H(2)O(2)-induced Ca(2+) overload in NRVM involves ERK1/2 MAP kinases: role for an NHE-1-dependent pathway

Postconditioning for salvage of ischemic skeletal muscle from reperfusion injury: efficacy and mechanism

We tested our hypothesis that postischemic conditioning (PostC) is effective in salvage of ischemic skeletal muscle from reperfusion injury and the mechanism involves inhibition of opening of the mitochondrial permeability transition pore (mPTP). In bilateral 8x13 cm pig latissimus dorsi muscle flaps subjected to 4 h ischemia, muscle infarction increased from 22+/-4 to 41+/-1% between 2 and 24 h reperfusion and remained unchanged at 48 (38+/-6%) and 72 (40+/-1%) h reperfusion (P<0.05; n=4 pigs). PostC induced by four cycles of 30-s reperfusion/reocclusion at the onset of reperfusion after 4 h ischemia reduced muscle infarction from 44+/-2 to 22+/-2% at 48 h reperfusion. This infarct protective effect of PostC was mimicked by intravenous injection of the mPTP opening inhibitor cyclosporin A or NIM-811 (10 mg/kg) at 5 min before the end of 4 h ischemia and was abolished by intravenous injection of the mPTP opener atractyloside (10 mg/kg) at 5 min before PostC (P<0.05; n=4-5 pigs). PostC or intravenous cyclosporin A injection at 5 min before reperfusion caused a decrease in muscle myeloperoxidase activity and mitochondrial free Ca2+ concentration and an increase in muscle ATP content after 4 h ischemia and 2 h reperfusion compared with the time-matched controls. These effects of PostC were abolished by intravenous injection of atractyloside at 5 min before PostC (P<0.05; n=6 pigs). These observations support our hypothesis that PostC is effective in salvage of ischemic skeletal muscle from reperfusion injury and the mechanism involves inhibition of opening of the mPTP.

Ecstasy produces left ventricular dysfunction and oxidative stress in rats

AIMS

Our aim was to determine whether the repeated, binge administration of 3,4-methylenedioxymethamphetamine (ecstasy; MDMA) produces structural and/or functional changes in the myocardium that are associated with oxidative stress.

METHODS AND RESULTS

Echocardiography and pressure-volume conductance catheters were used to assess left ventricular (LV) structure and function in rats subjected to four ecstasy binges (9 mg/kg i.v. for 4 days, separated by a 10 day drug-free period). Hearts from treated and control rats were used for either biochemical and proteomic analysis or the isolation of adult LV myocytes. After the fourth binge, treated hearts showed eccentric LV dilation and diastolic dysfunction. Systolic function was not altered in vivo; however, the magnitude of the contractile responses to electrical stimulation was significantly smaller in myocytes from rats treated in vivo with ecstasy compared with myocytes from control rats. The magnitude of the peak increase in intracellular calcium (measured by Fura-2) was also significantly smaller in myocytes from ecstasy-treated vs. control rats. The relaxation kinetics of the intracellular calcium transients were significantly longer in myocytes from ecstasy-treated rats. Ecstasy significantly increased nitrotyrosine content in the left ventricle. Proteomic analysis revealed increased nitration of contractile proteins (troponin-T, tropomyosin alpha-1 chain, myosin light polypeptide, and myosin regulatory light chain), mitochondrial proteins (Ub-cytochrome-c reductase and ATP synthase), and sarcoplasmic reticulum calcium ATPase.

CONCLUSION

The repeated binge administration of ecstasy produces eccentric LV dilation and dysfunction that is accompanied by oxidative stress. These functional responses may result from the redox modification of proteins involved in excitation-contraction coupling and/or mitochondrial energy production. Together, these results indicate that ecstasy has the potential to produce serious cardiac toxicity and ventricular dysfunction.

KCNA1 and TRPC6 ion channels and NHE1 exchanger operate the biological outcome of HGF/scatter factor in renal tubular cells

Hepatocyte growth factor (HGF) is a glycoprotein that induces in vitro epithelial tubular cell growth, motility, scattering and branching morphogenesis. The cell machineries that account for HGF biological effects are still unclear. In previous study, we found that HGF upregulated in epithelial tubular cell line (HK2) 3 genes: potassium channel KCNA1, calcium channel (transient receptor potential channel, subfamily C, member 6, TRPC6) and Na(+)/H(+) exchanger-1 (NHE1). In this study, we validated these results with reverse transcription PCR and WB analysis. To investigate whether KCNA1, TRPC6, NHE1 mediate the changes induced by HGF in HK2, we studied the effects of their inhibitors: 4-aminopyridine, charybdotoxin, dendrotoxin K inhibitors of KCNA1, lanthanum, N-(p-amylcinnamoyl) anthranilic acid inhibitors of TRPC6, 5-(N-ethyl-N-isopropyl)amiloride, cariporide inhibitors of NHE1. The inhibitors prevented HGF-induced growth, migration, cytoskeletal reorganization and tubulogenesis in HK2. These results indicate that KCNA1, TRPC6 and NHE1 are cell machineries that are exploited by HGF to effect its biological outcome in renal tubular cells.

