BACKGROUND:Our previous studies found that decreased expression of connexin 43 and its Ser368 phosphorylation after myocardial hypothermic ischemia-reperfusion was closely associated with decreased cardiac conduction velocity and reperfusion arrhythmia.OBJECTIVE:To observe the effect of changes in membrane-type matrix metalloproteinase 2,matrix metalloproteinase 2 and collagen type Ⅳ on the expression of connexin 43 and its Ser368 phosphorylation and electrical conduction in the myocardial extracellular matrix after hypothermic ischemia-reperfusion.METHODS:Sixteen Langendorff extracorporeal cardiac perfusion models were successfully established from SD rats and randomly divided into a control group(n=8)and a hypothermic ischemia-reperfusion group(n=8).The control group was balanced perfused with 37 ℃ Krebs-Henseleit solution for 15 minutes and then continued to be perfused with 37 ℃ Krebs-Henseleit solution for 90 minutes.The hypothermic ischemia-reperfusion group was balanced perfused with 37 ℃ Krebs-Henseleit solution for 15 minutes,and then the heart was arrested for 60 minutes by injection of 4 ℃ Thomas solution.During the cardiac arrest,the periphery was protected by 4 ℃ Krebs-Henseleit solution.Half-volume 4 ℃ Thomas solution was reperfused 30 minutes after the arrest.After stopping the arrest,the heart was reperfused with 37 ℃ Krebs-Henseleit solution for 30 minutes.The occurrence of arrhythmias,rebeating time,and the duration of arrhythmias were recorded from the immediate time point to the end of the reperfusion period.Conduction velocity,absolute inhomogeneity,and inhomogeneity index were measured using the Mapping Lab multi-channel electrophysiological mapping system at the time of balanced perfusion for 15 minutes(T1),reperfusion for 15 minutes/continuous perfusion for 90 minutes(T2),and reperfusion for 30 minutes/continuous perfusion for 105 minutes(T3).The relative expression levels of membrane-type matrix metalloproteinase 2,matrix metalloproteinase 2,collagen type Ⅳ,connexin 43,and its Ser368 phosphorylation in ventricular tissue were detected by western blot assay.RESULTS AND CONCLUSION:(1)No arrhythmia occurred in the control group.There were six cases of arrhythmia in the hypothermic ischemia-reperfusion group during reperfusion.Rebeating time and duration of arrhythmias were(25.38+12.02)and(158.67±67.68)seconds,respectively.(2)The conduction sochronal diagrams at T1,T2,and T3 in the control group were uniform and regular in direction,and the conduction velocity at T2 and T3 was not different from that at T1(P＞0.05).The conduction isochronal diagrams at T2 and T3 in the hypothermic ischemia-reperfusion group were uneven and irregular in direction,and the conduction velocity was slower than that at T1(P＜0.01).The conduction velocity at T2 and T3 in the hypothermic ischemia-reperfusion group was slower than that in the control group(P＜0.01).Conduction dispersion was greater in the hypothermic ischemia-reperfusion group than that in the control group at T2 and T3(P＜0.05).(3)Compared with the control group,the protein expressions of membrane-type matrix metalloproteinase 2 and matrix metalloproteinase 2 in the hypothermic ischemia-reperfusion group were increased(P＜0.05 or P＜0.01),and the protein expression levels of type Ⅳ collagen,connexin 43 and its Ser368 phosphorylation were decreased(P＜0.05 or P＜0.01).(4)The results indicate that after hypothermic ischemia-reperfusion,myocardial extracellular matrix remodeling may mediate the downregulation of myocardial connexin 43 and its Ser368 phosphorylation,slowed conduction velocity and increased conduction dispersion,thereby increasing the risk of arrhythmia.

BACKGROUND:Our previous studies found that decreased expression of connexin 43 and its Ser368 phosphorylation after myocardial hypothermic ischemia-reperfusion was closely associated with decreased cardiac conduction velocity and reperfusion arrhythmia.OBJECTIVE:To observe the effect of changes in membrane-type matrix metalloproteinase 2,matrix metalloproteinase 2 and collagen type Ⅳ on the expression of connexin 43 and its Ser368 phosphorylation and electrical conduction in the myocardial extracellular matrix after hypothermic ischemia-reperfusion.METHODS:Sixteen Langendorff extracorporeal cardiac perfusion models were successfully established from SD rats and randomly divided into a control group(n=8)and a hypothermic ischemia-reperfusion group(n=8).The control group was balanced perfused with 37 ℃ Krebs-Henseleit solution for 15 minutes and then continued to be perfused with 37 ℃ Krebs-Henseleit solution for 90 minutes.The hypothermic ischemia-reperfusion group was balanced perfused with 37 ℃ Krebs-Henseleit solution for 15 minutes,and then the heart was arrested for 60 minutes by injection of 4 ℃ Thomas solution.During the cardiac arrest,the periphery was protected by 4 ℃ Krebs-Henseleit solution.Half-volume 4 ℃ Thomas solution was reperfused 30 minutes after the arrest.After stopping the arrest,the heart was reperfused with 37 ℃ Krebs-Henseleit solution for 30 minutes.The occurrence of arrhythmias,rebeating time,and the duration of arrhythmias were recorded from the immediate time point to the end of the reperfusion period.Conduction velocity,absolute inhomogeneity,and inhomogeneity index were measured using the Mapping Lab multi-channel electrophysiological mapping system at the time of balanced perfusion for 15 minutes(T1),reperfusion for 15 minutes/continuous perfusion for 90 minutes(T2),and reperfusion for 30 minutes/continuous perfusion for 105 minutes(T3).The relative expression levels of membrane-type matrix metalloproteinase 2,matrix metalloproteinase 2,collagen type Ⅳ,connexin 43,and its Ser368 phosphorylation in ventricular tissue were detected by western blot assay.RESULTS AND CONCLUSION:(1)No arrhythmia occurred in the control group.There were six cases of arrhythmia in the hypothermic ischemia-reperfusion group during reperfusion.Rebeating time and duration of arrhythmias were(25.38+12.02)and(158.67±67.68)seconds,respectively.(2)The conduction sochronal diagrams at T1,T2,and T3 in the control group were uniform and regular in direction,and the conduction velocity at T2 and T3 was not different from that at T1(P＞0.05).The conduction isochronal diagrams at T2 and T3 in the hypothermic ischemia-reperfusion group were uneven and irregular in direction,and the conduction velocity was slower than that at T1(P＜0.01).The conduction velocity at T2 and T3 in the hypothermic ischemia-reperfusion group was slower than that in the control group(P＜0.01).Conduction dispersion was greater in the hypothermic ischemia-reperfusion group than that in the control group at T2 and T3(P＜0.05).(3)Compared with the control group,the protein expressions of membrane-type matrix metalloproteinase 2 and matrix metalloproteinase 2 in the hypothermic ischemia-reperfusion group were increased(P＜0.05 or P＜0.01),and the protein expression levels of type Ⅳ collagen,connexin 43 and its Ser368 phosphorylation were decreased(P＜0.05 or P＜0.01).(4)The results indicate that after hypothermic ischemia-reperfusion,myocardial extracellular matrix remodeling may mediate the downregulation of myocardial connexin 43 and its Ser368 phosphorylation,slowed conduction velocity and increased conduction dispersion,thereby increasing the risk of arrhythmia.

