Sustained Ischemia Research Articles

Cardioprotection From Ischemia/Reperfusion Injury

Because ischemic heart diseases (IHDs) are a major cause of mortality and heart failure, novel therapeutic approaches are expected to improve the clinical outcomes of patients with IHDs such as acute myocardial infarction and ischemic heart failure. Brief episodes of nonlethal ischemia and reperfusion before sustained ischemia or at the onset of reperfusion can reduce ischemia-reperfusion injury. These ischemic conditioning phenomena are termed "ischemic preconditioning" and "ischemic postconditioning", respectively. Furthermore, brief episodes of nonlethal ischemia and reperfusion applied to the organ or tissue distal to the heart reduce myocardial infarct size, known as "remote ischemic conditioning". The cardioprotection afforded by these ischemic conditionings can be used to treat patients with acute myocardial infarction or cardiac operations. Extensive research has determined that autacoids (eg, adenosine, bradykinin opioid) and cytokines, their respective receptors, kinase signaling pathways and mitochondrial modulation are involved in ischemic conditioning. Modification of these factors by pharmacological agents mimics the cardioprotection by ischemic conditioning and provides a novel therapeutic intervention for IHDs. Here, the potential mechanisms of ischemic conditioning and its "proof-of-concept" translational studies are reviewed. In the near future, large, multicenter, randomized, placebo-controlled, clinical trials will be required to determine whether pharmacological and ischemic conditioning can improve the clinical outcomes of patients with IHDs.

Electron paramagnetic resonance monitoring of ischemia‐induced myocardial oxygen depletion and acidosis in isolated rat hearts using soluble paramagnetic probes

A new low-field electron paramagnetic resonance approach for noninvasive measurements of myocardial oxygen tension and tissue acidity was developed. The approach was applied to monitor myocardial pO(2) and pH in a model of global no-flow ischemia (30 min) and reperfusion in isolated perfused rat hearts. The myocardial oxygen measurements were performed using deuterated Finland trityl radical probe. A rapid decrease in myocardial pO(2) from 160 mmHg to about 2 ± 1 mmHg was observed within the first minute of ischemia followed by incomplete restoration of pO(2) to 50 mmHg during 30 min of reperfusion. The lower oxygen concentration after ischemia was attributed to the 50% reduction in coronary flow after ischemia as a consequence of myocardial ischemia and reperfusion damage. Myocardial pH measurements using a specially designed imidazoline pH-sensitive nitroxide showed severe myocardial acidification to pH 6.25 during 30 min of ischemia. Preconditioning of the hearts with two 5-min periods of ischemia significantly reduced the acidification of myocardial tissue during sustained ischemia. Noninvasive electron paramagnetic resonance monitoring of myocardial oxygenation and pH may provide important insights into the mechanisms of ischemia and reperfusion injury and a background for development of new therapeutic approaches.

A combination of ischemic preconditioning and allopurinol protects against ischemic injury through a nitric oxide-dependent mechanism

This study examined the cytoprotective mechanisms of a combination of ischemic preconditioning (IPC) and allopurinol against liver injury caused by ischemia/reperfusion (I/R). Allopurinol (50 mg/kg) was intraperitoneally administered 18 and 1 h before sustained ischemia. A rat liver was preconditioned by 10 min of ischemia, followed by 10 min of reperfusion, and then subjected to 90 min of ischemia, followed by 5 h of reperfusion. Rats were pretreated with adenosine deaminase (ADA), 3,7-dimethyl-1-[2-propargyl]-xanthine (DMPX), and N-nitro- l-arginine methyl ester ( l-NAME) before IPC. Hepatic nitrite and nitrate and eNOS protein expression levels were increased by the combination of IPC and allopurinol. This increase was attenuated by ADA, DMPX, and l-NAME. I/R induced an increase in alanine aminotransferase activity, whereas it decreased the hepatic glutathione level. A combination of IPC and allopurinol attenuated these changes, which were abolished by ADA, DMPX, and l-NAME. The increase in the liver wet weight-to-dry weight ratio after I/R was attenuated by the combination of IPC and allopurinol. In contrast, hepatic bile flow was decreased after I/R, which was attenuated by the combination of IPC and allopurinol. These changes were restored by l-NAME. I/R induced a decrease in the level of mitochondrial dehydrogenase, whereas it increased mitochondrial swelling. A combination of IPC and allopurinol attenuated these changes, which were restored by ADA, DMPX, and l-NAME. Our findings suggest that a combination of IPC and allopurinol reduces post-ischemic hepatic injury by enhancing NO generation.

