delta-Opioid receptor stimulation enhances the growth of neonatal rat ventricular myocytes via the extracellular signal-regulated kinase pathway

1. The aims of the present study were to determine whether delta-opioid receptor stimulation enhanced proliferation of and to investigate the role of the extracellular signal-regulated kinase (ERK) pathway in ventricular myocytes from neonatal rats. 2. At concentratins ranging from 10 nmol/L to 10 micromol/L, [D-Ala2,D-Leu5]enkephalin (DADLE) concentration-dependently promoted myocardial growth and DNA synthesis and altered the cytoskeleton. 3. At 1 micromol/L, DADLE also increased the expression and phosphorylation of ERK. 4. These effects of 1 micromol/L DADLE were abolished by 10 micromol/L naltrindole, a selective delta-opioid receptor antagonist, 10 nmol/L U0126, a selective ERK antagonist, 1 micromol/L staurosporine, an inhibitor of protein kinase (PK) C, and 100 micromol/L Rp-adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt hydrate (Rp-cAMPS), an inhibitor of PKA. 5. In conclusion, delta-opioid receptor stimulation enhances the proliferation and development of the ventricular myocytes of neonatal rats. The ERK pathway and related signalling mechanisms, namely PKC and PKA, are involved.     

Activation of extracellular signal-regulated kinase during silibinin-protected, isoproterenol-induced apoptosis in rat cardiac myocytes is tyrosine kinase pathway-mediated and protein kinase C-dependent

Aim： To investigate the mechanism of silibinin-protected isoproterenol-induced apoptosis in rat cardiac myocytes. Methods： The viability of rat cardiac myocytes was measured by MTT method. The apoptotic ratio was measured by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling. Protein kinase C （PKC） activity assay was carried out according to the instructions of the PepTag non-radioactive protein kinase C assay kit. Western blot analysis was used to evaluate the level of Ras, Raf-1 and mitogen-activated protein kinase （MAPK） expression. Results： The protective effects of silibinin were significantly sup- pressed by inhibitors, including genistein, manumycin A and GW5074 [inhibitors for protein tyrosine kinases （PTK）, Ras and Raf- 1, respectively]. The exposure of rat cardiac myocytes to isoproterenol alone caused decreased PKC activity, which was prevented by pretreatment with silibinin dose-dependently. Simultaneously, the increased expression of Ras and Raf- 1 activated by silibinin were blocked by the PKC inhibitor, stauroporine. In addition, the extracellularly responsive kinase （ERK） inhibitor, PD98059, suppressed silibinin-protected apoptosis, whereas the p38 MAPK inhibitor, SB203580, protected cardiac myocytes from isoproterenolinduced injury, and the c-Jun N-terminal kinase （JNK） inhibitor, SP600125 had no protective effects. Furthermore, Westem blot analysis showed that the expres- sion of phosphorylated ERK was increased by silibinin, the expression of phos- phorylated p38 MAPK was decreased and total ERK, p38, JNK and phosphorylated JNK MAPK did not change after treatment with both isoproterenol and silibinin. Furthermore, pretreatment of cardiac myocyte with PKC, Ras and Raf inhibitors significantly blocked ERK phosphorylation. Conclusion： Silibinin is suggested to protect isoproterenol-induced rat cardiac myocyte apoptosis by activating the tyrosine kinase pathway, PKC and MAPK pathways.     

低氧预处理通过蛋白激酶C激活上调大鼠心室肌细胞K_(ATP)通道(英文)

目的:研究:1)在大鼠心室肌细胞,低氧预处理是否上调K_(ATP)通道活动;2)是否蛋白激酶C(PKC)参与了调节.方法:使用标准的全细胞膜片箝方法.记录经过不同预先处理的心肌细胞2,4-dinitrophenolDNP诱发的K_(ATP)通道电流.细胞预先处理分别为对照(CON),低氧复氧(HPC),佛波酯(PMA)和Chelerythrine 低氧复氧(CH HPC).结果:在测试电位0mV加入DNP 5分钟时CON,HPC,PMA和CH HPC组的膜电流值分别为:(3.5±1.9),(7.7±1.5),(7.5±3.3),(4.6±2.4)nA.与CON相比,HPC和PMA组的I_(K_ATP)显著增高(P<0.01),而CH HPC和CON相比则无显著意义(P>0.05).结论:1)低氧预处理激活PKC并显著加强心肌细胞 K_(ATP)通道活动;2)PKC的激活参与了K_(ATP)通道的上调.     

