ANTAGONISM BY RILUZOLE OF ENTRY OF CALCIUM EVOKED BY NMDA AND VERATRIDINE IN RAT CULTURED GRANULE CELLS - EVIDENCE FOR A DUAL MECHANISM OF ACTION

1 Intracellular calcium levels were measured in cultured cerebellar granule cells of the rat by use of the fluorescent dye, indo-1/AM. 2 Intracellular calcium levels were increased by depolarizing stimuli such as N-methyl-D-aspartate (NMDA) (100 mu M), glutamic acid (20 mu M), and veratridine (10 mu M). This increase was essentially due to entry of external calcium. 3 Riluzole (10 mu M) blocked responses to all the depolarizing agents. 4 Riluzole could still block the increase in intracellular calcium evoked by NMDA or glutamic acid when sodium channels were blocked by tetrodotoxin, suggesting that this effect is not mediated by a direct action of riluzole on the voltage-dependent sodium channel. 5 Pretreatment of the cells with pertussis toxin (0.1 mu g ml(-1)) did not modify the increases in intracellular calcium evoked by NMDA, glutamic acid or veratridine. 6 In pertussis toxin-treated cells, riluzole could no longer block responses to excitatory amino acids, but still blocked responses to veratridine. 7 It is concluded that riluzole has a dual action on cerebellar granule cells, both blocking voltage-dependent sodium channels and interfering with NMDA receptor-mediated responses via a pertussis toxin-sensitive mechanism. Furthermore, these two processes have been shown to be independent.