Label-Free Whole Cell Biosensing for High-Throughput Discovery of Activators and Inhibitors Targeting G Protein-Activated Inwardly Rectifying Potassium Channels

Dynamic mass redistribution (DMR)
and cellular dielectric spectroscopy
(CDS) are label-free biosensor technologies that capture real-time
integrated cellular responses upon exposure to extra- and intracellular
stimuli. They register signaling routes that are accompanied by cell
shape changes and/or molecular movement of cells proximal to the biosensor
to which they are attached. Here, we report the unexpected observation
that robust DMR and CDS signatures are also elicited upon direct stimulation
of G protein-activated inwardly rectifying potassium (GIRK) channels,
which are involved in the regulation of excitability in the heart
and brain. Using ML297, a small-molecule GIRK activator, along with
channel blockers and cytoskeletal network inhibitors, we found that
GIRK activation exerts its effects on cell shape by a mechanism which
depends on actin but not the microtubule network. Because label-free
real-time biosensing (i) quantitatively determines concentration dependency
of GIRK activators, (ii) accurately assesses the impact of GIRK channel
blockers, (iii) is high throughput-compatible, and (iv) visualizes
previously unknown cellular consequences downstream of direct GIRK
activation, we do not only provide a novel experimental strategy for
identification of GIRK ligands but also an entirely new angle to probe
GIRK (ligand) biology. We envision that DMR and CDS may add to the
repertoire of technologies for systematic exploitation of ion channel
function and, in turn, to the identification of novel GIRK ligands
in order to treat cardiovascular and neurological disorders.