EXPRESSION OF THE SODIUM-CHLORIDE COTRANSPORTER IN OSTEOBLAST-LIKE CELLS - EFFECTS OF THIAZIDE DIURETICS

The use of thiazide diuretics is associated with increased bone minera l density and, in some studies, with reduced incidence of fractures, s uggesting a potential role for these drugs in the treatment of osteopo rosis. Our objective was to examine the effects of thiazides on osteob last-like cells using the rat UMR-106 osteosarcoma cell line. Treatmen t of UMR-106 cells with chlorothiazide caused membrane depolarization and a rise of intracellular calcium but had no effect on adenosine 3', 5'-cyclic monophosphate accumulation. The rise of intracellular calciu m was partially inhibited by nifedipine and removal of extracellular c alcium, indicating calcium uptake from the extracellular media, as wel l as by thapsigargin or dantrolene, indicating contributions from calc ium release from intracellular stores. Reverse transcriptase-polymeras e chain reaction was used to isolate a partial cDNA clone for the thia zide-sensitive sodium-chloride cotransporter from UMR-106 cells that h ybridized to 5.0- and 11.0-kilobase mRNAs when Northern blot analysis was conducted. Antisense oligonucleotides to the sodium-chloride cotra nsporter specifically inhibited the chlorothiazide-induced depolarizat ion and rise of intracellular calcium and reduced immunofluorescence s taining for the sodium-chloride cotransporter protein in UMR-106 cells . We conclude that thiazide diuretics inhibit sodium-chloride cotransp orter activity in UMR-106 cells, thereby altering intracellular calciu m regulation. These results provide evidence for direct effects of thi azide diuretics on bone cells.