Regulation of amino acid transport and protein metabolism in myotubes derived from chicken muscle satellite cells by insulin-like growth factor-I

Publisher Website
Google Scholar
Abstract
The effects of insulin and insulin‐like growth factor‐I (IGF‐I) on amino acid transport and protein metabolism were compared in myotubes derived from chicken breast muscle satellite cells. Protein synthesis was assessed by continuous labelling with [3H]‐tyrosine. Protein degradation was estimated by the release of trichloroacetic acid (TCA) soluble radioactivity by cells which had been previously labelled with [3H]‐tyrosine for 3 days. Amino acid transport was measured in myotubes incubated in Dulbecco's modified Eagle's medium (DMEM) 0.5% bovine serum albumin (BSA) with or without insulin or IGF‐I. Subsequent [3H]‐aminoisobutyric acid (AIB) uptake was then measured in amino acid‐free medium. IGF‐I was more efficient than insulin at equimolar concentration (3.2 nmol/l) in stimulating protein synthesis (127 and 113% of basal, respectively) and inhibiting protein degradation (32% and 13% inhibition of protein degradation following 4 h incubation). Half maximal effective 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, with maximal stimulation of about 340% of basal. Cycloheximide (3.6 μmol/l) diminished IGF‐I‐stimulated AIB uptake by 55%. Chicken growth hormone had no effect on basal AIB uptake in these cells and neither glucagon nor dexamethasone had an effect on basal or IGF‐I‐stimulated AIB uptake. This study demonstrates an anabolic effect for IGF‐I in myotubes derived from primary chicken satellite cells which is mediated by the type I IGF receptor, since the cation‐independent mannose 6‐phosphate receptor does not bind IGF‐II in chicken cells.