scholarly journals When phosphorylated at Thr148, the β2-subunit of AMP-activated kinase does not associate with glycogen in skeletal muscle

2016 ◽  
Vol 311 (1) ◽  
pp. C35-C42 ◽  
Author(s):  
Hongyang Xu ◽  
Noni T. Frankenberg ◽  
Graham D. Lamb ◽  
Paul R. Gooley ◽  
David I. Stapleton ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Carbohydrate Binding ◽  
Binding Function ◽  
Physiological Relevance ◽  
Amp Activated Protein Kinase ◽  
Fast Twitch ◽  
Stimulation Of

The 5′-AMP-activated protein kinase (AMPK), a heterotrimeric complex that functions as an intracellular fuel sensor that affects metabolism, is activated in skeletal muscle in response to exercise and utilization of stored energy. The diffusibility properties of α- and β-AMPK were examined in isolated skeletal muscle fiber segments dissected from rat fast-twitch extensor digitorum longus and oxidative soleus muscles from which the surface membranes were removed by mechanical dissection. After the muscle segments were washed for 1 and 10 min, ∼60% and 75%, respectively, of the total AMPK pools were found in the diffusible fraction. After in vitro stimulation of the muscle, which resulted in an ∼80% decline in maximal force, 20% of the diffusible pool became bound in the fiber. This bound pool was not associated with glycogen, as determined by addition of a wash step containing amylase. Stimulation of extensor digitorum longus muscles resulted in 28% glycogen utilization and a 40% increase in phosphorylation of the downstream AMPK target acetyl carboxylase-CoA. This, however, had no effect on the proportion of total β2-AMPK that was phosphorylated in whole muscle homogenates measured by immunoprecipitation. These findings suggest that, in rat skeletal muscle, β2-AMPK is not associated with glycogen and that activation of AMPK by muscle contraction does not dephosphorylate β2-AMPK. These findings question the physiological relevance of the carbohydrate-binding function of β2-AMPK in skeletal muscle.

Endothelial cell products alter mammalian skeletal muscle function in vitro

1995 ◽  
Vol 73 (6) ◽  
pp. 736-741 ◽  
Author(s):  
C. L. Murrant ◽  
J. K. Barclay
Keyword(s):  
Skeletal Muscle ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Mammalian Skeletal Muscle ◽  
Skeletal Muscle Function ◽  
Endothelin 1 ◽  
Control Value ◽  
Endothelin 3 ◽  
Fast Twitch

We tested the hypothesis that endothelin and nitric oxide (NO) alter the force developed by fast-twitch and slow-twitch mammalian skeletal muscle, using a mouse skeletal muscle preparation trimmed to approximately 50% of the original diameter to decrease diffusion distances. We suspended trimmed soleus (SOL) and extensor digitorum longus (EDL) muscles in Krebs–Henseleit buffer (27 °C; pH 7.4) gassed with 95% O2 – 5% CO2. Muscles were stimulated once every 90 s for 500 ms at 50 Hz for SOL and 100 Hz for EDL. The force developed by trimmed SOL was 223.8 ± 9.1 mN/mm2 and by EDL was 247.3 ± 9.4 mN/mm2. Endothelin 1 (ET-1) had no effect on EDL but significantly accelerated the rate of decrease of developed force of SOL at concentrations of 10−10 mol/L and higher within 10 contractions. When ET-1 was removed, force returned toward control value. Endothelin 3 (ET-3) had no effect on either muscle. S-Nitroso-N-acetylpenicillamine (SNAP), a source of NO, increased developed force over time in both muscles, with a threshold of 10−6 mol/L. The effect was evident within 5 contractions in both muscles. Force remained elevated above control values after the removal of SNAP. Thus ET-1 attenuated and NO amplified mammalian skeletal muscle function.Key words: soleus, extensor digitorum longus, tetanic contractions, endothelin 1, endothelin 3, S-nitroso-N-acetylpenicillamine.

