The mu-opioid receptor in the 7315c tumor cell

Experiments were carried out to show that the 7315c tumor cell possesses mu-, but apparently not delta- or kappa-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 (Kd = 1.5 +/- 0.3 nM, Bmax = 50 fmol/mg). An irreversible alkylating agent, 2-(p-ethoxybenzyl) 1-diethylaminoethyl-5-isothiocyanobenzimidazole isothiocyanate (BIT), with selectivity for mu- over delta-opioid receptors, completely blocked [3H]Tyr-D-Ala-Gly-Phe-Met-NH2 ([3H]DALAMID) binding to 7315c cell membranes. Another irreversible alkylating agent, fentanyl isothiocyanate (FIT) with selectivity for delta- over mu-opioid receptors, had no effect on [3H]DALAMID binding. Since [3H]DALAMID binds equally well to mu- and delta-opioid receptors, these results indicate the presence of mu- but not delta-opioid receptors on 7315c cells. The Ki of U50488, a kappa selective ligand, for [3H]ethylketocyclazocine ([3H]EKC) binding sites was 400 +/- 100 nM, suggesting the absence of kappa-opioid receptors on the 7315c tumor cell. These results are consistent with the presence of mu-opioid receptors in 7315c tumor cells.