Effects of glutamine deprivation on glutamine transport and synthesis in primary culture of rat skeletal muscle.
The effects of deprivation and supplementation of exogenous glutamine (0.06 and 2.2 mM in the culture medium, respectively) were studied in mononucleated myoblasts and in multinucleated myotubes. Myoblasts cultured in glutamine-deprived medium showed reductions in plating efficiency and myotube fusion index. Myotubes grown in glutamine-supplemented cultures had higher intracellular glutamine concentrations than those grown in glutamine-deprived medium (67 +/- 4.2 vs. 46 +/- 3.6 nmol/mg cell protein, respectively) and glutamine-supplemented myotubes utilized glutamine, whereas glutamine-deprived myotubes released it. Glutamine deprivation for 12 h caused a significant, cycloheximide-blockable increase in the capacity for glutamine uptake via system Nm in both myoblasts and myotubes (maximum velocity increases of 23 +/- 5.3 and 35 +/- 4.2%, respectively), which was reversed by glutamine replenishment. Depriving myotubes of glutamine did not alter the kinetics of uptake of amino acid transport systems A, ASC, or L. Glutamine deprivation resulted in a threefold increase in glutamine synthetase activity, whereas glutaminase activity remained unchanged. System Nm and glutamine synthetase appear to undergo adaptive upregulation in glutamine-deprived muscle cells to compensate for the reduced exogenous glutamine supply.
Tadros
L B
LB
Department of Anatomy and Physiology, University of Dundee, Scotland.
Willhoft
N M
NM
Taylor
P M
PM
Rennie
M J
MJ
D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001216:Asparagine / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D005972:Glutaminase / Q000378:metabolism; D005973:Glutamine / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology*; D006639:Histidine / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D008717:Methionine Sulfoximine / Q000494:pharmacology; D009132:Muscles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013997:Time Factors; D014316:Tritium
D000596:Amino Acids; D007328:Insulin; D005973:Glutamine; D014316:Tritium; D008717:Methionine Sulfoximine; D006639:Histidine; D001216:Asparagine; D003513:Cycloheximide; D005972:Glutaminase; D005974:Glutamate-Ammonia Ligase