Role of insulin-induced reactive oxygen species in the insulin signaling pathway

Oxidants, including hydrogen peroxide (H2O2), have been recognized for years to mimic insulin action on glucose transport in adipose cells. Early studies also demonstrated the complementary finding that H2O2 was elaborated during treatment of cells with insulin, suggesting that cellular H2O2 generation was integral to insulin signaling. Recently, reactive oxygen species elicited by various hormones and growth factors have been shown to affect signal transduction pathways in various cell types. We recently reported that insulin-stimulated H2O2 modulates proximal and distal insulin signaling, at least in part through the oxidative inhibition of protein tyrosine phosphatases (PTPases) that negatively regulate the insulin action pathway. Nox4, a homologue in the family of NADPH oxidase catalytic subunits, was found to be prominently expressed in insulin-sensitive cells. By various molecular approaches, Nox4 was shown to mediate insulin-stimulated H2O2 generation and impact the insulin signaling cascade. Overexpression of Nox4 also significantly reversed the inhibition of insulin-stimulated receptor tyrosine phosphorylation by PTP1B, a widely expressed PTPase implicated in the negative regulation of insulin signaling, by inhibiting its catalytic activity. These recent studies have provided insight into Nox4 as a novel molecular link between insulin-stimulated reactive oxygen species and mechanisms involved in their modulation of insulin signal transduction.     

Insulin binding and glucose metabolism in adipocytes of streptozotocin-diabetic rats.

To investigate the mechanism of the cellular insulin insensitivity of diabetic rats, insulin binding, glucose transport, and glucose oxidation were studied in adipocytes from streptozotocin-diabetic rats. Increased insulin binding was found in cells from diabetic rats, and this was due to an increased number of insulin receptors rather than a change in receptor affinity. Basal and insulin-stimulated glucose oxidation was decreased in adipocytes from diabetic rats when the data are expressed in absolute terms or as percent increased above basal. Although the absolute rate of basal and insulin-stimulated glucose transport was decreased in adipocytes from diabetic rats, the percent increase above basal of insulin-stimulated glucose transport was not decreased. In conclusion, although the cellular insulin insensitivity exists in adipocytes from diabetic rats, the number of insulin receptors was increased, coupling between insulin receptors and the glucose transport system is intact in adipocytes from diabetic rats, and a defect in intracellular glucose metabolism rather than glucose transport plays a major role in the insulin insensitivity of adipocytes from diabetic rats.     

积雪草酸改善小鼠脂肪细胞胰岛素抵抗的机制研究

 目的： 观察番石榴叶三萜化合物积雪草酸对小鼠3T3-L1前脂肪细胞增殖、分化以及胰岛素抵抗脂肪细胞糖脂代谢的影响并探讨其作用机制。方法：MTT法检测药物对3T3-L1前脂肪细胞增殖的影响;油红O染色法观察药物对其分化的影响。地塞米松诱导建立脂肪细胞胰岛素抵抗模型,药物干预后采用葡萄糖氧化酶法检测培养液中葡萄糖消耗量;比色法检测游离脂肪酸浓度;ELISA法检测脂联素水平;Western blotting法检测过氧化物酶体增殖物激活受体γ（PPARγ）和蛋白酪氨酸磷酸酶1B(PTP1B)蛋白表达的变化。结果：与溶媒对照组相比,积雪草酸在10~100 μmol/L时能显著促进3T3-L1前脂肪细胞增殖,但明显抑制其分化（P<0.05或P<0.01）;在30和100 μmol/L时,无论是基础状态还是胰岛素刺激状态,均能显著增加胰岛素抵抗脂肪细胞葡萄糖的消耗,减少游离脂肪酸的产生（P<0.05）;其对胰岛素抵抗脂肪细胞的脂联素分泌和PPARγ蛋白表达无明显影响（P>0.05）,但能显著下调PTP1B蛋白的表达（P<0.05或P<0.01）。结论：积雪草酸能显著改善脂肪细胞胰岛素抵抗,增加胰岛素抵抗脂肪细胞葡萄糖的消耗和减少游离脂肪酸的产生,其机制可能是其下调胰岛素信号转导的负性调节因子PTP1B的表达,增强胰岛素信号转导,从而改善胰岛素抵抗。     

Hyperglycemia in vitro attenuates insulin-stimulated chemokinesis in normal human neutrophils. Role of protein kinase C activation.

