This data is in accordance with our

This data is in accordance with our recent results on the influence of cholesterol-depleting agent methyl-β-cyclodextrin on platelets (Borisova et al., 2011a). Dissipation of the proton electrochemical gradient of secretory granules by methyl-β-cyclodextrin did not evoke the release of endogenous glutamate from the platelets that was shown using the glutamate dehydrogenase assay (Borisova et al., 2011a). Nowadays, the role of the proton electrochemical gradient in the acidic compartments of platelets is discussed intensively. Dense acidic granules of platelets are able to accumulate Ca2+, which is a key messenger of platelet activation. V-ATPase-dependent proton gradient provides the driving force solely for the maintenance of accumulated Ca2+ in the acidic compartments of platelets, but its involvement in store refilling is negligible in human platelets (Lopez et al., 2005, Rosado, 2011). Depolarization of the Moniliformin sodium salt membrane occurs during platelet activation by ADP, thrombin, platelet-activating factor, etc. (Avdonin et al., 1991, Greenberg-Sepersky and Simons, 1984, Hallam and Rink, 1985, Mahaut-Smith et al., 1990, Sage and Rink, 1987, Wencel-Drake and Feinberg, 1985). Platelet activation by thrombin, collagen or ADP is accompanied by an increase in intracellular [Na+] (Borin and Siffert, 1990, Borin and Siffert, 1991, Rosskopf, 1999). However, an elevation of [Na+]i in activated platelets is accomplished by excessive work of Na+/H+ exchanger and/or a reduction in Na+/K+-ATPase activity (Borin and Siffert, 1991, Rosskopf, 1999, Samson et al., 2001). Hyperkalemia, the marked elevation of [K+] in serum, accompanies haemolysis, leucocytosis, acute renal failure, hypofunction of the adrenal cortex, lack of aldosterone, stroke, trauma, etc. A lack of transporter-mediated release of glutamate from platelets in response to elevated [K+] application (Fig. 4) allows us to suggest that under conditions of hyperkalemia platelets cannot enrich the plasma with glutamate by glutamate transporter reversal. Aggregation/activation of platelets can be regulated by NMDA, AMPA, kainate and mGlu receptors (Amisten et al., 2008, Sun et al., 2009). Taking into account our data on exocytotic release of glutamate from platelets, we calculated that platelets released approximately 3nmol of glutamate per 1mg of platelet proteins during activation by 0.5 NIH U/ml thrombin. Because the level of glutamate in the plasma is relatively high (∼30μM) (Aliprandi et al., 2005, Divino Filho et al., 1998), we suggest that glutamate signalling through glutamate receptors in platelets may be of value only when the extracellular space between platelets and/or platelets and other cells is small enough. In this case, glutamate released from platelets by exocytosis, that is, “glutamate waves”, can significantly increase the extracellular glutamate concentration. It is so when platelets are in closed connection with each other during their aggregation/activation, thereby making possible “synaptic-like interplatelet communications”. Otherwise, neighbouring platelets cannot be precisely regulated by released glutamate because of its relatively high level in surrounding blood plasma. It was shown that glutamate, at excitotoxic levels, caused a loss in human cerebral endothelial barrier integrity through activation of NMDA receptors, and thus breakdown in the blood brain barrier (Sharp et al., 2003). Therefore, glutamate transport in platelets is important not only for “synaptic-like interplatelet communications” in aggregated platelets, but also may influence small brain vessels permeability. In these cases, “glutamate waves” can stimulate certain signalling mechanisms. Recent evidence indicates the interrelation between changes in glutamate transport and metabolism in the brain and platelets (Aliprandi et al., 2005, do Nascimento et al., 2006, Rainesalo et al., 2003, Rolf et al., 1993, Yao et al., 2006, Zoia et al., 2004), and so the possible role of platelets as a diagnostic marker in various neurodegenerative diseases, such as amyotrophic lateral sclerosis, Parkinson's disease, Huntington's disease, Alzheimer's disease, multiple sclerosis, etc. (Behari and Shrivastava, 2013). Demonstrating the similarity with nerve terminals in: (1) glutamate uptake by glutamate transporters and mechanisms of its regulation; (2) accumulation of cytosolic glutamate into acidic compartments, dense secretory granules, by vesicular glutamate transporters and exocytotic release of glutamate during activation; (3) existence of NMDA, AMPA and mGlu 3, 4 receptors in the plasma membrane; platelets (in contrast to nerve terminals) cannot release glutamate in non-exocytotic manner (Fig. 9). Unstimulated release, heteroexchange and glutamate transporter reversal, even during dissipation of the proton electrochemical gradient of secretory granules, are not inherent to platelets isolated from human, rabbit and rat blood. Thus, platelets can be used as a peripheral marker/model for the analysis of glutamate uptake by nerve terminals, but not glutamate release, because the mechanisms of the latter are different in platelets and nerve terminals. Also, it is proposed that reverse function of vesicular glutamate transporters in platelet secretory granules is rather ambiguous.