title: Cortical delta-opioid receptors potentiate K+ homeostasis during anoxia and oxygen-glucose deprivation.
abstract: Central neurons are extremely vulnerable to hypoxic/ischemic insult, which is a major cause of neurologic morbidity and mortality as a consequence of neuronal dysfunction and death. Our recent work has shown that delta-opioid receptor (DOR) is neuroprotective against hypoxic and excitotoxic stress, although the underlying mechanisms remain unclear. Because hypoxia/ischemia disrupts ionic homeostasis with an increase in extracellular K(+), which plays a role in neuronal death, we asked whether DOR activation preserves K(+) homeostasis during hypoxic/ischemic stress. To test this hypothesis, extracellular recordings with K(+)-sensitive microelectrodes were performed in mouse cortical slices under anoxia or oxygen-glucose deprivation (OGD). The main findings in this study are that (1) DOR activation with [D-Ala(2), D-Leu(5)]-enkephalinamide attenuated the anoxia- and OGD-induced increase in extracellular K(+) and decrease in DC potential in cortical slices; (2) DOR inhibition with naltrindole, a DOR antagonist, completely abolished the DOR-mediated prevention of increase in extracellular K(+) and decrease in DC potential; (3) inhibition of protein kinase A (PKA) with N-(2-[p-bromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide dihydrochloride had no effect on the DOR protection; and (4) inhibition of protein kinase C (PKC) with chelerythrine chloride reduced the DOR protection, whereas the PKC activator (phorbol 12-myristate 13-acetate) mimicked the effect of DOR activation on K(+) homeostasis. These data suggest that activation of DOR protects the cortex against anoxia- or ODG-induced derangement of potassium homeostasis, and this protection occurs via a PKC-dependent and PKA-independent pathway. We conclude that an important aspect of DOR-mediated neuroprotection is its early action against derangement of K(+) homeostasis during anoxia or ischemia.
authors.affiliation: Department of Pediatrics, Section of Respiratory Medicine, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
authors.forename: Dongman
authors.initials: D
authors.lastname: Chao
authors.forename: David F
authors.initials: DF
authors.lastname: Donnelly
authors.forename: Yin
authors.initials: Y
authors.lastname: Feng
authors.forename: Alia
authors.initials: A
authors.lastname: Bazzy-Asaad
authors.forename: Ying
authors.initials: Y
authors.lastname: Xia
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D005947:Glucose / Q000172:deficiency*; D006706:Homeostasis / Q000502:physiology*; D002534:Hypoxia, Brain / Q000378:metabolism*; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D000701:Analgesics, Opioid; D004791:Enzyme Inhibitors; D007202:Indicators and Reagents; C114628:NTI compound; D017465:Receptors, Opioid, delta; D009271:Naltrexone; D016308:Enkephalin, Leucine-2-Alanine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D005947:Glucose; D011188:Potassium