Inhibitory effect of zacopride on ouabain-induced arrhythmias in adult rats

AIM: To investigate the effect of zacopride, an inward rectifier potassium channel agonist, on ouabain-induced arrhythmias in adult rats, and to explore the underlying electrophysiological mechanism.METHODS: Using ouabain to establish in vitro and in vivo arrhythmic rat models, the effects of zacopride on ouabain-induced arrhythmias were observed. The technique of whole-cell patch clamp was used to observe the effects of zacopride on inward rectifier potassium current (I_K1), resting membrane potential (RMP) and delayed afterdepolarizations (DADs) in single rat ventricular myocyte. RESULTS: Zacopride at 1 μmol/L significantly reduced total number of premature ventricular beats, and the duration and incidence of ventricular tachycardia and ventricular fibrillation induced by ouabain in rat hearts in vitro (P<0.05). In anesthetized rats, zacopride at 15 μg/kg significantly reduced total number of premature ventricular beats, and the duration and incidence of ventricular tachycardia and ventricular fibrillation induced by ouabain (P<0.05). I_K1 was significantly inhibited by ouabain (P<0.05), which was partially and even completely reversed by zacopride at 0.1~10 μmol/L. RMP value was significantly reduced by ouabain (P<0.05), and then increased to different levels after treatment with zacopride (0.1~10 μmol/L). Zacopride at 1 μmol/L showed its maximal effect and RMP was restored to normal level. Moreover, zacopride at 1 μmol/L markedly suppressed ouabain-induced DADs in single rat ventricular myocyte. The incidence of DADs decreased from 91.67% to 12.50% after zacopride was applied (P<0.05), and this effect was abolished by 1 μmol/L BaCl₂. CONCLUSION: Inward rectifier potassium channel agonist zacopride significantly inhibits ouabain-induced ventricular arrhythmias in adult rats. The mechanism is related to increased RMP level and inhibition of DADs by activation of I_K1 channel.     

Zacopride enhances inward rectifier potassium current (IK1) to antagonize arrhythmias

AIM: To investigate the effects of zacopride on aconitine or BaCl2-induced arrhythmias and involved ionic mechanisms. METHODS: The whole-cell patch-clamp technique was used to record the inward rectifier K+ current (IK1), Ca+ current (ICa-L), Na+ current (INa), transient outward K+ current (Ito), the resting membrane potential (RMP) and action potential (AP) in the single cell of rat ventricular myocardium. Two arrhythmic models were elicited by injection of 30 μg/kg aconitine or 4 mg/kg BaCl2 intravenously. Zacopride at dose of 15 μg/kg was administered immediately after the development of first sinus rhythm disorders to observe its effects on arrhythmias. The ECGs were recorded simultaneously. RESULTS: In voltage clamp mode, 0.1-10.0 μmol/L zacopride dose-dependently enhanced IK1 with no significant effects on ICa-L, INa and Ito (P>0.05). Zacopride at concentration of 1.0 μmol/L showed the most potent activity on IK1 with approximately 30% increment both in inward current and outward current (P<0.01). Correspondingly, 0.1-10.0 μmol/L zacopride hyperpolarized RMP and shortened the action potential duration (APD) in a concentration-dependent manner (P<0.01). Furthermore, 1.0 μmol/L zacopride abolished aconitine-induced delayed afterdepolarization (DAD) and triggered activity (TA). In vivo, zacopride (15 μg/kg) significantly shortened the duration of arrhythmias elicited by aconitine ［from (57.58±3.21) min to (38.25±2.59) min］ or BaCl2 ［from (49.31±2.46) min to (30.94±1.73) min］. CONCLUSION: As an agonist of IK1, zacopride enhanced IK1, hyperpolarized RMP and shortened APD, which may be the fundamental mechanisms underlying its antiarrhythmic effect. Enhancing IK1 might be a new antiarrhythmic strategy.     

