Effect of duration of ischemia on myocardial proteome in ischemia/reperfusion injury

Ischemia/reperfusion (I/R) injury is a serious problem resulting from clinical setting of coronary revascularization. Despite extensive studies on I/R injury, the molecular bases of cardiac dysfunction caused by I/R are still unknown, but are likely to result from alterations in protein expression. Isolated rat hearts were subjected to 15-30 min of no-flow ischemia without (Ischemia protocol) or with 30 min of reperfusion (I/R protocol). 2-DE analysis of heart proteins from both experimental protocols showed wide-ranging changes in protein levels. In the Ischemia protocol, 39 protein spots were changed in ischemic groups and those changes correlated with duration of ischemia. Ninety percent of the affected proteins were increased. In contrast to increased protein levels, the total messenger RNA (mRNA) level decreased approximately two fold. Compared to the Ischemia protocol, changes in protein levels in the I/R protocol did not correlate with the duration of ischemia and the degree of recovery of mechanical function. The decrease of affected protein from I/R protocol was associated with the increase in total protein level in reperfusate. Our studies show that the protein increase is correlated with the mechanical function of the I/R hearts and the increase is not likely associated with an increase in protein synthesis.     

Effect of the Rho kinase inhibitor Y-27632 on the proteome of hearts with ischemia-reperfusion injury

Growing attention has been given to the role of the Rho kinase pathway in the development of heart disease and ischemia/reperfusion (I/R) injury. Y‐27632 is a Rho kinase inhibitor demonstrated to protect against I/R injury, but the exact mechanism by which it does so remains to be elucidated. The goal of this project was to determine new targets by which Y‐27632 can protect the heart against I/R injury. Isolated rat hearts were perfused under aerobic conditions or subjected to I/R in the presence or absence of Y‐27632. Administration of Y‐27632 (1 μM) before ischemia and during the first 10 min of reperfusion resulted in complete recovery of cardiac function. 2‐D electrophoresis followed by MS identified four proteins whose levels were affected by Y‐27632 treatment. Lactate dehydrogenase and glyceraldehyde‐3‐phosphate dehydrogenase were significantly increased in the Y‐27632 treated group, while creatine kinase was normalized to control levels. In addition, we found increased level of two different molecular fragments of ATP synthase, which were normalized by Y‐27632. This increase suggests that during ischemia ATP synthase is subjected to degradation. The changes in metabolic enzymes' levels and their regulation by Y‐27632 suggest that the cardioprotective effect of Y‐27632 involves increased energy production.     

Enhanced death signaling in ozone-exposed ischemic-reperfused hearts

Although numerous advancements made in the field of human health have resulted in reduced deaths due to cardiovascular diseases (CVD), many patients with cardiac disease show no established risk. Therefore, other unknown factors may be responsible for the pathophysiology of CVD. Out of 350,000 sudden cardiac deaths each year in the United States, 60,000 deaths have been related to air pollution, suggesting a detrimental role of environmental pollutants in the development of CVD. The present study tested our hypothesis that chronic ozone exposure enhances the sensitivity to ischemia–reperfusion (I/R) injury in isolated perfused hearts. Sprague-Dawley rats were continuously exposed for 8 h/day for 28 and 56 days to filtered air or 0.8 ppm ozone. Isolated hearts were subjected to 30 min of global ischemia followed by 60 min of reperfusion. Cardiac function after I/R measured as left ventricular developed pressure (LVDP), +dP/dt, –dP/dt, and left ventricular end diastolic pressure (LVEDP) was significantly decreased and increased respectively in ozone-exposed I/R hearts compared to I/R hearts exposed to filtered air. The enhanced sensitivity to I/R injury upon ozone exposure was associated with increased myocardial TNF-α levels and lipid peroxidation and decreased myocardial activities of superoxidase dismutase (SOD) and IL-10. These data suggest that ozone-induced sensitivity to myocardial I/R injury may be due to promoting levels of oxidative stress as well as inflammatory mediators.     

