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Activation of Excitatory Amino Acid Receptors in the Rat Hippocampal Slice Increases Intracellular Cl − and Cell Volume
Author(s) -
Inglefield Jon R.,
SchwartzBloom Rochelle D.
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.1471-4159.1998.71041396.x
Subject(s) - ampa receptor , nmda receptor , kainate receptor , chemistry , cnqx , glutamate receptor , dnqx , biophysics , 2 amino 5 phosphonovalerate , hippocampal formation , ibotenic acid , neuroscience , biochemistry , biology , receptor , central nervous system , excitatory amino acid antagonists
The effects of glutamatergic excitotoxins on intracellular Cl − were investigated in the CA1 pyramidal cell layer of the hippocampal slice. Hippocampal slices from rats (14–19 days old) were loaded with 6‐methoxy‐ N ‐ethylquinolinium chloride (MEQ), a Cl − ‐sensitive fluorescent probe with a fluorescence intensity that correlates inversely with intracellular [Cl − ]. Slices were exposed for at least 10 min at 26–28°C to N ‐methyl‐ d ‐aspartate (NMDA; 100 µ M ) or α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA; 50 µ M ). A UV laser scanning confocal microscope was used to measure changes in MEQ fluorescence within area CA1 pyramidal cell soma. Both glutamate receptor agonists produced a rapid decrease in MEQ fluorescence that persisted after washout following a 10‐min exposure. The effects of NMDA and AMPA were prevented by the competitive antagonists 2‐amino‐5‐phosphonopentanoic acid and 6,7‐dinitroquinoxaline‐2,3‐dione, respectively. Neither tetrodotoxin nor picrotoxin prevented the effect of NMDA or AMPA, indicating the lack of involvement of presynaptic mechanisms. The effects of NMDA and AMPA on MEQ fluorescence were dependent on the levels of extracellular Cl − , but only NMDA responses were dependent on the levels of extracellular Na + . Removal of Ca 2+ from the superfusion medium did not alter the effects of NMDA or AMPA on MEQ fluorescence. In addition, neither the Ca 2+ ionophore ionomycin nor the L‐type voltage‐gated Ca 2+ channel agonist (Bay K 8644) decreased MEQ fluorescence. The effects of NMDA and AMPA on cell (somal) volume were also assessed with the fluorescent probe calcein acetoxymethyl ester. Both NMDA and AMPA decreased calcein fluorescence (indicating an increased cell volume), but this was preceded by the decrease in MEQ fluorescence (equivalent to an intracellular accumulation of ∼20 m M Cl − ). Thus, excitotoxins may cause Cl − influx via an anion channel other than the GABA A receptor and/or reduce Cl − efflux mechanisms to produce cell swelling. Such anionic shifts may promote neuronal excitability and cell death following an excitotoxic insult to the hippocampal slice.