Extracellular Contributions to Alcohol Modulation of Pentameric Ligand-Gated Ion Channels

Abstract

The behavioral effects of alcohol action on the human brain are widely known, but the mechanisms through which they occur are poorly understood. Glycine receptors play a role in neuronal modulation by alcohol, however, the exact molecular mechanisms through which this modulation occurs are unknown due to difficulties in high-resolution imaging of receptor structures. Bacterial receptor homolog, GLIC F238A, of known structure is modulated similarly to Glycine receptors and may prove a useful model to further investigate alcohol and anesthetic interactions with pentameric ligand-gated ion channels. Recent studies have shown that residues in extracellular Loop 2, particularly positions equivalent to D31 in GLIC, influence alcohol modulation in Glycine receptors. Based on these results, we predicted that point mutations D31N and D31S in Loop 2 in GLIC would reduce alcohol modulation of the GLIC F238A model system. To test this prediction, we generated site-directed mutations to quantify structural effects on ion channel gating and alcohol modulation using two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes. Preliminary results help to elucidate the role of Loop 2 in modulation of ion channels throughout this family, and inform the validation of GLIC as a model system for modulation of ligand-gated ion channels.