ISSN:
0730-2312
Keywords:
osteoblast 24/1
;
receptor
;
calcium channels
;
vitamin D
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
The Steroid hormon 1α, @5-Dihydroxyvitamin D3 has been shown to expert rapid effect (15 s to 5 min) in osteoblast. These occur in osteoblast-like cells lacking the nuclear vitamin D receptor, ROS 24/1, suggesting that a separate signalling system mediates the rapid action. These non-genomic action include rapid activation of phospholipase C and opening of calcium channels, pointing to a membrane localization of this signalling system. Previous studies have shown that the 1β epimer of 1α25-dihydroxyvitamina D3 can block these rapid action, indicating that the 1β epimer may bind to the recptor responsible for the rapid action sin a competative manner. We have assessed the displacement of 3H-1α,25dihydroxyvitamin D3 by vitamin D compounds, as well as the apparent dissociation constant of 1α25-dihydroxyvitamin D3 and its 1β epimer for the memberane receptor in membrane prepration from ROS 24/1 cells. Increasing concentrations of 1α25-dihydroxyvitamin D3, 7.25 nM to 725 nM, displaced 3H-1α25-dihydrxyvitamin D3 from the membranes with 725 nM of the hormone displacing 40-49% of the radioactivity. Similarly, 1β,25-dihydroxyvitamin D3, 7.25 nM and 72.5 nM, displaced 1α25-dihydroxyvitamin D3 binding while 25-hydroxyvitamin D3, 7.25 nM, did not. The apparent dissociation constant (KD) for 1α25-dihydroxyvitamin D3 was detrermined from displacement of 3H-1α25-dihydroxyvitamin D3 yielding a value of 8.1 × 10-7 M by Scatchard analysis. The KD for the 1β epimer determine from displacement of 3H-1α25-dihydroxyvitamin D3 was 4.8 × 10-7 M. The data suggest the presence of a receptor on the membrane of ROS 24/1 cells that reconize 1α25-dihydroxyvitamin D3 and its 1β epimer, but not 25-dihydroxyvitamin D3. Its ability to reconize the 1β epimer which appears to be a specific anagonist of the rapid effect of the hormone suggests that these studies may be the initial steps in the isolation and characterization of the signalling system mediating the rapid action of vitamin D.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcb.240560411
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