TRPM2 Channels Protect against Cardiac Ischemia-Reperfusion Injury: ROLE OF MITOCHONDRIA*

Cardiac TRPM2 channels were activated by intracellular adenosine diphosphate-ribose and blocked by flufenamic acid. In adult cardiac myocytes the ratio of G_Ca to G_Na of TRPM2 channels was 0.56 ± 0.02. To explore the cellular mechanisms by which TRPM2 channels protect against cardiac ischemia/reperfusion (I/R) injury, we analyzed proteomes from WT and TRPM2 KO hearts subjected to I/R. The canonical pathways that exhibited the largest difference between WT-I/R and KO-I/R hearts were mitochondrial dysfunction and the tricarboxylic acid cycle. Complexes I, III, and IV were down-regulated, whereas complexes II and V were up-regulated in KO-I/R compared with WT-I/R hearts. Western blots confirmed reduced expression of the Complex I subunit and other mitochondria-associated proteins in KO-I/R hearts. Bioenergetic analyses revealed that KO myocytes had a lower mitochondrial membrane potential, mitochondrial Ca²⁺ uptake, ATP levels, and O₂ consumption but higher mitochondrial superoxide levels. Additionally, mitochondrial Ca²⁺ uniporter (MCU) currents were lower in KO myocytes, indicating reduced mitochondrial Ca²⁺ uptake was likely due to both lower ψ_m and MCU activity. Similar to isolated myocytes, O₂ consumption and ATP levels were also reduced in KO hearts. Under a simulated I/R model, aberrant mitochondrial bioenergetics was exacerbated in KO myocytes. Reactive oxygen species levels were also significantly higher in KO-I/R compared with WT-I/R heart slices, consistent with mitochondrial dysfunction in KO-I/R hearts. We conclude that TRPM2 channels protect the heart from I/R injury by ameliorating mitochondrial dysfunction and reducing reactive oxygen species levels.     

Cardioprotective effect of MMP‐2‐inhibitor‐NO‐donor hybrid against ischaemia/reperfusion injury

Hypoxic injury of cardiovascular system is one of the most frequent complications following ischaemia. Heart injury arises from increased degradation of contractile proteins, such as myosin light chains (MLCs) and troponin I by matrix metalloproteinase 2 (MMP‐2). The aim of the current research was to study the effects of 5‐phenyloxyphenyl‐5‐aminoalkyl nitrate barbiturate (MMP‐2‐inhibitor‐NO‐donor hybrid) on hearts subjected to ischaemia/reperfusion (I/R) injury. Primary human cardiac myocytes and Wistar rat hearts perfused using Langendorff method have been used. Human cardiomyocytes or rat hearts were subjected to I/R in the presence or absence of tested hybrid. Haemodynamic parameters of heart function, markers of I/R injury, gene and protein expression of MMP‐2, MMP‐9, inducible form of NOS (iNOS), asymmetric dimethylarginine (ADMA), as well as MMP‐2 activity were measured. Mechanical heart function, coronary flow (CF) and heart rate (HR) were decreased in hearts subjected to I/R Treatment of hearts with the hybrid (1‐10 µmol/L) resulted in a concentration‐dependent recovery of mechanical function, improved CF and HR. This improvement was associated with decreased tissue injury and reduction of synthesis and activity of MMP‐2. Decreased activity of intracellular MMP‐2 led to reduced degradation of MLC and improved myocyte contractility in a concentration‐dependent manner. An infusion of a MMP‐2‐inhibitor‐NO‐donor hybrid into I/R hearts decreased the expression of iNOS and reduced the levels of ADMA. Thus, 5‐phenyloxyphenyl‐5‐aminoalkyl nitrate barbiturate protects heart from I/R injury.     

