Application of ion-selective microelectrodes to the detection of calcium release during bone resorption

In this work we apply calcium ion-selective liquid membrane microelectrodes to the investigation of the release of ionised calcium in real-time from bovine cortical bone slices in the presence of osteoclasts. The osteoclast is the cell responsible for the resorption (dissolution) of bone and excess bone resorption is implicated in diseases such as osteoporosis. Pretreatment of the bone slice with dilute solutions of ammonium fluoride was found to result in greater resistance to osteoclastic resorption. However, a detectable calcium Bur was still observed indicating that the cells were able to attach to the fluoride treated bone and carry out resorption. These data were confirmed by scanning electron microscopy which indicated that the number of bone resorption pits was not affected by the fluoride treatment, although the excavated area was markedly decreased in the presence of fluoride. The results of these studies indicate that the use of calcium-selective microelectrodes provide a feasible alternative assay of osteoclast activity to the conventional electron microscopic assay. The microelectrode technique enables real-time data to be obtained, whereas the conventional method requires a long (ca. 16-20 h) incubation of the cells on the bone slice. (C) 1999 Elsevier Science Ltd. All rights reserved.