CD4 + T Cells and Complement Independently Mediate Graft Ischemia in the Rejection of Mouse Orthotopic Tracheal Transplants

While microvascular injury is associated with chronic rejection, the cause of tissue ischemia during alloimmune injury is not yet elucidated. We investigated the contribution of T lymphocytes and complement to microvascular injury-associated ischemia during acute rejection of mouse tracheal transplants. Using novel techniques to assess microvascular integrity and function, we evaluated how lymphocyte subsets and complement specifically affect microvascular perfusion and tissue oxygenation in MHC-mismatched transplants. To characterize T cell effects on microvessel loss and recovery, we transplanted functional airway grafts in the presence and absence of CD4(+) and CD8(+) T cells. To establish the contribution of complement-mediated injury to the allograft microcirculation, we transplanted C3-deficient and C3-inhibited recipients. We demonstrated that CD4(+) T cells and complement are independently sufficient to cause graft ischemia. CD8(+) T cells were required for airway neovascularization to occur following CD4-mediated rejection. Activation of antibody-dependent complement pathways mediated tissue ischemia even in the absence of cellular rejection. Complement inhibition by CR2-Crry attenuated graft hypoxia, complement/antibody deposition on vascular endothelium and promoted vascular perfusion by enhanced angiogenesis. Finally, there was a clear relationship between the burden of tissue hypoxia (ischemia×time duration) and the development of subsequent airway remodeling. These studies demonstrated that CD4(+) T cells and complement operate independently to cause transplant ischemia during acute rejection and that sustained ischemia is a precursor to chronic rejection.

The effects of modulating eNOS activity and coupling in ischemia/reperfusion (I/R)

The in vivo role of endothelial nitric oxide synthase (eNOS) uncoupling mediating oxidative stress in ischemia/reperfusion (I/R) injury has not been well established. In vitro, eNOS coupling refers to the reduction of molecular oxygen to L-arginine oxidation and generation of L-citrulline and nitric oxide NO synthesis in the presence of an essential cofactor, tetrahydrobiopterin (BH(4)). Whereas uncoupled eNOS refers to that the electron transfer becomes uncoupled to L-arginine oxidation and superoxide is generated when the dihydrobiopterin (BH(2)) to BH(4) ratio is increased. Superoxide is subsequently converted to hydrogen peroxide (H(2)O(2)). We tested the hypothesis that promoting eNOS coupling or attenuating uncoupling after I/R would decrease H(2)O(2)/increase NO release in blood and restore postreperfused cardiac function. We combined BH(4) or BH(2) with eNOS activity enhancer, protein kinase C epsilon (PKC ε) activator, or eNOS activity reducer, PKC ε inhibitor, in isolated rat hearts (ex vivo) and femoral arteries/veins (in vivo) subjected to I(20 min)/R(45 min). When given during reperfusion, PKC ε activator combined with BH(4), not BH(2), significantly restored postreperfused cardiac function and decreased leukocyte infiltration (p < 0.01) while increasing NO (p < 0.05) and reducing H(2)O(2) (p < 0.01) release in femoral I/R veins. These results provide indirect evidence suggesting that PKC ε activator combined with BH(4) enhances coupled eNOS activity, whereas it enhanced uncoupled eNOS activity when combined with BH(2). By contrast, the cardioprotective and anti-oxidative effects of the PKC ε inhibitor were unaffected by BH(4) or BH(2) suggesting that inhibition of eNOS uncoupling during reperfusion following sustained ischemia may be an important mechanism.

