Effect of the neuroprotective agent riluzole on intracellular Ca2+ levels in IMR32 neuroblastoma cells

Riluzole is an effective neuroprotective drug. Its effect on intracellular free Ca2+ levels ([Ca2+](i)) has not been explored. This study examined the effect of riluzole on [Ca2+](i) in IMR32 neuroblastoma cells using fura-2 as a Ca2+ probe. Riluzole 0.1-1 mM increased [Ca2+](i) in a concentration-d ependent manner. Removal of extracellular Ca2+ inhibited the response by 52 +/- 5%. The [Ca2+](i) increase induced by 0.2 mM riluzole was unaltered by 0.1 mM La3+ or 10 muM verapamil, but was inhibited by 51 +/- 4% by 10 muM nifedipine. In Ca2+ -free medium, pretreatment with 1 muM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) reduced the 0.2 mM riluzole-indu ced Ca2+ release by 44 +/-3%; this reduction was augmented to 66 +/-5% by a dditionally depleting the Ca2+ stores in the Golgi complex with 50 muM bref eldin A. Inhibition of inositol 1,4,5-trisphosphate formation by 2 muM U731 22, a phospholipase C inhibitor. did not affect Ca2+ release induced by 0.2 muM riluzole. It was concluded that the neuroprotective agent riluzole inc reased [Ca2+](i) in IMR32 neuroblastoma cells concentration-dependently by releasing Ca2+ from multiple stores in an inositol 1,4,5-trisphosphate-inde pendent manner and also by inducing nifedipine-sensitive Ca2+ influx.