Effect of the myosin light chain kinase inhibitor ML-7 on the proteome of hearts subjected to ischemia-reperfusion injury

In the development of ischemia/reperfusion (I/R) injury, the role of the myosin light chain (MLC) phosphorylation has been given increased consideration. ML-7, a MLC kinase inhibitor, has been shown to protect cardiac function from I/R, however the exact mechanism remains unclear. Isolated rat hearts were perfused under aerobic conditions (controls) or subjected to I/R in the presence or absence of ML-7. Continuous administration of ML-7 (5 μM) from 10 min before onset of ischemia to the first 10 min of reperfusion resulted in significant recovery of heart contractility. Analysis of gels from two-dimensional electrophoresis revealed eight proteins with decreased levels in I/R hearts. Six proteins are involved in energy metabolism:ATP synthase beta subunit, cytochrome b-c1 complex subunit 1, 24-kDa mitochondrial NADH dehydrogenase, NADH dehydrogenase [ubiquinone] iron-sulfur protein 8, cytochrome c oxidase subunit, and succinyl-CoA ligase subunit. The other two proteins with decreased levels in I/R hearts are: peroxiredoxin-2 and tubulin. Administration of ML-7 increased level of succinyl-CoA ligase, key enzyme involved in the citric acid cycle. The increased level of succinyl-CoA ligase in I/R hearts perfused with ML-7 suggests that the cardioprotective effect of ML-7, at least partially, also may involve increase of energy production.     

Ischemia/reperfusion-induced myosin light chain 1 phosphorylation increases its degradation by matrix metalloproteinase 2

Degradation of myosin light chain 1 (MLC1) by matrix metalloproteinase 2 (MMP-2) during myocardial ischemia/reperfusion (I/R) has been demonstrated. However, the exact mechanisms controlling this process remain unknown. I/R increases the phosphorylation of MLC1, but the consequences of this modification are not known. We hypothesized that phosphorylation of MLC1 plays an important role in its degradation by MMP-2. To examine this, isolated perfused rat hearts were subjected to 20 min global ischemia followed by 30 min of aerobic reperfusion. I/R increased phosphorylation of MLC1 (as measured by mass spectrometry). When hearts were subjected to I/R in the presence of ML-7 (a myosin light-chain kinase inhibitor) or doxycycline (an MMP inhibitor), improved recovery of contractile function was observed compared to aerobic controls, and MLC1 was protected from degradation. Enzyme kinetic studies revealed an increased affinity of MMP-2 for the phosphorylated form of MLC1 compared to non-phosphorylated MLC1. We conclude that MLC1 phosphorylation is an important mechanism controlling the intracellular action of MMP-2 and promoting degradation of MLC1. These results further support previous findings implicating post-translational modifications of contractile proteins as a key factor in the pathology of cardiac dysfunction during and following ischemia.     

Dendroaspis natriuretic peptide protects the post-ischemic myocardial injury

The present study used isolated rat hearts to investigate whether (1) Dendroaspis natriuretic peptide (DNP) is protective against post-ischemic myocardial dysfunction, and (2) whether the cardioprotective effects of DNP is related to alteration of Bcl-2 family protein levels. The excised hearts of Sprague-Dawley rats were perfused on a Langendorff apparatus with Krebs-Henseleit solution with a gas mixture of 95% O2 and 5% CO2. Left ventricular end-diastolic pressure (LVEDP, mmHg), left ventricular developed pressure (LVDP, mmHg) and coronary flow (CF, ml/min) were continuously monitored. In the presence of 50 nM DNP, all hearts were perfused for a total of 100 min consisting of a 20 min pre-ischemic period followed by a 30 min global ischemia and 50 min reperfusion. Lactate dehydrogenase (LDH) activity in the effluent was measured during reperfusion. Treatment with DNP alone improved the pre-ischemic LVEDP and post-ischemic LVEDP significantly comparing with the untreated control hearts during reperfusion. However, DNP did not affect the LVDP, heart rate (HR, beats/min), and CF. Bcl-2, an anti-apoptotic protein expressed in ischemic myocardium of DNP+ischemia/reperfusion (I/R) group, was higher than that in I/R alone group. Bax, a pro-apoptotic protein expressed in ischemic myocardium of DNP+I/R group, has no significant difference compared with I/R alone group. These results suggest that the protective effects of DNP against I/R injury would be mediated, at least in part, through the increased ratio of Bcl-2 to Bax protein after ischemia-reperfusion.     

