Intracellular acidification is not a prerequisite for glutamate-triggered death of cultured hippocampal neurons

Glutamate decreased intracellular pH (pH_i) in cultured rat hippocampal neurons. The protonophore, FCCP (1μM), produced an acidification comparable to that produced by glutamate. Application of glutamate to FCCP-treated cells, returned pH_i to resting levels. This alkaline shift resulted from a glutamate-induced membrane depolarization that removed the driving force across the plasmalemma for H⁺ entry via FCCP. The endogenous protonophore, arachidonic acid (10 μM), produced pH_i changes similar to those elicited by FCCP. Because application of glutamate and FCCP in combination did not change pH_i, this treatment was used to determine the role of glutamate-induced acidification in neurotoxicity. FCCP (1 μM, 5 min) did not affect neuronal viability, either alone or in combination with various concentrations of glutamate, as indicated by the release of lactate dehydrogenase into the bathing medium. Thus, acidification was not the cause of glutamate-induced cell death although, it may be symptomatic of neurotoxic processes.