The uptake and release of D-[3H]
aspartate (used as a tracer for endogenous
glutamate and
aspartate) were studied in cultured glutamatergic neurons (cerebellar granule cells) and astrocytes at normal (5 mM) or high (55 mM)
potassium and under conditions of
hypoglycemia,
anoxia or "
ischemia" (combined
hypoglycemia and
anoxia). In glutamatergic neurons it was found that "ischemic" conditions led to a 2.4-fold increase in the
potassium-induced release of D-[3H]
aspartate as compared to normal conditions.
Hypoglycemia or
anoxia alone affected the release only marginally. The
ischemia-induced induced increase in the evoked D-[3H]
aspartate release was shown to be
calcium-dependent. In astrocytes no difference was found in the
potassium-induced release between the four conditions and the K+-induced release was not
calcium-dependent. The uptake of D-[3H]
aspartate was found to be stimulated at high
potassium in both glutamatergic neurons (98%) and in astrocytes (70%). This stimulation of
D-aspartate uptake, however, was significantly reduced under conditions of
anoxia or "
ischemia" in both cell types. In glutamatergic neurons (but not in astrocytes)
hypoglycemia also decreased the
potassium stimulation of
D-aspartate uptake. In a previous report it was shown, using the microdialysis technique, that during
transient cerebral ischemia in vivo the extracellular
glutamate content in hippocampus was increased eightfold. In the present paper it is shown that essentially no increase in extracellular
glutamate is seen under
ischemia when the perfusion is performed using
calcium-free,
cobalt-containing perfusion media. The results from the in vitro and in vivo experiments indicate that the
glutamate accumulated extracellularly under
ischemia in vivo originates from transmitter pools in glutamatergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)