Up-regulation of P2X7 receptor-mediated inhibition of GABA uptake by nerve terminals of the human epileptic neocortex.
Epilepsia
; 57(1): 99-110, 2016 Jan.
Article
in En
| MEDLINE
| ID: mdl-26714441
ABSTRACT
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 γ-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 [(3) H]GABA and [(14) C]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 µm) decreased [(3) H]GABA and [(14) C]glutamate uptake by nerve terminals of the neocortex of controls and patients with epilepsy. The inhibitory effect of BzATP (100 µm) was prevented by the selective P2X7R antagonist, A-438079 (3 µm). Down-modulation of [(14) C]glutamate uptake by BzATP (100 µm) was roughly similar in controls and patients with epilepsy, but the P2X7R agonist inhibited more effectively [(3) H]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.Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Synaptosomes
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Up-Regulation
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Neocortex
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Epilepsy
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Receptors, Purinergic P2X7
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Gamma-Aminobutyric Acid
Limits:
Adolescent
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Adult
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Aged
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Child
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Female
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Humans
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Male
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Middle aged
Language:
En
Journal:
Epilepsia
Year:
2016
Document type:
Article
Affiliation country: