Evidence for the presence of specific binding sites for corticoids in mouse liver plasma membranes

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Abstract
The specific binding of [3H]cortisol to plasma membranes purified from mouse liver, studied by the ultrafiltration method, shows the existence of specific binding sites for cortisol. The kinetic parameters of this binding areK D=4.4nm andB max=685 fmol/mg protein in presence of 1 μm of corticosterone. With respect to the binding of 4nm [3H]cortisol to the membrane, the affinities of the steroids decreased in the following order: deoxycorticosterone>corticosterone>progesterone>cortisol >prednisolone>testosterone>20β-hydroxyprogesterone >cortisone. Estradiol, dexamethasone, ouabain and triamcinolone acetonide do not have affinity for this binding site. Neither Ca2+ nor Mg2+ affected the binding of [3H]cortisol to the plasma membranes. Likewise, the presence of agonists and antagonists of alpha and beta-adrenergic receptors did not modify the binding of [3H]cortisol. The results suggest that the plasma membrane binding site characterized is more specific for corticoids and is different from nuclear glucocorticoid and progesterone receptors.

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