Activation of P2X₇ receptors decreases glutamate uptake and glutamine synthetase activity in RBA‐2 astrocytes via distinct mechanisms

Abstract

Glutamate clearance by astrocytes is critical for controlling excitatory neurotransmission and ATP is an important mediator for neuron‐astrocyte interaction. However, the effect of ATP on glutamate clearance has never been examined. Here we report that treatment of RBA‐2 cells, a type‐2‐like astrocyte cell line, with ATP and the P2X7 receptor selective agonist 3′‐O‐(4‐benzoylbenzoyl) adenosine 5′‐triphosphate (BzATP) decreased the Na+‐dependent [3H]glutamate uptake within minutes. Mechanistic studies revealed that the decreases were augmented by removal of extracellular Mg2+ or Ca2+, and was restored by P2X7 selective antagonist , periodate‐oxidized 2′,3′‐dialdehyde ATP (oATP), indicating that the decreases were mediated through P2X7 receptors. Furthermore, stimulation of P2X7 receptors for 2 h inhibited both activity and protein expression of glutamine synthetase (GS), and oATP abolished the inhibition. In addition, removal of extracellular Ca2+ and inhibition of protein kinase C (PKC) restored the ATP‐decreased GS expression but failed to restore the P2X7‐decreased [3H]glutamate uptake. Therefore, P2X7‐mediated intracellular signals play a role in the down‐regulation of GS activity/expression. Activation of P2X7 receptors stimulated increases in intracellular Na+ concentration ([Na+]i) suggesting that the P2X7‐induced increases in [Na+]i may affect the local Na+ gradient and decrease the Na+‐dependent [3H]glutamate uptake. These findings demonstrate that the P2X7‐mediated decreases in glutamate uptake and glutamine synthesis were mediated through distinct mechanisms in these cells.

Effects of Acute Perinatal Asphyxia in the Rat Hippocampus

“…However, additional experiments are necessary to better understand this feature. P2X 7 receptor activation is known to promote glutamate release in the hippocampus (Fellin et al 2006;Papp et al 2004;Sperlágh et al 2007) and it was recently described as being able to quickly inhibit [ 3 H] glutamate uptake in RBA-2 cells (Lo et al 2008). In line with these results, we observed a significant increase in P2X 7 expression after 15 min of PA, and its immunocontent returned to control levels 60 min after asphyxia.…”

Purinergic modulation of norepinephrine release and uptake in rat brain cortex: contribution of glial cells

“…In the hippocampus it has been shown that neuronal norepinephrine transporters are regulated by P2X receptors that trigger the release of norepinephrine by causing the inversion of the transporter function (Papp et al 2004). Astrocytes express several purinergic receptors (Abbracchio et al 2009) that modulate glutamate (Lo et al 2008;Zeng et al 2009) and GABA (Cristóvão-Ferreira et al 2011) transporters, but the influence of purinergic receptors in the modulation of norepinephrine transport by astrocytes has never been investigated.…”

Buyang Huanwu decoction increases the expression of glutamate transporter-1 and glutamate synthetase in association with PACAP-38 following focal ischemia

“…Ischemia preconditioning and certain agents, such as ceftriaxone, were reported to protect ischemic injury through upregulating GLT-1 (21). Additionally, the metabolic conversion of glutamate to glutamine by GS could accelerate the extracellular glutamate uptake by reducing the intracellular glutamate concentration, thus playing a protective role following ischemia (22). In the present study, the levels of GLT-1 and GS increased on day 3 in the ischemia group, indicating that an internal potential protective mechanism within the body is functioning.…”