原代培养骨骼肌细胞胰岛素抵抗模型的建立

目的:观察高脂负荷在胰岛素抵抗形成中的意义.方法:用不同浓度椋榈酸、胰岛素分别培养骨骼肌细胞2h、6h、12h、24h,对棕榈酸诱导组的一部分细胞给予1× 10-7M胰岛素刺激2h,用血糖检测试剂盒(GOD-POD)检测各组培养液中的葡萄糖含量,研究不同浓度棕榈酸、胰岛素对骨骼肌细胞摄取葡萄糖的影响,观察胰岛素的生理功效的变化.结果:0.6mM棕榈酸诱导12h以上或者5×101-M胰岛素诱导24h后,培养液中的葡萄糖浓度比正常组高且有显著性差异,表明细胞的糖代谢能力降低.经1×10-7M胰岛素刺激2h后的棕榈酸诱导组,培养液中葡萄糖的浓度与未经胰岛素刺激的棕榈酸诱导组相比无显著差异,胰岛素的生理功效降低,证实棕榈酸诱导组细胞已对胰岛素产生耐受.结论:高脂或高胰岛素条件均可诱导原代骨骼肌细胞胰岛素抵抗模型.     

罗格列酮对胰岛素抵抗人肝细胞Angpil3和LXRα基因表达的影响

研究罗格列酮对胰岛素抵抗人肝L02细胞Angptl3基因及与脂代谢相关的LXRα基因的影响.采用高胰岛素诱导法建立胰岛素抵抗模型(IR-L02),分别加入含有和不含罗格列酮的不同葡萄糖浓度培养液培养,用葡萄糖氧化酶-过氧化物酶法(GOD-POD法)检测培养液残存葡萄糖量,并用RT-PCR方法检测基因Angptl3、LXRα mRNA表达水平的变化.结果表明相同葡萄糖浓度下罗格列酮作用组(IR-R组)的培养液残存葡萄糖量比无罗格列酮作用组(IR组)减少;IR-R组的Angptl3、LXRα mRNA表达水平较IR组显著升高(P<0.05).     

罗格列酮对胰岛素抵抗人肝细胞Angpil3和LXRce基因表达的影响

研究罗格列酮对胰岛素抵抗人肝L02细胞Angptl3基因及与脂代谢相关的LXRα基因的影响。采用高胰岛素诱导法建立胰岛素抵抗模型（IR-L02）,分别加入含有和不含罗格列酮的不同葡萄糖浓度培养液培养,用葡萄糖氧化酶-过氧化物酶法（GOD—POD法）检测培养液残存葡萄糖量,并用RT-PCR方法检测基因Angptl3、LXRαmRNA表达水平的变化。结果表明相同葡萄糖浓度下罗格列酮作用组（IR—R组）的培养液残存葡萄糖量比无罗格列酮作用组（IR组）减少;IR—R组的Angptl3、LXRαmRNA表达水平较IR组显著升高（P〈0．05）。     

肌源性IL-6对骨骼肌细胞胰岛素抵抗的影响及其机制

目的:研究外源性钙负荷促进离体细胞肌源性IL-6释放,调节AMPK、p38MAPK等信号通路以改善胰岛素抵抗的效应。方法:以正常培养的C2C12细胞系和棕榈酸诱导形成胰岛素抵抗C2C12细胞系为实验对象。预实验通过不同浓度钙培养肌细胞24 h后,检测培养液葡萄糖浓度并在显微镜下观察其收缩的情况。正式试验1将细胞分为4组：A组为Control组(正常培养液培养),B组为IR组(0.6 mmol/L棕榈酸哺育细胞24 h后备用),C组为1 000 ng/ml IL-6哺育IR细胞48 h组(IL-6+IR组),D组为IL-6shRNA哺育正常细胞48 h组(IL-6shRNA组)。正式试验2将细胞分为3组：A组为IR组,B组为100μmol/L CaCl₂哺育IR细胞48 h组(钙哺育组,CaCl₂+IR组),C组为100μmol/L CaCl2和IL-6shRNA共哺育IR细胞48 h组(共哺育组,CaCl₂+IL-6shRNA+IR组),采用Real-time PCR方法检测IL-6 mRNA、GLUT mRNA表达水平...     

