scholarly journals Methionine metabolism by rat muscle and other tissues. Occurrence of a new carnitine intermediate

1987 ◽  
Vol 247 (1) ◽  
pp. 35-40 ◽  
Author(s):  
P W D Scislowski ◽  
B M Hokland ◽  
W I A Davis-van Thienen ◽  
J Bremer ◽  
E J Davis
Keyword(s):  
Skeletal Muscle ◽  
Methionine Metabolism ◽  
Rat Skeletal Muscle ◽  
Citrate Cycle ◽  
Kidney Mitochondria ◽  
Rat Muscle ◽  
Mammalian Tissues ◽  
Liver And Kidney ◽  
Oxidation Of Methionine

Perfused rat hindquarter preparations were shown to incorporate radioactivity from [U-14C]methionine into citrate-cycle intermediates, lactate, alanine, glutamate, glutamine and CO2. During perfusion, large amounts of methionine were also oxidized to methionine sulphoxide. The capacity for transamination of methionine or its oxo analogue, 4-methylthio-2-oxobutyrate, by muscle extracts was demonstrated. Rat skeletal muscle, heart, liver and kidney mitochondria, when incubated with the latter plus radiolabelled carnitine, formed a newly identified carnitine derivative, 3-methylthiopropionylcarnitine. It is concluded that the capacity for oxidation of methionine by a trans-sulphuration-independent pathway occurs in several mammalian tissues. The extent of inter-organ handling of intermediates in this pathway(s) is discussed.

scholarly journals Reversible ATP-induced inactivation of branched-chain 2-oxo acid dehydrogenase

1980 ◽  
Vol 192 (1) ◽  
pp. 155-163 ◽  
Author(s):  
R Odessey
Keyword(s):  
Skeletal Muscle ◽  
Liver Mitochondria ◽  
Initial Activity ◽  
Rat Skeletal Muscle ◽  
Kidney Mitochondria ◽  
Physiological Conditions ◽  
Acid Dehydrogenase ◽  
Skeletal Muscle Mitochondria ◽  
Branched Chain

The branched chain 2-oxo acid dehydrogenase from rat skeletal muscle, heart, kidney and liver mitochondria can undergo a reversible activation-inactivation cycle in vitro. Similar results were obtained with the enzyme from kidney mitochondria of pig and cow. The dehydrogenase is markedly inhibited by ATP and the inhibition is not reversed by removing the nucleotide. The non-metabolizable ATP analogue adenosine 5′-[beta gamma-imido] triphosphate can block the effect of ATP when added with the nucleotide, but has no effect by itself, nor can it reverse the inhibition in mitochondria preincubated with ATP. These findings suggest that the branched chain 2-oxo acid dehydrogenase undergoes a stable modification that requires the splitting of the ATP gamma-phosphate group. In skeletal muscle mitochondria the rate of inhibition by ATP is decreased by oxo acid substrates and enhanced by NADH. The dehydrogenase can be reactivated 10-20 fold by incubation at pH 7.8 in a buffer containing Mg2+ and cofactors. Reactivation is blocked by NaF (25 mM). The initial activity of dehydrogenase extracted from various tissues of fed rats varies considerably. Activity is near maximal in kidney and liver whereas the dehydrogenase in heart and skeletal muscle is almost completely inactivated. These studies emphasize that comparisons of branched chain 2-oxo acid dehydrogenase activity under various physiological conditions or in different tissues must take into account its state of activation. Thus the possibility exists that the branched chain 2-oxo acid dehydrogenase may be physiologically regulated via a covalent mechanism.

