AMPA receptor-mediated excitotoxicity in human NT2-N neurons results from loss of intracellular Ca2+ homeostasis following marked elevation of intracellular Na+.
Human NT2-N neurons express Ca2+-permeable alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid glutamate receptors (AMPA-GluRs) and become vulnerable to excitotoxicity when AMPA-GluR desensitization is blocked with cyclothiazide. Although the initial increase in intracellular Ca2+ levels ([Ca2+]i) was 1.9-fold greater in the presence than in the absence of cyclothiazide, Ca2+ entry via AMPA-GluRs in an early phase of the exposure was not necessary to elicit excitotoxicity in these neurons. Rather, subsequent necrosis was caused by a >40-fold rise in [Na+]i, which induced a delayed [Ca2+]i rise. Transfer of the neurons to a 5 mM Na+ medium after AMPA-GluR activation accelerated the delayed [Ca2+]i rise and intensified excitotoxicity. Low-Na+ medium-enhanced excitotoxicity was partially blocked by amiloride or dizocilpine (MK-801), and completely blocked by removal of extracellular Ca2+, suggesting that Ca2+ entry by reverse operation of Na+/Ca2+ exchangers and via NMDA glutamate receptors was responsible for the neuronal death after excessive Na+ loading. Our results serve to emphasize the central role of neuronal Na+ loading in AMPA-GluR-mediated excitotoxicity in human neurons.
Itoh
T
T
Division of Neurology, The Children's Hospital of Philadelphia, Pennsylvania 19104, USA.
Itoh
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A
Horiuchi
K
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Pleasure
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D
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000959:Antihypertensive Agents / Q000494:pharmacology; D001581:Benzothiadiazines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005110:Extracellular Space / Q000737:chemistry / Q000378:metabolism; D018698:Glutamic Acid / Q000633:toxicity; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007608:Kainic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D009498:Neurotoxins / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D018091:Receptors, AMPA / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D013111:Spider Venoms / Q000494:pharmacology; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D000959:Antihypertensive Agents; D001581:Benzothiadiazines; D002121:Calcium Channel Blockers; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; C044936:JSTX spider toxin; D009498:Neurotoxins; D018091:Receptors, AMPA; D019831:Sodium-Calcium Exchanger; D013111:Spider Venoms; D018698:Glutamic Acid; D009553:Nimodipine; D016291:Dizocilpine Maleate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D012964:Sodium; C004639:cyclothiazide; D011188:Potassium; D007608:Kainic Acid; D002118:Calcium