Ethosuximide: subunit- and Gβγ-dependent blocker and reporter of allosteric changes in GIRK channels

The antiepileptic drug ethosuximide (ETX) suppresses epileptiform activity in a mouse model of GNB1 syndrome, caused by mutations in Gβ ₁ protein, likely through the inhibition of G-protein gated K ⁺ (GIRK) channels. Here we show that ETX is a subunit-selective, allosteric blocker of GIRKs. The potency of ETX block is increased by the G protein subunit dimer Gβγ, the physiological activator of GIRKs. Molecular dynamics (MD) simulations and mutagenesis locate the ETX binding site in GIRK2 to a region associated with phosphatidylinositol-4,5-bisphosphate (PIP ₂ ) regulation, and suggest that ETX acts by closing the HBC gate and altering channel’s interaction with PIP ₂ . The apparent affinity of ETX block is highly sensitive to changes in channel gating caused by mutations in Gβ ₁ or GIRK subunits. Our findings pose GIRK as a potential therapeutic target for ETX, and ETX as a potent allosteric GIRK blocker and a tool for probing gating-related conformational changes in GIRK.