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Alkalinization Prolongs Recovery from Glutamate‐Induced Increases in Intracellular Ca 2+ Concentration by Enhancing Ca 2+ Efflux Through the Mitochondrial Na + /Ca 2+ Exchanger in Cultured Rat Forebrain Neurons
Author(s) -
Hoyt Kari R.,
Reynolds Ian J.
Publication year - 1998
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1998.71031051.x
Subject(s) - chemistry , intracellular , efflux , glutamate receptor , biochemistry , receptor
Increasing extracellular pH from 7.4 to 8.5 caused a dramatic increase in the time required to recover from a glutamate (3 µ M , for 15 s)‐induced increase in intracellular Ca 2+ concentration ([Ca 2+ ] i ) in indo‐1‐loaded cultured cortical neurons. Recovery time in pH 7.4 HEPES‐buffered saline solution (HBSS) was 126 ± 30 s, whereas recovery time was 216 ± 19 s when the pH was increased to 8.5. Removal of extracellular Ca 2+ did not inhibit the prolongation of recovery caused by increasing pH. Extracellular alkalinization caused rapid intracellular alkalinization following glutamate exposure, suggesting that pH 8.5 HBSS may delay Ca 2+ recovery by affecting intraneuronal Ca 2+ buffering mechanisms, rather than an exclusively extracellular effect. The effect of pH 8.5 HBSS on Ca 2+ recovery was similar to the effect of the mitochondrial uncoupler carbonyl cyanide p ‐(trifluoromethoxyphenyl)hydrazone (FCCP; 750 n M ). However, pH 8.5 HBSS did not have a quantitative effect on mitochondrial membrane potential comparable to that of FCCP in neurons loaded with a potential‐sensitive fluorescent indicator, 5,5′,6,6′‐tetrachloro‐1,1′,3,3′‐tetraethylbenzimidazolocarbocyanine iodide (JC‐1). We found that the effect of pH 8.5 HBSS on Ca 2+ recovery was completely inhibited by the mitochondrial Na + /Ca 2+ exchange inhibitor CGP‐37157 (25 µ M ). This suggests that increased mitochondrial Ca 2+ efflux via the mitochondrial Na 2+ /Ca 2+ exchanger is responsible for the prolongation of [Ca 2+ ] i recovery caused by alkaline pH following glutamate exposure.