Biomedical subjects

Henrik Galbo

Publications and source records attributed to Henrik Galbo.

At least 19 recordsLinked to original sources

PubMed2006

Decrease in intramuscular lipid droplets and translocation of HSL in response to muscle contraction and epinephrine.

A better understanding of skeletal muscle lipid metabolism is needed to identify the molecular mechanisms relating intramuscular triglyceride (IMTG) to muscle metabolism and insulin sensitivity. An increasing number of proteins have been reported to be associated with intracellular triglyceride (TG), among them the PAT family members: perilipin, ADRP (for adipocyte differentiation-related protein), and TIP47 (for tail-interacting protein of 47 kDa). Hormone-sensitive lipase (HSL) is thought to be the major enzyme responsible for IMTG hydrolysis in skeletal muscle. In adipocytes, regulation of HSL by intracellular redistribution has been demonstrated. The existence of such regulatory mechanisms in skeletal muscle has long been hypothesized but has never been demonstrated. The aim of this study was to characterize the PAT family proteins associated with IMTG and to investigate the effect of epinephrine stimulation or muscle contraction on skeletal muscle TG content and HSL intracellular distribution. Rat soleus muscles were either incubated with epinephrine or electrically stimulated for 15 min. Single muscle fibers were used for morphological analysis by confocal and transmission electron microscopy. We show a decrease in IMTG in response to both lipolytic stimuli. Furthermore, we identify two PAT family proteins, ADRP and TIP47, associated with IMTG. Finally, we demonstrate HSL translocation to IMTG and ADRP after stimulation with epinephrine or contraction.

Animals↗

PubMed2006

Sex differences in hormone-sensitive lipase expression, activity, and phosphorylation in skeletal muscle at rest and during exercise.

Women have been shown to use more intramuscular triacylglycerol (IMTG) during exercise than men. To investigate whether this could be due to sex-specific regulation of hormone-sensitive lipase (HSL) and to use sex comparison as a model to gain further insight into HSL regulation, nine women and eight men performed bicycle exercise (90 min, 60% Vo(2peak)), and skeletal muscle HSL expression, phosphorylation, and activity were determined. Supporting previous findings, basal IMTG content (P < 0.001) and net IMTG decrease during exercise (P < 0.01) were higher in women than in men and correlated significantly (r = 0.72, P = 0.001). Muscle HSL mRNA (80%, P = 0.11) and protein content (50%, P < 0.05) were higher in women than in men. HSL total activity increased during exercise (47%, P < 0.05) but did not differ between sexes. Accordingly, HSL specific activity (HSL activity per HSL protein content) increased during exercise (62%, P < 0.05) and was generally higher in men than in women (82%, P < 0.05). A similar pattern was observed for HSL Ser(659) phosphorylation, suggesting a role in regulation of HSL activity. Likewise, plasma epinephrine increased during exercise (P < 0.05) and was higher in men than in women during the end of the exercise bout (P < 0.05). We conclude that, although HSL expression and Ser(659) phosphorylation in skeletal muscle during exercise is sex specific, total muscle HSL activity measured in vitro was similar between sexes. The higher basal IMTG content in women compared with men is therefore the best candidate to explain the higher IMTG net hydrolysis during exercise in women.

Adult↗

PubMed2006

Muscle triacylglycerol and hormone-sensitive lipase activity in untrained and trained human muscles.

