Ligand binding profiles of delta-opioid receptor in human cerebral cortex membranes - Evidence of delta-opioid receptor heterogeneity

In this study, receptor binding profiles of opioid ligands for subtypes of opioid delta -receptors were examined employing [H-3]D-Pen(2),D-Pen(5)-enke phalin ([H-3]DPDPE) and [H-3]Ile(5,6)-deltorphin II ([H-3]Ile-Delt II) in h uman cerebral cortex membranes. [H-3]DPDPE, a representative ligand for del ta (1) sites, labeled a single population of binding sites with apparent af finity constant (Kd) of 2.72 +/- 0.21 nM and maximal binding capacity (Bmax ) value of 20.78 +/- 3.13 fmol/mg protein. Homologous competition curve of [H-3]Ile-Delt II, a representative ligand for delta (2) sites, was best fit by the one-site model (Kd = 0.82 +/- 0.07 nM). Bmax value (43.65 +/- 2.41 fmol/mg) for [H-3]Ile-Delt II was significantly greater than that for [H-3] DPDPE. DPDPE, [D-Ala(2),D-Leu(5)]enkephalin (DADLE) and 7-benzylidenaltrexo ne (BNTX) were more potent in competing for the binding sites of [H-3]DPDPE than for those of [H-3]Ile-Delt II. On the other hand, deltorphin II (Delt II), [D-Ser(2),Leu(5),Thr(6)]enkephalin (DSLET), naltriben (NTB) and naltr indole (NTI) were found to be equipotent in competing for [H-3]DPDPE and [H -3]Ile-Delt II binding sites. These results indicate that both subtypes of opioid delta -receptors, delta (1) and delta (2), exist in human cerebral c ortex with different ligand binding profiles. (C) 2001 Elsevier Science Inc . All rights reserved.