Effects of AMPA-receptor and voltage-sensitive sodium channel blockade on high potassium-induced glutamate release and neuronal death in vivo.
High extracellular potassium induces spreading depression-like depolarizations and elevations of extracellular glutamate. Both occur in the penumbra of a focal ischemic infarct, and may be responsible for the spread of cell death from the infarct core to the penumbra. We have modeled this situation with microdialysis of an isotonic high-potassium solution into the normal rat amygdala for 70 min. This elevates extracellular glutamate up to 8-fold or more and produces irreversibly damaged, acidophilic neurons. NMDA-receptor blockade protects neurons and reduces the elevation of extracellular glutamate. Here we investigated the effects of sodium channel blockade with the voltage-sensitive sodium channel blocker tetrodotoxin and the AMPA receptor antagonist 2,3-dihydroxy-6-nitro-1,2,3,4-tetrahydrobenzo(f)quinoxaline-7-sulfonamide disodium (NBQX disodium) on high potassium-induced neuronal death and extracellular glutamate elevations. The acidophilic neurons produced are necrotic by ultrastructural examination. Tetrodotoxin, at dialysate concentrations of 33, 330 and 3300 microM (only a small fraction is extracted by tissue), markedly reduced the elevations of glutamate in rat amygdala at nearly all time points during high-potassium perfusion, but it reduced tissue edema only at the highest concentration, and it was neuroprotective only if dialyzed prior to high-potassium microdialysis (at 330 microM concentration). Although both 250 microM (6.2% is extracted by tissue) and 500 microM NBQX reduced elevations of glutamate, neither was neuroprotective, and neuropil edema was not reduced by either concentration. Our results suggest that in vivo, sodium influx through voltage-sensitive sodium channels but not through ligand-gated AMPA receptor channels contributes to high potassium-induced neuronal necrosis.
Wu
Aiguo
A
Experimental Neurology Laboratory, VA Greater Los Angeles Healthcare System, Sepulveda Ambulatory Care Center and Nursing Home Care Unit, Sepulveda, CA 91343, USA.
Fujikawa
Denson G
DG
D000679:Amygdala / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D000818:Animals; D016923:Cell Death / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000187:drug effects / Q000378:metabolism*; D015640:Ion Channel Gating; D008297:Male; D009336:Necrosis; D009474:Neurons / Q000502:physiology* / Q000648:ultrastructure; D011188:Potassium / Q000008:administration & dosage* / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000502:physiology*; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D011810:Quinoxalines; D018091:Receptors, AMPA; D026941:Sodium Channel Blockers; D015222:Sodium Channels; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D018698:Glutamic Acid; D013779:Tetrodotoxin; D011188:Potassium