Fluoride selectively stimulates Na-dependent phosphate transport in osteoblast-like cells

The influence of fluoride (F) on the transport of Pi was investigated in the osteoblast-like cell line UMR-106. Exposure of cells to F induced a dose-related stimulation of the Na-coupled Pi transport. Pi transport was significantly increased 6 h after 1 mM F incubation, with maximal response observed at 24 h (F 38.0 +/- 2.3, vehicle 19.8 +/- 1.2 pmol.micrograms DNA-1.4 min-1; P less than 0.001). Na-dependent alanine transport was not changed by F. The selective effect of F on Pi transport was not associated with changes in adenosine 3',5'-cyclic monophosphate, cell proliferation, or alkaline phosphatase activity. However, it was completely blunted by inhibiting translational processes with cycloheximide. Furthermore, F enhanced the stimulatory effect on Pi transport of various mitogens such as fetal calf serum, insulin, and insulin-like growth factor I. In conclusion, F can selectively enhance the activity of the Pi transport system present in the plasma membrane of UMR 106 osteoblast-like cells by a mechanism that probably involves newly synthetized proteins.