The Protective Effect of Mitochondrial ATP-Sensitive K+ Channel Opener, Nicorandil, Combined With Na+/Ca2+ Exchange Blocker KB-R7943 on Myocardial Ischemia–Reperfusion Injury in Rat

Tetrandrine downregulates TRPV2 expression to ameliorate myocardial ischemia/reperfusion injury in rats via regulation of cardiomyocyte apoptosis, calcium homeostasis and mitochondrial function

Our previous study has indicated that tetrandrine (TET) can target miR-202-5p to repress the activation of transient receptor potential vanilloid type 2 (TRPV2), eventually ameliorating the progression of myocardial ischemia/reperfusion injury (MI/RI). This study is aimed to further ascertain the detailed mechanisms between TET and TRPV2 in MI/RI pathogenesis. Here, a myocardial I/R injury rat model and a hypoxia-reoxygenation (H/R) model in rat myocardial cell line (H9C2 cells) were established. We reported that pronounced upregulation of TRPV2 was observed in I/R rats and H/R-induced H9C2 cells. Silencing of TRPV2 could improve cardiac function and myocardial injury, reduced infarction size, and promoted cardiomyocyte proliferation in I/R rats. In I/R rats or H/R-induced H9C2 cells, cardiomyocyte apoptosis was inhibited by knocking-down TRPV2. Meanwhile, the silenced TRPV2 or TET treatment ameliorated the damaged mitochondrial structure, mitigated ROS generation, restored the impaired ΔΨM, inhibited mPTP opening and alleviated Ca2+ overload in H/R-induced H9C2 cells. The results obtained from the overexpression of TRPV2 were contrary to those depicted above. Moreover, TET could downregulate TRPV2 expression, while the overexpression of TRPV2 could reverse the above protective effects of TET in H/R-induced H9C2 cells. The results indicated that TET may function as a TRPV2 blocking agent, thereby attenuating the progression of MI/RI through modulation of cardiomyocyte apoptosis, calcium homeostasis and mitochondrial function. These findings offer a theoretical foundation for potential clinical application of TET therapy in patients with MI/RI.

Protective effect of nicorandil against myocardial ischemia/reperfusion injury mediated via IL33/ST2 signaling pathway

Myocardial ischemia-reperfusion injury (MI/RI), a complication of myocardial injury, is associated with high rates of mortality and disability. We aimed to explore the effect of nicorandil™ against MI/RI and investigated the underlying molecular mechanisms. In this in vitro study, hypoxia/reoxygenation (H/R) processing of H9c2 cells significantly suppressed the expressions of IL33 and ST2, reduced cell viability, increased production of reactive oxygen species, downregulated protein expression of Bcl-2, upregulated protein expressions of Bax, cleaved caspase3, and cleaved PARP, increased intracellular calcium overload, and induced cell apoptosis. Nicorandil processing reduced H/R-induced H9c2 cell damage. Nicorandil processing ameliorated the H/R-induced inhibition of the IL33 and ST2 expression in H9c2 cells. 5-Hydroxydecanoate blocked the effects of nicorandil on H9c2 cell viability, ROS production, and apoptosis and inhibited both IL33 and ST2. Similarly, the protective effect of nicorandil was restrained after inhibition of the IL33/ST2 pathway. Our findings suggest that the protective effect of nicorandil against H/R-induced H9c2 cell apoptosis was mediated through IL33/ST2 signaling pathway.

ABCC9 Is Downregulated and Prone to Microsatellite Instability on ABCC9tetra in Canine Breast Cancer

