摘要目的 探讨琥珀酸美托洛尔早期干预对陈旧性心肌梗死兔心脏组织缝隙连接蛋白43(Cx43)及其磷酸化(p-Cx43)水平的影响.方法 采用随机区组设计,以体重作为区组标志,将24只成年雄性新西兰大白兔分为假手术组(n=6)、早期干预组(n=6)、常规干预组(n=6)和心肌梗死组(n=6).早期干预组、常规干预组和心肌梗死组通过结扎左前降支建立心肌梗死模型,假手术组不结扎冠状动脉,其余操作相同.早期干预组和常规干预组分别于麻醉清醒后和心肌梗死24 h后以琥珀酸美托洛尔(12.5 mg/kg,溶于2 ml蒸馏水中)灌胃,假手术组和心肌梗死组以等量蒸馏水灌胃,每天1次.术后6h,以生物化学法检测血清心肌坏死标志物(血清乳酸脱氢酶和肌酸激酶)水平.术后40 d开胸暴露心脏,通过双极起搏电极测定心室颤动阈值.以免疫荧光法观察Cx43和p-Cx43在心室肌组织的分布情况.以Western blot检测心室肌组织Cx43及其磷酸化的蛋白表达水平.结果 (1)心肌梗死组的血清乳酸脱氢酶[(851.7 ±85.9)U/L比(332.3±39.6)U/L,P ＜0.01]和肌酸激酶[(1 192.7±105.3)U/L比(462.3 ±65.6)U/L,P＜0.01]水平均高于假手术组.(2)心肌梗死组的心室颤动阈值低于假手术组[(470.0 ±91.0)次/min比(683.3±60.9)次/min,P＜0.05];早期干预组[(633.3 ±43.2)次/min]和常规干预组[(645.0±30.8)次/min]的心室颤动阈值均高于心肌梗死组(P均＜0.05).(3)免疫荧光法检测显示,假手术组、早期干预组和常规干预组的Cx43主要位于闰盘内,与细胞长轴垂直,呈线状排列,侧向分布的Cx43较少;心肌梗死组则相反.与假手术组比较,心肌梗死组p-Cx43表达较少;与心肌梗死组比较,早期干预组和常规干预组p-Cx43表达较多;早期干预组p-Cx43的表达多于常规干预组.(4)心肌梗死组的p-Cx43蛋白/Cx43蛋白低于假手术组(0.165 ±0.011比0.363±0.046,P＜0.05);早期干预组(0.720±0.063)和常规干预组(0.364±0.030)的p-Cx43蛋白/Cx43蛋白均高于心肌梗死组(P均＜0.05);早期干预组的p-Cx43蛋白/Cx43蛋白高于常规干预组(P＜0.05).结论 琥珀酸美托洛尔通过改善陈旧性心肌梗死兔心脏组织Cx43的空间分布和磷酸化水平,提高心室颤动阈值,而且心肌梗死后早期(24h内)给药效果更明显.

abstractsObjective To investigate the early intervention effects of metoprolol on connexin 43 (Cx43) and phosphorylated Cx43 (p-Cx43) expression in rabbits with post myocardial infarction.Methods A total of 24 adult male New Zealand white rabbits were divided into sham group (n =6),early treatment group (n =6),routine treatment group (n =6),and myocardial infarction group (n =6) with a randomized block design blocked by weight.Myocardial infarction was induced by left anterior descending coronary artery (LAD) ligation.Rabbits in sham group received similar surgical procedure without LAD ligation.Metoprolol (12.5 mg/kg dissolved in 2 nl distilled water) was applied to rabbits in early treatment group and routine treatment group per gavage immediately after recovery from anesthesia and at 24 hours after myocardial infarction,respectively,then treated daily for 40 days.Rabbits in sham group and myocardial infarction group received 2 ml distilled water per gavage daily for 40 days.Plasma lactate dehydrogenase (LDH) and creatine kinase (CK) level were detected by automatic biochemistry analyzer after 6 hours in all rabbits.Ventricular fibrillation threshold (VFT) was measured in vivo by bipolar pacing electrodes at 40 days.Cx43 and p-Cx43 distribution in ventricular tissue was detected by immunofluorescence analyses.Cx43 and p-Cx43 protein level in ventricular tissue was determined by Western blot.Results (1) Plasma LDH ((851.7±85.9)U/L vs.(332.3 ±39.6)U/L,P＜0.01) and CK ((1 192.7 ± 105.3) U/L vs.(462.3 ± 65.6) U/L,P ＜0.01) were significantly higher in myocardial infarction group than in sham group (both P ＜0.01).(2) VFT was significantly lower in myocardial infarction group than that in sham group ((470.0±91.0) beats per minute vs.(683.3 ±60.9) beats per minute,P ＜0.05),and VFT was significantly higher in early treatment group ((633.3 ± 43.2) beats per minute) and routine treatment group ((645.0 ± 30.8) beats per minute) than in the myocardial infarction group (both P ＜ 0.05).(3)Immunofluorescence analyses showed that Cx43 was mainly localized in the intercalated disk,which was perpendicular to the cell long axis with linear arrangement,and less lateral distribution in sham group,early treatment group and routine treatment group,which was significantly different as the case in the myocardial infarction group.The expression of p-Cx43 in myocardial infarction group was less than in shan group,which was significantly upregulated in in early treatment group and routine treatment group when compared with myocardial infarction group,and expression of p-Cx43 was significantly higher in early treatment group than in routine treatment group.(4)The p-Cx43/Cx43 ratio of protein was significantly lower in myocardial infarction group than in sham group (0.165 ± 0.011 vs.0.363 ± 0.046,P ＜ 0.05),and significantly higher in early treatment group (0.720 ± 0.063) and routine treatment group (0.364 ± 0.030) than in myocardial infarction group (both P ＜ 0.05),and this ratio was significantly higher in early treatment group than in routine treatment group (P ＜ 0.05).Conclusion Metoprolol treatment,especially the early metoprolol treatment (within 24 hours after LAD ligation),could significantly improve VFT by ameliorating the distribution and dephosphorylation of myocardial Cx43 in rabbits with experimental myocardial infarction.