全国设施蔬菜生产可持续发展学术研讨会在沈阳召开

会议由中国园艺学会主办 ,中国农业工程学会设施园艺工程专业委员会协办 ,沈阳农业大学园艺系承办 ,于 2 0 0 0年 4月 19日至 2 2日在沈阳农业大学召开。来自我国 13个省、自治区、直辖市的与会代表共 78人 ,会议论文 4 3篇 ,由沈阳农业大学学报专刊发表。经承办单位和与会者努力 ,会议圆满成功。开幕式由中国园艺学会副理事长李树德研究员主持 ,辽宁省科技厅、农业厅、沈阳市副食品局、沈阳农业大学的领导到会祝贺并发表讲话。会议就确定的主题进行了大会发言 ,小组讨论及现场考察。代表们欣喜地看到 ,近 2 0年来我国蔬菜设施生产迅猛发展 …     

Receptor and signaling mechanisms involved in zacopride-induced potentiation of IK1

AIM: To investigate the receptor and signaling mechanisms involved in the potentiation of inward rectifier K⁺ current (I_K1) induced by zacopride, a potent 5-HT₃ receptor antagonist and 5-HT₄ receptor agonist. METHODS: The whole-cell patch clamp technique was used to record I_K1. 5-HT₄-receptor antagonist RS23597-190, 5-HT₃-receptor agonist m-chlorophenylbiguanide (m-CPBG), PKA inhibitor KT5720, PKC inhibitor GF109203X and PKG inhibitor KT5823 were applied respectively to determine the regulatory mechanism of I_K1. RESULTS: In the presence of RS23597-190 at concentration of 10 μmol/L which inhibited I_K1, zacopride at concentration of 1 μmol/L still increased I_K1 with the mean increment of 32.5% in inward current (at -100 mV, P<0.05). The I_K1 increment induced by zacopride was not inhibited by m-CPBG at concentration of 10 μmol/L (P>0.05). Furthermore, PKA inhibitor KT5720 at concentration of 5 μmol/L reversed the effect of zacopride (P<0.05), while PKC inhibitor GF109203X and PKG inhibitor KT5823 both at concentration of 5 μmol/L didn't influence the effect (P>0.05). CONCLUSION: Zacopride potentiates I_K1 via a PKA-mediated signaling pathway, which is independent on 5-HT₄ and 5-HT₃ receptors.     

Progress in brain protection with ischemic postconditioning

Cerebrocardiovascular diseases and stroke are serious threat to human health. More attentions focus on cerebral ischemia and the publications suggest that ischemic preconditioning prevents ischemic myocardium from ischemia/reperfusion injury, soon followed by preconditioning against cerebral ischemic injury. However, in clinical management, ischemia is often unpredictable. In recent years, researchers found that ischemic postconditioning and ischemic preconditioning obtained the similar effects on brain protection after cerebral ischemia. The endogenous protective mechanisms play a key role in protecting against brain ischemic injury. As a novel manner to protect against brain injury, postconditioning attenuates the infarct volume following brain ischemia/reperfusion and prompts the neurological recovery by prolonging the therapeutic time window. This article reviews the processes of ischemic, hypoxia, hypothermia and pharmacologic postconditioning, and the possible brain protection mechanisms activated by the signal transduction of serine/threonine kinase (Akt), phosphatidylinositol 3-kinase (PI3K), mitogen-activated protein kinase (MAPK), protein kinase C (PKC), and ATP-sensitive potassium channel (K_ATP) pathways.     

