STIMULATION OF GLUTAMATE UPTAKE AND NA,K-ATPASE ACTIVITY IN RAT ASTROCYTES EXPOSED TO ISCHEMIA-LIKE INSULTS

The postsynaptic actions of glutamate are rapidly terminated by high a ffinity glutamate uptake into glial cells. In this study we demonstrat e the stimulation of both glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures in response to sublethal ischemia-like insults . Primary cultures of neonatal rat cortical astrocytes were subjected to hypoxia, or to serum- and glucose-free medium, or to both condition s (ischemia). Cell death was assessed by propidium iodide staining of cell nuclei. To measure sodium pump activity and glutamate uptake, H-3 -glutamate and Rb-86 were both simultaneously added to the cell cultur e in the presence or absence of 2 mM ouabain. Na,K-ATPase activity was defined as ouabain-sensitive Rb-86 uptake. Concomitant transient incr eases (2-3 times above control levels) of both Na,K-ATPase and glutama te transporter activities were observed in astrocytes after 4-24 h of hypoxia, 4 h of glucose deprivation, and 2-4 h of ischemia. A 24 h isc hemia caused a profound loss of both activities in parallel with signi ficant cell death. The addition of 5 mM glucose to the cells after 4 h ischemia prevented the loss of both sodium pump activity and glutamat e uptake and rescued astrocytes from death observed at the end of 24 h ischemia. Reoxygenation after the 4 h ischemic event caused the selec tive inhibition of Na,K-ATPase activity. The observed increases in Na, K-ATPase activity and glutamate uptake in cultured astrocytes subjecte d to sublethal ischemia-like insults may model an important functional response of astrocytes in vivo by which they attempt to maintain ion and glutamate homeostasis under restricted energy and oxygen supply. ( C) 1997 Wiley-Liss, Inc.