Different pathways for activation of extracellular signal-regulated kinase through thromboxane A2 receptor isoforms

Thromboxane A2 receptor (TP) consists of two alternatively spliced isoforms, TPalpha and TPbeta, which differ in their cytoplasmic tails. In the present study, we examined the difference in signal transduction of TPalpha and TPbeta, using stably expressing cells of TPalpha and TPbeta. The cells expressing TPalpha (TPalpha-SC2) and TPbeta (TPbeta-SC15) were selected based on the similar binding sites of [3H]-SQ29548, a TP antagonist. U46619, a TP agonist, elicited phosphoinositide hydrolysis in TPalpha-SC2 and TPbeta-SC15 cells with a similar concentration-dependency. U46619 also caused the phosphorylation of extracellular signal-regulated kinase (ERK1/2) in both TPalpha-SC2 and TPbeta-SC15 cells. While the peak of the phosphorylation of ERK1/2 was observed 5 min after addition of U46619 in TPalpha-SC2 cells, the long lasting phosphorylation up to 60 min was in TPbeta-SC15 cells. U46619-induced phosphorylation of ERK1/2 at 5 min was inhibited by pertussis toxin in both cells, suggesting that G(i) is involved in the phosphorylation mediated via both TP isoforms. Interfering G(12/13) activity by overexpression of p115-RGS reduced U46619-induced ERK1/2 phosphorylation in TPbeta-SC15 cells, but not in TPalpha-SC2 cells. H89, an inhibitor of protein kinase A (PKA), reduced U46619-induced ERK1/2 phosphorylation in TPalpha-SC2 cells, but not in TPbeta-SC15 cells. These results indicate that G(i) may be involved in TP-mediated ERK1/2 phosphorylation in both isoforms. In addition, H89-sensitive kinase and G(12/13) may be involved in TP-mediated ERK1/2 phosphorylation in TPalpha and TPbeta, respectively.     

TVP1022 and propargylamine protect neonatal rat ventricular myocytes against doxorubicin-induced and serum starvation-induced cardiotoxicity

We recently reported that propargylamine derivatives such as rasagiline (Azilect) and its S-isomer TVP1022 are neuroprotective. The aim of this study was to test the hypothesis that the neuroprotective agents TVP1022 and propargylamine (the active moiety of propargylamine derivatives) are also cardioprotective. We specifically investigated the protective efficacy of TVP1022 and propargylamine in neonatal rat ventricular myocytes (NRVM) against apoptosis induced by the anthracycline chemotherapeutic agent doxorubicin and by serum starvation. We demonstrated that pretreatment of NRVM cultures with TVP1022 or propargylamine attenuated doxorubicin-induced and serum starvation-induced apoptosis, inhibited the increase in cleaved caspase 3 levels, and reversed the decline in Bcl-2/Bax ratio. These cytoprotective effects were shown to reside in the propargylamine moiety. Finally, we showed that TVP1022 neither caused proliferation of the human cancer cell lines HeLa and MDA-231 nor interfered with the anti-cancer efficacy of doxorubicin. These results suggest that TVP1022 should be considered as a novel cardioprotective agent against ischemic insults and against anthracycline cardiotoxicity and can be coadministered with doxorubicin in the treatment of human malignancies.     

Combined effect of protein kinase B inhibitor or extracellular signal-regulated kinase inhibitor against farnesyltransferase inhibition-induced apoptosis in SiHa cells

The present study investigated the combined effect of Akt or extracellular signal-regulated kinase (ERK) inhibition in the presence of farnesyltransferase inhibitor against human cervix and uterus tumor cell line SiHa cells. Farnesyltransferase inhibitor may induce apoptosis through the mitochondria-mediated process and inhibition of the MEK, ERK, and Akt activity. Inhibitors of Akt and ERK at low concentrations seem to prevent the farnesyltransferase inhibitor-induced apoptosis in cervical SiHa cells by suppressing the mitochondrial membrane permeability change that leads to cytochrome c release and caspase-3 activation. These effects may be associated with inhibition of the reactive oxygen species formation and glutathione depletion. In contrast, at higher concentrations more than 1 muM, the Akt inhibitor and ERK inhibitor seem to exhibit an additive toxic effect against farnesyltransferase inhibitor-induced apoptosis by increasing mitochondrial membrane permeability change and oxidative stress, which may not involve inhibition of MEK, ERK, and Akt activity.     