Effects of nitric oxide on spontaneous action potentials of guinea-pig left ventricular outflow tract under the conditions of ischemia/reperfusion

AIM: To study the electrophysiological effects of nitric oxide (NO) on the pacemaker cells in guinea-pig left ventricular outflow tract under the condition of ischemia/reperfusion (I/R). METHODS: The spontaneous slow action potentials of guinea-pig left ventricular outflow tract were recorded by conventional intracellular microelectrode technique. The effects of NO donor sodium nitroprusside (SNP) on the spontaneous slow action potentials under normal or I/R condition were investigated. RESULTS: SNP at concentrations of 1, 10 and 100 μmol/L but not 1000 μmol/L significantly increased velocity of diastolic depolarization (VDD) and rate of pacemaker firing (RPF), SNP at concentrations of 1, 10, 100 and 1 000 μmol/L notably increased maximal diastolic potential (MDP), amplitude of action potential (APA) and maximal rate of depolarization (V_max), shortened 50% and 90% of the duration (APD₅₀ and APD₉₀). In ischemia 10 min group, VDD and RPF were significantly decreased, APA and V_max were notably increased, and APD₅₀ and APD₉₀ were markedly lengthened compared with control group. In reperfusion 10 min group, VDD and RPF were significantly increased, MDP and APA were notably decreased, and APD₅₀ and APD₉₀ were markedly shortened compared with I 10 min group. In reperfusin 10 min group, the pacemaker activity was always irregular. In reperfusion 10 min group, the parameters of spontaneous slow action potentials restored to the levels of control group except for VDD and V_max. In 1, 10 and 100 μmol/L SNP+R groups, VDD and RPF were significantly increased than in ischemia 10 min group. In 1, 10, 100 and 1 000 μmol/L SNP+R groups, APA, APD₅₀ and APD₉₀ were restored to the levels of control group. CONCLUSION: SNP significantly increases the spontaneous activity of left ventricular outflow tract, and relieves the effects of I/R on the spontaneous slow action potential markedly.     

Cardioprotection of ischemic postconditioning against ischemia/reperfusion injury in isolated rat hearts

AIM: To investigate the protective role of postconditioning in myocardial ischemia/reperfusion in rats and its mechanisms. METHODS: Cardiac contractility was analyzed by the Langendorff method. Infarct size was determined by dual staining with triphenyltetrazolium chloride and Even's blue dye, and the cardiac arrhythmia was evaluated. postconditioning was conducted by 3 cycles of 30 s ischemia followed by 30 s of reperfusion at the beginning of subsequent persistent reperfusion. RESULTS: Left ventricular systolic pressure (LVSP) and maximal rise rate of ventricular pressure (+dp/dt_max) were higher during reperfusion in postconditioning group compared with control. postconditioning reduced the infarct size in ischemia/reperfusion rat hearts. The cardiac arrhythmia score was decreased in postconditioning group in the first 10 min of reperfusion followed by ischemia compared to control group. postconditioning had similar cardioprotective effect as preconditioning. 5-HD, a selective mitochondrial ATP-sensitive potassium channel (mitoK_ATP) inhibitor, blocked the amelioration of contract function provided by postconditioning. It also abolished the protective effect of postconditioning on cardiac arrhythmia score and infarct size. CONCLUSION: The results show that postconditioning has cardioprotective effect and attenuates reperfusion injury in ischemic heart. The effect might be partly through the activation of mitoK_ATP channel.     

Role of ATP-sensitive potassium channels in inhibitory effect of hydrogen sulfide on high glucose-induced injury in H9c2 cardiac cells

AIM: To investigate the roles of ATP-sensitive potassium (K_ATP) channels in high glucose-induced cardiac injury and the inhibitory effect of hydrogen sulfide (H₂S) on the cardiomyocyte injury. METHODS: The expression level of K_ATP channel protein was tested by Western blot. The cell viability was measured by CCK-8 assay. The number of apoptotic cells was observed by Hoechst 33258 nuclear staining. Mitochondrial membrane potential (MMP) was examined by JC-1 staining. RESULTS: After the H9c2 cells were treated with 35 mmol/L glucose (high glucose, HG) for 1~24 h, the protein level of K_ATP channel was significantly reduced at 6 h, 9 h, 12 h and 24 h, reaching the minimum level at 12 h and 24 h. Pretreatment of the cells with 400 μmol/L NaHS (a donor of H₂S) prior to exposure to HG for 12 h considerably blocked the down-regulation of K_ATP channels induced by HG. Pretreatment of the cells with 100 μmol/L mitochondrial K_ATP channel opener diazoxide, 50 μmol/L non-selective K_ATP channel opener pinacidil or NaHS obviously inhibited HG-induced injuries, leading to an increase in the cell viability, and decreases in the number of apoptotic cells and the MMP loss. Pretreatment with 100 μmol/L mitochondrial K_ATP channel antagonist 5-hydroxydecanoic acid or 1 mmol/L non-selective K_ATP channel antagonist glibenclamide attenuated the above cardioprotective effects of NaHS. CONCLUSION: K_ATP channels mediate the inhibitory effect of H₂S on HG-induced cardiac injury.     

