Effect of riluzole on cytosolic Ca²⁺ increase in human osteosarcoma cells

In human osteosarcoma MG63 cells, the effect of the neuroprotective drug riluzole on the intracellular Ca²⁺ concentration ([Ca²⁺]_i) was measured using fura-2. Riluzole (50-500 μmol/l) caused a rapid and sustained plateau increase in [Ca²⁺]_i in a concentration-dependent manner (EC₅₀ = 150 μmol/l). The riluzole-induced rise in [Ca²⁺]_i was prevented by 58 and 20% by extracellular Ca²⁺ removal and nifedipine, respectively, but was not changed by La³⁺ and verapamil. In Ca²⁺-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum (ER) Ca²⁺-ATPase, caused a monophasic increase in [Ca²⁺]_i, after which the increasing effect of riluzole on [Ca²⁺]_i was attenuated by 84%; also, pretreatment with riluzole abolished the thapsigargin-induced [Ca²⁺]_i increase. U73122, an inhibitor of phospholipase C, abrogated the ATP (but not riluzole)-induced rise in [Ca²⁺]_i. A low concentration (6 μmol/l) of riluzole selectively potentiated the bradykinin (but not ATP and histamine)- induced increase in [Ca²⁺]_i. These results suggest that riluzole rapidly increases [Ca²⁺]_i by stimulating both the extracellular Ca²⁺ influx via a nifedipine-sensitive pathway and intracellular Ca²⁺ release from the ER via an as yet unidentified mechanism(s).