心房颤动24h和48h对犬心房肌有效不应期及L型钙电流的影响

目的 研究犬心房颤动（房颤）持续24h和48 h,心房肌有效不应期和L型钙电流变化的一致性及其机制.方法 健康成年杂种犬18只,分为对照组、24 h房颤组、48 h房颤组,每组6只.600次/min起搏高右心房建立犬房颤模型,应用程序刺激的方法测定右心房有效不应期（ERP）,通过Langendorff左回旋支灌流分离心房肌细胞,并通过全细胞膜片钳技术记录L型钙电流（ICa-L）变化.应用免疫组织化学方法检测各组心房组织L型电压依赖性钙通道（LVDCC）α1c蛋白表达.用图像分析系统对组织化学抗原表达进行半定量分析.结果 所有实验动物均可诱发出房颤.心房ERP的变化在最初6h较对照组明显缩短,后直至48 h呈进行性缩短.快速起搏6h后ERP（129.50±8.64）ms较对照组（141.00±15.23）ms缩短（12.13±2.24）ms（P＜0.01）,24 h后心房ERP（123.00± 13.37） ms缩短（19.23±2.14）ms（P＜0.01）,48 h缩短（28.15±4.26）ms（P＜0.01）.同时在房颤持续过程中24h房颤可引起ICa-L电流密度（-4.83±0.30）pA/pF较对照组（-6.69±0.08）pA/pF减小,48 h（-3.70±0.50）pA/pF减少的程度更重.24 h房颤及48 h房颤犬的左、右心房组织LVDCC α1c蛋白表达均较对照组明显减少（P＜0.05）,48 h房颤组减少程度更重（P＜0.01）.结论 房颤持续24 h,心房肌ERP显著缩短、ICa-L密度降低.房颤持续48 h仍然维持L型钙通道改变特征.提示：钙通道阻断剂可用于持续24 h房颤,预防房颤复发.

Effects of 24 h and 48 h atrial fibrillation on L-type calcium currents in canine atrial myocytes

Objective To evaluate the effects of 24 h and 48 h atrial fibrillation（AF） on L-type calcium current （ICa-L）in atrial myocytes,and to investigate its possible mechanism and concordance.Methods Eighteen healthy adult mongrel canines were randomly divided into three groups：control group,24 h AF group and 48 h AF group,6 in each group.AF model was established by right atrial pacing with 600 bpm.The effective refractory period（ERP） of right atrial was measured by program stimulation.The atrial myocytes isolated from 24 h and 48 h AF canine,L-type calcium channel currents in atrial myocytes were recorded by patch clamp technique in the whole cell mode.The expressions of L-type voltage-dependent Ca2＋ channel（LVDCC） α1c protein in atrium were measured by immunohistochemistry in three groups,semi-quantitative analysis of α1c protein expression was performed with pathological image analytic system.Results In 24 h AF group and 48 h AF group,AF can be induced in all the experiment animal.The pattern of ERP with an rapid drop in 6 h followed by a more gradual decline during hours 6 through 48 as the result of rapid pacing.The mean ERP was decreased by （12.13 ± 2.24） ms after 6 hours of pacing （from 141.00 ± 15.23 to 129.50 ± 8.64） ms （P 〈 0.01）.Similarly,after 24 h pacing the mean ERP was decreased by （19.23 ± 2.14） ms （P〈 0.01）,and by （28.15 ±4.26） ms after 48 h pacing（P〈0.01）.Compared with control group（-6.69±0.08）pA/pF,the peak density of ICa-L was significantly reduced in 24 h AF group（-4.83±0.30）pA/pF,and it was reduced more in 48 h AF group（-3.70±0.50）pA/pF.Compared with control group,the protein expression of LVDCC α1c decreased significantly in group of 48 h and 24 h AF（P〈0.05）,but in the group of 48 h AF it decreased more （P〈0.01）.Conclusion The decrease of ICa-L may contribute to ionic basis of acute electrical remodeling of atrial cardiomyocytes caused by 24 h and 48 h AF in canine,which suggested that calcium channels blocker might prevent AF recurrence.