Neuropeptide Y (NPY) is an important neuromodulator in the central and peri
pheral nervous system. The peptide acts through different NPY receptor subt
ypes (Y1-Y5, y6) that belong to the family of G protein-coupled receptors.
In general, cellular responses to prolonged exposure to agonists of G prote
in-coupled receptors are attenuated, often through internalization of the r
eceptors and their bound ligands. In this study, a fluorescent labeled NPY
derivative was synthesized and characterized to investigate the internaliza
tion of NPY in the human neuroblastoma cell line SK-N-MC. Internalization w
as proven by binding experiments and subsequent acidic washing as well as b
y direct visualization by means of confocal laser scanning microscopy. Appr
oximately 20-30% of the fluorescent labeled NPY and a tritium-marked NPY we
re resistant to acid removal of cell surface-bound ligands indicating inter
nalization. Extracellular fluorescent labeled NPY was found to be distribut
ed heterogeneously in a clustered pattern, which suggests that the ligand-r
eceptor complex is collected in pits and caveolae followed by endocytosis.