This study was performed to test whether the inhibitory effect of elevated D-glucose concentrations on insulin-stimulated chemokinesis in normal human neutrophils is mediated by increase in protein kinase C (PKC) activity. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) at 0-100 nM dose-dependently inhibited neutrophil random locomotion in the absence of insulin. Sub-optimal concentrations of PMA (0.1-0.5 nM) inhibited the chemokinetic effect of 160 microU/mL insulin in a dose-dependent way. The specific PKC inhibitor bisindolylmaleimide (GF 109203x) did not affect the insulin-stimulated chemokinesis at 5 mM glucose but restored the chemokinetic effect of insulin at 15 mM glucose. These results therefore suggest that glucose-induced PKC activation may mediate the inhibitory effects of high glucose levels on insulin-stimulated chemokinesis in normal human neutrophils.     

TNF-α介导的11-β羟类固醇脱氢酶1表达和活性变化对3T3-L1脂肪细胞胰岛素敏感性的影响

目的：观察肿瘤坏死因子α（TNF-α）介导的11-β羟类固醇脱氢酶1（11-β HSD-1）表达和活性变化对3T3-L1脂肪细胞胰岛素敏感性的影响。方法:以TNF-α以及TNF-α分别与阿司匹林、2’-hydroxyflavanone和RU486联合作用3T3-L1脂肪细胞，然后检测细胞11-β HSD-1 mRNA表达和活性以及胰岛素刺激的葡萄糖摄取能力。 结果:TNF-α增加3T3-L1脂肪细胞11-β HSD-1 mRNA表达和活性，同时降低细胞胰岛素刺激的葡萄糖摄取。阿司匹林减轻了TNF-α对11-β HSD-1 mRNA表达和活性的上调作用，并减轻TNF-α对胰岛素刺激的葡萄糖摄取的抑制作用；11-β HSD-1活性特异抑制剂2’-hydroxyflavanone和皮质醇受体拮抗剂RU486也可减轻TNF-α对胰岛素刺激的葡萄糖摄取的抑制作用。结论:TNF-α可通过提高3T3-L1脂肪细胞11-β HSD-1的表达和活性而降低细胞对胰岛素的敏感性。     

短期和长期过氧化状态对HepG2细胞Sestrin2以及PKB胰岛素信号的影响

目的探讨短期和长期过氧化状态对Sestrin2（Sesn2）及PKB胰岛素信号的影响及调控机理。方法在人肝HepG2细胞株以葡萄糖氧化酶（GO）和含糖培养基共培养4h或16h分别造成细胞短期和长期氧化状态;或胰岛素刺激（15min或16h）,然后以蛋白印迹法检测Sesn2蛋白含量和胰岛素信号变化（如PKBSer473和Thr308磷酸化水平）。为明确Sesn2作用,用Sesn2siRNA沉默Sesn2后,探讨胰岛素信号及相关信号变化。结果GO和胰岛素处理均可明显增加HepG2细胞Sens2蛋白水平;GO短期（4h）处理可明显刺激胰岛素标志性信号分子PKBSer473的磷酸化并刺激细胞Sesn2蛋白升高;而长时间（16h）GO处理则可抑制胰岛素刺激的Sesn2表达作用;Sesn2siRNA转染后．可增强胰岛素刺激的PKBSer473和Thr308位点的磷酸化作用。因此,Sesn2对上述不同机制调控的两个PKB磷酸化位点均有抑制作用。结论HepG2细胞在短期氧化状态下,可激活PKB活性（PKBSer473磷酸化）并诱导Sesn2蛋白表达;长期过氧化及胰岛素刺激情况下能激活Sesn2功能,而Sesn2可分别通过对PKBSer473及PKBThr308两个活性位点的抑制性作用和调控。实现对胰岛素信号及PKB活性的长期负反馈平衡作用。     

