Dataset Information

Nitric oxide stimulates glucose transport and metabolism in rat skeletal muscle in vitro.

ABSTRACT: 1. The effects of the nitric oxide (NO) donor sodium nitroprusside (SNP) on the rates of glucose transport and utilization and its interaction with insulin were investigated in rat soleus muscle in vitro. SNP stimulated the rate of 2-deoxyglucose transport and insulin-mediated (100 mu-units/ml) rates of both net and [14C]lactate release and the rate of glucose oxidation. The effects of SNP were independent of the concentration-dependent effects of insulin on glucose metabolism. 2. SNP stimulated the insulin-stimulated rates of net and [14C]lactate release and glucose oxidation in a concentration-dependent manner. The rate of [14C]lactate release was also stimulated by another NO donor, (Z)-1-(N-[aminopropyl]-N-[4-(3-aminopropylammonio) butyl]-amino)-diazen-l-ium-1,2-diolate (spermine NONOate). 3. SNP at 5, 10 and 15 mM inhibited the insulin-stimulated rate of glycogen synthesis and this rate was further decreased at 20 and 25 mM SNP. SNP did not affect the rate of glycogen synthesis in the absence of insulin. 4. Haemoglobin, which is a NO scavenger, prevented the stimulation of the rates of [14C]lactate release by SNP or spermine NONOate. 5. The cGMP content was increased maximally (by approx. 80-fold) within 15 min by SNP (15 mM). The cGMP content, raised maximally by SNP, was significantly decreased by the guanylate cyclase inhibitor LY-83583 (10 microM). The cGMP analogue 8-bromo-cGMP (100 microM) significantly increased the rate of net lactate release. 6. LY-83583 significantly inhibited SNP-stimulated rates of 2-deoxyglucose transport, [4C]lactate release and glucose oxidation. Methylene Blue (another guanylate cyclase inhibitor) also inhibited SNP-stimulated rates of [14C]lactate release. 7. The results suggest that in rat skeletal muscle: (a) nitric oxide (from SNP or spermine NONOate) increases the rate of glucose transport and metabolism, an effect independent of insulin; (b) SNP inhibits insulin-mediated rates of glycogen synthesis; (c) SNP stimulates cGMP formation, which mediates, at least partly, the effects on glucose metabolism; (d) nitric oxide-mediated stimulation of glucose utilization might occur in fibre contraction. The implications of the effects of NO on glucose metabolism are discussed.

SUBMITTER: Young ME

PROVIDER: S-EPMC1218180 | biostudies-other | 1997 Feb

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:The principal goal of the present study was to test the hypothesis that cytokines modulate glucose transport in skeletal muscle by increasing nitric oxide production. Cultured L6 skeletal muscle cells were incubated in the presence of tumour necrosis factor-alpha, interferon-gamma or lipopolysaccharide (LPS) alone or in combination for 24 h. Neither cytokines nor LPS alone induced NO production, as measured by nitrite concentrations in the medium. However, when used in combination, the two cytokines significantly stimulated NO production, and this effect was synergistically enhanced by the presence of LPS. Reverse transcriptase-PCR (RT-PCR) analysis revealed that NO release was associated with the induction of inducible (macrophage-type) NO synthase (iNOS). The increase in iNOS expression was confirmed at the protein level by Western-blot analysis and NADPH/diaphorase histochemical staining. Cytokines and LPS markedly increased basal glucose transport in L6 myocytes. Insulin also stimulated basal glucose transport, but significantly less in cells chronically exposed to cytokines/LPS. The sensitivity of L6 muscle cells to insulin-stimulated glucose transport was also significantly decreased by cytokines/LPS treatment. The NOS inhibitor NG-nitro-l-arginine methyl ester (l-NAME) inhibited nitrite production in cytokine/LPS-treated cells, and this prevented the increase in basal glucose transport and restored muscle cell responsiveness to insulin. Cytokines/LPS exposure significantly increased GLUT1 transporter protein levels but decreased GLUT4 expression in L6 cells. l-NAME treatment prevented the increase in GLUT1 protein content but failed to restore GLUT4 transporter levels. These results demonstrate that cytokines and LPS affect glucose transport and insulin action by inducing iNOS expression and NO production in skeletal muscle cells. The data further indicate that cytokines and LPS increase the expression of the GLUT1 transporter protein by an NO-dependent mechanism.

Project description:The cellular mechanisms whereby prior exercise enhances insulin-stimulated glucose transport (GT) are not well understood. Previous studies suggested that a prolonged increase in phosphorylation of Akt substrate of 160 kDa (AS160) may be important for the postexercise increase in insulin sensitivity. In the current study, the effects of in vivo exercise and in vitro contraction on subsequent insulin-stimulated GT were studied separately and together. Consistent with results from previous studies, prior exercise resulted in an increase in AS160 (642)Thr phosphorylation immediately after exercise in rat epitrochlearis muscles, and this increase remained 3 h postexercise concomitant with enhanced insulin-stimulated GT. For experiments with in vitro contraction, isolated rat epitrochlearis muscles were electrically stimulated to contract in the presence or absence of rat serum. As expected, insulin-stimulated GT measured 3 h after electrical stimulation in serum, but not after electrical stimulation without serum, exceeded resting controls. Immediately after electrical stimulation with or without serum, phosphorylation of both AS160 (detected by phospho-Akt substrate, PAS, antibody, or phospho-(642)Thr antibody) and its paralog TBC1D1 (detected by phospho-(237)Ser antibody) was increased. However, both AS160 and TBC1D1 phosphorylation had reversed to resting values at 3 h poststimulation with or without serum. Increasing the amount of exercise (from 1 to 2 h) or electrical stimulation (from 5 to 10 tetani) did not further elevate insulin-stimulated GT. In contrast, the combination of prior exercise and electrical stimulation had an additive effect on the subsequent increase in insulin-stimulated GT, suggesting that these exercise and electrical stimulation protocols may amplify insulin-stimulated GT through distinct mechanisms, with a persistent increase in AS160 phosphorylation potentially important for increased insulin sensitivity after exercise, but not after in vitro contraction.

