Beclin-1 expression is upregulated by spermine in rat myocardial ische-mia-reperfusion injury

AIM: To observe the effects of spermine (SP) on myocardial ischemia-reperfusion (IR) injury in rats. METHODS: SD rats (weighing 220~250 g) were equally randomized to 3 groups:sham control group, in which the rats were only treated with thoracotomy; IR group, in which the rats were treated with ischemia for 30 min and reperfusion for 60 min; and IR+SP group, in which 0.5 mmol/L SP (2 mL/kg) was intravenously injected just 15 min before reperfusion. The morphological changes of myocardial tissues were assessed by HE staining. The levels of cardiac troponin I (cTnI) and creatine kinase isoenzyme MB (CK-MB) in plasma were determined. Myocardial infarct size and no-reflow range of the myocardium were measured by Evans blue and thioflavin S staining. Inflammatory responses in the myocardial tissues were detected by myeloperoxidase (MPO) assay. The autophagy function was detected by measuring the protein expression of beclin-1 by Western blot. RESULTS: The myocardial injury and inflammatory infiltration in IR+SP group were reduced under light microscope. Treatment with SP decreased the plasma levels of cTnI and CK-MB, and reduced the IR-induced infarct size and no-reflow range size of the left ventricle (P<0.05). Tissue MPO assay showed that myocardial inflammatory responses were attenuated in IR+SP group compared with IR group. Beclin-1 was upregulated in IR+SP group compared with IR group (P<0.05). CONCLUSION: Exogenous SP attenuates myocardial ischemia-reperfusion injury by upregulating the expression of beclin-1.     

Ischemic postconditioning reduces myocardial damage in rats suffering from limb ischemia-reperfusion

AIM: To investigate the protective effect of limb ischemic postconditioning on the myocardial damage in the rats suffering from limb ischemia-reperfusion (LIR). METHODS: Wistar rats were randomly divided into control group (C group), ischemia-reperfusion group (IR group) and ischemic post-conditioning group (IR+IPostC group). For conducting ischemic postconditioning, the rats in IR+IPostC group underwent 5 min of ischemia and 5 min of reperfusion on their hind limbs repeatedly after 4 h of ischemia, and then, 4 h of reperfusion was applied. The activity of superoxide dismutase (SOD), xanthine oxidase (XOD) and myeloperoxidase (MPO) was measured. The levels of malonaldehyde (MDA) in plasma and myocardial tissues, the levels of creatine kinase (CK), creatine kinase MB (CK-MB), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), α-hydroxybutyrate dehydrogenase (α-HBDH) and myocardial troponin I (cTnI) were also detected. The changes of ultrastructure in the myocardium were observed under electron microscope. RESULTS: Compared with C group,the levels of CK-MB, AST, LDH,α-HBDH and cTnI were all increased in IR and IR+IPostC groups. The levels of MDA and XOD also increased (P<0.05), but the activity of SOD decreased (P<0.05). However, compared with group IR, the levels of CK-MB, AST, LDH, α-HBDH and cTnI decreased (P<0.05) in IR+IPostC group.The levels of MDA and XOD also decreased (P<0.05), but the activity of SOD increased (P<0.05). Under electron microscope, the cardiac myofibrils arranged neatly, light and dark bands were clear, the mitochondrial cristae arranged closely and neatly, and the mitochondrial matrix densification was observed in C group. However, the cardiac fiber arrangement was disordered or disappeared, stromal edema was obvious, most or all mitochondrial cristae and membrane became fusion or disappeared, mitochondrial vacuolization and decrease in glycogen were obvious in IR group. In IR+IPostC group, the pathological changes mentioned above were attenuated somewhat than those in IR group. CONCLUSION: Ischemic postconditioning protects rat myocardium under limb ischemia-reperfusion.     

