Phospholipase C-dependent Ca 2+-sensing pathways leading to endocytosis and inhibition of the plasma membrane vacuolar H +-ATPase in osteoclasts

摘要

In osteoclasts, elevation of extracellular Ca 2+ is an endogenous signal that inhibits bone resorption. We recently found that an elevation of extracellular Ca 2+ decreased proton extrusion through the plasma membrane vacuolar H +-ATPase (V-ATPase) rapidly. In this study we investigated mechanisms underlying this early Ca 2+-sensing response, particularly in reference to the activity of the plasma membrane V-ATPase and to membrane retrieval. Whole cell clamp recordings allowed us to measure the V-ATPase currents and the cell capacitance (C m) simultaneously. C m is a measure of cell surface. Extracellular Ca 2+ (2.5-40 mM) decreased C m and the V-ATPase current simultaneously. The decreased C m, together with the enhanced uptake of a lipophilic dye (FM1-43), indicated that Ca 2+ facilitated endocytosis. The endocytosis was blocked by dynamin inhibitors (dynasore and dynamin-inhibitory peptide), by small interfering RNA (siRNA) targeting for dynanmin-2 and also by bafilomycin A 1, a blocker of V-ATPases. The extracellular Ca 2+-induced endocytosis and inhibition of the V-ATPase current were diminished by a phospholipase C inhibitor (U73122) and siRNA targeting for phospholipase C γ2 subunit. Holding the cytosolic Ca 2+ at either high (0.5-5 μM) or low levels or inhibiting calmodulin by an inhibitor (W7) or an antibody (anti-CaM) decreased the stimulated endocytosis and the inhibition of the V-ATPase current. These data suggest that extracellular Ca 2+ facilitated dynamin- and V-ATPase-dependent endocytosis in association with an inhibition of the plasma membrane V-ATPase. Phospholipase C, cytosolic Ca 2+, and calmodulin were involved in the signaling pathways. Membrane retrieval and the plasma membrane V-ATPase activity may cooperate during the early phase of Ca 2+-sensing response in osteoclasts.