Project description:L-Arginine (L-Arg), the precursor of nitric oxide (NO), plays an important role in muscle function. Fast-twitch glycolytic fibres are more susceptible to age-related atrophy than slow-twitch oxidative fibres. The effect of L-Arg/NO on protein metabolism of fast- and slow-twitch muscle fibres was evaluated in chickens. In Exp. 1, 48 chicks at 1 day old were divided into 4 groups of 12 birds and subjected to 4 treatments: basal diet without supplementation or supplemented with 1% L-Arg, and water supplemented with or without L-nitro-arginine methyl ester (L-NAME, 18.5 mM). In Exp. 2, 48 chicks were divided into 4 groups of 12 birds fed with the basal diet and subjected to the following treatments: tap water (control), tap water supplemented with L-NAME (18.5 mM), or molsidomine (MS, 0.1 mM), or 18.5 mM L-NAME + 0.1 mM MS (NAMS). The regulatory effect of L-Arg/NO was further investigated in vitro with myoblasts obtained from chicken embryo pectoralis major (PM) and biceps femoris (BF). In vivo, dietary L-Arg supplementation increased breast (+14.94%, P < 0.05) and thigh muscle mass (+23.40%, P < 0.05); whereas, MS treatment had no detectable influence. However, L-NAME treatment blocked the beneficial influence of L-Arg on muscle development. L-Arg decreased (P < 0.05) protein synthesis rate, phosphorylated mTOR and ribosomal protein S6 kinase beta-1 (p70S6K) levels in breast muscle, which was recovered by L-NAME treatment. In vitro, L-Arg or sodium nitroprusside (SNP) reduced protein synthesis rate, suppressed phosphorylated mTOR/p70S6K and decreased atrogin-1 and muscle RING finger 1 (MuRF1) in myoblasts from PM muscle (P < 0.05). L-NAME abolished the inhibitory effect of L-Arg on protein synthesis and the mTOR/p70S6K pathway. However, myoblasts from BF muscle showed the weak influence. Moreover, blocking the mTOR/p70S6K pathway with rapamycin suppressed protein synthesis of the 2 types of myoblasts; whereas, the protein expression of atrogin-1 and MuRF1 levels were restricted only in myoblasts from PM muscle. In conclusion, L-Arg/NO/mTOR/p70S6K pathway enhances protein accumulation and muscle development in fast-twitch glycolytic muscle in chickens. L-Arg/NO regulates protein turnover in a muscle fibre specific way, which highlights the potential clinical application in fast-twitch glycolytic muscle fibres.

Project description:Recently, we showed that administration of the angiotensin-converting enzyme inhibitor enalapril to aged rats attenuated muscle strength decline and mitigated apoptosis in the gastrocnemius muscle. The aim of the present study was to investigate possible mechanisms underlying the muscle-protective effects of enalapril. We also sought to discern the effects of enalapril mediated by nitric oxide (NO) from those independent of this signaling molecule. Eighty-seven male Fischer 344?×?Brown Norway rats were randomly assigned to receive enalapril (n?=?23), the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; n?=?22), enalapril + L-NAME (n?=?19), or placebo (n?=?23) from 24 to 27 months of age. Experiments were performed on the tibialis anterior muscle. Total NOS activity and the expression of neuronal, endothelial, and inducible NOS isoforms (nNOS, eNOS, and iNOS) were determined to investigate the effects of enalapril on NO signaling. Transcript levels of tumor necrosis factor-alpha (TNF-?) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1?) were assessed to explore actions of enalapril on inflammation and mitochondrial biogenesis, respectively. Protein expression of energy-sensing and insulin signaling mediators, including protein kinase B (Akt-1), phosphorylated Akt-1 (pAkt-1), mammalian target of rapamycin (mTOR), AMP-activated protein kinase subunit alpha (AMPK?), phosphorylated AMPK? (pAMPK?), and the glucose transporter GLUT-4, was also determined. Finally, the generation of hydrogen peroxide (H2O2) was quantified in subsarcolemmal (SSM) and intermyofibrillar (IFM) mitochondria. Enalapril increased total NOS activity, which was prevented by L-NAME co-administration. eNOS protein content was enhanced by enalapril, but not by enalapril + L-NAME. Gene expression of iNOS was down-regulated by enalapril either alone or in combination with L-NAME. In contrast, protein levels of nNOS were unaltered by treatments. The mRNA abundance of TNF-? was reduced by enalapril relative to placebo, with no differences among any other group. PCG-1? gene expression was unaffected by enalapril and lowered by enalapril + L-NAME. No differences in protein expression of Akt-1, pAkt-1, AMPK?, pAMPK?, or GLUT-4 were detected among groups. However, mTOR protein levels were increased by enalapril compared with placebo. Finally, all treatment groups displayed reduced SSM, but not IFM H2O2 production relative to placebo. Our data indicate that enalapril induces a number of metabolic adaptations in aged skeletal muscle. These effects result from the concerted modulation of NO and angiotensin II signaling, rather than from a dichotomous action of enalapril on the two pathways. Muscle protection by enalapril administered late in life appears to be primarily mediated by mitigation of oxidative stress and pro-inflammatory signaling.

Dataset Information

Nitric oxide stimulates glucose transport and metabolism in rat skeletal muscle in vitro.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets