β2-Adrenergic Receptor Agonist Clenbuterol Protects Against Acute Ischemia/Reperfusion-Induced Arrhythmia by Regulation of Akt/eNOS/NO/Cx43 Signaling Pathway.

Ventricular arrhythmias induced by ischemia/reperfusion injury limits the therapeutic effect of early reperfusion therapy for acute myocardial infarction. This study investigated the protective effects of the β2-adrenergic receptor (β2-AR) agonist clenbuterol against ischemia/reperfusion-induced arrhythmias and the underlying mechanism. Anesthetized rats were subjected to 10-min left coronary artery occlusion and 10-min reperfusion in vivo. Langendorff-perfused mice hearts were exposed to 10-min global ischemia and 10-min reperfusion. Arrhythmic events were recorded during early reperfusion. Hearts were collected for measuring nitric oxide (NO) concentration and immunoblotting of Connexin 43 (Cx43), endothelial nitric oxide synthase (eNOS), and protein kinase B (Akt). After the ischemia/reperfusion injury in anesthesia rats, clenbuterol markedly reduced the duration and incidence of ventricular tachycardia and ventricular fibrillation, and arrhythmia score, which was abrogated by selective β2-AR antagonist or Cx43 inhibitor. Furthermore, a marked increase in dephosphorylated Cx43 expression and a decrease in the ratio of phosphorylated Cx43 to total Cx43 were observed after the ischemia/reperfusion injury. Mechanistically, clenbuterol increased the phosphorylation of e-NOS and NO concentration, while L-NAME abolished Cx43 phosphorylation and the protective effect of clenbuterol. Clenbuterol also promoted Akt phosphorylation, and blockade of Akt inhibited eNOS phosphorylation and NO production, as well as Cx43 phosphorylation and protective effect of clenbuterol. The present study elucidates that β2-AR stimulation activates the Akt/eNOS signaling pathway, augments NO bioavailability, maintains Cx43 phosphorylation, and prevents Cx43 remodeling, ultimately attenuating arrhythmia induced by ischemia/reperfusion.