Field‐effect transistors that employ an electrolyte in place of a gate dielectric layer can accumulate ultrahigh‐density carriers not only on a well‐defined channel (e.g., a two‐dimensional surface) ...but also on any irregularly shaped channel material. Here, on thin films of 95% pure metallic and semiconducting single‐walled carbon nanotubes (SWNTs), the Fermi level is continuously tuned over a very wide range, while their electronic transport and absorption spectra are simultaneously monitored. It is found that the conductivity of not only the semiconducting but also the metallic SWNT thin films steeply changes when the Fermi level reaches the edges of one‐dimensional subbands and that the conductivity is almost proportional to the number of subbands crossing the Fermi level, thereby exhibiting a one‐dimensional nature of transport even in a tangled network structure and at room temperature.
Electrochemical carrier control of pure metallic and semiconducting single‐walled carbon nanotube (SWNT) films enable simultaneous measurements of the band filling by optical absorption spectroscopy and conductivity. The metallic SWNT film as well as the semiconducting SWNT film show substantial change in the conductivity by the subband filling.
A new method for investigating light‐emitting property in organic devices is demonstrated. We apply the ambipolar light‐emitting transistors (LETs) to directly observe the recombination zone, and ...find a strong link between the transistor performance and the zone size. This finding unambiguously indicates that the light emission comes from the electric‐field‐induced p‐i‐n homojunction in ambipolar LETs.
Exercise has beneficial effects on our health by stimulating metabolic activation of skeletal muscle contraction. Caffeine is a powerful metabolic stimulant in the skeletal muscle that has ergogenic ...effects, including enhanced muscle power output and endurance capacity. In the present study, we aim to characterize the metabolic signatures of contracting muscles with or without caffeine stimulation using liquid chromatography-mass spectrometry and capillary electrophoresis coupled to mass spectrometry. Isolated rat epitrochlearis muscle was incubated in the presence or absence or of 3 mM caffeine for 30 min. Electrical stimulation (ES) was used to induce tetanic contractions during the final 10 min of incubation. Principal component analysis and hierarchical clustering analysis detected 184 distinct metabolites across three experimental groups-basal, ES, and ES with caffeine (ES + C). Significance Analysis of Microarray identified a total of 50 metabolites with significant changes in expression, and 23 metabolites significantly changed between the ES and ES + C groups. Changes were observed in metabolite levels of various metabolic pathways, including the pentose phosphate, nucleotide synthesis, β-oxidation, tricarboxylic acid cycle, and amino acid metabolism. In particular, D-ribose 5-phosphate, IMP, O-acetylcarnitine, butyrylcarnitine, L-leucine, L-valine, and L-aspartate levels were higher in the ES + C group than in the ES group. These metabolic alterations induced by caffeine suggest that caffeine accelerates contraction-induced metabolic activations, thereby contributing to muscle endurance performance and exercise benefits to our health.
Caffeine decreases insulin sensitivity and insulin-stimulated glucose transport in skeletal muscle; however, the precise mechanism responsible for this deleterious effect is not understood fully. We ...investigated the effects of incubation with caffeine on insulin signaling in rat epitrochlearis muscle. Caffeine (≥1 mM, ≥15 min) suppressed insulin-stimulated insulin receptor substrate (IRS)-1 Tyr(612) phosphorylation in a dose- and time-dependent manner. These responses were associated with inhibition of the insulin-stimulated phosphorylation of phosphatidylinositol 3-kinase (PI3K) Tyr(458), Akt Ser(473), and glycogen synthase kinase-3β Ser(9) and with inhibition of insulin-stimulated 3-O-methyl-d-glucose (3MG) transport but not with inhibition of the phosphorylation of insulin receptor-β Tyr(1158/62/63). Furthermore, caffeine enhanced phosphorylation of IRS-1 Ser(307) and an IRS-1 Ser(307) kinase, inhibitor-κB kinase (IKK)-α/β Ser(176/180). Blockade of IKK/IRS-1 Ser(307) by caffeic acid ameliorated the caffeine-induced downregulation of IRS-1 Tyr(612) phosphorylation and 3MG transport. Caffeine also increased the phosphorylation of IRS-1 Ser(789) and an IRS-1 Ser(789) kinase, 5'-AMP-activated protein kinase (AMPK). However, inhibition of IRS-1 Ser(789) and AMPK phosphorylation by dantrolene did not rescue the caffeine-induced downregulation of IRS-1 Tyr(612) phosphorylation or 3MG transport. In addition, caffeine suppressed the phosphorylation of insulin-stimulated IRS-1 Ser(636/639) and upstream kinases, including the mammalian target of rapamycin and p70S6 kinase. Intravenous injection of caffeine at a physiological dose (5 mg/kg) in rats inhibited the phosphorylation of insulin-stimulated IRS-1 Tyr(612) and Akt Ser(473) in epitrochlearis muscle. Our results indicate that caffeine inhibits insulin signaling partly through the IKK/IRS-1 Ser(307) pathway, via a Ca(2+)- and AMPK-independent mechanism in skeletal muscle.
