Discrepant intracellular pH changes following intracellular Ca2+ increases induced by glutamate and Ca2+ ionophores in rat hippocampal neurons.
We investigated changes in intracellular pH (pHi) in relation to intracellular Ca2+ concentration ([Ca2+]i) in primary cultured hippocampal neurons treated with glutamate. [Ca2+]i and pHi were imaged with fluorescent dyes and confocal microscopy. Exposure to 1 mM glutamate for 10 min increased [Ca2+]i and evoked acidosis. These changes persisted for at least 60 min, even after removal of glutamate. The increase in [Ca2+]i and the acidosis were not observed in Ca2+-free solution and were attenuated in the presence of MK-801, an NMDA receptor antagonist. We also found that the increase in [Ca2+]i and acidosis could be induced by addition of Ca2+ to the extracellular solution in the cells pretreated 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 level as glutamate and increased pHi. Extracellular Ca2+ was also indispensable for the increase in [Ca2+]i and the alkalosis. These results suggest the followings: 1) intracellular acidosis by glutamate is dependent on the presence of extracellular Ca2+; 2) the acidosis does not result 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.
Division of Biological Chemistry & Biologicals, National Institute of Health Sciences, Tokyo, Japan.
M
M
Yamamoto
T
T
Kawanishi
T
T
Kiuchi
M
M
Ohta
I
I
Yokota
H
H
Ohata
K
K
Momose
K
K
Inoue
T
T
Hayakawa
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D018698:Glutamic Acid / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration / Q000187:drug effects*; D015759:Ionomycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D007476:Ionophores; D018698:Glutamic Acid; D015759:Ionomycin; D002118:Calcium