Investigating the ligand agonism and antagonism at the D(2long) receptor by dynamic mass redistribution.

The signalling of the D(2) receptor (D(2)R), a G protein-coupled receptor (GPCR), is a complex process consisting of various components. For the screening of D(2)R ligands, methods quantifying distinct second messengers such as cAMP or the interaction of the receptor with β-arrestin, are commonly employed. In contrast, a label-free biosensor technology like dynamic mass redistribution (DMR), where it is mostly unknown how the individual signalling pathways contribute to the DMR signal, provides a holistic readout of the complex cellular response. In this study, we report the successful application of the DMR technology to CHO-K1 cells stably expressing the human dopamine D(2long) receptor. In real-time kinetic experiments, studies of D(2)R reference compounds yielded results for agonists and antagonists that were consistent with those obtained by conventional methods and also allowed a discrimination between partial and full agonists. Furthermore, investigations on the signalling pathway in CHO-K1 hD(2long)R cells identified the Gα(i/o) protein as the main proximal trigger of the observed DMR response. The present study has shown that the DMR technology is a valuable method for the characterisation of putative new ligands and, due to its label-free nature, suggests its use for deorphanisation studies of GPCRs.