Identification and characterization of a sodium/calcium exchanger, NCX-1, in osteoclasts and its role in bone resorption.
We provide the first demonstration for a Na+/Ca2+ exchanger, NCX-1, in the osteoclast. We speculate that by using Na+ exchange, NCX-1 couples H+ extrusion with Ca2+ fluxes during bone resorption. Microspectrofluorimetry of fura-2-loaded osteoclasts revealed a rapid and sustained, but reversible, cytosolic Ca2+ elevation upon Na+ withdrawal. This elevation was abolished by the cytosolic introduction (by gentle permeabilization) of a highly specific Na+/Ca2+ exchange inhibitor peptide, XIP, but not its inactive analogue, sXIP. Confocal microscopy revealed intense plasma membrane immunofluorescence with an isoform-specific monoclonal anti-NCX-1 antibody applied to gently permeabilized osteoclasts. Electrophysiological studies using excised outside-in membrane patches showed a low-conductance, Na+-selective, dichlorobenzamil-sensitive, amiloride-insensitive channel that we tentatively assigned as being an NCX. Finally, to examine for physiological relevance, an osteoclast resorption (pit) assay was performed. There was a dramatic reduction of bone resorption following NCX-1 inhibition by dichlorobenzamil and XIP (but not with S-XIP). Together, the results suggest that a functional NCX, likely NCX-1, is involved in the regulation of osteoclast cytosolic Ca2+ and bone resorption.
Moonga
B S
BS
Mount Sinai Bone Program, Department of Medicine, Mount Sinai School of Medicine, and Bronx Veteran's Affairs Geriatric Research Education and Clinical Center, New York, New York 10029, USA.
Davidson
R
R
Sun
L
L
Adebanjo
O A
OA
Moser
J
J
Abedin
M
M
Zaidi
N
N
Huang
C L
CL
Zaidi
M
M
D000818:Animals; D001862:Bone Resorption; D002478:Cells, Cultured; D007150:Immunohistochemistry; D008564:Membrane Potentials; D010010:Osteoclasts / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000737:chemistry / Q000378:metabolism*
D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1