Mitochondrial reactive oxygen species activate the slow force response to stretch in feline myocardium

When the length of the myocardium is increased, a biphasic response to stretch occurs involving an initial rapid increase in force followed by a delayed slow increase called the slow force response (SFR). Confirming previous findings involving angiotensin II in the SFR, it was blunted by AT1 receptor blockade (losartan). The SFR was accompanied by an increase in reactive oxygen species (ROS) of approximately 30% and in intracellular Na(+) concentration ([Na(+)](i)) of approximately 2.5 mmol l(-1) over basal detected by H(2)DCFDA and SBFI fluorescence, respectively. Abolition of ROS by 2-mercapto-propionyl-glycine (MPG) and EUK8 suppressed the increase in [Na(+)](i) and the SFR, which were also blunted by Na(+)/H(+) exchanger (NHE-1) inhibition (HOE642). NADPH oxidase inhibition (apocynin or DPI) or blockade of the ATP-sensitive mitochondrial potassium channels (5HD or glybenclamide) suppressed both the SFR and the increase in [Na(+)](i) after stretch, suggesting that endogenous angiotensin II activated NADPH oxidase leading to ROS release by the ATP-sensitive mitochondrial potassium channels, which promoted NHE-1 activation. Supporting the notion of ROS-mediated NHE-1 activation, stretch increased the ERK1/2 and p90rsk kinases phosphorylation, effect that was cancelled by losartan. In agreement, the SFR was cancelled by inhibiting the ERK1/2 signalling pathway with PD98059. Angiotensin II at a dose that mimics the SFR (1 nmol l(-1)) induced an increase in .O(2)(-) production of approximately 30-40% detected by lucigenin in cardiac slices, an effect that was blunted by losartan, MPG, apocynin, 5HD and glybenclamide. Taken together the data suggest a pivotal role of mitochondrial ROS in the genesis of the SFR to stretch.

Role of oxygen in postischemic myocardial injury

Myocardial function is dependent on a constant supply of oxygen from the coronary circulation. A reduction of oxygen supply due to coronary obstruction results in myocardial ischemia, which leads to cardiac dysfunction. Reperfusion of the ischemic myocardium is required for tissue survival. Thrombolytic therapy, coronary artery bypass surgery and coronary angioplasty are some of the treatments available for the restoration of blood flow to the ischemic myocardium. However, the restoration of blood flow may also lead to reperfusion injury, resulting in myocyte death. Thus, any imbalance between oxygen supply and metabolic demand leads to functional, metabolic, morphologic, and electrophysiologic alterations, causing cell death. Myocardial ischemia reperfusion (IR) injury is a multifactorial process that is mediated by oxygen free radicals, neutrophil activation and infiltration, calcium overload, and apoptosis. Controlled reperfusion of the ischemic myocardium has been advocated to prevent the IR injury. Studies have shown that reperfusion injury and postischemic cardiac function are related to the quantity and delivery of oxygen during reperfusion. Substantial evidence suggests that controlled reoxygenation may ameliorate postischemic organ dysfunction. In this review, we discuss the role of oxygenation during reperfusion and subsequent biochemical and pathologic alterations in reperfused myocardium and recovery of heart function.

Mechanism of Na+/Ca2+ exchanger activation by hydrogen peroxide in guinea-pig ventricular myocytes

Using the whole-cell voltage clamp, we examined the mechanism of activation of the Na(+)/Ca(2+) exchanger (NCX) by hydrogen peroxide (H(2)O(2)) in isolated guinea-pig cardiac ventricular myocytes. Exposure to H(2)O(2) increased the NCX current. The effect was inhibited by cariporide, an inhibitor of the Na(+)/H(+) exchanger (NHE), suggesting that there are NHE-dependent and -independent pathways in the effect of H(2)O(2) on NCX. In addition, both pathways were blocked by edaravone, a hydroxyl radical (*OH) scavenger; pertussis toxin, a Galpha(i/o) protein inhibitor; and U0126, an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK). On the other hand, wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, inhibited only the NHE-dependent pathway, while PP2, a Src family protein tyrosine kinase inhibitor, inhibited only the NHE-independent pathway. Taken together, our data suggest that H(2)O(2) increases the NCX current via two signal transduction pathways. The common pathway is the conversion of H(2)O(2) to *OH, which activates Galpha(i/o) protein and a mitogen-activated protein (MAP) kinase signaling pathway. Then, one pathway activates NHE with a PI3K-dependent mechanism and indirectly increases the NCX current. Another pathway involves activation of a Src family tyrosine kinase.

Calcium signaling phenomena in heart diseases: a perspective

Ca(2+) is a major intracellular messenger and nature has evolved multiple mechanisms to regulate free intracellular (Ca(2+))(i) level in situ. The Ca(2+) signal inducing contraction in cardiac muscle originates from two sources. Ca(2+) enters the cell through voltage dependent Ca(2+) channels. This Ca(2+) binds to and activates Ca(2+) release channels (ryanodine receptors) of the sarcoplasmic reticulum (SR) through a Ca(2+) induced Ca(2+) release (CICR) process. Entry of Ca(2+) with each contraction requires an equal amount of Ca(2+) extrusion within a single heartbeat to maintain Ca(2+) homeostasis and to ensure relaxation. Cardiac Ca(2+) extrusion mechanisms are mainly contributed by Na(+)/Ca(2+) exchanger and ATP dependent Ca(2+) pump (Ca(2+)-ATPase). These transport systems are important determinants of (Ca(2+))(i) level and cardiac contractility. Altered intracellular Ca(2+) handling importantly contributes to impaired contractility in heart failure. Chronic hyperactivity of the beta-adrenergic signaling pathway results in PKA-hyperphosphorylation of the cardiac RyR/intracellular Ca(2+) release channels. Numerous signaling molecules have been implicated in the development of hypertrophy and failure, including the beta-adrenergic receptor, protein kinase C, Gq, and the down stream effectors such as mitogen activated protein kinases pathways, and the Ca(2+) regulated phosphatase calcineurin. A number of signaling pathways have now been identified that may be key regulators of changes in myocardial structure and function in response to mutations in structural components of the cardiomyocytes. Myocardial structure and signal transduction are now merging into a common field of research that will lead to a more complete understanding of the molecular mechanisms that underlie heart diseases. Recent progress in molecular cardiology makes it possible to envision a new therapeutic approach to heart failure (HF), targeting key molecules involved in intracellular Ca(2+) handling such as RyR, SERCA2a, and PLN. Controlling these molecular functions by different agents have been found to be beneficial in some experimental conditions.