Correlation of food intake in lambs with adipocyte glucose metabolism and NEFA release

1. Experiments were conducted with lambs to determine the correlation between food intake, rate of glucose incorporation into CO(2) and lipids, and rate of lipid mobilization by their isolated omental adipocytes.2. During the interval between weaning and slaughter average daily dry matter (ADDM) intakes of the individual lambs were significantly correlated with average daily gains; however, the ratio of ADDM intake to body wt.((3/4)) was similar in all individuals.3. The average size of adipocytes for each lamb, as determined by lipid: protein ratios, was not significantly correlated with food intake.4. Oxidation of glucose to CO(2) and the total measured glucose incorporation by the adipocytes were significantly and negatively correlated with lamb ADDM intakes at low levels of glucose (0.1 mg/ml.), whereas rates of lipogenesis from glucose were similar for all intake levels.5. Insulin-induced increases in glucose utilization were positively and significantly correlated with ADDM intakes to the extent that insulin had over twice the effect on the adipocytes from high-intake lambs as it had on those from low-intake lambs. The minimum effective dose of insulin necessary to significantly increase glucose utilization by the adipocytes was also positively and significantly correlated with the ADDM intakes of the lambs.6. Basal NEFA release rates were higher for adipocytes from low-intake lambs. Epinephrine significantly increased NEFA release rates, independent of lamb intakes.7. A larger number of adipocytes in the high-intake lambs means that they would have a greater total potential to lower blood glucose, particularly when they are under the effects of normal circulating levels of insulin. The amount of glucose removed from the glucose pool could be the feed-back signal which results in a high long-term food intake.     

Dissection of signals controlling T cell function and activation: H7, an inhibitor of protein kinase C, blocks induction of primary T cell proliferation by suppressing interleukin (IL)2 receptor expression without affecting IL2 production

T cell activation induced via cross-linking of the T cell receptor (TcR) stimulates hydrolysis of phosphatidylinositol to the second messengers diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). DAG is necessary for the activation and function of protein kinase C (PKC) which is suggested to play a key role in the cascade of signal transduction when translocated from the cytosol to the cell membrane. In this report, we investigated responses of resting vs. activated Ly-2+ and L3T4+ T lymphocytes in the presence of the PKC inhibitor H7 [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine]. H7 inhibited the induction of primary T cell proliferation, while interleukin 2 (IL 2) production was fully retained. The effect of the PKC inhibitor on primary T cells depended on the type of ligand interacting with the TcR: increasing doses of concanavalin A or of immobilized anti-CD3 monoclonal antibody (mAb), but not of anti-V beta 8 or of anti-TcR alpha/beta mAb, partly overcame the blockade, indicating a differential signaling compared to the former stimuli. The blockade of T cell proliferation by H7 was not due to an inhibition of PKC translocation, but occurred even 4-8 h after T cell induction and correlated with a significant reduction of IL 2 receptor (IL 2R) expression. In contrast, the mRNA levels of IL 2R and the cellular proto-oncogenes c-fos and c-myc were not affected. On activated T cells, H7 neither blocked proliferation nor IL2R expression. Consequently, H7 dissects the signal resulting in T cell proliferation from those governing the triggering of other T cell functions, i.e. IL 2 production, during primary responses of Ly-2+ or L3T4+ murine T lymphocytes.     

Over-expression of NYGGF4 (PID1) inhibits glucose transport in skeletal myotubes by blocking the IRS1/PI3K/AKT insulin pathway

IntroductionDefects in insulin-stimulated glucose uptake in muscle are the important early events in the pathogenesis of insulin resistance. NYGGF4 (also named PID1) is a recently discovered gene which is suggested to be associated with obesity-associated insulin resistance. In this study, we aimed to investigate the effects of NYGGF4 on glucose uptake and insulin signaling in rat skeletal muscle cells.MethodsRat L6 myoblasts were transfected with either an empty vector or an NYGGF4-expressing vector and induced to differentiate into mature L6 skeletal myotubes. Glucose uptake was determined by measuring uptake of 2-deoxy-d-[³H] glucose. Immunoblotting was performed to detect the translocation of insulin-sensitive glucose transporter 4 (GLUT4). Immunoblotting was also used to measure phosphorylation and total protein levels of the insulin signaling proteins including insulin receptor (IR), insulin receptor substrate 1 (IRS1), Akt, extracellular signal-regulated kinase 1 and 2 (ERK1/2), p38, and c-Jun-N-terminal kinase (JNK).ResultsNYGGF4 over-expression in L6 skeletal myotubes reduced insulin-stimulated glucose uptake and impaired insulin-stimulated GLUT4 translocation. It also diminished insulin-stimulated tyrosine phosphorylation of IRS1 and serine phosphorylation of Akt without affecting the phosphorylation of IR, ERK1/2, p38, or JNK.ConclusionsOver-expression of NYGGF4 inhibits glucose transport in skeletal myotubes by blocking the IRS1/PI3K/AKT insulin pathway. These observations highlight the potential role of NYGGF4 in glucose homeostasis and the development of insulin resistance in obesity.     

PKC-mediated modulation of L-type calcium channels may contribute to fat-induced insulin resistance

Increased intracellular free calcium [Ca2+]i has been noted in adipocytes, platelets, and leukocytes of subjects with insulin resistance syndrome or allied disorders. In rodent studies, measures which increase [Ca2+]i in adipocytes and skeletal muscle are associated with impaired insulin signaling, attributable at least in part to diminished ability of insulin to activate phosphoserine phosphatase-1 (PP-1). In fat-fed insulin resistant rats, pre-treatment with a drug that selectively chelates intracellular calcium eliminates about half of the decrement in insulin-stimulated glucose uptake induced by fat feeding; since this chelator does not influence the insulin sensitivity of chow-fed rats, it is reasonable to suspect that fat feeding boosts [Ca2+]i in skeletal muscle, and that this effect is partially responsible for the associated reduction in insulin sensitivity. Clinical insulin resistance is associated with increased levels of triglycerides and other fatty acid metabolites in muscle fibers; this can give rise to diacylglycerol-mediated activation of PKC, which in turn compromises insulin signaling by triggering kinase cascades that phosphorylate IRS-1 on key serine residues. Yet there is also evidence that, in skeletal muscle, PKC activity up-regulates the function of L-type calcium channels, increasing their maximal conductance while left-shifting their voltage dependence. Thus, the PKC activation associated with fat overexposure might be expected to boost basal [Ca2+]i in skeletal muscle, potentially impeding insulin-mediated activation of PP-1. This hypothesis is consistent with several clinical studies demonstrating that long-acting inhibitors of L-type calcium channels can improve insulin sensitivity in overweight hypertensives; it should be readily testable in rodent models of fat-induced insulin resistance. Since parathyroid hormone can act on adipocytes and muscle to boost [Ca2+]i, mild secondary hyperparathyroidism associated with low calcium intakes and poor vitamin D status may contribute to insulin resistance, consistent with certain clinical and epidemiological findings. Magnesium, often thought of as a mild calcium antagonist, appears to have favorable effects on insulin sensitivity and risk for diabetes, and recent evidence indicates that increases of intracellular magnesium within the physiological range can diminish calcium influx through phosphorylated L-type calcium channels. It will be of interest to determine whether calcium antagonism does indeed underlie the favorable influence of good magnesium status on insulin function. A report that chromium picolinate can induce the plasmalemmal Ca2+-ATPase in smooth muscle cells, raises the possibility that modulation of calcium transport might play a role in the insulin-sensitizing efficacy of bioactive chromium.     

