We describe methods based on live cell fluorescent microscopy and mass
spectrometry to characterize the mechanism of endosomal cAMP production and its
regulation using the parathyroid hormone (PTH) type 1 receptor as a prime
example. These methods permit to measure rapid changes of cAMP levels in
response to PTH, kinetics of endosomal ligand–receptor interaction, pH
changes associated with receptor trafficking, and to identify the endosomal
receptor interactome.