Calcium dependence of rapid astrocyte death induced by transient hypoxia, acidosis, and extracellular ion shifts.
Exposure to hypoxic, acidic, ion-shifted Ringer (HAIR) for 15-40 min has been shown to cause rapid astrocyte death upon reperfusion with normal media. The ion shifts of the HAIR solution included a rise in extracellular K(+) (e.g., [K(+)](o)) and a fall in [Na(+)](o), [Cl(-)](o), and [Ca(2+)](o), characteristic of ischemic-traumatic brain insults. We investigated the ionic basis of the HAIR-induced injury. After HAIR exposure, reperfusion in 0 Ca(2+)/EGTA media completely protected astrocytes. Preincubation of cells in BAPTA-AM ester was also protective, indicating that the injury was triggered by Ca(2+) influx during reperfusion. Neither nimodipine, CNQX, APV, nor TTX reduced injury. Astrocyte death could be blocked by 100 microM Ni(2+) or 100 microM benzamil, suggesting involvement of Na(+)-Ca(2+) exchange. KB-R7943, which preferentially inhibits reverse Na(+)-Ca(2+) exchange, also protected astrocytes. Elevation of [K(+)](o) was not necessary for astrocyte death. However, when [Na(+)](o) was maintained at 151 mM throughout the HAIR protocol, cell death was markedly reduced. We postulate that [Na(+)](o) shifts aid reversal of Na(+)-Ca(2+) exchange by favoring cytosolic Na(+) loading. Possible means of astrocytic Na(+) accumulation are discussed.
Bondarenko
A
A
Department of Neurosurgery, New York University School of Medicine, New York, New York 10016, USA.
Chesler
M
M
D000138:Acidosis / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000166:cytology* / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000493:pharmacokinetics*; D016923:Cell Death / Q000502:physiology*; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D002712:Chlorides / Q000493:pharmacokinetics; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D005452:Fluoresceins; D005456:Fluorescent Dyes; D002546:Ischemic Attack, Transient / Q000378:metabolism; D007552:Isotonic Solutions / Q000737:chemistry; D011188:Potassium / Q000493:pharmacokinetics; D051381:Rats; D000077331:Ringer's Solution; D012964:Sodium / Q000493:pharmacokinetics
D002614:Chelating Agents; D002712:Chlorides; D005452:Fluoresceins; D005456:Fluorescent Dyes; D007552:Isotonic Solutions; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D000077331:Ringer's Solution; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium; D011188:Potassium; D002118:Calcium