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

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Abstract
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 .times. 10-10-2.1 .times. 10-7 M) and analyzed by a least-squares curve-fitting method. A single, high-affinity binding class with a dissociation constant of 1 .times. 10-8 M (25.degree. 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 .mchgt. 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 .times. 10-13 vs. 3.0 .+-. 0.5 .times. 10-13 mol/mg protein). In the presence of a 1-fold 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 .times. 10-13 vs. 4.0 .+-. 0.5 .times. 10-13 mol/mg DNA). These results and the measured lengths of proximal and distal tubules yielded estimates of a higher proximal content (3- to 6-fold) compared to distal content of glucocorticoid receptors.

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