Pharmacological delta1- and delta2-opioid receptor subtypes in the human neuroblastoma cell line SK-N-BE: no evidence for distinct molecular entities.
The two pharmacological delta-opioid receptor subtypes, delta1 and delta2, have been defined on the basis of pharmacological tools but remain to be characterized at the molecular level, since only a single cDNA has been cloned. The present study aimed to investigate the pharmacological properties of delta1- and delta2-opioid subtypes expressed in the human neuroblastoma cell line SK-N-BE and to characterize their putative corresponding mRNAs. Binding experiments using "selective" delta1- and delta2-opioid agonists and antagonists revealed the presence of two binding sites, demonstrating the presence of these delta1-opioid subtypes as they were previously described. The activation of these pharmacological subtypes by the selective agonists induced the incorporation of [alpha-(32)P]azidoanilide-GTP into Galpha(i2)/Galpha(0) subunits with the same efficiency and potency and inhibited adenosine 3', 5'-cyclic monophosphate (cAMP) accumulation with similar efficiency, while their sustained activation for 15 min induced a cross-desensitization. The "selective" delta1 and delta2 antagonists, 7-benzylidenenaltrexone and naltrindole benzofuran, respectively, were found to be as potent in blocking the inhibition of cAMP accumulation induced by both [D-Pen(2,5)]enkephalin and Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH(2). The possibility that delta-opioid subtypes could arise from alternative splicing was ruled out by reverse transcription-polymerase chain reaction (RT-PCR) experiments and the sequencing of PCR products, which revealed the presence of a single transcript encoding for the delta-opioid receptor. Different possibilities which could account for the delta-opioid receptor heterogeneity observed in the SN-N-BE cell line are discussed.
Allouche
S
S
Laboratoire des Neurosciences, Université de CAEN, CNRS UMR 6551, BP 5229, 14074, CAEN, France. allouche-s@chu-caen.fr
Hasbi
A
A
Ferey
V
V
Sola
B
B
Jauzac
P
P
Polastron
J
J
D000262:Adenylyl Cyclases / Q000378:metabolism; D000701:Analgesics, Opioid / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D009447:Neuroblastoma; D009842:Oligopeptides / Q000494:pharmacology*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors / Q000145:classification / Q000187:drug effects* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
D000701:Analgesics, Opioid; D009842:Oligopeptides; D012333:RNA, Messenger; D017465:Receptors, Opioid, delta; C060208:deltorphin I, Ala(2)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases