INVESTIGADORES
SCODELARO BILBAO Paola Gabriela
congresos y reuniones científicas
Título:
Participation of a protein phosphatase in the regulation of intracellular calcium concentration in osteoblasts by olpadronate and lidadronate
Autor/es:
GRACIELA SANTILLÁN,; KATZ SEBASTIÁN,; STOCKMAN GASTÓN,; SCODELARO BILBAO, PAOLA GABRIELA; MORELLI SUSANA,; RICARDO BOLAND,; ROLDÁN EMILIO,
Lugar:
Rio de Janeiro
Reunión:
Congreso; IOF World Congress on Osteoporosis; 2004
Institución organizadora:
International Osteoporosis Foundation (IOF)
Resumen:
In previous studies we found that the bisphosphonates (BPs)
olpadronate (OPD) and NH2-olpadronate (lidadronate; LID) are
able to regulate, in the short term, cytosolic Ca2+ levels ([Ca2+]i)
in ROS 17/2.8 rat osteoblastic-like cells. This effect is dependent
on prestimulation with the osteotropic agent ATP and due mainly
to influx of the cation from the outside through voltage-operated
calcium channels (VDCC) and purinergic activation of PLC. In
the present work, we evaluated the mechanism by which these BPs
modulate the Ca2+ response in osteoblasts. By using Fura-2-
loaded ROS17/2.8 cells, cytoplasmic Ca2+ changes were recorded
by fluorimetry. The bisphosphonate-induced rapid changes in
[Ca2+]i were not observed in a Ca2+ )free medium or in medium
with 1.5 mM Ca2+ plus 5 lM nifedipine or 5 lM verapamil,
involving extracellular Ca2+influx through VDCC channels in
BPs effects. The protein phosphatase inhibitors orthovanadate
and sodium fluoride mimicked the purinergic-dependent BPs-induced
Ca2+ response at low concentrations (1200 lM) but at
higher levels caused a more sustained Ca2+influx blocking the
action of BPs. Previous binding assays using [3H]-olpadronate in
whole cells showed the presence of a specific, saturable and high
affinity binding site for OPD. We now observed that an important
proportion of the BPs binder is located in the osteoblast plasma
membrane. In addition, like olpadronate and lidadronate, 8 mM
p-nitro-phenylphosphate or a´ -naphthylphosphate (phosphatase
substrates), compete for binding to this site, whereas purinergic
agonists and antagonists, and both protein phosphatase inhibitors
(0.28 mM) did not displace [3H]OPD. These results suggest the
existence of cell membrane target for bisphosphonates, presumably
a protein phosphatase, through which BPs modulate the
purinergic Ca2+signaling and in turn trigger a cellular response in
osteoblasts.