Glycogenesis and glyconeogenesis in skeletal muscle: effects of pH and hormones

1990 ◽  
Vol 258 (4) ◽  
pp. E693-E700 ◽  
Author(s):  
A. Bonen ◽  
J. C. McDermott ◽  
M. H. Tan
Keyword(s):  
Skeletal Muscle ◽  
Soleus Muscle ◽  
Extensor Digitorum Longus ◽  
Muscle Fibers ◽  
Extensor Digitorum ◽  
Effects Of Ph ◽  
Slow Twitch ◽  
Highly Correlated ◽  
Fast Twitch

We examined the effects of selected hormones and pH on the rates of glyconeogenesis (L-[U-14C]-lactate----glycogen) and glycogenesis (D-[U-14C]glucose----glycogen) in mouse fast-twitch (FT) and slow-twitch muscles incubated in vitro (37 degrees C). Glyconeogenesis and glycogenesis increased linearly with increasing concentrations of lactate (5-20 mM) and glucose (2.5-10 mM), respectively, in both muscles. Glyconeogenesis was approximately three- to fourfold greater in the extensor digitorum longus (EDL) than in the soleus, whereas basal glycogenesis was twofold greater in the soleus muscle than in the EDL. Lactate accounted for up to 5% of the glycogen formed in the soleus and up to 32% in the EDL relative to the rates of glycogenesis (i.e., 5 mM glucose + 10 nM insulin) in each muscle. Corticosterone (10(-12)-10(-6) M) failed to alter glyconeogenesis, whereas this hormone reduced glycogenesis. Insulin (10 nM) markedly stimulated glycogenesis but failed to stimulate glyconeogenesis. The rates of both glycogenesis and glyconeogenesis were pH sensitive, with optimal rates at pH 6.5-7.0 in both muscles. Glyconeogenesis increased by 49% in the soleus and by 39% EDL at pH 6.5 compared with pH 7.4. Glycogenesis increased in the soleus (SOL) and EDL in the absence (SOL: +22%; EDL: +52%) and presence of insulin (SOL: +22%; EDL: +51%) at pH 6.5 when compared with pH 7.4. In additional experiments with the perfused rat hindquarter, rates of glyconeogenesis were shown to be highly correlated with proportion of FT muscle fibers in a muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Identification in skeletal muscle of a distinct extracellular pool of amino acids, and its role in protein synthesis

1971 ◽  
Vol 121 (5) ◽  
pp. 817-827 ◽  
Author(s):  
R. C. Hider ◽  
E. B. Fern ◽  
D. R. London
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Incubation Medium ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Longus Muscle ◽  
Kinetics Of

1. The kinetics of radioactive labelling of extra- and intra-cellular amino acid pools and protein of the extensor digitorum longus muscle were studied after incubations with radioactive amino acids in vitro. 2. The results indicated that an extracellular pool could be defined, the contents of which were different from those of the incubation medium. 3. It was concluded that amino acids from the extracellular pool, as defined in this study, were incorporated directly into protein.

Myosin light chain phosphorylation-dephosphorylation in mammalian skeletal muscle

1982 ◽  
Vol 242 (3) ◽  
pp. C234-C241 ◽  
Author(s):  
D. R. Manning ◽  
J. T. Stull
Keyword(s):  
Skeletal Muscle ◽  
Light Chain ◽  
Extensor Digitorum Longus ◽  
Myosin Light Chain ◽  
Extensor Digitorum Longus Muscle ◽  
Extensor Digitorum ◽  
Mammalian Skeletal Muscle ◽  
Phosphate Content ◽  
Longus Muscle ◽  
Fast Twitch

Phosphorylation of the myosin light chain 2 (LC2) subunit was examined in rat fast-twitch and slow-twitch skeletal muscles in response to repetitive stimulation at 23 and 35 degrees C and on incubation of fast-twitch skeletal muscle with isoproterenol. After a 1-s tetany at 35 degrees C, LC2 phosphate content in extensor digitorum longus muscle increased rapidly and transiently from 0.21 to 0.51 mol phosphate/mol LC2. This pattern of phosphorylation was similar to that observed at 23 degrees C. Increases in LC2 phosphate content were dependent on the frequency and duration of stimulation. In soleus muscle LC2 phosphate content was minimal following a 1-s tetany but increased markedly following more prolonged tetanies. On incubation of extensor digitorum longus muscle with isoproterenol (20 microM), LC2 phosphate content did not change, whereas phosphorylase a levels increased. A positive correlation existed between LC2 phosphate content and potentiation of peak twitch tension in both types of muscles, suggesting a physiological function for LC2 phosphorylation.

Effects of exercise and glycogen depletion on glyconeogenesis in muscle

1994 ◽  
Vol 76 (4) ◽  
pp. 1753-1758 ◽  
Author(s):  
A. Bonen ◽  
D. A. Homonko
Keyword(s):  
Skeletal Muscle ◽  
Muscle Glycogen ◽  
Extensor Digitorum Longus ◽  
Treadmill Exercise ◽  
Glycogen Depletion ◽  
Epinephrine Injection ◽  
Slow Twitch ◽  
Glycogen Repletion ◽  
Fast Twitch

In the present study, we investigated the hypotheses that 1) skeletal muscle glyconeogenesis will increase after exercise, 2) greater changes in glyconeogenesis will be observed after exercise in fast-twitch muscles than in slow-twitch muscles, and 3) glycogen repletion will reduce the rates of glyconeogenesis. Mouse soleus and extensor digitorum longus (EDL) glycogen depots were reduced to the same levels by treadmill exercise (60 min) or epinephrine injection (75 micrograms/100 g body wt ip). Untreated animals were used as controls. We were able to prevent glycogen repletion by incubating muscles in vitro with sorbitol (75 mM) and to increase glycogen concentrations in vitro by incubating muscles with glucose (75 mM). The experimental results showed that glyconeogenesis was increased by exercise (EDL, +51%; soleus, +82%) when glycogen levels were kept low. When glycogen depots were increased, the rate of glyconeogenesis was lowered in the exercised EDL (P < 0.05) but not in the soleus (P > 0.05). Reductions in muscle glycogen by epinephrine did not change the rate of glyconeogenesis in EDL, either when glycogen depots were kept low or were repleted (P > 0.05). In contrast, in the soleus, epinephrine-induced reductions in glycogen did stimulate glyconeogenesis (P < 0.05). Analyses in EDL showed that in nonexercised muscles glycogen concentrations were minimally effective in altering the rates of glyconeogenesis. A 30% decrement in glycogen increased glyconeogenesis by 5% in resting muscles, whereas the same decrement increased glyconeogenesis by 51% in exercised muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Regulation of total and myofibrillar protein breakdown in rat extensor digitorum longus and soleus muscle incubated flaccid or at resting length

1990 ◽  
Vol 267 (1) ◽  
pp. 37-44 ◽  
Author(s):  
P O Hasselgren ◽  
M Hall-Angerås ◽  
U Angerås ◽  
D Benson ◽  
J H James ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Total Protein ◽  
Extensor Digitorum Longus ◽  
Myofibrillar Protein ◽  
Extensor Digitorum ◽  
Protein Breakdown ◽  
Breakdown Rate ◽  
Net Production ◽  
Breakdown Rates

The present study characterized total and myofibrillar protein breakdown rates in a muscle preparation frequently used in vitro, i.e. incubated extensor digitorum longus (EDL) and soleus (SOL) muscles of young rats. Total and myofibrillar protein breakdown rates were assessed by determining net production by the incubated muscles of tyrosine and 3-methylhistidine (3-MH) respectively. Both amino acids were determined by h.p.l.c. Both total and myofibrillar protein breakdown rates were higher in SOL than in EDL muscles and were decreased by incubating the muscles maintained at resting length, rather than flaccid. After fasting for 72 h, total protein breakdown (i.e. tyrosine release) was increased by 73% and 138% in EDL muscles incubated flaccid and at resting length respectively. Net production of tyrosine by SOL muscle was not significantly altered by fasting. In contrast, myofibrillar protein degradation (i.e. 3-MH release) was markedly increased by fasting in both muscles. When tissue was incubated in the presence of 1 munit of insulin/ml, total protein breakdown rate was inhibited by 17-20%, and the response to the hormone was similar in muscles incubated flaccid or at resting length. In contrast, myofibrillar protein breakdown rate was not altered by insulin in any of the muscle preparations. The results support the concepts of individual regulation of myofibrillar and non-myofibrillar proteins and of different effects of various conditions on protein breakdown in different types of skeletal muscle. Thus determination of both tyrosine and 3-MH production in red and white muscle is important for a more complete understanding of protein regulation in skeletal muscle.

