Amino-acid release from human cerebral cortex during simulated ischaemia in vitro

Abstract

The aim of the present study was to investigate the release of amino-acids in human cerebral cortex during membrane depolarization and simulated ischaemia (energy deprivation). Superfluous tissue from temporal Iobe resections for epilepsy was cut into 500 microns thick slices and incubated in vitro. Membrane depolarization with 50 mM K+ caused a release of glutamate, aspartate, GABA and glycine, but not glutamine or leucine. The release of glutamate and GABA was Ca(++)-dependent. Slices were exposed to simulated ischaemia (energy deprivation; ED) by combined glucose/oxygen deprivation. This caused a Ca(++)-independent release of glutamate, aspartate, GABA, glycine, and taurine which started after 8 min, peaked at the end or shortly after the 27 min period of ED, and returned to control levels within 11 min following termination of ED. Preloaded D-[3H]aspartate was released both during K(+)-stimulation and ED. Release of D-[3H]aspartate during ED was delayed compared to glutamate supporting an initial phase of synaptic glutamate release. Uptake of L-[3H]glutamate was increased during the period of glutamate release, suggesting passive diffusion across the cell membrane or enhanced transport efficacy in cellular elements with functioning uptake mechanisms.

On the regulation of ischaemia‐induced glutamate efflux from rat cortex by GABA; in vitro studies with GABA, clomethiazole and pentobarbitone

“…In con®rmation of earlier reports (e.g. Hegstad et al, 1996) ischaemia-induced glutamate release was inhibited dosedependently by GABA, maximal concentrations inhibiting 60 ± 70% of the ischaemia-induced glutamate e ux. The e ect of GABA was fully antagonized both by bicuculline, a competitive antagonist that acts at the agonist binding site on the GABA A receptor complex and by picrotoxin, a compound which occludes the open channel of the GABA A receptor complex.…”

“…Benveniste et al, 1984;Baldwin et al 1994). However the magnitude of release observed here was similar to that reported in human cerebral cortex tissue in vitro (Hegstad et al, 1996). Hypoxia alone (without removal of glucose) also induced glutamate release (Baldwin et al, 1994), albeit of a somewhat lower magnitude than that produced by simulated ischaemia (current study).…”

“…The ischaemia-induced e ux exhibited little sensitivity to removal of extracellular calcium. Our results cannot totally exclude a calcium-dependent component of e ux, but clearly the majority of glutamate e ux is calcium-independent, in line with that seen in other in vitro studies (Kauppinen et al, 1988;Szatkowski & Attwell, 1994;Hegstad et al, 1996;Polischuk et al, 1998;Saransaari & Oja, 1998). This calcium-independence is somewhat paradoxical, given that the excitotoxic cascade of ischaemia-induced glutamate e ux in vivo is usually assumed to involve some synaptic, and hence calcium-dependent, release (Strijbos et al, 1996;Lee et al, 1999;Dirnagl et al, 1999).…”

“…It has previously been reported that exposing cerebral tissue to ischaemic conditions in vitro can induce glutamate release and this has been demonstrated using cerebral tissue from both rat (Taylor et al, 1995;Roettger & Lipton, 1996;Saransaari & Oja, 1997) and human (Hegstad et al, 1996). The results from the current study con®rmed these ®ndings in prisms of rat cortex, simulating ischaemia by use of a hypoxic medium, with no added glucose.…”

Difference between Plasma Concentrations of Three Amino Acids in Patients with Ischemic and Hemorrhagic Stroke

“…Melani and colleagues used the brain microdialysis technique and demonstrated that after middle cerebral artery occlusion in the rat taurine was increased in the dialysate samples [34]. Interestingly, Heystad et al's study on the human cerebral cortex slice indicated that during membrane depolarization and simulated ischemia, the taurine release was increased [35]. Moreover, Castillo et al studied on 100 patients with infarction in the territory of the middle cerebral artery and reported that during the acute phase of cerebrovascular ischemia, the taurine concentration rise in the blood and cerebrospinal fluid [36].…”