Effect of diazoxide postconditioning on cardiac function and mitochondrial cardiolipin in isolated rat heart

AIM: To investigate the effect of diazoxide (D) postconditioning on Cardiac function and mitochondrial cardiolipin in isolated rat heart and to explore the protective effect of ATP sensitive potassium channel on diazo-xide postconditioning myocardium. METHODS: The myocardial ischemia/reperfusion injury model in isolated rat hearts was established by Langendorff apparatus. The isolated rat hearts were randomized into 4 groups (n=8): control group (control), myocardial ischemia/reperfusion injury group (I/R), diazoxide postconditioning group (I/R+D), 5- hydroxy decanoic acid (5-HD) plus diazoxide postconditioning group (I/R+5-HD+D). The hearts in each group were started with 20 min perfusion for equilibration. The hearts in control group perfused for 70 min; The hearts in I/R group was global ischemia for 40 min after ischemia reperfusion at 4 ℃ ST. Thomas cardioplegia, then reperfusion for 30 min; The hearts in I/R+D group were treated with diazoxide (50 μmol/L) in K-H perfusion for 5 min after global ischemia for 40 min, then reperfusion for 25 min; The hearts in I/R+5-HD+D group were treated with 5-HD (100 μmol/L) in K-H perfusion for 5 min before diazoxide postconditioning, then reperfusion for 20 min. The heart rate, coronary outflow volume, heart function, myocardial enzymes and myocardial mitochondrial cardiolipin at the end of perfusion in each group were determined. RESULTS: Compared with control group and I/R+D group, the heart rate, the concentration of heart phospholipid and the coronary outflow volume were reduced, the heart function was significantly impaired the contents of myocardial enzymes were increased in I/R group. However, no significant difference between I/R group and I/R+5-HD+D group was observed. CONCLUSION: The diazoxide postconditioning protects the myocardium by increasing mitochondrial cardiolipin content, reducing the release of myocardial enzymes, improving heart function and reducing myocardial reperfusion injury. The myocardial protective effect of diazoxide is completely blocked by 5- hydroxy decanoic acid.     

Effects of simulated ischemia/reperfusion on spontaneous action potentials in primary cultured sinoatrial node cells and the influence of pinacidil

AIM: To study the effects of ischemia/reperfusion (I/R) on primary cultured sinoatrial node (SAN) cells and the influence of pinacidil (a K_ATP channel activator). METHODS: The SAN cells were isolated from newborn rats and purified. The 48 h cultured cells were cultivated in following mediums: simulated reperfusion solution as normal control, simulated ischemia/reperfusion solution (I/R), Pinacidil+I/R (P+I/R), 5-HD+P+I/R and 5-HD+I/R. Spontaneous action potentials were recorded by ruptured-patch whole-cell technique in current clamp (I=0) and the maximum diastolic potential (MDP), upstroke velocity (UV), action potential overshoot (APO), interbeat interval (IBI) and action potential durations at 50% repolarization (APD₅₀) were measured. RESULTS: Compared with control group, simulated ischemia/reperfusion shorten APD₅₀, reduced UV, MDP and APO. Exposed to pinacidil, MDP of cells in I/R groups was hyperpolarized; IBI, UV and APO were increased; APD₅₀ was shorten. 5-HD couldn't block the effects of pinacdil on APD₅₀, IBI and MDP, but reversed its actions on increasing UV and APO. CONCLUSIONS: Pinacidil made changes of AP in I/R group by opening different K_ATP channels of SAN cells. The role of this changes on protection in SAN cells during ischemia/reperfusion requires further investigation.     

