Early functional GPCR assays rely primarily on the measurement of G-protein-mediated 2nd messenger. Taking advantage of the continuously deepening understanding of GPCR signal transduction, many G-protein-independent pathways are used to detect the activity of GPCRs, and may provide additional information for the functional selectivity of candidate compounds. With the combination of automated imaging systems and label-free detection systems, such assays are now suitable for high-throughput screening (HTS).
