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  • Title: Cultured osteoblasts from normal and hypophosphatemic mice: calcitriol receptors and biological response to the hormone.
    Author: Delvin EE, Richard P, Desbarats M, Ecarot-Charrier B, Glorieux FH.
    Journal: Bone; 1990; 11(2):87-94. PubMed ID: 2162697.
    Abstract:
    The content and affinity of calcitriol receptors were analyzed in cultured osteoblasts from normal and hypophosphatemic mice. Hypertonic cell extracts were prepared by sonication followed by centrifugation at 200,000 g x 30 min. Analysis, at saturating levels of labeled 1,25(OH)2D3, revealed that binding of the hormone was dependent on the density of the cells plated and on the length of time in culture. It reached a maximum at 5 days of culture when 1.0 x 10(6) cells were plated. Under those conditions the binding capacity of Hyp osteoblasts was 6306 +/- 1267 sites/ng protein (mean +/- SEM) not different from N cells (7594 +/- 1713). The dissociation constant (Kd) was 18.3 +/- 5.4 and 20.0 +/- 5.7 pM for mutant and normal mouse osteoblasts respectively (NS). In both genotypes, a single peak for specific binding, migrating at approximately 3.0-3.5 S was observed by sucrose gradient centrifugation. 25-hydroxycholecalciferol-24-hydroxylase (24-OHase) was induced at 1 and 10 nM 1,25(OH)2D3 in a dose-dependent fashion. However, the induction was higher in mutant than in normal cells when the medium contained 1 mM and 2 mM phosphate salts. The difference vanished when cells were incubated in the presence of 3 and 4 mM phosphate salts. The effect of calcitriol on cultured osteoblasts was also analyzed in terms of collagen synthesis and alkaline phosphatase activity. In the range of 10(-10) M to 10(-7) M, 1,25(OH)2D3 was found to inhibit collagen synthesis in a dose-dependent fashion. At physiological levels, 1,25(OH)2D3 (10(-11)M-10(-10)M), stimulated alkaline phosphatase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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