We investigated the protective effect of Brazilian propolis, a natural resinous substance produced by honeybees, against glycation stress in mouse skeletal muscles. Mice were divided into four ...groups: (1) Normal diet + drinking water, (2) Brazilian propolis (0.1%)-containing diet + drinking water, (3) normal diet + methylglyoxal (MGO) (0.1%)-containing drinking water, and (4) Brazilian propolis (0.1%)-containing diet + MGO (0.1%)-containing drinking water. MGO treatment for 20 weeks reduced the weight of the extensor digitorum longus (EDL) muscle and tended to be in the soleus muscle. Ingestion of Brazilian propolis showed no effect on this change in EDL muscles but tended to increase the weight of the soleus muscles regardless of MGO treatment. In EDL muscles, Brazilian propolis ingestion suppressed the accumulation of MGO-derived advanced glycation end products (AGEs) in MGO-treated mice. The activity of glyoxalase 1 was not affected by MGO, but was enhanced by Brazilian propolis in EDL muscles. MGO treatment increased mRNA expression of inflammation-related molecules, interleukin (IL)-1β, IL-6, and toll-like receptor 4 (TLR4). Brazilian propolis ingestion suppressed these increases. MGO and/or propolis exerted no effect on the accumulation of AGEs, glyoxalase 1 activity, and inflammatory responses in soleus muscles. These results suggest that Brazilian propolis exerts a protective effect against glycation stress by inhibiting the accumulation of AGEs, promoting MGO detoxification, and reducing proinflammatory responses in the skeletal muscle. However, these anti-glycation effects does not lead to prevent glycation-induced muscle mass reduction.
•Salicylate (SAL) has antidiabetic effects in humans.•Skeletal muscle contributes to whole-body glucose homeostasis.•We found that SAL is acutely taken up into rat skeletal muscles.•We also found ...that SAL stimulates 5′-AMP-activated protein kinase (AMPK).•The beneficial effects of SAL may be mediated by skeletal muscle AMPK.
Salicylate (SAL) has been recently implicated in the antidiabetic effect in humans. We assessed whether 5′-AMP-activated protein kinase (AMPK) in skeletal muscle is involved in the effect of SAL on glucose homeostasis. Rat fast-twitch epitrochlearis and slow-twitch soleus muscles were incubated in buffer containing SAL. Intracellular concentrations of SAL increased rapidly (<5min) in both skeletal muscles, and the Thr172 phosphorylation of the α subunit of AMPK increased in a dose- and time-dependent manner. SAL increased both AMPKα1 and AMPKα2 activities. These increases in enzyme activity were accompanied by an increase in the activity of 3-O-methyl-d-glucose transport, and decreases in ATP, phosphocreatine, and glycogen contents. SAL did not change the phosphorylation of insulin receptor signaling including insulin receptor substrate 1, Akt, and p70 ribosomal protein S6 kinase. These results suggest that SAL may be transported into skeletal muscle and may stimulate AMPK and glucose transport via energy deprivation in multiple muscle types. Skeletal muscle AMPK might be part of the mechanism responsible for the metabolic improvement induced by SAL.