Tumorigenesis is associated with metabolic abnormalities and genomic instability. Microsatellite mutations, including microsatellite instability (MSI) and loss of heterozygosity (LOH), are associated with the functional impairment of some tumor-related genes. To investigate the role of MSI and LOH in sporadic breast tumors in canines, 22 tumors DNA samples and their adjacent normal tissues were evaluated using polyacrylamide gel electrophoresis and silver staining for 58 microsatellites. Quantitative real-time polymerase chain reaction, promoter methylation analysis and immunohistochemical staining were used to quantify gene expression. The results revealed that a total of 14 tumors (6 benign tumors and 8 breast cancers) exhibited instability as MSI-Low tumors. Most of the microsatellite loci possessed a single occurrence of mutations. The maximum number of MSI mutations on loci was observed in tumors with a lower degree of differentiation. Among the unstable markers, FH2060 (4/22), ABCC9tetra (4/22) and SCN11A (6/22) were high-frequency mutation sites, whereas FH2060 was a high-frequency LOH site (4/22). The ABCC9tetra locus was mutated only in cancerous tissue, although it was excluded by transcription. The corresponding genes and proteins were significantly downregulated in malignant tissues, particularly in tumors with MSI. Furthermore, the promoter methylation results of the adenosine triphosphate binding cassette subfamily C member 9 (ABCC9) showed that there was a high level of methylation in breast tissues, but only one case showed a significant elevation compared with the control. In conclusion, MSI-Low or MSI-Stable is characteristic of most sporadic mammary tumors. Genes associated with tumorigenesis are more likely to develop MSI. ABCC9 protein and transcription abnormalities may be associated with ABCC9tetra instability.

Study on the protective effects of danshen-honghua herb pair (DHHP) on myocardial ischaemia/reperfusion injury (MIRI) and potential mechanisms based on apoptosis and mitochondria

CONTEXT

Danshen, the dried root and rhizome of Salvia miltiorrhiza Bunge (Labiatae) and honghua, the dried flower of Carthamus tinctorius L. (Compositae) as the herb pair was used to treat cardiovascular diseases (CVD).

OBJECTIVE

To study the effects of DHHP on MIRI and mechanisms based on apoptosis and mitochondria.

MATERIALS AND METHODS

36 SD rats (n = 6) were randomly divided into control group (Con), the ischaemia-reperfusion group (IR), positive control (Xinning tablets, XNT, 1 g/kg/d) and DHHP (1.2, 2.4, and 4.8 g/kg/d). Except for Con, the other groups were intragastrically administrated for 5 d, the rat hearts were isolated to establish the MIRI model in vitro for evaluating the effects of DHHP on MIRI. 24 SD rats (n = 6) were randomly divided into Con, IR, DPPH2.4 (2.4 g/kg/d) and DPPH 2.4 + Atractyloside (ATR) (2.4 + 5 mg/kg/d), administered intragastrically for 5 d, then treated with ATR (5 mg/kg/d) by intraperitoneal injection in DPPH2.4 + ATR group, took rat hearts to establish MIRI model in vitro for revealing mechanism.

RESULTS

Myocardial infarct sizes were, respectively, 0.35%, 40.09%, 15.84%, 30.13%, concentrations of NAD⁺ (nmol/gw/w) were 144, 83, 119, and 88, respectively, in Con, IR, DHHP2.4, DHHP2.4 + ATR group. Cleaved caspase-3 were 0.3, 1.6, 0.5 and 1.3% and cleaved caspase-9 were 0.2, 1.1, 0.4 and 0.8%, respectively, in Con, IR, DHHP2.4 and DHHP2.4 + ATR group. The beneficial effects of DHHP on MIRI were reversed by ATR.

CONCLUSIONS

The improvement of MIRI by DHHP may be involved in inhibiting MPTP opening, decreasing oxidative damage, alleviating ischaemic injury and inhibiting cardiomyocyte apoptosis.

Down-regulation of GAS5 ameliorates myocardial ischaemia/reperfusion injury via the miR-335/ROCK1/AKT/GSK-3β axis

