title: delta-opioid receptor mobilization of intracellular calcium in SH-SY5Y cells: lack of evidence for delta-receptor subtypes.
abstract: delta-opioid receptor agonists mobilize intracellular Ca2+([Ca2+]i) in SH-SY5Y cells when applied in the presence of muscarinic agonists. The putative delta 1 receptor agonist [D-Pen2,D-Pen5]-enkephalin (DPDPE) elevated [Ca2+]i with an EC50 of 11 nM and the putative delta 2 agonist deltorphin II elevated [Ca2+]i, with an EC50 of 14 nM. The maximal elevations of [Ca2+]i caused by both agonists were not different, nor were maximally effective concentrations of DPDPE (1 microM) and deltorphin II (1 microM) applied together more effective than either agonist applied alone. The elevations of [Ca2+]i caused by DPDPE (1 microM) and deltorphin II (1 microM), in the presence of carbachol, desensitized rapidly with continued opioid exposure and the cross-desensitization between PDPDE and deltorphin II was complete. The putative delta 1 selective antagonist 7-benzylidenenaltrexone (BNTX) and the putative delta 2 selective antagonist naltriben both reduced the elevations of [Ca2+]i caused by DPDPE (30 nM) and deltorphin II (10 nM), by greater than 50% at concentrations of less than 10 nM. In SH-SY5Y cells delta-receptor mediated elevation of [Ca2+]i is mediated by a population of receptors, which does not discriminate between agonists and antagonists purportedly selective for delta 1 or delta 2 receptors.
authors.affiliation: Department of Pharmacology, University of Bristol, UK.
authors.forename: M A
authors.initials: MA
authors.lastname: Connor
authors.forename: M J
authors.initials: MJ
authors.lastname: Keir
authors.forename: G
authors.initials: G
authors.lastname: Henderson
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000494:pharmacology*; D009842:Oligopeptides / Q000494:pharmacology*; D017465:Receptors, Opioid, delta / Q000819:agonists* / Q000378:metabolism
chemical_list: D004745:Enkephalins; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; C060209:deltorphin II, Ala(2)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D002118:Calcium