棕榈酸的组织吸收分布及对骨骼肌胰岛素抵抗的影响

脂肪酸代谢紊乱是Ⅱ型糖尿病的主要致病因素之一。棕榈酸是血液中含量最高的游离脂肪酸。我们建立了大鼠颈静脉置管输注棕榈酸的模型,发现血液中的大部分棕榈酸被骨骼肌组织所吸收。以棕榈酸处理的C2C12骨骼肌细胞为实验模型发现,棕榈酸进入骨骼肌细胞后的中间代谢产物(磷脂和甘油二酯)的累积,会造成内质网应激及胰岛素抵抗。提示血液中棕榈酸含量的升高可能通过骨骼肌的胰岛素抵抗机制,影响Ⅱ型糖尿病的发生和发展。     

十子代平方水煎液对原代骨骼肌细胞胰岛素抵抗模型的影响

本实验观察十子代平方对原代骨骼肌细胞胰岛素抵抗模型的影响,探讨其改善胰岛素抵抗的作用机制。对原代骨骼肌细胞应用5×10-7mol/L胰岛素干预12 h建立胰岛素抵抗模型,应用十子代平方高、中、低浓度(400、100、25μg/m L)(SZDP-H、SZDP-M、SZDP-L)对造模成功的骨骼肌细胞进行干预,同时另设正常组、模型组,吡格列酮组(40μmol/L)作对照,药物干预24 h后用葡萄糖氧化酶法测定骨骼肌细胞上清液葡萄糖剩余量,采用Western-blot方法测定该方药物干预后骨骼肌细胞AKT、GSK-3β蛋白的表达。实验结果表明十子代平方可以改善骨骼肌细胞胰岛素抵抗模型的葡萄糖代谢,增加AKT和磷酸化位点Ser473蛋白表达,降低GSK-3β蛋白表达,增加其磷酸化位点Ser9蛋白表达。十子代平方可能通过调节AKT/GSK3β通路的机制改善胰岛素抵抗模型骨骼肌细胞的葡萄糖代谢。     

人肾小球血管内皮细胞胰岛素抵抗模型的建立

目的:采用不同浓度的棕榈酸与葡萄糖在体外诱导建立人肾小球内皮细胞(Human glomerular endothelial cells,HRGEC)胰岛素抵抗模型。方法:以人肾小球内皮细胞为研究对象,不同浓度棕榈酸(100,200,300,400,500μmol/L)与不同浓度的葡萄糖(20,30,40,50,60 mmol/L)分别作用细胞24小时和48小时,应用MTT法和葡萄糖氧化酶法检测棕榈酸和葡萄糖对HRGEC存活率与葡萄糖消耗量的影响,蛋白免疫印迹法检测P-IRS、IRS、AKT和p-AKT (Ser473)的影响。结果:1、当棕榈酸500μmol/L干预细胞24小时,与正常组比较,细胞活性显著下降(P0.01),棕榈酸浓度大于或等于300μmol/L干预细胞48小时,细胞存活率显著降低(P0.01)。与空白组比较,300μmol/L、400μmol/L、500μmol/L棕榈酸干预细胞24小时能够明显的降低细胞的葡萄糖消耗(P0.05);200μmol/L、300μmol/L、400μmol/L、500μmol/L干预细胞48小时能够明显的降低细胞的葡萄糖消耗(P0.01)。2、不同浓度葡萄糖刺激人肾小球内皮细胞(HGREC)24小时和48小时,与空白组比较,各组细胞的存活率与对照组比较均无显著变化(P0.05)。与空白组比较,40mmol/L、50 mmol/L、60 mmol/L葡萄糖干预细胞24小时能够降低人肾小球内皮细胞的葡萄糖消耗(P0.05)。与空白组比较,30mmol/L、40mmol/L、50 mmol/L、60 mmol/L葡萄糖干预细胞48小时能够明显降低人肾小球内皮细胞的葡萄糖消耗量(P0.01)。3、不同浓度的葡萄糖刺激人肾小球内皮细胞(HGREC)24小时后,结果显示,50 mmol/L、60 mmol/L葡萄糖刺激细胞24小时能降低P-IRS/IRS和p-AKT/AKT (Ser473)的水平(P0.01),而其他组无明显显著变化(P0.05)。结论:高糖诱导方法能够建立HRGEC细胞胰岛素抵抗模型,具有建模周期短、容易重复、可控性强的优点,可用于糖尿病胰岛素抵抗机制的研究和中药成分的筛选研究。     