Establishment and evaluation of rat heart ischemia-reperfusion injury model in vivo

AIM: To establish and evaluate a rat model of heart ischemia-reperfusion injury in vivo. METHODS: Seventy-two male Sprague-Dawley rats weighing(250±50)g were randomly divided into sham operation group(sham), ischemia-reperfusion group(I/R) and normal group. The animals were anesthetized and heparinized. Myocardial ischemia-reperfusion was induced by ligating the left anterior descending coronary artery with "U-shape tube" for 35 min followed by 120 min or 240 min reperfusion in vivo. The heart infarct size was measured by triphenyltetrazolium chloride(TTC) staining. The myocardial cell apoptotic index was determined by the method of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling(TUNEL). Immunohistochemical method was used to detect the expression of Bcl-2 and Bax in rat ischemia myocardium. The blood level of MB isoenzyme of creatine kinase(CK-MB),cardiac troponin I(cTnI),nitric oxide(NO),malondialdehyde(MDA), total superoxide dismutase(T-SOD)and glutathione peroxidase(GSH-Px) were detected after reperfusion for 2 h and 4 h. RESULTS: Compared with normal group and sham group, there were obvious changes of ST-T segment and Q wave in the electrocardiogram of I/R group. The blood level of CK-MB, cTnI, NO, MDA and GSH-Px in I/R group increased(P<0.05,P<0.01) after reperfusion for 2 h and 4 h, and the blood level of T-SOD in I/R group after reperfusion for 2 h and 4 h also increased(P<0.05). The heart infarct size in I/R group was the largest as compared to other groups. Among these groups, the apoptotic index of I/R group was the highest and the Bcl-2/Bax ratio in I/R group decreased(P<0.01).CONCLUSION: The rat model of heart ischemia-reperfusion injury in vivo can be successfully established with the "U-shape tube". There are obviously changes of heart infarct size, blood level of CK-MB, cTnI, NO, MDA, T-SOD and GSH-Px, myocardial apoptotic index and Bcl-2/Bax ratio between I/R rats and control animals.     

Effects of Shensongyangxin capsule on ventricular electrical properties,structural remodeling and cardiac function in diabetic rats

AIM：To determine the effects of Shensongyangxin capsule (SSYX) on the ventricular electrical properties, structural remodeling and cardiac function in the rats with diabetes mellitus (DM). METHODS：Male SD rats (n=45) were randomly divided into control group (n=15), DM group (n=15) and SSYX group (n=15). The rats in DM group and SSYX group were injected with streptozotocin (60 mg/kg, ip), while the rats in control group were given normal saline (1 mL/kg, ip). The blood samples were collected 72 h after treatment for determining the blood glucose levels in DM group and SSYX group. The model rats in SSYX group were administered with SSYX (1 g·kg-1·d-1, ig) for 6 weeks, while the other rats received normal saline (2 mL·kg-1·d-1, ig). The echocardiography was used to assess the cardiac function, and the lead II electrocardiogram was also recorded in all the animals. The radioimmunoassay and Masson trichrome staining were used to measure the plasma levels of endothelin-1 (ET-1) and the collagen deposition in the ventricles, respectively. A whole Langendorff-perfused heart model was used to conduct the electrophysiologic study. The monophasic action potential (MAP) and the ventricular effective refractory period (VERP) were recorded in the left anterior free wall (LAF), and the burst pacing was used to induce ventricular arrhythmia (VA). RESULTS：Compared with control group, the VERP, action potential duration (APD), QT interval, incidence of VA, degree of myocardial fibrosis and plasma level of ET-1 were increased, while the cardiac function was declined in DM group. Compared with DM group, the VERP, APD, QT interval, incidence of VA, degree of myocardial fibrosis and plasma level of ET-1 were all decreased, while the cardiac function was improved in SSYX group. CONCLUSION：SSYX attenuates the electrical and structural remodeling and improves the cardiac function in DM rats.     

X-ray irradiation increases sensitivity of myocardium to ischemia/reperfusion injury in rats

AIM：To observe the sensitivity of myocardium to ischemia/reperfusion (I/R) injury in the rats with chest radiotherapy. METHODS：The radiation-induced heart disease model was established by local 20 Gy of X-ray irradiation in the chest. Male Wistar rats (n=42) were randomly divided into 6 groups:sham trauma group, trauma group, sham trauma+sham operation group, sham trauma +I/R group, trauma+sham operation group and trauma+I/R group. The rats were subjected to 30 min of ischemia and 1 h of reperfusion 2 week after trauma. The left ventricular developed pressure (LVDP) and ±dp/dtmax were recorded by BL-410 biological signal recording and analysis system. The serum cardiac troponin I (cTnI) and creatine kinase isoenzyme (CK-MB) were measured by ELISA. The myocardial infarct size was determined by nitroblue tetrazolium(NBT) staining method and BI2000 image analysis software. RESULTS：Compared with sham trauma+I/R group, significant decreases in LVDP and ±dp/dtmax were observed in trauma+I/R group (P<0.01) with significant increases in the infarct size and the concentrations of cTnI and CK-MB (P<0.01). CONCLUSION:Chest X-ray irradiation increases the sensitivity of myocardium to I/R injury in rats.     