Role of ATP-sensitive potassium channels in inhibitory effect of hydrogen sulfide on high glucose-induced inflammation mediated by necroptosis in H9c2 cardiac cells

AIM: To investigate the role of ATP-sensitive potassium (K_ATP) channels in the inhibitory effect of hydrogen sulfide (H₂S) on high glucose(HG)-induced inflammation mediated by necroptosis in H9c2 cardiac cells.METHODS: The expression levels of receptor-interacting protein 3 (RIP3; an indicator of necroptosis) and cyclooxyge-nase-2 (COX-2) were determined by Western blot. The levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) were detected by ELISA.RESULTS: After H9c2 cardiac cells were treated with 35 mmol/L glucose (HG) for 24 h, the expression of RIP3 was significantly increased. Pre-treatment of the cells with 100 μmol/L diazoxide (DZ; a K_ATP channel opener) or 400 μmol/L NaHS (a donor of H₂S) for 30 min considerably blocked the up-regulation of RIP3 induced by HG. Moreover, pre-treatment of the cells with 100 μmol/L 5-hydroxydecanoic acid (5-HD; a K_ATP channel blocker) attenuated the inhibitory effect of NaHS on HG-induced up-regulation of RIP3. On the other hand, co-treatment of the cells with 100 μmol/L necrostatin-1 (a specific inhibitor of necroptosis) or pre-treatment of the cells with 100 μmol/L DZ or 400 μmol/L NaHS attenuated HG-induced inflammatory responses, evidenced by decreases in the expression of COX-2 and secretion levels of IL-1β and TNF-α. However, pre-treatment of the cells with 100 μmol/L 5-HD significantly attenuated the above anti-inflammatory effects of NaHS.CONCLUSION: K_ATP channels play an important role in the inhibitory effect of H₂S on HG-induced inflammation mediated by necroptosis in H9c2 cardiac cells.     

Proteomic study of myocardial mitochondria with ischemia/reperfusion injury and pinacidil postconditioning in isolated rat hearts

AIM: To investigate the protective effect of pinacidil postconditioning on rat myocardium suffering ischemia/reperfusion injury by mitochondrial proteomics. METHODS: Langendorff apparatus was used to establish the model of myocardial ischemia/reperfusion injury. Sprague-Dawley rats were randomly divided into 2 groups: pinacidil postconditioning group (Pina group) and ischemia/reperfusion injury group (I/R group). After 20 min of perfusion with K-H solution, the perfusion was suspended for 40-min (global ischemia) follow by 60 min of reperfusion in I/R group. In Pina group at the end of 40 min global ischemia, the isolated hearts were perfused with K-H solution containing pinacidil (50 μmol/L) for 2 min followed 58-min perfusion with regular K-H solution. Total proteins extracted from the mitochondria were applied to the two-dimensional gel electrophoresis (2-DE). The differentially expressed protein spots over 2 times were evaluated by a software. Then they were subjected to in-gel digestion, and analyzed by spectrometry. RESULTS: The expression levels of NDUFA10, NDUFS2 and NDUFV2 were elevated but those of IDHA and ECH1 were decreased in Pina group compared with I/R group. Interestingly, 2 spots in the 2-DE map were identified as ATPase subunit δ. The expression levels of one spot was elevated, while the other was decreased. CONCLUSION: Pinacidil postconditioning may decrease the degree of increased expression levels of NDUFA10, NDUFS2 and NDUFV2, promote the expression of IDHA and ECH1, and induce the phosphorylation of ATPase subunit δ, which may be related to the protective mechanism of pinacidil postconditioning.     