糖皮质激素对3T3-L1脂肪细胞PI-3K、p38 MAPK磷酸化的影响

目的： 观察地塞米松对3T3-L1脂肪细胞糖转运活动的影响,及介导糖转运的胰岛素信号通路PI-3K/AKT、p38 MAPK途径在其中的作用,探讨糖皮质激素诱导脂肪细胞胰岛素抵抗的可能机制。方法: 将3T3-L1脂肪细胞与1 μmol/L地塞米松共孵育48 h,加或不加100 nmol/L胰岛素继续温育30min。以葡萄糖氧化酶法测定3T3-L1脂肪细胞中糖转运活动,以Western blotting测定3T3-L1脂肪细胞Glut4的表达及分布、Akt、phospho-Akt、p38 MAPK、phospho-p38 MAPK的蛋白表达水平。结果: 地塞米松抑制3T3-L1脂肪细胞的糖转运活动。对细胞内总Glut4蛋白表达无影响,但抑制了胰岛素刺激的Glut4转位,同时抑制了胰岛素激活的Akt、p38 MAPK磷酸化水平。结论: 地塞米松抑制胰岛素激活的PI-3K/Akt、p38 MAPK信号途径,影响Glut4的转位及活性,下调胰岛素刺激的葡萄糖转运,并可能由此诱导胰岛素抵抗的发生。     

Insulin hypersensitivity in mice lacking the V1b vasopressin receptor

We have reported that [Arg⁸]-vasopressin-stimulated insulin release is blunted in islet cells isolated from V1b receptor-deficient ( V1bR ^−/−) mice. In this study, we used V1bR ^−/− mice to examine the physiological role of the V1b receptor in regulating blood glucose levels in vivo , and we found that the fasting plasma glucose, insulin and glucagon levels were lower in V1bR ^−/− mice than in wild-type ( V1bR ^+/+) mice. Next, we evaluated glucose tolerance by performing an intraperitoneal glucose tolerance test (GTT). The plasma glucose and insulin levels during the GTT were lower in V1bR ^−/− mice than in V1bR ^+/+ mice. An insulin tolerance test (ITT) revealed that, after insulin administration, plasma glucose levels were lower in V1bR ^−/− mice than in V1bR ^+/+ mice. In addition, a hyperinsulinaemic–euglycaemic clamp study showed that the glucose infusion rate was increased in V1bR ^−/− mice, indicating that insulin sensitivity was enhanced at the in vivo level in V1bR ^−/− mice. Furthermore, we found that the V1b receptor was expressed in white adipose tissue and that insulin-stimulated phosphorylation of Akt as an important signaling molecule was increased in adipocytes isolated from V1bR ^−/− mice. Thus, the blockade of the V1b receptor could result, at least in part, in enhanced insulin sensitivity by altering insulin signalling in adipocytes.     

Real-time imaging elucidates the role of H(2)O(2) in regulating kinetics of epidermal growth factor-induced and Src-mediated tyrosine phosphorylation signaling

Reversible oxidation is emerging as an important regulatory mechanism in protein tyrosine phosphorylation. Generation of hydrogen peroxide (H(2)O(2)), upon growth factor stimulation, is hypothesized to inhibit activity of protein tyrosine phosphatases (PTPs). This ensures that protein tyrosine kinases can elevate the steady-state level of protein tyrosine phosphorylation, which then allows propagation of the tyrosine phosphorylation signal. However, the effects of H(2)O(2) on the kinetics of tyrosine phosphorylation signaling remain poorly understood, especially in living cells. Therefore, we used a genetically encoded Src kinase-specific biosensor based on fluorescence resonance energy transfer (FRET) to image the kinetics of the Src-mediated tyrosine phosphorylation signaling (Src signaling) induced by epidermal growth factor (EGF). We examined the kinetics under increased and decreased H(2)O(2) levels. Through a straightforward, quantitative analysis method which characterized the signaling kinetics, we demonstrated that H(2)O(2) modulated the amplitude and duration of the signal by inhibiting PTPs' activity. Our evidence also suggested the effect of H(2)O(2) on Src activation is mediated by H(2)O(2)-dependent inhibition of PTPs. Furthermore, we provide evidence showing global elevation of intracellular H(2)O(2) level attenuates EGF-induced Src signaling.     

