ROLE OF CALCIUM IN SIGMA-MEDIATED NEUROPROTECTION IN RAT PRIMARY CORTICAL-NEURONS

Since unique calcium dynamics have been reported for toxic (40-80 M) a nd non-toxic (5-10 mu M) concentrations of glutamate, we evaluated the effect of neuroprotective sigma ligands on glutamate and potassium ch loride (KCl)-stimulated changes in [Ca2+](i) using 12-15 day old prima ry rat neuronal cortical cultures. In approximately 80% of the neurons tested, 80 mu M glutamate caused a sustained calcium flux previously shown to be associated with neurotoxicity. The majority of sigma ligan ds that were evaluated altered glutamate-induced calcium flux. For exa mple, the primary effect of maximally neuroprotective concentrations o f the sigma ligands dextromethorphan, (+)-pentazocine, (+)-cyclazocine , (+)-SKF 10047, carbetapentane and haloperidol was a shift from a sus tained, to either a biphasic or a monophasic transient calcium respons e indicative of neuroprotection. (+)-3-PPP, previously shown not to be neuroprotective in this model system, failed to alter glutamate-induc ed calcium flux. In contrast to glutamate, KCl (50 mM) produced change s in [Ca2+](i) which were not neurotoxic to the neurons as measured by LDH release. The primary response observed in 59% of the neurons trea ted with 50 mM KCI alone was an initial spike in [Ca2+](i) which abrup tly declined then plateaued above basal levels throughout the 12 min o f analysis (modified sustained response). The highly selective sigma l igands produced a shift from the modified sustained response to a mono phasic transient calcium response. Again, (+)-3-PPP had no effect on K Cl-induced calcium dynamics. Of the PCP-related sigma ligands only (+) -SKF-10047 consistently attenuated the KCl-induced calcium flux. Colle ctively, these results indicate that modulation of [Ca2+](i) through r eceptor and voltage-gated calcium channels contributes significantly t o sigma mediated neuroprotection.