Regulation of amino acid transport and protein metabolism in myotubes derived from chicken muscle satellite cells by insulin-like growth factor-I.
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 mumol/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.
Duclos
M J
MJ
INRA, Station de Recherches Avicoles, Endocrinologie de la Croissance et du Métabolisme, Nouzilly, France.
Chevalier
B
B
Goddard
C
C
Simon
J
J
D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002478:Cells, Cultured; D002645:Chickens; D003561:Cytarabine / Q000494:pharmacology; D013006:Growth Hormone / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000166:cytology / Q000378:metabolism*
D000596:Amino Acids; D000621:Aminoisobutyric Acids; D009124:Muscle Proteins; D003561:Cytarabine; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone