OSTEOCLASTS EXPRESS THE B2 ISOFORM OF VACUOLAR H-ATPASE INTRACELLULARLY AND ON THEIR PLASMA-MEMBRANES()

Osteoclasts express high levels of vacuolar H+-ATPase (V-ATPase) in th eir ruffled membranes, driving the secretion of H+ required for normal bone resorption. Previous reports have suggested that the B subunit o f the osteoclast V-ATPase differs from those expressed in kidney and o ther tissues. In this study, B subunit isoform-specific antibodies and cDNA probes were used to examine which B subunit isoform is expressed in osteoclasts and osteoclast-like cells. Immunoblotting and RNA hybr idization analysis were used to demonstrate that cells from an osteocl ast-rich mouse bone marrow culture model express the B2 but not the B1 subunit isoform. Immunocytochemical staining of murine osteoclasts ge nerated in vitro and of native rat osteoclasts in bone sections showed that the B2 but not the B1 isoform was expressed at high levels and w as polarized to the ruffled membrane. Human marrow cultures and monocy te-derived macrophages, used as models for osteoclasts, also expressed the B2 but not the B1 subunit isoform. These results indicate that V- ATPases containing the B2 subunit isoform mediate osteoclast bone reso rption.