REGULATION OF AMINO-ACID-TRANSPORT AND PROTEIN-METABOLISM IN MYOTUBESDERIVED FROM CHICKEN MUSCLE SATELLITE CELLS BY INSULIN-LIKE GROWTH FACTOR-I

The effects of insulin and insulin-like growth factor-I (IGF-I) on ami no acid transport and protein metabolism were compared in myotubes der ived from chicken breast muscle satellite cells. Protein synthesis was assessed by continuous labelling with [H-3]-tyrosine. Protein degrada tion was estimated by the release of trichloroacetic acid (TCA) solubl e radioactivity by cells which had been previously labelled with [H-3] -tyrosine for 3 days. Amino acid transport was measured in myotubes in cubated in Dulbecco's modified Eagle's medium (DMEM) 0.5% bovine serum albumin (BSA) with or without insulin or IGF-1. Subsequent [H-3]-amin oisobutyric acid (AIB) uptake was then measured in amino acid-free med ium. IGF-I was more efficient than insulin at equimolar concentration (3.2 nmol/1) in stimulating protein synthesis (127 and 113% of basal, respectively) and inhibiting protein degradation (32% and 13% inhibiti on of protein degradation following 4 h incubation). Half maximal effe ctive concentrations for stimulation of AIB uptake were 0.27 +/- 0.03 nmol/l and 34.8 +/- 3.1 nmol/l for IGF-I and insulin respectively, wit h maximal stimulation of about 340% of basal. Cycloheximide (3.6 mumol /l) diminished IGF-I-stimulated AIB uptake by 55%. Chicken growth horm one had no effect on basal AIB uptake in these cells and neither gluca gon nor dexamethasone had an effect on basal or IGF-I-stimulated AIB u ptake. This study demonstrates an anabolic effect for IGF-I in myotube s derived from primary chicken satellite cells which is mediated by th e type I IGF receptor, since the cation-independent mannose 6-phosphat e receptor does not bind IGF-II in chicken cells. (C) 1993 Wiley-Liss, Inc.