Motility and resorption: osteoclastic activity in vitro

Rabbit osteoclasts (OCs), separated mechanically from long bones, were seeded on to glass or plastic substrates or slabs of sperm whale dentine (SWD). Cells were cultured in MEM with 10% FCS with or without added salmon calcitonin (SCT) at dosages of 0.001, 0.1 and 1 IU/ml. Although most rabbit SCT-treated OCs on the non-biological substrates showed inhibition of peripheral ruffling activity and motility at dosages that stop rat OC movement, resorption still occurred on the dentine. Thus such inhibition is unreliable as a general indicator for resorptive capability. Resorption lacunae were observed at all times from 6 h onwards. Using stereophotogrammetric techniques, the following minimum values were obtained from 24 h cultures: highest hourly rate of resorption of dentine for single OC, 570 micron3/h; average rate 165 micron3/h; mean total volume dentine removed per Howship's lacuna complex, 3,885 micron3; average value for plan area of surface attacked per OC, 1,450 micron2.