Monoclonal antibodies against the putative divalent cation-receptor that is located on parathyroid cells do not stain isolated rat osteoclasts.

Abstract

It has been reported that osteoclastic function is regulated by calcium-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-receptor that has been demonstrated on parathyroid cells. Studies with fura-2 loaded adherent single cells showed that an increase in extracellular 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 course of the [Ca2+]i increase varied considerably from cell to cell. Less than half of the cells responded with a rapid transient increase whereas the rest responded with a slow increase that reached a plateau within 1-2 minutes. When [Ca2+]e was changed back to 0.5 mM, a slow decrease in [Ca2+]i was monitored. Immunohistochemical staining with two different monoclonal antibodies, recognizing the putative Ca2+ receptor on parathyroid cells, did not indicate any staining on freshly isolated rat osteoclasts. Thus, our data demonstrate that an increase in [Ca2+]e causes an elevation of [Ca2+]i in osteoclasts. This increase is not mediated via the putative cation-receptor found on parathyroid cells.