Change in Intracellular pH Causes the Toxic Ca2+ Entry via NCX1 in Neuron- and Glia-Derived Cells

Brain hypoxia or ischemia causes acidosis and the intracellular accumulation of Ca2+ in neuron. The aims of the present study were to elucidate the interaction between intracellular pH and Ca2+ during transient acidosis and its effects on the viability of neuronal and glial cells. Intracellular Ca2+ and pH were measured using the fluorescence of fura-2 and 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester in neuroblastoma (IMR-32), glioblastoma (T98G), and astrocytoma (CCF-STTG1) cell lines. The administration of 5 mM propionate caused intracellular acidification in IMR-32 and T98G cells but not in CCF-STTG1 cells. After the removal of propionate, the intracellular pH recovered to the resting level. The intracellular Ca2+ transiently increased upon the removal of propionate in IMR-32 and T98G cells but not in CCF-STTG1 cells. The transient Ca2+ increase caused by the withdrawal of intracellular acidification was abolished by the removal of external Ca2+, diminished by a reduction of external Na+, and inhibited by benzamil. Transient acidosis caused cell death, whereas the cells were more viable in the absence of external Ca2+. Benzamil alleviated cell death caused by transient acidosis in IMR-32 and T98G cells but not in CCF-STTG1 cells. These results suggest that recovery from intracellular acidosis causes a transient increase in cytosolic Ca2+ due to reversal of Ca2+ transport via Na+/Ca2+ exchanger coactivated with Na+/H+ exchanger, which can cause cell death.