Extracellularly applied ruthenium red and cyclic adp ribose elevate
cytosolic ca2+ in isolated rat osteoclasts.
Adebanjo, Olugbenga A., Vijai S. Shankar, Michael Pazianas, Bruce J.
Simon, F. Anthony Lai, Christopher L. H. Huang, and Mone Zaidi.
The Bone Research Unit, Division of Biochemical Medicine, St.
George's Hospital Medical School, London SW17 0RE, UK; Division of
Endocrinology and Metabolism and Center for Osteoporosis, University
of Arkansas College of Medicine, and GRECC at the VA Hospital, Little
Rock AR 72205, USA; National Institute for Medical Research, Mill
Hill, London, UK; The Physiological Laboratory, University of
Cambridge, Cambridge CB2 3EG, UK
APStracts 2:0187F, 1995.
We have demonstrated recently that the divalent cation-sensing
receptor on the osteoclast, the Ca2+ receptor (CaR), is a functional
component of a cell-surface expressed ryanodine receptor-like
molecule (RyR). The objective of the present study was to further
characterize this putative RyR using the two well-known cell
-impermeant RyR modulators, ruthenium red and cyclic adenosine
diphosphate ribose (cADPr). We found that, when applied
extracellularly, both ruthenium red (5 x 10-8 M to 10-4 M) and cADPr
(5 x 10-6 M) triggered an elevation of cytosolic [Ca2+].
Depolarization of the cell membrane by the application of 0.1 M-[K+]
in the presence of 5 x 10-6 M-valimomycin resulted in a
concentration-dependent increase in the magnitude of the cytosolic
Ca2+ response to extracellular ruthenium red (5 x 10-9 and 5 x 10-5
M), a phenomenon that was not seen when osteoclasts were
hyperpolarized using 5 x 10-3 M-[K+] with 5 x 10-6 M-valimomycin. In
the presence of an intact, non-leaky, cell membrane, these results
would favor a plasma membrane locus of action for the two modulators.
Furthermore, pretreatment of osteoclasts with either modulator
resulted in a markedly attenuated cytosolic Ca2+ transient elicited
in response to the CaR agonist, Ni2+, thus confirming an interaction
between the cADPr- and ruthenium red-sensitive sites and the
osteoclast CaR. The inhibition of the cytosolic Ca2+ response to Ni2+
induced by ruthenium red remained unchanged in the face of membrane
potential changes. Finally, the cytosolic Ca2+ response to caffeine
(5 x 10-4 M), another RyR modulator, was also strongly attenuated by
pretreatment with ruthenium red (5 x 10-9 M). We conclude that both
ruthenium red and cADPr act on plasma membrane-resident sites, and
that both these sites interact with the process of divalent cation
-sensing.
Received 14 June 1995; accepted in final form 20 September 1995.
APS Manuscript Number F191-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95