MONOCLONAL-ANTIBODIES AGAINST THE PUTATIVE DIVALENT CATION-RECEPTOR THAT IS LOCATED ON PARATHYROID CELLS DO NOT STAIN ISOLATED RAT OSTEOCLASTS

It has been reported that osteoclastic function is regulated by calciu m-induced alterations in cytoplasmic free calcium ([Ca2+]i), possibly through a specific receptor. We have investigated whether osteoclasts, isolated from neonatal rat long bones, possess the divalent cation-re ceptor that has been demonstrated on parathyroid cells. Studies with f ura-2 loaded adherent single cells showed that an increase in extracel lular Ca2+ ([Ca2+]e) from 0.5 mM to 10 mM resulted in an increase in [ Ca2+]i in isolated rat osteoclasts, from a basal value of 94.7 +/- 16. 2 to 150.6 +/- 22.4 nM (means +/- SEM; n = 14). The shape and time cou rse of the [Ca2+]i increase varied considerably from cell to cell. Les s than half of the cells responded with a rapid transient increase whe reas the rest responded with a slow increase that reached a plateau wi thin 1-2 minutes. When [Ca2+]e was changed back to 0.5 mM, a slow decr ease in [Ca2]i was monitored. Immunohistochemical staining with two di fferent monoclonal antibodies, recognizing the putative Ca2+ receptor on parathyroid cells, did not indicate any staining on freshly isolate d rat osteoclasts. Thus, our data demonstrate that an increase in [Ca2 +]e causes an elevation of [Ca2+]i in osteoclasts. This increase is no t mediated via the putative cation-receptor found on parathyroid cells .