Growth arrest‐specific transcript 5 (GAS5), along non‐coding RNA (LncRNA), is highly expressed in hypoxia/reoxygenation (H/R)‐cardiomyocytes and promotes H/R‐induced apoptosis. In this study, we determined whether down‐regulation of GAS5 ameliorates myocardial ischaemia/reperfusion (I/R) injury and further explored its mechanism. GAS5 expression in cardiomyocytes and rats was knockdown by transfected or injected with GAS5‐specific small interfering RNA or adeno‐associated virus delivering small hairpin RNAs, respectively. The effects of GAS5 knockdown on myocardial I/R injury were detected by CCK‐8, myocardial enzyme test, flow cytometry, TTC and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining. qRT‐PCR and luciferase reporter assay were carried out to analyse the relationship between GAS5 and miR‐335. The regulation of GAS5 on Rho‐associated protein kinase 1 (ROCK1) expression, the activation of PI3K/AKT/GSK‐3β pathway and mitochondrial permeability transition pore (mPTP) opening was further evaluated. The results indicated that GAS5 knockdown enhanced the viability, decreased apoptosis and reduced the levels of lactate dehydrogenase and creatine kinase‐MB in H/R‐treatment cardiomyocytes. Meanwhile, down‐regulation of GAS5 limited myocardial infarct size and reduced apoptosis in I/R‐heart. GAS5 was found to bind to miR‐335 and displayed a reciprocal inhibition between them. Furthermore, GAS5 knockdown repressed ROCK1 expression, activated PI3K/AKT, thereby leading to inhibition of GSK‐3β and mPTP opening. These suppressions were abrogated by miR‐335 inhibitor treatment. Taken together, our results demonstrated that down‐regulation of GAS5 ameliorates myocardial I/R injury via the miR‐335/ROCK1/AKT/GSK‐3β axis. Our findings suggested that GAS5 may be a new therapeutic target for the prevention of myocardial I/R injury.

miR-202-5p protects rat against myocardial ischemia reperfusion injury by downregulating the expression of Trpv2 to attenuate the Ca 2+ overload in cardiomyocytes

BACKGROUND

This study was aimed to unveil micro RNA (miRNA) expression profiles in myocardial ischemia-reperfusion (MI/R) rats and explore whether and how dysregulated miRNAs were involved in the initiation and progression of MI/R in a calcium-dependent manner.

METHOD AND RESULTS

Rat model of MI/R was established and cardiomyocytes isolated from neonatal rats cardiomyocytes were induced. Both miRNA and messenger RNA expression profiles were analyzed by Microarray. Quantitative reverse-transcription polymerase chain reaction, immunoblotting, bioinformatics analysis, dual-luciferase reporter gene assay, hematoxylin and eosin, Evans blue, and triphenyl tetrazolium chloride were also used in this study. Serum concentrations of myocardial enzymes (phosphocreatine kinase [CK], creatine kinase [CK-MB], lactate dehydrogenase [LDH]), cardiomyocytes loadage of Ca²⁺ , as well as the expression level of inositol 1,4,5-trisphosphate receptors (IP3R) and sarcoplasmic reticulum Ca²⁺ -ATPase 2a (SERCA2a) were measured, respectively. Effects of upregulation or downregulation of miR-202-5p or Trpv2 on these indicators were investigated in vivo and in vitro. In MI/R rats and hypoxia/reoxygenation-induced NCMs, miR-202-5p was downregulated, while Trpv2 was upregulated. Trpv2 was a promising target of miR-202-5p and negatively regulated by miR-202-5p. Upregulation of miR-202-5p or downregulation of Trpv2 significantly reduced the serum concentration of myocardial enzymes, as well as cardiomyocyte-produced reactive oxygen species, but inhibition of miR-202-5p or overexpression of Trpv2 brought the worsening situation for these indicators. Besides, upregulation of miR-202-5p upregulation or downregulation of Trpv2 also inhibited Ca²⁺ overload in cardiomyocytes, accompanied with the increase of SERCA2a and suppression of IP3R. The reduced damage degree and infarct size in myocardial tissue were contrarily worsened by miR-202-5p inhibitor.

CONCLUSION

Overexpression of miR-202-5p or downregulation of its downstream Trpv2 presented the cardioprotective effects to MI/R rats.

Lycopene restores the effect of ischemic postconditioning on myocardial ischemia‑reperfusion injury in hypercholesterolemic rats

