Anti-seizure mechanisms of midazolam and valproate at the β2(L51M) variant of the GABAA receptor

Abstract

Genetic sequencing is identifying an expanding number of variants of GABA_A receptors associated with human epilepsies. We identified a new de novo variant of the β2 subunit (β2L51M) of the inhibitory GABA_A receptor associated with seizures. Our analysis determined the pathogenicity of the variant and the effects of anti-seizure medications. Our data demonstrates that the variant reduced cell surface trafficking and peak GABA-gated currents. Synaptic currents mediated by variant-containing receptors decayed faster than wild-type and single receptor currents showed that the variant shortened the duration of receptor activity by decreasing receptor open times. We tested the effects of the anti-seizure medications, midazolam, carbamazepine and valproate and found that all three enhance variant receptor surface expression. Additionally, midazolam restored receptor function by increasing single receptor active periods and synaptic current decay times towards wild-type levels. By contrast, valproate increased synaptic peak currents, event frequency and promoted synaptic bursting. Our study identifies a new disease-causing variant to the GABA_A receptor, profiles its pathogenic effects and demonstrates how anti-seizure drugs correct its functional deficits.

Keywords: Anti-seizure drugs; Epilepsy; GABA(A) receptor; Valproate; Variants.