Effectiveness of direct GIRK activators varied somewhat between the two platforms (review Figure ?Number77c with ?with7f),7f), yet pEC50 calculation portrayed 551 while more potent than ML297 and 553 for both methods, and, moreover, classified all remaining analogs while inactive. 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 effect of GIRK channel blockers, (iii) is definitely high throughput-compatible, and (iv) visualizes previously unfamiliar cellular effects downstream of direct GIRK activation, we do not only provide a novel experimental strategy for recognition 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 systems for systematic exploitation of ion channel AVN-944 function and, in turn, to the recognition of novel GIRK ligands in order to treat cardiovascular and neurological disorders. Intro As G protein-gated inwardly rectifying potassium (GIRK, Kir3) channels are implicated in an increasing quantity of pathologies, they may be gaining focus as focuses on for pharmacological treatment.1,2 They exist as hetero- or homotetrameric constructions comprised of one or more of four subunits (GIRK1-4), depending on cells distribution.3,4 GIRKs are activated by G subunits of stimulated Gi protein-coupled receptors, thereby inducing neurons and cardiac pacemaker cells to hyperpolarize and, as such, regulate cellular excitability within heart and AVN-944 mind. GIRK channels have also been linked to pathologies related to perturbations of rhythmic action potential firing, such as epilepsy, cardiac arrhythmias, and Alzheimers disease among others.1,3?6 In order to fight these diseases, unrelenting search for new pharmacological treatment options has been underway. The recent development of the small molecule GIRK activator AVN-944 ML297 is definitely one such example that has shown positive effects in preclinical models of epilepsy,7 panic,8 and Alzheimers disease.9 Yet, identification of new GIRK channel agonists with subtype selectivity and tissue specificity is still an ongoing endeavor in search for molecules with therapeutic potential. Currently available methods for the investigation of ion channels and their ligands include automated electrophysiology and ion-specific fluorescence dyes.10,11 The former requires electrical access to the cell interior by either sealing a microelectrode onto the cell surface with gigaohm resistance (classical patch clamp) or dislodging the cells using their substrate in order to perform automated measurements (automated patch AVN-944 clamp).10 The second option relies on dyes which are loaded onto and caught within cells, where they react sensitively to influx of specific ions or changes in potential.11 Both techniques, with patch clamping still considered as gold standard, are powerful, yet technically challenging, time consuming, and only offer an insight into a channels conducting function and upstream regulatory elements. Optical-based dynamic mass redistribution (DMR) and cellular dielectric spectroscopy (CDS) are label-free biosensor platforms. They may be well established for the detection of integrated reactions in real-time when living cells are exposed to pharmacologically active stimuli.12?28 Rather than relying on specific endpoints, such as changes in electrical potentials or accumulation of ions, both biosensors deliver more complex time-resolved activity profiles of entire cells, without the need for physical access to cells or artificial labels (Figure ?Number11a,b). In addition to their initial purpose of visualizing activity of signaling-competent proteins within living cells, we here display that DMR and CDS also serve to monitor the cellular consequences that happen ATF1 upon direct GIRK channel activation. We present the molecular underpinnings associated with GIRK-mediated cell shape changes and raise the possibility that this mode of activation may be mechanistically unique from your endogenous Gi- activation pathway. Therefore, our results do not only present a novel method for detection of previously unrecognized GIRK-mediated downstream effects but also have important implications for GIRK ligand drug discovery. Open in a separate window Number 1 Label-free readouts visualize ML297-induced responses inside a GIRK1/2-specific manner. (a) DMR assay: cells are located on top of a resonant AVN-944 waveguide grating biosensor and exposed to polychromatic light at wavelengths between 827 and 832.5 nm. The composition of the optical grating and properties of the cells result in penetration of light 150 nm into the cells37?39 (part of detectable DMR). In this area, a specific wavelength of light is definitely reflected, whereas the rest is soaked up. If addition of pharmacological stimuli prospects to changes in cellular morphology, the optical denseness within the detection zone is modified leading to a change in the reflected wavelength . Compounds that cause a decrease in mass proximal to the biosensor (yellow trace) shift the reflected light to shorter wavelengths, whereas an increase of.