The influence of Zn on signaling pathways and attachment of Mytilus galloprovincialis haemocytes to extracellular matrix proteins

The present study investigates the cytotoxic mechanisms induced by zinc (Zn) in haemocytes of mussel Mytilus galloprovincialis. Haemocytes play a key role in the immune defence of mussels. Micromolar concentration of Zn (50 microM) play an important role in the elevation of pHi and increase in Na+ influx in haemocytes. The observed effects were inhibited by the Na+/H+ exchanger (NHE) inhibitor, ethyl-N-isopropyl-amiloride (EIPA). Furthermore, our results showed that Zn caused an increase in O(-)(2) production that was reversed after NHE inhibition. Phorbol ester (PMA) caused a significant rise both in pHi and Na+ influx as well as in O(-)(2) production. These effects were reversed by calphostin C. Our results indicated that Zn also enhanced haemocyte attachment to both BSA and laminin which was reversed by EIPA and calphostin C. The enhancement of haemocytes attachment to both BSA and laminin after Zn suggests that it is likely to play a signal role in cytoskeleton-dependent process of cell growth and migration in mussel M. galloprovincialis haemocytes. We conclude that Zn induces a signaling pathway with the involvement of NHE, PKC, O(-)(2) and alpha1- and beta-adrenergic receptors.

Functional link between TNF biosynthesis and CaM-dependent activation of inducible nitric oxide synthase in RAW 264.7 macrophages

Inflammatory responses stimulated by bacterial endotoxin LPS involve Ca2+-mediated signaling, yet the cellular sensors that determine cell fate in response to LPS remain poorly understood. We report that exposure of RAW 264.7 macrophage-like cells to LPS induces a rapid increase in CaM abundance, which is associated with the modulation of the inflammatory response. Increases in CaM abundance precede nuclear localization of key transcription factors (i.e., NF-κB p65 subunit, phospho-c-Jun, Sp1) and subsequent increases in the proinflammatory cytokine TNF-α and inducible nitric oxide synthase (iNOS). Cellular apoptosis after LPS challenge is blocked upon inhibition of iNOS activity using the pharmacological inhibitor 1400W. LPS-mediated iNOS expression and apoptosis also were inhibited by siRNA-mediated silencing of TNF induction, indicating TNF induction both precedes and is necessary for subsequent regulation of iNOS expression. Increasing the level of cellular CaM by stable transfection results in reductions in LPS-induced expression of TNF and iNOS, along with reduced activation of their transcriptional regulators and concomitant protection against apoptosis. Thus the level of CaM available for Ca2+-dependent signaling regulation plays a key role in determining the expression of the proinflammatory and proapoptotic cascade during cellular activation by LPS. These results indicate a previously unrecognized central role for CaM in maintaining cellular homeostasis in response to LPS such that, under resting conditions, cellular concentrations of CaM are sufficient to inhibit the biosynthesis of proinflammatory mediators associated with macrophage activation. Although CaM and iNOS protein levels are coordinately increased as part of the oxidative burst, limiting cellular concentrations of CaM due to association with iNOS (and other high-affinity binders) commit the cell to an unchecked inflammatory cascade leading to apoptosis.

Inhibiting p90 ribosomal S6 kinase prevents (Na+)-H+ exchanger-mediated cardiac ischemia-reperfusion injury

BACKGROUND

Pharmacological and genetic studies indicate that the (Na+)-H+ exchanger isoform 1 (NHE1) plays a critical role in myocardial ischemia and reperfusion (I/R) injury. We found that p90 ribosomal S6 kinase (RSK) phosphorylated serine 703 of NHE1, stimulating 14-3-3 binding and NHE1 activity. Therefore, we hypothesized that inhibiting RSK in cardiomyocytes would prevent NHE1 activation and decrease I/R-mediated injury.

METHODS AND RESULTS

To examine the role of RSK in vivo, we generated transgenic mice with cardiac-specific overexpression of dominant negative RSK (DN-RSK-TG). DN-RSK-TG hearts demonstrated normal basal cardiac function and morphology. However, myocardial infarction (left coronary artery occlusion for 45 minutes) in DN-RSK-TG hearts was significantly reduced at 24 hours of reperfusion from 46.9+/-5.6% area at risk in nontransgenic littermate controls to 26.0+/-4.2% in DN-RSK-TG (P<0.01). Cardiomyocyte apoptosis was significantly reduced after I/R in DN-RSK (0.9+/-0.2%) compared with nontransgenic littermate controls (6.2+/-2.6%). Importantly, activation of RSK and interaction of 14-3-3 with NHE1, necessary for agonist-stimulated NHE1 activity, were increased by I/R and inhibited by 70% in DN-RSK-TG (P<0.01). Next, we transduced rat neonatal cardiomyocytes with adenovirus-expressing DN-RSK (Ad.DN-RSK) and measured NHE1 activity. The baseline rate of pH recovery in acid-loaded cells was equal in cells expressing LacZ or DN-RSK. However, NHE1 activation by 100 micromol/L H2O2 was significantly inhibited in cells expressing DN-RSK (0.16+/-0.02 pH units/min) compared with Ad.LacZ (0.49+/-0.13 pH units/min). Apoptosis induced by 12 hours of anoxia followed by 24 hours' reoxygenation was significantly reduced in cells expressing Ad.DN-RSK (18.6+/-2.0%) compared with Ad.LacZ (29.3+/-5.4%).