环氧二十碳三烯酸抑制剂通过AKT/FoxO1信号通路抑制棕榈酸诱导的心肌细胞凋亡

目的观察14,15-环氧二十碳三烯酸(14,15-epoxyeicosatrienoic acid,14,15-EET)及其抑制剂14,15-环氧二十碳-5(Z)-烯酸(14,15-epoxyeicosa-5(Z)-enoic acid,14,15-EEZE)对棕榈酸(palmitate acid,PA)诱导心肌细胞凋亡的作用及机制。方法 14,15-EET和14,15-EEZE单独或联合作用于PA诱导后的H9c2细胞,采用噻唑蓝比色法检测细胞增殖,流式细胞术检测细胞凋亡,免疫印迹法测定细胞p-AKT和p-Fox O1蛋白表达水平。结果流式细胞术检测显示,PA诱导下H9c2细胞凋亡率上升,14,15-EET的作用可降低细胞凋亡率,而加用14,15-EEZE使细胞凋亡率上升,14,15-EEZE的单独作用也可提高PA诱导下H9c2细胞的凋亡率。免疫印迹分析显示,PA可降低H9c2细胞p-AKT和p-Fox O1蛋白表达水平,14,15-EET的作用可使p-AKT和p-Fox O1蛋白表达水平明显上升,而加用14,15-EEZE后p-AKT和p-Fox O1的蛋白表达水平明显下降,14,15-EEZE的单独作用可使PA诱导下H9c2细胞的p-AKT和p-Fox O1的表达水平明显下降。结论 14,15-EET可能通过促进AKT/Fox O1信号通路活性抑制棕榈酸诱导的H9c2细胞凋亡,而其抑制剂14,15-EEZE可能通过抑制AKT/Fox O1信号通路活性抑制14,15-EET的抗棕榈酸诱导H9c2心肌细胞凋亡的作用。     

津力达对高脂诱导的胰岛素抵抗ApoE~(-/-)小鼠骨骼肌甘油三酯相关酶的影响

目的探究津力达对高脂诱导的胰岛素抵抗Apo E-/-小鼠骨骼肌甘油三酯相关基因的影响。方法将8只雄性C57BL/6J小鼠设为正常组(A组);40只雄性Apo E-/-小鼠喂养16周后分为模型组(B组)、罗格列酮组(C组)、津力达低剂量组(D组)、津力达中剂量组(E组)、津力达高剂量组(F组),开始灌胃给药,连续8周。采用酶法、BCA蛋白浓度法测定骨骼肌TG含量;OGTT评价小鼠的胰岛素抵抗程度;RT-PCR和Western blot测定小鼠骨骼肌HSL、ATGL、PPARγmRNA和蛋白表达。结果津力达能够不同程度降低小鼠的FBG、TC、TG和LDLC,升高HDL-C;下调FIns水平,提高ISI,明显改善小鼠糖耐量异常;津力达能够不同程度的上调小鼠HSL、ATGL、PPARγmRNA和蛋白表达。结论津力达能够通过调节骨骼肌甘油三酯相关酶的表达,改善高脂诱导的Apo E-/-小鼠的胰岛素抵抗。     

高糖高脂联合低剂量链脲佐菌素对版纳微型猪肝脏损伤和蛋白激酶B表达的影响

目的观察高糖高脂联合低剂量链脲佐菌素(streptozotocin,STZ)对版纳微型猪糖、脂代谢紊乱、肝组织病理改变及其蛋白激酶B(protein kinase B,PKB)磷酸化的影响,并探讨其机制。方法高糖高脂联合低剂量STZ诱导云南版纳微型猪2型糖尿病模型,每月末测定血糖、血脂、胰岛素,HE、PAS和苏丹Ⅳ染色观察肝脏显微结构。12个月末处死动物,real time-PCR和Western blotting检测肝组织PKB mRNA和总蛋白表达及PKB丝氨酸473(PKB-Ser473)的磷酸化水平。结果喂养12月后,与正常对照组比较,模型组显示高血糖、血脂障碍及胰岛素缺乏(P0.05)。肝脏脂肪病变,肝糖原合成显著减少;PKB mRNA及蛋白表达增高(P0.05),但PKB磷酸化降低(P0.05)。结论高糖高脂联合STZ可诱导版纳微型猪发生胰岛素抵抗、糖尿病,促进肝脏脂质蓄积,抑制糖原合成,可能与信号分子PKB抑制有关。     

Phosphorylation of the Rat Skeletal Muscle Sodium Channel by Cyclic AMP-Dependent Protein Kinase

