Effects of the anion channel blocker DIDS on ouabain- and high K(+)-induced release of amino acids from the rat cerebral cortex

Ischemia induces release of endogenous amino acids from the cerebral cortex and cerebellum of developing and adult mice

Ischemia enhanced release of endogenous neuroactive amino acids from cerebellar and cerebral cortical slices. More glutamate was released in adult than developing mice. Taurine release enhanced by K⁺ stimulation and ischemia was more than one magnitude greater than that of GABA or glutamate in the developing cerebral cortex and cerebellum, while in adults the releases were almost comparable. Aspartate release was prominently enhanced by both ischemia and K⁺ stimulation in the adult cerebral cortex. In the cerebellum K⁺ stimulation and ischemia evoked almost 10-fold greater GABA release in 3-month olds than in 7-day olds. The release of taurine increased severalfold in the cerebellum of 7-day-old mice in high-K⁺ media, whereas the K⁺-evoked effect was rather small in adults. In 3-month-old mice no effects of K⁺ stimulation or ischemia were seen in the release of aspartate, glycine, glutamine, alanine, serine, or threonine. The releases from the cerebral cortex and cerebellum were markedly different and also differed between developing and adult mice. In developing mice only the release of inhibitory taurine may be large enough to counteract the harmful effects of excitatory amino acids in ischemia in both cerebral cortex and cerebellum, in particular since at that age the release of glutamate and aspartate cannot be described as massive.

A potentially critical role of phospholipases in central nervous system ischemic, traumatic, and neurodegenerative disorders

Phospholipases are a diverse group of enzymes whose activation may be responsible for the development of injury following insult to the brain. Amongst the numerous isoforms of phospholipase proteins expressed in mammals are 19 different phospholipase A2's (PLA2s), classified functionally as either secretory, calcium dependent, or calcium independent, 11 isozymes belonging to three structural groups of PLC, and 3 PLD gene products. Many of these phospholipases have been identified in selected brain regions. Under normal conditions, these enzymes regulate the turnover of free fatty acids (FFAs) in membrane phospholipids affecting membrane stability, fluidity, and transport processes. The measurement of free fatty acids thus provides a convenient method to follow phospholipase activity and their regulation. Phospholipase activity is also responsible for the generation of an extensive list of intracellular messengers including arachidonic acid metabolites. Phospholipases are regulated by many factors including selective phosphorylation, intracellular calcium and pH. However, under abnormal conditions, excessive phospholipase activation, along with a decreased ability to resynthesize membrane phospholipids, can lead to the generation of free radicals, excitotoxicity, mitochondrial dysfunction, and apoptosis/necrosis. This review evaluates the critical contribution of the various phospholipases to brain injury following ischemia and trauma and in neurodegenerative diseases.

Lubeluzole attenuates K(+)-evoked extracellular accumulation of taurine in the striatum of healthy rats and rats with hepatic failure

Lubeluzole is a newly designed neuroprotectant which has proved effective in the treatment of experimental stroke in rats, mainly by inhibition of the glutamate-activated NO pathway, but also by counteracting osmotic stress by a mechanism associated with the release of the osmotically active amino acid taurine (Tau). Here we show that lubeluzole administered i.p. decreases by 25% the high (50 mM) K+-evoked accumulation of Tau in striatal microdialysates of healthy rats and by 34% in rats with thioacetamide-induced hepatic failure, where the increased extracellular accumulation of Tau signifies ongoing hepatic encephalopathy. Lubeluzole does not affect the nonstimulated accumulation of Tau in either group of rats. The results indicate that lubeluzole may be effective in ameliorating ionic or osmotic stress in a range of pathological conditions involving the rise of extracellular K+, and also in decreasing the vulnerability to stress in rats with hepatic failure.