CONCLUSIONS

In summary, RSK is a novel regulator of cardiac NHE1 activity by phosphorylating NHE1 serine 703 and a new pathological mediator of I/R injury in the heart.

Molecular mechanisms of apoptosis induced by ajoene in 3T3-L1 adipocytes

OBJECTIVE

Determine the biochemical pathways involved in induction of apoptosis by ajoene, an organosulfur compound from garlic.

RESEARCH METHODS AND PROCEDURES

Mature 3T3-L1 adipocytes were incubated with ajoene at concentrations up to 200 microM. Viability and apoptosis were quantified using an MTS-based cell viability assay and an enzyme-linked immunosorbent assay for single-stranded DNA (ssDNA), respectively. Intracellular reactive oxygen species (ROS) production was measured based on production of the fluorescent dye, dichlorofluorescein. Activation of the mitogen-activated protein kinases extracellular signal-regulating kinase 1/2 (ERK) and c-Jun-N-terminal kinase (JNK) was shown by Western blot. Western blot was also used to show activation of caspase-3, translocation of apoptosis-inducing factor (AIF) from mitochondria to nucleus, and cleavage of 116-kDa poly(ADP-ribose) polymerase (PARP)-1.

RESULTS

Ajoene induced apoptosis of 3T3-L1 adipocytes in a dose- and time-dependent manner. Ajoene treatment resulted in activation of JNK and ERK, translocation of AIF from mitochondria to nucleus, and cleavage of 116-kDa PARP-1 in a caspase-independent manner. Ajoene treatment also induced an increase in intracellular ROS level. Furthermore, the antioxidant N-acetyl-L-cysteine effectively blocked ajoene-mediated ROS generation, activation of JNK and ERK, translocation of AIF, and degradation of PARP-1.

DISCUSSION

These results indicate that ajoene-induced apoptosis in 3T3-L1 adipocytes is initiated by the generation of hydrogen peroxide, which leads to activation of mitogen-activated protein kinases, degradation of PARP-1, translocation of AIF, and fragmentation of DNA. Ajoene can, thus, influence the regulation of fat cell number through the induction of apoptosis and may be a new therapeutic agent for the treatment of obesity.

Allopurinol modulates reactive oxygen species generation and Ca2+ overload in ischemia-reperfused heart and hypoxia-reoxygenated cardiomyocytes

Myocardial oxidative stress and Ca2+ overload induced by ischemia-reperfusion may be involved in the development and progression of myocardial dysfunction in heart failure. Xanthine oxidase, which is capable of producing reactive oxygen species, is considered as a culprit regarding ischemia-reperfusion injury of cardiomyocytes. Even though inhibition of xanthine oxidase by allopurinol in failing hearts improves cardiac performance, the regulatory mechanisms are not known in detail. We therefore hypothesized that allopurinol may prevent the xanthine oxidase-induced reactive oxygen species production and Ca2+ overload, leading to decreased calcium-responsive signaling in myocardial dysfunction. Allopurinol reversed the increased xanthine oxidase activity in ischemia-reperfusion injury of neonatal rat hearts. Hypoxia-reoxygenation injury, which simulates ischemia-reperfusion injury, of neonatal rat cardiomyocytes resulted in activation of xanthine oxidase relative to that of the control, indicating that intracellular xanthine oxidase exists in neonatal rat cardiomyocytes and that hypoxia-reoxygenation induces xanthine oxidase activity. Allopurinol (10 microM) treatment suppressed xanthine oxidase activity induced by hypoxia-reoxygenation injury and the production of reactive oxygen species. Allopurinol also decreased the concentration of intracellular Ca2+ increased by enhanced xanthine oxidase activity. Enhanced xanthine oxidase activity resulted in decreased expression of protein kinase C and sarcoendoplasmic reticulum calcium ATPase and increased the phosphorylation of extracellular signal-regulated protein kinase and p38 kinase. Xanthine oxidase activity was increased in both ischemia-reperfusion-injured rat hearts and hypoxia-reoxygenation-injured cardiomyocytes, leading to reactive oxygen species production and intracellular Ca2+ overload through mechanisms involving p38 kinase and extracellular signal-regulated protein kinase (ERK) via sarcoendoplasmic reticulum calcium ATPase (SERCA) and protein kinase C (PKC). Xanthine oxidase inhibition with allopurinol modulates reactive oxygen species production and intracellular Ca2+ overload in hypoxia-reoxygenation-injured neonatal rat cardiomyocytes.

Physiology and pathophysiology of Na+/H+ exchange and Na+ -K+ -2Cl- cotransport in the heart, brain, and blood

Maintenance of a stable cell volume and intracellular pH is critical for normal cell function. Arguably, two of the most important ion transporters involved in these processes are the Na+/H+ exchanger isoform 1 (NHE1) and Na+ -K+ -2Cl- cotransporter isoform 1 (NKCC1). Both NHE1 and NKCC1 are stimulated by cell shrinkage and by numerous other stimuli, including a wide range of hormones and growth factors, and for NHE1, intracellular acidification. Both transporters can be important regulators of cell volume, yet their activity also, directly or indirectly, affects the intracellular concentrations of Na+, Ca2+, Cl-, K+, and H+. Conversely, when either transporter responds to a stimulus other than cell shrinkage and when the driving force is directed to promote Na+ entry, one consequence may be cell swelling. Thus stimulation of NHE1 and/or NKCC1 by a deviation from homeostasis of a given parameter may regulate that parameter at the expense of compromising others, a coupling that may contribute to irreversible cell damage in a number of pathophysiological conditions. This review addresses the roles of NHE1 and NKCC1 in the cellular responses to physiological and pathophysiological stress. The aim is to provide a comprehensive overview of the mechanisms and consequences of stress-induced stimulation of these transporters with focus on the heart, brain, and blood. The physiological stressors reviewed are metabolic/exercise stress, osmotic stress, and mechanical stress, conditions in which NHE1 and NKCC1 play important physiological roles. With respect to pathophysiology, the focus is on ischemia and severe hypoxia where the roles of NHE1 and NKCC1 have been widely studied yet remain controversial and incompletely elucidated.

