Possible heterogeneity of glucocorticoid receptors: Studies on liver and heart cytosols

Abstract

After incubation of liver and heart cytosol preparations with 4 × 10 −8 M [ 3H]-TA (triamcinolone acetonide), passing the incubate through a phosphocellulose (PC) column, thermal activation, and chromatography on a second PC-column, three glucocorticoid-binding components were found, which eluted at about 0.32 M, 0.43 M and 0.51 M KCl. Fractions detected are believed to be specific glucocorticoid-binding proteins, since their labeling by [ 3H]-TA is eliminated by heating the cytosol for 30 min at 37°C or the addition of excess non-labeled TA. The first glucocorticoid-binding component is readily absorbed during passage of thermally activated cytosol through DEAE-cellulose while the two latereluting components are more weakly retained by this synthetic polycation. These components interact with DNA-cellulose and can be eluted in the narrow range of elute KCl concentrations. The values of [ 3H]-TA-binding to the liver glucocorticoid-binding fractions are several times higher than for heart cytosol. Nevertheless, three peaks of the activated form of heart cytosol receptor complexes can be detected, more or less evidently, at the same elution positions on the PC column at various endocrine states of animals, in normal female and male subjects, in experimental thyreotoxicosis, and in glucocorticoid deficiency caused by adrenalectomy. In the latter case specific [ 3H]-TA binding was increased more than 2-fold in each of the three glucocorticoid-binding fractions. Incorporation of [ 3H]-TA into the three glucocorticoid-binding fractions of heart cytosol is severely depressed by a 100-fold excess of non-labeled deoxycorticosterone (DOC), while in liver cytosol preparations diluted as much as 5-fold and containing amounts of [ 3H]-TA receptor complexes comparable to that of heart cytosol, this cannot be achieved. Estimation of specific [ 3H]-aldosterone binding to heart cytosol of both intact and adrenalectomized rats showed that none of the glucocorticoid-binding fractions described can be attributed to a “pure” mineralocorticoid receptor.