A subtype-selective photoswitchable agonist for precise manipulation of GABA receptors.

BACKGROUND AND PURPOSE

Neuronal inhibition is largely mediated by type-A GABA receptors (GABARs), a family of ligand-gated chloride-permeable channels, which can be sub-classified by their subunit composition. Unravelling the function and distribution of each GABAR subtype is essential for a holistic understanding of GABAergic inhibition in health and diseases. Photopharmacology, a technique that utilises light-sensitive compounds to precisely manipulate endogenous proteins, is powerful for this purpose. To resolve the molecular complexity of neuronal inhibition, we aimed to develop subtype-selective photoswitchable agonists for GABARs.

EXPERIMENTAL APPROACH

Inspired by THIP (gaboxadol), an agonist selective for δ subunit-containing GABARs (δ-GABARs), we merged a photoswitch moiety (azobenzene) with an analogue of THIP (isoguvacine) to construct Az-IGU. Using whole-cell voltage-clamp recording, Az-IGU was tested on 13 GABAR subtypes expressed in human embryonic kidney (HEK) cells. Optical activation of endogenous GABARs was examined via electrophysiology in cultured cortical neurons.

KEY RESULTS

In HEK cells, Az-IGU exerted reversible photo-agonism selectively for α4β3δ and α6β3δ GABARs, two major mediators of tonic inhibition. Pharmacological and mutagenesis studies suggested that activation of the α4β3δ GABAR involves interaction between Az-IGU and the GABA-binding pocket and is strongly correlated with the spontaneous activity of the receptor. In cultured cortical neurons, photoisomerisation of Az-IGU triggered responses that enabled reversible control of action potential firing.

CONCLUSIONS AND IMPLICATIONS

GABARs are potential therapeutic targets for many disorders. However, their physiological and pathophysiological roles remain largely unexplored. Az-IGU may enable photopharmacological studies of α4/6β3δ GABARs, providing new opportunities for biomedical and neurobiological applications.