Delta-opioid receptors modulate neurogenic smooth muscle contractions and mucosal ion transport in the porcine distal small intestine. We compared specific δ-opioid binding sites in neuronal membranes isolated from the inner submucosal plexus and myenteric plexus of this gut region. In both preparations, the δ-opioid receptor antagonist naltrindole displaced [3H]diprenorphine from two binding sites. [3H]Naltrindole bound specifically to a single high-affinity site that was displaced by δ-opioid receptor ligands with the rank order of affinity: naltriben >7-benzylidenenaltrexone>deltorphin II>[D-Pen2, D-Pen 5] enkephalin. Relative decreases in δ-opioid receptor agonist affinity in the presence of Na+ and other ions differed in submucosal and myenteric membranes. The κ-opioid receptor antagonist norbinaltorphimine displaced [3H]naltrindole binding in myenteric membranes (Ki=7.2 nM). Delta-opioid receptors in submucosal and myenteric plexuses of porcine ileum appear to differ in some respects.
Bibliographical noteFunding Information:
This investigation was supported in part by National Institutes of Health grants R01 DA-10200 and T32 DA-07234.
- Diprenorphine (Pig)
- Enteric nervous system
- Opioid receptor