Expression of the na-cl cotransporter in osteoblast-like cells:
effects of thiazide diuretics.
Barry, Elizabeth L. R., Frank A. Gesek, Mark R. Kaplan, Steven C.
Hebert, and Peter A. Friedman.
Department of Pharmacology and Toxicology, Dartmouth Medical
School, Hanover, New Hampshire 03755; and Department of Medicine,
Brigham and Women's Hospital and Harvard Medical School, Boston,
Massachusetts 02115
APStracts 3:0264C, 1996.
The use of thiazide diuretics is associated with increased bone
mineral density and, in some studies, with reduced incidence of
fractures suggesting a potential role for these drugs in the
treatment of osteoporosis. Our objective was to examine the effects
of thiazides on osteoblast-like cells using the rat UMR-106
osteosarcoma cell line. Treatment of UMR-106 cells with
chlorothiazide caused membrane depolarization and a rise of
intracellular calcium ([Ca2+]i), but had no effect on cAMP
accumulation. The rise of [Ca2+]i was partially inhibited by
nifedipine and removal of extracellular calcium, indicating calcium
uptake from the extracellular media, as well as by thapsigargin or
dantrolene, indicating contributions from calcium release from
intracellular stores. Reverse transcriptase-PCR was used to isolate a
partial cDNA clone for the thiazide-sensitive sodium-chloride
cotransporter from UMR-106 cells that hybridized to 5.0 and 11.0 kB
mRNAs upon Northern blot analysis. Antisense oligonucleotides to the
sodium-chloride cotransporter specifically inhibited the
chlorothiazide-induced depolarization and rise of [Ca2+]i, and
reduced immunofluorescence staining for the sodium-chloride
cotransporter protein in UMR-106 cells. We conclude that thiazide
diuretics inhibit sodium-chloride cotransporter activity in UMR-106
cells thereby altering intracellular calcium regulation. These
results provide evidence for direct effects of thiazide diuretics on
bone cells.
Received 11 April 1996; accepted in final form 24 July 1996.
APS Manuscript Number C200-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996