Extracellular pH modulates N-methyl-D-aspartate receptor-mediated neurotoxicity and calcium accumulation in rat cortical cultures.

The effect of extracellular pH (pHo) on the excitotoxicity of N-methyl-D-aspartate (NMDA) in cultured rat cortical cells was studied. Treatment of cells with 500 microM NMDA for 15 min at various pH's in a range from 6.5 to 8.0 progressively enhanced staining with Trypan blue and release of lactate dehydrogenase with increased pH after 18 h of culture following treatment. The cytotoxic effect of high concentration of K+ (40 mM) or veratridine (10 microM) was also directly related to the increase in pHo. Free calcium accumulation in cells on addition of NMDA increased parallel to pHo. Changes in intracellular pH were estimated to be minor compared with extracellular changes. Specific NMDA antagonists could block both the NMDA- and membrane depolarization-induced neurotoxicity and calcium accumulation completely. These results suggest that the proton concentration outside of cells attenuates NMDA-induced neurotoxicity by blocking calcium accumulation.