Ischemic postconditioning (IPoC) has been demonstrated to prevent myocardial ischemia-reperfusion injury (MIRI), but its cardioprotective effect is abrogated by hypercholesterolemia. The aim of the present study was to determine whether lycopene (LP), a type of carotenoid, can restore the cardioprotective effect of IPoC in hypercholesterolemic rats. Male Wistar rats were fed a cholesterol-enriched diet for 12 weeks to establish a hypercholesterolemic model. The rat hearts were isolated and subjected to 30 min ischemia and 60 min reperfusion using a Langendorff apparatus. LP was administered to the rats intraperitoneally for 5 consecutive days prior to ischemia and reperfusion. Myocardial pathological changes, infarct size and cell apoptosis were measured by hematoxylin and eosin, triphenyltetrazolium chloride and TUNEL staining, respectively. The changes in endoplasmic reticulum (ER) stress markers, the reperfusion injury salvage kinase (RISK) pathway and mitochondrial apoptosis-related proteins were detected by western blotting. Overall, the results demonstrated that low-dose LP in combination with IPoC ameliorated myocardial histopathological changes, reduced the infarct size and release of cardiac enzymes, and decreased cardiomyocyte apoptosis in hypercholesterolemic rats, but no beneficial effects were achieved by the same dose of LP or IPoC treatment were used alone. Furthermore, the combination of LP and IPoC inhibited the expression of glucose-regulated protein 78 and C/EBP homologous protein, increased the phosphorylation levels of AKT, ERK1/2 and glycogen synthase kinase-3β, repressed mitochondrial permeability transition pore opening, and reduced the expression of cytochrome c, cleaved caspase-9 and cleaved caspase-3. Collectively, these findings demonstrated that LP can restore the cardioprotective effects of IPoC on MIRI in hypercholesterolemic rats, and this restoration by LP was mediated by inhibition of ER stress and reactivation of the RISK pathway in hypercholesterolemic rat myocardium.

Hypercholesterolemia aggravates myocardial ischemia reperfusion injury via activating endoplasmic reticulum stress-mediated apoptosis

The effect of hypercholesterolemia on myocardial ischemia reperfusion injury (MIRI) is in controversy and the underlying mechanism is still not well understood. In the present study, we firstly detected the effects of hypercholesterolemia on MIRI and the role of endoplasmic reticulum (ER) stress-mediated apoptosis pathway in this process. The infarct size was determined by TTC staining, and apoptosis was measured by the TUNEL method. The marker proteins of ER stress response and ER stress-mediated apoptosis pathway were detected by Western blot. The results showed that high cholesterol diet-induced hypercholesterolemia significantly increased the myocardial infarct size, the release of myocardium enzyme and the ratio of apoptosis, but did not affect the recovery of cardiac function. Moreover, hypercholesterolemia also remarkably up-regulated the expressions of ER stress markers (glucose-regulated protein 78 and calreticulin) and critical molecules in ER stress-mediated apoptosis pathway (CHOP, caspase 12, phospho-JNK). In conclusion, our study demonstrated that hypercholesterolemia enhanced myocardial vulnerability/sensitivity to ischemia reperfusion injury involved in aggravation the ER stress and activation of ER stress-mediated apoptosis pathway and it gave us a new insight into the underlying mechanisms associated with hypercholesterolemia-induced exaggerated MIRI and also provided a novel target for preventing MIRI in the presence of hypercholesterolemia.

The protective effect of Na+/Ca2+ exchange blocker kb-r7943 on myocardial ischemia-reperfusion injury in hypercholesterolemic rat

KB-R7943 reduces lethal reperfusion injury under normal conditions, but its effectiveness under certain pathological states is in dispute. In the present study, we sought to determine the effect of KB-R7943 in hyperlipidemic animals and assess if the K ATP (+) are involved in the protective mechanisms. In group 1 (G1), isolated rat hearts underwent 25 min global ischemia (GI) and 120 min reperfusion (R). In group 2 (G2), G1 was repeated but the animals were subjected to a 1.5 % cholesterol-enriched diet during 6 weeks (hypercholesterolemic animals). In group 3 (G3), G2 was repeated but 1 μM KB-R7943 was added to the perfusate for 10 min from the start of reperfusion. In group 4 (G4), G3 was repeated, and glibenclamide (K ATP (+) , blocker, 0.3 μM) was administered. The infarct size was measured by triphenyltetrazolium. The infarct size was 35 ± 5.0 % in G1 and 46 ± 8.7 % in G2 (P < 0.05); KB-R7943 reduced the infarct size (28.6 ± 3.3 % in G3 vs. G2, P < 0.05). In addition, KB-R7943 attenuated apoptotic cell (G3 vs. G2, P < 0.05), but glibenclamide abolished the effect reached by KB-R7943. Thus, diet-induced hypercholesterolemia enhances myocardial injury; KB-R7943 reduces infarct size and apoptosis in hyperlipidemic animals through the activation of K(+)ATP channels.

