title: Highly specific binding of 1,25-dihydroxycholecalciferol in bone cytosol.
abstract: A method developed initially for the detection of high-affinity binding of glucocorticoids in the cytosol from foetal rat calvaria has been adapted for metabolites of vitamin D. Consistent displacement of [3H]1,25-dihydroxycholecalciferol ([3H]1,25(OH)2D3) by unlabelled 1,25(OH)2D3 was obtained with an apparent dissociation constant (Kd) of 2.3 x 10(-9) mol/l. The specificity of this binding was examined by competition experiments. Displacement of labelled 1,25(OH)2D3 by a 100-fold excess of unlabelled metabolites, expressing the fall with unlabelled 1,25(OH)2D3 as 100%, was as follows: 25-hydroxycholecalciferol (25(OH)D3), 61%; 24,25-dihydroxycholecalciferol, 29%; cholecalciferol, 3%. These are similar to results for the chick mucosa nuclear 1,25(OH)2D3 receptor. No displacement was obtained with corticosterone, testosterone, oestradiol or progesterone. When [3H]25(OH)D3 was used as ligand, a displacement curve with unlabelled 25(OH)D3 indicated only binding with a greater Kd (approximately 10(-7) mol/l). These data suggest a direct action of 1,25(OH)2D3 on bone which is similar to that of steroid hormones on their target tissues.
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000196:embryology / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004100:Dihydroxycholecalciferols / Q000378:metabolism*; D006887:Hydroxycholecalciferols / Q000378:metabolism*; D008722:Methods; D051381:Rats
chemical_list: D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols