Effects of angiotensin II on sodium potassium pumps, endogenous ouabain, and aldosterone in bovine zona glomerulosa cells

Angiotensin (Ang) II stimulates secretions of aldosterone and an endogenous ouabain-like steroid (EO) from bovine adrenal zona glomerulosa (BAG) cells . The BAG cell sodium pump, a possible target of EO, affects aldosterone se cretion although little is known about this pump. Here, we describe the eff ects of Ang II on the characteristics of this transporter and steroid secre tions. Under serum-free conditions, H-3-ouabain bound to a single class of sites on BAG cells. Binding of label was time and concentration dependent, was sensitive to extracellular potassium ions, and was displaced by ouabain and digoxin with EC50 of approximate to 218 and approximate to 232 nmol/L, respectively. Sodium pump-mediated Rb-86 uptake was inhibited by ouabain ( EC50 approximate to 301 nmol/L). Ang II dose dependently augmented secretio ns of EO and aldosterone, increased ouabain-sensitive Rb-86 uptake and H-3- ouabain binding, and increased the affinity for H-3-ouabain binding (K-d, f rom 205 to 80 nmol/L) with no change in the maximal number of sodium pumps (5.45X10(6)) per cell. Losartan blacked all effects of Ang II except EO sec retion, which was inhibited by PD123319. We conclude that BAG cells express sodium pumps in high density and bind ouabain to a single class of low-aff inity sites. The characteristics of the sodium pumps protect BAG cells from EO autotoxicity but may exclude them from mediating feedback inhibition of EO secretion. The effects of Ang II on sodium pump activity, ouabain bindi ng affinity, and aldosterone secretion are mediated via Ang II type 1 recep tors, whereas Ang II type 2 receptors augment EO secretion. The role of the Ang II-mediated increase in the ouabain sensitivity of BAG cell sodium pum ps in the secretions of aldosterone and EO remains to be elucidated.