Kavalactones protect neural cells against amyloid beta peptide-induced neurotoxicity via extracellular signal-regulated kinase 1/2-dependent nuclear factor erythroid 2-related factor 2 activation

One hallmark of Alzheimer's disease is the accumulation of amyloid beta-peptide (AP), which can initiate a cascade of oxidative events that may result in neuronal death. Because nuclear factor erythroid 2-related factor 2 (Nrf2) is the major regulator for a battery of genes encoding detoxifying and antioxidative enzymes via binding to the antioxidant response element (ARE), it is of great interest to find nontoxic activators of Nrf2 rendering neuronal cells more resistant to AP toxicity. Using ARE-luciferase assay and Western blot, we provide evidence that the kavalactones methysticin, kavain, and yangonin activate Nrf2 time- and dose-dependently in neural PC-12 and astroglial C6 cells and thereby up-regulate cytoprotective genes. Viability and cytotoxicity assays demonstrate that Nrf2 activation is able to protect neural cells from amyloid beta-(1-42) induced neurotoxicity. Down-regulation of Nrf2 by small hairpin RNA as well as extracellular signal-regulated kinase 1/2 inhibition abolishes cytoprotection. We further give evidence that kavalactone-mediated Nrf2 activation is not dependent on oxidative stress production. Our results demonstrate that kavalactones attenuate amyloid beta-peptide toxicity by inducing protective gene expression mediated by Nrf2 activation in vitro. These findings indicate that the use of purified kavalactones might be considered as an adjunct therapeutic strategy to combat neural demise in Alzheimer disease and other oxidative stress-related diseases.     

Cytoplasmic vacuolation in cultured rat astrocytes induced by an organophosphorus agent requires extracellular signal-regulated kinase activation

There are various toxic chemicals that cause cell death. However, in certain cases deleterious agents elicit various cellular responses prior to cell death. To determine the cellular mechanisms by which such cellular responses are induced is important, but sufficient attention has not been paid to this issue to date. In this study, we showed the characteristic effects of an organophosphorus (OP) agent, bis(pinacolyl methyl)phosphonate (BPMP), which we synthesized for the study of OP nerve agents, on cultured rat astrocytes. Morphologically, BPMP induced cytoplasmic vacuolation and stellation in the rat astrocytes. Cytoplasmic vacuolation is a cell pathological change observed, for example, in vacuolar degeneration, and stellation has been reported in astrocytic reactions against various stimuli. By pretreatment with cycloheximide, a protein synthesis inhibitor, stellation was inhibited, although vacuolation was not. Cell staining with a mitochondrion-selective dye indicated that the vacuolation probably occurs in the mitochondria that are swollen and vacuolatred in the center. Interestingly, the extracellular signal-regulated kinase (ERK) cascade inhibitor inhibited vacuolation and, to some extent, stellation. These results suggest that the ERK signaling cascade is important for the induction of mitochondrial vacuolation. We expect that a detailed study of these astrocytic reactions will provide us new perspectives regarding the variation and pathological significance of cell morphological changes, such as vacuolar degeneration, and also the mechanisms underlying various neurological disorders.     

Influence of extracellular K+ concentrations on quinidine-induced K+ current inhibition in rat ventricular myocytes

Hypokalaemia is one of the important risk factors for development of torsades de pointes. We recently reported that hypokalaemia increased the electrocardiographic QT interval in rats treated with quinidine, but did not alter the arrhythmogenic potency of quinidine. In this study, we have investigated the influence of extracellular potassium concentration ([K+]o) on the inhibition of several types of cardiac potassium currents by quinidine. Such types of currents include the delayed rectifier potassium current (I(K)), the transient outward current (Ito), and the inward rectifier potassium current (I(K1)), as measured in isolated rat ventricular cells using patch-clamp techniques. Concentration-dependent effects of quinidine on I(K), Ito, and I(K1) were evaluated under both normal ([K+]o = 5.4 mM) and hypokalaemic ([K+]o = 3.5 mM) conditions. In contrast to both I(K) and Ito, which were barely influenced by changes in [K+]o, I(K1) was significantly inhibited by hypokalaemia. Furthermore, while quinidine suppressed both I(K) and Ito in a concentration-dependent manner, the inhibitory potency of quinidine on these currents was not influenced by changes in [K+]o. The respective normal and hypokalaemic IC50 values for quinidine were 11.4 and 10.0 microM (I(K)), and 17.6 and 17.3 microM (Ito). Although higher concentrations of quinidine were required to inhibit I(K1), the inhibitory potency of quinidine was also found to be insensitive to changes in [K+]o. Thus, in rats, the inhibitory potency of quinidine for the K+ current-types I(K), Ito and I(K1) is barely influenced by changes in [K+]o. These findings are consistent with our previous report showing that the QT-prolonging potency of quinidine was not altered under hypokalaemic conditions. However, whilst hypokalaemia does not affect I(K) or Ito, it can inhibit I(K1) and can result in QT prolongation in-vivo.     

