Oral Presentation 2014 International Biophysics Congress

Modulating the active periods of GABAA receptors (#103)

Angelo Keramidas 1 , Christine Dixon 1 , Joe W. Lynch 1
  1. Queensland Brain Institute, St Lucia, QLD, Australia

The γ-aminobutyric acid A receptor (GABAAR) is the main mediator of neuronal inhibition in the brain. It’s a major therapeutic target for the treatment of some neurological/psychiatric disorders, such as epilepsy, anxiety and insomnia. The drugs of choice for treatment of these disorders are benzodiazepine site ligands, which modulate GABAAR function. Our understanding of how these drugs alter GABAAR function remains both rudimentary and contentious.

To address this deficiency we aimed to develop a consensus activation mechanism for the GABAAR, and apply it to benzodiazepine site ligand modulation. We used single channel analysis and rapid ligand application to excised membrane patches expressing five isoforms (α1β2γ2L, α1β2γ2S, α1β2γ1, α2β2γ2L and α2β2γ1) of synaptic GABAAR. An activation mechanism with two GABA binding steps, three conducting and three non-conducting configurations was derived from single channel data. We then used this mechanism to simulate ensemble currents that agreed well with recorded macropatch currents for each receptor. A key feature of single channel activity was the subunit-dependent duration of an active period (cluster). α2-containing receptors exhibited longer clusters, which our mechanism suggests is due to a higher affinity for GABA. A substantial increase in the cluster duration was also observed in α1β2γ2S receptors when exposed to two benzodiazepine site ligands, eszopiclone and zolpidem. Our mechanism suggests that here the drugs modulated receptor activity by altering transition states downstream of the ligand binding steps. Our results demonstrate that cluster length is a key functional property of the GABAAR, and show how benzodiazepine site ligands modulate this property.