Submitted on December 21, 2006
Accepted on July 17, 2007
Aldosterone modulates If current through gene expression in cultured neonatal rat ventricular myocytes
Takao Muto1, Norihiro Ueda2, Tobias Opthof3, Tomoko Ohkusa4, Kohzo Nagata5, Shinsuke Suzuki4, Yukiomi Tsuji6, Mitsuru Horiba7, Jong-Kook Lee6, Haruo Honjo7, Kaichiro Kamiya6, Itsuo Kodama6, and Kenji Yasui1*
1 Department of Bio-informaiton Analysis, Research Insitute of Environmental Medicine, Nagoya University, Nagoya, Japan
2 Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
3 Experimental and Molecular Cardiology Groups, Academic Center, Amsterdam, Netherlands; Department of Medical Physiology, University Medical Center Utrecht, Utrecht, Netherlands
4 Yamaguchi University School of Medicine, Yamaguchi, Japan
5 Department of Medical Technology, Nagoya University School of Health Sciences, Nagoya, Japan
6 Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Aichi-Ken, Japan
7 Department of Cardiovascular Research, Research Insitute of Environmental Medicine, Nagoya University, Nagoya, Japan
* To whom correspondence should be addressed. E-mail: kenji{at}riem.nagoya-u.ac.jp.
Mineralocorticoid receptor (MR) antagonists decrease the incidence of sudden cardiac death in patients with heart failure as has been reported in two clinical trials (RALES and EPHESUS). Aldosterone has been shown to increase the propensity to arrhythmias by changing the expression or function of various ion channels. In this study we investigate the effect of aldosterone on the expression of If channels in cultured neonatal rat ventricular myocytes, using the whole-cell patch clamp technique, real-time PCR and Western blotting. Incubation with 10 nM aldosterone for 17-24 hours significantly accelerates the rate of spontaneous beating by increasing diastolic depolarization. If current elicited by hyperpolarization from -50 mV to -130 mV significantly increases by 10nM aldosterone (by 1.9 fold). Exposure to aldosterone for 1.5 hours increases HCN2 mRNA by 26.3 % and HCN4 mRNA by 47.2 %, whereas HCN1 mRNA expression remains unaffected. Aldosterone (24 hours incubation) increases the expression of HCN2 protein (by 60.0 %) and HCN4 protein (by 84.8 %), but not HCN1 protein. MR antagonists (1 µM eplerenone or 0.1 µM spironolactone) abolish the increase of If channel expression (currents, mRNA and protein levels) by 10 nM aldosterone. In contrast, 1 µM aldosterone down-regulated If channel gene expression. Glucocorticoid receptor antagonist (100 nM RU38486) did not affect the increase of If current by 10 nM aldosterone. These findings suggest that aldosterone in physiological concentrations up-regulates If channel gene expression by MR activation in cardiac myocytes and may increase excitability, which may have a potential proarrhythmic bearing under pathophysiological conditions.
