Extracellular signal-regulated kinase and p38 mitogen-activated protein kinase mediate macrophage proliferation induced by oxidized low-density lipoprotein

We previously reported that oxidized low-density lipoprotein (Ox-LDL)-induced expression of granulocyte/macrophage colony-stimulating factor (GM-CSF) via PKC, leading to activation of phosphatidylinositol-3 kinase (PI-3K), was important for macrophage proliferation [J Biol Chem 275 (2000) 5810]. The aim of the present study was to elucidate the role of extracellular-signal regulated kinase 1/2 (ERK1/2) and of p38 MAPK in Ox-LDL-induced macrophage proliferation. Ox-LDL-induced proliferation of mouse peritoneal macrophages assessed by [3H]thymidine incorporation and cell counting assays was significantly inhibited by MEK1/2 inhibitors, PD98059 or U0126, and p38 MAPK inhibitors, SB203580 or SB202190, respectively. Ox-LDL-induced GM-CSF production was inhibited by MEK1/2 inhibitors but not by p38 MAPK inhibitors in mRNA and protein levels, whereas recombinant GM-CSF-induced macrophage proliferation was inhibited by p38 MAPK inhibitors but enhanced by MEK1/2 inhibitors. Recombinant GM-CSF-induced PI-3K activation and Akt phosphorylation were significantly inhibited by SB203580 but enhanced by PD98059. Our results suggest that ERK1/2 is involved in Ox-LDL-induced macrophage proliferation in the signaling pathway before GM-CSF production, whereas p38 MAPK is involved after GM-CSF release. Thus, the importance of MAPKs in Ox-LDL-induced macrophage proliferation was confirmed and the control of MAPK cascade could be targeted as a potential treatment of atherosclerosis.     

Timing of mitogen-activated protein kinase (MAPK) activation in the rat pineal gland

Activation of members of the mitogen-activated protein kinase (MAPK) family of signaling cascades is a tightly controlled event in rat pinealocytes. Cell culture studies indicate that whereas the NE-->cGMP activation of p42/44MAPK is rapid and transient, the NE-->cAMP activation of p38MAPK is slower and more sustained. The decline in the p42/44MAPK response is in part due to the induction of MAPK phosphatase-1 by NE. In comparison, p38MAPK activation is tightly coupled to the synthesis and degradation of an upstream element in its activation cascade. Whole animal studies confirm activation of p42/44MAPK occurring during the early part of night and precedes p38MAPK activation. Studies with selective MAPK inhibitors reveal a modulating effect of MAPKs on arylalkylamine-N-acetyltransferse (AA-NAT) activity, with involvement of p42/44MAPK in the induction of AA-NAT and p38MAPK participating in the amplitude and duration of the AA-NAT response. These effects of p42/44MAPK and p38MAPK on AA-NAT activity match their timing of activation. Taken together, our studies on the timing of MAPK activation and regulation of AA-NAT by MAPKs add to the importance of MAPKs in regulating the circadian biology of the pineal gland.     

Adrenergic regulation of mitogen-activated protein kinase in rat pinealocytes: opposing effects of protein kinase A and protein kinase G

The role of adrenergic stimulation in the regulation of mitogen-activated protein kinase (MAPK) in rat pinealocytes was investigated by measuring phosphorylated MAPK using Western blot analysis and a MAPK enzymatic assay. Stimulation with the endogenous neurotransmitter, norepinephrine (NE; a mixed alpha- and beta-adrenergic agonist), concentration dependently increased the phosphorylation of both p44 and p42 isoforms of MAPK. This effect of NE was blocked by PD98059 and U0126 (two inhibitors of MEK). Treatment with prazosin or propranolol significantly reduced the effect of NE on MAPK phosphorylation, suggesting the involvement of both alpha- and beta-adrenergic receptors. Investigation into the intracellular mechanisms of NE action revealed that the increase in MAPK phosphorylation was blocked by KT5823 (a protein kinase G inhibitor), but was enhanced by H89 (a protein kinase A inhibitor). Calphostin C (a protein kinase C inhibitor) and KN93 (a Ca2+/calmodulin-dependent protein kinase inhibitor) also attenuated NE-mediated MAPK activation, but to a lesser degree. Furthermore, inhibition of MAPK phosphorylation by (Bu)2cAMP was effective in reducing MAPK activation by (Bu)2cGMP, an active phorbol ester or ionomycin. These results indicate that the effect of NE on MAPK phosphorylation represents mainly the integration of two signaling mechanisms, protein kinase A and protein kinase G, each having an opposite effect on MAPK phosphorylation.     