During exercise, triacylglycerol (TG) is recruited in skeletal muscles. We hypothesized that both muscle hormone-sensitive lipase (HSL) activity and TG recruitment would be higher in trained than in untrained subjects in response to prolonged exercise. Healthy male subjects (26 +/- 1 years, body moss index 23.3 +/- 0.5 kg m(-2)), either untrained (N = 8, VO(2max) 3.8 +/- 0.2 l min(-1)) or trained (N = 8, VO(2max) 5.1 +/- 0.1 l min(-1)), were studied. Before and after 3-h exercise (58 +/- 1% VO(2max)), a biopsy was taken. Muscle citrate synthase (32 +/- 2 vs. 47 +/- 6 mumol g(-1) min(-1) d.w.) and beta-hydroxy-acyl-CoA-dehydrogenase (38 +/- 3 vs. 52 +/- 5 mumol g(-1) min(-1) d.w.) activities were lower in untrained than in trained subjects (p < 0.05). Throughout the exercise, fat oxidation was higher in trained than in untrained subjects (p < 0.05). Muscle HSL activity was similar at rest (0.72 +/- 0.08 and 0.74 +/- 0.03 mU mg(-1) protein) and after exercise (0.71 +/- 0.1 and 0.68 +/- 0.03 mU mg(-1) protein) in untrained and trained subjects. At rest, the chemically determined muscle TG content (37 +/- 8 and 26 +/- 5 mmol g(-1) d.w.) was similar (p > 0.05), and after exercise it was unchanged in untrained and lower (p < 0.05) in trained subjects (41 +/- 9 and 10 +/- 2 mmol g((1) d.w.). Determined histochemically, TG was decreased (p < 0.05) after exercise in type I and II fibres. Depletion of TG was not different between fibre types in untrained, but tended to be higher (p = 0.07) in type I compared with type II fibres in trained muscles. In conclusion, HSL activity is similar in untrained and trained skeletal muscles both before and after prolonged exercise. However, the tendency to higher muscle TG recruitment during exercise in the trained subjects suggests a difference in the regulation of HSL or other lipases during exercise in trained compared with untrained subjects.

Adult↗

PubMed2006

Noradrenaline-induced increases in calcium and tension in skeletal muscle conductance and resistance arteries from rats with post-infarction heart failure.

We tested the hypothesis that arterial reactivity to noradrenaline is augmented in congestive heart failure (CHF), which could contribute to the deleterious changes in peripheral vascular resistance and compliance in this condition. From male Wistar rats with post-infarction CHF and sham-operated rats, skeletal muscle conductance and resistance arteries (mean lumen diameters: 514 and 186 microm) were isolated and mounted on wire myographs, and wall tension was recorded in response to cumulative application of acetylcholine and noradrenaline to the vessel segments. In a subset of experiments, wall tension and cytosolic free calcium ion concentration [Ca(2+)](i) were recorded simultaneously during noradrenaline application, using wire myography and the FURA-2 technique. No significant differences were found in the arterial baseline levels of [Ca(2+)](i) or tension between CHF and sham rats. In the resistance arteries of CHF rats, the noradrenaline-induced increases in [Ca(2+)](i) were significantly enhanced (P=0.003). Despite the augmented [Ca(2+)](i) levels, the tension responses to noradrenaline were unaltered in these arteries. In the conductance arteries, there were no significant differences in noradrenaline-induced [Ca(2+)](i) or tension responses between CHF and control rats. CHF did not alter vascular morphology or change vascular relaxations to acetylcholine in either type of artery. In conclusion, these results do not support the contention that arterial reactivity to noradrenaline is augmented in the skeletal muscle vascular bed in CHF. On the contrary, the unchanged contractile responsiveness in the resistance arteries despite the enhanced levels of [Ca(2+)](i) during noradrenaline application suggests that the contractile function of these vessels is compromised in CHF. Neither vascular remodeling, endothelial dysfunction nor changes in baseline vascular tone could be demonstrated in the skeletal muscle vascular bed of this animal model of heart failure.

Acetylcholine↗

PubMed2006

Imaging of insulin signaling in skeletal muscle of living mice shows major role of T-tubules.

Insulin stimulates glucose transport in skeletal muscle by glucose transporter GLUT4 translocation to sarcolemma and membrane invaginations, the t-tubules. Although muscle glucose uptake plays a key role in insulin resistance and type 2 diabetes, the dynamics of GLUT4 translocation and the signaling involved are not well described. We have now developed a confocal imaging technique to follow trafficking of green fluorescent protein-labeled proteins in living muscle fibers in situ in anesthetized mice. Using this technique, by imaging the dynamics of GLUT4 translocation and phosphatidylinositol 3,4,5 P(3) (PIP(3)) production in response to insulin, here, for the first time, we delineate the temporal and spatial distribution of these processes in a living animal. We find a 10-min delay of maximal GLUT4 recruitment and translocation to t-tubules compared with sarcolemma. Time-lapse imaging of a fluorescent dye after intravenous injection shows that this delay is similar to the time needed for insulin diffusion into the t-tubule system. Correspondingly, immunostaining of muscle fibers shows that insulin receptors are present throughout the t-tubule system. Finally, PIP(3) production, an early event in insulin signaling, progresses slowly along the t-tubules with a 10-min delay between maximal PIP(3) production at sarcolemma compared with deep t-tubules following the appearance of dye-labeled insulin. Our findings in living mice indicate a major role of the t-tubules in insulin signaling in skeletal muscle and show a diffusion-associated delay in insulin action between sarcolemma and inner t-tubules.

