Gap junctions(GJ) form the chemical signal channels between cardiocytes.The core proteins of these channels are the connexins(Cx).The quantity or distribution of Cx will lead to the remodeling of GJ, which contributed to arrhythmia and remodeling following the acute myocardial infarction.GJ remodeling is the key reason and pathological basis of arrhythmia following acute myocardial infarction.How to increase the number of myocardial cells and lighten or reverse the heart reconstitution have become a focal point.In the acute myocardial infarction cell transplantation treatment, stem cells are characterized by self-renewal and multi-directional differentiation have been paid great attention.This study summarized the basis and clinical research of GJ structure, function, distribution, remodeling and stem cell transplantation treatment following myocardial infarction.

BACKGROUND:Cell transplantation can repair damaged myocardial tissue.However,whether transplaned cells and host cells formed an effective electricity and mechanical couple or whether reconstruction of connexin (Cx) and arrhythmia formed,are still unclear.OBJECTIVE:It is hypothesized that arrhythmia can be treated by changing Cx levels and intervening abnormal GJ channel.Moreover,to explore the effects of bone marrow mesenchyma stem cells (MSCs) on the expression of Cx43 and Cx45 in rata with myocardial infarction.DESIGN,TIME AND SETTING:The randomized controlled animal study was performed at the Experimental Center,Guangxi Medical University from January 2008 to May 2009.MATERIALS:A total of 180 Wistar rats were randomly divided into four groups:normal control,sham operation,myocardial infarction,and MSCs,with 45 animals in each group.Each group was then divided into 3 subgroups (n=15) according to 4 weeks,8 weeks and 12 weeks post-transplantation.Additional 20 healthy,Wistar rats,aged 1 month,were selected to harvest MSCs.METHODS:The third passage of MSCs was induced by 5-aza like cardiomyocytes for 4 weeks,labeled with DAPI at 2 hours before transplantation.Models of acute myocardial infarction were established in all groups except sham operation group.At day 7 after model preparation,2×10~(10) /L MSCs were infused into the edge and center of myocardial infarcted region by multipoint injection.Rats in the myocardial infarction group were subjected to an equal volume of saline as wall as those in the normal control and sham operation groups.MAIN OUTCOME MEASURES:The mRNA expressions of Cx43,Cx45 were assayed by fluorescence quantitative PCR.RESULTS:The mRNA expression of Cx43 among each groups had no difference at weeks 4,8 and 12 after intervention in the normal areas.Compared to the normal areas,Cx43 mRNA reduced significantly at ischamic zone in the myocardial infarction group and MSCs group (P＜0.01),with notably increased of Cx45 mRNA expression (P＜0.01).Compared to myocardial infarction group,Cx43 mRNA expression was statistically higher in the MSCs group at the same points (P ＜ 0.01),and the Cx45 mRNA dramatically declined (P ＜ 0.01).CONCLUSION:Acute myocardial infarction reduces the mRNA expression of Cx43 and increases the Cx45 mRNA expression.The exogenous cells transplantation can upturn the mRNA expression of Cx43 in the border-zone of the infarcted area,and down-regulate the Cx45 mRNA expression in the border-zone of the infarcted area.

BACKGROUND: Stem cell transplantation in repairing infarct myocardium and in improving cardiac function has been widely accepted. However, whether transplanted cells and host cells formed an effective electricity and mechanical couple, whether a relevant independent electrical system with contractile function formed or whether severe malignant ventricular arrhythmia formed, are still unclear.OBJECTIVE: To investigate electrophysiological abnormaltiy and left ventricular remodeling in rats with myocardial infarction following allogenic bone marrow mesenchymal stem cell (BMSC) transplantation.DESIGN, TIME AND SETTING: The randomized controlled animal study was performed at the Experimental Center, Guangxi Medical University from December 2005 to October 2008.MATERIALS: A total of 120 healthy Wistar rats were equally randomized into normal control, sham operation, saline control and cell transplantation groups. Healthy Wister rats aged 1 month were selected to harvest bone marrow.METHODS: At the third passage, rat BMSCs were collected and treated with 5-aza, and differentiated into cerdiomyocytes.BMSCs were labeled with DAPI at 2 hours before transplantation. In the saline control and cell transplantation groups, rat models of myocardial infarction were established by ligating the left anterior descending coronary artery. In the sham operation group, the coronary artery was not ligated, but only braid. At 7 days following ligation, BMSCs in the cell transplantation group at 2×10-1/L were infused into the edge and center of myocardial infarct region by multipoint injection. Rats in the other three groups were subjected to an equal volume of saline.MAIN OUTCOME MEASURES: Electrocardiogram and cardiac electrophysiology were performed. Ultrasonic cardiography was used to detect left ventricular function. Infarct size was determined. DAPl-labeled donor cell migration and distribution was observed with a fluorescence microscope.RESULTS: BMSCs could differentiate into cardiacmuscle cell-like cells which were capable of pulsing spontaneously, expressing cardiactoponin T and forming myofilament in vitro. Compared with the saline control group, PR interval, QRS duration and ventdcular effective refractory period shortened, ventricular fibrillation threshold increased at 4, 8 and 12 weeks (P < 0.05); left ventricular internal diameter at end-systole reduced, and left ventricular ejection fraction and shortening traction was significantly increased (P< 0.05). At 8 and 12 weeks, infarct size was significantly smaller (P < 0.05). At 4 weeks, DAPl-labeled BMSCs could be seen under the fluorescence microscope, and still could he detected at 12 weeks. However, the fluorescence became weak with prolonged time.CONCLUSION: BMSCs have the plasticity of differentiating into cardiac muscle cell-like cells, which can modulate theelectrophysiological abnormality and left ventricular remodeling following myocardial infarction.

