Objective: To explore the role of angiotensin receptor type I (AT1)-calcineurin (CaN) signaling pathway in transient outward potassium ion channel (Ito) remolding in hypertrophic atrial myocytes of neonatal rats. Methods: 1 day old neonatal rats’ atrial myocytes were isolated and the cells were divided into 4 groups:①Control group, normal cells were cultured for 24 h,②Stretching group, the cells were cultured for 24 h with mechanical stretching to induce hypertrophy,③Telmisartan group, the cells were treated by telmisartan at 1 μmol/L for 1 h, then cultured for 24 h and ④Cyclosporin-A (CsA) group, the cells were treated by CsA at 0.25 μg/ml for 1 h, then cultured for 24 h. The ratios of protein/DNA in myocytes were compared between Control group and Stretching group, cell hypertrophy was deifned by mRNA expression of atrial natriuretic peptide (ANP). Ito changes were detected by whole-cell patch clamping technique, proteins expressions of Kv4.3 and CaN A subunit were examined by Western blot analysis. Results: Compared with Control group, Stretching group showed obviously decreased Ito density and Kv4.3 protein expression, while increased CaN A protein expression; Compared with Stretching group, the above effects were reduced in Telmisartan group and CsA group. Conclusion: AT1-CaN signaling pathway was involved in the regulation of Ito channel remodeling in hypertrophic atrial myocytes of neonatal rats.

AIM:To investigate the effect of angiotensin II type 1 receptor (AT1R)-calcineurin (CaN) signa-ling pathway on the expression of sodium current channel Nav 1.5 at mRNA and protein levels in the hypertrophic ventricu-lar myocytes from neonatal rats .METHODS:The ventricular myocytes were isolated from the ventricles of 1-day-old neo-natal Sprague-Dawley rats and were divided into 4 groups according to different drug intervention as control group , pheny-lephrine (PE) group, losartan (Los)+PE group and cyclosporin A (CsA)+PE group.The method of RNA interference mediated by adenovirus carrying short hairpin RNA ( shRNA) was used to knock down the gene which encodes the beta subtype of CaN A subunit (CnAβ) and the cells were divided into 4 groups as Ad-Null group, Ad-Null+PE group, Ad-CnAβshRNA1 group and Ad-CnAβshRNA1+PE group.The mRNA expression of brain natriuretic peptide ( BNP) ,β-my-osin heavy chain (β-MHC) and Nav1.5 was detected by RT-qPCR.The protein levels of CnAβand Nav1.5 in the whole-cell extracts were determined by Western blot analysis .RESULTS:Treatment of the neonatal rat ventricular myocytes with PE for 24 h increased the protein-to-DNA ratio and the mRNA expression of BNP and β-MHC.The size of the cell surface was also increased after PE treatment .Treatment of the cells with PE increased the protein expression of CnAβ, and re-duced the protein expression of Nav 1.5.Both Los and CsA prevented those effects of PE .The mRNA expression of Nav1.5 was reduced by PE , and no significant difference of Nav 1.5 mRNA expression among PE group , Los+PE group and CsA+PE group was observed .Silencing of CnAβin the neonatal rat ventricular myocytes using Ad-CnAβshRNA1 inhibited the ability of PE to increase the mRNA expression of BNP , and diminished the ability of PE to reduce the protein expression of Nav1.5.CONCLUSION:AT1 R-CaN signaling pathway participates in regulating protein expression of Nav 1.5 in the hy-pertrophic ventricular myocytes from neonatal rats .