Abstract
Vacuolar-type ATPase (V-ATPase) located in osteoclast plasma membrane transports protons, and forms an acidic environment essential for bone resorption. During differentiation to osteoclasts, expression of V-ATPase subunits increases. In this study, we investigated ATPase activity and subunit association of this enzyme, using osteoclasts differentiated in vitro, in order to understand the role and regulation of the enzymatic activity during differentiation. Unexpectedly, the specific activity decreased in osteoclasts, compared to that in progenitor cells. Furthermore, V-ATPase subunits dissociated each other in osteoclasts. These results indicate that the subunits do not function as proton pumps even though they increase in osteoclasts. It is likely that osteoclasts need to attach to bone to receive a signal to form functional V-ATPase on the plasma membrane.