Cadmium effects on ros production and DNA damage via adrenergic receptors stimulation: role of Na+/H+ exchanger and PKC

The objective of the present study was to elucidate the events that are involved in reactive oxygen species (ROS) production and DNA damage after adrenergic receptors stimulation by cadmium, in relation to cAMP, protein kinase C (PKC) and Na+/H+ exchanger (NHE). Cadmium (50 microM) caused increased levels of ROS with a concomitant increase in DNA damage in digestive gland of Mytilus galloprovincialis. Either the use of EIPA, a NHE blocker, or calphostin C, the inhibitor of PKC, reduced cadmium effects. Cells treated with alpha1-, alpha2-, beta- and beta1- adrenergic antagonists together with cadmium reversed cadmium alone effects, while the respective adrenergic agonists, phenylephrine and isoprenaline, mimic cadmium effects. Moreover, cadmium caused an increase in the levels of cAMP in digestive gland cells that were reversed after NHE and PKC inhibition as well as in the presence of each type of adrenergic antagonist. The different sensitivity of alpha1-, alpha2-, beta-, beta1- adrenergic receptors on ROS, cAMP production and DNA damage possibly leads to the induction of two signaling pathways that may be interacting or to the presence of a compensatory pathway that acts in concert with the alpha- and beta- adrenergic receptors. In these signaling pathways PKC and NHE play significant role.

Effects of [5-(2-methoxy-5-fluorophenyl)furan-2-ylcarbonyl]guanidine (KR-32560), a novel sodium/hydrogen exchanger-1 inhibitor, on myocardial infarct size and ventricular arrhythmias in a rat model of ischemia/reperfusion heart injury

The cardioprotective effects of the novel sodium/hydrogen exchanger-1 (NHE-1) inhibitor KR-32560 {[5-(2-methoxy-5-fluorophenyl)furan-2-ylcarbonyl]guanidine} were studied in an anesthetized rat model of 30-min ischemia / 2.5-h reperfusion heart injury. KR-32560 (0.01 - 1 microM) dose-dependently inhibited NHE-1-mediated rabbit platelet swelling induced by intracellular acidification. KR-32560 at 0.1 and 1.0 mg/kg (i.v. bolus, given 10 min before ischemia) reduced infarct size from 65.9% (control) to 49.7% and 32.7%, respectively, while reducing the extension of myocardial injury (mm(3)/g of left heart weight) from 405.1 (control) to 302.9 and 185.4, respectively (all P<0.05 vs control). KR-32560 dose-dependently reduced the total number of ventricular premature beats (VPBs) during ischemia from 510.2 (control) to 353.8 and 134.2 beats (all P<0.05, n = 6), while reducing ventricular tachycardia (VT) incidence from 49.3 (control) to 26.8 and 4.3 and VT duration from 249.2 s (control) to 150.5 and 26.7 s (all P<0.05, n = 6). KR-32560 dose-dependently reduced ventricular fibrillation (VF) incidence from 19.0 (control) to 9.2 and 1.2 and VF duration from 88.0 s to 34.5 and 2.8 s (all P<0.05, n = 6). KR-32560 also exerted similar effects on reperfusion arrhythmias, except for VPBs. These results indicate that KR-32560 may exert significant cardioprotective effects in ischemia/reperfusion heart injury.

Cardioprotective effects of [5-(2-methyl-5-fluorophenyl)furan-2-ylcarbonyl]guanidine (KR-32568) in an anesthetized rat model of ischemia and reperfusion heart injury

The effects of a novel sodium/hydrogen exchanger-1 (NHE-1) inhibitor, KR-32568, were studied in an anesthetized rat model of 30 min ischemia/2.5 h reperfusion heart injury. KR-32568 dose-dependently inhibited NHE-1-mediated rabbit platelet swelling induced by intracellular acidification. In our anesthetized rat model, KR-32568 reduced infarct size from 67 (control) to 43 and 24% at 0.1 and 1.0 mg/kg (i.v. bolus, given 10 min before ischemia), respectively. KR-32568 at the same doses also significantly reduced the total number of ventricular premature beats during ischemia/reperfusion from 530 (control) to 266 and 115 beats, ventricular tachycardia (VT) incidence from 51 (control) to 21 and 8, VT duration from 238 s (control) to 63 and 33 s, ventricular fibrillation (VF) incidence from 17 (control) to 8 and 0, and VF duration from 85 s to 18 and 1 s. These results indicate that KR-32568 may exert potent cardioprotective effects in rats via inhibition of sodium/hydrogen exchanger-1.

Intracellular signaling following myocardial stretch: an autocrine/paracrine loop

The stretch of adult papillary muscle elicits a chain of autocrine/paracrine events in which the Na(+)/H(+) exchanger (NHE-1) activation is the central step. This activation is induced by a sequential angiotensin II-endothelin (Ang II-ET) release and results in an increase in intracellular Na(+) (Na(+)(i)) without significant changes in intracellular pH. The increase in Na(+)(i) negatively shifts the reverse potential of the Na(+)/Ca(2+) exchanger (NCX) thus inducing cell Ca(2+) influx that augments myocardial contractility. This increase in force represents the mechanical counterpart of the autocrine/paracrine mechanism triggered by stretch and has been called the slow force response (SFR) to stretch.

