title: Agonist-selective effects of opioid receptor ligands on cytosolic calcium concentration in rat striatal neurons.
abstract: BACKGROUND
  Buprenorphine is an opioid receptor ligand whose mechanism of action is incompletely understood.
  
  
  METHODS
  Using Ca(2+) imaging, we assessed the effects of buprenorphine, β-endorphin, and morphine on cytosolic Ca(2+) concentration [Ca(2+)](i), in rat striatal neurons.
  
  
  RESULTS
  Buprenorphine (0.01-1 μM) increased [Ca(2+)](i) in a dose-dependent manner in a subpopulation of rat striatal neurons. The effect of buprenorphine was largely reduced by naloxone, a non-selective opioid receptor antagonist, but not by μ, κ, δ or NOP-selective antagonists. β-Endorphin (0.1 μM) increased [Ca(2+)](i) with a lower amplitude and slower time course than buprenorphine. Similar to buprenorphine, the effect of β-endorphin was markedly decreased by naloxone, but not by opioid-selective antagonists. Morphine (0.1-10 μM), did not affect [Ca(2+)](i) in striatal neurons.
  
  
  CONCLUSIONS
  Our results suggest that buprenorphine and β-endorphin act on a distinct type/subtype of plasmalemmal opioid receptors or activate intracellular opioid-like receptor(s) in rat striatal neurons.
authors.affiliation: Department of Pharmacology, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: G Cristina
authors.initials: GC
authors.lastname: Brailoiu
authors.forename: Elena
authors.initials: E
authors.lastname: Deliu
authors.forename: Robert
authors.initials: R
authors.lastname: Hooper
authors.forename: Nae J
authors.initials: NJ
authors.lastname: Dun
authors.forename: Ashiwel S
authors.initials: AS
authors.lastname: Undieh
authors.forename: Martin W
authors.initials: MW
authors.lastname: Adler
authors.forename: Khalid
authors.initials: K
authors.lastname: Benamar
authors.forename: Eugen
authors.initials: E
authors.lastname: Brailoiu
mesh_terms: D000818:Animals; D002047:Buprenorphine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D008024:Ligands; D009020:Morphine / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000819:agonists*; D001615:beta-Endorphin / Q000494:pharmacology
chemical_list: D005456:Fluorescent Dyes; D008024:Ligands; D009292:Narcotic Antagonists; D009294:Narcotics; D011957:Receptors, Opioid; C051844:norbinaltorphimine; D002047:Buprenorphine; D009271:Naltrexone; D001615:beta-Endorphin; D009020:Morphine; D002118:Calcium; D016257:Fura-2