DO NITROUS-OXIDE AND HALOTHANE INFLUENCE OPIOID RECEPTOR-BINDING IN SH-SY5Y HUMAN NEUROBLASTOMA-CELLS

The site of interaction of opioids and inhalation anaesthetic agents is unknown, but may be at the level of the opioid receptor. In this study we have used SH-SY5Y human neuroblastoma cells, which express both mu and delta receptors, to examine the effects of halothane on the receptor binding profiles of [H-3]diprenorphine (DPN), an opioid receptor antagonist, and [H-3] [D-Ala(2),MePhe(4), Gly(ol)(5)]enkephalin (DAMGO), a mu receptor selective agonist. Binding of [H-3]DPN and [3H] DAMGO was performed at 37 degrees C for 60 min in the presence of air, nitrous oxide (75%) or air containing halothane (0.5-5.0% v/v). Compared with air controls, neither 75% nitrous oxide nor 0.5, 1.0, 2.0 and 5.0% halothane influenced DPN binding variables. Binding of [H-3]DAMGO was unaffected by 1.0% halothane, but 5.0% halothane reduced the affinity, with a modest increase in K-d (1.15 (0.16) to 1.7 (0.2) nmol litre(-1)) without effect on Bmax. Our data suggest that the site of opioid and volatile anaesthetic interaction is not at the opioid receptor.