Signaling pathways for monocyte chemoattractant protein 1-mediated extracellular signal-regulated kinase activation

G protein-coupled receptors (GPCRs) initiate diverse down-stream signaling events in response to ligand stimulation, as rapid activation of the extracellular signal-regulated kinase ERK1 and ERK2. The chemokine monocyte chemoattractant protein-1 (MCP-1) is the agonist for several chemokine receptors that belong to the GPCR superfamily, CCR2 being the most important. Stimulation of mitogen-activated protein kinases (MAPKs) by MCP-1 has been implicated in integrin activation and chemotaxis, but the molecular pathways down-stream of the receptors remain unclear. To dissect the cascade of events leading to MAPK activation upon CCR2 receptor stimulation, several specific inhibitors and mutants of signal transduction proteins were used in monocytic cells endogenously expressing CCR2 and/or in human embryonic kidney-293 cells transfected with CCR2B receptors and epitope-tagged ERK1. We show that ERK activation by MCP-1 involves heterotrimeric Gi protein subunits, protein kinase C, phosphoinositide-3-kinase, and Ras. On the other hand, the activity of cytosolic tyrosine kinases, epidermal growth factor receptor transactivation, or variations in intracellular calcium levels are not required for the mitogenic activation elicited by MCP-1. In addition, we find that internalization of CCR2B itself is not necessary for efficient MCP-1-induced activation of ERK, although a dynamin mutant partially inhibits ERK stimulation. These results suggest that different parallel pathways are being activated that lead to the full activation of the mitogen-activated protein kinase cascade and that internalization of other signaling proteins but not of the receptor is required for complete ERK activation.     

Cell-specific extracellular signal-regulated kinase activation by multiple G protein-coupled receptor families in hippocampus

Several families of G protein-coupled receptors (GPCR) have been shown to activate extracellular signal-regulated kinase (ERK) in transfected cells and non-neuronal systems. However, little is known about GPCR activation of ERK in brain. Because ERK is an important component in the regulation of synaptic plasticity, in this study we examined ERK activation by three families of GPCR that respond to major neuromodulatory neurotransmitters in the hippocampus. We used an immunocytochemical approach to examine ERK activation by muscarinic acetylcholine (mAChR), metabotropic glutamate (mGluR), and beta-adrenergic (beta-AR) receptors in CA1 neurons of mouse hippocampal slices. Because these GPCR families comprise receptors coupling to each of the major heterotrimeric G proteins, we examined whether ERK activation differs according to G-protein coupling. By using immunocytochemistry, we were able to examine not only whether each family of receptors activates ERK, but also the cellular populations and subcellular distributions of activated ERK. We demonstrated that M1 mAChRs and group I mGluRs, both of which are Gq-coupled receptors, activate ERK in CA1 pyramidal neurons, although activation in response to mAChR is more robust. The G(i/o)-coupled group II mGluRs activate ERK in glia scattered throughout CA1, and Gs-coupled beta-AR receptors activate ERK in scattered interneurons. Thus, we demonstrated that GPCR coupling to Gq, G(i/o), and Gs all activate ERK in the hippocampus, although each does so with unique properties and distributions.     

Protein kinase C activation by Helicobacter pylori in human gastric epithelial cells limits interleukin-8 production through suppression of extracellular signal-regulated kinase

Helicobacter pylori (H. pylori) infection of gastric epithelial cells has been shown to induce interleukin (IL)-8 production, but the signal transduction mechanism leading to IL-8 production has not been clearly defined. Here, we investigate the role of protein kinase C (PKC) in the mechanism of induction of IL-8 release by H. pylori in human gastric epithelial cells. In MKN45 cells, H. pylori-induced IL-8 release was enhanced by treatment with PKC inhibitors (GF109203X and calphostin C) and PKC depletion, which completely inhibited PKC activity. Moreover, PKC inhibitors and PKC depletion increased extracellular signal-regulated kinase (ERK) activity and phosphorylation, but not calcium/calmodulin-dependent protein kinase II (CaMK II) activity, in response to H. pylori infection. PKC activated by H. pylori inhibited activation of ERK induced by H. pylori without affecting the CaMK II activity and negatively regulated IL-8 production in human gastric epithelial cells.     

