MODULATION OF THE OSTEOCLAST CA2- POSSIBLE LINKAGE BETWEEN CA2+ SENSING AND EXTRACELLULAR ACIDIFICATION( RECEPTOR BY EXTRACELLULAR PROTONS )

We report a sensitivity of the osteoclast cell surface Ca2+ receptor t o extracellular protons. Freshly isolated rat osteoclasts were exposed to the known agonists of the Ca2+ receptor, Ca2+ and Ni2+, in extrace llular solutions set at different pH values. Decreasing the extracellu lar pH from 7.8 to 4.0 units markedly potentiated the cytosolic Ca2+ s ignals elicited in response to Ca2+ receptor activation by either Ni2 (50 mu M, 500 mu M or 5 mM) or Ca2+ (5 mM). Each response consisted o f a rapid and usually transient elevation of cytosolic [Ca2+]. Maximal cytosolic [Ca2+] responses were obtained at pH values of 6.6 (for 5 m M-[Ni2+]) and 4.0 units (for 5 mM-[Ca2+]). Finally, the effects of ext racellular pH persisted in Ca2+-free, EGTA-containing solutions, sugge sting a modulation of intracellular Ca2+ release. (C) 1994 Academic Pr ess, Inc.