Simvastatin potenciates PGI(2) release induced by HDL in human VSMC: effect on Cox-2 up-regulation and MAPK signalling pathways activated by HDL

High density lipoproteins (HDL) induce prostacyclin (PGI(2)) release in vascular smooth muscle cells (VSMC) by up-regulation of cyclooxygenase-2 (Cox-2). Our goal was to analyse the mechanisms underlying this effect, and its potential modulation by HMG-CoA reductase inhibition in human VSMC. The contribution of mitogen-activated protein kinase (MAPK) signalling pathways was assessed by Western blot analysis and using specific inhibitors [PD098059 for p42/44 MAPK kinase (MEK); SB203580 for p38 MAPK or L-JNKI1 for c-Jun N-terminal kinase-1 (JNK-1)]. HDL-induced PGI(2) release was inhibited by rofecoxib (a specific Cox-2 inhibitor, 5 microM). HDL induced the early activation of p42 MAPK, p38 MAPK and JNK-1. p42/44 MAPK was the major pathway involved in both Cox-2 up-regulation and PGI(2) synthesis; p38 MAPK was also involved in both processes while JNK inhibition only affected PGI(2) synthesis. Pertussis toxin (an inhibitor of Galphai/Galphao proteins) prevented MAPK activation and inhibited both Cox-2 up-regulation and PGI(2) release. Genistein (a tyrosine kinase inhibitor) inhibited PGI(2) release without affecting MAPK activation or Cox-2 up-regulation. Simvastatin (0.1-1 microM) increased HDL-induced PGI(2) release ( approximately 45% at 1 microM) but did not significantly modify early MAPK activation or Cox-2 expression. Simvastatin alone did not significantly affect PGI(2) release. Our results suggest that mechanisms associated with G protein-coupled receptor activation, trigger Cox-2 up-regulation and PGI(2) release via multiple MAPK signalling pathways in VSMC. The mechanism is independent of tyrosine kinase receptors, although cytosolic tyrosine kinases could activate Cox-2 post-translationally. The potential contribution of HDL to vascular homeostasis, via increases in PGI(2) synthesis, could be enhanced by HMG-CoA reductase inhibitors.     

Differential roles of extracellular signal-regulated kinase 1/2 and p38MAPK in mechanical load-induced procollagen alpha1(I) gene expression in cardiac fibroblasts