Cyclic AMP-dependent phosphorylation of the rat brain sodium channel was reported to be restricted to five sites within an approximately 210 amino acid region of the primary sequence that is deleted in the homologous sodium channel from rat skeletal muscle. We find that, in spite of this deletion, the rat muscle sodium channel alpha-subunit is also an excellent substrate for phosphorylation by this kinase both in primary muscle cells in tissue culture and in vitro after isolation from adult muscle. Sodium channel protein purified from adult rat skeletal muscle was readily phosphorylated in vitro by the catalytic subunit of the bovine cyclic AMP-dependent protein kinase (PKa). Only the 260,000 MW alpha-subunit was labeled, with a maximum level of incorporation in vitro of approximately 0.5 mol [32P]phosphate per mole of channel protein. The beta-subunit of the channel is not phosphorylated under these conditions. In primary rat skeletal muscle cells in culture, incorporation of phosphate into the channel alpha-subunit is stimulated 1.3- to 1.5-fold by treatment of the cells with forskolin. Phosphorylation of the sodium channel isolated from these cells could also be demonstrated in vitro using PKa. This in vitro phosphorylation could be inhibited 80-90% by pretreatment of the cells in culture with forskolin, suggesting that the sites labeled in vitro by PKa were the same as those phosphorylated in the intact cells by the endogenous cyclic AMP-dependent kinase. In both the adult muscle channel and the channel from muscle cells in culture, phosphorylation by PKa was limited to serine residues.(ABSTRACT TRUNCATED AT 250 WORDS)     

Myristic acid specifically stabilizes diacylglycerol kinase δ protein in C2C12 skeletal muscle cells

Decreased levels of the δ isozyme of diacylglycerol kinase (DGK) in skeletal muscle attenuate glucose uptake and, consequently, are critical for the pathogenesis of type 2 diabetes. We recently found that free myristic acid (14:0), but not free palmitic acid (16:0), increased the DGKδ protein levels and enhanced glucose uptake in C2C12 myotube cells. However, it has been unclear how myristic acid regulates the level of DGKδ2 protein. In the present study, we characterized the myristic acid-dependent increase of DGKδ protein. A cycloheximide chase assay demonstrated that myristic acid, but not palmitic acid, markedly stabilized DGKδ protein. Moreover, other DGK isozymes, DGKη and ζ, as well as glucose uptake-related proteins, such as protein kinase C (PKC) α, PKCζ, Akt and glycogen synthase kinase 3β, failed to be stabilized by myristic acid. Furthermore, DGKδ was not stabilized in cultured hepatocellular carcinoma cells, pancreas carcinoma cells or neuroblastoma cells, and only a moderate stabilizing effect was observed in embryonic kidney cells. A proteasome inhibitor and a lysosome inhibitor, MG132 and chloroquine, respectively, partly inhibited DGKδ degradation, suggesting that myristic acid prevents, at least in part, the degradation of DGKδ by the ubiquitin-proteasome system and the autophagy-lysosome pathway. Overall, these results strongly suggest that myristic acid attenuates DGKδ protein degradation in skeletal muscle cells and that this attenuation is fatty acid-, protein- and cell line-specific. These new findings provide novel insights into the molecular mechanisms of the pathogenesis of type 2 diabetes mellitus.     

Phosphoenolpyruvate-dependent protein kinase activity in rat skeletal muscle

Phosphoenolpyruvate-dependent protein kinase activity has been demonstrated in the soluble fraction of rat skeletal muscle. The reaction was not due to the formation of ATP in the incubation mixture. Cyclic AMP, calcium, ATP and a number of phosphate acceptor proteins did not stimulate the reaction. One 32P-labelled protein (Mr 25000) was observed on SDS gels. The phosphorylated protein contained acid stable phosphoserine as a major phosphorylated amino acid. The phosphorylation reaction in crude extracts was not directly proportional to the amount of protein, but typical of a two-component system; i.e., kinase and substrate. The chromatography of soluble proteins on Ultrogel AcA44 separated the phosphate acceptor protein(s) from the phosphoenolpyruvate-dependent protein kinase activity.     

