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 [Ca2+](o), characteristic of ischemic-traumatic brain insults. We investigated the ionic basis of the HAIR-induced injury. After HAIR exposure, reperfusion in 0 Ca2+/EGTA media completely protected astrocytes. Preincubation of cells in BAPTA-AM ester was also protective, indicating that the injury was triggered by Ca2+ influx during reperfusion. Neither nimodipine, CNQX, APV, nor TTX reduced injury. Astrocyte death could be blocked by 100 muM Ni2+ or 100 muM benzamil, suggesting involvement of Na+-Ca2+ exchange. KB-R7943, which preferentially inhibits reverse Na+-Ca2+ 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+-Ca2+ exchange by favoring cytosolic Na+ loading. Possible means of astrocytic Na+ accumulation are discussed. GLIA 34:143-149, 2001. (C) 2001 Wiley-Liss, Inc.