Fluorescence correlation spectroscopy (FCS) and photon counting histogram (PCH) analysis are powerful ways to study mobility and stoichiometry of G protein coupled receptor complexes, within microdomains of single living cells. However, relating thes... Read More about Fluorescence correlation spectroscopy, combined with bimolecular fluorescence complementation, reveals the effects of ?-arrestin complexes and endocytic targeting on the membrane mobility of neuropeptide Y receptors.