Neuroprotection by fructose-1,6-bisphosphate involves ROS alterations via p38 MAPK/ERK

Fructose-1,6-bisphosphate (FBP) is a glucose metabolism intermediate that shows a neuroprotective action in animal models of ischemia and other injuries. The intracellular mechanism of FBP on neuroprotection has not been previously defined. Here, we examined whether FBP has a neuroprotective effect against excitotoxicity, and whether it affects the production of reactive oxygen species (ROS), which are involved in the MAPK pathway in cortical neurons. FBP prevented neuronal death in a dose-dependent manner following 24 h of treatment with the excitotoxin, NMDA. After 8 h of NMDA treatment, we observed FBP-induced inhibition of the production of intracellular ROS, and at the earlier time FBP suppressed NMDA-induced p-p38 and p-ERK expression. In addition, MAPK inhibitors reduced NMDA-induced excitotoxicity and also ROS production. Taken together, our results suggest that the neuroprotective effects of FBP could be explained by down-regulation of free radical production through the p38MAPK/ERK pathway.

In vivo adenosine receptor preconditioning reduces myocardial infarct size via subcellular ERK signaling

The protective effects of adenosine receptor acute preconditioning (PC) are well known; however, the signaling mechanism mediating this effect has not been determined in in vivo models. The purpose of this study was to determine the role of the extracellular signal-regulated kinase (ERK) pathway in mediating adenosine PC in in vivo rat myocardium. Open-chest rats were submitted to 25 min of coronary artery occlusion and 2 h of reperfusion. ERK activation was assessed by measuring total and dually phosphorylated p44/42 ERK isoforms in nuclear and/or myofilament, mitochondrial, cytosolic, and membrane fractions. Adenosine receptor PC with the A1/A2a agonist 1S-[1a,2b,3b,4a(S*)]-4-[7-[[2-(3-chloro-2-thienyl)-1-methylpropyl]amino]-3H-imidazo[4,5-b]pyridyl-3-yl]cyclopentane carboxamide (AMP-579) reduced infarct size from 49 +/- 3% to 29 +/- 3%, an effect that was blocked by the mitogen-activated protein kinase-ERK inhibitor U-0126. ERK isoforms were present in all fractions, with the greatest expression in the cytosolic fraction and the least in the mitochondrial fraction. AMP-579 treatment increased preischemic p44/42 ERK phosphorylation in all fractions 2.7- to 6.9-fold. Reperfusion increased ERK isoform activation in all fractions, but there were no differences between control and AMP-579 hearts. Preischemic increases in phospo-p44/p42 ERK with AMP-579 were blunted by U-0126, although only in mitochondrial and membrane compartments. The PC effects of AMP-579 on infarct size and ERK were blunted by both the A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine and, surprisingly, the A2a antagonist ZM-241385. These results indicate that the unique adenosine receptor agonist AMP-579 exerts its beneficial effects in vivo via both A1 and A2a receptor modulation of subcellular ERK isoform signaling.

Aldosterone Rapidly Activates Na+/H+ Exchange in M-1 Cortical Collecting Duct Cells via a PKC-MAPK Pathway

BACKGROUND

In this study, the mechanism of the rapid non-genomic effect of aldosterone on Na(+)/H(+) exchanger (NHE)-mediated intracellular pH (pH(i)) recovery from an acid load in murine M-1 cortical collecting duct cells was assessed.

METHODS

Spectrofluorescence microscopy and Western blot analysis was carried out and NH(4)Cl was used to induce the acid load.

RESULTS

Aldosterone (10 nM) induced a rapid (<5 min) concentration-dependent increase in pH(i) recovery in M-1 cells, an effect mimicked by its precursor deoxycorticosterone (1 nM). This response was unaffected by the mineralocorticoid receptor (MR) antagonist spironolactone (10 microM) but was significantly reduced by the NHE antagonists 5'-(N-ethyl- N-isopropyl)amiloride (EIPA) (20 microM) and cariporide (1 microM). The PKC inhibitor chelerythrine chloride (1 microM) significantly attenuated the aldosterone-induced increase in NHE1 activity. HBDDE (80 microM), a PKC(alpha) inhibitor, inhibited the rapid aldosterone effect whereas rottlerin (15 microM), a PKC(delta) antagonist, did not. The glucocorticoid receptor agonists hydrocortisone (1 microM) and dexamethasone (100 nM) decreased NHE activity, whereas the synthetic mineralocorticoid fludrocortisone (1 nM) had no significant effect. MAPK inhibition using PD98059 (25 microM) significantly attenuated the rapid aldosterone effect; Western blot analysis showed that aldosterone activation of ERK 1/2 was unaffected by pretreatment with spironolactone but was inhibited following chelerythrine chloride.

CONCLUSION

Aldosterone causes a rapid non-genomic increase in NHE1 activity in M-1 cells via a PKC(alpha )/MAPK pathway independent of the classical MR.

Hypoxic postconditioning reduces cardiomyocyte loss by inhibiting ROS generation and intracellular Ca2+ overload

