Ivermectin activates GIRK channels in a PIP 2 -dependent, G βγ -independent manner and an amino acid residue at the slide helix governs the activation.

Key Points: Ivermectin (IVM) is a widely used antiparasitic drug in humans and pets which activates glutamate-gated Cl ^- channel in parasites. It is known that IVM binds to the transmembrane domains (TMs) of several ligand-gated channels, such as Cys-loop receptors and P2X receptors. We found that the G-protein-gated inwardly rectifying K ⁺ (GIRK) channel, especially GIRK2, is activated by IVM directly in a G _βγ -independent manner, but the activation is dependent on phosphatidylinositol-4,5-biphosphate (PIP ₂ ). We identified a critical amino acid residue of GIRK2 for activation by IVM, Ile82, located in the slide helix between the TM1 and the N-terminal cytoplasmic tail domain (CTD). The results demonstrate that the TM-CTD interface in GIRK channel, rather than the TMs, governs IVM-mediated activation and provide us with novel insights on the mode of action of IVM in ion channels.
Abstract: Ivermectin (IVM) is a widely used antiparasitic drug in humans and pets which activates glutamate-gated Cl ^- channel in parasites. It is also known that IVM binds to the transmembrane domains (TMs) of several ligand-gated channels, such as Cys-loop receptors and P2X receptors. In this study, we found that the G-protein-gated inwardly rectifying K ⁺ (GIRK) channel is activated by IVM directly. Electrophysiological recordings in Xenopus oocytes revealed that IVM activates GIRK channel in a phosphatidylinositol-4,5-biphosphate (PIP ₂ )-dependent manner, and that the IVM-mediated GIRK activation is independent of G _βγ subunits. We found that IVM activates GIRK2 more efficiently than GIRK4. In cultured hippocampal neurons, we also observed that IVM activates native GIRK current. Chimeric and mutagenesis analyses identified an amino acid residue unique to GIRK2 among the GIRK family, Ile82, located in the slide helix between the TM1 and the N-terminal cytoplasmic tail domain (CTD), which is critical for the activation. The results demonstrate that the TM-CTD interface in GIRK channels, rather than the TMs, governs IVM-mediated activation. These findings provide us with novel insights on the mode of action of IVM in ion channels that could lead to identification of new pharmacophores which activate the GIRK channel.
(© 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.)