Up-regulation of P2X7 receptor-mediated inhibition of GABA uptake by nerve terminals of the human epileptic neocortex

作者：Barros Barbosa Aurora R; Fonseca Ana L; Guerra Gomes Sonia; Ferreirinha Fatima; Santos Agostinho; Rangel Rui; Graca Lobo M; Correia de Sa Paulo; Miguel Cordeiro J

来源：Epilepsia, 2016, 57(1): 99-110.

DOI：10.1111/epi.13263

• Epilepsy
• GABA
• Glutamate
• High-affinity transporters
• P2X7R
• MTLE

Objective: Thirty percent of patients with epilepsy are refractory to medication. The majority of these patients have mesial temporal lobe epilepsy (MTLE). This prompts for new pharmacologic targets, like ATP-mediated signaling pathways, since the extracellular levels of the nucleotide dramatically increase during in vitro epileptic seizures. In this study, we investigated whether sodium-dependent high-affinity c-aminobutyric acid (GABA) and glutamate uptake by isolated nerve terminals of the human neocortex could be modulated by ATP acting via slow-desensitizing P2X7 receptor (P2X7R).
Methods: Modulation of [H-3] GABA and [C-14] glutamate uptake by ATP, through activation of P2X7R, was investigated in isolated nerve terminals of the neocortex of cadaveric controls and patients with drug-resistant epilepsy (non-MTLE or MTLE) submitted to surgery. Tissue density and distribution of P2X7R in the human neocortex was assessed by Western blot analysis and immunofluorescence confocal microscopy.
Results: The P2X7R agonist, 2'(3')-O-(4-benzoylbenzoyl) ATP (BzATP, 3-100 mu M) decreased [H-3] GABA and [C-14] glutamate uptake by nerve terminals of the neocortex of controls and patients with epilepsy. The inhibitory effect of BzATP (100 mu M) was prevented by the selective P2X7R antagonist, A-438079 (3 mu M). Down-modulation of [C-14] glutamate uptake by BzATP (100 mu M) was roughly similar in controls and patients with epilepsy, but the P2X7R agonist inhibited more effectively [H-3] GABA uptake in the epileptic tissue. Neocortical nerve terminals of patients with epilepsy express higher amounts of the P2X7R protein than control samples.
Significance: High-frequency cortical activity during epileptic seizures releases huge amounts of ATP, which by acting on low-affinity slowly desensitizing ionotropic P2X7R, leads to down-modulation of neuronal GABA and glutamate uptake. Increased P2X7R expression in neocortical nerve terminals of patients with epilepsy may, under high-frequency firing, endure GABA signaling and increase GABAergic rundown, thereby unbalancing glutamatergic neuroexcitation. This study highlights the relevance of the ATP-sensitive P2X7R as an important negative modulator of GABA and glutamate transport and prompts for novel antiepileptic therapeutic targets.

• 出版日期2016-1