The functional monitoring of GPCR linked to different activation pathways The sensitivity of the assay parallels those of standard assays such as calcium and cAMP measurements. The adjoining figure shows the results of monitoring the activation of histamine H1 receptor (Gq) (top panel), Dopamine 1 receptor (Gs) (middle panel), and 5HT1 receptor (Gi) (bottom panel) all expressed in the CHO cell background. The RT-CES® ®system can also be used for functional monitoring of endogenous GPCR activation in cell lines and primary cells.