Changes of heart function and serum cardiac troponin I in early type 2 diabetic rats

AIM: To observe the changes of heart function and the expression of serum cardiac troponin I(cTnI) in early type 2 diabetic rats, and to explore the role of cTnI in the development of type 2 diabetes and early diabetic cardiomyopathy.METHODS: The type 2 diabetes rat model was established by an injection of streptozotocin after high fat diet(5 weeks). The rats were randomly divided into control group, model group of 2 weeks, and model group of 4 weeks. M-mode echocardiography was performed for echocardiographic measurements. Fasting blood glucose(FBG), total cholesterol(TC), triglyceride(TG), high density lipoprotein-cholesterol(HDL-C), low density lipoprotein- cholesterol(LDL-C), fasting insulin(FINS) and cTnI levels were tested. HE staining was used to observe the pathological changes of myocardial structures. The alteration of cTnI in myocardium was determined by Western blot.RESULTS: Compared with normal group, the levels of TC, TG and LDL-C in type 2 diabetic rats were significantly increased, HDL-C levels were significantly reduced. Cardiac histological analysis revealed that type 2 diabetes induced cardiomyocytes degeneration and necrosis. The expression of cTnI increased significantly in diabetic groups compared to control group, and that in model group of 4 weeks increased far more than that in model group of 2 weeks(P<0.05).CONCLUSION: The increased level of cTnI and the change of the heart function may be associated with the development diabetic cardiomyopathy. These changes are valuable for the early clinical diagnosis of myocardial injury in diabetic cardiomyopathy.     

Effects of HES 130/0.4 on no-reflow after myocardial ischemia-reperfusion injury in rats

AIM: To observe the effects and mechanisms of hydroxyethylstarch(HES) 130/0.4 on no-reflow phenomenon after myocardial ischemia-reperfusion in rats. METHODS: SD rats were randomly divided into 4 groups:sham operation group, ischemia-reperfusion(IR, treated with normal saline) group, normal saline ischemia-reperfusion(NS-IR, treated with NS) group and HES ischemia-reperfusion(HES-IR, treated with HES) group. Myocardial infarct size and no-reflow range were determined by staining methods, and the activities of myocardial enzymes(CK-MB, cTnI and MPO) were measured. Meanwhile, cardiac microvascular endothelial cells of the rat were cultured and divided into 4 groups:control group, hypoxia/reoxygenation(H/R) group, NS-H/R group and HES-H/R group. Acute ischemia reperfusion models were simulated, and the concentration of calcium ions was measured. The relative cell activity was evaluated by CCK-8 assay, and the apoptotic rate was detected by flow cytometry. RESULTS: In HES-IR group, the myocardial infarct size, the no-reflow zone, CK-MB, cTnI and MPO activity were all significantly lower than those in IR group(P<0.05). In microvascular endothelial cells, the concentration of calcium ions and the apoptotic rate in HES-H/R group were significantly decreased, while the relative cell activity increased compared with H/R group(P<0.05). CONCLUSION: HES reduces no-reflow in acute myocardial ischemia-reperfusion. The mechanism may be involved in the inhibition of both the infiltration of neutrophils and the calcium overload of endothelial cells.     

Pathogenesis of early cardiac myocyte damage after severe crush injury

AIM:To study the changes of plasma atrial natriuretic peptide(ANP), endothelin-1 (ET-1) and serum cardiac troponin I(cTnI) levels and the effects of ANP and ET-1 on myocardium in crush injury rats.METHODS:Crush injury was produced in SD rats,the serum levels of cardiac enzyme and cardiac troponin I,plasma levels of ANP and ET-1 were studied by automated biochemical analyzer,automated chemiluminescence assay and radioimmunoassay. RESULTS:The plasma ET-1 level was much lower,the levels of plasma ANP and serum cardiac enzyme and cTnI were much higher after crush injury than those of the control group(P＜0.05).CONCLUSION:ANP and ET-1 may play an important role in cardiomyocyte injury in the early stage of crush injury.     

