[³H]ethylketocyclazocine binding to NCB-20 hybrid neurotumor cells

Ethylketocyclazocine (EKC) binds to two sites on NCB-20 neuroblastoma x Chinese hamster brain hybrid cells (K(DH) = 2 nM, B(max) = 21,000 sites/cell; K(DL) = 27 nM, B(max) = 140,000 sites/cell. The high-affinity site has been characterized as a σ opiate receptor. The low-affinity site is relatively benzomorphan-specific, opioid peptides, morphine, etorphine, and naloxone do not compete at it. Rank order of potency among benzomorphans is (+)-EKC > Mr 2267 > (+) - ketocyclazocine > (+) -SKF 1004> bremazocine > cyclazocine. Among other drugs of interest that inhibit [³H]EKC binding are phencyclidine and its analogues, K(i) values for which are 0.2-40 μM. Stereoselectivity is the reverse of other opioid receptors: (+) - EKC >>> (-) - EKC, Mr 2267 > Mr 2266, (+) - SKF 10047 > (-) - SKF 10047. The site is sensitive to trypsin, but not to N-ethylmaleimide. Binding is insensitive to nucleotides, slightly sensitive to physiological concentrations of sodium, magnesium, and manganese ions and to EDTA but not EGTA.