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.

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.