INSULIN-LIKE GROWTH FACTOR-I-STIMULATED GLUCOSE-TRANSPORT IN MYOTUBES DERIVED FROM CHICKEN MUSCLE SATELLITE CELLS

The effects of insulin and insulin-like growth factor-I (IGF-1) on glucose transport were compared in myotubes derived from chicken breast muscle satellite cells in vitro. Myotubes were incubated (for 0.5 or 4 h) with or without glucose in the presence or absence of insulin or IGF-I. Glucose uptake was subsequently measured by the incorporation of 2-[1,2-H-3(N)] deoxy-D-glucose ([H-3]2DG) in glucose-free medium (10 min at 20-degrees-C). Glucose uptake was almost completely abolished by the addition of cytochalasin B or phloretin. It was increased by a decrease in glucose concentration in the incubation medium. Insulin (5 mg/1) stimulated [H-3]2DG uptake to a maximum of 43 +/- 10% above basal after 30-min incubation and 101 +/- 15% after 4-h incubation. IGF-I and insulin at equimolar concentrations (25 mug/l and 20 mug/l respectively) were almost equipotent after 0.5 h but after 4-h incubation IGF-I was 17-fold more potent, suggesting that this 'late' effect was mediated through the IGF-I receptor. Incubation with cycloheximide suggested that the effect of IGF-I involved increased protein synthesis. The results suggest that chicken myotubes express a glucose transporter which is regulated by IGF-I and glucose concentration. However, they do not appear to express a typical insulin-responsive transport s stem.