Effects of atorvastatin on release of endothelial microparticles and myocardial apoptosis in rats with acute myocardial infarction

AIM: To investigate the effect of atorvastatin(AT) on the release of endothelial microparticles(EMP) and myocardial apoptosis in the rats with myocardial infarction. METHODS: SD male rats(n=24) were randomly divided into 3 groups:sham operation(sham) group, myocardial infarction(MI) group and MI+AT group. The rat model of acute myocardial infarction was prepared by coronary artery ligation. At 2 h and 24 h after modeling, the peripheral blood was collected to detect creatine kinase-MB(CK-MB) and cardiac troponin T(cTnT). The circulating levels of EMP were measured by flow cytometry. The myocardial apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling(TUNEL) assay. RESULTS: At 2 h after modeling, the level of CK-MB was significantly increased in MI group compared with sham group, and the level of EMP and the myocardial apoptotic rate were significantly increased in MI group and MI+AT group compared with sham group. At 24 h after modeling, the level of EMP was significantly increased in MI group compared with sham group. The levels of CK-MB, cTnT, EMP and the myocardial apoptotic rate were significantly decreased in MI+AT group compared with MI group. Moreover, the level of CK-MB in MI group was significantly increased at 24 h compared with that at 2 h after modeling. The levels of CK-MB, cTnT and EMP were significantly decreased in MI+AT group at 24 h compared with those at 2 h after modeling. CONCLUSION: Ator-vastatin may reduce the level of EMP and the myocardial apoptotic rate in the rats with acute myocardial infarction, indicating that atorvastatin plays a role in protecting endothelium.     

Effect of hypercholesterolemia on the ionic currents in cardiac ventricular myocytes of rats

AIM: To determine whether chronic hypercholesterolemia affects ionic currents on cardiac ventricular myocytes of rats. METHODS: Whole-cell patch-clamp technique was used to record the ionic currents in single cardiac myocytes isolated from normal cholesterolemia and hypercholesterolemia rats. RESULTS: In the hypercholesterol group (group Ⅱ), serum total-cholesterol level was significantly higher than that of normal group (group Ⅰ) ［(3.10±0.62)mmol·L-1 vs (1.18±0.37)mmol·L-1, P<0.01, n=20］. The serum triglyceride content of group II was remarkably higher than that of group Ⅰ ［(1.51±0.30)mmol·L-1 vs (0.43±0.15)mmol·L-1, P<0.01, n=20］. In ventricular myocytes of rats, 50% repolarization of action potential duration (APD50) prolonged from (70.86±8.12)ms (group Ⅰ) to (116.16±6.90)ms (group Ⅱ) (n=10 in each group, P<0.01); APD90 prolonged from (95.10±7.27)ms (group Ⅰ) to (144.04±7.39)ms (group Ⅱ) (n=10 in each group, P<0.01); at the test potential of -120 mV, Ik1 increased from (-16.98±4.54) pA/pF(group Ⅰ) to (-19.92±4.08) pA/pF (group Ⅱ) (n=12 in each group, P<0.05); at the test potential of 0 mV, ICa-L decreased from (-8.56±1.29) pA/pF (group Ⅰ) to (-5.24±0.90) pA/pF (group Ⅱ) (n=10 in each group, P<0.01); at the test potential of +60 mV, Ito decreased from (13.20±1.97) pA/pF (group Ⅰ) to (10.30±1.97) pA/pF (group Ⅱ) (n=8 in each group, P<0.05). CONCLUSION: Hypercholesterolemia affects the ionic currents on cardiomyocytes of rats greatly, which may be the ionic mechanism of cardiac toxicity induced by hypercholesterolemia.     

Effect of captopril on prolongation of action potential duration and reduction Ik in ischemia pig ventricular myocytes

AIM: To evaluate the effect of captopril on action potential duration and outward delayed rectification potassium current (Ik). METHODS: Action potentials were recorded using a conventional glass microelectrode filled with 3 mol/L KCl solution. Membrane patch clamp whole cell recording technique was used to investigate the Ik current maximum in the holding potential -50 mV, lasting time 100 ms, command potential +40 mV. RESULTS: The action potential duration of 30%, 50% repolarization (APD30, APD50) and ERP were significantly prolonged, but APD90 wasn't prolonged significantly when captopril group compared with ischemic group. The amplitude of Ik increased significantly in ischemic group, but significantly decreased in captopril group and in captopril+ischemic group. The shapes of current-voltage relationship were unchanged among groups, but significantly upward in ischemic group and downward in captopril and captopril+ischemic group. CONCLUSION: Captopril exerts electrophysiologic action due to decreasing delay outward rectification potassium current and prolonging action potential duration of APD30, APD50 and ERP.     

