scholarly journals Effect of carbohydrate supplementation on postexercise GLUT-4 protein expression in skeletal muscle

1999 ◽  
Vol 87 (6) ◽  
pp. 2290-2295 ◽  
Author(s):  
Chia-Hua Kuo ◽  
Desmond G. Hunt ◽  
Zhenping Ding ◽  
John L. Ivy
Keyword(s):  
Skeletal Muscle ◽  
Protein Expression ◽  
Muscle Glycogen ◽  
Protein Concentration ◽  
Translational Efficiency ◽  
Carbohydrate Supplementation ◽  
Glut 4 ◽  
Red Muscle ◽  
Fast Twitch ◽  
Glucose Availability

The effect of carbohydrate supplementation on skeletal muscle glucose transporter GLUT-4 protein expression was studied in fast-twitch red and white gastrocnemius muscle of Sprague-Dawley rats before and after glycogen depletion by swimming. Exercise significantly reduced fast-twitch red muscle glycogen by 50%. During a 16-h exercise recovery period, muscle glycogen returned to control levels (25.0 ± 1.4 μmol/g) in exercise-fasted rats (24.2 ± 0.3 μmol/g). However, when carbohydrate supplementation was provided during and immediately postexercise by intubation, muscle glycogen increased 77% above control (44.4 ± 2.1 μmol/g). Exercise-fasting resulted in an 80% increase in fast-twitch red muscle GLUT-4 mRNA but only a 43% increase in GLUT-4 protein concentration. Conversely, exercise plus carbohydrate supplementation elevated fast-twitch red muscle GLUT-4 protein concentration by 88% above control, whereas GLUT-4 mRNA was increased by only 40%. Neither a 16-h fast nor carbohydrate supplementation had an effect on fast-twitch red muscle GLUT-4 protein concentration or on GLUT-4 mRNA in sedentary rats, although carbohydrate supplementation increased muscle glycogen concentration by 40% (35.0 ± 0.9 μmol/g). GLUT-4 protein in fast-twitch white muscle followed a pattern similar to fast-twitch red muscle. These results indicate that carbohydrate supplementation, provided with exercise, will enhance GLUT-4 protein expression by increasing translational efficiency. Conversely, postexercise fasting appears to upregulate GLUT-4 mRNA, possibly to amplify GLUT-4 protein expression on an increase in glucose availability. These regulatory mechanisms may help control muscle glucose uptake in accordance with glucose availability and protect against postexercise hypoglycemia.

scholarly journals Role of insulin on exercise-induced GLUT-4 protein expression and glycogen supercompensation in rat skeletal muscle

2004 ◽  
Vol 96 (2) ◽  
pp. 621-627 ◽  
Author(s):  
Chia-Hua Kuo ◽  
Hyonson Hwang ◽  
Man-Cheong Lee ◽  
Arthur L. Castle ◽  
John L. Ivy
Keyword(s):  
Skeletal Muscle ◽  
Protein Expression ◽  
Muscle Glycogen ◽  
White Muscle ◽  
Insulin Response ◽  
Exercise Session ◽  
Carbohydrate Supplementation ◽  
Glut 4 ◽  
Red Muscle

The purpose of this study was to investigate the role of insulin on skeletal muscle GLUT-4 protein expression and glycogen storage after postexercise carbohydrate supplementation. Male Sprague-Dawley rats were randomly assigned to one of six treatment groups: sedentary control (Con), Con with streptozocin (Stz/C), immediately postexercise (Ex0), Ex0 with Stz (Stz/Ex0), 5-h postexercise (Ex5), and Ex5 with Stz (Stz/Ex5). Rats were exercised by swimming (2 bouts of 3 h) and carbohydrate supplemented immediately after each exercise session by glucose intubation (1 ml of a 50% wt/vol). Stz was administered 72-h before exercise, which resulted in hyperglycemia and elimination of the insulin response to the carbohydrate supplement. GLUT-4 protein of Ex0 rats was 30% above Con in fast-twitch (FT) red and 21% above Con in FT white muscle. In Ex5, GLUT-4 protein was 52% above Con in FT red and 47% above Con in FT white muscle. Muscle glycogen in FT red and white muscle was also increased above Con in Ex5 rats. Neither GLUT-4 protein nor muscle glycogen was increased above Con in Stz/Ex0 or Stz/Ex5 rats. GLUT-4 mRNA in FT red muscle of Ex0 rats was 61% above Con but only 33% above Con in Ex5 rats. GLUT-4 mRNA in FT red muscle of Stz/C and Stz/Ex0 rats was similar but significantly elevated in Ex5/Stz rats. These results suggest that insulin is essential for the increase in GLUT-4 protein expression following postexercise carbohydrate supplementation.