Identification of capillary blood pressure levels at which capillary collapse is likely in a tissue subjected to large compressive and shear deformations

Pressure ulcers (PU) are localised damage to skin and underlying tissues, caused by sustained tissue deformations and ischaemia. PU typically appear in insensitive or immobile patients, e.g. those with spinal cord injury (SCI) or geriatric patients. As these patients often experience fluctuations in blood pressure, and are also exposed to high-shear loads in their weight-bearing soft tissues during wheelchair sitting or bed rest, we used an inverse finite element method to determine the effects of capillary blood pressure (CBP) and shear deformations on occurrence of mechanical collapse in capillaries. We studied collapse in straight, U-shaped and bifurcated capillaries. All model configurations were consistent in demonstrating that the level of CBP has a considerable influence on the likelihood of capillary collapse in the physiological CBP range, particularly if shear is present. Our modelling therefore suggests that low CBP is a ‘suspect’ risk factor for PU in SCI and geriatric patients.

Reprint of: Mitochondria: Their role in ganglion cell death and survival in primary open angle glaucoma

Retinal ganglion cell axons within the globe are functionally specialised being richly provided with many mitochondria. Mitochondria produce the high energy that is required for nerve conduction in the unmylenated part of the ganglion cell axons and for the maintenance of optimum neuronal function. We proposed that in the initiation of glaucoma (POAG) an alteration in the quality of blood flow dynamics in the optic nerve head results in sustained or intermittent ischemia of a defined nature. This results in normal mitochondrial function being negatively affected and as a consequence retinal ganglion cell function is compromised. Ganglion cells in this state are now susceptible to secondary insults which they would normally tolerate. One secondary insult to ganglion cell mitochondria in such a state might be light entering the eye. Other insults to the ganglion cells might come from substances such as glutamate, prostaglandins and nitric oxide released from astrocytes and microglia in the optic nerve head region. Such cascades of events initiated by ischemia to the optic nerve head region ultimately cause ganglion cells to die at different rates.

New Cell Therapy Using Bone Marrow-Derived Stem Cells/Endothelial Progenitor Cells to Accelerate Neovascularization in Healing of Experimental Ulcerative Colitis

Inflammatory bowel disease (IBD): ulcerative colitis (UC) and Crohn disease (CD) are characterized by recurrent inflammation and ulceration of intestinal and/or colonic mucosa and an inappropriate and delayed healing. Current therapies with, e.g., anti-TNFα antibody (infliximab) and other anti-inflammatory drugs (e.g., mesalamine) do not induce sustained remission, complete healing or prevent recurrence of UC. Although the pathogenesis of UC is not fully understood, pathologic angiogenesis has been postulated as a critical pathogenic component in UC. Recent studies demonstrated that the poor healing, chronic inflammation in colon of UC could be the result of microvascular dysfunction and endothelial barrier defect, resulting in sustained tissue hypoperfusion and ischemia in the colon. Previously, regeneration of injured endothelium and neovascularization were believed to rely solely on the migration and proliferation of neighboring endothelial cells from existing blood vessels. However, accumulating evidence shows that additional mechanisms may exist, and may be mediated by the circulating pool of bone marrow-derived endothelial progenitor cells (BMD-EPC). Furthermore, stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 have been demonstrated to play an important role in the "homing" of BMD-EPC to injured sites and neovascularization in tissue repair. Recent studies by others and us showed reduced BMD-EPC levels in the circulation of IBD patients and rats with experimental UC. However, the potential therapeutic effect of BMD-EPC on neovascularization and colonic mucosal repair in UC has not been elucidated. In this review, we discussed the possibility that impaired contribution of BMD-EPC (i.e., decreased release of BMD-EPC from bone marrow to circulation and/or blocked/impaired homing of BMD-EPC to colonic lesions) may be a critical component of mechanisms in the incomplete/delayed healing of UC, and may offer a novel form of cell therapy for IBD.

