GPCR second messenger assays
Following activation, GPCRs transmit information within cells via the modulation of two second messengers, cyclic AMP for Gi/s coupled receptors and inositol-triphosphate (IP3) for Gq coupled receptors.
While cAMP accumulates in the presence of a phosphodiesterase inhibitor (e.g. IBMX), IP3 is unstable and rapidly enters the metabolic inositol phosphate cascade. However, in the presence of lithium chloride, IP1, a metabolic product of IP3, accumulates and offers a viable biomarker for the visualization of Gq-coupled receptor activity.