scholarly journals Characteristics of L-glutamine transport in perfused rat skeletal muscle.

1987 ◽  
Vol 393 (1) ◽  
pp. 283-305 ◽  
Author(s):  
H S Hundal ◽  
M J Rennie ◽  
P W Watt
Keyword(s):  
Skeletal Muscle ◽  
Rat Skeletal Muscle ◽  
Glutamine Transport

Glutamine transport and metabolism in denervated rat skeletal muscle

1990 ◽  
Vol 259 (2) ◽  
pp. E148-E154 ◽  
Author(s):  
H. S. Hundal ◽  
P. Babij ◽  
P. W. Watt ◽  
M. R. Ward ◽  
M. J. Rennie
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Maximal Activity ◽  
Resting Membrane Potential ◽  
Na Channel ◽  
Synthetase Activity ◽  
Glutamine Synthetase Activity ◽  
Rat Skeletal Muscle ◽  
Glutamine Transport ◽  
Recovery Of Vmax

Rat skeletal muscle glutamine fell by 40% from 4.18 to 2.5 mumols/g wet weight (P less than 0.01) after 4 days of denervation. Over the same period net glutamine efflux from denervated hindlimbs [i.e., arteriovenous (a-v) concentration differences x blood flow] increased 3.5-fold (from -6.72 +/- 1.73 to -26 +/- 4.81 nmol.min-1.g-1, P less than 0.001). Gastrocnemius glutamine synthetase activity fell 48% after denervation (from 475 +/- 81 to 248 +/- 39 nmol.min-1.g-1, P less than 0.001), but glutaminase activity was not significantly altered (17 nmol.min-1.g-1). The maximal activity (Vmax) of the unidirectional Na(+)-dependent glutamine transporter (system Nm) was depressed by 45% from 1,020 +/- 104 to 571 +/- 9 nmol.min-1.g-1 (P less than 0.01), but the concentration at which transport was half maximal (Km) was not significantly altered (control 8.1 +/- 0.6 mM; denervated 6.52 +/- 0.12). Hindlimb denervation resulted in an increase of intramuscular Na+ by 17% and a fall of K+ by 12%, and the resting membrane potential in isolated muscles decreased from -75 +/- 10 to -59.5 +/- 5.5 mV. Membrane potential of perfused denervated muscle, isolated after acute addition of the Na+ channel blocker tetrodotoxin (TTX, 3 microM), repolarized to -66.4 +/- 3.2 mV. In perfused denervated preparations TTX caused an acute recovery of Vmax of unidirectional glutamine transport to 848 +/- 75 nmol.min-1.g-1; Km was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of glutamine transport in primary tissue culture of rat skeletal muscle

1993 ◽  
Vol 265 (1) ◽  
pp. E135-E144 ◽  
Author(s):  
L. B. Tadros ◽  
P. M. Taylor ◽  
M. J. Rennie
Keyword(s):  
Skeletal Muscle ◽  
Tissue Culture ◽  
Maximum Velocity ◽  
Significant Inhibition ◽  
Neonatal Rat ◽  
Rat Skeletal Muscle ◽  
Glutamine Transport ◽  
Primary Tissue Culture ◽  
Primary Tissue ◽  
Glutamine Uptake

Glutamine transport was studied in preconfluent monolayered, mononucleated myoblasts (4 days old) and in fused, multinucleated, differentiated myotubes (10 days old), both prepared from neonatal rat skeletal muscle. The initial (60 s) rate of 50 microM glutamine uptake in myoblasts and myotubes was stereospecific, saturable, and largely (80%) Na+ dependent. At glutamine concentrations of 0.01–1 mM, Na(+)-dependent uptake showed saturation kinetics: in myoblasts, the Michaelis constant (Km) was 197 +/- 38 microM, maximum velocity (Vmax) was 1,165 +/- 60 pmol.min-1.mg protein-1; in myotubes, Km was 174 +/- 51 microM and Vmax was 1,435 +/- 47 pmol.min-1.mg protein-1. The Na(+)-dependent glutamine uptake was Li+ tolerant in both myoblasts and myotubes. The Na(+)-dependent uptake of 50 microM L-[3H]glutamine was investigated in the presence of various amino acids at 0.01–10 mM. Histidine and asparagine competitively inhibited glutamine uptake, but inhibition by serine was noncompetitive; glutamate, arginine, leucine, and 2-aminobicyclo(2,2,1)heptane-2-carboxylate (BCH) had no significant inhibitory effects; 2-(methyl-amino)isobutyrate (MeAIB) caused a small but significant inhibition. In parallel with a stimulation of glucose transport, addition of insulin stimulated Na(+)-dependent glutamine uptake within 1 h by a maximum of 27% in myoblasts and 42% in myotubes (half-maximal stimulation at 0.3 nM insulin). Glucagon had no effect. Kinetic analysis revealed that the insulin-stimulated increase in glutamine transport was due to a Vmax effect, which was cycloheximide inhibitable. The insulin-stimulated increase was Li+ tolerant and not inhibited by MeAIB or cysteine at 1 mM. The results indicate that the predominant glutamine transporter of neonatal rat skeletal muscle cells in primary tissue culture in System Nm. System Nm also appears to be the major insulin-sensitive glutamine transport component in skeletal muscle. Primary muscle culture appears to be a useful preparation for studying glutamine transport and its regulation.

Effects of insulin and exercise on amino acid transport in rat skeletal muscle

1994 ◽  
Vol 266 (2) ◽  
pp. C524-C530 ◽  
Author(s):  
P. A. King
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Acute Exercise ◽  
Acid Transport ◽  
Rat Skeletal Muscle ◽  
Plasma Membrane Vesicles ◽  
System A ◽  
Alanine Transport ◽  
Glutamine Transport

In the present study, the initial rates of amino acid transport by isolated rat skeletal muscle plasma membrane vesicles were investigated. This approach facilitates the study of the transport of naturally occurring amino acids independent of the effects of cellular metabolism. Alanine and glutamine influxes were measured using a rapid filtration technique. Transport was examined in the presence and absence of Na and the properties of membranes from control, insulin-treated, or acutely exercised rats were studied. Both alanine and glutamine were transported by Na-dependent processes. The values for maximum rate of transport (Vmax) for Na-dependent alanine and glutamine transport were 203 and 224 pmol.mg-1.s-1, respectively. The K1/2 values were 2.9 mM alanine and 1.9 mM glutamine. The Vmax for Na-dependent alanine transport was increased by insulin treatment of the animal and by acute exercise. 2-(Methylamino)-isobutyric acid (MeAIB) partially inhibited the control Na-dependent alanine influx and completely inhibited the increase due to insulin or exercise treatment, indicating the importance of both system A and a non-system A, Na-dependent carrier for alanine transport. The Vmax for Na-dependent MeAIB uptake was also increased by insulin or exercise treatments of the rats. Unlike alanine, Na-dependent glutamine transport was not affected by insulin.

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