Modulation of the osteoclast Ca2+ receptor by extracellular protons: possible linkage between Ca2+ sensing and extracellular acidification.
We report a sensitivity of the osteoclast cell surface Ca2+ receptor to extracellular protons. Freshly isolated rat osteoclasts were exposed to the known agonists of the Ca2+ receptor, Ca2+ and Ni2+, in extracellular solutions set at different pH values. Decreasing the extracellular pH from 7.8 to 4.0 units markedly potentiated the cytosolic Ca2+ signals elicited in response to Ca2+ receptor activation by either Ni2+ (50 microM, 500 microM or 5 mM) or Ca2+ (5 mM). Each response consisted of a rapid and usually transient elevation of cytosolic [Ca2+]. Maximal cytosolic [Ca2+] responses were obtained at pH values of 6.6 (for 5 mM-[Ni2+]) and 4.0 units (for 5 mM-[Ca2+]). Finally, the effects of extracellular pH persisted in Ca(2+)-free, EGTA-containing solutions, suggesting a modulation of intracellular Ca2+ release.
Adebanjo
O A
OA
Bone Unit, St. George's Hospital Medical School, London, U.K.
Shankar
V S
VS
Pazianas
M
M
Zaidi
A
A
Simon
B
B
Huang
C L
CL
Zaidi
M
M
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D016257:Fura-2; D006863:Hydrogen-Ion Concentration; D009532:Nickel / Q000494:pharmacology; D010010:Osteoclasts / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013050:Spectrometry, Fluorescence
D002135:Calcium-Binding Proteins; D004533:Egtazic Acid; D009532:Nickel; D002118:Calcium; D016257:Fura-2