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Background/Aims: Cardiac fibrosis after myocardial infarction (MI) has been identified as a key factor in the development of heart failure, but the mechanisms undelying cardiac fibrosis remained unknown. microRNAs (miRNAs) are novel mechanisms leading to fibrotic diseases, including cardiac fibrosis. Previous studies revealed that miR-22 might be a potential target. However, the roles and mechanisms of miR-22 in cardiac fibrosis remained ill defined. The present study thus addressed the impact of miR-22 in cardiac fibrosis. Methods: After seven days following coronary artery occlusion in mice, tissues used for histology were collected and processed for Masson's Trichrome staining. In addition, cardiac fibroblasts were transfected with mimics and inhibitors of miR-22 using Lipofectamin 2000, and luciferase activity was measured in cell lysates using a luciferase assay kit. Western blotting was used to detect the expression of collagen1, α-SMA and TGFβRI proteins levels, and real time-PCR was employed to measure the Col1α1, Col3α1, miR-22 and TGFβRI mRNA levels. Results: In this study, we found that miR-22 was dynamically downregulated following MI induced by permanent ligation of the left anterior descending coronary artery for 7 days, an effect paralleled by significant collagen deposition. Inhibition of miR-22 with AMO-22 resulted in increased expression of Col1α1, Col3α1 and fibrogenesis in cultured cardiac fibroblasts. Conversely, overexpression of miR-22 in cultured cardiac fibroblasts significantly abrogated angiotensin II-induced collagen formation and fibrogenesis. Furthermore, we found that TGFβRI is a direct target for miR-22, and downregulation of TGFβR may have mediated the antifibrotic effect of miR-22. Conclusion: Our data clearly demonstrate that miR-22 acts as a novel negative regulator of angiotensin II-induced cardiac fibrosis by suppressing the expression of TGFβRI in the heart and may represent a new potential therapeutic target for treating cardiac fibrosis.

Background and purpose: Activation of muscarinic M3 mucarinic acetylcholine receptors (M3-mAChRs) has been previously shown to confer short-term cardioprotection against ischaemic injuries. However, it is not known whether activation of these receptors can provide delayed cardioprotection. Consequently, the present study was undertaken to investigate whether stimulation of M3-mAChRs can induce delayed preconditioning in rats, and to characterize the potential mechanism. Experimental approach: Rats were pretreated (24 h), respectively, with M3-mAChRs agonist choline, M3-mAChRs antagonist 4-DAMP or M2-mAChRs antagonist methoctramine followed by the administration of choline. This was followed by 30 min of ischaemia and then 3 h of reperfusion. Ischaemia-induced arrhythmias and ischaemia-reperfusion (I/R)-induced infarction were determined. The phosphorylation status of connexin43 (Cx43) after 30 min ischaemia, and the expression level of Hsp70, cyclooxygenase-2 (COX-2) and iNOS effected by administration of choline were also measured. Key results: Compared to the control group, pretreatment with choline significantly decreased ischaemia-induced arrhythmias, reduced the total number of ventricular premature beats, the duration of ventricular tachycardia episodes and markedly reduced I/R-induced infarct size. Furthermore, choline attenuated ischaemia-induced dephosphorylation of Cx43, and up-regulated the expression of Hsp70 and COX-2. Administration of 4-DAMP abolished these changes, while methoctramine had no effect. Conclusions and implications:Our results suggest that stimulation of M3-mAChRs with choline elicits delayed preconditioning, which we propose is the result of up-regulation of the expression of COX-2 and inhibition of the ischaemia-induced dephosphorylation of Cx43. Therefore, M3-mAChRs represent a promising target for rendering cardiomyocytes tolerant to ischaemic injury.

The present study was designed to study the effects of As₂O₃ on QT interval prolongation and to explore the potential ionic mechanisms in isolated rat ventricular cardiomyocytes. The rats of As₂O₃ group were treated with 0.8 mg·kg^-1·d^-1 As₂O₃ intravenously for 7 days consecutively and the control group with saline. The ECG was recorded to calculate heart rate-corrected QT interval (QTc). Single cardiomyocytes were isolated by using collagenase II, and the action potential duration (APD) and ion currents were recorded by whole-cell patch clamp. [Ca²⁺]_>i was examined by confocal laser scanning microscopy. Our data showed that both QTc and APD were prolonged significantly after As₂O₃treatment. Meanwhile, As₂O₃ suppressed I _K1 and shifted the reversal potential to more positive direction. Moreover, the density of I _Ca,L was augmented significantly, and the steady-state activation curve became more negative, whereas, the inactivation and reactivation of I _Ca,L were not changed notably after As₂O₃ administration. Furthermore, the maximal [Ca²⁺] _i was enhanced obviously by either KCl or caffeine stimulation in As₂O₃-treated cardiomyocytes. Our results show that the potential mechanism of As₂O₃-induced QT interval prolongation in rat might be relative to disturbing the fine balance of transmembrane currents ( increasing I _Ca,L and decreasing I _K1) and causing APD prolongation.