Cardioprotection by ischemic postconditioning is abolished in depressed rats: role of Akt and signal transducer and activator of transcription-3

Ischemic postconditioning (IPC) represents one of the most effective cardioprotective strategies against myocardial ischemia/reperfusion. Depression is commonly present in patients with coronary heart disease. However, whether depression interferes with the cardioprotection of IPC during myocardial ischemia/reperfusion and their underlying mechanisms remain largely unknown. Isolated hearts from chronic mild stress induced-depressed rats and non-depressed rats were subjected to 30min of regional ischemia followed by 120min of reperfusion in the presence or absence of IPC (consisting of 6 cycles of 10s of reperfusion and 10s of ischemia immediately after the sustained ischemia). Myocardial infarct size, creatine kinase (CK) and cardiac troponin T (cTnT) release, cardiac function and phosphorylated AKT and signal transducer and activator of transcription-3 (STAT-3) were measured. IPC significantly prevented the hearts from myocardial ischemia/reperfusion injury by decreasing infarct size, and CK and cTnT release in coronary effluent, and improving cardiac functional recovery in non-depressed rats. However, these cardioprotective effects of IPC were not observed in depressed rats. In addition, IPC had no effects on the phosphorylation of AKT and STAT-3 at reperfusion in depressed hearts, although it markedly increased the phosphorylation of AKT and STAT-3 at reperfusion in non-depressed hearts. In conclusion, these data indicate that cardioprotection by IPC is abolished during myocardial ischemia/reperfusion in depressed rats, and the underlying mechanisms are probably related to the impaired activation of AKT and STAT-3 at reperfusion.

Mitochondrial expression of ATPase is increased in late preconditioned myocardium and transmural energy is more favorable during sustained low flow ischemia

Mitochondrial expression of ATPase is increased in late preconditioned myocardium and transmural energy is more favorable during sustained low flow ischemia

Muscle Deoxygenation during Sustained and Intermittent Isometric Exercise in Hypoxia

It is reported that the rate of locomotor muscle fatigue development during intermittent isometric exercise in hypoxia is accelerated compared with normoxia. In contrast, when sustained isometric contractions are used, some studies do not show any effect of hypoxia on fatigue development. Increased intramuscular pressure during sustained isometric exercise causes substantial and sustained ischemia, even in normoxia. Therefore, we hypothesized that the difference in muscle deoxygenation between normoxia and hypoxia would be small during sustained exercise compared with intermittent exercise and that this may contribute to the inconsistent findings. Subjects performed sustained and intermittent isometric, unilateral, and submaximal knee-extension exercises (60% maximal voluntary contraction to exhaustion) while breathing normoxic (inspired O2 fraction = 0.21) or hypoxic gas mixtures (inspired O2 fraction = 0.10-0.12). Muscle oxygenation (deoxyhemoglobin/myoglobin and tissue oxygenation index) using near-infrared spectroscopy and surface EMG were measured from the left vastus lateralis. During intermittent isometric exercise in hypoxia, increases in deoxyhemoglobin/myoglobin and reductions of tissue oxygenation index were larger (P < 0.05) than those in normoxia. The rate of rise in integrated EMG during intermittent exercise was accelerated (P < 0.05) in hypoxia. In contrast, there were no significant differences in changes in near-infrared spectroscopy variables and integrated EMG during sustained isometric exercise between normoxia and hypoxia. These results suggest that muscle deoxygenation is exaggerated during intermittent isometric exercise in hypoxia compared with normoxia, whereas during sustained isometric exercise, the extent of muscle deoxygenation is the same between normoxia and hypoxia. The different extent of muscle deoxygenation during sustained and intermittent isometric exercise in normoxia and hypoxia could affect muscle fatigability, which results from the varied rate of accumulation of metabolites.