辛伐他汀改善大鼠心肌梗死后心室重塑与p-ERK1/2的关系

目的探讨辛伐他汀对大鼠心肌梗死后心室重塑的影响及其与磷酸化细胞外信号调节激酶1/2(p-ERK1/2)的关系。方法结扎Wistar大鼠冠状动脉左前降支建立心肌梗死模型,大鼠随机分为4组(n=8~10):心肌梗死对照组、辛伐他汀20、40mg处理组和假手术组。4wk后心脏超声检测各组心脏形态和功能,免疫组化法和Western blot检测p-ERK1/2表达。结果与假手术组相比,心肌梗死对照组及辛伐他汀处理组左室舒张末期内径(LVEDd)、左室后壁厚度(LVPWd)明显增加(P<0.01),左室射血分数(LVEF)、短轴缩短率(FS)、每博输出量(SV)和心输出量(CO)明显降低(P<0.01),心肌p-ERK1/2表达明显升高(P<0.01)。与心肌梗死对照组相比,辛伐他汀处理组LVEDd、LVPWd明显减少(P<0.01),LVEF、FS、SV和CO明显升高(P<0.01),心肌p-ERK1/2表达明显下降(P<0.01);其中辛伐他汀40mg组比20mg组心肌p-ERK1/2表达下降更明显(P<0.05)。结论辛伐他汀改善心肌梗死后心室重塑和心功能,其机制可能与下调心肌p-ERK1/2表达有关。     

Orthovanadate stimulates cAMP phosphodiesterase 3 activity in isolated rat hepatocytes through mitogen-activated protein kinase activation dependent on cAMP-dependent protein kinase

Orthovanadate (vanadate) as well as insulin stimulated phosphodiesterase 3 (PDE3) in the particulate fraction of rat hepatocytes. The vanadate-induced activations of PDE3 and mitogen-activated protein kinase (MAPK) were inhibited by H-89 and PD98059, suggesting that the MAPK activation via cAMP-dependent protein kinase (PKA) and MAPK kinase is involved in the vanadate action. On the other hand, the insulin-induced activations of PDE3 and Akt were inhibited by wortmannin, suggesting involvement of the Akt activation via phosphatidylinositol 3-kinase (PI3K) in the insulin action. The vanadate-induced activations of PKA and PDE3 were inhibited in part by propranolol or genistein, suggesting that vanadate may exert its actions via dual signaling pathways of beta-adrenergic receptors and receptor tyrosine kinases of growth factors. Vanadate, in contrast to insulin, did not promote the phosphorylation of insulin receptor substrate-1. The vanadate-induced increase in the phosphorylation of a main isoform of MAPKs, p44 protein, was detected by immunoblotting migration patterns of SDS-PAGE. A partially purified PDE3 activity was increased by addition of MAPK or Akt to the reaction mixture, suggesting that MAPK as well as Akt acts upstream of PDE3. The activation of PDE3 by insulin was independent of a transient increase in the MAPK activity, probably due to the dephosphorylated inactivation mediated by the induced activation of MAPK phosphatases (MKPs). Vanadate did not affect the MKP activity. These results indicate that vanadate stimulates the particulate PDE3 activity by activating mainly p44 MAPK via a PKA-dependent process, and that it differs from insulin with regard to a phosphorylation cascade of PDE3 activation.     

Hyposmotic challenge modulates function of L-type calcium channel in rat ventricular myocytes through protein kinase C

Aim:

To study the effects and mechanisms by which hyposmotic challenge modulate function of L-type calcium current (I_Ca,L) in rat ventricular myocytes.

Methods:

The whole-cell patch-clamp techniques were used to record I_Ca,L in rat ventricular myocytes.

Results:

Hyposmotic challenge(∼220 mosmol/L) induced biphasic changes of I_Ca,L, a transient increase followed by a sustained decrease. I_Ca,L increased by 19.1%±6.1% after short exposure (within 3 min) to hyposmotic solution. On the contrary, long hyposmotic challenge (10 min) decreased I_Ca,L to 78.1%±11.0% of control, caused the inactivation of I_Ca,L, and shifted the steady-state inactivation curve of I_Ca,L to the right. The decreased I_Ca,L induced by hyposmotic swelling was reversed by isoproterenol or protein kinase A (PKA) activator foskolin. Hyposmotic swelling also reduced the stimulated I_Ca,L by isoproterenol or foskolin. PKA inhibitor H-89 abolished swelling-induced transient increase of I_Ca,L, but did not affect the swelling-induced sustained decrease of I_Ca,L. NO donor SNAP and protein kinase G (PKG) inhibitor Rp-8-Br-PET-cGMPS did not interfere with swelling-induced biphasic changes of I_Ca,L. Protein kinase C (PKC) activator PMA decreased I_Ca,L and hyposmotic solution with PMA reverted the decreased I_Ca,L by PMA. PKC inhibitor BIM prevented the swelling-induced biphasic changes of I_Ca,L.