scholarly journals IMPLICATIONS OF HYPERGLYCEMIA FOR POST-EXERCISE RESYNTHESIS OF GLYCOGEN IN TROUT SKELETAL MUSCLE

1994 ◽  
Vol 189 (1) ◽  
pp. 69-84 ◽  
Author(s):  
T West ◽  
P Schulte ◽  
P Hochachka
Keyword(s):  
Skeletal Muscle ◽  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Glucose Concentration ◽  
Plasma Glucose Level ◽  
White Muscle ◽  
Glucose Utilization ◽  
Glucose Turnover ◽  
Red Muscle ◽  
Glucose Availability

Rates of whole-body glucose turnover and muscle-specific glucose utilization were determined in rainbow trout (Oncorhynchus mykiss) at rest and at intervals during recovery from burst swimming. Plasma glucose level was high in the experimental animals (range 6­38 mmol l-1), but hyperglycemia was not related specifically to exercise. Estimated glucose turnover, 19.3±2.6 (rest) and 15.8±3.9 µmol min-1 kg-1 (recovery), was also highly variable, but was linearly associated with plasma glucose concentration (turnover=0.97[glucose]+0.57, r=0.93) in both resting and recovering fish. While utilization of glucose in the whole animal was clearly responsive to plasma glucose availability, estimated total skeletal muscle disposal of glucose accounted for less than 15 % of glucose turnover, indicating that glucose was utilized largely by tissues other than locomotory muscle. Rates of glucose utilization in white muscle (range 0.5­4 nmol min-1 g-1) provide direct evidence that glucose, regardless of plasma concentration, accounted for less than 10 % of glycogen repletion during exercise recovery. In red muscle, glucose uptake was influenced by plasma glucose level below 10­12 mmol l-1 (utilization range 1­15 nmol min-1 g-1), but was independent of glucose concentration above about 12 mmol l-1 (utilization plateaued at 15­20 nmol min-1 g-1). Trout red muscle is similar to mammalian white muscle in the sense that glucose is estimated to account incompletely for glycogen restoration (25­60 %), suggesting dependence on both glycogenesis and glyconeogenesis during recovery. It is concluded that hyperglycemia may be important to the pattern of substrate incorporation into red muscle glycogen and to the rate of repletion observed, but glucose availability has, as predicted from earlier indirect studies, little relevance to white muscle glycogen restoration. The regulatory mechanisms that govern apparently very high glucose turnover rates during extreme hyperglycemia, concomitant with low disposal rates in skeletal muscle, require further investigation.

Effect of endurance training on glucose transport capacity and glucose transporter expression in rat skeletal muscle

1990 ◽  
Vol 259 (6) ◽  
pp. E778-E786 ◽  
Author(s):  
T. Ploug ◽  
B. M. Stallknecht ◽  
O. Pedersen ◽  
B. B. Kahn ◽  
T. Ohkuwa ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Glucose Transport ◽  
Glucose Transporter ◽  
Training Session ◽  
Residual Effect ◽  
Exercise Session ◽  
Transport Capacity ◽  
Glut 1 ◽  
Glut 4 ◽  
Fast Twitch

