Effect of Glutamate and Inhibitors of Various Pathways of Free Radical Production on Na+,K+-ATPase Activity and Accumulation of Lipids Peroxidation Products in Rat Brain Cortex Synaptosomes

It has been shown that treatment of the rat brain cortex synaptosomes with glutamate produced both a significant reduction in Na⁺,K⁺-ATPase activity and accumulation of products of lipid peroxidation (LPO) like malone dialdehyde, dienoic conjugates, and Schiff bases. A suppression of different routes of free radical production in cytosol by quinacrine, indomethacin, and allopurinol (blockers of phospholipase A₂, cyclooxygenases, and xanthine oxidases, respectively) as well as by MK-801 (a antagonist of MDA-receptors) prevented or lowered significantly the effect of glutamate on Na⁺,K⁺-ATPase activity. No significant effect of glutamate on the Na⁺,K⁺-ATPase activity was also observed in the presence of L-NAME (inhibitor of NO-synthase). Inhibitors of the arachidonate and NO-synthase pathway of free radical production also prevented accumulation of LPO end products in the rat brain cortex under the effect of glutamate. In the presence of rotenone and olygomycin (blockers of mitochondrial electron transport and ATP synthase, respectively), glutamate led to even a greater inactivation of Na⁺,K⁺-ATPase and accumulation of malone dialdehyde. The data obtained suggest that at early stages of ischemia the neurotoxic effect of glutamate is due to an inflow of calcium ions through NMDA receptors and activation of different pathways of free radical production in cytosol of nerve cells. At these stages, protective functions of mitochondria appear to predominate due to their ability to accumulate calcium ions and to prevent an excessive increase of the cytosol calcium concentration under the effect of excitatory amino acids.