Irreversible binding kinetics of neuropeptide y Ligands to Y-2 but not to Y-1 and Y-5 receptors

Neuropeptide Y (NPY) receptors type 1 (Y-1), type 2 Y-2) and type 5 (Y-5) 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 Y-1 and recombinant mouse Y-5 receptors. Recombinant ( HEK293) and endogenous (SMS-KAN) human Y-2 receptors bound both radiolabels comparable to the Y-1 receptors, but only minimal (similar to 20%) dissociation of both radiolabels was observed after long incubation time (>8 h). Furthermore, neither peptide nor small molecule Y-2 ligands efficiently competed for binding to Y 2 receptors once association binding had been initiated. The Y-2-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 Y-2 receptors in contrast to Y-1 and Y-5 receptors bind their ligands in an irreversible manner. Copyright (C) 2005 S. Karger AG, Basel.