Yiqi-Yangyin recipe attenuates myocardial ischemia-reperfusion injury in diabetic rats by activation of ERK/Nrf2/HO-1 pathway

AIM: To explore the effect of Yiqi-Yangyin recipe on myocardial ischemia-reperfusion injury (MIRI) in rats with diabetes mellitus (DM) and the possible mechanism. METHODS: The rats were divided into normal group (control group), DM sham operation (DM-S) group, DM+MIRI group, low-, medium-and high-dose Yiqi-Yang-yin recipe (TL, TM and TH) groups (7.5, 15 and 30 g/kg decoction of Yiqi-Yangyin recipe by gavage), and Nrf2 inhibitor (bardoxolone methyl) group (30 mg/kg bardoxolone methyl by intragastric administration). The gavage volume was 1 mL/kg. There were 15 rats in each group, and they were administered continuously for 7 d. The tail vein blood was collec-ted after the last administration to detect the blood sugar and lipid levels in the rats. The serum levels of cardiac troponin I (cTnI), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-10 were measured by ELISA. Echocardiography was used to detect the changes of cardiac function in the rats after blood collection. After cardiac function test, the rats were sacrificed to obtain cardiac tissues, and the volume changes of myocardial infarction were assessed by triphenylte-trazole chloride staining. The histopathological changes of myocardium was observed by HE staining. The cardiomyocyte apoptosis was determined by TUNEL assay. The protein levels of phosphorylated extracellular signal-regulated kinase (p-ERK), nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in the myocardium were determined by Western blot. The myocardial activity of superoxide dismutase (SOD) was measured by nitro blue tetrazolium method, the content of malondialdehyde (MDA) was tested by thiobarbituric acid method, and the production of reactive oxygen species (ROS) was analyzed by iron ion reduction method. RESULTS: Compared with control group, the levels of fasting blood glucose (FBG), total cholesterol (TC) and triglyceride (TG) in DM-S group and DM+MIRI group were significantly elevated, while the level of high-density lipoprotein cholesterol (HDL-C) was significantly lowered (P<0.05). Compared with DM-S group and DM+MIRI group, the levels of FBG, TC, TG in TL, TM, TH and bardoxolone methyl groups were significantly decreased, while HDL-C level was significantly increased (P<0.05). Compared with control group and DM-S group, heart rate (HR) and left ventricular end-diastolic pressure (LVEDP) were increased in DM+MIRI group, mean arterial pressure (MAP), left ventricular systolic pressure (LVSP) and left ventricular ejection fraction (LVEF) were decreased, serum levels of cTnI, TNF-α, IL-1β and IL-10 were increased, the myocardial infarction volume percentage was increased, the myocardial cell breakage and necrosis were increased, the myocardial cell apoptotic rate was increased, the protein levels of p-ERK1/2, Nrf2 and HO-1 were decreased, MDA and ROS levels were increased, and the activity of SOD was decreased (P<0.05). Compared with DM+MIRI group, HR and LVEDP were decreased in TL, TM, TH and bardoxolone methyl groups, MAP, LVSP and LVEF were increased, the serum levels of cTnI, TNF-α, IL-1β and IL-10 were decreased, the myocardial infarction volume percentage was decreased, myocardial cell breakage and necrosis were decreased, myocardial cell apoptotic rate was decreased, the protein levels of p-ERK1/2, Nrf2 and HO-1 were increased, the MDA and ROS levels were decreased, and the activity of SOD was increased (P<0.05). CONCLUSION: Yiqi-Yangyin recipe protects the myocardial tissue of DM+MIRI rats from injury and reduces the oxidative stress level, which may be achieved by activating ERK/Nrf2/HO-1 pathway.     

