Opioid binding site in EL-4 thymoma cell line

Using EL-4 thymoma cell-line we found a binding site similar to the k opioid receptor of the nervous system. The Scatchard analysis of the binding of [3H] bremazocine indicated a single site with a K/sub D/ = 60 +/- 17 nM and Bmax = 2.7 +/- 0.8 pmols/106 cells. To characterize this binding site, competition studies were performed using selective compounds for the various opioid receptors. The k agonist U-50,488H was the most potent displacer of [3H] bremazocine with an IC50 value = 0.57μM. The two steroisomers levorphanol and dextrorphan showed the same affinity for this site. While morphine, [D-Pen2, D-Pen5] enkephalin and β-endorphin failed to displace, except at very high concentrations, codeine demonstrated a IC50 = 60μM, that was similar to naloxone. 32 references, 3 figures, 2 tables