Animals↗

PubMed2005

Ca(2+) sensitisation of force production by noradrenaline in femoral conductance and resistance arteries from rats with postinfarction congestive heart failure.

In this study we tested the hypothesis that arterial myofilament Ca(2+) sensitivity and/or the Ca(2+) sensitising effect of noradrenaline (NA) is enhanced in post-infarction congestive heart failure (CHF), which could contribute to the high peripheral vascular resistance in this condition. Femoral skeletal muscle resistance and conductance arteries (mean lumen diameters of 159 and 519 microm) from rats with CHF and sham-operated control rats were used. Isometric tension development and intracellular free calcium concentration ([Ca(2+)](i)) were measured simultaneously in isolated vessel segments using wire myography and the FURA-2 fluorescence technique. In conductance and resistance arteries, the resting levels of [Ca(2+)](i) and tension in physiological saline solution (PSS) and active tension in response to single doses of 125 mM K(+) (KPSS) were unaffected by CHF. During cumulative application of extracellular Ca(2+) to arteries depolarised with 125 mM K(+) or activated with 30 microM NA, [Ca(2+)](i) and vessel wall tension were similar in CHF and control rats. However, the conductance arteries showed significantly higher calcium sensitivity than resistance arteries in these experiments. We conclude that an abnormality in the sensitivity of the contractile apparatus to Ca(2+), or in NA-induced Ca(2+) sensitisation in arterial vascular smooth muscle cells is unlikely to contribute to the ubiquitously elevated vascular resistance associated with CHF. However, our data demonstrate significant differences in vascular Ca(2+) handling, myofilament Ca(2+) sensitivity and tension development between resistance and conductance arteries, regardless of CHF.

Animals↗

PubMed2005

Transcriptome and proteome analysis of soleus muscle of hormone-sensitive lipase-null mice.

Hormone-sensitive lipase (HSL), a key enzyme in fatty acid mobilization in adipocytes, has been demonstrated also in skeletal muscle. To gain further insight into the role and importance of HSL in skeletal muscle, a transcriptome analysis of soleus muscle of HSL-null mice was performed. A total of 161 transcripts were found to be differentially expressed. Increased mRNA levels of fructose-1,6-bisphosphatase, fructose-2,6-bisphosphatase, and phosphorylase kinase gamma1A suggest a higher glycogen flux in soleus muscle of HSL-null mice. An observed increase in the utilization of glycogen stores supports this finding. Moreover, an increased amount of intramyocellular lipid droplets, observed by transmission electron microscopy, suggests decreased mobilization of lipid stores in HSL-null mice. To complement the transcriptome data, protein expression analysis was performed. Five spots were found to be differentially expressed: pyruvate dehydrogenase E1alpha, creatine kinase (CK), ankyrin-repeat domain 2, glyceraldehyde-3-phosphate dehydrogenase, and one protein yet to be identified. The increased protein level of CK indicates creatine phosphate degradation to be of increased importance in HSL-null mice. The results of this study suggest that in the absence of HSL, a metabolic switch from reliance on lipid to carbohydrate energy substrates takes place, supporting an important role of HSL in soleus muscle lipid metabolism.

Animals↗

PubMed2005

Prevention of hyperglycemia in Zucker diabetic fatty rats by exercise training: effects on gene expression in insulin-sensitive tissues determined by high-density oligonucleotide microarray analysis.

Exercise training (ET) causes metabolic improvement in the prediabetic and diabetic states. However, only little information exists on the changes to ET at the transcriptional level in insulin-sensitive tissues. We have investigated the gene expression changes in skeletal muscle, liver, fat, and pancreatic islets after ET in male Zucker diabetic fatty (ZDF) rats. Eighteen ZDF rats (7 weeks old) were divided in a control and ET group. Exercise was performed using a motorized treadmill (20 m/min 1 hour daily for 6 days a week). Blood glucose, weight, and food intake were measured weekly. After 5 weeks, blood samples, soleus muscle, liver, visceral fat (epididymal fat pads), and islet tissue were collected. Gene expression was quantified with Affymetrix RG-U34A array (16 chips). Exercise training ameliorates the development of hyperglycemia and reduces plasma free fatty acid and the level of glucagon-insulin ratio (P < .05). In skeletal muscle, the expression of 302 genes increased, whereas that of 119 genes decreased. These changes involved genes related to skeletal muscle plasticity, Ca(2+) signals, energy metabolism (eg, glucose transporter 1, phosphorylase kinase), and other signaling pathways as well as genes with unknown functions (expressed sequence tags). In the liver, expression of 148 genes increased, whereas that of 199 genes decreased. These were primarily genes involved in lipogenesis and detoxification. Genes coding for transcription factors were changed in parallel in skeletal muscle and liver tissue. Training did not markedly influence the gene expression in islets. In conclusion, ET changes the expression of multiple genes in the soleus muscle and liver tissue and counteracts the development of diabetes, indicating that ET-induced changes in gene transcription may play an important role en the prevention of diabetes.