Sensitivity of protein tyrosine phosphatase activity to the redox environment, cytochrome C, and microperoxidase

Protein tyrosine phosphatase activity depends on a catalytic thiolate group on an acidic cysteine residue that is sensitive to reactive oxygen species. Representative of this family of enzymes is protein tyrosine phosphatase 1B (PTP1B), a major target for type 2 diabetes therapy. PTP1B is sensitive to hydrogen peroxide (H2O2) in vitro and in cells. It is also sensitive to glutathionylation by glutathione disulfide (GSSG). The sensitivity of PTP1B to the redox state of its environment was partially characterized in vitro by examination of phosphatase activity in the presence of various concentrations of glutathione (GSH) and GSSG. Enzyme sensitivity to glutathionylation was dependent on the amount of available thiol groups and increased as GSH concentration was increased. The half-inhibitory concentration for H2O2 was much less than that of GSSG in the presence of low concentrations of GSH, indicating that reaction with H2O2 is much more likely than is glutathionylation by GSSG. PTP1B and a related oxidant-sensitive phosphatase, PTEN, were also sensitive to the lipid peroxidation by-product 4-hydroxynonenal. Furthermore, PTP1B was inhibited by cytochrome c and microperoxidase. Taken together, these data suggest that not only H2O2, but also a variety of redox-active metabolites and hemes can oxidatively inactivate PTPs with potentially profound implications for signal transduction.     

CTRP3下调炎症因子表达改善胰岛素抵抗的3T3-L1脂肪细胞胰岛素敏感性

 目的:观察脂肪因子C1q/TNF相关蛋白3（CTRP3）对胰岛素抵抗的3T3-L1脂肪细胞胰岛素敏感性的效应及机制。方法:通过软脂酸培养构建3T3-L1脂肪细胞胰岛素抵抗模型,以不同浓度重组CTRP3蛋白（10、50、250、1 250 μg/L）干预12 h,以及250 μg/L CTRP3干预不同时间（2、6、12、24 h）,以葡萄糖氧化酶法检测葡萄糖消耗量,以2-脱氧-［3H］-葡萄糖摄入法检测葡萄糖转运率,以酶联免疫吸附（ELISA）法检测上清中肿瘤坏死因子α（TNF-α）及白细胞介素6（IL-6）的含量,以荧光实时定量PCR（real-time PCR）检测TNF-α、IL-6及葡萄糖转运子4（GLUT-4）的mRNA表达水平,以Western blotting检测GLUT-4蛋白表达水平。结果:与正常对照组（NC）相比,胰岛素抵抗组（IR）葡萄糖摄取率及葡萄糖消耗量分别降低了50.6%及57.9%（均P<0.01）;与IR组相比,干预组随CTRP3浓度增加,葡萄糖消耗量分别增加22.1%、42.9%、76.6%及80.5%（均P<0.01）,葡萄糖摄取率分别增加39.0%、68.0%、108.0%及111.0%（均P<0.01）;250 μg/L CTRP3干预时间增加,葡萄糖摄取率分别增加23.0%、79.0%、 109.0%及114.0%（均P<0.01）;250 μg/L CTRP3干预12 h,上清中的TNF-α及IL-6浓度分别降低了17.4%及17.1%（均P<0.01）,其mRNA相对表达量分别下降了26.0%及18.9%（均P<0.01）,而GLUT-4 mRNA及蛋白相对表达量分别增加了61.5%及55.6%（均P<0.01）。结论: CTRP3具有改善胰岛素抵抗的3T3-L1脂肪细胞胰岛素敏感性的作用,其机制可能与下调炎症因子表达、改善胰岛素信号转导和增加葡萄糖转运子表达等有关。     

Protein kinase Cδ is a critical component of Dectin-1 signaling in primary human monocytes

