Characterization of ZFOR1, a putative delta-opioid receptor from the teleost zebrafish ( Danio rerio)

ZFOR1 is a putative opioid receptor from zebrafish brain which has 66% homology with the mammalian δ-opioid receptor. When expressed in HEK293 cells ZFOR1 bound the non-selective opioid antagonist [ 3H]diprenorphine with high affinity. However, the binding of this ligand was not readily displaced by opioids selective for μ, δ or κ opioid receptors (affinities>1000 nM). Rather non-selective ligands showed good affinity, as did the non-peptide δ-ligand BW373U86 (Ki 69 nM), the δ-antagonist naltrindole (Ki 28 nM) and the peptide β-endorphin (Ki 37 nM). Agonist binding to the receptor encoded by ZFOR1 receptor stimulated the binding of [ 35S]GTPγS confirming coupling to G proteins. Study of the receptor should contribute to understanding of the evolution of the opioid system.