Adipose Tissue↗

PubMed2005

Hormone-sensitive lipase as mediator of lipolysis in contracting skeletal muscle.

The authors propose that the enzyme hormone-sensitive lipase (HSL), which is the rate-limiting enzyme for hydrolysis of triacylglycerol in adipocytes, also regulates the intramyocellular triacylglycerol mobilization and is controlled by mechanisms similar to those regulating glycogen phosphorylase. From an exercise perspective, it is fascinating that the primary enzymatic setting allows simultaneous mobilization of all major extramuscular and intramuscular energy stores.

Animals↗

PubMed2005

Expression profiling reveals differences in metabolic gene expression between exercise-induced cardiac effects and maladaptive cardiac hypertrophy.

While cardiac hypertrophy elicited by pathological stimuli eventually leads to cardiac dysfunction, exercise-induced hypertrophy does not. This suggests that a beneficial hypertrophic phenotype exists. In search of an underlying molecular substrate we used microarray technology to identify cardiac gene expression in response to exercise. Rats exercised for seven weeks on a treadmill were characterized by invasive blood pressure measurements and echocardiography. RNA was isolated from the left ventricle and analysed on DNA microarrays containing 8740 genes. Selected genes were analysed by quantitative PCR. The exercise program resulted in cardiac hypertrophy without impaired cardiac function. Principal component analysis identified an exercise-induced change in gene expression that was distinct from the program observed in maladaptive hypertrophy. Statistical analysis identified 267 upregulated genes and 62 downregulated genes in response to exercise. Expression changes in genes encoding extracellular matrix proteins, cytoskeletal elements, signalling factors and ribosomal proteins mimicked changes previously described in maladaptive hypertrophy. Our most striking observation was that expression changes of genes involved in beta-oxidation of fatty acids and glucose metabolism differentiate adaptive from maladaptive hypertrophy. Direct comparison to maladaptive hypertrophy was enabled by quantitative PCR of key metabolic enzymes including uncoupling protein 2 (UCP2) and fatty acid translocase (CD36). DNA microarray analysis of gene expression changes in exercise-induced cardiac hypertrophy suggests that a set of genes involved in fatty acid and glucose metabolism could be fundamental to the beneficial phenotype of exercise-induced hypertrophy, as these changes are absent or reversed in maladaptive hypertrophy.

Animals↗

PubMed2004

Regulation of hormone-sensitive lipase activity and Ser563 and Ser565 phosphorylation in human skeletal muscle during exercise.

Hormone-sensitive lipase (HSL) catalyses the hydrolysis of myocellular triacylglycerol (MCTG), which is a potential energy source during exercise. Therefore, it is important to elucidate the regulation of HSL activity in human skeletal muscle during exercise. The main purpose of the present study was to investigate the role of 5'AMP-activated protein kinase (AMPK) in the regulation of muscle HSL activity and Ser565 phosphorylation (the presumed AMPK target site) in healthy, moderately trained men during 60 min bicycling (65%). Alpha2AMPK activity during exercise was manipulated by studying subjects with either low (LG) or high (HG) muscle glycogen content. HSL activity was distinguished from the activity of other neutral lipases by immunoinhibition of HSL using an anti-HSL antibody. During exercise a 62% higher (P < 0.01) alpha2AMPK activity in LG than in HG was paralleled by a similar difference (61%, P < 0.01) in HSL Ser565 phosphorylation but without any difference between trials in HSL activity or MCTG hydrolysis. HSL activity was increased (117%, P < 0.05) at 30 min of exercise but not at 60 min of exercise. In both trials, HSL phosphorylation on Ser563 (a presumed PKA target site) was not increased by exercise despite a fourfold increase (P < 0.001) in plasma adrenaline. ERK1/2 phosphorylation was increased by exercise in both trials (P < 0.001) and was higher in LG than in HG both at rest and during exercise (P = 0.06). In conclusion, the present study suggests that AMPK phosphorylates HSL on Ser565 in human skeletal muscle during exercise with reduced muscle glycogen. Apparently, HSL Ser565 phosphorylation by AMPK during exercise had no effect on HSL activity. Alternatively, other factors including ERK may have counterbalanced any effect of AMPK on HSL activity.

