The Effects Of Pravastatin On HCN Channels And Variation Of HCN Channels After Myocardiac Infarction In Rats

Backgroud and objective: The reasons of ventricular cells electric remodeling post myocardial infarction may be a series of complex molecular and celluar mechanisms,and this may be the reason of arrhythmogenesis.Research on molecular structure of cardiac ion channel indicated that it is the hyperpolarization-activated cyclic nucleotide-gated cation channel subunit which encoded If current.The HCN family includes 4 isoforms. HCN channels are highly expressed in pacemaker cells, but in working cardial cell,the expression are low.In adult rat ventricular cells,HCN2 is the mainly subunit, there is a small quantity of HCN4. In sinus node and Purkinje cells, the hyperpolarization-activated inward current (If) is considered to contribute significantly to the spontaneous diastolic depolarization phase.In pacemaker cells, If is believed to be the major current determining the diastolic depolarization phase.Researches has shown that change of expression or function of HCN channel may have a potential proarrhythmic under pathophysiological conditions. Recent research of large scale randomized clinical trial has shown additional beneficial pleiotropic effects independent of the simple cholesterol lowering effect, especially antiarrhythmic effect.At present,the mechanisms of anti-arrhythmias are unclear.Therefore,the purpose of this study was to investigate variation of expressions of HCN channels post myocardial infarction and to evaluate the effects of pravastatin on expressions of HCN channels,we try to find the mechanism of antiarrhythmic effect. Methods: The AMI rat model was established by ligation of the left anterior descending coronary artery,the Sham-operated rats underwent the same procedure except for the ligation.20 infarcted rats were randomly divided into 4 groups(n=5 in each group): AMI24h group,AMI1w group,AMI4w group and pravastatin treated group(20mg.kg-1.d-1,drug was orally given to AMI rats by gastric gavate once a day for 4 weeks.)and meanwhile, Sham-operated group of each time point was established(n=5).Harvest right ventricular myocardial tissues at each time point,the expressions of HCN2,HCN4mRNA were evaluated by Real Time PCR and the expressions of HCN2,HCN4 protein were evaluated by Western blot.Results: The expressions of HCN2 mRNA and protein were increased significantly at 4week after AMI compared with sham-operated group,and the expression of HCN4 mRNA was increased also. The expressions of HCN2 mRNA and protein were decreased in pravastatin treated group compare with AMI4week group,there was no significant difference between pravastatin treated group and AMI 4-week group.We were failed to detect the expression of HCN4 protein in each group.Conclusion: The level of HCN2 mRNA,protein and HCN4mRNA are upregulated,the reason below may support it:1) Aldosterone level is increased post myocardial infarction, and aldosterone can up-regulates HCN2 mRNA,protein and HCN4mRNA expression by Mineralocorticoid receptor MR activation in cardiac myocytes;2) Pathologic myocyte hypertrophy after AMI accompany with increase of HCN2 and HCN4 level;3) Endothelin-1 level is increased post myocardial infarction, and ET-1 can up-regulate mRNA levels for HCN2 and HCN4.Pravastatin pertly inhibited the up-regulate of expression of HCN2.The reason below may support it :1)Pravastatin interrupt RASS, degrade the level of aldosterone;2) Pravastatin alleviate cardiomyocyte hypertrophy;3) Pravastatin decrease level of ET-1,thus attenuated the factor of that which up-regulate HCN level.