Phospholipase C-dependent Ca2+-sensing pathways leading to endocytosis and inhibition of the plasma membrane vacuolar H+-ATPase in osteoclasts.
In osteoclasts, elevation of extracellular Ca2+ is an endogenous signal that inhibits bone resorption. We recently found that an elevation of extracellular Ca2+ decreased proton extrusion through the plasma membrane vacuolar H+-ATPase (V-ATPase) rapidly. In this study we investigated mechanisms underlying this early Ca2+-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 Ca2+ (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 Ca2+ 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 Ca2+-induced endocytosis and inhibition of the V-ATPase current were diminished by a phospholipase C inhibitor (U73122) and siRNA targeting for phospholipase C gamma2 subunit. Holding the cytosolic Ca2+ at either high (0.5-5 microM) 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 Ca2+ facilitated dynamin- and V-ATPase-dependent endocytosis in association with an inhibition of the plasma membrane V-ATPase. Phospholipase C, cytosolic Ca2+, and calmodulin were involved in the signaling pathways. Membrane retrieval and the plasma membrane V-ATPase activity may cooperate during the early phase of Ca2+-sensing response in osteoclasts.
Sakai
Hiromu
H
Department of Physiology, Graduate School of Medicine, Osaka City University, Japan.
Moriura
Yoshie
Y
Notomi
Takuya
T
Kawawaki
Junko
J
Ohnishi
Keiko
K
Kuno
Miyuki
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D034281:Dynamins / Q000378:metabolism; D025802:Electric Capacitance; D004705:Endocytosis; D005110:Extracellular Space / Q000378:metabolism; D051379:Mice; D010010:Osteoclasts / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000502:physiology*; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors* / Q000502:physiology
D002147:Calmodulin; D010738:Type C Phospholipases; D025262:Vacuolar Proton-Translocating ATPases; D034281:Dynamins; D002118:Calcium