Measuring surface expression and endocytosis of GPCRs using whole-cell ELISA.

G protein-coupled receptors (GPCRs) constitute a large class of cell surface receptors that recognize a wide array of ligands and mediate a diverse spectrum of signaling pathways. Measuring their surface expression in cellular context is a critical aspect of studying their signaling pathways and cellular outcomes. Upon addition of agonist, GPCRs typically undergo internalization and traffic from the plasma membrane to endosomal compartments. Although radioligand binding has been the primary assay to measure GPCR surface expression and internalization, whole-cell ELISA has now emerged as a powerful alternative approach. Here, we present a step-by-step whole-cell ELISA protocol for measuring relative surface expression and agonist-induced internalization of GPCRs containing engineered N-terminal epitope tag and recombinantly expressed in heterologous cells.