beta-funaltrexamine and Brain-Neoplasms

The potential interactions of natively expressed mu-opioid and opioid receptor-like (ORL1) receptors were studied by exposing intact BE(2)-C cells to agonists or antagonists for 1 h. Pretreatment with the mu-opioid receptor agonist, [D-Ala(2), N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO), or the ORL1 receptor agonist, orphanin FQ/nociceptin desensitized both mu-opioid and ORL1 receptor responses. beta-Funaltrexamine (beta-FNA) pretreatment also blocked both mu-opioid and ORL1 receptor responses, but only mu-opioid receptor binding was reduced. Moreover, beta-FNA (1 microM) failed to inhibit specific ORL1 receptor binding.

Topics: Brain Neoplasms; Cyclic AMP; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Humans; Morphine; Naltrexone; Narcotic Antagonists; Narcotics; Neuroblastoma; Nociceptin; Nociceptin Receptor; Opioid Peptides; Receptors, Opioid; Receptors, Opioid, mu; Tumor Cells, Cultured

The irreversible opioid receptor antagonists naloxonazine and beta-funaltrexamine have been used to determine whether multiple mu-opioid receptors exist on undifferentiated SH-SY5Y human neuroblastoma cells. Naloxonazine binds irreversibly to the mu 1-opioid receptor subtype and reversibly to the mu 2-opioid receptor subtype. On SH-SY5Y cells naloxonazine afforded a Ki of 3.4 +/- 0.7 nM, and was fully reversible, indicating the mu-opioid receptor population on SH-SY5Y cells was solely of the mu 2-opioid receptor subtype. The alkylating agent beta-funaltrexamine was maximally able to alkylate only 60% of the mu-opioid receptor sites on SH-SY5Y cells, labelled with [3H]diprenorphine or [3H][D-Ala2,MePhe4,Gly(ol)5]enkephalin (DAMGO). The reversible binding of naloxonazine and the insensitivity of a percentage of the mu-opioid receptor sites to alkylation by beta-funaltrexamine suggests that differences do exist in the mu 2-opioid receptor population on undifferentiated SH-SY5Y cells. This may indicate further heterogeneity or the inability of beta-funaltrexamine to alkylate all relevant nucleophilic groups in a single population of receptors.

Topics: Amino Acid Sequence; Animals; Brain Neoplasms; Cerebral Cortex; Diprenorphine; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Humans; Ligands; Molecular Sequence Data; Naloxone; Naltrexone; Neuroblastoma; Rats; Receptors, Opioid, mu; Somatostatin; Tumor Cells, Cultured