N‐butylidenephthalide Attenuates Ventricular Arrhythmias by Preservation of Connexin43 in Rats with Myocardial Infarction

Abstract

We have recently demonstrated that n‐butylidenephthalide, a major phthalide ingredient of Angelica sinensis, inhibits glycogen synthase kinase (GSK)‐3β and consequently attenuates free radical production. Connexin43 playing a role in ventricular arrhythmia after myocardial infarction is sensitive to redox status. This study was to determine whether n‐butylidenephthalide attenuated arrhythmias through modulating GSK‐3β/free radicals‐induced connexin43 by activating phosphoinositide‐3 kinase (PI3K)/Akt after myocardial infarction. After coronary ligation, male Wistar rats were randomized to either vehicle or n‐butylidenephthalide for 4 weeks. To assess the role of peroxynitrite in connexin43 phosphorylation, we also assessed 3‐morpholinosydnonimine (a peroxynitrite generator). Myocardial superoxide and nitrotyrosine levels were significantly increased and connexin43 levels were substantially decreased after induced myocardial infarction. These changes of superoxide, nitrotyrosine and connexin43 levels were blunted after n‐butylidenephthalide administration, as assessed by biochemistry, immunofluorescent analysis, Western blotting, and real‐time quantitative RT‐PCR. During programmed electrical stimulation, arrhythmic scores were significantly lower in the n‐butylidenephthalide‐treated infarcted rats than those in the vehicle‐treated infarcted rats. n‐butylidenephthalide significantly increased Akt and GSK‐3β phosphorylation in the border zone compared to vehicle after infarction. Inhibition of PI3K/Akt signaling by LY294002 and wortmannin prevented GSK‐3β phosphorylation to a similar extent, and blocked the effects of n‐butylidenephthalide on increased connexin43 phosphorylation. n‐butylidenephthalide‐treated hearts had significantly increased connexin43 phosphorylation, which was significantly decreased after adding 3‐morpholinosydnonimine. The long‐term administration of n‐butylidenephthalide was associated with decreased free radicals content and increased connexin43 levels through the PI3K/Akt‐dependent GSK‐3β pathway, which attenuated ventricular arrhythmias after infarction.