Abstract
The vacuolar type H+-ATPase (V-ATPase) expressed in the plasma membrane is the the primary proton secreting mechanism responsible for osteoclastic bone resorption. The V-ATPase is a multi-subunit complex composed of a membrane sector (V0) and a catalytic sector (V1). Since V0 acts as a passive H+ conductor, voltage may be a key controller for the H+ secretion. We examined voltage-dependency of the H+ transport via H+-translocating component of V0, subunit c: the cDNA was obtained from murine osteoclasts, cloned and expressed in COS7 cells. The pH recovery from cell acidosis in transformed cells were recorded under a variety of pH gradients. Cations and anions were replaced by NMDG+ and aspartate−. At the pH gradient of 1.8, outward currents were increased by depolarization. The I-V curve shifted to more positive voltages by acidifying the extracellular solution. N,N,-Dicyclohexylcarbodiimide (DCCD), an inhibitor of subunit c, blocked the depolarization-dependent pH recovery and the outward currents. These data suggest that depolarization potentiates H+ efflux via subunit c localized at the plasma membrane. The membrane potential of osteoclasts, changing over a wide range (-120-0 mV), may regulate the H+ secretion in the absence of ATP-hydrolysis. [Jpn J Physiol 54 Suppl:S69 (2004)]