魔芋花粉的低温和超低温保存

利用干燥法和玻璃化法，魔芋花粉能够在4℃下保存1个月，－20℃下保存6个月；魔芋花粉经液氮超低温（－196℃）保存后，有明显的“冷刺激”现象，即保存花粉比新鲜花粉有更高的离体萌发率。     

Effects of adiponectin on expression of connexin 43 in rat myocardium during ischemia-reperfusion

AIM: To observe the effects of adiponectin(APN) on the expression of connexin 43 (Cx43) in rat myocardium during ischemia-induced arrhythmias. METHODS: The SD rats were randomly divided into 4 groups (n=12): sham operation group (SM group), ischemia and reperfusion group (I/R group), I/R+adiponectin(APN1) group: pre-ischemia with 3.5 μg/kg of APN; I/R+APN2 group: post-ischemia with 3.5 μg/kg of APN. The incidence of ventricular arrhythmias and ventricular arrhythmia score (VAS) were determined. The expression of Cx43 in the ischemic myocardium was studied by the techniques of immunohistochemistry and RT-PCR. The levels of malondialdehyde(MDA) and superoxide dismutase(SOD) were measured by the methods of xanthine oxidase and thiobarbituric acid. The expression of endothelial nitric oxide synthase (eNOS) at mRNA and protein levels was determined by RT-PCR and Western blotting,respectively.The morphological changes of the myocardial tissues were observed under electronic microscope. RESULTS: The VAS and concentration of MDA increased obviously and the activity of SOD was decreased in I/R group as compared with SM group (P<0.01). The expression of Cx43 was evidently decreased and the distribution of Cx43 in the myocardium was disturbed. The expression of eNOS at mRNA and protein levels was decreased in I/R group (P<0.05). The ultrastructure of ventricular myocardium was abnormal in I/R group. Compared with I/R group, APN obviously decreased the VAS caused by ischemia and reperfusion (P<0.01) no matter the drug was given before or after ischemia. APN increased the activity of SOD, inhibited the MDA content in serum, and resulted in normal distribution of Cx43 and increased the expression of Cx43 and eNOS. Compared with I/R group, the changes of heart ultrastructure attenuated greatly in APN group, but didn't recover to normal state. CONCLUSION: Adiponectin antagonizes the arrhythmias during myocardial ischemia and reperfusion via inhibiting oxidative stress and regulating Cx43.     

Role of cAMP signaling in cardioprotective mechanism of ischemic postconditioning

AIM: To assess the role of the cAMP signaling in cardioprotection by brief intermittent ischemia at the time of onset of reperfusion (i.e. postconditioning). METHODS: The model of rat myocardial ischemia/reperfusion (I/R) was used. The left ventricular functions were assessed by measuring the left ventricular developed pressure (LVDP) and the coronary flow (CF). The injury of myocardium was further confirmed by detecting the releases of lactate dehydrogenase(LDH) and creatine kinase(CK) in coronary effluent. The mRNA expression of caspase-3, bcl-2 and bax in myocardium was determined by real-time PCR. RESULTS: I/R treatment led to the decrease in LVDP and CF, and the increase in the releases of CK and LDH in coronary artery effluent. The mRNA expression of caspase-3 and bax/bcl-2 ratio was up-regulated simultaneously. Postconditioning treatment relieved the injury induced by I/R, which was enhanced by the specific phosphodiesterase 4(PDE4) inhibitor rolipram. On the other hand, the specific adenylyl cyclase inhibitor SQ22536 attenuated those protective effects of postconditioning. CONCLUSION: The cAMP signaling participates in the protective effect of postconditioning on heart from I/R injury, and the effect may be associated with the regulation of apoptosis.     

