Role of Na+-H+ and Na+-Ca2+ exchange in hypoxia-related acute astrocyte death.
Cultured astrocytes do not succumb to hypoxia/zero glucose for up to 24 h, yet astrocyte death following injury can occur within 1 h. It was previously demonstrated that astrocyte loss can occur quickly when the gaseous and interstitial ionic changes of transient brain ischemia are simulated: After a 20-40-min exposure to hypoxic, acidic, ion-shifted Ringer (HAIR), most cells died within 30 min after return to normal saline (i.e., "reperfusion"). Astrocyte death required external Ca2+ and was blocked by KB-R7943, an inhibitor of reversed Na+-Ca2+ exchange, suggesting that injury was triggered by a rise in [Ca2+]i. In the present study, we confirmed the elevation of [Ca2+]i during reperfusion and studied the role of Na+-Ca2+ and Na+-H+ exchange in this process. Upon reperfusion, elevation of [Ca2+]i was detectable by Fura-2 and was blocked by KB-R7943. The low-affinity Ca2+ indicator Fura-FF indicated a mean [Ca2+]i rise to 4.8+/-0.4 microM. Loading astrocytes with Fura-2 provided significant protection from injury, presumably due to the high affinity of the dye for Ca2+. Injury was prevented by the Na+-H+ exchange inhibitors ethyl isopropyl amiloride or HOE-694, and the rise of [Ca2+]i at the onset of reperfusion was blocked by HOE-694. Acidic reperfusion media was also protective. These data are consistent with Na+ loading via Na+-H+ exchange, fostering reversal of Na+-Ca2+ exchange and cytotoxic elevation of [Ca2+]i. The results indicate that mechanisms involved in pH regulation may play a role in the fate of astrocytes following acute CNS injuries.
Bondarenko
Alexander
A
Department of Neurosurgery, New York University School of Medicine, New York, New York 10016, USA.
Svichar
Nataliya
N
Chesler
Mitchell
M
D000208:Acute Disease; D000818:Animals; D001253:Astrocytes / Q000378:metabolism* / Q000473:pathology; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D016923:Cell Death / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016257:Fura-2 / Q000031:analogs & derivatives* / Q000494:pharmacology; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D020925:Hypoxia-Ischemia, Brain / Q000378:metabolism*; D017136:Ion Transport / Q000502:physiology; D007552:Isotonic Solutions / Q000494:pharmacology; D051381:Rats; D015427:Reperfusion Injury / Q000378:metabolism; D000077331:Ringer's Solution; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D004791:Enzyme Inhibitors; D007552:Isotonic Solutions; D019831:Sodium-Calcium Exchanger; D017923:Sodium-Hydrogen Exchangers; C087512:fura F; D006859:Hydrogen; D000077331:Ringer's Solution; D012964:Sodium; D002118:Calcium; D016257:Fura-2