Glucocorticoid receptors in rat kidney cortical tubules enriched in proximal and distal segments.

Cytoplasmic and nuclear binding of [3H]triamcinolone acetonide was assessed in isolated rat kidney cortical tubules, enriched in distal (fraction A) or in proximal segments (fraction B). The concentration dependence of specific [3H]triamcinolone acetonide binding in cytoplasm was determined (range = 4.4 X 10(-10) to 2.1 X 10(-7) M) and analyzed by a least-squares curve-fitting method. A single, high-affinity binding class with a dissociation constant of 1 X 10(-8) M (25 degrees C) was obtained in both fractions A and B. Based on competition for the [3H]triamcinolone acetonide sites, the following sequence of affinities was obtained: triamcinolone acetonide = dexamethasone > progesterone = corticosterone > d-aldosterone > 17 beta-estradiol. These specificities imply that these sites are glucocorticoid receptors. Fraction B contained 1.6 times more cytosol sites for [3H]triamcinolone acetonide than fraction A (5.0 +/- 0.5 X 10(-13) vs. 3.0 +/- 0.5 X 10(-13) mol/mg protein). In the presence of a onefold excess of d-aldosterone specific cytoplasmic binding of [3H]triamcinolone acetonide was 1.4-fold greater in fraction B than in fraction A, and specific nuclear binding was 1.3-fold greater in fraction B than in fraction A (5.1 +/- 0.6 X 10(-13) vs 4.0 +/- 0.5 X 10(-13) mol/mg DNA). These results and the measured lengths of proximal and distal tubules yielded estimates of a higher proximal content (three- to sixfold) compared to distal content of glucocorticoid receptors.