Objective To investigate the effects of ischemic postconditioning on apoptosis, structural and functional changes of mitochondria induced by myocardial isehemia/reperfusion (I/R) injury of rabbits and potential mechanism. Methods Eighty healthy rabbits were divided randomly into five groups: sham operation group ( Group Sham) , ischemic reperfusion group (Group IR) , ischemic preconditioning group (Group IP) , ischemic postconditioning group (Group PC) and 5-HD plus ischemic postconditioning group (Group PC +5-HD). All rabbits in the five groups were killed 4 h after reperfusion. The hearts were quickly collected for microscopy by TUNEL. We observed ultrastructural changes of myocardium under electron microscope and examined mitochondrial membrane potential and Ca~(2+) concentration, MDA content and SOD activity of myocardial mitochondria. Results Compared with group IR, the damage of mitoehondrial ultrastrueture was milder, the apoptosis rate decreased and Ca concentration and MDA content were much lower in group IP and group PC ( P < 0. 05 ). Mitochondrial membrane potential and SOD activity of myocardial mitochondria in group IP and group PC was significantly higher than that in group IR(P<0.05). The protective effect of PC against I/R injury was partially counteracted by 5-HD .Conclusion Ischemic posteonditioning can protect the heart from I/R injury, this is supported by improvement mitochondrial ultrastructure and by decreasing apoptosis, increasing mitochondrial membrane potential and SOD activity, alleviating Ca~(2+) overload and decreasing MDA content in myocardial mitochondria. The cardio protective effects may be explained by mitochondrial ATP sensitive potassium channel.

Objective To investigate the alterations of connexin 43 (Cx43) expression and its distribution at different stages of myocardial infarction (MI) in rats after transplantation of allogenic mesenchymal stem cells (MSCs).Methods Wistar rats were ligated on the left anterior descending coronary artery to make MI models.They were injected with allogenic MSCs,which were induced by 5-aza and labelled by DAPI,during the second operation after 7 days of MI.In subgroups,MSCs were detected by fluorescence microscope.Cx43 expression and GJ distribu-tion were examined by immunohistochemistry after 4,8 or 12 weeks respectively.Results MSCs differentiated into cardiac muscle cell-like cells which were capable of pulsing spontaneously,expressing cTnT and forming myofilament in vitro.Transplanted MSCs can survive in MI host and upregulate Cx43 expression and normalize Cx43 distribution at ischemic zones after 4,8 and 12w.No change of Cx43 was seen at infarcted zones.Conclusion MSCs have the plasticity of differentiating into cardiac muscle cell-like cells which can continuously upregulate Cx43 expression and normalize Cx43 distribution at ischemic zones after 4,8 and 12w.

Objective To establish a stable,repeatable and long-lasting rat model of myocardial infarction,and to evaluate the feasibility of monitoring electrophysiological changes and left ventricular function after myocardial infarction by electrocardiography (ECG) and ultrasonic cardiography(UCG). Methods Wistar rats were ligated on the left anterior descending coronary artery after anaesthesia with 10% chloral hydrate and machinery assisted respiration. Then they were monitored by ECG and UCG afer 4,8 and 12 weeks,and were sacrificed and pathologically examined at 12 weeks after operation. Results The rat model of myocardial infarction was established with a survival rate of 83.3% at 72 hours after the operation and 73.3% at 12 weeks after the operation. In the myocardial infarction group,the PR,QRS,QT and QTc intervals were statistically significantly longer than that in the sham operation group. UCG showed that the left ventricular internal diameter at end-diastole (LVIDd) and the left ventricular internal diameter at end-systole (LVIDs) were statiscally significantly higher in the infarction group,and the ejection fraction (EF) and fractional shortening (FS) significantly lower than those in the sham operation group. Long-lasting pathological changes can be seen in the tissues at 12 weeks after operation. Conclusions The method used in the present study is an simple,less injurious and highly successful technique,and the changes in electrophysiology and left ventricular function can be well monitored by ECG and UCG at different times during this period.