Characterization of neuropeptide Y binding sites in rat cardiac ventricular membranes

Neuropeptide Y (NPY) binding sites in rat cardiac ventricular membranes have been characterized in detail. 125I-NPY bound to the membranes with high affinity. Binding was saturable, reversible and specific, and depended on time, pH and temperature. Analysis of the binding data obtained under optimal conditions, 2 hr, 18 degrees C and at pH 7.5, revealed the presence of low and high affinity binding sites. The high affinity binding sites had an apparent dissociation constant (Kd) of 0.38 nM and a binding capacity (Bmax) of 7.13 fmol/mg protein. The apparent Kd and Bmax for low affinity binding sites were 22.34 nM and 261.25 fmol/mg protein, respectively. Peptides unrelated to NPY did not compete with 125I-NPY for the binding sites even at 1 microM concentrations, whereas homologous peptides, peptide YY (PYY) and pancreatic polypeptide (PP), and NPY(13-36) inhibited 125I-NPY binding but with lower potency compared to NPY. 125I-NPY binding was sensitive to the nonhydrolyzable GTP analog, Gpp(NH)p, suggesting that the NPY receptor is coupled to the adenylate cyclase system. The ventricular membrane receptor characterized in this study may play an important role in mediating the physiological effects of NPY in the heart.