| Backgroud and objective: The survival myocardium in infarcted border zones of post-AMI heart always play a critical role in the occurrence of post-infarcted ventricular arrhythmias. Electric remodeling resulted from abnormal activity of the ion channels on the myocardial membrane may be an important mechanism of arrhythmo -genesis. Researches indicated that it was the hyperpolarization-activated cyclic nucleotide-gated cation channel subunit which encoded If current. The HCN gene family includes 4 isoforms. HCN channels are highly expressed in pacemaker cells, but low in working cardial cell. In adult rat ventricular cells,HCN2 is the predominant subunit, there are a small quantity of HCN4. HCN channels is considered to contribute significantly to the spontaneous diastolic depolarization phase, participating pacemaker activity in pacemaker cells on physiological conditions. Researches has shown that changes of expression or activation of HCN channel may have a potential proarrhythmic under pathophysiological conditions. The KCNE gene family encodes ionophorous protein with 1 transmembrane domain. They function asβ-subunits of voltage-gated cation channels by associating withα-subunits and modulating their properties.KCNE1,KCNE2 are mainly dispersed in myocardium, participating the regulation of properties of voltage-gated cation channels and affecting the repolarization ofⅡ,Ⅲphases of active potential.Abnormal expression of them will influence the physiological nature of ion channels. Therefore,the purpose of this study was to investigate the dynamic changes and regularity of expression of HCN2,HCN4,KCNE1,KCNE2 mRNA and protein in infarcted border zones of post-AMI heart and suply more theoretical foundations in mechanism of infarcted ventricular arrhythmogenesis.Methods: The AMI rat model was established by ligation of the left anterior descending coronary artery.20 infarcted rats were randomly divided into 4 groups(n=5 in each group): AMI 24h group,AMI 1w group,AMI 2w group and AMI 2w group,the Sham-operated rats underwent the same procedure except for the ligation,they were also randomly divided into 4 groups(n=5 in each group). Harvest left ventricular infarcted border zone myocardial tissues at each time,meanwhile,corresponding myocardial tissues were harvested in Sham-operated rats.The expression of HCN2,HCN4,KCNE1,KCNE2 mRNA were assessed by RT-PCR and the expression of protein were assessed by Western blot.HCN2 and HCN4 protein were detected by immunohistochemistry.Results: The expression of HCN2,HCN4,KCNE1,KCNE2 mRNA and protein were detected in Sham-operated rats. The expression of them in infarcted border zone muscular tissues in each time point underwent a dynamic change process respectively : (1),The expression of HCN2 and HCN4 : two of them exhibited an ascending tendency at 24 hours after AMI, reached peak value at 1 week after AMI,decreased gradually after that.But the expression of HCN2 channel were also increased compared with sham-operated group at 4 weeks after AMI,but there was no significant difference in HCN4. (2),The expression of KCNE1 and KCNE2:The expression of KCNE1 was increased significantly at 24 hours after AMI,after that, KCNE1 continued to increase and reached peak value at 2 weeks after AMI, but decreased at 4 weeks after AMI.The expression of mRNA was no significant difference between sham-operated group and AMI group,but protein was significantly higher than sham-operated group at 4 weeks.The expression of KCNE2 was also increased significantly at 24 hours after AMI ,reached peak value at 1 week after AMI, decreased gradually after that.The tendency of expression of mRNA and protein expression were opposite compared with KCNE1 at 4 weeks.Conclusion: The expression of HCN2,HCN4,KCNE1,KCNE2 mRNA and protein were detected in normal rats.The level of the expression of them in infarcted border zone muscular tissues are upregulated and underwent a dynamic change process at different time.That may be the result of intereaction of a series of pathologic factors such as ischemic,hypoxia,high concentration of potassium,acidosis,deficiency of energy,assemblage of metabolites,activation of neuroendocrine system after AMI. |
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