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Binding characteristics of a membrane receptor that recognizes 1α25‐dihydroxyvitamin D 3 and its epimer, 1β,25‐dihydroxyvitamin D 3
Author(s) -
Baran Daniel T.,
Ray Rahul,
Sorensen Ann Marie,
Honeyman Thomas,
Holick Michael F.
Publication year - 1994
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240560411
Subject(s) - calcitriol receptor , epimer , vitamin d and neurology , dissociation constant , receptor , chemistry , steroid hormone , membrane , steroid , stereochemistry , biophysics , endocrinology , biochemistry , hormone , biology
The Steroid hormon 1α, @5‐Dihydroxyvitamin D 3 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 D 3 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 3 H‐1α,25dihydroxyvitamin D 3 by vitamin D compounds, as well as the apparent dissociation constant of 1α25‐dihydroxyvitamin D 3 and its 1β epimer for the memberane receptor in membrane prepration from ROS 24/1 cells. Increasing concentrations of 1α25‐dihydroxyvitamin D 3 , 7.25 nM to 725 nM, displaced 3 H‐1α25‐dihydrxyvitamin D 3 from the membranes with 725 nM of the hormone displacing 40–49% of the radioactivity. Similarly, 1β,25‐dihydroxyvitamin D 3 , 7.25 nM and 72.5 nM, displaced 1α25‐dihydroxyvitamin D 3 binding while 25‐hydroxyvitamin D 3 , 7.25 nM, did not. The apparent dissociation constant (K D ) for 1α25‐dihydroxyvitamin D 3 was detrermined from displacement of 3 H‐1α25‐dihydroxyvitamin D 3 yielding a value of 8.1 × 10 −7 M by Scatchard analysis. The K D for the 1β epimer determine from displacement of 3 H‐1α25‐dihydroxyvitamin D 3 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 D 3 and its 1β epimer, but not 25‐dihydroxyvitamin D 3 . 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.