TNFα in myocardial ischemia/reperfusion, remodeling and heart failure

TNFα is crucially involved in the pathogenesis and progression of myocardial ischemia/reperfusion injury and heart failure. The formation and release of TNFα and its downstream signal transduction cascade following activation of its two receptor subtypes are characterized. Myocardial TNFα and TNF receptor activation have an ambivalent role in myocardial ischemia/reperfusion injury and protection from it. Excessive TNFα expression and subsequent cardiomyocyte TNF receptor type 1 stimulation induce contractile dysfunction, hypertrophy, fibrosis and cell death, while a lower TNFα concentration and subsequent cardiomyocyte TNF receptor type 2 stimulation are protective. Apart from its concentration and receptor subtype, the myocardial action of TNFα depends on the duration of its exposure and its localization. While detrimental during sustained ischemia, TNFα contributes to ischemic preconditioning protection, no matter whether it is the first, second or third window of protection, and both TNF receptors are involved in the protective signal transduction cascade. Finally, the available clinical attempts to antagonize TNFα in cardiovascular disease, notably heart failure, are critically discussed.

ENOS is required for acute in vivo ischemic preconditioning of the heart: effects of ischemic duration and sex

Ischemic preconditioning (IPC) is a powerful phenomenon that provides potent cardioprotection in mammalian hearts; however, the role of endothelial nitric oxide (NO) synthase (eNOS)-mediated NO in this process remains highly controversial. Questions also remain regarding this pathway as a function of sex and ischemic duration. Therefore, we performed extensive experiments in wild-type (WT) and eNOS knockout (eNOS(-/-)) mice to evaluate whether the infarct-limiting effect of IPC depends on eNOS, ischemic periods, and sex. Classical IPC was induced by three cycles of 5 min of regional coronary ischemia separated by 5 min of reperfusion and was followed by 30 or 60 min of sustained ischemia and 24 h of reperfusion. The control ischemia-reperfusion protocol had 30 or 60 min of ischemia followed by 24 h of reperfusion. Protection was evaluated by measuring the myocardial infarct size as a percentage of the area at risk. The major findings were that regardless of sex, WT mice exhibited robust IPC with significantly smaller myocardial infarction, whereas eNOS(-/-) mice did not. IPC-induced cardiac protection was absent in eNOS(-/-) mice of both Jackson and Harvard origin. In general, female WT mice had smaller infarctions compared with male WT mice. Although prolonged ischemia caused significantly larger infarctions in WT mice of both sexes, they were consistently protected by IPC. Importantly, prolonged myocardial ischemia was associated with increased mortality in eNOS(-/-) mice, and the survival rate was higher in female eNOS(-/-) mice compared with male eNOS(-/-) mice. In conclusion, IPC protects WT mice against in vivo myocardial ischemia-reperfusion injury regardless of sex and ischemic duration, but the deletion of eNOS abolishes the cardioprotective effect of classical IPC.

Postconditioning and protection from reperfusion injury: where do we stand? * Position Paper from the Working Group of Cellular Biology of the Heart of the European Society of Cardiology

Ischaemic postconditioning (brief periods of ischaemia alternating with brief periods of reflow applied at the onset of reperfusion following sustained ischaemia) effectively reduces myocardial infarct size in all species tested so far, including humans. Ischaemic postconditioning is a simple and safe manoeuvre, but because reperfusion injury is initiated within minutes of reflow, postconditioning must be applied at the onset of reperfusion. The mechanisms of protection by postconditioning include: formation and release of several autacoids and cytokines; maintained acidosis during early reperfusion; activation of protein kinases; preservation of mitochondrial function, most strikingly the attenuation of opening of the mitochondrial permeability transition pore (MPTP). Exogenous recruitment of some of the identified signalling steps can induce cardioprotection when applied at the time of reperfusion in animal experiments, but more recently cardioprotection was also observed in a proof-of-concept clinical trial. Indeed, studies in patients with an acute myocardial infarction showed a reduction of infarct size and improved left ventricular function when they underwent ischaemic postconditioning or pharmacological inhibition of MPTP opening during interventional reperfusion. Further animal studies and large-scale human studies are needed to determine whether patients with different co-morbidities and co-medications respond equally to protection by postconditioning. Also, our understanding of the underlying mechanisms must be improved to develop new therapeutic strategies to be applied at reperfusion with the ultimate aim of limiting the burden of ischaemic heart disease and potentially providing protection for other organs at risk of reperfusion injury, such as brain and kidney.

