Effects of adrenaline on whole-body glucose metabolism and insulin-mediated regulation of glycogen synthase and PKB phosphorylation in human skeletal muscle

Glucagon-like peptide-1 (GLP-1) has been shown to have insulin-like effects upon the metabolism of glucose in rat liver, muscle and fat, and on that of lipids in rat and human adipocytes. These actions seem to be exerted through specific receptors which, unlike that of the pancreas, are not - at least in liver and muscle - cAMP-associated. Here we have investigated the effect, its characteristics, and possible second messengers of GLP-1 on the glucose metabolism of human skeletal muscle, in tissue strips and primary cultured myocytes. In muscle strips, GLP-1, like insulin, stimulated glycogen synthesis, glycogen synthase a activity, and glucose oxidation and utilization, and inhibited glycogen phosphorylase a activity, all of this at physiological concentrations of the peptide. In cultured myotubes, GLP-1 exerted, from 10(-13) mol/l, a dose-related increase of the D-[U-(14)C]glucose incorporation into glycogen, with the same potency as insulin, together with an activation of glycogen synthase a; the effect of 10(-11) mol/l GLP-1 on both parameters was additive to that induced by the equimolar amount of insulin. Synthase a was still activated in cells after 2 days of exposure to GLP-1, as compared with myotubes maintained in the absence of peptide. In human muscle cells, exendin-4 and its truncated form 9-39 amide (Ex-9) are both agonists of the GLP-1 effect on glycogen synthesis and synthase a activity; but while neither GLP-1 nor exendin-4 affected the cellular cAMP content after 5-min incubation in the absence of 3-isobutyl-1-methylxantine (IBMX), an increase was detected with Ex-9. GLP-1, exendin-4, Ex-9 and insulin all induced the prompt hydrolysis of glycosylphosphatidylinositols (GPIs). This work shows a potent stimulatory effect of GLP-1 on the glucose metabolism of human skeletal muscle, and supports the long-term therapeutic value of the peptide. Further evidence for a GLP-1 receptor in this tissue, different from that of the pancreas, is also illustrated, suggesting a role for an inositolphosphoglycan (IPG) as at least one of the possible second messengers of the GLP-1 action in human muscle.

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Fasting inhibits insulin-mediated glycolysis and anaplerosis in human skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1991.261.5.e598 ◽

1991 ◽

Vol 261 (5) ◽

pp. E598-E605 ◽

Cited By ~ 3

Author(s):

C. E. Castillo ◽

A. Katz ◽

M. K. Spencer ◽

Z. Yan ◽

B. L. Nyomba

Keyword(s):

Skeletal Muscle ◽

Human Skeletal Muscle ◽

Glycogen Synthase ◽

Fat Free Mass ◽

Whole Body ◽

Glucose Disposal ◽

Glycolytic Flux ◽

Quadriceps Femoris Muscle ◽

Before And After ◽

Femoris Muscle

uglycemic (approximately 5.5 mM) hyperinsulinemic (60 mU.m-2.min-1) clamps were performed for 2 h after a 10-h fast and after a prolonged (72-h) fast. Biopsies were obtained from the quadriceps femoris muscle before and after each clamp. The rate of whole body glucose disposal was approximately 50% lower during the clamp after the 72-h fast (P less than or equal to 0.001). The increase in carbohydrate (CHO) oxidation (which is proportional to glycolysis) during the clamp after the 10-h fast (to 13.8 +/- 1.5 mumol.kg fat free mass-1.min-1) was completely abolished during the clamp after the 72-h fast (1.7 +/- 0.6; P less than or equal to 0.001). During the clamp after the 10-h fast, postphosphofructokinase (PFK) intermediates and malate in muscle increased, whereas glutamate decreased (P less than or equal to 0.05-0.001 vs. basal) and citrate did not change. During the clamp after the 72-h fast, there were no significant changes in post-PFK intermediates or glutamate (P greater than 0.05 vs. basal), but there was a decrease in citrate (P less than or equal to 0.01 vs. basal). Euglycemic hyperinsulinemia increased glycogen synthase fractional activity in muscle under both conditions but to a greater extent after the 72-h fast (P less than or equal to 0.01). It is concluded that insulin (after 10-h fast) increases glycolytic flux and the content of malate in muscle, which is probably due to increased anaplerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