Regulatory effect of miR-214-5p on myocardial injury and immune response in ischemia-reperfusion rats by targeting PAK4

AIM: To investigate the effect of microRNA-214-5p (miR-214-5p) on myocardial injury and immune response in rats with ischemia-reperfusion (I/R) by targeting p21-activated protein kinase 4 (PAK4). METHODS: The rats were divided into sham group, I/R group, Ad-Scramble group, and Ad-miR-214 group (n=9). Adenovirus was injected into 6 different sites on the anterior wall of the left ventricle of the rats. Four days later, the I/R model was constructed by suturing the left anterior descending coronary artery. The expression level of miR-214 was detected by RT-qPCR. Myocardial injury was observed by HE staining. The levels of heart damage markers (CK-MB, Mb, and cTnI) and inflammatory factors (IL-6, IL-1β and TNF-α) were measured by ELISA. The rate of cardiomyocyte apoptosis was analyzed by flow cytometry. The content of MDA and the activity of SOD were detected by commercially available kits. Target genes were predicted by genetic software and verified by dual-luciferase reporter assay. The protein levels of caspase-3, caspase-9, Bcl-2, Bax, PAK4, p-Akt and p-mTOR were determined by Western blot. RESULTS: miR-214 was down-regulated in the cardiomyocytes of I/R rats (P<0.01). Over-expression of miR-214-5p attenuated myocardial injury in the I/R rats, down-regulated the expression of CK-MB, Mb and cTnI, decreased the apoptotic rate of cardiomyocytes, up-regulated the expression of Bcl-2, down-regulated Bax, caspase-3 and caspase-9 expression, increased SOD activity, and decreased the content of MDA, IL-6, IL-1β and TNF-α (P<0.01). The binding sites of miR-214-5p and PAK4 were pre-sent in the 3’-UTR, and over-expression of miR-214-5p up-regulated the protein levels of PAK4, p-Akt and p-mTOR (P<0.01). CONCLUSION: miR-214-5p over-expression attenuates myocardial injury in I/R rats by targeting PAK4, inhibits cardiomyocyte apoptosis, oxidative stress and inflammation, and activates the PI3K/Akt/mTOR pathway.     

Abietic acid alleviates AGEs-induced apoptosis and endoplasmic reticulum stress in cardiomyocytes via inducing autophagy

AIM: This study aims to explore the effect of abietic acid (AA) on advanced glycosylation end products (AGEs)-induced apoptosis and endoplasmic reticulum stress in H9c2 cardiomyocytes. METHODS: H9c2 cells were divided into 5 groups. The cells in control group were treated with saline for 24 h. The cells in AGEs treatment group were treated with AGEs (100 mg/L) for 24 h. The cells in AGEs+AA (10, 25 and 50 μmol/L) groups were simulta-neously treated with AGEs (100 mg/L) and AA (10, 25 and 50 μmol/L) for 24 h. The cell viability was measured by MTT assay. The protein levels of myoglobin (Mb), creatine kinase MB isoenzyme (CK-MB), cardiac troponin I (cTnI), C/EBP homologous protein (CHOP), cleaved caspase-12, GADD34, BiP, LC3, P62 and beclin 1 were determined by Western blot. The levels of lactate dehydrogenase (LDH) were measured by ELASA. The apoptosis was analyzed by flow cytometry. RESULTS: The low concentration (<50 μmol/L) of abietic acid had no obvious effect on the viability of H9c2 cells. The high concentration (>50 μmol/L) of abietic acid decreased the viability of H9c2 cells. The levels of Mb, CK-MB, cTnI and LDH in AGEs group were higher than those in control group (P<0.05). Compared with AGEs group, the levels of Mb, CK-MB, cTnI and LDH in AGEs+AA (10, 25 and 50 μmol/L) groups were obviously reduced (P<0.05). Abietic acid at concentrations of 10, 25 and 50 μmol/L inhibited AGEs-induced apoptosis, elevated the protein levels of CHOP and cleaved caspase-12, and attenuated expression of GADD34 and BiP (P<0.05). Moreover, abietic acid at concentrations of 10, 25 and 50 μmol/L suppressed AGEs-induced decreased ratio of LC3-Ⅱ/LC3-Ⅰ and expression of beclin 1, and enhanced the expression of P62 (P<0.05). 3-Methyladenine, an inhibitor of autophagy, reversed the effect of abietic acid on the protein levels of LC3, Mb, cleaved caspase-12 and BiP (P<0.05). CONCLUSION: Abietic acid alleviates AGEs-induced apoptosis and endoplasmic reticulum stress in H9c2 cardiomyocytes via inducing autophagy.     

