Aldosterone nuclear receptors in kidneys of chick embryo

We have studied the properties of the nuclear receptors for aldosterone in kidneys of chick embryo. Aliquots of 0.4 M KO nuclear extracts were incubated with [ 3H]aldosterone with or without 1 μM RU28362, a potent glucocorticoid analog. Scatchard analyses of binding data revealed two classes of binding sites with K a of 0.26 and 0.03 × 10 9 M −1 and N max of 330 fmol and 620 fmol/mg DNA respectively. In presence of RU28362, however, we observed only a single class of binding sites with a K a of 1.02 × 10 8 M −1 and a N max of 90 fmol/mg DNA. Competition studies performed in presence of RU28362 showed that aldosterone was the more effective competitor followed by corticosterone, progesterone, deoxycorticosterone, dexamethasone, cortisol, triamcinolone acetonide and cortisone. The nuclear complexes had a sedimentation coefficient in the area of 8 S which changed to 4–5 S in the presence of 0.4 M KCl. This effect of KCl was prevented by the addition of 10 mM sodium molybdate. Always in the presence of the glucocorticoid analog, by DEAE-c chromatography we observed a major specific aldosterone-binding fraction which was eluted with 0.2 M KCl. This fraction sedimented at 8.4 S in the absence of sodium molybdate and KCl. In the absence of RU28362, DNA-c columns retained only a small portion of the nuclear complexes which were eluted with KCl. These complexes sedimented, on sucrose gradient, at 4.6 and 3.1 S, whereas those which did not bind to DNA-c had a sedimentation coefficient of 8 S. In the presence of RU28362, the majority of bound [ 3H]aldosterone remained in the column flow-through fraction; when this fraction was further analyzed on DEAE-c, complexes were eluted with 0.2 and 0.3 M KCl. These data indicate that nuclear receptors for aldosterone are present in small number in kidneys of chick embryo and that they are mostly in the 8 S form.