title: Insulin signaling in human skeletal muscle: time course and effect of exercise.
abstract: Activation of early steps in the insulin signaling cascade in human skeletal muscle was investigated using a one-step euglycemic-hyperinsulinemic (approximately 100 pU/ml) clamp in seven healthy young men 3 h after one-legged exercise. Concomitant insulin stimulation (three- to six-fold [P < 0.05]) of thigh glucose clearance, muscle insulin receptor tyrosine kinase (IRTK), insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation, and IRS-1-associated phosphatidylinositol 3-kinase (PI 3-kinase) was observed in the rested leg. Twenty minutes after cessation of insulin infusion, the level of these parameters returned toward basal. A twofold higher insulin-stimulated glucose clearance in the exercised compared with the rested thigh was accompanied by unaltered maximal IRTK activation and IRS-1 tyrosine phosphorylation, and by a decreased (approximately 50%, P < 0.05) maximal IRS-1 associated PI 3-kinase activation. Prior exercise caused significantly faster insulin-stimulated tyrosine phosphorylation of IRS-1, PI 3-kinase activity, and glucose clearance compared with those in the rested thigh. In conclusion, physiological hyperinsulinemia activates IRTK, IRS-1 tyrosine phosphorylation, and PI 3-kinase in human skeletal muscle. However, increased insulin action after exercise is not caused by potentiation of these steps in the insulin signaling cascade. In contrast, at steady state, paradoxically decreased insulin-stimulated IRS-1-associated PI 3-kinase activity was observed in exercised muscle. Thus, the activity of IRS-1-associated PI 3-kinase and glucose uptake may not always be tightly coupled during insulin stimulation in human muscle.
authors.affiliation: Copenhagen Muscle Research Centre, August Krogh Institute, University of Copenhagen, Denmark. jwojtaszew@aki.ku.dk
authors.forename: J F
authors.initials: JF
authors.lastname: Wojtaszewski
authors.forename: B F
authors.initials: BF
authors.lastname: Hansen
authors.forename: B
authors.initials: B
authors.lastname: Kiens
authors.forename: E A
authors.initials: EA
authors.lastname: Richter
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D015309:Glucose Clamp Technique; D006801:Humans; D006946:Hyperinsulinism; D007262:Infusions, Intravenous; D007328:Insulin / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007700:Kinetics; D007866:Leg; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply / Q000187:drug effects / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine; D005082:Physical Exertion / Q000502:physiology*; D011972:Receptor, Insulin / Q000378:metabolism; D012146:Rest / Q000502:physiology; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D001786:Blood Glucose; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D019000:Phosphotyrosine; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D005947:Glucose