We have shown that intermittent interruption of immediate reflow at reperfusion (i.e., postconditioning) reduces infarct size in in vivo models after ischemia. Cardioprotection of postconditioning has been associated with attenuation of neutrophil-related events. However, it is unknown whether postconditioning before reoxygenation after hypoxia in cultured cardiomyocytes in the absence of neutrophils confers protection. This study tested the hypothesis that prevention of cardiomyocyte damage by hypoxic postconditioning (Postcon) is associated with a reduction in the generation of reactive oxygen species (ROS) and intracellular Ca(2+) overload. Primary cultured neonatal rat cardiomyocytes were exposed to 3 h of hypoxia followed by 6 h of reoxygenation. Cardiomyocytes were postconditioned after the 3-h index hypoxia by three cycles of 5 min of reoxygenation and 5 min of rehypoxia applied before 6 h of reoxygenation. Relative to sham control and hypoxia alone, the generation of ROS (increased lucigenin-enhanced chemiluminescence, SOD-inhibitable cytochrome c reduction, and generation of hydrogen peroxide) was significantly augmented after immediate reoxygenation as was the production of malondialdehyde, a product of lipid peroxidation. Concomitant with these changes, intracellular and mitochondrial Ca(2+) concentrations, which were detected by fluorescent fluo-4 AM and X-rhod-1 AM staining, respectively, were elevated. Cell viability assessed by propidium iodide staining was decreased consistent with increased levels of lactate dehydrogenase after reoxygenation. Postcon treatment at the onset of reoxygenation reduced ROS generation and malondialdehyde concentration in media and attenuated cardiomyocyte death assessed by propidium iodide and lactate dehydrogenase. Postcon treatment was associated with a decrease in intracellular and mitochondrial Ca(2+) concentrations. These data suggest that Postcon treatment reduces reoxygenation-induced injury in cardiomyocytes and is potentially mediated by attenuation of ROS generation, lipid peroxidation, and intracellular and mitochondrial Ca(2+) overload.

Calcium, ATP, and ROS: a mitochondrial love-hate triangle

The mitochondrion is at the core of cellular energy metabolism, being the site of most ATP generation. Calcium is a key regulator of mitochondrial function and acts at several levels within the organelle to stimulate ATP synthesis. However, the dysregulation of mitochondrial Ca2+homeostasis is now recognized to play a key role in several pathologies. For example, mitochondrial matrix Ca2+overload can lead to enhanced generation of reactive oxygen species, triggering of the permeability transition pore, and cytochrome c release, leading to apoptosis. Despite progress regarding the independent roles of both Ca2+and mitochondrial dysfunction in disease, the molecular mechanisms by which Ca2+can elicit mitochondrial dysfunction remain elusive. This review highlights the delicate balance between the positive and negative effects of Ca2+and the signaling events that perturb this balance. Overall, a “two-hit” hypothesis is developed, in which Ca2+plus another pathological stimulus can bring about mitochondrial dysfunction.

Comparative biology of the ubiquitous Na+/H+ exchanger, NHE1: lessons from erythrocytes

By virtue of their electroneutral exchange of intracellular H+ for extracellular Na+, the Na+/H+ exchangers (NHE1-NHE8) play a pivotal role in many physiological processes. This review focuses on the ubiquitous plasma membrane isoform, NHE1. Particular attention is given to the roles and regulation of NHE1 in erythrocytes, in their own right and as model systems, but pertinent findings from non-erythroid cells are also discussed. NHE1 plays a key role in the regulation of cell volume and pH, and consequently in the control of such diverse processes as blood O2/CO2 transport, and cell proliferation, motility, and survival. Disturbances in NHE1 function are involved in important pathological states such as hypoxic cell damage and cancer development. NHE1 has a predicted topology of 12 transmembrane domains, and a hydrophilic C-terminus thought to be the major site for NHE1 regulation. NHE1 is highly conserved throughout the vertebrate phylum, particularly in the transmembrane region and the proximal part of the C-terminus. In non-erythroid, and probably also in erythroid cells, this part of the hydrophilic C-terminus interacts with multiple binding partners important for NHE1 function. Erythrocyte NHE1s from mammalian, amphibian, and teleost species are activated by cell shrinkage, decreased pH(i), inhibition of Ser/Thr protein phosphatases, and activation of Ser/Thr protein kinases, i.e., many of the stimuli activating NHE1 in non-erythroid cells. In erythrocytes of many lower vertebrates, NHE1 is activated during hypoxia and is an important modulator of hemoglobin oxygen affinity. Sensitivity of NHE1 to oxygenation status has recently been described also in non-erythroid mammalian cells.

Reactive oxygen species (ROS) control the expression of Bcl-2 family proteins by regulating their phosphorylation and ubiquitination

We examined the influence of ROS on the phosphorylation and complex formation of Bcl-2 family proteins in Mn-superoxide dismutase (SOD) antisense-transfected squamous cell carcinoma cells, OSC-4 cells. The increase of intracellular ROS level induced by cis-diamminedichloroplatinum (CDDP) and gamma-ray treatment was greater in antisense-transfected cells than in control vector-transfected cells, and apoptosis was more extensively induced in the former. Antisense-transfected cells expressed high levels of Bax and Bak, but low levels of Bcl-2 and Bcl-XL when treated with CDDP, peplomycin, 5-fluorouracil or gamma-rays. After treatment with these agents, the phosphorylation of protein kinase A, Bcl-2 (Thr56) and Bad (Ser155) was increased, especially in antioxidant (N-acetylcysteine and pyrrolidine dithiocarbamate)-pretreated control cells, but the phosphorylation levels were very low in the antisense-transfected cells. Bcl-2 ubiquitination was increased, but ubiquitination of Bad and Bax was decreased in the antisense-transfected cells, although their ubiquitination was increased by the antioxidants. These results reveal that ROS induce apoptosis by regulating the phosphorylation and ubiquitination of Bcl-2 family proteins, resulting in increased proapoptotic protein levels and decreased antiapoptotic protein expression.

