Evidence for the Presence of a Proton Pump of the Vacuolar H+- ATPase Type in the Ruffled Borders of Osteoclasts

Microsomal membrane vesicles prepared either from chicken medullary bone or isolated osteoclasts were shown to have ATP-dependent H+-transport activity. This activity was N-ethylmaleimide-sensitive but resistant to oligomycin and orthovanadate, suggesting a vacuolar-type ATPase. Furthermore, immunological cross-reactivity of 60- and 70-kD osteoclast membrane antigens with Neurospora crassa vacuolar ATPase was observed when analyzed by immunoblotting. Same antibodies labeled only osteoclasts in chicken and rat bone in immunohistochemistry. Immunoelectronmicroscopy localized these antigens in apical membranes of rat osteoclasts and kidney intercalated cells of inner stripe of outer medulla. Pretreatment of animals with parathyroid hormone enhanced the immunoreaction in the apical membranes of osteoclasts. No immunoreaction was seen in osteoclasts when antibodies against gastric H+, K+- ATPase were used. These results suggest that osteoclast resorbs bone by secreting protons through vacuolar H+- ATPase.