Immunoreactivity to a monoclonal antibody (OS-3) is shared by osteoclasts and bicarbonate-secreting cells

OS-3, a monoclonal antibody raised against macrophagic cells derived from c ultured rat glomeruli, reacts with the plasma membrane of various bicarbona te-secreting cells such as epithelial cells of the pancreatic excretory duc t and type IP intercalated cells of the kindney, suggesting that the antige nic molecule of OS-3 is involved in bicarbonate production and/or secretion , Since osteoclasts must vigorously extrude bicarbonate to maintain cytopla smic pH in a physiologic range during proton secretion, we examined the loc alization of OS-3 immunoreactivity in the bone tissue to determine the invo lvement of the detected molecule in the transmembrane transport of bicarbon ate in osteoclasts. The OS-3 selectively stained the basolateral plasma mem brane of osteoclasts. Ultrastructurally, the immunoreactivity with OS-3 was associated with small cytoplasmic projections and microplicae of the basol ateral plasma membrane. This finding suggests that osteoclasts express the molecule common to bicarbonate-secreting cells to utilize it for bicarbonat e transport during bone resorption.