Chromatographic studies on interconversions of “non-activated” and “activated” forms of glucocorticoid-receptor complexes from rat heart cytosol

Abstract

These studies focus on the activation of glucocorticoid-receptor complexes in heart, a tissue that, despite its importance as a glucocorticoid target, has received relatively little study in terms of its receptors. DEAE-Sephadex A50 mini-column chromatography of 3H-dexamethasone-receptor complexes from rat heart cytosol reveals two peaks of bound hormone, which, by elution characteristics, correspond to “non-activated” and “activated” forms of liver cytosol glucocorticoid-receptor complexes. An increase in temperature to 20°C or treatment with 10 mM theophylline or 0.4 M KCl causes transformation of receptor-bound [ 3H]-dexamethasone from the peak of non-activated to the peak of activated form; 10 mM ATP does not influence this process. Molybdate ions (1−100 mM) completely block activation of glucocorticoid-receptor complexes, and fluoride ions (100 mM) do so partially. Moreover, molybdate can also transform temperature-activated complexes to the non-activated form. This inhibiting effect persists after removal of free molybdate ions from the medium. These data imply that the mechanism of glucocorticoid-receptor complex activation in heart resembles that in other glucocorticoid-responsive tissues. However, the finding that molybdate can reverse the conversion of receptors from the non-activated to the activated form, as judged by DEAE-Sephadex chromatography, differs from previous reports. This result implies that, if molybdate prevents receptor inactivation by blocking dephosphorylation (as has been proposed), the ion must also act in some other way as well in promoting the reversal.