| Objective:Hyperpolarization-activated cyclic nucleotide-gated channels (HCN channels) are the important ion channels for automatic depolarization in phase4. Its decreased expression in the sinus node may cause sick sinus syndrome and weaken the inhibition effect on the ectopic pacemaker; while its increased expression in the atrium and the pulmonary vein may cause ectopic tachyarrhythmias. The incidence of atrial fibrillation increases with aging and its mechanism is associated with the diminished function of sinus node function and the enhanced automaticity of ectopic foci. At present, there is less study on the correlation between the expression of HCN channels in the sinus node, the atria and the pulmonary vein during aging and the aging atrial fibrillation. Thus, the studies on the expression of HCN channels in the atria, pulmonary vein and sinus node at dIfferent ages and dIfferent rhythms are beneficial to further defining the molecular biological mechanisms of aging atrial fibrillation and providingtheoretical foundations and new ideas to the mechanism research and treatment of atrial fibrillation. The research subjects include:(1) comparison of the electrophysiological properties of adult dogs with sinus rhythm, aged dogs with sinus rhythm and aged dogs with atrial fibrillation as well as the dIfference on mRNA and protein expression of HCN2and HCN4channels in the sinus node, left and right atria and pulmonary vein;(2) comparison of the dIfference on mRNA and protein expression of HCN2and HCN4channels in the right atrium of adult patients with sinus rhythm, aged patients with sinus rhythm and aged patients with atrial fibrillation who underwent cardiac surgeries and the difference on the micro-RNA-1,133expression;(3) treatment onaged dogs with atrial fibrillation by Ivabradine (specIfic HCN channels inhibitor) and comparison the incidence and duration of atrial fibrillationas well as the difference on mRNA expression of HCN2and HCN4channels.Method:The first part of this study:30beagles were divided into the adult group with sinus rhythm, the aged group with sinus rhythm and the aged group with atrial fibrillation according to ages and rhythms,10in each group. The beagles in the aged group with atrial fibrillation were implanted with the pacemaker and underwent rapid atrial pacemaking (600times/min). The effective refractory period, dispersion of effective refractory period, rate adaption of effective refractory period and corrected sinus node recovery time were compared. The difference on mRNA and protein expression in sinus node, left and right atria and pulmonary vein are compared through semi-quantitative and real-time fluorescent PCR as well as western blot. The second part of this study:the right atrium samples of patients who must have cardiac surgery were collected. The difference on mRNA and protein expression was compared through semi-quantitative and real-time fluorescent PCR as well as western blot. Meanwhile, the difference on microRNA-1,133was compared through real-tinefluorescent PCR. The third part of this study:the aged beagles implanted with pacemaker were divided into two groups; one group was given Ivabradine and the other group was fed with no drugs. After4weeks, atrial fibrillation was induced. The incidence and duration of atrial fibrillation were observed; mRNA and protein expression of HCN2and HCN4channels in the sinus node, left and right atria and pulmonary vein were detected through real-time fluorescent PCR.Results:Compared with the adult dogs with sinus rhythm, mRNA expression of HCN2and HCN4channels in sinus node of the aged dogs with sinus rhythm decreased, while the expression in left and right atria and pulmonary vein enhanced. Compared with the aged dogs with sinus rhythm, the expression of HCN2and HCN4channels in sinus node of the aged dogs with atrial fibrillationfurther decreased and the expression in left and right atria further enhanced, while the expression of HCN2channels in pulmonary vein showed no difference and the expression of HCN4channels enhanced.(2) Compared with the adult patients with sinus rhythm, mRNA and protein expression of HCN2and HCN4channels in right atriumof aged patients with sinus rhythm enhanced and the expression of microRNA-1,133decreased. Compared with the aged patients with sinus rhythm, the expression of HCN2and HCN4channels of the aged patients with atrial fibrillation further enhanced and the expression of microRNA-1,133further decreased.(3) No difference on the incidence of atrial fibrillation was observed between the Ivabradinegroup and the control group. However, after the induction, the duration of atrial fibrillationin the Ivabradine group decreased significantly. No difference on mRNA expression of HCN2and HCN4channels in left and right atria was observed.Conclusion:(1) Aging and atrial fibrillation decrease the expression of HCN2and HCN4channels in the sinus node of beagles and enhance the expression in left and right atria and pulmonary vein. It is indicated that HCN channel may be one of the pathogenesis of aging atrial fibrillation.(2) Aging and atrial fibrillationenhance the expression of HCN2and HCN4channels in the right atrium of peopleand decrease the expression of microRNA-1,133.(3) Ivabradine can shorten the duration of atrial fibrillation, which may be the effective drug for preventing and treating atrial fibrillation. This study indicates that aging reserves the expression of HCN channels in the sinus node, left and right atria and pulmonary vein, which leads to the incidence and maintenance of aging atrial fibrillation. As the specIfic inhibitor of HCN channels, Ivabradine may be the effective drug for preventing and treating atrial fibrillation. |
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