DEMONSTRATION OF A 1,25-DIHYDROXYCHOLECALCIFEROL CYTOPLASMIC RECEPTOR-LIKE BINDER IN MOUSE KIDNEY

Abstract

Isolated mouse renal tubule cells have been employed to demonstrate the presence of a specific highaffinity cytoplasmic binding protein for 1,25-dihydroxycholecalciferol (1,25(OH)₂D₃) in kidney. This receptorlikemacromolecule sedimented at 3.2 S in hypertonic sucrose density gradients. Scatchard analysis of [³H]1,25-(OH)₂D₃ binding at 0 C revealed an apparent K_d of 0.2 nM and a concentration of binding sites of 50 fmol/mg cytosol protein. In competition experiments, the binder exhibited a low affinity for other vitamin D₃ metabolites;the order of potency was 1,25(OH)₂D₃ » 25OHD₃ > I01OHD₃ > 24R,25(OH)₂D₃. The sedimentation properties,binding affinity, and specificity of this 1,25(OH)₂D₃ binding protein are strikingly similar to the receptors inrat intestine, mouse bone, and human intestine. The demonstration of a renal receptor-like binder adds furthersupport to theconcept that the kidney_is a 1,25(OH)₂D₃ target organ.