scholarly journals Role of Adenosine 5′-Monophosphate-Activated Protein Kinase in Interleukin-6 Release from Isolated Mouse Skeletal Muscle

Endocrinology ◽  
2009 ◽  
Vol 150 (2) ◽  
pp. 600-606 ◽  
Author(s):  
Stephan Glund ◽  
Jonas T. Treebak ◽  
Yun Chau Long ◽  
Romain Barres ◽  
Benoit Viollet ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Extensor Digitorum Longus ◽  
Protein Release ◽  
Extensor Digitorum ◽  
Whole Body ◽  
Wild Type ◽  
Amp Activated Protein Kinase ◽  
Respective Wild Type

IL-6 is released from skeletal muscle during exercise and has consequently been implicated to mediate beneficial effects on whole-body metabolism. Using 5-aminoimidazole-4-carboxamide-1-β-4-ribofuranoside (AICAR), a pharmacological activator of 5′-AMP-activated protein kinase (AMPK), we tested the hypothesis that AMPK modulates IL-6 release from isolated muscle. Skeletal muscle from AMPKα2 kinase-dead transgenic, AMPKα1 knockout (KO) and AMPKγ3 KO mice and respective wild-type littermates was incubated in vitro, in the absence or presence of 2 mmol/liter AICAR. Skeletal muscle from wild-type mice was also incubated with the AMPK activator A-769662. Incubation of mouse glycolytic extensor digitorum longus and oxidative soleus muscle for 2 h was associated with profound IL-6 mRNA production and protein release, which was suppressed by AICAR (P &lt; 0.001). Basal IL-6 release from soleus was increased between AMPKα2 kinase-dead and AMPKα1 KO and their respective wild-type littermates (P &lt; 0.05), suggesting AMPK participates in the regulation of IL-6 release from oxidative muscle. The effect of AICAR on muscle IL-6 release was similar between AMPKα2 KD, AMPKα1 KO, and AMPKγ3 KO mice and their respective wild-type littermates (P &lt; 0.001), indicating AICAR-mediated suppression of IL-6 mRNA expression and protein release is independent of AMPK function. However, IL-6 release from soleus, but not extensor digitorum longus, was reduced 45% by A-769662. Our results on basal and A-769662-mediated IL-6 release provide evidence for a role of AMPK in the regulation of IL-6 release from oxidative skeletal muscle. Furthermore, in addition to activating AMPK, AICAR suppresses IL-6 release by an unknown, AMPK-independent mechanism. Using transgenic and knockout mouse models to perturb AMP-activated protein kinase (AMPK) signaling, we provide evidence that AMPK-dependent pathways regulate IL-6 release from isolated oxidative skeletal muscle.

scholarly journals Exercise training reduces skeletal muscle membrane arachidonate in the obese (fa/fa) Zucker rat

1998 ◽  
Vol 85 (5) ◽  
pp. 1898-1902 ◽  
Author(s):  
Kerry J. Ayre ◽  
Stephen D. Phinney ◽  
Anna B. Tang ◽  
Judith S. Stern
Keyword(s):  
Skeletal Muscle ◽  
Insulin Sensitivity ◽  
Exercise Training ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Zucker Rats ◽  
Muscle Membrane ◽  
Positive Effects ◽  
Fast Twitch ◽  
White Gastrocnemius

Compared with the lean ( Fa/−) genotype, obese ( fa/fa) Zucker rats have a relative deficiency of muscle phospholipid arachidonate, and skeletal muscle arachidonate in humans is positively correlated with insulin sensitivity. To assess the hypothesis that the positive effects of exercise training on insulin sensitivity are mediated by increased muscle arachidonate, we randomized 20 lean and 20 obese weanling male Zucker rats to sedentary or treadmill exercise groups. After 9 wk, fasting serum, three skeletal muscles (white gastrocnemius, soleus, and extensor digitorum longus), and heart were obtained. Fasting insulin was halved by exercise training in the obese rat. In white gastrocnemius and extensor digitorum longus (fast-twitch muscles), but not in soleus (a slow-twitch muscle) or heart, phospholipid arachidonate was lower in obese than in lean rats ( P < 0.001). In all muscles, exercise in the obese rats reduced arachidonate ( P < 0.03, by ANOVA contrast). We conclude that improved insulin sensitivity with exercise in the obese genotype is not mediated by increased muscle arachidonate and that reduced muscle arachidonate in obese Zucker rats is unique to fast-twitch muscles.