Palmitic Acid Anilide-Induced Respiratory Burst In Human Polymorphonuclear Leukocytes is Inhibited by a Protein Kinase C Inhibitor, Ro 31-8220

Human polymorphonuclear leukocytes (PMNL) were exposed to palmitic acid anilide, an impurity in the case oils that caused the Spanish Toxic Oil Syndrome in 1981, and to the corresponding fatty acid, palmitic acid. The effects of these compounds were studied on the production of reactive oxygen metabolites (ROM) and changes in the levels of free intracellular calcium. Palmitic acid anilide induced the production of reactive oxygen metabolites in PMNL. Interestingly, the palmitic acid anilide-induced respiratory burst was completely blocked by a protein kinase C inhibitor, Ro 31-8220. Moreover, palmitic acid anilide additively amplified the production of ROM caused by a chemotactic peptide, formyl-Methionyl-Leucyl-Phenylalanine (FMLP). In contrast, palmitic acid anilide did not have any effect on the production of ROM induced by a tumor promoter, phorbol myristate acetate (PMA). Palmitic acid, in turn, did not markedly induce the production of ROM nor did it amplify the agonist-induced respiratory burst. Neither of the compounds, alone or in combination with FMLP, affected the levels of intracellular calcium in PMNL. These results indicate that the aniline moiety in palmitic acid modifies its effects on the activation of human PMNL, and the subsequent oxidative burst. The present results also suggest that palmitic acid anilide may activate PMNL through a protein kinase C-dependent mechanism. © 1997 Elsevier Science Inc.     

Palmitic acid suppresses apolipoprotein M gene expression via the pathway of PPARβ/δ in HepG2 cells

It has been demonstrated that apolipoprotein M (APOM) is a vasculoprotective constituent of high density lipoprotein (HDL), which could be related to the anti-atherosclerotic property of HDL. Investigation of regulation of APOM expression is of important for further exploring its pathophysiological function in vivo. Our previous studies indicated that expression of APOM could be regulated by platelet activating factor (PAF), transforming growth factors (TGF), insulin-like growth factor (IGF), leptin, hyperglycemia and etc., in vivo and/or in vitro. In the present study, we demonstrated that palmitic acid could significantly inhibit APOM gene expression in HepG2 cells. Further study indicated neither PI-3 kinase (PI3K) inhibitor LY294002 nor protein kinase C (PKC) inhibitor GFX could abolish palmitic acid induced down-regulation of APOM expression. In contrast, the peroxisome proliferator-activated receptor beta/delta (PPAR_β/δ) antagonist GSK3787 could totally reverse the palmitic acid-induced down-regulation of APOM expression, which clearly demonstrates that down-regulation of APOM expression induced by palmitic acid is mediated via the PPAR_β/δ pathway.     

Palmitic acid acutely stimulates glucose uptake via activation of Akt and ERK1/2 in skeletal muscle cells

Chronic exposure to saturated fatty acids can cause insulin resistance. However, the acute effects of fatty acids are not clear and need to be elucidated because plasma fatty acid concentrations fluctuate postprandially. Here, we present the acute effects of palmitate (PA) on skeletal muscle cells and their underlying molecular mechanisms. Immuno-fluorescence results showed that PA rapidly induced GLUT4 translocation and stimulated glucose uptake in rat skeletal muscle cell line L6. Phosphorylation of AMP-activated protein kinase (AMPK), Akt, and extracellular signal-related kinase1/2 (ERK1/2) was enhanced by PA in a time-dependent manner. Cell surface-bound PA was sufficient to stimulate Akt phosphorylation. The inhibitors of PI3 kinase (PI3K), AMPK, Akt, and ERK1/2 could decrease PA-induced glucose uptake, and PI3K inhibitor decreased AMPK, Akt, and ERK1/2 phosphorylation. Weakening AMPK activity reduced phosphorylation of Akt but not ERK1/2, and Akt inhibitor could not affect ERK1/2 activation either. Meanwhile, ERK1/2 inhibitors had no effect on Akt phosphorylation. Taken together, our data suggest that PA-mediated glucose uptake in skeletal muscle cells may be stimulated by the binding of PA to cell surface and followed by PI3K/AMPK/Akt and PI3K/ERK1/2 pathways independently.     

