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Am J Physiol Cell Physiol 264: C287-C295, 1993;
0363-6143/93 $5.00
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AJP - Cell Physiology, Vol 264, Issue 2 C287-C295, Copyright © 1993 by American Physiological Society

ARTICLES

1,25-Dihydroxyvitamin D3 inhibits Na(+)-dependent phosphate transport in osteoblastic cells

J. Green, K. V. Luong, C. R. Kleeman, L. H. Ye and C. Chaimovitz
Laboratory of Membrane Biology, Research Institute, Cedars-Sinai Medical Center, University of California School of Medicine, Los Angeles 90048.

In the present work we investigated the influence of vitamin D3 metabolites on Na(+)-dependent phosphate (Pi) transport in the clonal osteoblastic cell line UMR-106. The vitamin D3 metabolite 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] dose-dependently inhibited Pi transport with a half-maximal concentration of approximately 5 x 10(-11) M. The effect of 1,25(OH)2D3 was first observed after 8 h of preincubation period. Inhibition of phosphate uptake was relatively specific for the 1,25(OH)2D3 analogue of vitamin D3. The potency order was 1,25(OH)2D3 >> 24,25-dihydroxyvitamin D3 > 25-[3H]hydroxyvitamin D3. Kinetically, 1,25(OH)2D3 decreased the maximal velocity of the phosphate uptake system, whereas the affinity for phosphate was unaffected. Activation of protein kinase C (PKC) in UMR-106 cells stimulated Na(+)-dependent Pi transport. Nonetheless, the inhibitory effect of 1,25(OH)2D3 on Pi transport was not related to downregulation of PKC. Chemical determination of intracellular Pi showed a 50% reduction after 24-h preincubation with 10(-8) M 1,25(OH)2D3. We conclude that 1,25(OH)2D3 inhibits Na(+)-dependent phosphate transport in osteoblastic cells. This in turn leads to intracellular Pi depletion. The physiological implication of this phenomenon on the effects of vitamin D on osteoblasts in situ is discussed.


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[Abstract] [Full Text] [PDF]


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