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 [3H]diprenorphine (DPN), an opioid receptor antagonist, and [3H] [D-Ala2,MePhe4, Gly(ol)5]enkephalin (DAMGO), a mu receptor selective agonist. Binding of [3H]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 [3H]DAMGO was unaffected by 1.0% halothane, but 5.0% halothane reduced the affinity, with a modest increase in Kd (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.