[Microcinematographic study of in vitro fusion between blood monocytes and differentiated osteoclasts]

The cell cycle of osteoclasts is hard to define, because regularly new nuclei enter in, and old nuclei are extruded from these polynucleated elements. The "transit-time" of a single nucleus averages 9-11 days in dogs and the factors conditioning this renewal are unknown. With the aim of elucidating in vitro the conditions necessary for the entrance of new nuclei in the polycarions, cultures of purified osteoclasts from medullary bone of laying hens and monocytes from circulating blood of the same animals have been performed after a previous period of 5 days of separate cultures each one of these two cell types. Part of the monocytes added to the osteoclast cultures, after a variable period of time entered in the polycarions by an active process of membrane fusion. Some phases of the process have been visualized at phase contrast and confirmed by time-lapse microcinematography and scanning electron microscopy.