Electrophysiological characterization of ion channels in osteoclasts isolated from human deciduous teeth

Ion channels contribute to several important processes in osteoclasts, including proton transport and volume regulation. Although ion channels have been described in osteoclasts from several species, little is known about their properties in human osteoclasts. We devised a method for isolation of authentic human osteoclasts from deciduous teeth undergoing root resorption, and characterized currents in these cells using patch-clamp techniques. Three types of K+ current were identified. Hyperpolarization elicited an inwardly rectifying K+ current in most osteoclasts, which was inhibited by Ba2+ in a voltage- and time-dependent manner. Depolarization elicited an outwardly rectifying and tetraethylammonium-sensitive current, consistent with a large-conductance Ca2+-dependent K+ channel. In addition to these basal currents, extracellular adenosine 5′-triphosphate (ATP) elicited a linear current that was identified as a Ca2+-dependent K+ current, based on its reversal potential close to that predicted for K+, its blockade by quinine, and its activation by Ca2+ ionophore. Last, an outwardly rectifying current was observed to activate spontaneously or in response to ATP, with properties of a swelling-activated Cl− current. This current reversed direction close to the Cl− equilibrium potential and was blocked by the anion channel blocker, niflumic acid, identifying it as a Cl− current. In summary, we have developed a novel method for isolation of authentic human osteoclasts and have characterized K+ and Cl− currents. Cl− current mediates charge compensation during electrogenic H+ transport, so activation of Cl− current may contribute to the stimulatory effects of extracellular ATP on bone resorption.