Contractile properties of single-skinned skeletal muscle fibres of the extensor digitorum longus muscle of the Australian short-nosed echidna

2005 ◽  
Vol 53 (4) ◽  
pp. 237
Author(s):  
Anthony J. Bakker ◽  
Ann L. Parkinson ◽  
Stewart I. Head
Keyword(s):  
Skeletal Muscle ◽  
Extensor Digitorum Longus ◽  
Contractile Properties ◽  
Extensor Digitorum ◽  
Muscle Fibres ◽  
Force Response ◽  
Response Data ◽  
The Mean ◽  
Fast Twitch ◽  
Skeletal Muscle Fibres

Eutherian mammal fast-twitch muscle fibres share similar contractile activation properties, suggesting that these properties are highly conserved in mammals. To investigate this hypothesis, we examined the contractile properties of skeletal muscle from the order Monotremata, a mammalian order that separated from eutherians 150 million years ago. The Ca2+- and Sr2+-activation properties of single mechanically skinned skeletal muscle fibres from the extensor digitorum longus (EDL) muscle of the short-nosed echidna were determined. Sigmoidal curves fitted to force response data plotted as a function of pCa (–log[Ca2+]), had a mean slope of 4.32 ± 0.28 and a mean pCa50 and pCa10 value of 6.18 ± 0.01 and 6.41 ± 0.02 respectively (n = 20). The mean pSr50, pSr10 and slope values of curves fitted to the force-response data after activation with Sr2+ were 4.80 ± 0.03, 5.29 ± 0.07 and 2.75 ± 0.18 respectively (n = 20). The mean pCa50–pSr50 value for the echidna EDL fibres was 1.37 ± 0.04. In five of the echidna fibres, exposure to submaximal Ca2+ concentrations produced myofibrillar force oscillations (mean frequency, 0.13 ± 0.01 Hz), a phenomenon found only in eutherian slow and intermediate muscle fibres. These results show that echidna EDL fibres generally have similar contractile properties to eutherian fast-twitch skeletal muscle fibres, such as those found in the EDL of the rat.

scholarly journals Stimulation of both aerobic glycolysis and Na+-K+-ATPase activity in skeletal muscle by epinephrine or amylin

1999 ◽  
Vol 277 (1) ◽  
pp. E176-E186 ◽  
Author(s):  
J. Howard James ◽  
Kenneth R. Wagner ◽  
Jy-Kung King ◽  
Rebecca E. Leffler ◽  
Radha Krishna Upputuri ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Atpase Activity ◽  
Extensor Digitorum Longus ◽  
Aerobic Glycolysis ◽  
Lactate Production ◽  
Extensor Digitorum ◽  
Atp Production ◽  
High Concentrations ◽  
First Time ◽  
Stimulation Of

Epinephrine and amylin stimulate glycogenolysis, glycolysis, and Na+-K+-ATPase activity in skeletal muscle. However, it is not known whether these hormones stimulate glycolytic ATP production that is specifically coupled to ATP consumption by the Na+-K+pump. These studies correlated glycolysis with Na+-K+-ATPase activity in resting rat extensor digitorum longus and soleus muscles incubated at 30°C in well-oxygenated medium. Lactate production rose three- to fourfold, and the intracellular Na+-to-K+ratio (Na+/K+) fell with increasing concentrations of epinephrine or amylin. In muscles exposed to epinephrine at high concentrations (5 × 10−7 and 5 × 10−6 M), ouabain significantly inhibited glycolysis by ∼70% in either muscle and inhibited glycogenolysis by ∼40 and ∼75% in extensor digitorum longus and soleus, respectively. In the absence of ouabain, but not in its presence, statistically significant inverse correlations were observed between lactate production and intracellular Na+/K+for each hormone. Epinephrine had no significant effect on oxygen consumption or ATP content in either muscle. These results suggest for the first time that stimulation of glycolysis and glycogenolysis in resting skeletal muscle by epinephrine or amylin is closely linked to stimulation of active Na+-K+transport.

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