Effect of the neuroprotective agent riluzole on intracellular Ca ²⁺ levels in IMR32 neuroblastoma cells

Riluzole is an effective neuroprotective drug. Its effect on intracellular free Ca ²⁺ levels ([Ca ²⁺] _i) has not been explored. This study examined the effect of riluzole on [Ca ²⁺] _i in IMR32 neuroblastoma cells using fura-2 as a Ca ²⁺ probe. Riluzole 0.1-1 mM increased [Ca ²⁺] _i in a concentration-dependent manner. Removal of extracellular Ca ²⁺ inhibited the response by 52±5%. The [Ca ²⁺] _i increase induced by 0.2 mM riluzole was unaltered by 0.1 mM La ³⁺ or 10 μM verapamil, but was inhibited by 51±4% by 10 μM nifedipine. In Ca ²⁺ -free medium, pretreatment with 1 μM thapsigargin (an endoplasmic reticulum Ca ²⁺ pump inhibitor) reduced the 0.2 mM riluzole-induced Ca ²⁺ release by 44±3%; this reduction was augmented to 66±5% by additionally depleting the Ca ²⁺ stores in the Golgi complex with 50 μM brefeldin A. Inhibition of inositol 1,4,5-trisphosphate formation by 2 μM U73122, a phospholipase C inhibitor, did not affect Ca ²⁺ release induced by 0.2 μM riluzole. It was concluded that the neuroprotective agent riluzole increased [Ca ²⁺] _i in IMR32 neuroblastoma cells concentration-dependently by releasing Ca ²⁺ from multiple stores in an inositol 1,4,5-trisphosphate-independent manner and also by inducing nifedipine-sensitive Ca ²⁺ influx.