The μ-opioid receptor in the 7315c tumor cell

Abstract

Experiments were carried out to show that the 7315c tumor cell possesses μ-, but apparently not δ- or κ-opioid receptors. The binding data for [ 3H]Tyr-D-Ala-Gly-Me-Phe-Gly-ol ([ 3H]DAGO) indicate the presence of one class of high affinity site (K d = 1.5 ± 0.3 nM, B max = 50 fmol/mg). An irreversible alkylating agent, 2-(p-ethoxybenzyl)-1-diethylaminoethyl-5-isothiocyanobenzimidazole i isothiocyanate (BIT), with selectivity for μ- over δ-opioid receptors, completely blocked [ 3H]Tyr-D-Ala-Gly-Phe-Met-NH 2 ([ 3H]DALAMID) binding to 7315c cell membranes. Another irreversible alkylating agent, fentanyl isothiocyanate (FIT) with selectivity for δ- over μ-opioid receptors, had no effect on [ 3H]DALAMID binding. Since [ 3H]DALAMID binds equally well to μ- and δ-opioid receptors, these results indicate the presence of μ- but not δ-opioid receptors on 7315c cells. The K i of U50488, a κ selective ligand, for [ 3H]ethylketocyclazocine ([ 3H]EKC) binding sites was 400 ± 100 nM, suggesting the absence of κ-opioid receptors on the 7315c tumor cell. These results are consistent with the presence of μ-opioid receptors in 7315c tumor cells.