Further chemical differentiation of type I and type II adrenocorticosteroid receptors in mouse brain cytosol: evidence for a new class of glucocorticoid receptors.

There are at least two classes of intracellular receptors for adrenocorticosteroid hormones in brain. Type I receptors have a high affinity for the naturally occurring gluco- and mineralocorticoids, corticosterone (CORT) and aldosterone (ALDO), respectively, and a very low affinity for synthetic glucocorticoids such as dexamethasone (DEX). type II receptors have a high affinity for the synthetic glucocorticoids, a lower affinity for CORT and a very low affinity for ALDO. In recent studies with mouse brain cytosol we have found a number of other biochemical differences between these two receptor types. In the present study, brain cytosol from adrenalectomized mice was prepared in HEPES buffer and subjected to various potentially inactivating treatments prior to assessment of Type I and Type II receptor specific binding capacity by incubation for 24 h at 0 degrees C with [3H]ALDO +/- [1H]RU 26988 (to prevent or permit the cross-binding of [3H]ALDO to Type II receptors) or [3H]DEX +/- [1H]Prorenone (to prevent or permit the cross-binding of [3H]DEX to Type I receptors), respectively. These studies revealed that 10-20% of the high-affinity (Kd = 3 nM) [3H]DEX specific binding capacity remained even after extensive, high concentration and repeated pretreatments with dextran-coated charcoal (DDC. to remove endogenous sulfhydryl-reducing reagents and other biochemicals). These procedures had little effect on Type I receptors. Further analyses revealed that DCC-resistant [3H]DEX binders were not Type I receptors since they were not saturated by [1H]Prorenone. These binders were also not inactivated by aging steroid-free cytosol at 0 degree C or by treating it with buffers containing 0.3 M KCl. Since these