Conclusion:

Hyposmotic challenge induced biphasic changes of I_Ca,L, a transient increase followed by a sustained decrease, in rat ventricular myocytes through PKC pathway, but not PKG pathway. PKA system could be responsible for the transient increase of I_Ca,L during short exposure to hyposmotic solution.     

Caveolae-independent activation of protein kinase A in rat neonatal myocytes

Cardiomyocytes express both beta(1)- and beta(2)-adrenergic receptors, and these receptors play a differential role in chronotropic and inotropic effects of the heart. Caveolae are known as an important regulator of G-protein-coupled receptor signaling. In the present report, we examined whether caveolae have a role in beta-adrenergic receptor-stimulated cAMP production and protein kinase A activation in neonatal myocytes. Isoproterenol-stimulated cAMP production was mediated by beta(1)- and beta(2)-subtypes, which depends on the receptor number of each subtype. However, protein kinase A activation was exclusively mediated by the beta(1)-subtype. Disruption of caveolae by methyl-beta-cyclodextrin treatment did not affect the relative contribution of subtypes to isoproterenol-stimulated cAMP production. beta(1)-Subtype-mediated protein kinase A activation was also not affected by the disruption of caveolae. These results suggest that beta(1)-adrenergic receptor-mediated protein kinase A activation is compartmentalized and independent of caveolae.     

ERK/MAPK信号转导途径在急性髓系白血病发病机制中的作用

目的:研究急性髓系白血病细胞外信号调节激酶(ERK)/丝裂原活化蛋白激酶(M APK)的表达水平及其意义。方法:以急性髓系白血病细胞株HL-60细胞,31例初治急性髓系白血病(AM L)、14例AM L完全缓解(CR)和15例正常供髓者骨髓细胞为研究对象,应用流式细胞术检测磷酸化ERK 1/2信号分子的表达。结果:HL-60细胞,初治AM L、AM L-CR及正常骨髓细胞均表达磷酸化ERK 1/2,但表达水平不同。HL-60、初治AM L细胞与AM L-CR、正常细胞相比,磷酸化ERK 1/2表达水平均显著增高(P<0.05),高表达磷酸化ERK 1/2的初治AM L比例为80.6%(25/31)。结论:ERK/M APK信号途径的构成性激活在急性髓系白血病的发病中起重要作用。     

Effect of training on activation of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase pathways in rat soleus muscle

1. The effect of a chronic programme of either low- or moderate-to-high-intensity treadmill running on the activation of the extracellular-signal regulated protein kinase (ERK1/2) and the p38 mitogen-activated protein kinase (MAPK) pathways was determined in rat muscle. 2. Sprague-Dawley rats were assigned to one of three groups: (i) sedentary (NT; n = 8); (ii) low-intensity training (8 m/min; LIT; n = 16); and (iii) moderate-to-high-intensity training (28 m/min; HIT; n = 16). The training regimens were planned so that animals covered the same distance and had similar glycogen utilization for both LIT and HIT exercise sessions. 3. A single bout of LIT or HIT following 8 weeks of training led to a twofold increase in the phosphorylation of ERK1/2 (P = 0.048) and a two- to threefold increase in p38 MAPK (P = 0.005). Extracellular signal-regulated kinase 1/2 phosphorylation in muscle sampled 48 h after the last exercise bout was similar to sedentary values, while p38 MAPK phosphorylation was 70-80% lower than sedentary. One bout of LIT or HIT increased total ERK1/2 and p38 MAPK expression, with the magnitude of this increase being independent of prior exercise intensity or duration. Extracellular signal- regulated kinase 1/2 expression was increased three- to fourfold in muscle sampled 48 h after the last exercise bout irrespective of the prior training programme (P = 0.027), but p38 MAPK expression was approximately 90% lower than sedentary values. 4. In conclusion, exercise-training of different intensities/ durations results in selective postexercise activation of intracellular signalling pathways, which may be one mechanism regulating specific adaptations induced by diverse training programmes.