Accumulation of glutamate is regulated by calcium and protein kinase C in rat hippocampal slices exposed to ischemic states

Abstract

There is now convincing evidence that excessive accumulation of the excitatory amino acid glutamate (Glu) in the extracellular space is toxic to neurons. However, the regulation of the release and uptake of Glu in producing this toxic concentration has not been adequately ascertained. The authors report that in hippocampal slices, the output of Glu significantly increased under in vitro ischemic states. Glu in the extracellular space increased fivefold. Since daurisoline, a drug that blocks N-type Ca2+ channels, or Ca(2+)-free solution potently and effectively lowered this stimulated output, it was hypothesized that the Glu output is mediated by Ca2+ influx in nerve terminals. When the slices were incubated for 30 minutes under ischemic state, daurisoline caused only small alterations in the postischemic accumulation of Glu. However, Glu accumulation was markedly attenuated by H-7, but not by calmidazolium, facilitated by PDB whereas 8-bromo-cAMP was without effect. It appears therefore that during a 30-minute ischemic insult, protein kinase C (PKC) was involved in the Glu accumulation of supernatant. A direct demonstration of this concept was obtained by showing significant increases in PKC activation in presynaptic nerve terminals (from 1.34 +/- 0.1 to 9.34 +/- 0.89 U) following 30 minutes of ischemia. DNQX, a non-NMDA receptor antagonist, potently reduced PKC activities and decreased extra Glu accumulation. Also observed was the inhibition of 1-[3H]-Glu uptake into synaptosomes by PDB. These results provide direct evidence that Ca2+ influx enhances Glu release, which in turn leads to inhibition of its reuptake, and is coupled with PKC activities in presynaptic nerve terminals.

Neuroprotection by Peptide Growth Factors against Anoxia and Nitric Oxide Toxicity Requires Modulation of Protein Kinase C

“…In addition, some of the toxic effects of NO may be linked to the activity of PKC (Maiese et al, 1993b,c). PKC ac tivity can regulate the release of glutamate (Lu et al, 1993) during ischemia, and down-regulation of PKC activity has been shown to protect neurons Vol. 15, No.…”

“…For example, protein kinase C (PKC) can alter the toxic effects of both anoxia and NO. During cerebral ischemia, increased levels of PKC are present in the hippocampal CAl region (Cardell et al, 1990;Hara et al, 1990) and PKC activity can regulate the release of glu tamate (Lu et al, 1993), suggesting that PKC activation may lead to ischemic neuronal dam age. During periods of global ischemia, agents that decrease PKC activity can prevent neuronal damage (Hara et al, 1990).…”

Hypoxia-ischemia and retinal ganglion cell damage

“…Glutamate, the excitatory neurotransmitter in the retina, is released by photoreceptors, bipolar cells and ganglion cells and mediates the transfer of visual signals from the retina to the brain (Massey 1990). However, augmented release of glutamate and its accumulation in extracellular spaces in hypoxic-ischemic conditions leading to activation of glutamate receptors has been implicated in hypoxic/ischemic neuronal death (Benveniste et al 1984; Lu et al 1993). Glutamate neurotoxicity is considered as the underlying problem in retinal neuropathies and neurodegenerative conditions such as glaucoma (Dreyer 1998).…”

Alterations of G‐protein Coupling Function in Phosphoinositide Signalling Pathways of Rat Hippocampus by Ischaemic Brain Injury

“…The discovery of glutamate as an excitotoxin in the central nervous system has contributed to the understanding of the molecular mechanisms underlying the pathogenesis of ischaemic neuron damage (Meldrum, 1985;Rothman and Olney, 1986;Lu et al, 1991aLu et al, , 1993. It is known that brain regions enriched in glutamate receptors, including the hippocampus, are particularly vulnerable to ischaemic neuronal damage (Jorgenson e t a l .…”