AMP-Activated Protein Kinases↗

PubMed2004

Physical training may enhance beta-cell function in type 2 diabetes.

In healthy young subjects, training increases insulin sensitivity but decreases the capacity to secrete insulin. We studied whether training changes beta-cell function in type 2 diabetic patients. Patients, stratified into "moderate" and "low" secretors according to individual C-peptide responses to an intravenous glucagon test, were randomly assigned to a training program [ergometer cycling 30-40 min/day, including at least 20 min at 75% maximum oxygen consumption (Vo(2 max)), 5 days/wk for 3 mo] or a sedentary schedule. Before and after the intervention (16 h after last training bout), a sequential hyperglycemic (90 min at 11, 18, and 25 mM) clamp was performed. An intravenous bolus of 5 g of arginine was given at the end. Training increased Vo(2 max) 17 +/- 13% and decreased heart rate during submaximal exercise (P < 0.05). During the 3 mo of sedentary lifestyle, insulin and C-peptide responses to the clamp procedures were unchanged in both moderate and low secretors. Likewise, no change in beta-cell response was seen after training in the low secretors (n = 5). In contrast, moderate secretors (n = 9) showed significant increases in beta-cell responses to 18 and 25 mM hyperglycemia and to arginine stimulation. Glucagon responses to arginine as well as measures of insulin sensitivity and Hb A(1c) levels were not altered by training. In conclusion, in type 2 diabetic patients, training may enhance beta-cell function if the remaining secretory capacity is moderate but not if it is low. The improved beta-cell function does not require changes in insulin sensitivity and Hb A(1c) concentration.

Adaptation, Physiological↗

PubMed2004

Contractions induce phosphorylation of the AMPK site Ser565 in hormone-sensitive lipase in muscle.

Intramyocellular triglyceride is an important energy store which is related to insulin resistance. Mobilization of fatty acids from this pool is probably regulated by hormone-sensitive lipase (HSL), which has recently been shown to exist in muscle and to be activated by epinephrine via PKA and by contractions via PKC and ERK. 5' AMP-activated protein kinase (AMPK) is an intracellular fuel gauge which regulates metabolism. In this study we incubated rat soleus muscle to investigate if AMPK influences HSL during 5min of repeated tetanic contractions. An eightfold increase in AMPK activity was accompanied by a 2.5-fold increase in phosphorylation of the AMPK-site Ser(565) in HSL (p<0.05). Inhibition of PKC by Calphostin C abolished the contraction-mediated HSL activation while HSL-Ser(565) phosphorylation was not reduced. The study indicates that during contractions AMPK phosphorylates HSL in Ser(565), but this phosphorylation is not directly responsible for the contraction-induced activation of HSL.

AMP-Activated Protein Kinases↗

PubMed2004

Regulation and role of hormone-sensitive lipase in rat skeletal muscle.

