Increase in chloride-dependent L-glutamate transport activity in synaptic membrane after in vitro ischemic treatment

The effect of energy failure on Cl(-)-dependent L-glutamate (L-Glu) transport was examined with an in vitro preparation. Rat brain slices were incubated in low oxygen and glucose-deprived medium (in vitro ischemia), and a synaptic membrane fraction was prepared from the slices. Cl(-)-dependent L-[3H]Glu uptake into vesicles increased about twofold after 20 min of in vitro ischemia. The increased L-[3H]Glu uptake was inhibited by L-Glu, DL-2-amino-4-phosphonobutyrate, L-homocysteic acid, L-cystine, 4,4'-diisothiocyano-2,2'-disulfonic stilbene, and removal of Cl-. Uptakes of Na(+)-dependent L-[3H]Glu, [3H]GABA, and [3H]taurine were not changed by the in vitro ischemia. In vitro ischemia increased the Vmax value without affecting the Km value. The increased L-[3H]Glu uptake by in vitro ischemia was reduced by subsequent incubation in a normoxic glucose-containing solution. ATP content in brain slices decreased to < 10% of control values by in vitro ischemia for 10 min. The decrease in ATP content was restored by subsequent incubation in normoxic glucose-containing solution. Treatment with veratrine, 2,4-dinitrophenol, carbonyl cyanide m-chlorophenylhydrazone, and NaCN in normoxic conditions increased L-[3H]Glu uptake with a concomitant decrease in ATP content in slices. These results suggest that Cl(-)-dependent L-Glu transport activity in synaptic membranes increases in ischemia- or hypoxia-induced brain energy failures.