Proteomics of ischemia and reperfusion injuries in rabbit myocardium with and without intervention by an oxygen-free radical scavenger

A brief period of ischemia followed by timely reperfusion may lead to prolonged, yet reversible, contractile dysfunction (myocardial stunning). Damage to the myocardium occurs not only during ischemia, but also during reperfusion, where a massive release of oxygen-free radicals (OFR) occurs. We have previously utilized 2-DE and MS to define 57 protein spot changes during brief ischemia/reperfusion (15 min ischemia, 60 min reperfusion; 15I/60R) injury in a rabbit model (White, M. Y., Cordwell, S. J., McCarron, H. C. K., Prasan, A. M. et al., Proteomics 2005, 5, 1395-1410) and shown that the majority of these occur because of physical and/or chemical PTMs. In this study, we subjected rabbit myocardium to 15I/60R in the presence of the OFR scavenger N-(2-mercaptopropionyl) glycine (MPG). Thirty-seven of 57 protein spots altered during 15I/60R remained at control levels in the presence of MPG (15I/60R + MPG). Changes to contractile proteins, including myosin light chain 2 (MLC-2) and troponin C (TnC), were prevented by the addition of MPG. To further investigate the individual effects of ischemia and reperfusion, we generated 2-DE gels from rabbit myocardium subjected to brief ischemia alone (15I/0R), and observed alterations of 33 protein spots, including 18/20 seen in both 15I/60R-treated and 15I/60R + MPG-treated tissue. The tissue was also subjected to ischemia in the presence of MPG (15I/0R + MPG), and 21 spot changes, representing 14 protein variants, remained altered despite the presence of the OFR scavenger. These ischemia-specific proteins comprised those involved in energy metabolism (lactate dehydrogenase and ATP synthase alpha), redox regulation (NADH ubiquinone oxidoreductase 51 kDa and GST Mu), and stress response (Hsp27 and 70, and deamidated alpha B-crystallin). We conclude that contractile dysfunction associated with myocardial stunning is predominantly caused by OFR damage at the onset of reperfusion, but that OFR-independent damage also occurs during ischemia. These ischemia-specific protein modifications may be indicative of early myocardial injury.     

Specific enhancement of sarcomeric response to Ca2+ protects murine myocardium against ischemia-reperfusion dysfunction

Alteration in myofilament response to Ca2+ is a major mechanism for depressed cardiac function after ischemia-reperfusion (I/R) dysfunction. We tested the hypothesis that hearts with increased myofilament response to Ca2+ are less susceptible to I/R. In one approach, we studied transgenic (TG) mice with a constitutive increase in myofilament Ca2+ sensitivity in which the adult form of cardiac troponin I (cTnI) is stoichiometrically replaced with the embryonic/neonatal isoform, slow skeletal TnI (ssTnI). We also studied mouse hearts with EMD-57033, which acts specifically to enhance myofilament response to Ca2+. We subjected isolated, perfused hearts to an I/R protocol consisting of 25 min of no-flow ischemia followed by 30 min of reperfusion. After I/R, developed pressure and rates of pressure change were significantly depressed and end-diastolic pressure was significantly elevated in nontransgenic (NTG) control hearts. These changes were significantly blunted in TG hearts and in NTG hearts perfused with EMD-57033 during reperfusion, with function returning to nearly baseline levels. Ca2+- and cross bridge-dependent activation, protein breakdown, and phosphorylation in detergent-extracted fiber bundles were also investigated. After I/R NTG fiber bundles exhibited a significant depression of cross bridge-dependent activation and Ca2+-activated tension and length dependence of activation that were not evident in TG preparations. Only NTG hearts demonstrated a significant increase in cTnI phosphorylation. Our results support the hypothesis that specific increases in myofilament Ca2+ sensitivity are able to diminish the effect of I/R on cardiac function.     

