[Characterization of dexamethasone-binding protein from the rat myocardium]

Kinetic and apparent equilibrium studies of the binding reaction steroid + receptor in equilibrium with steroid - receptor (SR) reveal a specific binding of dexamethasone and several other synthetic and natural glucocorticoids to a limited number of binding sites in the myocardium cytosol. In contrast to the binding sites of natural steroids the dexamethasone binding sites are heat sensitive. In the sucrose gradient with a low ionic strength, SR-complex sedimented at 9.5 S, heating to 25 degrees C for 20 min or increase in the ionic strength lead to a decrease in the molecular weight of the complex. A rapid temperature-dependent nuclear uptake of cytoplasmic SR-complexes was demonstrated, which was not saturable at physiologic concentrations of SR-complexes and a low ionic strength of the incubation media. All the described properties of dexamethasone-binding protein are characteristic of receptors involved in the biological effects of glucocorticoids.