THE OSTEOCLAST AS A UNICELLULAR PROTON-TRANSPORTING EPITHELIUM

Osteoclasts dissolve bone mineral by the vectorial secretion of hydrogen ion at their osseous attachment site. To accomplish this, the osteoclast employs a vacuolar H+ ATPase that is polarized to the specialized proton-secreting plasma membrane domain, the ruffled border. Physiologically and biochemically, they resemble the specialized proton-secreting intercalated cells of the renal collecting duct, which also use a polarized vacuolar H+ ATPase to effect trans-epithelial hydrogen ion transport. Studies on the mechanism of hydrogen ion transport by the kidney may therefore provide insights into the control of acid secretion by the osteoclast.