The effect of 10 wk endurance swim training on 3-O-methylglucose (3-MG) uptake (at 40 mM 3-MG) in skeletal muscle was studied in the perfused rat hindquarter. Training resulted in an increase of approximately 33% for maximum insulin-stimulated 3-MG transport in fast-twitch red fibers and an increase of approximately 33% for contraction-stimulated transport in slow-twitch red fibers compared with nonexercised sedentary muscle. A fully additive effect of insulin and contractions was observed both in trained and untrained muscle. Compared with transport in control rats subjected to an almost exhaustive single exercise session the day before experiment both maximum insulin- and contraction-stimulated transport rates were increased in all muscle types in trained rats. Accordingly, the increased glucose transport capacity in trained muscle was not due to a residual effect of the last training session. Half-times for reversal of contraction-induced glucose transport were similar in trained and untrained muscles. The concentrations of mRNA for GLUT-1 (the erythrocyte-brain-Hep G2 glucose transporter) and GLUT-4 (the adipocyte-muscle glucose transporter) were increased approximately twofold by training in fast-twitch red muscle fibers. In parallel to this, Western blot demonstrated a approximately 47% increase in GLUT-1 protein and a approximately 31% increase in GLUT-4 protein. This indicates that the increases in maximum velocity for 3-MG transport in trained muscle is due to an increased number of glucose transporters.

scholarly journals Fibre-type specific modification of the activity and regulation of skeletal muscle pyruvate dehydrogenase kinase (PDK) by prolonged starvation and refeeding is associated with targeted regulation of PDK isoenzyme 4 expression

2000 ◽  
Vol 346 (3) ◽  
pp. 651-657 ◽  
Author(s):  
Mary C. SUGDEN ◽  
Alexandra KRAUS ◽  
Robert A. HARRIS ◽  
Mark J. HOLNESS
Keyword(s):  
Skeletal Muscle ◽  
Protein Expression ◽  
Pyruvate Dehydrogenase ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Pyruvate Dehydrogenase Kinase ◽  
Acid Cycle ◽  
Slow Twitch ◽  
Fast Twitch ◽  
Anterior Tibialis

Using immunoblot analysis with antibodies raised against recombinant pyruvate dehydrogenase kinase (PDK) isoenzymes PDK2 and PDK4, we demonstrate selective changes in PDK isoenzyme expression in slow-twitch versus fast-twitch skeletal muscle types in response to prolonged (48 h) starvation and refeeding after starvation. Starvation increased PDK activity in both slow-twitch (soleus) and fast-twitch (anterior tibialis) skeletal muscle and was associated with loss of sensitivity of PDK to inhibition by pyruvate, with a greater effect in anterior tibialis. Starvation significantly increased PDK4 protein expression in both soleus and anterior tibialis, with a greater response in anterior tibialis. Starvation did not effect PDK2 protein expression in soleus, but modestly increased PDK2 expression in anterior tibialis. Refeeding for 4 h partially reversed the effect of 48-h starvation on PDK activity and PDK4 expression in both soleus and anterior tibialis, but the response was more marked in soleus than in anterior tibialis. Pyruvate sensitivity of PDK activity was also partially restored by refeeding, again with the greater response in soleus. It is concluded that targeted regulation of PDK4 isoenzyme expression in skeletal muscle in response to starvation and refeeding underlies the modulation of the regulatory characteristics of PDK in vivo. We propose that switching from a pyruvate-sensitive to a pyruvate-insensitive PDK isoenzyme in starvation (a) maintains a sufficiently high pyruvate concentration to ensure that the glucose → alanine → glucose cycle is not impaired, and (b) may ‘spare’ pyruvate for anaplerotic entry into the tricarboxylic acid cycle to support the entry of acetyl-CoA derived from fatty acid (FA) oxidation into the tricarboxylic acid cycle. We further speculate that FA oxidation by skeletal muscle is both forced and facilitated by upregulation of PDK4, which is perceived as an essential component of the operation of the glucose-FA cycle in starvation.