Preconditioning attenuates ischemia-reperfusion-induced remodeling of Na+-K+-ATPase in hearts

The aim of this study was to determine whether changes in protein content and/or gene expression of Na+-K+-ATPase subunits underlie its decreased enzyme activity during ischemia and reperfusion. We measured protein and mRNA subunit levels in isolated rat hearts subjected to 30 min of ischemia and 30 min of reperfusion (I/R). The effect of ischemic preconditioning (IP), induced by three cycles of ischemia and reperfusion (10 min each), was also assessed on the molecular changes in Na+-K+-ATPase subunit composition due to I/R. I/R reduced the protein levels of the alpha2-, alpha3-, beta1-, and beta2-isoforms by 71%, 85%, 27%, and 65%, respectively, whereas the alpha1-isoform was decreased by <15%. A similar reduction in mRNA levels also occurred for the isoforms of Na+-K+-ATPase. IP attenuated the reduction in protein levels of Na+-K+-ATPase alpha2-, alpha3-, and beta2-isoforms induced by I/R, without affecting the alpha1- and beta1-isoforms. Furthermore, IP prevented the reduction in mRNA levels of Na+-K+-ATPase alpha2-, alpha3-, and beta1-isoforms following I/R. Similar alterations in protein contents and mRNA levels for the Na+/Ca2+ exchanger were seen due to I/R as well as IP. These findings indicate that remodeling of Na+-K+-ATPase may occur because of I/R injury, and this may partly explain the reduction in enzyme activity in ischemic heart disease. Furthermore, IP may produce beneficial effects by attenuating the remodeling of Na+-K+-ATPase and changes in Na+/Ca2+ exchanger in hearts after I/R.     

Attenuation of antioxidative capacity enhances reperfusion injury in aged rat myocardium after MI/R

Mortality due to ischemic cardiovascular diseases is significantly higher in elderly than in young adults. Myocardial ischemia-reperfusion (MI/R) can induce oxidative stress and an inflammatory response. We hypothesized that increased vulnerability of aged myocardium to reperfusion injury could be caused by decreased antioxidative capacity, rather than increased oxidant production, after MI/R. Aged (20-mo-old) and young (4-mo-old) male F344BN rats were subjected to 30 min of myocardial ischemia by ligation of the left main coronary artery followed by release of the ligature and 4 h of reperfusion. Four experimental groups were studied: young sham-operated rats, aged sham-operated rats, young rats subjected to MI/R, and aged rats subjected to MI/R. MI/R significantly increased infiltrated leukocyte number and myeloperoxidase (MPO) activity in perinecrotic areas of hearts of young rats compared with aged MI/R rats. These changes in infiltrated leukocyte number and MPO activity were associated with an increase in superoxide generation in perinecrotic areas from hearts of young rats compared with aged rats. Plasma levels of TNF-alpha and IL-1beta were significantly higher in young than in aged MI/R rats. However, plasma 8-hydroxy-2'-deoxyguanosine levels and creatine kinase activity were increased in aged compared with young MI/R rats. Increased reperfusion damage in aged rats was associated with a significant decrease in plasma ratio of GSH to GSSG. Our results suggest that enhanced ischemia-reperfusion injury in aged rat hearts may be related to reduced antioxidative capacity, rather than increased reactive oxygen species production. These findings contribute to a better understanding of effects of aging on oxidative stress and inflammatory responses of the heart after MI/R.     