Insulin increases thermogenesis in rat skeletal muscle following exercise

1985 ◽  
Vol 248 (1) ◽  
pp. E148-E151
Author(s):  
T. W. Balon ◽  
A. Zorzano ◽  
M. N. Goodman ◽  
N. B. Ruderman
Keyword(s):  
Skeletal Muscle ◽  
Insulin Secretion ◽  
Glycogen Synthesis ◽  
O2 Consumption ◽  
Rat Skeletal Muscle ◽  
Additional Energy ◽  
Rat Muscle ◽  
Prior Exercise ◽  
Increase Insulin Secretion ◽  
Stimulation Of

Insulin increased O2 consumption in isolated perfused rat muscle for upward of 2 h after a treadmill run. Insulin did not increase O2 consumption in nonexercised rats, nor did prior exercise increase O2 consumption in the absence of added insulin. The stimulation of glycogen synthesis by insulin was also enhanced in muscle of previously exercised rats. The additional energy required for this was not sufficient to account for the increase in O2 consumption, however. The results indicate that insulin increases thermogenesis in skeletal muscle after exercise. They also raise the possibility that in intact organisms the thermogenic effect of foods that increase insulin secretion could be increased by prior exercise.

Cytosolic citrate and malonyl-CoA regulation in rat muscle in vivo

1999 ◽  
Vol 276 (6) ◽  
pp. E1030-E1037 ◽  
Author(s):  
Asish K. Saha ◽  
D. Ross Laybutt ◽  
David Dean ◽  
Demetrios Vavvas ◽  
Elena Sebokova ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Plasma Insulin ◽  
Fatty Acyl ◽  
Rat Skeletal Muscle ◽  
Euglycemic Hyperinsulinemic Clamp ◽  
Whole Cell ◽  
Rat Muscle ◽  
Malonyl Coa ◽  
Cell Concentrations

In liver, insulin and glucose acutely increase the concentration of malonyl-CoA by dephosphorylating and activating acetyl-CoA carboxylase (ACC). In contrast, in incubated rat skeletal muscle, they appear to act by increasing the cytosolic concentration of citrate, an allosteric activator of ACC, as reflected by increases in the whole cell concentrations of citrate and malate [Saha, A. K., D. Vavvas, T. G. Kurowski, A. Apazidis, L. A. Witters, E. Shafrir, and N. B. Ruderman. Am. J. Physiol. 272 ( Endocrinol. Metab. 35): E641–E648, 1997]. We report here that sustained increases in plasma insulin and glucose may also increase the concentration of malonyl-CoA in rat skeletal muscle in vivo by this mechanism. Thus 70 and 125% increases in malonyl-CoA induced in skeletal muscle by infusions of glucose for 1 and 4 days, respectively, and a twofold increase in its concentration during a 90-min euglycemic-hyperinsulinemic clamp were all associated with significant increases in the sum of whole cell concentrations of citrate and/or malate. Similar correlations were observed in muscle of the hyperinsulinemic fa/fa rat, in denervated muscle, and in muscle of rats infused with insulin for 5 h. In muscle of 48-h-starved rats 3 and 24 h after refeeding, increases in malonyl-CoA were not accompanied by consistent increases in the concentrations of malate or citrate. However, they were associated with a decrease in the whole cell concentration of long-chain fatty acyl-CoA (LCFA-CoA), an allosteric inhibitor of ACC. The results suggest that increases in the concentration of malonyl-CoA, caused in rat muscle in vivo by sustained increases in plasma insulin and glucose or denervation, may be due to increases in the cytosolic concentration of citrate. In contrast, during refeeding after starvation, the increase in malonyl-CoA in muscle is probably due to another mechanism.

scholarly journals Concentration of Caveolin-3 at the Neuromuscular Junction in Young and Old Rat Skeletal Muscle Fibers

2003 ◽  
Vol 51 (9) ◽  
pp. 1113-1118 ◽  
Author(s):  
Bruce M. Carlson ◽  
Jean A. Carlson ◽  
Eduard I. Dedkov ◽  
Ian S. McLennan
Keyword(s):  
Skeletal Muscle ◽  
Neuromuscular Junction ◽  
Muscle Fibers ◽  
Normal Aging ◽  
Rat Skeletal Muscle ◽  
Phenotypic Characteristics ◽  
Adult Rat ◽  
Rat Muscle ◽  
Functional Implications ◽  
Old Rats

