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Both PKA and Epac pathways mediate N-acetylcysteine-induced Connexin43 preservation in rats with myocardial infarction.

Lee TM, Lin SZ, Chang NC - PLoS ONE (2013)

Bottom Line: Cardiac remodeling was shown to be associated with reduced gap junction expression after myocardial infarction.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Cardiology Section, Tainan Municipal An-Nan Hospital-China Medical University, Tainan, Taiwan ; Department of Medicine, China Medical University, Taichung, Taiwan ; Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.

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.

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Cx43 mRNA expression and ventricular arrhythmias.A, LV Cx43 mRNA levels. Each mRNA was normalized to an mRNA level of cyclophilin. The number of animals in each group is indicated in parentheses. *p<0.05 compared with sham and NAC-treated group. B, Inducibility quotient of ventricular arrhythmias by programmed electrical stimulation 4 weeks after MI. The number of animals in each group is indicated in parentheses. *p<0.05 compared with sham and NAC-treated group; †p<0.05 compared with sham.
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pone-0071878-g004: Cx43 mRNA expression and ventricular arrhythmias.A, LV Cx43 mRNA levels. Each mRNA was normalized to an mRNA level of cyclophilin. The number of animals in each group is indicated in parentheses. *p<0.05 compared with sham and NAC-treated group. B, Inducibility quotient of ventricular arrhythmias by programmed electrical stimulation 4 weeks after MI. The number of animals in each group is indicated in parentheses. *p<0.05 compared with sham and NAC-treated group; †p<0.05 compared with sham.

Mentions: To determine whether the preserved Cx43 at the border zone of NAC-treated rats was due to an upregulation at the mRNA levels, Cx43 mRNA expression was quantified by real-time RT-PCR. The Cx43 mRNA expression showed a significant downregulation at the border zone in the vehicle compared with sham (Figure 4A). In NAC-treated infarcted rats, the Cx43 mRNA expression was significantly increased than those in the vehicle.


Both PKA and Epac pathways mediate N-acetylcysteine-induced Connexin43 preservation in rats with myocardial infarction.

Lee TM, Lin SZ, Chang NC - PLoS ONE (2013)

Cx43 mRNA expression and ventricular arrhythmias.A, LV Cx43 mRNA levels. Each mRNA was normalized to an mRNA level of cyclophilin. The number of animals in each group is indicated in parentheses. *p<0.05 compared with sham and NAC-treated group. B, Inducibility quotient of ventricular arrhythmias by programmed electrical stimulation 4 weeks after MI. The number of animals in each group is indicated in parentheses. *p<0.05 compared with sham and NAC-treated group; †p<0.05 compared with sham.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756050&req=5

pone-0071878-g004: Cx43 mRNA expression and ventricular arrhythmias.A, LV Cx43 mRNA levels. Each mRNA was normalized to an mRNA level of cyclophilin. The number of animals in each group is indicated in parentheses. *p<0.05 compared with sham and NAC-treated group. B, Inducibility quotient of ventricular arrhythmias by programmed electrical stimulation 4 weeks after MI. The number of animals in each group is indicated in parentheses. *p<0.05 compared with sham and NAC-treated group; †p<0.05 compared with sham.
Mentions: To determine whether the preserved Cx43 at the border zone of NAC-treated rats was due to an upregulation at the mRNA levels, Cx43 mRNA expression was quantified by real-time RT-PCR. The Cx43 mRNA expression showed a significant downregulation at the border zone in the vehicle compared with sham (Figure 4A). In NAC-treated infarcted rats, the Cx43 mRNA expression was significantly increased than those in the vehicle.

Bottom Line: Cardiac remodeling was shown to be associated with reduced gap junction expression after myocardial infarction.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Cardiology Section, Tainan Municipal An-Nan Hospital-China Medical University, Tainan, Taiwan ; Department of Medicine, China Medical University, Taichung, Taiwan ; Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.

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.

Show MeSH
Related in: MedlinePlus