ERK Is Regulated by Sodium-Proton Exchanger in Rat Aortic Vascular Smooth Muscle Cells

The purposes of this study were to test 1) the relationship between two widely studied mitogenic effector pathways, and 2) the hypothesis that sodium-proton exchanger type 1 (NHE-1) is a regulator of extracellular signal-regulated protein kinase (ERK) activation in rat aortic smooth muscle (RASM) cells. Angiotensin II (Ang II) and 5-hydroxytryptamine (5-HT) stimulated both ERK and NHE-1 activities, with activation of NHE-1 preceding that of ERK. The concentration-response curves for 5-HT and Ang II were superimposable for both processes. Inhibition of NHE-1 with pharmacological agents or by isotonic replacement of sodium in the perfusate with choline or tetramethylammonium greatly attenuated ERK activation by 5-HT or Ang II. Similar maneuvers significantly attenuated 5-HT- or Ang II-mediated activation of MEK and Ras but not transphosphorylation of the epidermal growth factor (EGF) receptor. EGF receptor blockade attenuated ERK activation, but not NHE-1 activation by 5-HT and Ang II, suggesting that the EGF receptor and NHE-1 work in parallel to stimulate ERK activity in RASM cells, converging distal to the EGF receptor but at or above the level of Ras in the Ras-MEK-ERK pathway. Receptor-independent activation of NHE-1 by acute acid loading of RASM cells resulted in the rapid phosphorylation of ERK, which could be blocked by pharmacological inhibitors of NHE-1 or by isotonic replacement of sodium, closely linking the proton transport function of NHE-1 to ERK activation. These studies identify NHE as a new regulator of ERK activity in RASM cells.

Identification of Na+/H+exchange as a new target for toxic polycyclic aromatic hydrocarbons in liver cells

The ubiquitous environmental pollutants polycyclic aromatic hydrocarbons are responsible for important carcinogenic and apoptotic effects, whose mechanisms are still poorly understood, owing to the multiplicity of possible cellular targets. Among these mechanisms, alterations of ionic homeostasis have been suggested. In this work, the effects of benzo(a)pyrene [B(a)P] on pHi were tested in the rat liver F258 epithelial cell line, using the fluoroprobe carboxy-SNARF-1. After a 48-h treatment, B(a)P (50 nM) induced an alkalinization, followed by an acidification after 72 h and the development of apoptosis. Determinations of pH(i) recovery following an acid load showed an increased acid efflux at 48 h. Cariporide inhibited both the early alkalinization and the increased acid efflux, thus suggesting the involvement of Na+/H+ exchanger 1 (NHE1). Besides, alpha-naphtoflavone (alpha-NF), an inhibitor of CYP1A1-mediated B(a)P metabolism, prevented all pH(i) changes, and NHE1 activation was blocked by the antioxidant thiourea, which inhibited CYP1A1 metabolism-dependent H2O2 production. Regarding B(a)P-induced apoptosis, this was prevented by alpha-NF and bongkrekic acid, an inhibitor of mitochondria-dependent apoptosis. Interestingly, apoptosis was significantly reduced by cariporide. Taken together, our results indicate that B(a)P, via H2O2 produced by CYP1A1-dependent metabolism, induces an early activation of NHE1, resulting in alkalinization; this appears to play a significant role in mitochondria-dependent B(a)P-induced apoptosis.

Do clinically relevant transthoracic defibrillation energies cause myocardial damage and dysfunction?

Sufficiently strong defibrillation shocks will cause temporary or permanent damage to the heart. Weak defibrillation shocks do not cause any damage to the heart but also do not defibrillate. A relevant and practical question is what range of shock energies is most likely to defibrillate while not causing damage to the heart. This question is most difficult to answer in the pre-hospital defibrillation setting where the patients' size and shape vary, placement of the defibrillation patches vary, and the etiology of their arrhythmia varies. Unlike internal defibrillators, which are tested at implantation, efficacy of an external defibrillator is determined only once, when it is most needed. This review discusses shock damage and dysfunction caused by monophasic waveforms as well as biphasic waveforms. Evidence is presented suggesting that for perfused hearts, the threshold for damage is well above any shock size delivered clinically. For non-perfused hearts, both in humans and animals, evidence is presented that monophasic shocks of up to 5 J/kg do not cause any more cardiac damage/dysfunction than that associated with smaller shocks and that much of this damage is caused by the ischemic period itself rather than the shock. Although many patients can be defibrillated with 150 J (2.2 J/kg) biphasic shocks, some patients may require biphasic shocks up to 360 J (5 J/kg) to be defibrillated. Studies still need to be performed comparing the efficacy and damaging effects of 360 J biphasic shocks to 150 J biphasic shocks. Until those studies are completed, it seems reasonable to use the same 360 J (5 J/kg) energy limit for biphasic shocks as for monophasic shocks.

Age, cell signalling and cardioprotection

For many years investigators have been researching methods of preconditioning the myocardium against ischaemia-induced damage; however, a majority of this research has been carried out in young animals and cells. Normal ageing is accompanied by changes in the human myocardium that decrease its capacity to tolerate and respond to various forms of stress. Also, the likelihood of experiencing an ischaemic stress and other cardiovascular complications increases as an individual ages; therefore, an aged population would benefit most from cardioprotective treatments. Methods currently known to provide cardioprotection (or preconditioning) include exercise, heat stress, oxidative stress, brief ischaemia, stretch and certain pharmacological interventions. It is unclear whether the aged myocardium can adapt to a preconditioning stimulus; however, many researchers have observed age-related alterations in the expression and activation of proteins key to the cardioprotective process. These proteins include heat shock protein 70 (HSP70), nitric oxide synthase (NOS), the sodium-hydrogen exchanger (NHE), and the mitogen-activated protein (MAP) kinases c-Jun N-terminal Kinase (JNK), extracellular signal-regulated kinase (ERK), and p38. Therefore, the purpose of the current review will be to outline the current knowledge of these cardioprotective agents in an aged myocardium. Interactions among the cardioprotective agents outlined herein suggest that age-related changes in the myocardium will need to be better understood before cardioprotective interventions that have been proved effective in young animals can be applied to an aged human population.