Zymosan, a mimic of fungal pathogens, and its opsonized form (ZOP) are potent stimulators of monocyte NADPH oxidase, resulting in the production of O(2)(.-), which is critical for host defense against fungal and bacterial pathogens and efficient immune responses; however, uncontrolled O(2)(.-) production may contribute to chronic inflammation and tissue injury. Our laboratory has focused on characterizing the signal transduction pathways that regulate NADPH oxidase activity in primary human monocytes. In this study, we examined the involvement of various pattern recognition receptors and found that Dectin-1 is the primary receptor for zymosan stimulation of O(2)(.-) via NADPH oxidase in human monocytes, whereas Dectin-1 and CR3 mediate the activation by ZOP. Further studies identified Syk and Src as important signaling components downstream of Dectin-1 and additionally identified PKCδ as a novel downstream signaling component for zymosan-induced O(2)(.-) as well as phagocytosis. Our results show that Syk and Src association with Dectin-1 is dependent on PKCδ activity and expression and demonstrate direct binding between Dectin-1 and PKCδ. Finally, our data show that PKCδ and Syk but not Src are required for Dectin-1-mediated phagocytosis. Taken together, our data identify Dectin-1 as the major PRR for zymosan in primary human monocytes and identify PKCδ as a novel downstream signaling kinase for Dectin-1-mediated regulation of monocyte NADPH oxidase and zymosan phagocytosis.     

Calphostin C is an inhibitor of contraction, but not insulin-stimulated glucose transport, in skeletal muscle.

Wortmannin selectively impairs insulin-stimulated glucose transport in skeletal muscle. To search for an inhibitor specific for contraction-stimulated glucose transport, we screened a number of calmodulin and PKC inhibitors for their ability to impair contraction- and insulin-stimulated 2-deoxyglucose uptake in incubated rat soleus muscles. In concentrations that did not reduce contraction-induced force output, among calmodulin inhibitors W-7 inhibited both contraction- and insulin-stimulated glucose transport by up to 50% (P < 0.05), while Calmidazolium impaired only insulin-stimulated glucose transport (P < 0.05), and Trifluoperazine and Phenoxybenzamine did not influence glucose transport. In concentrations that did not reduce force generation, among PKC inhibitors Calphostin C specifically inhibited contraction-stimulated glucose transport (P < 0.05), whereas insulin-stimulated transport was impaired by Rottlerin and Bisindolylmaleimide I (P < 0.05), and both contraction- and insulin-stimulated glucose transport were inhibited by RO-31-8220 (P < 0.05). Calphostin C did not reduce contraction-induced increase in AMP-activated protein kinase (AMPK) activity. In conclusion, we have identified specific inhibitors of both contraction- and insulin-stimulated glucose transport. Both calmodulin and different isoenzymes of the PKC family may be involved in contraction- and insulin-stimulated glucose transport. Calphostin C does not influence glucose transport during contractions via stimulation of AMPK. Calphostin C may be used to unravel signal transduction in contraction-stimulated glucose transport.     

Insulin responsiveness of diaphragm tissue and adipose cellularity in mice selected for rapid growth

Four lines of mice, two lines selected for rapid growth (large body weights) (M16 and H6) and their unselected control lines (ICR and C2, respectively), were examined for traits related to obesity. The M16 line is obese while the other three lines are normal in body composition at 10 weeks of age when fed stock diet. In experiment I, mice were fed stock diet and examined at intervals from 4 to 22 weeks of age. Mice were fed either a high-carbohydrate or high-fat diet in experiment II and examined at 4, 6 and 10 weeks of age. The traits measured were serum glucose, serum insulin and in vitro insulin responsiveness of diaphragm muscle. Epididymal adipose cellularity was determined at 10 weeks of age. Insulin responsiveness was determined for the diaphragm muscle by 2-deoxyglucose uptake. Body weights differed significantly (M16 greater than H6 greater than ICR greater than C2, P less than 0.01). The M16 obese line was hyperglycemic and mildly hyperinsulinemic while the H6 line was hypoglycemic and normoinsulinemic. Basal 2-deoxyglucose uptakes by diaphragm muscle were similar among lines while the insulin-stimulated uptake by M16 and H6 lines was less (P less than 0.01) than the stimulated uptake by their control lines. Diet did not affect basal uptakes, but high-fat diets reduced (P less than 0.01) the insulin stimulated uptakes when compared to the high-carbohydrate diet. Selected lines had more and larger epididymal adipocytes than control lines when fed the stock diet (P less than 0.01). Decreased insulin responsiveness of muscle tissue among the lines occurred concomitantly with an increase in adipocyte size.