Steroid receptors in osteoblasts.
Using the whole-cell incubation system at 37 degrees C, the specific bindings for 3H-dexamethasone, 3H-estradiol-17 beta, 3H-dihydrotestosterone and 3H-R5020 were measured in the purified, putative osteoblasts isolated from fetal rat calvaria by collagenase digestion. More than 90% of the purified cells contained intense alkaline phosphatase activity. The specific binding for 3H-dexamethasone with high affinity and low capacity was demonstrated in the isolated osteoblasts. Most of the binding was found in the nuclear fraction, indicating nucler binding of the 3H-dexamethasone-receptor complex. The apparent dissociation constant (Kd) for 3H-dexamethasone was estimated to be 3.3 x 10(-9)M and the number of binding sites was calculated to be 65 fmol/ml (4 x 10(6) cells) or 9,750 binding sites per cell. High salt: sucrose gradient analysis of nuclear extracts revealed a radioactive 4.0 S peak. These results indicate that the purified osteoblasts are among the target cells for glucocorticoids. On the other hand, the specific bindings for 3H-estradiol-17 beta and 3H-dihydrotestosterone were not detectable in the isolated osteoblasts, which suggests that estrogens and androgens act on osteoblasts only indirectly.
D000818:Animals; D001667:Binding, Competitive; D003907:Dexamethasone / Q000378:metabolism; D013196:Dihydrotestosterone / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism*; D011397:Promegestone / Q000378:metabolism; D051381:Rats; D011987:Receptors, Steroid / Q000378:metabolism*
D011987:Receptors, Steroid; D013196:Dihydrotestosterone; D004958:Estradiol; D003907:Dexamethasone; D011397:Promegestone