EFFECTS OF FEEDING AND FOOD DEPRIVATION ON OXYGEN CONSUMPTION, MUSCLE PROTEIN CONCENTRATION AND ACTIVITIES OF ENERGY METABOLISM ENZYMES IN MUSCLE AND BRAIN OF SHALLOW-LIVING (SCORPAENA GUTTATA) AND DEEP-LIVING (SEBASTOLOBUS ALASCANUS) SCORPAENID FISHES

1993 ◽  
Vol 181 (1) ◽  
pp. 213-232 ◽  
Author(s):  
T. H. Yang ◽  
G. N. Somero
Keyword(s):  
Skeletal Muscle ◽  
Metabolic Rate ◽  
Food Deprivation ◽  
Enzyme Activities ◽  
Protein Concentration ◽  
White Muscle ◽  
Muscle Protein ◽  
Metabolism Enzymes ◽  
Red Muscle ◽  
Ad Libitum

The effects of feeding and fasting were examined on the deep-living short-spine thornyhead (Sebastolobus alascanus) and the confamilial shallow-living spotted scorpionfish (Scorpaena guttata) to determine whether the low metabolic rate of the deeper-living species was in part a consequence of food deprivation in its habitat. Laboratory acclimation for periods of 90–115 days under either ad libitum feeding or complete fasting did not lead to similar rates of respiration in individuals of the two species held under identical conditions. Respiration of fish fed ad libitum was 52 % (S. guttata) or 68 % (S. alascanus) higher than for fasted fish of the same species. Furthermore, the metabolic rates of freshly collected specimens of S. alascanus resembled those of laboratory-fasted fish. In white skeletal muscle, both total protein concentration and the activities of four enzymes of ATP metabolism, lactate dehydrogenase (LDH) and pyruvate kinase (PK) of glycolysis, malate dehydrogenase (MDH) and citrate synthase (CS, a citric acid cycle indicator), were lower in S. alascanus than in S. guttata. Within a species, protein concentration and activities of the four enzymes in white muscle, but not in brain, were higher in fed than in starved fish, although these differences were greater in S. alascanus than in S. guttata. During fasting, LDH and PK activity in white muscle of S. alascanus decreased much more than MDH and CS activity; decreases in enzyme activities in red muscle were smaller than those in white muscle. Activities of enzymes in white skeletal muscle of field-collected S. alascanus generally resembled those of the fasted specimens. In contrast, red muscle of field- collected S. alascanus, compared with that of either fed or starved laboratory-held specimens, had a highly glycolytic poise (high LDH and PK activities relative to MDH and CS activities), which may suggest that muscle enzyme activities in the field-collected fish reflect adaptation to the low oxygen level in its adult habitat, the oxygen minimum layer. The strong correlations found between tissue biochemical properties and respiration rate allow us to develop a predictive index for metabolic rate from simple biochemical analyses, e.g. white muscle protein content or CS activity. We conclude that the low metabolic rate of S. alascanus is due to at least four depth-related factors: reduced abundance of food, low temperature, low ambient oxygen concentration and darkness, which may select for reduced locomotory activity.

Abstract 20140: Minibrain Relate Kinase / Dyrk1B Links Skeletal Muscle Glycolytic Metabolism with Insulin Resistance and Causes Metabolic Syndrome

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Mohsen Fathzadeh ◽  
Ali Reza Keramati ◽  
Gwang Go ◽  
Rajvir Singh ◽  
Kazem Sarajzadeh ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Skeletal Muscle ◽  
Metabolic Syndrome ◽  
Protein Expression ◽  
Ppar Gamma ◽  
Glycolytic Metabolism ◽  
Expression Levels ◽  
Fiber Composition ◽  
Mutation Carriers ◽  
Fast Twitch

