Abstract
Neuropeptide Y (NPY) and peptide YY (PYY) are homologous 36 amino acid amidated peptides that often, but not always, exert similar actions and binding profiles. The present study of cultured cells confirms that both peptides as well as radioiodinated analogs, i.e.
125I-Bolton-Hunter-NPY (
125I-BH-NPY) and
125I-peptide YY (
125I-PYY), show high affinity to binding sites/receptors of the previously proposed Y1- and Y2-subtypes, selectively expressed by the human neuroblastoma cell lines, SK-N-MC and SK-N-BE(2), respectively. In contrast, bovine adrenal chromaffin cells did not bind
125I-PYY, while displaying high affinity
125I-BH-NPY sites, and may therefore represent a cell type expressing a recently proposed Y3-type of (NPY-preferring) receptors. Several non-labeled fragments/analogs have been used in displacement experiments to further characterize the structural requirements for Y1-, Y2-, and Y3-type binding. In every instance, specific binding was reduced by addition of 5′-guanylylimidodiphosphate [Gpp(NH)p], indicating that the three receptor subtypes belong to the G-protein-coupled superfamily of receptors. Moreover, in both neuroblastoma cell lines, the peptides elicited, with appropriate orders of potency, reduction of forskolin-stimulated adenosine 3′,5′-cyclic monophosphate (cAMP) accumulation. Finally, NPY-evoked
45Ca
2+ influx was observed in SK-N-MC and in chromaffin cells. A common dual coupling mechanism of NPY/PYY receptors, i.e. to reduction of cAMP and to Ca
2+ elevation, is therefore suggested to exist, although both phenomena could not be demonstrated in every cell type.
