Our laboratory was among the first to propose the existence of δ receptor subtypes: a δ site thought to be associated with a μ-δ-opioid receptor complex termed the δcx binding site and δ site not associated with the μ-δ-opioid receptor complex, termed the δncx site. In previous studies, we assayed the δcx site with [3H][d-Ala2,d-Leu5]enkephalin using rat brain membranes depleted of δncx sites by pretreatment with the site-directed acylating agent, (+)-trans-SUPERFIT. In the present study, we investigated, using (+)-trans-SUPERFIT-pretreated membranes, the possibility of heterogeneity of the δcx binding site. Two sites were resolved: the δcx-1 site at which μ ligands are potent noncompetitive inhibitors and δ ligands are weak competitive inhibitors, and the δcx-2 site has a δ-like ligand-selectivity profile, several experiments distinguished it from the δncx site. Two lines of evidence suggest that the δncx site corresponds to the cloned δ receptor. One, the δ receptor was cloned from the NG108-15 cell line, and this receptor, like the δncx binding site, irreversibly binds SUPERFIT and (+)-trans-SUPERFIT. Secondly, administration of δ-antisense DNA selectively decreases δncx binding. Viewed collectively, the major finding of this study is the discovery of a novel SUPERFIT-insensitive and δ-antisense-insensitive δcx-2 binding site.
- Antisense DNA
- Opioid receptors
- δ Receptor
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience