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

Abstract.

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-dependent 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 µM verapamil, but was inhibited by 51±4% by 10 µM nifedipine. In Ca²⁺-free medium, pretreatment with 1 µM thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor) reduced the 0.2 mM riluzole-induced Ca²⁺ release by 44±3%; this reduction was augmented to 66±5% by additionally depleting the Ca²⁺ 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 Ca²⁺ release induced by 0.2 µM riluzole. It was concluded that the neuroprotective agent riluzole increased [Ca²⁺]_i in IMR32 neuroblastoma cells concentration-dependently by releasing Ca²⁺ from multiple stores in an inositol 1,4,5-trisphosphate-independent manner and also by inducing nifedipine-sensitive Ca²⁺ influx.