OBJECTIVE AND METHODS: We have previously demonstrated that mechanical loading of cardiac fibroblasts leads to increased synthesis and gene expression of the extracellular matrix protein collagen. We hypothesised that the upregulation of procollagen gene expression in cardiac fibroblasts, in response to cyclic mechanical load, is mediated by one or more members of the MAP kinase family. To test this hypothesis, the effect of mechanical load on the activation of extracellular signal-regulated kinase (ERK) 1/2, p46/54JNK, and p38MAPK was examined in rat cardiac fibroblasts. RESULTS: Peak phosphorylation of ERK 1/2, p38MAPK kinases, and p46/54JNK was observed following 10-20 min of continuous cyclic mechanical load. Mechanical load significantly increased procollagen alpha1(I) mRNA levels up to twofold above static controls after 24 h. This increase was completely abolished by the MEK 1/2 inhibitor U0126, with no effect on basal levels. In contrast, SB203580, a specific inhibitor of p38MAPK, enhanced both basal and stretch-stimulated levels of procollagen mRNA. Consistent with this finding, selective activation of the p38MAPK signalling pathway by expression of MKK6(Glu), a constitutive activator of p38MAPK, significantly reduced procollagen alpha1(I) promoter activity. SB203580-dependent increase in procollagen alpha1(I) was accompanied by ERK 1/2 activation, and inhibition of this pathway completely prevented SB203580-induced procollagen alpha1(I) expression. CONCLUSIONS: These results suggest that mechanical load-induced procollagen alpha1(I) gene expression requires ERK 1/2 activation and that the p38MAPK pathway negatively regulates gene expression in cardiac fibroblasts. These pathways are likely to be key in events leading to matrix deposition during heart growth and remodelling induced by mechanical load.     

Integrins play a critical role in mechanical stress-induced p38 MAPK activation

Mechanical stress activates various hypertrophic responses, including activation of mitogen-activated protein kinases (MAPKs) in cardiac myocytes. Stretch activated extracellular signal-regulated kinases partly through secreted humoral growth factors, including angiotensin II, whereas stretch-induced activation of c-Jun NH(2)-terminal kinases and p38 MAPK was independent of angiotensin II. In this study, we examined the role of integrin signaling in stretch-induced activation of p38 MAPK in cardiomyocytes of neonatal rats. Overexpression of the tumor suppressor PTEN, which inhibits outside-in integrin signaling, strongly suppressed stretch-induced activation of p38 MAPK. Overexpression of focal adhesion kinase (FAK) antagonized the effects of PTEN, and both tyrosine residues at 397 and 925 of FAK were necessary for its effects. Stretch induced tyrosine phosphorylation and activation of FAK and Src. Stretch-induced activation of p38 MAPK was abolished by overexpression of FAT and CSK, which are inhibitors of the FAK and Src families, respectively, and was suppressed by overexpression of a dominant-negative mutant of Ras. Mechanical stretch-induced increase in protein synthesis was suppressed by SB202190, a p38 MAPK inhibitor. These results suggest that mechanical stress activates p38 MAPK and induces cardiac hypertrophy through the integrin-FAK-Src-Ras pathway in cardiac myocytes.     

Erythropoietin protects the infant heart against ischemia–reperfusion injury by triggering multiple signaling pathways

The immediate protective effect of erythropoietin (EPO) against ischemia in heart suggests a role beyond hematopoiesis and the treatment of anemia. We determined the role of JAK/STAT and Ras/Rac/MAPK in the protective effect of EPO against ischemia–reperfusion injury in infant rabbit heart. EPO (1.0 U/ml) administered 15 minutes prior to 30–minutes global ischemia and 35 minutes reperfusion resulted in increased recovery of postischemic ventricular developed pressure in rabbit hearts. EPO exerted its immediate cardioprotective effect via activation of multiple signaling pathways by: 1) phosphorylation and activation of JAK1/2, STAT3 and STAT5A but not of STAT1 and STAT5B, 2) phosphorylation and activation of PI₃ kinase and its downstream kinases Akt and Rac, 3) activation of PKC, Raf, MEK1/2, p42/44 MAPK and p38 MAPK. Pretreatment with Wortmannin abolished EPO–induced Akt activation and phosphorylation. Pretreatment with Chelerythrine followed by EPO treatment resulted in partial inhibition of Raf activation, and abolished PKC and p38 MAPK activation without any effect on Akt, MEK1/2 and p42/44 MAPK. PD98059 abolished MEK1/2 and p42/44 MAPK activation with no effect on Akt, Raf and p38 MAPK activation. SB203580 inhibited only p38 MAPK activation by EPO. We can conclude EPO increases immediate cardioprotection through the activation of multiple signal transduction pathways.     