Cardiac IKs as repolarization reserve plays a role in gender difference of diabetic QT prolongation

AIM: To explore the basic ionic mechanisms underlying long-QT syndrome by observing the changes of slowly activating outward rectifying potassium current (I_Ks) and its proteins in abnormal QT prolongation in different genders of diabetic rabbits.METHODS: A single injection of pre-warmed (37 ℃) alloxan (140 mg/kg) was used to establish a rabbit model of insulin-dependent diabetes mellitus. Eight weeks after alloxan injection, the levels of blood glucose in the rabbits were monitored and standard lead II electrocardiogram was recorded. The myocardial cells were isolated from the ventricle of the rabbits via enzymatic digestion. Whole-cell patch clamp technique was performed to study the action potential duration (APD) and I_Ks. The changes of both KvLQT1 and mink proteins were detected by Western blotting analysis.RESULTS: The QT interval and APD were prolonged apparently both in male and female diabetic rabbits. The increased APD/QT-I of the male diabetic rabbits is more remarkable than that of the female. The I_Ks step current density of the male diabetic rabbits was decreased at test potentials ranging from+40 mV to+70 mV compared with that of the control animals (P<0.05), which was lowered from (3.08±0.67) pA/pF (n=17) to (1.27±0.20) pA/pF (n=16) at+70 mV. However, the I_Ks step current density of the female diabetic rabbits was increased at test potentials ranging from 0 mV to+70 mV compared with that of control group (P<0.05), which was increased from (1.56±0.20) pA/pF (n=13) to (3.65±0.50) pA/PF (n=14) at+70 mV. The expression of KvLQT1 and mink in male diabetic group decreased by 21.6% and 18.5%, respectively. However, the expression of KvLQT1 and mink in female diabetic group were increased by 42.3% and 20.5%, respectively.CONCLUSION: The I_Ks may be a protective factor in the early period of diabetic development in female rabbits. As a repolarization reserve, cardiac I_Ks is likely to restrict the effects of excessively slowing repolarization.     

Electrophysiological changes in rat ventricular myocardium at different stages of experimental diabetes

AIM: To explore the probable mechanisms of diabetes-induced arrhythmias. METHODS: Diabetes was induced in male SD rats, using a single injection of alloxan into tail vein. Untreated age-matched animals were used as controls. All animals were observed by 2, 4, 6 and 8 weeks, respectively. Transmembrane potentials were recorded with conventional glass microelectrodes. RESULTS: Action potential duration(APD) at all level (APD10, APD20, APD30, APD50, APD70, APD90) was significantly lengthened in right ventricular papillary muscle from week 2 of diabetes. At week 8, APD was more lengthened at any level of repolarization than that at week 2. No differences were observed in the maximum rate of depolarization(V_max), overshoot(OS) and action potential amplitude(APA) as well as the resting membrane potential(RP) from the 2th to 8th week of diabetes. CONCLUSION: The results indicate that prolongation of APD may be prominently responsible for the increased incidence of cardiac re-entry-arrhythmias and sudden death, especially at late stages of diabetes.     

Effects of action potential duration restitution on ventricular arrhythmia in chronic heart failure rabbit hearts

AIM: To determine the effects of action potential duration restitution (APDR) on ventricular arrhythmia (VA) in Langendorff-perfused chronic heart failure (CHF) rabbit hearts. METHODS:Twenty male New Zea-land rabbits were equally divided into 2 groups randomly: control (CTL) group and CHF group. CHF was induced by abdominal aortic banding for 14 d. The echocardiography was applied to assess the cardiac function and structural change in both groups 4 weeks after the end of modeling. In the whole Langendorff-perfused hearts, the monophasic action potential (MAP) and the effective refractory period (ERP) were recorded and measured in ventricular chamber, and the action potential duration (APD) curves were also constructed in both groups. The burst pacing was used to induce APD alternans and VA. RESULTS: Compared with the same sites of CTL group, the 90% of MAP duration (MAPD90), the ERP, the maximal slope (Smax) of APDR curves were increased in CHF group (all P<0.05). The VAs in CHF group were easier to be induced than those in CTL group (all P<0.05). The coefficients of variation of Smax (COV-Smax) of APDR curves in CHF group were greater than those in CTL group (all P<0.05).CONCLUSION: Both Smax and COV-Smax of APDR curves increase during CHF to facilitate the ventricular arrhythmia.     