AIM:To investigate the effect of conditioned medium from hypoxia/reoxygenation(H/R)-treated rat cardiac fibroblasts(CFs)on gap junction between cardiomyocytes and determine whether its mechanism is related to matrix metalloproteinase 2(MMP2)activity.METHODS:(1)H9c2 cells were randomly divided into five groups:con-trol group,normal group,ARP-100 group,H/R group,and H/R+ARP-100 group.Scrape loading/dye transfer assay was used to assess the gap junction function.Western blot was used to detect the expression and phosphorylation levels of Cx43.Gelatin zymography assay was performed to measure MMP2 activity.(2)SD rats were randomly divided into control group,ARP-100 group,ischemia-reperfusion(I/R)group,and I/R+ARP-100 group,with 8 rats in each group.Micro-electrode array technology was used to record the type and duration of arrhythmia.Immunohistochemistry experiment was performed to assess expression levels and distribution of Cx43 in myocardial tissues.RESULTS:Compared with the con-trol group,the H/R group showed decreased protein expression of Cx43(P＜0.01),narrowed distance of lucifer yellow dif-fusion(P＜0.01),and increased MMP2 activity(P＜0.01).ARP-100 attenuated H/R-induced gap junction dysfunction(P＜0.05).The arrhythmia score was also reduced after perfusion with ARP-100(P＜0.01).CONCLUSION:H/R-treated rat CFs can inhibit gap junction between cardiomyocytes,and its mechanism may involve increased MMP2 activity.

Objective:To evaluate the effects of exosomes derived from cardiac fibroblasts treated with hypothermic hypoxia-reoxygenation on ventricular electrical conduction during hypothermic cardiac ischemia-reperfusion (I/R) in rats.Methods:SPF neonatal Sprague-Dawley rats of either sex, aged 1-2 days, were used, and primary cardiac fibroblasts were extracted by differential adhesion method. The cells were passaged for 2-4 generations. When the cell density reached 60%-70%, the cells were transferred and exposed to 95% N 2 + 5% CO 2 for 1 h at 4 ℃, and then exposed to 95% air + 5% CO 2 for 24-48 h at 37 ℃, and then exosomes were extracted. Twenty-four SPF healthy adult male Sprague-Dawley rats, aged 2-3 months, weighing 280-360 g, were divided into 3 groups ( n=8 each) according to the random number table method: control group (group C), hypothermic cardiac IR group (I/R group) and exosome + hypothermic cardiac IR group (Exo-IR group). At 48 h before equilibrium perfusion, 1.5 ml (200 μg) of exosomes secreted by cardiac fibroblasts treated with hypothermic hypoxia-reoxygenation was injected into the tail vein in Exo-IR group, and PBS 1.5 ml was injected into the tail vein in C group and IR group each. Group C received 110 min equilibration perfusion. After 20 min of equilibration, the perfusion was suspended for 60 min (global ischemia) followed by 30 min of reperfusion in IR and Exo-IR groups. Microelectrode arrays were applied at 20 min of equilibrium perfusion and 15 and 30 min of reperfusion to obtain myocardial conduction velocity (CV), absolute conduction inhomogeneity (P 5-95) and inhomogeneity index (P 5-95/P 50) on the left ventricular surface of isolated rat hearts. Results:Compared with group C, the CV was significantly decreased at 15 and 30 min of reperfusion, and P 5-95 and P 5-95/P 50 were increased in IR and Exo-IR groups ( P<0.05). Compared with IR group, CV was significantly increased at 15 and 30 min of reperfusion, and P 5-95 and P 5-95/P 50 were decreased in Exo-IR group ( P<0.05). Conclusions:Exosomes derived from cardiac fibroblasts treated with hypothermic hypoxia-reoxygenation can improve ventricular electrical conduction during hypothermic cardiac I/R in rats.