Abstract Objective 5′-adenosine monophosphate-activated protein kinase (AMPK) is a key molecule of metabolic enhancement in skeletal muscle. We investigated whether metformin (MET) acts directly on ...skeletal muscle, is transported into skeletal muscle via organic cation transporters (OCTs), and activates AMPK. Materials/Methods Isolated rat epitrochlearis and soleus muscles were incubated in vitro either in the absence or in the presence of MET. The activation status of AMPK, the intracellular energy status, and glucose and MET transport activity were then evaluated. The effect of cimetidine, which is an OCT inhibitor, on AMPK activation was also examined. Results MET (10 mmol/L, ≥ 60 min) increased the phosphorylation of Thr172 at the catalytic α subunit of AMPK in both muscles. AMPK activity assays showed that both AMPKα1 and AMPKα2 activity increased significantly. The AMPK activation was associated with energy deprivation, which was estimated from the ATP, phosphocreatine (PCr), and glycogen content, and with increased rates of 3- O -methyl- d -glucose (3MG) transport. MET did not change the basal phosphorylation status of insulin receptor signaling molecules. MET was transported into the cytoplasm in a time-dependent manner, and cimetidine suppressed MET-induced AMPK phosphorylation and 3MG transport. Conclusion These results suggest that MET is acutely transported into skeletal muscle by OCTs, and stimulates AMPKα1 and α2 activity in both fast- and slow-twitch muscle types, at least in part by reducing the energy state.
Heat stress (HS) stimulates heat shock protein (HSP) 72 mRNA expression, and the period after an increase in HSP72 protein is characterized by enhanced glucose metabolism in skeletal muscle. We have ...hypothesized that, prior to an increase in the level of HSP72 protein, HS activates glucose metabolism by acutely stimulating 5′‐AMP‐activated protein kinase (AMPK). Rat epitrochlearis muscle was isolated and incubated either with or without HS (42°C) for 10 and 30 min. HS for 30 min led to an increase in the level of Hspa1a and Hspa1b mRNA but did not change the amount of HSP72 protein. However, HS for both 10 and 30 min led to a significant increase in the rate of 3‐O‐methyl‐d‐glucose (3MG) transport, and the stimulatory effect of 3MG transport was completely blocked by cytochalasin B. HS‐stimulated 3MG transport was also inhibited by dorsomorphin but not by wortmannin. HS led to a decrease in the concentration of ATP, phosphocreatine, and glycogen, to an increase in the level of phosphorylation of AMPKα Thr172, and to an increase in the activity of both AMPKα1 and AMPKα2. HS did not affect the phosphorylation status of insulin receptor signaling or Ca2+/calmodulin‐dependent protein kinase II. These results suggest that HS acts as a rapid stimulator of insulin‐independent glucose transport, at least in part by stimulating AMPK via decreased energy status. Although further research is warranted, heat treatment of skeletal muscle might be a promising method to promote glucose metabolism acutely.
Heat stress (HS) acutely stimulated glucose transport prior to an increase in the levels of heat shock protein 72 (HSP72) protein in isolated rat skeletal muscle. HS also led to a decrease in muscle energy status, and to an increase in the activity of 5′‐AMP‐activated protein kinase (AMPK). Heat treatment of skeletal muscle might be a promising method to promote glucose metabolism acutely.
We measured the forest biomass and biometrically derived net primary production (NPP) in a cool-temperate deciduous forest stand beneath a flux tower. NPP was calculated as the sum of the living ...biomass of new-season tissue in all organs (
B) and biomass of new-season tissue lost due to death (
L). Annual leaf-litter production was adopted as
L. We regarded the total tree growth in the stand as
B, and examined three methods for estimating
B to discuss the practicality of continuous measurement of NPP to compare with corresponding estimates of eddy-covariance based net ecosystem exchange (NEE). The three methods were diameter at breast height (DBH)–growth allometry by stem analysis of sample trees (SA method), DBH–growth allometry by core sample analysis of sample trees (CS method) and direct measurement of stem growth by tree census (TC method). The total annual tree growth in the forest stand estimated by the SA, CS and TC methods was 2.26, 1.60 and 2.38
Mg
ha
−1, respectively, and NPP was 5.64, 4.98 and 5.74
Mg
ha
−1. The slope of the regression of DBH against annual tree growth was slightly smaller for the CS method than for the SA method; the CS method underestimated the growth of several sample trees that had no clear main stem and, as a result, greatly underestimated B. To estimate B, the SA and CS methods depend on the use of DBH–growth allometry. Thus, it is difficult to determine species-dependent growth in natural mixed forests by these methods if only a few sample trees are used. In contrast, the TC method can directly and continuously measure the growth of all tree stems. Therefore, the TC method is the most suitable method for measuring NPP through annual measurements of tree diameter and leaf-litter production allowing for direct comparison with eddy-covariance based estimate of NEE.
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