A Ras-Dependent Chloride Current Activated by Adrenocorticotropin in Rat Adrenal Zona Glomerulosa Cells

Abstract

In the present study, we report that ACTH induces a transient chloride current. The lack of correlation between ACTH-induced cAMP production and amplitude of the Cl− current, as well as the absence of stimulation by forskolin or 8Br-cAMP indicated that the ACTH-induced current was not cAMP-dependent. We explored the possibility that one or several elements of the Ras/Raf MAPK cascade were involved. Indeed, we found that ACTH at 10−10m induced activation of Ras. Inhibition of the current by QEHA peptide, a Gβγ sequestrant, demonstrated that Gβγ subunits transduced the message. Blockage of the Ras activation using an inhibitor of farnesyl transferase (BZA-5B) or the monoclonal antibody H-Ras(259) abrogated the current. Moreover, the addition of Ras-GTPγS in the pipette medium gave rise to the Cl− current. Treatment of the cells with BZA decreased the aldosterone secretion induced by 10−10m ACTH but not that induced by 10−8m ACTH, confirming the involvement of Ras in steroid secretion. We conclude that ACTH triggers a Cl− current through the activation of the Ras protein by Gβγ subunits. This current, activated at physiological ACTH concentrations (1 to 100 pm) where cAMP production is very low, could play a significant role in aldosterone production.