Abstract
Cardiac remodeling was shown to be associated with reduced gap junction expression after myocardial infarction. A reduction in gap junctional proteins between myocytes may trigger ventricular arrhythmia. Therefore, we investigated whether N-acetylcysteine exerted antiarrhythmic effect by preserving connexin43 expression in postinfarcted rats, focusing on cAMP downstream molecules such as protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). Male Wistar rats after ligating coronary artery were randomized to either vehicle, or N-acetylcysteine for 4 weeks starting 24 hours after operation. Infarct size was similar between two groups. Compared with vehicle, cAMP levels were increased by N-acetylcysteine treatment after infarction. Myocardial connexin43 expression was significantly decreased in vehicle-treated infarcted rats compared with sham operated rats. Attenuated connexin43 expression and function were blunted after administering N-acetylcysteine, assessed by immunofluorescent analysis, dye coupling, Western blotting, and real-time quantitative RT-PCR of connexin43. Arrhythmic scores during programmed stimulation in the N-acetylcysteine-treated rats were significantly lower than those treated with vehicle. In an ex vivo study, enhanced connexin43 levels afforded by N-acetylcysteine were partially blocked by either H-89 (a PKA inhibitor) or brefeldin A (an Epac-signaling inhibitor) and completely blocked when H-89 and brefeldin A were given in combination. Addition of either the PKA specific activator N6Bz or Epac specific activator 8-CPT did not have additional increased connexin43 levels compared with rats treated with lithium chloride alone. These findings suggest that N-acetylcysteine protects ventricular arrhythmias by attenuating reduced connexin43 expression and function via both PKA- and Epac-dependent pathways, which converge through the inactivation of glycogen synthase kinase-3β.
Highlights
Cardiac remodeling was shown to be associated with gap junction heterogeneities after myocardial infarction (MI) [1]
We show that Cx43 activated through the inactivation of glycogen synthase kinase-3b (GSK-3b) by NAC-induced cAMP-protein kinase A (PKA) and cAMPEpac signaling attenuated ventricular arrhythmias after MI
Our present study shows for the first time that chronic treatment for 4 weeks with NAC leads to preserved Cx43 phosphorylation, total amount and function probably through a cAMP-dependent GSK-3b pathway and attenuates ventricular arrhythmias in infarcted rats
Summary
Cardiac remodeling was shown to be associated with gap junction heterogeneities after myocardial infarction (MI) [1]. A dysfunction of the cardiac gap junction, which contributes to electrical cell-to-cell coupling, is one of essential factors known to generate arrhythmias. These channels permit molecules with molecular masses of less than 1 kDa, such as small metabolites, ions, and intracellular signaling molecules (i.e., glutathione [GSH], cyclic 39,59-adenosine monophosphate [cAMP]), to pass through [2]. A reduction in gap junctional coupling between myocytes may be an important morphological feature that could interact with altered membrane properties in diseased myocardium [4]. Cx43 gene transfer has been shown to attenuate arrhythmia susceptibility in the healed border zone after MI [8]
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