Characterization of non-opioid [3H]Dynorphin A-(1-13) Binding Sites in the Rat Heart

The binding characteristics of [3H]Dynorphin A-(1-13) ([3H]Dyn A-(1-13)) were examined in membrane preparations of rat heart. Saturation binding studies with increasing concentrations between 2.5 and 500 nM indicated that [3H]Dyn A-(1-13) binds to a single population of sites with a Kd of 285 nM and a Bmax of 215 pmol/mg protein. [3H]Dyn A-(1-13) binding is sensitive to trypsin treatment and it is inhibited by Zn2+ and Mg2+ with IC50 values of 159 and 310 μM, respectively. Dyn A and related peptides competes with the binding of [3H]Dyn A-(1-13) with the following order of potency: Dyn A-(1-13) > Dyn A > Dyn B > α-neo-endorphin > Dyn A-(1-8). The non-opioid peptides Dyn A-(2-13), Dyn A-(3-13) and Dyn A-(5-13) are as potent (Ki of 0.35, 0.44 and 0.59 μM, respectively) as Dyn A-(1-13) (Ki of 0.36 μM) in inhibiting [3H]Dyn A-(1-13) binding while Leu-enkephalin (Leu-Enk) exhibits no inhibitory effect at 100 μM. Selective ligands for kappa (κ: U-50, 488H, U-69, 593), mu (μ: [D-Ala2, MePhe4, Glyol5]Enk) and delta (δ: [D-Ser2, Thr6]Leu-Enk) opioid receptors as well as for phencyclidine (PCP: MK-801, TCP) and sigma (σ: (+)-SKF-10047, DTG, 3(+)-PPP) receptors show little or no inhibition of [3H]Dyn A-(1-13) binding at 100 μM. These results indicate that the heart contains a low affinity high capacity binding site for Dyn A and related peptides, distinct from opioid, PCP and σ receptors.