Corticosteroids increase intracellular free sodium ion concentration via glucocorticoid receptor pathway in cultured neonatal rat cardiomyocytes

Background

Glucocorticoids as well as mineralocorticoid have been shown to play essential roles in the regulation of electrical and mechanical activities in cardiomyocytes. Excess of these hormones is an independent risk factor for cardiovascular disease. Intracellular sodium ([Na⁺]_i) kinetics are involved in cardiac diseases, including ischemia, heart failure and hypertrophy. However, intrinsic mediators that regulate [Na⁺]_i in cardiomyocytes have not been widely discussed. Moreover, the quantitative estimation of altered [Na⁺]_i in cultured cardiomyocytes and the association between the level of [Na⁺]_i and the severity of pathological conditions, such as hypertrophy, have not been precisely reported.

Methods and results

We herein demonstrate the quantitative estimation of [Na⁺]_i in cultured neonatal rat cardiomyocytes following 24 h of treatment with corticosterone, aldosterone and dexamethasone. The physiological concentration of glucocorticoids increased [Na⁺]_i up to approximately 2.5 mM (an almost 1.5-fold increase compared to the control) in a dose-dependent manner; this effect was blocked by a glucocorticoid receptor (GR) antagonist but not a mineralocorticoid receptor antagonist. Furthermore, glucocorticoids induced cardiac hypertrophy, and the hypertrophic gene expression was positively and significantly correlated with the level of [Na⁺]_i. Dexamethasone induced the upregulation of Na⁺/Ca^{2 +} exchanger 1 at the mRNA and protein levels.

Conclusions

The physiological concentration of glucocorticoids increases [Na⁺]_i via GR. The dexamethasone-induced upregulation of NCX1 is partly involved in the glucocorticoid-induced alteration of [Na⁺]_i in cardiomyocytes. These results provide new insight into the mechanisms by which glucocorticoid excess within a physiological concentration contributes to the development of cardiac pathology.