Inhibition of Na+/Ca2+ exchange enhances delayed neuronal death elicited by glutamate in cerebellar granule cell cultures.

Experiments have been carried out on the primary cerebellar granule cell cultures from 7- to 8-day-old Wistar rats. To study a possible contribution of Na+/Ca2+ exchange to the toxic effect of glutamate, two amiloride derivatives, 3',4'-dichlorobenzamil (DCB) and 5-(N-4-chlorobenzyl)-2',4'-dimethylbenzamil (CBDMB), known to be the potent inhibitors of this exchange system, were used. Addition of DCB or CBDMB (at 30 and 10 microM, respectively) to a 25 microM glutamate solution dramatically enhanced the delayed neuronal death observed during the 4 h after termination of glutamate treatment. Similar but insignificantly smaller effects were obtained when these agents were added to the cultures in the post-glutamate period. Removal of Na+ (by substituting for choline chloride) from the external Mg2+-free solution in the post-glutamate period also enhanced a delayed neuronal damage. The data obtained suggest that Na+/Ca2+ exchanger does not constitute the route for Ca2+ entry during the post-glutamate period but, on the contrary, attenuates glutamate neurotoxicity providing Ca2+ extrusion from the cells under the conditions of a sustained Ca2+ influx.