Bisphosphonates (BPs) reduce bone pain and fractures by balancing the osteoblast/osteoclast ratio. The behavior of ion channels in the presence of BPs is not known. To investigate this, the effect… Click to show full abstract
Bisphosphonates (BPs) reduce bone pain and fractures by balancing the osteoblast/osteoclast ratio. The behavior of ion channels in the presence of BPs is not known. To investigate this, the effect of zoledronic acid BP (ZOL) (3 × 10−8 to 5 × 10−4 M) treatment, on ion channels, cell proliferation, and mineralization, has been investigated on preosteoclast-like cells, RAW264.7, preosteoblast-like cells MC3T3-E1, and rat/mouse native bone marrow-derived osteoblasts. In whole-cell patch clamp on cell line- and bone marrow-derived osteoblasts, ZOL potentiated outward currents. On RAW264.7, ZOL (10−4 M)-evoked current was reduced by the Kv channel blocker tetraethylammonium hydrochloride (TEA), but not by the selective TRPV1-channel antagonist capsazepine. On MC3T3-E1 cells and bone marrow-derived osteoblasts, ZOL-evoked current (5 × 10−8 to 10−4 M) was reduced by capsazepine, whereas the selective TRPV1-channel agonist capsaicin potentiated the control current. In the cell proliferation assay, 72 h incubation of RAW264.7 and MC3T3-E1 cells with ZOL reduced proliferation, with IC50 values of 2.62 × 10−7 M and 2.02 × 10−5 M, respectively. Mineralization of MC3T3-E1 cells and bone marrow-derived osteoblasts was observed in the presence of capsaicin and ZOL (5 × 10−8–10−7 M); ZOL effects were antagonized by capsazepine. In summary, the ZOL-induced activation of TRPV1 channel mediates the mineralization of osteoblasts and counterbalances the antiproliferative effects, increasing the IC50. This mechanism is not operative in osteoclasts lacking the TRPV1 channel.
               
Click one of the above tabs to view related content.