Reducing Effect in Footing Resistance Against Heavy Impulse Current : Observation of Streamer in the Soil

ページ付に誤植あり（[486]→[386]）The streamer in the soil, which is considered to cause the reducing effect in footing resistance against heavy impulse current can be observed directly by means of an embedded film, intermediate electrode or chopped wave. By these observations, the form, size, propagating step and velocity of streamer in the soil have become clear

Association of Glycative Stress With Motor and Muscle Function

Glycative stress is a type of biological stress caused by non-enzymatic glycation reactions, which include advanced glycation end product (AGE) formation, AGE accumulation, glycation-driven dysfunction of proteins and cellular signaling, inflammation, oxidation, and tissue damage. Increased glycative stress derived from hyperglycemia and lifestyle disorders is a risk factor in metabolic and age-related diseases, such as type 2 diabetes, cardiovascular disease, cancer, Alzheimer’s disease, osteoporosis, and dementia. Studies have shown that AGE accumulation is correlated with the age-related loss of muscle mass and power output, also called sarcopenia. Mechanistically, dysfunctions of contractile proteins, myogenic capacity, and protein turnover can cause glycative stress-induced skeletal muscle dysfunction. Because the skeletal muscle is the largest metabolic organ in the body, maintaining skeletal muscle health is essential for whole-body health. Increasing awareness and understanding of glycative stress in the skeletal muscle in this review will contribute to the maintenance of better skeletal muscle function

AMPK is indispensable for overload-induced muscle glucose uptake and glycogenesis but dispensable for inducing hypertrophy in mice

Chronic muscle loading (overload) induces skeletal muscles to undergo hypertrophy and to increase glucose uptake. Although AMP-activated protein kinase (AMPK) reportedly serves as a negative regulator of hypertrophy and a positive regulator of glucose uptake, its role in overload-induced skeletal muscle hypertrophy and glucose uptake is unclear. This study aimed to determine whether AMPK regulates overload-induced hypertrophy and glucose uptake in skeletal muscles. To this end, skeletal muscle overload was induced through unilateral synergist ablations in wild-type (WT) and transgenic mice, expressing the dominant-negative mutation of AMPK (AMPK-DN). After 14 days, parameters, including muscle fiber cross-sectional area (CSA), glycogen level, and in vivo [3 H]-2-deoxy-D-glucose uptake, were assessed. No significant difference was observed in body weight or blood glucose level between the WT and AMPK-DN mice. However, the 14-day muscle overload activated the AMPK pathway in WT mice skeletal muscle, whereas this response was impaired in the AMPK-DN mice. Despite a normal CSA gain in each fiber type, the AMPK-DN mice demonstrated a significant impairment of overload-induced muscle glucose uptake and glycogenesis, compared to WT mice. Moreover, 14-day overload-induced changes in GLUT4 and HKII expression levels were reduced in AMPK-DN mice, compared to WT mice. This study demonstrated that AMPK activation is indispensable for overload-induced muscle glucose uptake and glycogenesis; however, it is dispensable for the induction of hypertrophy in AMPK-DN mice. Furthermore, the AMPK/GLUT4 and HKII axes may regulate overload-induced muscle glucose uptake and glycogenesis

Methylglyoxal reduces molecular responsiveness to 4 weeks of endurance exercise in mouse plantaris muscle

Endurance exercise triggers skeletal muscle adaptations, including enhanced insulin signaling, glucose metabolism, and mitochondrial biogenesis. However, exercise-induced skeletal muscle adaptations may not occur in some cases, a condition known as exercise-resistance. Methylglyoxal (MG) is a highly reactive dicarbonyl metabolite and has detrimental effects on the body such as causing diabetic complications, mitochondrial dysfunction, and inflammation. This study aimed to clarify the effect of methylglyoxal on skeletal muscle molecular adaptations following endurance exercise. Mice were randomly divided into 4 groups (n = 12 per group): sedentary control group, voluntary exercise group, MG-treated group, and MG-treated with voluntary exercise group. Mice in the voluntary exercise group were housed in a cage with a running wheel, while mice in the MG-treated groups received drinking water containing 1% MG. Four weeks of voluntary exercise induced several molecular adaptations in the plantaris muscle, including increased expression of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α), mitochondria complex proteins, toll-like receptor 4 (TLR4), 72-kDa heat shock protein (HSP72), hexokinase II, and glyoxalase 1; this also enhanced insulin-stimulated Akt Ser473 phosphorylation and citrate synthase activity. However, these adaptations were suppressed with MG treatment. In the soleus muscle, the exercise-induced increases in the expression of TLR4, HSP72, and advanced glycation end products receptor 1 were inhibited with MG treatment. These findings suggest that MG is a factor that inhibits endurance exercise-induced molecular responses including mitochondrial adaptations, insulin signaling activation, and the upregulation of several proteins related to mitochondrial biogenesis, glucose handling, and glycation in primarily fast-twitch skeletal muscle

Glycative stress and skeletal muscle dysfunctions: as an inducer of "Exercise-Resistance."

Skeletal muscle, the largest tissue in the body, is often overlooked for its role as a locomotor organ, however over the past few decades it has been revealed that it also has an important role as a metabolic organ. In recent years, its role as an endocrine organ that controls the homeostatic functions of organs throughout the body mediated by myokine secretion has come under close scrutiny. Skeletal muscle is indispensable for our daily life activities, and in order to maintain its function, it is necessary to understand the factors that deteriorate muscle function and establish a countermeasure. Glycative stress has recently received attention as a factor that impairs skeletal muscle function. Accumulation of advanced glycation end products (AGEs) in skeletal muscle impairs contractile function and myogenic potential. Furthermore, AGEs in the blood elicit inflammatory signals through binding to RAGE (Receptor for AGEs) expressed on muscle cells, resulting in muscle proteolysis. Habitual exercise is important to mitigate the negative effects of such glycative stress on skeletal muscle. On the other hand, it is known that the beneficial effects of exercise vary among individuals. The state in which the effects of exercise are difficult to obtain is called "exercise-resistance, " and we hypothesize that glycative stress may be one of the causes of exercise-resistance. In this paper, we will discuss the possibility of glycative stress as an inducer of exercise resistance and summarize its impacts on skeletal muscle

Regulatory Mechanism of Skeletal Muscle Glucose Transport by Phenolic Acids

Type 2 diabetes mellitus (T2DM) is one of the most severe public health problems in the world. In recent years, evidences show a commonness of utilization of alternative medicines such as phytomedicine for the treatment of T2DM. Phenolic acids are the most common compounds in non-flavonoid group of phenolic compounds and have been suggested to have a potential to lower the risk of T2DM. Skeletal muscle is the major organ that contributes to the pathophysiology of T2DM. Studies have shown that several phenolic acids (caffeic acid, chlorogenic acid, gallic acid, salicylic acid, p-coumaric acid, ferulic acid, sinapic acid) have antidiabetic effects, and these compounds have been implicated in the regulation of skeletal muscle glucose metabolism, especially glucose transport. Glucose transport is a major regulatory step for whole-body glucose disposal, and the glucose transport processes are regulated mainly through two different systems: insulin-dependent and insulin-independent mechanism. In this chapter, we reviewed recent experimental evidences linking phenolic acids to glucose metabolism focusing on insulin-dependent and insulin-independent glucose transport systems and the upstream signaling events in skeletal muscle

Caffeine modulates phosphorylation of insulin receptor substrate-1 and impairs insulin signal transduction in rat skeletal muscle

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 Ser9 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 Ser307 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 Ser789 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 Tyr612 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