Ligand‐induced μ opioid receptor internalization in enteric neurons following chronic treatment with the opiate fentanyl

Abstract

Morphine differs from most opiates for its poor ability to internalize μ opioid receptors (μORs). However, chronic treatment with morphine produces adaptational changes at the dynamin level, which enhance the efficiency of acute morphine stimulation to promote μOR internalization in enteric neurons. This study tested the effect of chronic treatment with fentanyl, a μOR internalizing agonist, on ligand-induced endocytosis and the expression of the intracellular trafficking proteins, dynamin and ß arrestin, in enteric neurons using organotypic cultures of the guinea pig ileum. In enteric neurons from guinea pigs chronically treated with fentanyl, μOR immunoreactivity was predominantly at the cell surface following acute exposure to morphine with a low level of μOR translocation, slightly higher than in neurons from naïve animals. This internalization was not due to morphine direct effect because it was also observed in neurons exposed to medium alone. By contrast, D-Ala2-N-Me-Phe4-Gly-ol5-enkephalin (DAMGO), a potent μOR-internalizing agonist, induced pronounced and rapid μOR endocytosis in enteric neurons from animals chronically treated with fentanyl or from naïve animals. Chronic fentanyl treatment did not alter dynamin or β-arrestin expression. These findings indicate that prolonged activation of μORs with an internalizing agonist such as fentanyl does not enhance the ability of acute morphine to trigger μOR endocytosis nor induces changes in intracellular trafficking proteins, as observed with prolonged activation of μORs with a poorly internalizing agonist such as morphine. Cellular adaptations induced by opiate chronic treatment might be ligand dependent and vary with the agonist efficiency to induce receptor internalization.

Insights into the Role of Opioid Receptors in the GI Tract: Experimental Evidence and Therapeutic Relevance

“…DAMGO, a selective MOR agonist with high internalizing efficiency, retains its ability to induce MOR internalization in neurons chronically stimulated with either morphine or fentanyl. This result indicates that chronic activation of MOR does not impair receptor trafficking in enteric neurons (Patierno et al , 2011; Anselmi et al , 2013). Different ligands might also affect the recycling pathways as suggested by the report that internalized MORs remain in the cytoplasm for at least 2 hours following stimulation with loperamide while DAMGO- and morphiceptin- (MOR agonist) activated receptors recycle back to the membrane within 2 hours (Lay et al , 2016).…”

“…This response is prevented by treatment with a dynamin inhibitor or neuronal transfection with a mutant dynamin, in the absence of a change in ß-arrestin levels (Duraffourd et al , 2014). By contrast, in enteric neurons chronically exposed to fentanyl, morphine-activated MORs do not internalize and dynamin localization and levels are unchanged (Anselmi et al , 2013). DAMGO, a selective MOR agonist with high internalizing efficiency, retains its ability to induce MOR internalization in neurons chronically stimulated with either morphine or fentanyl.…”

Effects of prolonged anesthesia with dexmedetomidine, fentanyl, or remifentanil on the self-renewal of mouse embryonic stem cells

“…Opioids can activate three classes of opioid receptors (μORs, δORs, and κORs) to modulate a variety of biological processes (Anselmi et al, 2013). Many opiates serve as important drugs for pain-control.…”

Opioid receptor desensitization: mechanisms and its link to tolerance

“…U50,488 and dynorphin A (1-17), but neither etorphine nor levorphanol, promote a time-, and concentration-dependent internalization of hKOR (Li et al, 2003 ). In several reports, morphine was described as a poor internalizing agonist of MOR in HEK cells (Keith et al, 1998 ; Whistler and Von Zastrow, 1998 ; Schulz et al, 2004 ; Just et al, 2013 ) but also in enteric neurons (Anselmi et al, 2013 ) and in brain slice from transgenic mice expressing a FLAG-tagged MOR (Arttamangkul et al, 2008 ). In few publications, MOR was shown to internalize upon morphine exposure.…”