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Glucosamine Regulation of Glucose Metabolism in Cultured Human Skeletal Muscle Cells: Divergent Effects on Glucose Transport/Phosphorylation and Glycogen Synthase in Non-Diabetic and Type 2 Diabetic Subjects1

Endocrinology ◽

10.1210/endo.140.9.6974 ◽

1999 ◽

Vol 140 (9) ◽

pp. 3971-3980 ◽

Cited By ~ 26

Author(s):

Theodore P. Ciaraldi ◽

Leslie Carter ◽

Svetlana Nikoulina ◽

Sunder Mudaliar ◽

Donald A. McClain ◽

...

Keyword(s):

Skeletal Muscle ◽

Glucose Metabolism ◽

Glucose Transport ◽

Human Skeletal Muscle ◽

Glycogen Synthase ◽

Muscle Cells ◽

Skeletal Muscle Cells ◽

Insulin Responsiveness ◽

Type 2 Diabetic

Abstract Chronic exposure (48 h) to glucosamine resulted in a dose-dependent reduction of basal and insulin-stimulated glucose uptake activities in human skeletal muscle cell cultures from nondiabetic and type 2 diabetic subjects. Insulin responsiveness of uptake was also reduced. There was no change in total membrane expression of either GLUT1, GLUT3, or GLUT4 proteins. While glucosamine treatment had no significant effects on hexokinase activity measured in cell extracts, glucose phosphorylation in intact cells was impaired after treatment. Under conditions where glucose transport and phosphorylation were down regulated, the fractional velocity (FV) of glycogen synthase was increased by glucosamine treatment. Neither the total activity nor protein expression of glycogen synthase were influenced by glucosamine treatment. The stimulation of glycogen synthase by glucosamine was not due totally to soluble mediators. Reflective of the effects on transport/phosphorylation, total glycogen content and net glycogen synthesis were reduced after glucosamine treatment. These effects were similar in nondiabetic and type 2 cells. In summary: 1) Chronic treatment with glucosamine reduces glucose transport/phosphorylation and storage into glycogen in skeletal muscle cells in culture and impairs insulin responsiveness as well. 2) Down-regulation of glucose transport/phosphorylation occurs at a posttranslational level of GLUTs. 3) Glycogen synthase activity increases with glucosamine treatment. 4) Nondiabetic and type 2 muscle cells display equal sensitivity and responsiveness to glucosamine. Increased exposure of skeletal muscle to glucosamine, a substrate/precursor of the hexosamine pathway, alters intracellular glucose metabolism at multiple sites and can contribute to insulin resistance in this tissue.

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Inhibition of Glycogen Synthase Kinase 3 Improves Insulin Action and Glucose Metabolism in Human Skeletal Muscle

Diabetes ◽

10.2337/diabetes.51.7.2190 ◽

2002 ◽

Vol 51 (7) ◽

pp. 2190-2198 ◽

Cited By ~ 127

Author(s):

S. E. Nikoulina ◽

T. P. Ciaraldi ◽

S. Mudaliar ◽

L. Carter ◽

K. Johnson ◽

...