Caveolin-3, a muscle-specific member of the caveolin family, is strongly localized to the neuromuscular junction (NMJ) in adult rat muscle fibers, where it co-localizes with α-bungarotoxin staining. In 24-month-old rats, less distinct staining corresponds with the normal aging changes in the NMJ. After denervation, the pattern and intensity of staining begin to break up as early as 3 days, and by 10 days little staining remains. The functional implications of this concentration of caveolin-3 at the NMJ remain obscure, but it is possible that its absence could account for some of the phenotypic characteristics of individuals with caveolin-3 mutations.

scholarly journals Skeletal muscle mitochondrial β-oxidation. A study of the products of oxidation of [U-14C]hexadecanoate by h.p.l.c. using continuous on-line radiochemical detection

1988 ◽  
Vol 253 (2) ◽  
pp. 541-547 ◽  
Author(s):  
N J Watmough ◽  
A K Bhuiyan ◽  
K Bartlett ◽  
H S Sherratt ◽  
D M Turnbull
Keyword(s):  
Skeletal Muscle ◽  
Proteolytic Enzymes ◽  
Rat Skeletal Muscle ◽  
Beta Oxidation ◽  
Citrate Cycle ◽  
Mitochondrial Fractions ◽  
On Line ◽  
14Co2 Release

Well-coupled mitochondrial fractions were prepared from rat skeletal muscle without the use of proteolytic enzymes. The products of [U-14C]hexadecanoate oxidation by rat skeletal muscle mitochondrial fractions were analysed by h.p.l.c. with on-line radiochemical detection. In the presence of 1 mM-carnitine, 70% of the products is acetylcarnitine. In agreement with Veerkamp et al. [Veerkamp, van Moerkerk, Glatz, Zuurveld, Jacobs & Wagenmakers (1986) Biochem. Med. Metab. Biol. 35, 248-259] 14CO2 release is shown to be an unreliable estimate of flux through beta-oxidation in skeletal muscle mitochondrial fractions. The flux through beta-oxidation is recorded unambiguously polarographically in the presence of 1 mM-carnitine and the absence of citrate cycle intermediates.

Insulin does not hyperpolarize rat muscle by means of a ouabain-inhibitable process

1981 ◽  
Vol 241 (3) ◽  
pp. C145-C149 ◽  
Author(s):  
K. Zierler ◽  
E. Rogus
Keyword(s):  
Skeletal Muscle ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum Longus Muscle ◽  
Extensor Digitorum ◽  
Electrogenic Pump ◽  
Rat Skeletal Muscle ◽  
Rat Muscle ◽  
Longus Muscle ◽  
Stimulation Of

Experiments were designed to test the hypothesis that insulin-induced hyperpolarization of rat skeletal muscle is mediated by stimulation of a ouabain-inhibitable electrogenic pump. Parallel experiments were carried out on rat caudofemoralis with isoproterenol, known to hyperpolarize rat skeletal muscle by stimulation of such a pump. Ouabain (10(-5) M) completely inhibited isoproterenol-induced hyperpolarization within 15 min but had no effect on half-maximal insulin-induced hyperpolarization. Ouabain (10(-6) M) inhibited isoproterenol effect by 60% during a period of 5–15 min. Ouabain (10(-4) M) had no effect on insulin-induced hyperpolarization within 10 min but depolarized during the next 10 min. In a separate series of studies in rat extensor digitorum longus muscle, 10(-5) M ouabain increased intracellular Na+ within 14 min. It is concluded that in rat caudofemoralis muscle, insulin-induced hyperpolarization is not mediated by a ouabain-inhibitable electrogenic pump.

scholarly journals AMP deaminase histochemical activity and immunofluorescent isozyme localization in rat skeletal muscle.

