Mineralocorticoid Receptor-Like Aldosterone-Binding Protein in Cell Culture*

Receptors for mineralocorticoids have been characterized in kidney and to a lesser extent in certain extrarenal tissues but these receptors have not yet been identified in cells in culture. In the current studies we report the presence of mineralocorticoid receptor-like aldosterone-binding proteins in cloned lines of cultured rat pituitary tumor cells (GC, GH3 sublines) that synthesize and secrete GH and, in some cases, PRL. The apparent Kd of these sites for aldosterone determined from a Scatchard analysis of the binding by intact cells at 37 C is 1 nM, and about 8000 sites per cell were detected. The affinity of the receptors for several steroids is in the order of 9a-fluorocortisol > aldosterone > deoxycorticosterone > cortisol > prednisolone » dexamethasone ≍β-methasone > testosterone > triamcinolone ≍ estradiol. In intact cells and under cell-free conditions, aldosterone stimulates a temperature-dependent nuclear binding of these binding proteins. Under the cell-free conditions, this is inhibited by ...