We have identified a novel nonconservative mutation in Minibrain related serine/threonine kinase (Mirk/ Dyrk1B) in outlier kindreds with metabolic syndrome. The mutation substitutes cysteine for arginine (R102C) and segregates with most traits of metabolic syndrome, including central obesity, diabetes and hypertension. Oral glucose tolerance test (OGTT) in young nondiabetic mutation carriers revealed insulin resistance compared to noncarrier family members. Since skeletal muscle (SM) is the largest organ for glucose uptake and metabolism, we obtained Vastus Lateralis biopsies of mutation carriers and their unaffected relatives and examined them for gene/protein expression by deep RNA sequencing (RNA-Seq) and Western blot analysis and for fiber composition by immunostaining. The fiber composition data demonstrated fewer slow-twitch fibers (35% vs. 75%) and more fast -twitch fibers (65% vs. 25%) in SM of mutation carriers vs. controls. Interestingly, there were increased protein expression levels of fast-twitch fiber type proteins (MYH11, MYLPF), pyruvate dehydrogenase kinase, pyruvate kinase, and neuronal nitric oxide synthase in SM of mutation carriers vs. noncarriers. Consistent with these findings, the protein expression levels of the master regulator of cellular energy metabolism mitochondrial biogenesis, PPAR-gamma coactivator (PGC-1a), were reduced and the nuclear expression levels of FOXO1 and NFAT were increased. Similar findings were observed when wildtype and mutant (R102C) Dyrk1B were overexpressed in C2C12 cells. The overexpression of the kinase deficient Dyrk1B (Y271/273F) similarly resulted in reduced expression of PGC-1a and increased expression of nuclear FOXO1, suggesting kinase independent effects. Taken together, these findings suggest that enhanced kinase-independent activities of Dyrk1B, either through increased expression or by its gain of function mutation R102C induce insulin resistance by promoting glycolytic metabolism and reducing oxidative phosphorylation. In conclusion, Dyrk1B is a potential target for development of novel drugs that aim to enhance skeletal muscle insulin sensitivity.

Shift from slow- to fast-twitch muscle fibres in skeletal muscle of newborn heterozygous and homozygous myostatin-knockout piglets

2019 ◽  
Vol 31 (10) ◽  
pp. 1628 ◽  
Author(s):  
Mei-Fu Xuan ◽  
Zhao-Bo Luo ◽  
Jun-Xia Wang ◽  
Qing Guo ◽  
Sheng-Zhong Han ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Expression ◽  
Muscle Development ◽  
Transforming Growth Factor ◽  
Myogenic Differentiation ◽  
Muscle Fibres ◽  
Skeletal Muscle Development ◽  
Cross Sectional ◽  
Gene And Protein Expression ◽  
Fast Twitch

Myostatin (MSTN) is a member of the transforming growth factor-β superfamily that negatively regulates skeletal muscle development. A lack of MSTN induces muscle hypertrophy and increases formation of fast-twitch (Type II) muscle fibres. This study investigated muscle development in newborn heterozygous (MSTN+/−) and homozygous (MSTN−/−) MSTN-knockout piglets. Detailed morphological and gene and protein expression analyses were performed of the biceps femoris, semitendinosus and diaphragm of MSTN+/−, MSTN−/− and wild-type (WT) piglets. Haematoxylin–eosin staining revealed that the cross-sectional area of muscle fibres was significantly larger in MSTN-knockout than WT piglets. ATPase staining demonstrated that the percentage of Type IIb and IIa muscle fibres was significantly higher in MSTN−/− and MSTN+/− piglets respectively than in WT piglets. Western blotting showed that protein expression of myosin heavy chain-I was reduced in muscles of MSTN-knockout piglets. Quantitative reverse transcription–polymerase chain reaction revealed that, compared with WT piglets, myogenic differentiation factor (MyoD) mRNA expression in muscles was 1.3- to 2-fold higher in MSTN+/− piglets and 1.8- to 3.5-fold higher MSTN−/− piglets (P<0.05 and P<0.01 respectively). However, expression of myocyte enhancer factor 2C (MEF2C) mRNA in muscles was significantly lower in MSTN+/− than WT piglets (P<0.05). MSTN plays an important role in skeletal muscle development and regulates muscle fibre type by modulating the gene expression of MyoD and MEF2C in newborn piglets.

scholarly journals The effects of muscle contraction and insulin on glucose-transporter translocation in rat skeletal muscle

1994 ◽  
Vol 297 (3) ◽  
pp. 539-545 ◽  
Author(s):  
J T Brozinick ◽  
G J Etgen ◽  
B B Yaspelkis ◽  
J L Ivy
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membrane ◽  
Muscle Contraction ◽  
Glucose Uptake ◽  
Protein Concentration ◽  
Glucose Transporter ◽  
Cytochalasin B ◽  
Protein Distribution ◽  
Sprague Dawley ◽  
Glut 4