Intramyocellular triacylglycerol (TG) is an important energy store, and the energy content of this depot is higher than the energy content of the muscle glycogen depot. It has recently been shown that the mobilization of fatty acids from this TG pool may be regulated by the neutral lipase hormone-sensitive lipase (HSL). This enzyme is known to be rate limiting for intracellular TG hydrolysis in adipose tissue. The presence of HSL has been demonstrated in all muscle fibre types by Western blotting of muscle fibres isolated by collagenase treatment or after freeze-drying. The content of HSL varies between fibre types, being higher in oxidative fibres than in glycolytic fibres. When analysed under conditions optimal for HSL, neutral lipase activity in muscle can be stimulated by adrenaline as well as by contractions. These increases are abolished by the presence of anti-HSL antibody during analysis. Moreover, immunoprecipitation with affinity-purified anti-HSL antibody causes similar reductions in muscle HSL protein concentration and in measured neutral lipase responses to contractions. The immunoreactive HSL in muscle is stimulated by adrenaline via beta-adrenergic activation of cAMP-dependent protein kinase (PKA). From findings in adipocytes it is likely that PKA phosphorylates HSL at residues Ser(563), Ser(659) and Ser(660). Contraction probably also enhances muscle HSL activity by phosphorylation, because the contraction-induced increase in HSL activity is elevated by the protein phosphatase inhibitor okadaic acid and reversed by alkaline phosphatase. A novel signalling pathway in muscle by which HSL activity may be stimulated by protein kinase C (PKC) via extracellular signal-regulated kinase (ERK) has been demonstrated. In contrast to previous findings in adipocytes, in muscle the activation of ERK is not necessary for stimulation of HSL by adrenaline. However, contraction-induced HSL activation is mediated by PKC, at least partly via the ERK pathway. In fat cells ERK is known to phosphorylate HSL at Ser(600). Hence, phosphorylation of different sites may explain the finding that in muscle the effects of contractions and adrenaline on HSL activity are partially additive. In line with the view that the two stimuli act by different mechanisms, training increases contraction-mediated HSL activation but diminishes adrenaline-mediated HSL activation in muscle. In conclusion, HSL is present in skeletal muscle and can be activated by phosphorylation in response to both adrenaline and muscle contractions. Training increases contraction-mediated HSL activation, but decreases adrenaline-mediated HSL activation in muscle.

Animals↗

PubMed2003

Hormone-sensitive lipase null mice exhibit signs of impaired insulin sensitivity whereas insulin secretion is intact.

Lipid metabolism plays an important role in glucose homeostasis under normal and pathological conditions. In adipocytes, skeletal muscle, and pancreatic beta-cells, lipids are mobilized from acylglycerides by the hormone-sensitive lipase (HSL). Here, the consequences of a targeted disruption of the HSL gene for glucose homeostasis were examined. HSL null mice were slightly hyperglycemic in the fasted, but not fed state, which was accompanied by moderate hyperinsulinemia. During glucose challenges, however, disposal of the sugar was not affected in HSL null mice, presumably because of release of increased amounts of insulin. Impaired insulin sensitivity was further indicated by retarded glucose disposal during an insulin tolerance test. A euglycemic hyperinsulinemic clamp revealed that hepatic glucose production was insufficiently blocked by insulin in HSL null mice. In vitro, insulin-stimulated glucose uptake into soleus muscle, and lipogenesis in adipocytes were moderately reduced, suggesting additional sites of insulin resistance. Morphometric analysis of pancreatic islets revealed a doubling of beta-cell mass in HSL null mice, which is consistent with an adaptation to insulin resistance. Insulin secretion in vitro, examined by perifusion of isolated islets, was not impacted by HSL deficiency. Thus, HSL deficiency results in a moderate impairment of insulin sensitivity in multiple target tissues of the hormone but is compensated by hyperinsulinemia.

Adipocytes↗

PubMed2003

Contractions activate hormone-sensitive lipase in rat muscle by protein kinase C and mitogen-activated protein kinase.

Intramuscular triacylglycerol is an important energy store and is also related to insulin resistance. The mobilization of fatty acids from this pool is probably regulated by hormone-sensitive lipase (HSL), which has recently been shown to exist in muscle and to be activated by both adrenaline and contractions. Adrenaline acts via cAMP-dependent protein kinase (PKA). The signalling mediating the effect of contractions is unknown and was explored in this study. Incubated soleus muscles from 70 g male rats were electrically stimulated to perform repeated tetanic contractions for 5 min. The contraction-induced activation of HSL was abolished by the protein kinase C (PKC) inhibitors bisindolylmaleimide I and calphostin C and reduced 50% by the mitogen-activated protein kinase kinase (MEK) inhibitor U0126, which also completely blocked extracellular signal-regulated kinase (ERK) 1 and 2 phosphorylation. None of the inhibitors reduced adrenaline-induced HSL activation in soleus muscle. Both phorbol-12-myristate-13-acetate (PMA), which activates PKC and, in turn, ERK, and caffeine, which increases intracellular Ca2+ without eliciting contraction, increased HSL activity. Activated ERK increased HSL activity in supernatant from basal but not from electrically stimulated muscle. In conclusion, in muscle, PKC can stimulate HSL through ERK. Contractions and adrenaline enhance muscle HSL activity by different signalling mechanisms. The effect of contractions is mediated by PKC, at least partly via the ERK pathway.

