DISCREPANT INTRACELLULAR PH CHANGES FOLLOWING INTRACELLULAR CA2-NEURONS( INCREASES INDUCED BY GLUTAMATE AND CA2+ IONOPHORES IN RAT HIPPOCAMPAL)

We investigated changes in intracellular pH (pHi) in relation to intra cellular Ca2+ concentration ([Ca2+]i) in primary cultured hippocampal neurons treated with glutamate. [Ca2+]i and pHi were imaged with fluor escent dyes and confocal microscopy. Exposure to I mM glutamate for 10 min increased [Ca2+]i and evoked acidosis. These changes persisted fo r at least 60 min, even after removal of glutamate. The increase in [C a2+]i and the acidosis were not observed in Ca2+-free solution and wer e attenuated in the presence of MK-801, an NMDA receptor antagonist. W e also found that the increase in [Ca2+]i and acidosis could be induce d by addition of Ca2+ to the extracellular solution in the cells pretr eated with glutamate in Ca2+-free solution, even if glutamate did not exist in the extracellular solution. On the other hand, ionomycin and Br-A23187, calcium ionophores, increased [Ca2+]i to almost the same le vel as glutamate and increased pHi. Extracellular Ca2+ was also indisp ensable for the increase in [Ca2+]i and the alkalosis. These results s uggest the followings: 1) intracellular acidosis by glutamate is depen dent on the presence of extracellular Ca2+; 2) the acidosis does not r esult from only the increase in [Ca2+]i; and 3) glutamate induces the irreversible disorder of regulatory mechanisms of [Ca2+]i not only by Ca2+-dependent process, but also by Ca2+-independent process.