The effect of electrically induced muscle contraction, insulin (10 m-units/ml) and electrically-induced muscle contraction in the presence of insulin on insulin-regulatable glucose-transporter (GLUT-4) protein distribution was studied in female Sprague-Dawley rats during hindlimb perfusion. Plasma-membrane cytochalasin B binding increased approximately 2-fold, whereas GLUT-4 protein concentration increased approximately 1.5-fold above control with contractions, insulin, or insulin + contraction. Microsomal-membrane cytochalasin B binding and GLUT-4 protein concentration decreased by approx. 30% with insulin or insulin + contraction, but did not significantly decrease with contraction alone. The rate of muscle glucose uptake was assessed by determining the rate of 2-deoxy[3H]glucose accumulation in the soleus, plantaris, and red and white portions of the gastrocnemius. Both contraction and insulin increased glucose uptake significantly and to the same degree in the muscles examined. Insulin + contraction increased glucose uptake above that of insulin or contraction alone, but this effect was only statistically significant in the soleus, plantaris and white gastrocnemius. The combined effects of insulin + contraction of glucose uptake were not fully additive in any of the muscles investigated. These results suggest that (1) insulin and muscle contraction are mobilizing two separate pools of GLUT-4 protein, and (2) the increase in skeletal-muscle glucose uptake due to insulin + contraction is not due to an increase in plasma-membrane GLUT-4 protein concentration above that observed for insulin or contraction alone.

Changes in insulin-stimulated glucose transport and GLUT-4 protein in rat skeletal muscle after training

1997 ◽  
Vol 83 (6) ◽  
pp. 2043-2047 ◽  
Author(s):  
Kentaro Kawanaka ◽  
Izumi Tabata ◽  
Shigeru Katsuta ◽  
Mitsuru Higuchi
Keyword(s):  
Skeletal Muscle ◽  
Protein Content ◽  
Glucose Transport ◽  
Protein Concentration ◽  
Control Level ◽  
Training Effect ◽  
Swimming Training ◽  
Rat Skeletal Muscle ◽  
Glut 4 ◽  
Insulin Responsiveness

Kawanaka, Kentaro, Izumi Tabata, Shigeru Katsuta, and Mitsuru Higuchi. Changes in insulin-stimulated glucose transport and GLUT-4 protein in rat skeletal muscle after training. J. Appl. Physiol. 83(6): 2043–2047, 1997.—After running training, which increased GLUT-4 protein content in rat skeletal muscle by <40% compared with control rats, the training effect on insulin-stimulated maximal glucose transport (insulin responsiveness) in skeletal muscle was short lived (24 h). A recent study reported that GLUT-4 protein content in rat epitrochlearis muscle increased dramatically (∼2-fold) after swimming training (J.-M. Ren, C. F. Semenkovich, E. A. Gulve, J. Gao, and J. O. Holloszy. J. Biol. Chem. 269, 14396–14401, 1994). Because GLUT-4 protein content is known to be closely related to skeletal muscle insulin responsiveness, we thought it possible that the training effect on insulin responsiveness may remain for >24 h after swimming training if GLUT-4 protein content decreases gradually from the relatively high level and still remains higher than control level for >24 h after swimming training. Therefore, we examined this possibility. Male Sprague-Dawley rats swam 2 h a day for 5 days with a weight equal to 2% of body mass. Approximately 18, 42, and 90 h after cessation of training, GLUT-4 protein concentration and 2-[1,2-3H]deoxy-d-glucose transport in the presence of a maximally stimulating concentration of insulin (2 mU/ml) were examined by using incubated epitrochlearis muscle preparation. Swimming training increased GLUT-4 protein concentration and insulin responsiveness by 87 and 85%, respectively, relative to age-matched controls when examined 18 h after training. Forty-two hours after training, GLUT-4 protein concentration and insulin responsiveness were still higher by 52 and 51%, respectively, in muscle from trained rats compared with control. GLUT-4 protein concentration and insulin responsiveness in trained muscle returned to sedentary control level within 90 h after training. We conclude that 1) the change in insulin responsiveness during detraining is directly related to muscle GLUT-4 protein content, and 2) consequently, the greater the increase in GLUT-4 protein content that is induced by training, the longer an effect on insulin responsiveness persists after the training.

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)

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