1992 ◽  
Vol 40 (7) ◽  
pp. 931-946 ◽  
Author(s):  
J L Thompson ◽  
R L Sabina ◽  
N Ogasawara ◽  
D A Riley
Keyword(s):  
Skeletal Muscle ◽  
Vascular Tissue ◽  
Immunofluorescence Microscopy ◽  
Capillary Endothelium ◽  
Kinetic Properties ◽  
Amp Deaminase ◽  
Rat Skeletal Muscle ◽  
Connective Tissues ◽  
Functional Roles ◽  
Liver And Kidney

The cellular distribution of AMP deaminase (AMPda) isozymes was documented for rat soleus and plantaris muscles, utilizing immunofluorescence microscopy and immunoprecipitation methods. AMPda is a ubiquitous enzyme existing as three distinct isozymes, A, B and C, which were initially purified from skeletal muscle, liver (and kidney), and heart, respectively. AMPda-A is primarily concentrated subsarcolemmally and intermyofibrillarly within muscle cells, while isozymes B and C are concentrated within non-myofiber elements of muscle tissue. AMPda-B is principally associated with connective tissues surrounding neural elements and the muscle spindle capsule, and AMPda-C is predominantly associated with circulatory elements, such as arterial and venous walls, capillary endothelium, and red blood cells. These specific localizations, combined with documented differences in kinetic properties, suggest multiple functional roles for the AMPda isozymes or temporal segregation of similar AMPda functions. Linkage of the AMPda substrate with adenosine production pathways at the AMP level and the localization of isozyme-C in vascular tissue suggest a regulatory role in the microcirculation.

The effects of amino acids on glucose metabolism of isolated rat skeletal muscle are independent of insulin and the mTOR/S6K pathway

2009 ◽  
Vol 297 (3) ◽  
pp. E785-E792 ◽  
Author(s):  
Karin Stadlbauer ◽  
Barbara Brunmair ◽  
Zsuzsanna Szöcs ◽  
Michael Krebs ◽  
Anton Luger ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Glucose Metabolism ◽  
Glucose Oxidation ◽  
Cultured Cells ◽  
Glycogen Synthesis ◽  
Mammalian Target Of Rapamycin ◽  
Rat Skeletal Muscle ◽  
Rat Muscle ◽  
Isolated Rat

Two mechanisms have been proposed for the modulation of skeletal muscle glucose metabolism by amino acids. Whereas studies on humans and cultured cells suggested acute insulin desensitization via mammalian target of rapamycin (mTOR) and its downstream target p70 S6 kinase (S6K), investigations using native specimens of rat muscle hinted at impairment of glucose oxidation by competition for mitochondrial oxidation. To better understand these seemingly contradictory findings, we explored the effects of high concentrations of mixed amino acids on fuel metabolism and S6K activity in freshly isolated specimens of rat skeletal muscle. In this setting, increasing concentrations of amino acids dose-dependently reduced the insulin-stimulated rates of CO2 production from glucose and palmitate (decrease in glucose oxidation induced by addition of 5.5, 11, 22, and 44 mmol/l amino acids: −16 ± 3, −25 ± 7, −44 ± 4, −62 ± 4%; P < 0.02 each). This effect could not be attributed to insulin desensitization, because it was not accompanied by any reduction of insulin-stimulated glucose transport [+12 ± 16, +17 ± 22, +21 ± 33, +13 ± 12%; all nonsignificant (NS)] or glycogen synthesis (+1 ± 6, −5 ± 6, −9 ± 8, +6 ± 5%; all NS) and because it persisted without insulin stimulation. Abrogation of S6K activity by the mTOR blocker rapamycin failed to counteract amino acid-induced inhibition of glucose and palmitate oxidation, which therefore was obviously independent of mTOR/S6K signaling (decrease in glucose oxidation by addition of 44 mmol/l amino acids: without rapamycin, −60 ± 4%; with rapamycin, −50 ± 13%; NS). We conclude that amino acids can directly affect muscle glucose metabolism via two mechanisms, mTOR/S6K-mediated insulin desensitization and mitochondrial substrate competition, with the latter predominating in isolated rat muscle.

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