Diurnal variation in p42/44 mitogen-activated protein kinase in the rat pineal gland

In this study, we investigated whether there was a diurnal difference in mitogen-activated protein kinase (p42/44(MAPK)) phosphorylation in the rat pineal gland. Under a lighting regimen with 12h of darkness, there was a two- to four-fold increase in phosphorylated levels of MAPK kinase 1/2 (MEK1/2) and p42/44(MAPK) 2h after onset of darkness, an increase that was sustained for 8h. The increases in phosphorylated levels of MEK1/2 and p42/44(MAPK) occurred without increases in MEK1/2 and p42/44(MAPK) proteins. When rats were treated with propranolol 1h before onset of darkness or subjected to continuous light exposure during the dark phase, the nocturnal increase in MEK1/2 and p42/44(MAPK) phosphorylation was reduced. Acute light exposure during darkness caused a decline in MEK1/2 and p42/44(MAPK) phosphorylation within 30 min of light exposure. These results indicate the presence of a diurnal difference in MEK1/2 and p42/44(MAPK) phosphorylation in the rat pineal gland that is under adrenergic control.     

Distinct roles of p42/p44ERK and p38 MAPK in oxidant-induced AP-1 activation and cardiomyocyte hypertrophy

Cardiac hypertrophy is an adaptive response to a number of heart diseases including myocardial infarction. Although it can be compensatory at first, sustained hypertrophy is often a transition to heart failure. We have found that cardiomyocytes in culture can survive mild doses of H₂O₂ but develop hypertrophy involving activation of p70 S6 kinase 1 (p70S6K1). Here, the role of p42/p44^ERK and p38 MAPK in oxidant-induced hypertrophy is tested. H₂O₂-induced phosphorylation (activation) of p42/p44^ERK and p38 within 10 min of 200 μM H₂O₂ exposure. Although p42/p44^ERK remained highly phosphorylated from 60 to 120 min, the level of p38 phosphorylation reached highest at 60 min and started to decline at 90 min. Inhibiting ERKs with PD98059 attenuated H₂O₂-induced AP-1 activation but did not affect H₂O₂-induced p70S6k1 activation or cardiomyocyte enlargement as measured by increases in cell volume and protein content. In contrast, the p38 inhibitor SB202190 has not inhibitory effect on AP-1 activation but partially prevented H₂O₂ from inducing p70S6K1 activation and cell enlargement. These data suggest that while p42/p44^ERK participates in gene expression associated with hypertrophy, p38 may regulate cell size increase by p70S6K1 activation.     

Tauroursodesoxycholate-induced choleresis involves p38(MAPK) activation and translocation of the bile salt export pump in rats

BACKGROUND & AIMS: Canalicular secretion of bile acids is stimulated by tauroursodesoxycholate (TUDC). This study investigates the underlying mechanisms. METHODS: TUDC effects on mitogen-activated protein (MAP) kinases, taurocholate (TC) excretion, proteolysis, and the localization of the bile salt export pump (Bsep) were studied in rat hepatocytes and perfused liver. RESULTS: TUDC induced a transient and concentration-dependent activation of p38(MAPK) and of extracellular signal-regulated kinase 2 (Erk-2), but not of c-Jun-N-terminal kinase (JNK). In perfused liver, TUDC concentrations of 20 micromol/L was sufficient to elicit the MAP kinase responses and TC choleresis. SB 202190, a specific inhibitor of p38(MAPK), had no effect on TUDC- induced Erk activation but abolished the stimulatory effect of TUDC on TC excretion in perfused liver, indicating the requirement of p38(MAPK) in addition to the reported Erk dependence for the choleretic response. TUDC-induced stimulation of TC excretion was accompanied by a p38(MAPK)-dependent insertion of subcanalicular immunoreactive Bsep into the canalicular membrane. In addition TUDC induced a p38(MAPK)-sensitive inhibition of proteolysis. CONCLUSIONS: TUDC-induced stimulation of canalicular TC excretion involves a MAP kinase-dependent translocation of subcanalicular Bsep to the canalicular membrane. Dual activation of Erks and p38(MAPK) is required for the choleretic effect of both TUDC and hypo-osmotic cell swelling.     