Changes of transmural repolarization heterogeneity and ion currents in rabbits with left ventricular hypertrophy

AIM: To investigate the changes of transmural repolarization heterogeneity and ion currents in rabbits with left ventricular hypertrophy. METHODS: Ventricular hypertrophy was induced by a partial constriction of the abdominal aorta in rabbits. Myocytes were isolated by a two steps enzymological method. The sub-endocardial (Endo) and sub-epicardium (Epi) tissues were separated from other region (midmyocardium, Mid) with a razor. Whole cell patch clamp technique was used to record the action potential and ion currents. RESULTS: The action potentials duration at 90% repolarization (APD₉₀) of Epi, Mid and Endo were all prolonged significantly in hypertrophy group compared to control group. This prolongation of APD₉₀ was more pronounced in Mid (26.0%±2.7%) than that in Epi (14.0%±1.6%) and Endo (10.0%±1.1%). The transmural repolarization heterogeneity was increased significantly in the hypertrophy group. The I_Ks and I_to density in Epi, Mid and Endo was decreased significantly in hypertrophy group compared to those in control group. This decrease in I_Ks and I_to density was more pronounced in Mid than in Epi and Endo. No significantly difference of I_Ca,L and I_Kr density between hypertrophy group and control group in three layers was observed. The I_K1 density decreased significantly in hypertrophy group compared to control group, but the extent of the decrease had no differences among the three layers. CONCLUSIONS: The transmural repolarization heterogeneity increases significantly in rabbit hypertrophied ventricle. The decrease in transmural heterogeneity of I_to and I_Ks is the main causes.     

Effects of remifentanil on monophasic action potential and transmural dispersion of repolarization in rabbit myocardium

AIM: To study the effect of remifentanil on monophasic action potential and transmural dispersion of repolarization (TDR) in the 3-layer myocardium of isolated rabbit hearts. METHODS: Adult rabbits (n=18, 2.0 ~ 2.5 kg) were used to isolate the hearts for preparing Langendorff perfusion model. The hearts were randomly divided into 3 groups after perfusion with K-H solution for 15 min: the perfusion in control group (C group) continued for 60 min; the hearts in remifentanil group (R group) were perfused with 12 μg/L remifentanil K-H solution for 60 min; the hearts in remifentanil+aminophylline group (RA group) were given 60-min perfusion of 12 μg/L K-H remifentanil+30 mg/L aminophylline. The HR and 3 layers of myocardial monophasic action potential (MAP) in the left ventricular anterior wall were recorded at time points after balanced infusion for 15 min (T₀), and continued perfusion for 15 min (T₁), 30 min (T₂) and 60 min (T₃). The monophasic action potential duration of repolarization at 90% (MAPD₉₀) and the transmural dispersion of repolarization (TDR) were calculated. The early afterdepolarization, delay afterdepolarization and arrhythmia were also observed. RESULTS: In R group, slower HR and prolonger MAPD₉₀ and TDR at T₁~T₃ were observed as compared with those at T₀ (P<0.05). R group showed slower HR and longer MAPD₉₀ and TDR than C group and RA group (P<0.05). CONCLUSION: Remifentanil slows the HR, extends the MAPD₉₀ and increases the TDR, thus being prone to induce reentry. Aminophylline makes HR faster and MAPD₉₀ shorter, thereby reducing the TDR.     

Characteristics of ventricular electrophysiology in a right ventricular rapid pacing-induced canine heart failure model

AIM: To research the characteristics of ventricular electrophysiology in right ventricular rapid pacing-induced congestive heart failure (CHF) dogs.METHODS: Dogs (n=16) were randomly divided into 2 groups: the control (n=7) and the CHF group (n=9) induced by rapid right ventricular pacing at 240 pulse·min-1 for 4 to 5 weeks.The electrophysiologic parameters were evaluated by the technique of standard electric stimulation and monophasic action potential (MAP) recording.RESULTS: (1) Ventricular effective refractory period (VERP),ventricular MAP duration (MAPD90),ventricular late repolarization duration (VLRD) and intra-ventricular conduction time (IVCT) were prolonged by 26% (P<0.01),43% (P<0.01),318% (P<0.05),and 19% (P<0.01),respectively in CHF group.(2)The ratio of VERP to MAPD₉₀ (VERP/MAPD₉₀) was decreased by 13% (P<0.05) in CHF group.(3) The dispersion of ventricular recovery time (VRT-D) was increased by 185% (P<0.01) in CHF group.(4) The ventricular fibrillation threshold (VFT) was decreased by 48% (P<0.01) in CHF group.CONCLUSION: The abnormal electrophysiological changes in the CHF condition may be contributing factors of lethal ventricular arrhythmias and sudden cardiac deaths in CHF.