Effect of riluzole on Ca²⁺ movement and cytotoxicity in Madin-Darby canine kidney cells

Riluzole is a drug used in the treatment of amyotrophic lateral sclerosis; however, its in vitro action is unclear. In this study, the effect of riluzole on intracellular Ca²⁺ concentration ([Ca²⁺]_i) in Madin-Darby canine kidney (MDCK) cells was investigated using the Ca ²⁺-sensitive fluorescent dye, fura-2. Riluzole (100-500 μM) caused a rapid and sustained increase of [Ca²⁺]_i in a concentration-dependent manner (EC₅₀ = 150 μM). Some 40 and 50% of this [Ca²⁺]_i increase was prevented by the removal of extracellular Ca²⁺ and the addition of La³⁺, respectively, but was unchanged by dihydropyridines, verapamil and diltiazem. In Ca ²⁺-free medium, thapsigargin - an inhibitor of the endoplasmic reticulum (ER) Ca²⁺-ATPase - caused a monophasic [Ca ²⁺]_i increase, after which the increasing effect of riluzole on [Ca²⁺]_i was attenuated by 70%; in addition, pre-treatment with riluzole abolished thapsigargin-induced [Ca ²⁺]_i increases. U73122, an inhibitor of phospholipase C (PLC), abolished ATP (but not riluzole)-induced [Ca²⁺]_i increases. At concentrations of 250 and 500 μM, riluzole killed 40 and 95% cells, respectively. The cytotoxic effect of riluzole (250 μM) was unaltered by pre-chelating cytosolic Ca²⁺ with BAPTA. Collectively, in MDCK cells, riluzole rapidly increased [Ca²⁺]_i by stimulating extracellular Ca²⁺ influx via an La³⁺-sensitive pathway and intracellular Ca²⁺ release from the ER via, as yet, unidentified mechanisms. Furthermore, riluzole caused Ca²⁺-unrelated cytotoxicity in a concentration-dependent manner.