Signal transduction of bombesin-induced circular smooth muscle cell contraction in cat esophagus

AIM: To investigate the mechanism of bombesin-induced circular smooth muscle cell contraction in cat esophagus. METHODS: Specific G protein or phospholipase C involved in cat esophagus contraction was identified, muscle cells were permeabilized with saponin. After per-meabilization of muscle cells, the Gi3 antibody inhibited bombesin-induced smooth muscle cell contraction. RESULTS: Incubation of permeabilized circular muscle cells with PLC-β3 antibody could inhibit bombesin-induced contraction. H-7, chelerythrine (PKC inhibitor) and genistein (protein tyrosine kinase inhibitor) inhibited bombesin-induced contraction, but DAG kinase inhibitor, R59949, could not inhibit it. To examine which mitogen-activated protein kinase (MAPK) was involved in bombesin-induced contraction, the specific MAPK inhibitors (MEK inhibitor, PD98059 and p38 MAPK inhibitor, SB202190) were used. Preincubation of PD98059 blocked the contraction induced by bombesin in a concentration-dependent manner. However, SB202190 had no effects on contraction. CONCLUSION: Bombesin-induced circular muscle cell contraction in cat esophagus is madiated via a PKC or a PTK-dependent pathway or p44/p42 MAPK pathway.     

P38 MAPK inhibition enhancing ATO-induced cytotoxicity against multiple myeloma cells

The resistance to arsenic trioxide (ATO) treatment is relatively common (55–80%) in multiple myeloma patients. This study found that ATO at clinically achievable concentrations (2–7 μmol/l) activated p38 mitogen-activated protein kinase (MAPK) in both myeloma cell lines and primary myeloma cells, a finding not previously well-documented in myeloma cells. Inhibition of p38 MAPK activation by pharmacological inhibitors (SB203580) or downregulation of p38 MAPK by siRNA significantly increased the apoptosis and/or growth inhibition induced by ATO treatment in myeloma cells. Combination of ATO and p38 MAPK inhibition abolished the interleukin-6 enhanced protection of myeloma cells against ATO treatment. The ATO-resistant cell line developed in our laboratory showed an increase in p38 MAPK activation. The increase of apoptosis by the combination of ATO and SB203580 was accompanied by the activation of caspase-9 and caspase-8 suggesting that both extrinsic and intrinsic apoptotic pathways are involved. Additionally, the p38 MAPK activation by ATO was associated with increased phosphorylation and upregulated expression of Heat shock protein 27. These results suggest that ATO-induced p38 MAPK activation plays an important role in the resistance to ATO in myeloma cells and that p38 MAPK inhibition may overcome resistance to ATO treatment in myeloma patients.     

