A number of experimental data

A number of experimental data declare a tight interdependence between the pathological changes of glutamate transport in ARRY-380 and consequent alterations in glutamate transport and activity/expression of glutamate metabolizing enzymes in platelets (Aliprandi et al., 2005, Behari and Shrivastava, 2013, do Nascimento et al., 2006, Rainesalo et al., 2003, Yao et al., 2006, Zoia et al., 2004). In infantile autism, platelet level of serotonin was significantly increased, whereas glutamate, glutamine, aspartate and GABA contents were considerably decreased in comparison with the control (Rolf et al., 1993). It is noteworthy that higher level of plasma glutamate and lower level of plasma glutamine accompanied high-functioning autism in children (Shimmura et al., 2011). Besides platelets per se, glutamate may also serve as a potent regulator of other cells in situ. Glutamate is recognized as an important signalling molecule in differentiation of megakaryoblastic cells (Genever et al., 1999), in support of self-renewal of pluripotent cells (Cappuccio et al., 2005), and in the interaction of antigen-presenting cells and T lymphocytes (Pacheco et al., 2006). Glutamate released from platelets also contributes to allograft rejection through glutamate receptor signalling (Swaim et al., 2010). Na+-dependent glutamate uptake, the exocytotic release of glutamate during platelet activation, as well as glutamate receptor-mediated regulation of platelet aggregation/activation are documented in the literature (Amisten et al., 2008, Borisova et al., 2011a, Franconi et al., 1998, Gawaz, 2001, Kasatkina and Borisova, 2010, Mangano and Schwarcz, 1981, Sun et al., 2009, Tremolizzo et al., 2006). In contrast, non-exocytotic release of glutamate, which is one of the most important characteristics of glutamate transport in presynaptic nerve terminals of the brain (Grewer et al., 2008, Jabaudon et al., 2000, Rossi et al., 2007), has not yet been assessed in platelets. The term “non-exocytotic release of glutamate” is used to describe unstimulated release, release by heteroexchange triggered by transportable inhibitor of glutamate transporters, and transporter-mediated release of glutamate, that is, glutamate transporter reversal. In nerve terminals, the origin of unstimulated glutamate release has not yet been completely identified, however, it is suggested that the neurotransmitter enters the extracellular space in part due to spontaneous exocytosis, via swelling-activated anion channels, cystine-glutamate exchange and trans-membrane diffusion (Cavelier and Attwell, 2005, Jabaudon et al., 1999, Rutledge et al., 1998). A balance between unstimulated release and uptake of glutamate determines the extracellular level of the neurotransmitter, which is important for tonic activation of post- and presynaptic glutamate receptors. An increased extracellular level of glutamate over-activates glutamate receptors and causes neurotoxicity. In the synaptic cleft (without stimulation), the concentration of glutamate is less than 1μM, whereas, it consists of ∼30μM in the human plasma (Divino Filho et al., 1998, Aliprandi et al., 2005) that may be considered as the extracellular level of glutamate for platelets. Therefore, the ambient glutamate concentration for platelets is at least ten times higher than that for nerve terminals. The aim of this study is to assess whether or not non-exocytotic release of glutamate takes place in platelets. The availability of non-exocytotic glutamate release from platelets or lack thereof is of interest because of the following: (1) extracellular glutamate per se is a modulator of platelet function; (2) possible physiological role of platelets in the maintenance of extracellular glutamate homeostasis of the mammalian CNS via removing of excess extracellular glutamate from brain interstitial fluids to blood plasma (Gottlieb et al., 2003, Kuo et al., 2001, O’Kane et al., 1999, Wang et al., 2004); (3) possible contribution of glutamate released from platelets by glutamate transporter reversal to an increase in the plasma glutamate concentration in ischaemic stroke (Castillo et al., 1996) and other neurological disorders (Aliprandi et al., 2005) as well as at the site of injury and in elevated plasma [K+]; and (4) the suggested similarities of platelets with nerve terminals that underlie the possible usage of platelets as a model of glutamate transport in the presynapse, and a peripheral marker for the analysis of the alterations in the functioning of glutamate transporters in the brain.