CHARACTERIZATION OF A TRIPLE OPIOID SYSTEM IN THE HUMAN NEUROBLASTOMANMB CELL-LINE

The human neuroblastoma NMB cell line was found to contain the three t ypes of opioid receptors (60% delta 25% kappa and 15% mu). The opioid receptors were negatively coupled to adenylyl-cyclase, Maximal reducti on in cAMP content was achieved by selectively activating single recep tor types, indicating the co-presence of the various opioid receptors in the same cells. The opioid receptors in NMB cells were up-regulated following prolonged exposure to the opioid antagonist naloxone and do wn-regulated following chronic treatment with the opioid agonist etorp hine. Down-regulation was time-, dose- and temperature-dependent and w as inhibited by colchicine and sodium azide. The NMB culture is presen ted as an excellent experimental model for studying the selective acti vation and regulation of the different opioid receptor types when they are co-expressed in the same neuron, as well as for studying interact ions between the various opioid receptors.