Rat erythrocytes express the anionic amino acid transport protein EAAC1

Remote Ischaemic Preconditioning Accelerates Brain to Blood Glutamate Efflux via EAATs-mediated Transport

Remote ischaemic conditioning (RIC) becomes an attractive strategy for the endogenous stimulation of mechanisms protecting neurons against ischaemia. Although the processes underlying the RIC are not clearly understood, the homeostasis of glutamate seems to play an important role. The present study is focused on the investigation of the brain to blood efflux of glutamate in a condition mimicking ischaemia-mediated excitotoxicity and remote ischaemic preconditioning (RIPC). The animals were pre-treated with a hind-limb tourniquet one hour before the intraventricular administration of glutamate and its release was monitored as the concentration of glutamate/glutathione in blood and liquor for up to 1 h. The transport mediated by excitatory amino acid transporters (EAATs) was verified by their inhibition with Evans Blue intraventricular co-administration. RIPC mediated the efflux of glutamate exceeding from CSF to blood in the very early stage of intoxication. As a consequence, the blood level of glutamate rose in a moment. EAATs inhibition confirmed the active role of glutamate transporters in this process. In the blood, elevated levels of glutamate served as a relevant source of antioxidant glutathione for circulating cells in RIPC-treated individuals. All of those RIPC-mediated recoveries in processes of glutamate homeostasis reflect the improvement of oxidative stress, suggesting glutamate-accelerated detoxication to be one of the key mechanisms of RIPC-mediated neuroprotection.

Accelerated capacity of glutamate uptake via blood elements as a possible tool of rapid remote conditioning mediated tissue protection

Recently, the function of blood cells in remote ischemic conditioning (RIC) mediated neuroprotection was undoubtedly confirmed. In the present paper, we have focused on the role of blood elements in glutamate homeostasis. The blood of remote conditioned (tolerant) animals was incubated ex vivo with 100 μM glutamate, and the quantitative and qualitative changes of excitatory amino acid transporters (EAAT 1, 2, and 3) were determined. We confirmed RIC mediated accelerated sequestration of extracellular glutamate via EAATs and altered distribution of that amino acid between plasma and cell elements compared to non-tolerant counterparts. The activity of EAATs was elevated in erythrocytes and monocytes, while the density of transporters was not affected. Quantitative changes of EAAT1 density were detected solely in platelets where the forced scavenging was independent of EAATs inhibition. Surprisingly, the trafficking of immunovisualised EAAT2 and 3 raised at tolerant erythrocytes and monocytes. We have found that protein synthesis underlined this process. On the other hand, depletion of protein synthesis did not significantly affect the scavenging capacity of those cell populations. Our work has demonstrated that the elevated blood scavenging of glutamate overdose could be one of the potential mechanisms underlying RIC mediated tissue protection.

Chemical activation of a high-affinity glutamate transporter in human erythrocytes and its implications for malaria-parasite–induced glutamate uptake

Human erythrocytes have a low basal permeability to L-glutamate and are not known to have a functional glutamate transporter. Here, treatment of human erythrocytes with arsenite was shown to induce the uptake of L-glutamate and D-aspartate, but not that of D-glutamate or L-alanine. The majority of the arsenite-induced L-glutamate influx was via a high-affinity, Na+-dependent system showing characteristics of members of the “excitatory amino acid transporter” (EAAT) family. Western blots and immunofluorescence assays revealed the presence of a member of this family, EAAT3, on the erythrocyte membrane. Erythrocytes infected with the malaria parasite Plasmodium falciparum take up glutamate from the extracellular environment. Although the majority of uptake is via a low-affinity Na+-independent pathway there is, in addition, a high-affinity uptake component, raising the possibility that the parasite activates the host cell glutamate transporter.