Within the continuous quest for the discovery of pharmacologically interesting compounds, the development
of new and superior drug screening assays is desired. In recent years, the use of label-free techniques
has paved the way for an alternative high-throughput screening method. An example is the Epic® opticalbased
biosensor that relies on dynamic mass redistribution (DMR) for detection. So far, DMR assays have
been mostly used to study G protein-coupled receptor (GPCR) pharmacology. Here, we demonstrate the
utility of this assay for investigating ligand-gated ion channel receptors. Using the immortalized IMR-32
neuroblastoma cell line, which expresses relatively high levels of several endogenous GABAA receptor subunits,
we show that GABA produces concentration-dependent cellular responses that can be measured
and quantified in real-time. With the aid of the GABAA receptor-specific agonist muscimol and the selective
antagonists gabazine and bicuculline, we confirm that the data corresponds to that of a GABAA receptor.
Based on quantitative real-time PCR measurements, the subunits α3, α5, β3 and θ are the most likely candidates
for integration into functional receptors. Our demonstration that label-free methods such as the Epic
technology can be used to characterize endogenous GABAA receptors in the IMR-32 cell line is exemplary
for the superfamily of ligand-gated ion channel receptors, and holds interesting perspectives in relation to
identifying novel mechanisms of action.