title: Hypoxia Induces Internalization of κ-Opioid Receptor.
abstract: It has been demonstrated that κ-opioid receptor agonists can reduce hypoxia-ischemia brain injury in animal models. However, it is unclear how the κ-opioid receptor responds to hypoxia-ischemia. In the current study, the authors used an in vitro model of oxygen-glucose deprivation and reoxygenation to explore how κ-opioid receptors respond to hypoxia and reoxygenation.
  
  
  
  Mouse neuroblastoma Neuro2A cells were stably transfected with mouse κ-opioid receptor-tdTomato fusion protein or Flag-tagged mouse κ-opioid receptor, divided into several groups (n = 6 to 12), and used to investigate the κ-opioid receptor movement. Observations were performed under normal oxygen, at 30 min to 1 h after oxygen-glucose deprivation and at 1 h after reoxygenation using high-resolution imaging techniques including immunoelectronmicroscopy in the presence and absence of κ-opioid receptor antagonist, dynamin inhibitors, potassium channel blockers, and dopamine receptor inhibitor.
  
  
  
  Hypoxic conditions caused the κ-opioid receptor to be internalized into the cells. Inhibition of dynamin by Dyngo-4a prevented the receptor internalization. Interestingly, a specific κ-opioid receptor antagonist norbinaltorphimine blocked internalization, suggesting the involvement of activation of a specific κ-opioid receptor. κ-Opioid receptor internalization appears to be reversed by reoxygenation. Quantities of intracellular κ-opioid receptor-associated gold particles as demonstrated by immunoelectron microscopy were increased from 37 to 85% (P < 0.01) after oxygen-glucose deprivation. Potassium channel blockers and dopamine receptor inhibitor failed to block hypoxia-induced κ-opioid receptor internalization.
  
  
  
  Hypoxia induces reversible κ-opioid receptor internalization, which was inhibited by selective κ-opioid receptor antagonists or dynamin inhibitor, and can be reversed by reoxygenation in neuroblastoma cells, indicating the modulating effects between κ-opioid receptor and hypoxia via κ-opioid receptor activation and the dynamin-dependent mechanism.
authors.affiliation: From the Department of Anesthesia, Beijing Tongren Hospital, Capital Medical University, Beijing, China (C.X., X.L.); Department of Anesthesiology and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania (C.X., X.L., C.C., H.B., R.L.); and Department of Anesthesia, Beijing Shijitan Hospital, Capital Medical University, Beijing, China (T.L.).
authors.forename: Chunhua
authors.initials: C
authors.lastname: Xi
authors.forename: Xuan
authors.initials: X
authors.lastname: Liang
authors.forename: Chunhua
authors.initials: C
authors.lastname: Chen
authors.forename: Hasan
authors.initials: H
authors.lastname: Babazada
authors.forename: Tianzuo
authors.initials: T
authors.lastname: Li
authors.forename: Renyu
authors.initials: R
authors.lastname: Liu
mesh_terms: D000818:Animals; D018929:Cell Culture Techniques; D004195:Disease Models, Animal; D034281:Dynamins / Q000037:antagonists & inhibitors; D006835:Hydrazones; D000860:Hypoxia / Q000378:metabolism*; D066298:In Vitro Techniques; D051379:Mice; D009284:Naphthols; D017473:Receptors, Opioid, kappa / Q000378:metabolism*
chemical_list: D006835:Hydrazones; D009284:Naphthols; D017473:Receptors, Opioid, kappa; C568360:dyngo-4a; D034281:Dynamins