血管紧张素Ⅱ对人脐静脉内皮细胞p38丝裂素激活蛋白激酶通路的作用

目的探讨血管紧张素Ⅱ(AngⅡ)激活人脐静脉内皮细胞(HUVECs)p38丝裂素激活蛋白激酶(p38MAPK)信号转导通路的作用。方法用含20%胎牛血清的DMEM培养基与CO_2培养箱(5%CO_2+95%空气)培养HUVECs。待细胞生长至80%融合时,无血清培养16h后分组:(1)AngⅡ不同时点观察组:用AngⅡ(终浓度100 nmol/L)分别刺激细胞0、5、10、15、30、45 min和60 min。(2)AngⅡ不同剂量作用组:分别用终浓度为0、10、100、1000 nmol/L和10 000 nmol/L的AngⅡ刺激细胞15 min。(3)AngⅡ+p38MAPK特异性抑制剂SB202190组:在AngⅡ(终浓度100 nmol/L)刺激前30 min,分别将1000 nmol/L和5000 nmol/L(终浓度)的SB202190加入培养基,共同孵育30 min。上述各组作用一定时间后收集细胞,用Western blot方法测定细胞p38MAPK磷酸化表达。结果 AngⅡ(100 nmol/L)可诱导HUVECs p38MAPK磷酸化表达,15～30 min达到高峰,分别升高2.25和2.51倍(P<0.005,n=5),随时间呈峰形变化;AngⅡ呈剂量依赖性诱导HUVECs p38MAPK磷酸化,在AngⅡ100 nmol/L时p38MAPK磷酸化表达即有明显增强,在AngⅡ刺激剂量为1000 nmol/L和10 000 nmol/L时,p38MAPK磷酸化表达分别增加2.03和2.11倍(P<0.005,n=5);p38MAPK特异性抑制剂SB202190可显著抑制HUVECs p38MAPK磷酸化,且呈剂量依赖性,5000 nmol/L SB202190的抑制率为53.9%(P<0.01,n=6)。结论 AngⅡ可激活人脐静脉内皮细胞p38MAPK信号通路。     

Ischemic preconditioning involves dual cardio-protective axes with p38MAPK as upstream target

The existing literature indicates a crucial role of p38 MAP (mitogen-activated protein) kinase (p38MAPK) and its downstream target MAPKAP kinase 2 (MK2) in ischemic preconditioning (IPC). Accordingly, deletion of MK2 gene should abolish the cardioprotective ability of IPC. Interestingly, we were able to partially precondition the hearts from MK2(-/-) knockout mice suggesting the existence of an as yet unknown alternative downstream target of p38MAPK. A recent study from our laboratory also determined a crucial role of CREB (cyclic AMP response element binding protein) in IPC. Since CREB is a downstream target of MSK-1 (mitogen- and stress-activated protein kinase-1) situated at the crossroad of ERK (extracellular receptor kinase) and p38MAPK signaling pathways, we reasoned that MSK-1 could be a downstream molecular target for p38MAPK and ERK signaling in the IPC hearts. To test this hypothesis, the rat hearts were subjected to IPC by four cyclic episodes of 5 min ischemia and 10 min reperfusion. As expected, IPC induced the activation of ERK1/2, p38MAPK, MK2 and HSP (heat shock protein) 27 as evidenced by their increased phosphorylation; and the inhibition of p38MAPK with SB203580 almost completely, and the inhibition of ERK1/2 with PD098059 partially, abolished cardioprotective effects of IPC. Inhibition of MSK-1 with short hairpin RNA (shRNA) also abolished the IPC-induced cardioprotection. SB203580 partially blocked the effects of MSK-1 suggesting that MSK-1 sits downstream of p38MAPK. shRNA-MSK-1 blocked the contribution of both p38MAPK and ERK1/2 as it is uniquely situated at the downstream crossroad of both of these MAP kinases. Although MSK-1 sits downstream of both ERK1/2 and p38MAPK, ERK1/2 activation appears to play less significant role compared to p38MAPK, since its inhibition blocked MSK activation only partially. Consistent with these results, shRNA-MSK-1 blocked the partial PC in MK2(-/-) hearts, and in combination with SB203580, completely abolished the PC effects in the wild-type hearts. The IPC-induced survival signaling was almost completely inhibited with SB203580, and only partially with PD 098059 as evidenced from the inhibition patterns of IPC induced activation of CREB, Akt and Bcl-2. Again SB203580 alone or in combination with shRNA-MSK-1 inhibited IPC induced survival signal comparatively, suggesting that MSK-1 exists downstream of p38MAPK. Taken together, these results indicate for the first time MSK-1 as an alternative (other than MK2) downstream target for p38MAPK, which also transmits survival signal through the activation of CREB.     