Keyword(s):

Skeletal Muscle ◽

Glucose Metabolism ◽

Insulin Action ◽

Human Skeletal Muscle ◽

Glycogen Synthase ◽

Glycogen Synthase Kinase ◽

Glycogen Synthase Kinase 3

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Unlike insulin, amino acids stimulate p70S6Kbut not GSK-3 or glycogen synthase in human skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00146.2003 ◽

2004 ◽

Vol 286 (4) ◽

pp. E523-E528 ◽

Cited By ~ 27

Author(s):

Zhenqi Liu ◽

Yangsong Wu ◽

Edward W. Nicklas ◽

Linda A. Jahn ◽

Wendie J. Price ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Amino Acid ◽

Human Skeletal Muscle ◽

Glycogen Synthase ◽

Glycogen Synthesis ◽

Whole Body ◽

Glucose Disposal ◽

Vastus Lateralis Muscle ◽

Euglycemic Hyperinsulinemic Clamp

Insulin stimulates muscle glucose disposal via both glycolysis and glycogen synthesis. Insulin activates glycogen synthase (GS) in skeletal muscle by phosphorylating PKB (or Akt), which in turn phosphorylates and inactivates glycogen synthase kinase 3 (GSK-3), with subsequent activation of GS. A rapamycin-sensitive pathway, most likely acting via ribosomal 70-kDa protein S6 kinase (p70S6K), has also been implicated in the regulation of GSK-3 and GS by insulin. Amino acids potently stimulate p70S6K, and recent studies on cultured muscle cells suggest that amino acids also inactivate GSK-3 and/or activate GS via activating p70S6K. To assess the physiological relevance of these findings to normal human physiology, we compared the effects of amino acids and insulin on whole body glucose disposal, p70S6K, and GSK-3 phosphorylation, and on the activity of GS in vivo in skeletal muscle of 24 healthy human volunteers. After an overnight fast, subjects received intravenously either a mixed amino acid solution (1.26 μmol·kg-1·min-1× 6 h, n = 9), a physiological dose of insulin (1 mU·kg-1·min-1euglycemic hyperinsulinemic clamp × 2 h, n = 6), or a pharmacological dose of insulin (20 mU·kg-1·min-1euglycemic hyperinsulinemic clamp × 2 h, n = 9). Whole body glucose disposal rates were assessed by calculating the steady-state glucose infusion rates, and vastus lateralis muscle was biopsied before and at the end of the infusion. Both amino acid infusion and physiological hyperinsulinemia enhanced p70S6Kphosphorylation without affecting GSK-3 phosphorylation, but only physiological hyperinsulinemia also increased whole body glucose disposal and GS activity. In contrast, a pharmacological dose of insulin significantly increased whole body glucose disposal, p70S6K, GSK-3 phosphorylation, and GS activity. We conclude that amino acids at physiological concentrations mediate p70S6Kbut, unlike insulin, do not regulate GSK-3 and GS phosphorylation/activity in human skeletal muscle.

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Effects of insulin infusion on human skeletal muscle pyruvate dehydrogenase, phosphofructokinase, and glycogen synthase. Evidence for their role in oxidative and nonoxidative glucose metabolism.

Journal of Clinical Investigation ◽

10.1172/jci113118 ◽

1987 ◽

Vol 80 (3) ◽

pp. 655-663 ◽

Cited By ~ 131

Author(s):

L J Mandarino ◽

K S Wright ◽

L S Verity ◽

J Nichols ◽

J M Bell ◽

...

Keyword(s):

Skeletal Muscle ◽

Glucose Metabolism ◽

Pyruvate Dehydrogenase ◽

Human Skeletal Muscle ◽

Insulin Infusion ◽

Glycogen Synthase

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RPS6 phosphorylation occurs to a greater extent in the periphery of human skeletal muscle fibers, near focal adhesions, after anabolic stimuli

AJP Cell Physiology ◽

10.1152/ajpcell.00357.2021 ◽

2021 ◽

Author(s):

Nathan Hodson ◽

Michael Mazzulla ◽

Maksym N. H. Holowaty ◽

Dinesh Kumbhare ◽

Daniel R. Moore

Keyword(s):

