Chronic Effects of Aldosterone on Cardiac EC Coupling and Oxidant Stress

Our previous work investigated the role of aldosterone in the function of atrial myocytes. Among other effects, aldosterone promoted a striking 2-fold increase in the density of Ca2+ current (ICa) and a moderated increase of 30% in cell membrane capacitance (Cm, suggesting hypertrophy). Ca2+ and ROS were identified to participate but only on the effect on Cm. The objective of this work was twofold: (a) to determine whether aldosterone regulates ROS generation; and (b) to reexamine the potential of aldosterone to increase ICa, using a low Ca2+ buffering internal solution—this allows recording Ca2+ transients as well. Adult rat cardiomyocytes were chronically incubated with 1 μM aldosterone. Subsequently, ICa and Ca2+ transients were recorded under whole-cell patch clamp. CM-H2CDFDA was used to monitor ROS. Under the present conditions, aldosterone did not alter the peak amplitude of ICa. However, it promoted a significative increase in the magnitude of both Cm and Ca2+ transients (20-50%). The caffeine-sensitive Ca2+ store was not significantly altered, indicating an enhancement of the gain of excitation-contraction coupling at constant SR Ca2+ load. As suspected, aldosterone promoted a 75% increase in ROS production, which: became evident after 2-d of treatment, reaches a maximum in 4-6d, and presents an EC50 of 1.2 nM (Hill coefficient of 0.9). This effect may be explained by a potential regulation of the activity/expression of NADPH oxidase (NOX) and aldehyde dehydrogenase (ALDH). Thus, we used activators (Alda-1) and inhibitors (daidzin) of ALDH and found that they can either, prevent (Alda-1) or reproduce (daidzin) the stimulated ROS production. The possible contribution of NOX has yet to be examined along with the potential of these enzymes to mediate hypertrophy. These results may contribute to explaining a previously observed correlation between aldosterone levels and atrial dysfunction.