WITHDRAWN: Hypercholesterolemia aggravates myocardial ischemia reperfusion injury via activating endoplasmic reticulum stress-mediated apoptosis

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Curcumin inhibits proliferation of gastric cancer cells by impairing ATP-sensitive potassium channel opening

BACKGROUND

This study was aimed to investigate whether ATP-sensitive potassium channel (KATP) is involved in curcumin's anti-proliferative effects against gastric cancer.

METHODS

In an in vitro study, gastric cancer cell line SGC-7901 was treated with curcumin at serial concentrations and co-administrated with the KATP opener, diazoxide. The effect of curcumin and diazoxide on proliferation were assessed by MTT assay. Mitochondrial membrane potential (MMP) was studied by flow cytometry detection of rhodamine 123 staining. Apoptosis was evaluated by flow cytometry detection of Annexin V propidium iodide double staining. In an in vivo study, SGC-7901 cells were planted into nude mice as xenografts. Animals were treated with curcumin co-administered with diazoxide. Tumor volume and tumor weight were observed.

RESULTS

Curcumin incubation significantly induced loss of MMP in SGC-7901 cells in a dose- dependent manner (P < 0.05); the cell apoptotic rate also dramatically increased after curcumin incubation in a dose-dependent manner (P < 0.05). After co-administration with diazoxide, however, we found that both the MMP-loss-inducing and the apoptosis-inducing effects of curcumin in SGC-7901 cells were significantly impaired (all P < 0.05). As a result, the proliferation of SGC-7901 cells was maintained by diazoxide treatment.

CONCLUSIONS

Impaired mitoKATP opening causes MMP loss, and is involved in curcumin-induced apoptosis in gastric cancer.

Inhibition of the cardiac ATP-dependent potassium current by KB-R7943

KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea) was developed as a specific inhibitor of the sarcolemmal sodium-calcium exchanger (NCX) with potential experimental and therapeutic use. However, in cardiomyocytes KB-R7943 also effectively blocks several K(+) currents including the delayed rectifier, IKr, and background inward rectifier, IK1. In the present study we analyze the effects of KB-R7943 on the ATP-dependent potassium current (IKATP) recorded by whole-cell patch-clamp in ventricular cardiomyocytes from a mammal (mouse) and a fish (crucian carp). IKATP was induced by external application of a mitochondrial uncoupler CCCP (3×10(-7) M) and internal perfusion of the cell with ATP-free pipette solution. A weakly inwardly rectifying current with a large outward component, recorded in the presence of CCCP, was blocked with 10(-5) M glibenclamide by 56.1±4.6% and 56.9±3.6% in crucian carp and mouse ventricular myocytes, respectively. In fish cardiomyocytes IKATP was blocked by KB-R7943 with an IC50 value of 3.14×10(-7) M, while in mammalian cells IC50 was 2.8×10(-6) M (P<0.05). 10(-5) M KB-R7943 inhibited CCCP-induced IKATP by 99.9±0.13% and 97.5±1.2% in crucian carp and mouse ventricular myocytes, respectively. In crucian carp the IKATP is about an order of magnitude more sensitive to KB-R7943 than the background IK1, but in mammals IKATP and IK1 are almost equally sensitive to KB-R7943. Therefore, the ability of KB-R7943 to block IKATP should be taken into account together with INCX inhibition when investigating possible cardioprotective effects of this compound.

Protective effect of Na(+)/Ca (2+) exchange blocker KB-R7943 on myocardial ischemia-reperfusion injury in hypercholesterolemic rats

