Modulating ALDH2 reveals a differential dependence on ROS for hypertrophy and SR Ca²⁺ release in aldosterone-treated...

Growing evidence links high aldosterone levels with atrial fibrillation and other heart diseases. Here, we have investigated the functional consequences of culturing adult rat atrial myocytes with aldosterone, at the level of cell size, homeostasis of Ca²⁺, reactive oxygen species (ROS), and nitrogen oxide (NO). The protein levels of NO synthase (NOS), aldehyde dehydrogenase 2 (ALDH2), NADPH oxidase (NOX), and Na⁺-Ca²⁺ exchanger (NCX) were also studied. Aldosterone did not alter the expression of these proteins, except for the NCX, which was enhanced by nearly 100%. Additionally, the hormone inhibited and stimulated, respectively, the production of NO and ROS (the effect on ROS appeared after 24 h of treatment and reached a maximum by 4-6 days, with an EC₅₀ of 1.2 nM). These changes in reactive species generation were blunted by tetrahydrobiopterin (BH₄, a NOS cofactor), suggesting the involvement of an uncoupled NOS. An activator (Alda-1) and an inhibitor (daidzin) of ALDH2 were used, to determine if this enzyme activity is related to aldosterone effects, through possible modulation of ROS. Aldosterone produced a ∼10% increase in cell size and, remarkably, this hypertrophic effect, along with the corresponding changes in ROS and NO, were all mimicked by daidzin and prevented by Alda-1. Something different happened with SR Ca²⁺ release. Aldosterone increased both the magnitude of Ca²⁺ transients and the incidence of spontaneous Ca²⁺ oscillations, but these actions were not reproduced by daidzin. Moreover, rather than being prevented, they were further promoted by Alda-1, which also increased the rate of SR Ca²⁺ reuptake. These results suggest that NOS and ALDH2 may prevent some adverse consequences of aldosteronism (in the case of ALDH2, at the expense of exacerbating SR Ca²⁺ release). Our data also suggest a hierarchical model in which aldosterone promotes: SR Ca²⁺ release, then ROS production, and finally hypertrophy.