Postconditioning in mouse hearts is inhibited by blocking the reverse mode of the sodium–calcium exchanger☆

Ischemic postconditioning and inhibition of the reverse mode of the sodium-calcium exchanger (NCX) are both cardioprotective. We hypothesized that a combination of these techniques might have an additive effect mediated by protein kinases (see below). Isolated perfused mouse hearts were subjected to 35 min of ischemia and 60 min of reperfusion. Each series had its own control ischemia group, the other groups were postconditioning with three cycles of 10 s of reperfusion and 10 s of ischemia immediately after sustained ischemia; the vehicle of the NCX blocker KB-R7943 was added to the perfusate 5 min before ischemia in series 1; KB-R7943 was added to the perfusate 5 min before ischemia with and without postconditioning in series 2; KB-R7943 was added to the perfusate for 5 min from the start of reperfusion with and without postconditioning in series 3. Infarct size was measured and cardiac function was evaluated. Phosphorylation of AKT, ERK1/2, PKCdelta and PKCepsilon was measured by immunoblotting. Postconditioning alone reduced infarct size by 37% and activated AKT (P=0.02). Blockade of NCX reduced infarct size when applied before ischemia (29%) and at start of reperfusion (32%). Combining NCX blockade with postconditioning abolished cardioprotection despite phosphorylation of ERK1/2 (P=0.03) and PKCepsilon (P=0.01).

Mitochondria: Their role in ganglion cell death and survival in primary open angle glaucoma

Retinal ganglion cell axons within the globe are functionally specialised being richly provided with many mitochondria. Mitochondria produce the high energy that is required for nerve conduction in the unmylenated part of the ganglion cell axons and for the maintenance of optimum neuronal function. We proposed that in the initiation of glaucoma (POAG) an alteration in the quality of blood flow dynamics in the optic nerve head results in sustained or intermittent ischemia of a defined nature. This results in normal mitochondrial function being negatively affected and as a consequence retinal ganglion cell function is compromised. Ganglion cells in this state are now susceptible to secondary insults which they would normally tolerate. One secondary insult to ganglion cell mitochondria in such a state might be light entering the eye. Other insults to the ganglion cells might come from substances such as glutamate, prostaglandins and nitric oxide released from astrocytes and microglia in the optic nerve head region. Such cascades of events initiated by ischemia to the optic nerve head region ultimately cause ganglion cells to die at different rates.

Kinases and phosphatases in ischaemic preconditioning: a re-evaluation

Activation of several protein kinases occurs during myocardial ischaemia and during subsequent reperfusion. In contrast to the intensive investigation into the significance of kinase activation in cardioprotection, relatively little is known about the role of the phosphatases in this regard. The aim of this study was to re-evaluate the putative roles of PP1 and PP2A in ischaemia/reperfusion and in triggering ischaemic preconditioning. Isolated perfused working rat hearts were subjected to sustained global (15 or 20 min) or regional ischaemia (35 min), followed by reperfusion. Hearts were preconditioned using global ischaemia (1 x 5 or 3 x 5 min, alternated with 5 min reperfusion). To inhibit both PP1 and PP2A cantharidin (5 muM) was used. To inhibit PP2A only, okadaic acid (7.5 nM) was used. The drugs were administered during the preconditioning protocol, before onset of sustained ischaemia (pretreatment) or during reperfusion. Endpoints were mechanical recovery during reperfusion, infarct size and activation of PKB/Akt, p38 MAPK and ERK p42/p44, as determined by Western blot. Pretreatment of hearts with okadaic acid or cantharidin caused a significant reduction in mechanical recovery after 15 or 20 min global ischaemia. Administration of the drugs during an ischaemic preconditioning protocol abolished functional recovery during reperfusion and significantly increased infarct size. Administration of the drugs during reperfusion had no deleterious effects and increased functional recovery in 3 x PC hearts. To find an explanation for the differential effects of the inhibitors depending on the time of administration, hearts were freeze-clamped at different time points during the perfusion protocol. Administration of cantharidin before 5 min ischaemia activated all kinases. Subsequent reperfusion for 5 min without the drug maintained activation of the kinases until the onset of sustained ischaemia. Cantharidin given during preconditioning was associated with activation of p38MAPK and PKB/Akt during reperfusion after sustained ischaemia. However, administration of the drug during reperfusion only after sustained ischaemia caused activation of both PKB/Akt and ERK p42/p44. Phosphatase inhibition immediately prior to the onset of sustained ischaemia or during preconditioning abolishes protection during reperfusion, while inhibition of these enzymes during reperfusion either had no effect or enhanced the cardioprotective effects of preconditioning. It is proposed that inhibition of phosphatases during reperfusion may prolong the period of RISK activation and hence protect the heart.