Overexpression of the Na+/H+ exchanger and ischemia-reperfusion injury in the myocardium

In the myocardium, the Na(+)/H(+) exchanger isoform-1 (NHE1) activity is detrimental during ischemia-reperfusion (I/R) injury, causing increased intracellular Na(+) (Na(i)(+)) accumulation that results in subsequent Ca(2+) overload. We tested the hypothesis that increased expression of NHE1 would accentuate myocardial I/R injury. Transgenic mice were created that increased the Na(+)/H(+) exchanger activity specifically in the myocardium. Intact hearts from transgenic mice at 10-15 wk of age showed no change in heart performance, resting intracellular pH (pH(i)) or phosphocreatine/ATP levels. Transgenic and wild-type (WT) hearts were subjected to 20 min of ischemia followed by 40 min of reperfusion. Surprisingly, the percent recovery of rate-pressure product (%RPP) after I/R improved in NHE1-overexpressing hearts (64 +/- 5% vs. 41 +/- 5% in WT; P < 0.05). In addition, NMR spectroscopy revealed that NHE1 overexpressor hearts contained higher ATP during early reperfusion (levels P < 0.05), and there was no difference in Na(+) accumulation during I/R between transgenic and WT hearts. HOE642 (cariporide), an NHE1 inhibitor, equivalently protected both WT and NHE1-overexpressing hearts. When hearts were perfused with bicarbonate-free HEPES buffer to eliminate the contribution of HCO(3)(-) transporters to pH(i) regulation, there was no difference in contractile recovery after reperfusion between controls and transgenics, but NHE1-overexpressing hearts showed a greater decrease in ATP during ischemia. These results indicate that the basal activity of NHE1 is not rate limiting in causing damage during I/R, therefore, increasing the level of NHE1 does not enhance injury and can have some small protective effects.     

Cardioprotective effect of isorhamnetin against myocardial ischemia reperfusion (I/R) injury in isolated rat heart through attenuation of apoptosis

In this study, we investigated the effects of isorhamnetin on myocardial ischaemia reperfusion (I/R) injury in Langendorff-perfused rat hearts. Isorhamnetin treatment (5, 10 and 20 μg/mL) significantly alleviated cardiac morphological injury, reduced myocardial infarct size, decreased the levels of marker enzymes (LDH and CK) and improved the haemodynamic parameters, reflected by the elevated levels of the left ventricular developed pressure (LVDP), coronary flow (CF) and the maximum up/down velocity of left ventricular pressure (+dp/dt_max). Moreover, isorhamnetin reperfusion inhibited apoptosis of cardiomyocytes in the rats subjected to cardiac I/R in a dose-dependent manner concomitant with decreased protein expression of Bax and cleaved-caspase-3, as well as increased protein expression of Bcl-2. In addition, I/R-induced oxidative stress was manifestly mitigated by isorhamnetin treatment, as showed by the decreased malondialdehyde (MDA) level and increased antioxidant enzymes activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px). These results indicated that isorhamnetin exerts a protective effect against I/R-induced myocardial injury through the attenuation of apoptosis and oxidative stress.     

Anti-apoptotic protection afforded by cardioplegic celsior and histidine buffer solutions to hearts subjected to ischemia and ischemia/reperfusion