Adipocytes↗

PubMed2003

Disruption of microtubules in rat skeletal muscle does not inhibit insulin- or contraction-stimulated glucose transport.

Insulin and muscle contractions stimulate glucose transport in skeletal muscle through a translocation of intracellular GLUT4 glucose transporters to the cell surface. Judged by immunofluorescence microscopy, part of the GLUT4 storage sites is associated with the extensive microtubule cytoskeleton found in all muscle fibers. Here, we test whether microtubules are required mediators of the effect of insulin and contractions. In three different incubated rat muscles with distinct fiber type composition, depolymerization of microtubules with colchicine for < or =8 h did not inhibit insulin- or contraction-stimulated 2-deoxyglucose transport or force production. On the contrary, colchicine at least partially prevented the approximately 30% decrease in insulin-stimulated transport that specifically developed during 8 h of incubation in soleus muscle but not in flexor digitorum brevis or epitrochlearis muscles. In contrast, nocodazole, another microtubule-disrupting drug, rapidly and dose dependently blocked insulin- and contraction-stimulated glucose transport. A similar discrepancy between colchicine and nocodazole was also found in their ability to block glucose transport in muscle giant "ghost" vesicles. This suggests that the ability of insulin and contractions to stimulate glucose transport in muscle does not require an intact microtubule network and that nocodazole inhibits glucose transport independently of its microtubule-disrupting effect.

Animals↗

PubMed2003

The effect of graded exercise on IL-6 release and glucose uptake in human skeletal muscle.

In this study, the hypothesis that the release of interleukin (IL)-6 from human muscle is linked to exercise intensity and muscle glucose uptake was investigated. In the overnight fasted state, seven healthy males performed knee extension exercise, kicking with both legs, each at 25 % of maximal power (W(max)) for 45 min (eliciting 23 +/- 1 % of pulmonary maximal oxygen uptake, V(O2,max)) and then simultaneously with one leg at 65 % and the other leg at 85 % W(max) for 35 min (40 +/- 1 % of pulmonary V(O2,max)). Blood was sampled from a femoral artery and both femoral veins, and blood flow was determined by thermodilution. Thigh plasma flow (0.15 +/- 0.01, 1.4 +/- 0.2, 2.0 +/- 0.1 and 2.3 +/- 0.2 l min(-1) thigh(-1) at rest and 25 %, 65 % and 85 % W(max), respectively) and thigh oxygen uptake (0.02 +/- 0.01, 0.27 +/- 0.03, 0.48 +/- 0.04 and 0.55 +/- 0.05 l min(-1) thigh(-1) at rest and 25 %, 65 % and 85 % W(max), respectively) increased with increasing exercise intensity (P < 0.05). Also, thigh IL-6 release (0.4 +/- 0.1, 1.3 +/- 0.5, 1.5 +/- 0.6 and 2.5 +/- 0.7 ng min(-1) thigh(-1) at rest and 25 %, 65 % and 85 % W(max), respectively) and thigh glucose uptake (0.05 +/- 0.01, 0.3 +/- 0.05, 0.75 +/- 0.16, 1.07 +/- 0.15 mmol min(-1) thigh(-1) at rest and 25 %, 65 % and 85 % W(max), respectively) increased with increasing exercise intensity (P < 0.05). During the last 35 min of exercise, arterial catecholamine concentrations were higher (P < 0.05) than at rest and during low-intensity exercise. During exercise, thigh IL-6 release was positively related to both thigh glucose uptake (P < 0.001) and thigh glucose delivery (P < 0.005), but not to thigh glucose extraction. Thigh IL-6 release was also positively related to arterial plasma adrenaline concentration. The pre-exercise muscle glycogen concentration tended to correlate with the arteriovenous IL-6 concentration difference at rest, and the postexercise glycogen concentration was inversely correlated with IL-6 release during the final 35 min of exercise. In conclusion, the study indicates that IL-6 release from human muscle is positively related to exercise intensity, arterial adrenaline concentration and muscle glucose uptake. This supports the hypothesis that IL-6 may be linked to the regulation of glucose homeostasis during exercise. The observation of a relationship between IL-6 release and muscle glycogen store both at rest and after exercise suggests that IL-6 may act as a carbohydrate sensor.

Adult↗