We examined changes in electrical and morphological properties of rat osteoclasts in response to prostaglandin (PG)E2. PGE2 (>10 nM) stimulated an outwardly rectifying Cl− current in a concentration-dependent manner and caused a long-lasting depolarization of cell membrane. This PGE2-induced Cl− current was reversibly inhibited by 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), and tamoxifen. The anion permeability sequence of this current was I− > Br− ≈ Cl− > gluconate−. When outwardly rectifying Cl− current was induced by hyposmotic extracellular solution, no further stimulatory effect of PGE2 was seen. Forskolin and dibutyryl adenosine 3′,5′-cyclic monophosphate (DBcAMP) mimicked the effect of PGE2. The PGE2-induced Cl− current was inhibited by pretreatment with guanosine 5′- O-2-(thiodiphosphate) (GDPβS), Rp-adenosine 3′,5′-cyclic monophosphorothioate (Rp-cAMPS), N-(2-[ p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide dihydrochloride (H-89), and protein kinase A inhibitors. Even in the absence of nonosteoclastic cells, PGE2 (1 μM) reduced cell surface area and suppressed motility of osteoclasts, and these effects were abolished by Rp-cAMPS or H-89. PGE2 is known to exert its effects through four subtypes of PGE receptors (EP1–EP4). EP2 and EP4 agonists (ONO-AE1-259 and ONO-AE1-329, respectively), but not EP1 and EP3 agonists (ONO-DI-004 and ONO-AE-248, respectively), mimicked the electrical and morphological actions of PGE2 on osteoclasts. Our results show that PGE2 stimulates rat osteoclast Cl− current by activation of a cAMP-dependent pathway through EP2 and, to a lesser degree, EP4 receptors and reduces osteoclast motility. This effect is likely to reduce bone resorption.
Inhibitory Effect of LGS and ODE Isolated from the Twigs of Syringa oblata subsp. dilatata on RANKL-Induced Osteoclastogenesis in Macrophage Cells