Aldosterone increases T-type calcium currents in human adrenocarcinoma (H295R) cells by inducing channel expression

In adrenal glomerulosa cells, low-threshold voltage-activated (T-type) calc ium channels are known to play a crucial role in coupling physiological var iations of extracellular potassium to aldosterone biosynthesis. On the othe r hand, aldosterone itself has been recently shown to regulate Ca2+ current s in its target cells. In the present study, we have investigated the effec t of aldosterone on Ca2+ channels of the steroidogenic human adrenocarcinom a cell line, using both electrophysiological and molecular techniques. Cell incubation with aldosterone (1 mum) for 24 h increased by 39% the density of T-type calcium currents, as assessed with the patch clamp technique. Thi s effect of aldosterone was not related to a modification of T channel acti vation and inactivation properties. In contrast, L-type calcium currents re mained unaffected by aldosterone treatment. The mineralocorticoid receptor antagonist, spironolactone, blunted the aldosterone-induced increase in T-t ype calcium current. By RT-PCR, we detected in human adrenocarcinoma cells the presence of mRNA coding for the alpha (1) subunits of three different c alcium channels and the alpha C-1 and alpha D-1 isoform of L channels. The presence of mRNA coding for the mineralocorticoid receptor was also found i n these cells. Aldosterone treatment induced a 36% increase of mRNA coding for alpha D-1, as assessed by real-time PCR. This aldosterone-evoked stimul ation of mRNA expression was maximal at 24-48 h and reversed by spironolact one, suggesting a receptor-mediated genomic effect of aldosterone. Pregneno lone production in response to KCl stimulation was increased after aldoster one treatment, in parallel to T channel expression, confirming the essentia l role of these channels in the steroidogenic response to potassium. Taken together, these data indicate that, in human adrenocarcinoma cells, aldoste rone increases, through an autocrine pathway, the expression of T-type calc ium channels and therefore modifies the ability of these cells to respond t o steroidogenic agonists.