Irreversible binding kinetics of neuropeptide Y ligands to Y2 but not to Y1 and Y5 receptors.

Neuropeptide Y (NPY) receptors type 1 (Y1), type 2 Y2) and type 5 (Y5) were tested for their kinetic properties to bind radiolabeled NPY or PYY. Rapid association and dissociation was observed with recombinant (HEK293 cells) and endogenous (SK-N-MC cells) human Y1 and recombinant mouse Y5 receptors. Recombinant (HEK293) and endogenous (SMS-KAN) human Y2 receptors bound both radiolabels comparable to the Y1 receptors, but only minimal ( approximately 20%) dissociation of both radiolabels was observed after long incubation time (>8 h). Furthermore, neither peptide nor small molecule Y2 ligands efficiently competed for binding to Y2 receptors once association binding had been initiated. The Y2-selective antagonist BIIE0246 behaved as an insurmountable antagonist in functional assays when pre-incubated for 30 min before agonist addition, but was a competitive antagonist when co-applied with the agonist. These data show that Y2 receptors in contrast to Y1 and Y5 receptors bind their ligands in an irreversible manner. Copyright (c) 2005 S. Karger AG, Basel.