Dynamic changes of the concentration of nitric oxide in ischemic myocardium and its mechanism

AIM: The study was undertaken to explore the dynamic changes of the concentration of nitric oxide(NO) in ischemic myocardium and its mechanism.METHODS: In vivo myocardial ischemia of mice and in vitro perfused isolated heart of rat were used in the experiment. The effects of severity and time of ischemia on NO production, NOS activity and mRNA were examined, respectively. RESULTS: There was a considerable difference (P<0.01) in the concentration of NO between ischemia group [(9.12±1.40) μmol/L] and control group [(20.16±1.67) μmol/L] after Pit(30 U/kg) administration, and the concentration of NO of ischemic group significantly decreased [(9.17±1.33) μmol/L] compared with control group [(19.90±1.95) μmol/L] after 30 minutes of ischemia. Also, the concentration of NO after Pit(20 U/L) administration in K-H and 15 min of ischemia was (15.41±2.00) μmol/L and (15.09±2.00) μmol/L respectively in vitro, significantly lower than control group [(23.83±2.33) μmol/L and (23.63±2.52) μmol/L]. In addition, compared with control group, the number of NOS positive cells, NOS activity as well as mRNA expression in atrial muscle and ventricular muscle of ischemic group were markedly reduced, respectively. CONCLUSION: Myocardial ischemia could reduced the NO level in myocardium, down-regulation of NOS mRNA could be the possible mechanism.     

Effect of heat shock precondition on reperfusion arrhythmia in rats

AIM:To investigate the effect of the heat shock response on the reperfusion arrhythmias(RAs) and the possible mechanism involved. METHODS:Fifty-five Sprague Dawley rats were randomly divided into 2 groups: the heat shock group (group H,n=29) and the control group (group C,n=26). The rats in group H were preconditioned with heat shock 24 hours before, and that in group C were not. The hearts of 16 rats in group H and 16 in group C were exercised and mounted on a non-circulating Langendorff perfusion apparatus and perfused retrogradely with modified K-H buffer and mimic ischemia/reperfusion was applied. Additionally, conventional intracellular microelectrode techniques were used for recording such electrophysiological parameters as resting potential(RP), action potential amplitude(APA), over shot(OS), maximum depolarization velocity(Vmax) of the hearts of other 13 rats in group H and 10 in group C. RESULTS:①Prior heat stress significantly decreased reperfusion arrhythmia. ②The amount of CK release in the effluent in group H was much less than that in group C. ③Myocardial HSP70 content was elevated significantly in group H. ④Heat stress significantly increased myocardial anti-oxydases activity and decreased lipid peroxydative products. Additionally, heat stress significantly reduced the Vmax of action potential. It indicated that rapid Na⁺ channel of papillary muscles may be inhibited by heat shock. The degree of change of Vmax after ischemia in H group was significantly less than that in group C. And the time of reperfusoin with Tyrode's solution till the action potential appeared as large as that before perfusion with mimic ischemic solution is shorter in group H than in group C. CONCLUSION:Heat shock pretreatment markedly reduces ischemia/reperfusion-induced injury of heart and ventricular arrhythmias in rats and this effect may be associated with the inhibition of rapid Na⁺ channel of papillary muscles by heat shock and the increase in myocardial HSP70 and anti-oxydase activity.     

RISK signaling pathway in myocardial preconditioning and postconditioning

The anti-apoptotic pro-survival kinase signaling cascades, phosphatidylinositol-3-OH kinase (PI3K)-Akt and p42/p44 extra-cellular signal-regulated protein kinases (ERK 1/2), which have been termed the reperfusion injury salvage kinase (RISK) pathway, are involved in cellular survival. In myocardial ischemic preconditioning, pharmacological preconditioning, ischemic postconditioning and pharmacological postconditioning, the activation of these kinase cascades at the time of reperfusion has been demonstrated to confer cardioprotection against reperfusion-induced injury. Targeting the RISK signaling pathway may provide a novel strategy to salvaging viable myocardium and limiting infarct size during myocardial ischemia-reperfusion.     