Adrenergic regulation and diurnal rhythm of p38 mitogen-activated protein kinase phosphorylation in the rat pineal gland

In this study, we investigated adrenergic and photoneural regulation of p38MAPK phosphorylation in the rat pineal gland. Norepinephrine (NE), the endogenous neurotransmitter, dose-dependently increased the levels of phosphorylated MAPK kinase 3/6 (MKK3/6) and p38MAPK in rat pinealocytes. Time-course studies showed a gradual increase in MKK3/6 and p38MAPK phosphorylation that peaked between 1 and 2 h and persisted for 4 h post NE stimulation. In cells treated with NE for 2 and 4 h, the inclusion of prazosin or propranolol reduced NE-induced MKK3/6 and p38MAPK phosphorylation, indicating involvement of both alpha- and beta-adrenergic receptors for the sustained response. Whereas treatment with dibutyryl cAMP or ionomycin mimicked the NE-induced MKK3/6 and p38MAPK phosphorylation, neither dibutyryl cGMP nor 4beta-phorbol 12-myristate 13-acetate had an effect. The NE-induced increase in MKK3/6 and p38MAPK phosphorylation was blocked by KT5720 (a protein kinase A inhibitor) and KN93 (a Ca(2+)/calmodulin-dependent kinase inhibitor), but not by KT5823 (a protein kinase G inhibitor) or calphostin C (a protein kinase C inhibitor). In animals housed under a lighting regimen with 12 h of light, MKK3/6 and p38MAPK phosphorylation increased in the rat pineal gland at zeitgeber time 18. The nocturnal increase in p38MAPK phosphorylation was blocked by exposing the animal to constant light and reduced by treatment with propranolol, a beta-adrenergic blocker. Together, our results indicate that activation of p38MAPK is under photoneural control in the rat pineal gland and that protein kinase A and intracellular Ca(2+) signaling pathways are involved in NE regulation of p38MAPK.     

Activation of p38 MAPK induced by a multi-cycle ischaemic preconditioning protocol is associated with attenuated p38 MAPK activity during sustained ischaemia and reperfusion

The role of p38 mitogen-activated protein kinase (MAPK) in ischaemic preconditioning remains controversial. Since most previous studies focussed on events only during sustained ischaemia, the aim of this study was to establish the activation pattern of p38 MAPK during a multicycle preconditioning protocol, sustained ischaemia as well as reperfusion and to correlate these events with functional recovery of the isolated perfused rat heart. Isolated perfused rat hearts were preconditioned by 3x5 min global ischaemia followed by 25 min global ischaemia and 30 min reperfusion. Non-preconditioned hearts were subjected to 25 min global ischaemia and 30 min reperfusion. Hearts were freeze-clamped and p38 MAPK activation in tissue lysates was assessed by standard Western blotting techniques, using a dual phospho-p38 MAPK antibody as well as a non-radioactive IP-kinase assay. The results showed that transient dual phosphorylation and activation of p38 MAPK occurs during a 3x5 min preconditioning protocol: the activation was maximal during the first episode, becoming progressively lower during the second and third episodes. p38 MAPK activation was significantly less during both sustained ischaemia and reperfusion in preconditioned hearts, when compared with non-preconditioned hearts. Attenuation of p38 MAPK activity during sustained ischaemia and reperfusion was associated with improved functional recovery. The effect of inhibition of p38 MAPK activation on cardioprotection was further evaluated in adult, isolated cardiomyocytes. Administration of SB 203580 (1-10 microM) before and during the preconditioning protocol, had no effect on cell morphology and viability after 2 h hypoxia, compared to untreated preconditioned cardiomyocytes. When administered to non-preconditioned cells before the onset of 2 h hypoxia, it caused a significant improvement in both morphology and viability. In summary, the results suggest that attenuation of the kinase activity during sustained ischaemia and reperfusion may be an essential element of the preconditioning process.