The
mineralocorticoid receptor has been implicated in the development of several cardiac pathologies and could participate in the high incidence of lethal ventricular arrhythmias associated with
hyperaldosteronism. We have observed previously that
aldosterone markedly increases in vitro the rate of spontaneous contractions of isolated neonate rat ventricular myocytes, a putative proarrhythmogenic condition if occurring in vivo. In the present study, we investigated the effect of
glucocorticoids, the involvement of the
glucocorticoid receptor, and the modulation of their action by redox agents.
Aldosterone and
glucocorticoids exerted in vitro a similar, concentration-dependent chronotropic action on cardiomyocytes, which was mediated by both the
mineralocorticoid and
glucocorticoid receptors. However, the relative contribution of each receptor was different for each agonist, at each concentration.
Angiotensin II induced a similar response that was entirely dependent on the activity of the
glucocorticoid receptor.
Corticosteroid action was modulated by the redox state of the cells, with oxidation increasing the response while reducing conditions partially preventing it. When only the
mineralocorticoid receptor was functionally present in the cells, oxidation was necessary to reveal
glucocorticoid action, but no obvious competition with
mineralocorticoids was observed when both agonists where simultaneously present. In conclusion,
corticosteroids exert a strong chronotropic action in ventricular cardiomyocytes, mediated by both the
mineralocorticoid and
glucocorticoid receptors and modulated by the redox state of the cell. This phenomenon is believed to be because of cell electric remodeling and could contribute in vivo to the deleterious consequence of inappropriate receptor activation, leading to increased susceptibility of patients to arrhythmias.