Acute effect of fatty acids on metabolism and mitochondrial coupling in skeletal muscle

Acute effects of free fatty acids (FFA) were investigated on: (1) glucose oxidation, and UCP-2 and -3 mRNA and protein levels in 1 h incubated rat soleus and extensor digitorium longus (EDL) muscles, (2) mitochondrial membrane potential in cultured skeletal muscle cells, (3) respiratory activity and transmembrane electrical potential in mitochondria isolated from rat skeletal muscle, and (4) oxygen consumption by anesthetized rats. Long-chain FFA increased both basal and insulin-stimulated glucose oxidation in incubated rat soleus and EDL muscles and reduced mitochondrial membrane potential in C2C12 myotubes and rat skeletal muscle cells. Caprylic, palmitic, oleic, and linoleic acid increased O₂ consumption and decreased electrical membrane potential in isolated mitochondria from rat skeletal muscles. FFA did not alter UCP-2 and -3 mRNA and protein levels in rat soleus and EDL muscles. Palmitic acid increased oxygen consumption by anesthetized rats. These results suggest that long-chain FFA acutely lead to mitochondrial uncoupling in skeletal muscle.     

Acute effect of fatty acids on metabolism and mitochondrial coupling in skeletal muscle

Acute effects of free fatty acids (FFA) were investigated on: (1) glucose oxidation, and UCP-2 and -3 mRNA and protein levels in 1 h incubated rat soleus and extensor digitorium longus (EDL) muscles, (2) mitochondrial membrane potential in cultured skeletal muscle cells, (3) respiratory activity and transmembrane electrical potential in mitochondria isolated from rat skeletal muscle, and (4) oxygen consumption by anesthetized rats. Long-chain FFA increased both basal and insulin-stimulated glucose oxidation in incubated rat soleus and EDL muscles and reduced mitochondrial membrane potential in C2C12 myotubes and rat skeletal muscle cells. Caprylic, palmitic, oleic, and linoleic acid increased O(2) consumption and decreased electrical membrane potential in isolated mitochondria from rat skeletal muscles. FFA did not alter UCP-2 and -3 mRNA and protein levels in rat soleus and EDL muscles. Palmitic acid increased oxygen consumption by anesthetized rats. These results suggest that long-chain FFA acutely lead to mitochondrial uncoupling in skeletal muscle.     

Bradykinin and Phorbol Dibutyrate Activate Phospholipase D in PC12 Cells by Different Mechanisms

Bradykinin is known to activate phospholipase D in PC12 cells. Because bradykinin may also activate protein kinase C in these cells, the possible role of this kinase in mediating the action of bradykinin was investigated. Phospholipase D activity in PC12 cells was assayed by measuring the formation of [3H]phosphatidylethanol in cells prelabeled with [3H]palmitic acid and incubated in the presence of ethanol. The phorbol ester phorbol dibutyrate mimicked the effect of bradykinin on [3H]phosphatidylethanol formation. The protein kinase C inhibitor staurosporine (1 microM) significantly attenuated the effect of phorbol dibutyrate (35-70%) but did not block bradykinin-stimulated [3H]phosphatidylethanol formation. In addition, the effect of phorbol dibutyrate was additive with that of bradykinin. Prolonged treatment of PC12 cells with phorbol dibutyrate (24 h), which depletes cells of protein kinase C, greatly attenuated bradykinin-stimulated [3H]phosphatidylethanol accumulation in intact cells. This treatment caused a 55% decrease in both fluoride-stimulated [3H]phosphatidylethanol production in the intact cell and phospholipase D activity as assessed by an in vitro assay using an exogenous substrate. Therefore, the effect of prolonged phorbol dibutyrate pretreatment on bradykinin-stimulated [3H]phosphatidylethanol production could not be attributed exclusively to the depletion of protein kinase C. Thus, although the data with phorbol ester suggest that activation of protein kinase C leads to an increase in phospholipase D activity, this kinase probably does not play a role in mediating the effect of bradykinin. Finally, although pretreatment with phorbol dibutyrate completely blocked bradykinin-stimulated [3H]phosphatidylethanol production in the intact cell, it only partially (approximately 50%) inhibited bradykinin-stimulated [3H]diacylglycerol formation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protein kinase activity of the insulin receptor from muscle

The insulin receptor is associated with a protein kinase activity. This has been shown for the receptor of liver, fat, and some other tissues which are not primary targets of insulin action. Here kinase activity is demonstrated for the insulin receptor of rat skeletal and cardiac muscle with similar characteristics. Insulin (10(-7) mol/l) stimulates phosphorylation of the 95-kDa receptor subunit 3- to 18-fold. The effect is detectable at 10(-10) mol/l insulin; the ED50 is approx. 3 X 10(-9) mol/l. The kinase phosphorylates exogenous substrate as well, and it is recovered after immunoprecipitation of the receptor with antireceptor antibody suggesting that kinase activity is intrinsic to the muscle receptor.