1,25-Dihydroxyvitamin D3 inhibits Na (+) -dependent phosphate transport in osteoblastic cells
Green, J.; Luong, K.V.; Kleeman, C.R.; Ye, L.H.; Chaimovitz, C.
American Journal of Physiology 264(2 Pt 1): C287-C295
1993
ISSN/ISBN: 0002-9513 PMID: 8447362 Document Number: 406147
The influence of vitamin D3 metabolites on Na+-dependent phosphate (Pi) transport in the clonal osteoblastic cell line UMR-106 was studied. 1,25(OH)2D3 dose-dependently inhibited Pi transport with a half-maximal concentration of ~5 x 10-11 M. The effect of 1,25(OH)2D3 was first observed after 8 h of preincubation. 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-[superscript 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 estimation of intracellular Pi showed a 50% reduction after a 24-h preincubation with 10-8M 1,25(OH)2D3. It is concluded 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.