05) in denervated muscle (DEN). In control muscle (SHAM), insulin increased levels of surface-detectable GLUT-4 (i.e., translocated GLUT-4) 1.8-fold (P < 0.05), whereas DEN surface GLUT-4 was not increased by insulin (P > 0.05). Insulin treatment in vivo induced a rapid appearance of phosphoSer(473)]Akt-alpha in SHAM 3 min after insulin injection. In DEN, phosphoSer(473)]Akt-alpha also appeared at 3 min, but Ser(473)-phosphorylated Akt-alpha was 36% lower than in SHAM (P < 0. 05). In addition, total Akt-alpha protein in DEN was 37% lower than in SHAM (P < 0.05). Akt-alpha kinase activity was lower in DEN at two insulin levels tested: 0.1 U insulin/rat (-22%, P < 0.05) and 1 U insulin/rat (-26%, P < 0.01). These data indicate that short-term (24-h) denervation, which lowers insulin-stimulated glucose transport, is associated with decreased Akt-alpha activation and impaired insulin-stimulated GLUT-4 appearance at the muscle surface.