A comparison of the glucocorticoid receptor in cytosol from rat liver and hippocampus.

The [3H]corticosterone- and [3H]dexamethasone-binding proteins in cytosol from liver and hippocampus of the rat were compared by isoelectric focusing analysis in slabs of polyacrylamide gel. A single peak of radioactivity with a pI of 6.1--6.2 was obtained during analysis of cytosol from both liver and hippocampus using either corticosterone or dexamethasone as radiolabelled ligand, provided the tissue was carefully perfused with buffer prior to preparation of cytosol. Rat serum or insufficiently perfused tissue contained a corticosterone-binding component with pI of 5.2--5.5 representing corticosteroid-binding globulin. Limited trypsin digestion resulted in fragmentation of the dexamethasone- and corticosterone-binding protein in cytosol from liver and hippocampus. Incubation of radiolabelled cytosol with 0.5 microgram of trypsin/A280--310nm of cytosol gave a sharp radioactive peak with a pI of 5.9--6.1 when analyzed by isoelectric focusing; when 5.0 microgram of trypsin/A280--310nm of cytosol was used, a double peak with pI values of 5.9--6.1 and 6.3--6.5, respectively, was seen. The same trypsin-induced peaks were seen with both [3H]dexamethasone and [3H]corticosterone as ligands. The substrate specificity and the sensitivity of this glucocorticoid binder for limited trypsin digestion is in good agreement with what was previously found for the glucocorticoid receptor in rat liver cytosol. It is concluded that cytosol from liver and hippocampus contains an identical or very similar receptor for glucocorticoid hormones.