Role of the gap junction in ischemic preconditioning in the heart

The gap junction plays roles not only in electrical coupling of cardiomyocytes but also in intercellular transport of biologically active substances. Furthermore, the gap junction participates in decision making on cell survival versus cell death in various types of cells, and a part of reperfusion injury in the heart has been indicated to be gap junction mediated. The contribution of gap junction communication (GJC) and/or mitochondrial "hemichannels" to protective signaling during the trigger phase of ischemic preconditioning (IPC) is suggested by observations that IPC failed to protect the heart when GJC was blocked during IPC. Although ischemia suppresses both electrical and chemical GJC, chemical GJC persists for a considerable time after electrical GJC is lost. IPC facilitates the ischemia-induced suppression of chemical GJC, whereas IPC delays the reduction of electrical GJC after ischemia. The inhibition of GJC during sustained ischemia and reperfusion by GJC blockers mimics the effect of IPC on myocardial necrosis. IPC induces distinct effects on the interaction of connexin-43 with protein kinases, and the phosphorylation of connexin-43 at Ser368 by PKCepsilon is a primary mechanism of inhibition of chemical GJC by IPC. Several lines of evidence support the notion that the modulation of GJC is a part of the mechanism of IPC-induced protection against myocardial necrosis and arrhythmias, though what percentage of IPC protection is attributable to the inhibition of GJC during ischemia-reperfusion still remains unclear.

Memory phase of the cardioprotective effect of isoflurane preconditioning on isolated rat myocardium

Objective To investigate the memory phase of the protective effect of isoflurane preconditioning (IsoP) on rat myocardium. Methods 24 isolated SD rat hearts were divided into four groups: IR, M1, M2 and M3 groups (n=6) according to the time of washout before ischemia. After equilibration, the hearts were perfused for 20 min, 10 min and 0 min in M1, M2 and M3 groups respectively, using Langen dorff apparatus, then received two cycles IsoP and followed by 10 min, 20 min and 30 min washout respectively. All the hearts were subjected to 30 min sustained ischemia and 60 min reperfusion. LVEDP, LVDP, and-dp/ dtmax were recorded. The release of CK and LDH in the outflow and the size of survival myocardium area were measured. Results During reperfusion, the recovery of LVEDP was lower in M1, M2 and M3 groups than that in IR group (P＜0.01). LVDP in M1 and M2 groups increased (P＜0.05). The percentage of recovery of LVDPxHR in M1 and M2 groups at 30 min and 60 min of reperfusion were higher than that in IR group (P＜0.05). The release of CK in memory groups significantly decreased (P＜0.05) and the contents of LDH in M1 group was lower than other groups (P＜0.05). The percentage of survival area of myocardium in M1 and M2 groups was higher than that in IR group and M3 group (P＜0.05). Conclusion The best memory phase of the cardioprotective effect of IsoP is about 20min in isolated rat heart. Key words: Isoflurane preconditioning; Cardiopmtection; Ischemia/reperfusion injury; Memory phase

Femininity and sarcolemmal KATP channels: a matter of the heart and the heart of the matter

Femininity and sarcolemmal K_ATP channels: a matter of the heart and the heart of the matter