Skeletal Muscle ◽

Focal Adhesion ◽

Human Skeletal Muscle ◽

Muscle Fibers ◽

Focal Adhesions ◽

Immunofluorescent Staining ◽

Whole Body ◽

Vastus Lateralis Muscle ◽

Cell Periphery ◽

Rps6 Phosphorylation

Following anabolic stimuli (mechanical loading and/or amino acid provision) the mechanistic target of rapamycin complex 1 (mTORC1), a master regulator of protein synthesis, translocates toward the cell periphery. However, it is unknown if mTORC1-mediated phosphorylation events occur in these peripheral regions or prior to translocation (i.e. in central regions). We therefore aimed to determine the cellular location of a mTORC1-mediated phosphorylation event, RPS6Ser240/244, in human skeletal muscle following anabolic stimuli. Fourteen young, healthy males either ingested a protein-carbohydrate beverage (0.25g/kg protein, 0.75g/kg carbohydrate) alone (n=7;23±5yrs;76.8±3.6kg;13.6±3.8%BF, FED) or following a whole-body resistance exercise bout (n=7;22±2yrs;78.1±3.6kg;12.2±4.9%BF, EXFED). Vastus lateralis muscle biopsies were obtained at rest (PRE) and 120 and 300min following anabolic stimuli. RPS6Ser240/244 phosphorylation measured by immunofluorescent staining or immunoblot was positively correlated (r=0.76, p<0.001). Peripheral staining intensity of p-RPS6Ser240/244 increased above PRE in both FED and EXFED at 120min (~54% and ~138% respectively, p<0.05) but was greater in EXFED at both post-stimuli time points (p<0.05). The peripheral-central ratio of p-RPS6240/244 staining displayed a similar pattern, even when corrected for total RPS6 distribution, suggesting RPS6 phosphorylation occurs to a greater extent in the periphery of fibers. Moreover, p-RPS6Ser240/244 intensity within paxillin-positive regions, a marker of focal adhesion complexes, was elevated at 120min irrespective of stimulus (p=0.006) before returning to PRE at 300min. These data confirm that RPS6Ser240/244 phosphorylation occurs in the region of human muscle fibers to which mTOR translocates following anabolic stimuli and identifies focal adhesion complexes as a potential site of mTORC1 regulation in vivo.

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Increased concentrations of glycogen synthase protein in skeletal muscle of patients with NIDDM

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1995.269.1.e27 ◽

1995 ◽

Vol 269 (1) ◽

pp. E27-E32 ◽

Cited By ~ 1

Author(s):

M. Lofman ◽

H. Yki-Jarvinen ◽

M. Parkkonen ◽

J. Lindstrom ◽

L. Koranyi ◽

...

Keyword(s):

Skeletal Muscle ◽

Glucose Metabolism ◽

Protein Concentration ◽

Glycogen Synthase ◽

Glycogen Metabolism ◽

Dependent Diabetes Mellitus ◽

Euglycemic Hyperinsulinemic Clamp ◽

Control Subjects ◽

Significant Difference ◽

Glycogen Synthase Activity

To examine whether changes in the glycogen synthase protein concentration contribute to impaired insulin-stimulated glycogen metabolism in patients with noninsulin-dependent diabetes mellitus (NIDDM), muscle biopsies were taken before and after a 4-h euglycemic hyperinsulinemic clamp to measure glycogen synthase activity and glycogen synthase protein concentrations in 14 patients with NIDDM and in 17 control subjects. Nonoxidative glucose metabolism was reduced by 64% in patients with NIDDM compared with control subjects and correlated with insulin-stimulated glycogen synthase activity (r = 0.55, P < 0.05). The concentration of glycogen synthase protein in skeletal muscle was higher in patients with NIDDM than in control subjects (6.75 +/- 0.88 vs. 4.41 +/- 0.50 counts.min-1.micrograms protein-1, P < 0.05), whereas there was no significant difference in glycogen synthase mRNA concentration between the two groups. The glycogen synthase protein concentration correlated inversely with the rate of nonoxidative glucose metabolism (r = -0.63, P < 0.05). These findings indicate that the amount of glycogen synthase protein is increased in skeletal muscle of patients with NIDDM. The increase in the glycogen synthase protein may serve to compensate for a functional defect in the activation of the enzyme by insulin.

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