Reverse-mode activation of the Na(+)/Ca(2+) exchanger (NCX) during reperfusion following ischemia contributes to Ca(2+) overload and cardiomyocyte injury. KB-R7943, a selective reverse-mode NCX inhibitor, reduces lethal reperfusion injury under non-ischemic conditions. However, the effectiveness of this compound under ischemic conditions is unclear. In the present study, we studied the effects of KB-R7943 in an animal model of hyperlipidemia. We further assessed whether the K ATP (+) channels are involved in potential protective mechanisms of KB-R7943. Twelve rats were fed normal chow, while 48 animals were fed a high cholesterol diet. The hearts from the control and hypercholesterolemic rats were subjected to 25 min of global ischemia followed by a 120-min reperfusion. Before this, hearts from hypercholesterolemic rats either received no intervention (cholesterol control group) or were pre-treated with 1 μM KB-R7943 and 0.3 μM of K ATP (+) blocker glibenclamide or glibenclamide alone. The infarction sizes (triphenyltetrazolium assay) were 35 ± 5.0 % in the control group, 46 ± 8.7 % in the cholesterol control group (p < 0.05 vs. control group), 28.6 ± 3.3 % in the KB-R7943 group (p < 0.05 vs. cholesterol control group), 44 ± 5 % in the KB-R7943 and glibenclamide group, and 47 ± 8.5 % in the glibenclamide group (p < 0.05 vs. control group). Further, KB-R7943 attenuated the magnitude of cell apoptosis (p < 0.05 vs. cholesterol control group). These beneficial effects were abolished by glibenclamide. In conclusion, diet-induced hypercholesterolemia enhances myocardial injury. Selective reverse-mode NCX inhibitor KB-R7943 reduces the infarction size and apoptosis in hyperlipidemic animals through the activation of K ATP (+) channels.

High‑dose fasudil preconditioning and postconditioning attenuate myocardial ischemia‑reperfusion injury in hypercholesterolemic rats

Fasudil may induce preconditioning and postconditioning against myocardial ischemia‑reperfusion injury in normal rats, however, their effectivenesses in hypercholesterolemia remains to be determined. The study aimed to investigate whether fasudil induces preconditioning and postconditioning in hypercholesterolemic rats and to determine the roles of the phosphoinositol 3‑kinase (PI3K)/Akt/endothelial nitric oxide synthase (eNOS) pathway and mitochondrial KATP (m‑KATP) channels in this process. Isolated rat hearts underwent 30 min global ischemia and 120 min reperfusion. Low‑ (1 mg/kg) or high‑dose (10 mg/kg) fasudil was administered 15 min prior to ischemia and at the initial onset of reperfusion. 5‑Hydroxydecanoic acid (5HD), an m‑KATP channel blocker, at 10 mg/kg was administered 5 min prior to reperfusion. Myocardial infarct size was estimated by 2,3,5‑triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) and creatine kinase‑MB (CK‑MB) were analyzed from coronary effluents. Phosphorylation of Akt and eNOS was measured by immunoblotting. High‑dose fasudil‑induced preconditioning and postconditioning significantly reduced infarct size and the release of LDH and CK‑MB and increased the phosphorylation of Akt and eNOS compared with the control group, whereas low‑dose fasudil did not exert these beneficial effects. In addition, the cardioprotection of high‑dose fasudil‑induced preconditioning and postconditioning are blocked by 5HD. Low‑dose fasudil‑induced preconditioning and postconditioning are abrogated by hypercholesterolemia, while high‑dose fasudil restores the cardioprotection, which is involved in upregulation of the PI3K/Akt/eNOS pathway and inducing the opening of the m‑KATP channel.

Protective mechanism of nicorandil on rat myocardial ischemia-reperfusion

OBJECTIVES

To study the protective mechanism of nicorandil on myocardial ischemia-reperfusion injury.

METHODS

Fifty rats were randomly divided into five groups, four of which were operated on to produce myocardial ischemia-reperfusion. Nicorandil (5 mg/kg) was administrated by intravenous injection to three of the groups. The myocardial ultrastructure was observed by electron microscope. The expression levels of the antiapoptotic protein Bcl-2 and the pro-apoptotic protein Bax were detected by immunohistochemical staining with rhodamine 123. The mitochondrial membrane potential was detected by spectrophotometry.

RESULTS

The activity of lactate dehydrogenase (LDH) and malondialdehyde (MDA) content was decreased and the activity of superoxide dismutase (SOD) was increased in the three nicorandil groups, compared with those in the group without nicorandil (P < 0.01, P < 0.05). The positive staining level of the expressed Bcl-2 was increased and the expressed Bax was decreased (P < 0.01) in the three nicorandil groups, compared with those in the group without nicorandil. The mitochondrial inner membrane potential was increased in the three nicorandil groups compared with that in the group without nicorandil (P < 0.05).

CONCLUSION

A suitable level of nicorandil has a protective effect on rats' myocardial ischemia-reperfusion injury, and is mainly based on the opening of the mitochondrial KATP channel and the lowing of Ca overload.