Inhibition of Acid Sensing Ion Channel 3 Aggravates Seizures by Regulating NMDAR Function

Abstract

The existing data about whether acid sensing ion channels (ASICs) are proconvulsant or anticonvulsant are controversial. Particularly, acid sensing ion channel 3 (ASIC3) is the most sensitive to extracellular pH and has the characteristic ability to generate a biphasic current, but few studies have focused on the role of ASIC3 in seizure. Here we found ASIC3 expression was increased in the hippocampus of pilocarpine induced seizure rats, as well as in hippocampal neuronal cultures undergoing epileptiform discharge elicited by Mg²⁺-free media. Furthermore, ASIC3 blockade by the selective inhibitor APETx2 shortened seizure onset latency and increased seizure severity compared with the control in the pilocarpine induced seizure model. Incubation with APETx2 enhanced the excitability of primary cultured hippocampal neurons in Mg²⁺-free media. Notably, the aggravated seizure was associated with upregulation of the N-methyl-D-aspartate subtype of glutamate receptors (NMDARs), increased NMDAR mediated excitatory neurotransmission and subsequent activation of the Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and cAMP-response element binding protein (CREB) signaling pathway. Moreover, co-immunoprecipitation confirmed the interaction between ASIC3 and NMDAR subunits, and NMDARs blockade prevented the aggravated seizure caused by ASIC3 inhibition. Taken together, our findings suggest that ASIC3 inhibition aggravates seizure and potentiates seizure induced hyperexcitability at least partly by the NMDAR/CaMKII/CREB signaling pathway, which implies that ASIC3 agonists may be a promising approach for seizure treatment.

Keywords: APETx2; Acid sensing ion channel 3 (ASIC3); Ca2+/calmodulin-dependent protein kinase II (CaMKII); Epilepsy; N-methyl-D-aspartate subtype of glutamate receptors (NMDARs); Seizure; cAMP-response element binding protein (CREB).