Glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures exposed to ischemia.

In this study we demonstrate the stimulation of both glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures in response to a sublethal ischemic insult in vitro. To measure sodium pump activity and glutamate uptake, 3H-glutamate and 86Rb were simultaneously added to the cultures in the presence or absence of 2 mM ouabain. Na,K-ATPase activity was defined as ouabain-sensitive 86Rb uptake. Cell death was assessed by exclusion of the vital dye, calcein-AM from cells. Concomitant transient increases (2-3 fold above control levels) in both Na,K-ATPase and glutamate transporter activities were observed in astrocytes after 2-4 hours of ischemia. By contrast, 24 hours of ischemia caused a profound loss of both activities which paralleled significant cell death. The addition of 5 mM glucose to the cells after 4 hours of ischemia prevented the loss of sodium pump activity and glutamate uptake, and rescued astrocytes from the lethal effects of 24 hours of ischemia.