Opening of ATP-sensitive K+ channels protects H9c2 cardiac cells against high glucose-induced injury and inflammation by inhibiting TLR4/NF-κB pathway

AIM: To investigate whether the opening of ATP-sensitive K⁺(K_ATP) channels protects H9c2 cardiac cells against high glucose(HG)-induced injury and inflammation by inhibiting the Toll-like receptor 4(TLR4)/nuclear factor-κB(NF-κB) pathway. METHODS: The protein levels of TLR4 and NF-κB p65 were determined by Western blot. The levels of interleukin-1β(IL-1β) and tumor necrosis factor-α(TNF-α) were detected by ELISA. The cell viability was measured by CCK-8 assay. Mitochondrial membrane potential(MMP) was examined by rhodamine 123(Rh 123) staining followed by photofluorography. The intracellular levels of reactive oxygen species(ROS) were detected by 2', 7'-dichlorfluorescein- diacetate(DCFH-DA) staining followed by photofluorography. The number of apoptotic cells was observed by Hoechst 33258 nuclear staining followed by photofluorography. RESULTS: After the H9c2 cardiac cells were treated with HG(35 mmol/L glucose) for 24 h, the protein levels of TLR4 and phosphorylated NF-κB p65(p-NF-κB p65) were significantly increased. Pretreatment of the cells with 100 μmol/L diazoxide(DZ, a K_ATP channel opener) for 30 min before exposure to HG considerably blocked the up-regulation of the TLR4 and p-NF-κB protein levels induced by HG. Moreover, co-treatment of the cells with 30 μmol/L TAK-242(an inhibitor of TLR4) obviously inhibited the HG-induced up-regulation of the p-NF-κB p65 protein level. On the other hand, pretreatment of the cells with 100 μmol/L DZ had a clear myocardial protection effect, which attenuated the HG-induced cytotoxicity, inflammatory response, mitochondrial damage, oxidative stress and apoptosis, evidenced by an increase in the cell viability, and decreases in the levels of IL-1β and TNF-α, MMP loss, ROS generation and the number of apoptotic cells. Similarly, co-treatment of H9c2 cardiac cells with 30 μmol/L TAK-242 or 100 μmol/L PDTC(an inhibitor of NF-κB) and HG for 24 h also obviously reduced the above injuries and inflammation induced by HG.CONCLUSION: The opening of K_ATP channels protects H9c2 cardiac cells against HG-induced injury and inflammation by inhibiting the TLR4/NF-κB pathway.     

Zacopride attenuates pressure overload-induced ventricular remodeling in rats

AIM:To investigate the protective effect of zacopride (ZAC) on the pressure-overload left ventricular remodeling in the rats induced by coarctation of abdominal aorta. METHODS:Male Sprague-Dawley (SD) rats with pressure overload were induced by the coarctation of abdominal aorta. The model rats were intraperitoneally administered with ZAC, chloroquine (Chlor), and zacopride+chlorquine (ZAC+Chlor). The study duration was 8 weeks. The cardiac structure and function were assessed by echocardiography. The heart weight/body weight (HW/BW) ratio and the left ventricular weight/body weight (LVW/BW) ratio were calculated. The changes of structure and shape in myocardial tissue were observed with HE staining. The ultrastructure of the myocytes was observed under transmission electron microscope. The inward rectifier potassium channel (I_K1) protein expression was determined by Western blot. The mRNA expression of Kir2.1 was detected by RT-PCR. RESULTS:Compared with vehicle group, ZAC improved cardiac function, as indicated by the decreased left ventricular end-diastolic dimension (LVEDD) and left ventricular end systolic dimension (LVESD) (P<0.05), and the increased left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS) (P<0.01). The HW/BW and LVW/BW ratios were significantly decreased, and the cross-sectional area of the cardiomyocytes was significantly less in ZAC group than that in vehicle group (P<0.01). The ultrastructure of the myocytes was significantly improved. Chlor blocked the protective effect of zacopride on the pressure-overload left ventricular remodeling. The protein level of I_K1 and mRNA expression of Kir2.1 in the cardiac tissues in ZAC group were significantly increased compared with vehicle group (P<0.01). CONCLUSION:I_K1 agonist ZAC significantly attenuates pressure overload-induced ventricular remodeling in rats.