Cardiomyocytes undergo apoptosis in response to ischemia and ischemia/reperfusion (I/R). During heart preservation, inhibition of apoptosis is critical to avoid organ failure. We aimed to compare the protection afforded by Celsior (Cs) and Histidine buffer solution (HBS) against apoptotic signaling in hearts subjected to moderate (4 h) versus severe (6 h) ischemia alone or followed by 30 min reperfusion. The impact of gender on cardioplegic protection was also explored. Hearts from male and female Wistar-Han rats were divided by gender in distinct groups: control, perfusion_control, ischemia, and I/R. Ischemia and I/R groups were divided in subgroups Cs or HBS, and subjected to 4 or 6 h ischemia alone or followed by reperfusion. Proteins involved in apoptotic signaling (p53, Bax, Fas, FasL, and Flip) were quantified by Western blot in mitochondria and/or whole tissue. Caspases 3, 8, and 9-like activities were measured and hemodynamic parameters were monitored. Ischemia activated p53/Bax signaling. After I/R, HBS-preserved hearts had lower p53/Bax content in mitochondrial fractions than Cs-preserved hearts. The p53/Bax decrease in tissue samples was mostly observed in females. Caspase 3-like activity was increased in HBS-preserved male hearts. The heart rate was decreased in Cs and HBS-preserved hearts. Fas protein levels remained unaltered in all conditions but soluble FasL increased from 4 to 6 h preservation in Cs and HBS. Hearts from male rats were more prone to apoptosis and myocardial dysfunction. HBS and Cs were not effective in inhibiting apoptotic signaling although HBS presented best overall results. Both solutions should be improved to prevent apoptosis and myocardial dysfunction after I/R.     

Differences in ischemia-reperfusion-induced endothelial changes in hearts perfused at constant flow and constant pressure

Isolated hearts subjected to ischemia-reperfusion (I/R) exhibit depressed cardiac performance and alterations in subcellular function. Since hearts perfused at constant flow (CF) and constant pressure (CP) show differences in their contractile response to I/R, this study was undertaken to examine mechanisms responsible for these I/R-induced alterations in CF-perfused and CP-perfused hearts. Rat hearts, perfused at CF (10 ml/min) or CP (80 mmHg), were subjected to I/R (30 min global ischemia followed by 60 min reperfusion), and changes in cardiac function as well as sarcolemmal (SL) Na(+)-K(+)-ATPase activity, sarcoplasmic reticulum (SR) Ca(2+) uptake, and endothelial function were monitored. The I/R-induced depressions in cardiac function, SL Na(+)-K(+)-ATPase, and SR Ca(2+)-uptake activities were greater in hearts perfused at CF than in hearts perfused at CP. In hearts perfused at CF, I/R-induced increase in calpain activity and decrease in nitric oxide (NO) synthase (endothelial NO synthase) protein content in the heart as well as decrease in NO concentration of the perfusate were greater than in hearts perfused at CP. These changes in contractile activity and biochemical parameters due to I/R in hearts perfused at CF were attenuated by treatment with l-arginine, a substrate for NO synthase, while those in hearts perfused at CP were augmented by treatment with N(G)-nitro-l-arginine methyl ester, an inhibitor of NO synthase. The results indicate that the I/R-induced differences in contractile responses and alterations in subcellular organelles between hearts perfused at CF and CP may partly be attributed to greater endothelial dysfunction in CF-perfused hearts than that in CP-perfused hearts.     

The effect of continuous light exposure of rats on cardiac response to ischemia-reperfusion and NO-synthase activity

Factors modulating cardiac susceptibility to ischemia-reperfusion (I/R) are permanently attracting the attention of experimental cardiology research. We investigated, whether continuous 24 h/day light exposure of rats can modify cardiac response to I/R, NO-synthase (NOS) activity and the level of oxidative load represented by conjugated dienes (CD) concentration. Two groups of male adult Wistar rats were studied: controls exposed to normal light/dark cycle (12 h/day light, 12 h/day dark) and rats exposed to continuous light for 4 weeks. Perfused isolated hearts (Langendorff technique) were exposed to 25 min global ischemia and subsequent 30 min reperfusion. The recovery of functional parameters (coronary flow, left ventricular developed pressure, contractility and relaxation index) during reperfusion as well as the incidence, severity and duration of arrhythmias during first 10 min of reperfusion were determined. The hearts from rats exposed to continuous light showed more rapid recovery of functional parameters but higher incidence, duration and severity of reperfusion arrhythmias compared to controls. In the left ventricle, the NOS activity was attenuated, but the CD concentration was not significantly changed. We conclude that the exposure of rats to continuous light modified cardiac response to I/R. This effect could be at least partially mediated by attenuated NO production.