ABSTRACT
kappa(3) opioid receptors have a unique binding and analgesic profile, as originally defined by naloxone benzoylhydrazone (NalBzoH). Although antisense studies demonstrated the close relationship between kappa(3) opioid and Orphan opioid receptor-like receptor (ORL1) and implied they were generated from the same gene, these studies also revealed differences in the sensitivity profiles of NalBzoH and orphanin FQ/nociceptin (OFQ/N), indicating that they were not identical. To help define the relationship between kappa(3) and ORL1 receptors, we utilized BE(2)-C human neuroblastoma cells that natively express functional ORL1 and kappa(3) opioid receptors. (125)I-[Tyr(14)]OFQ/N binds to a single population of receptors in BE(2)-C cells. Competition binding and adenylyl cyclase studies clearly illustrated marked selectivity differences between the ORL1 and the kappa(3) sites. Furthermore, antisense DNA targeting ORL1 blocked the inhibition of cAMP by OFQ/N, but not by NalBzoH. Thus, the receptor mechanisms mediating the activity of OFQ/N and NalBzoH in BE(2)-C cells are distinct.
Subject(s)
Naloxone/pharmacology , Opioid Peptides/pharmacology , Receptors, Opioid, kappa/drug effects , Receptors, Opioid/drug effects , Tumor Cells, Cultured/drug effects , Antisense Elements (Genetics)/pharmacology , Binding Sites/drug effects , Binding Sites/physiology , Binding, Competitive/drug effects , Binding, Competitive/physiology , Cell Membrane/drug effects , Cell Membrane/metabolism , Cyclic AMP/metabolism , Humans , Naloxone/analogs & derivatives , Neuroblastoma , Opioid Peptides/metabolism , Radioligand Assay , Receptors, Opioid/chemistry , Receptors, Opioid/metabolism , Receptors, Opioid, kappa/chemistry , Receptors, Opioid, kappa/metabolism , Subcellular Fractions/drug effects , Subcellular Fractions/metabolism , Tumor Cells, Cultured/metabolism , Nociceptin Receptor , NociceptinABSTRACT
The potential interactions of natively expressed mu-opioid and opioid receptor-like (ORL1) receptors were studied by exposing intact BE(2)-C cells to agonists or antagonists for 1 h. Pretreatment with the mu-opioid receptor agonist, [D-Ala(2), N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO), or the ORL1 receptor agonist, orphanin FQ/nociceptin desensitized both mu-opioid and ORL1 receptor responses. beta-Funaltrexamine (beta-FNA) pretreatment also blocked both mu-opioid and ORL1 receptor responses, but only mu-opioid receptor binding was reduced. Moreover, beta-FNA (1 microM) failed to inhibit specific ORL1 receptor binding.
Subject(s)
Brain Neoplasms/metabolism , Naltrexone/analogs & derivatives , Narcotic Antagonists/pharmacology , Neuroblastoma/metabolism , Cyclic AMP/metabolism , Enkephalin, Ala(2)-MePhe(4)-Gly(5)-/metabolism , Humans , Morphine/pharmacology , Naltrexone/pharmacology , Narcotics/pharmacology , Opioid Peptides/pharmacology , Receptors, Opioid/agonists , Receptors, Opioid, mu/antagonists & inhibitors , Tumor Cells, Cultured , Nociceptin Receptor , NociceptinABSTRACT
The role of nitric oxide in long-term potentiation of the nicotinic pathway of synaptic transmission in the isolated superior cervical ganglia of rat was studied. Long-term potentiation was induced by a brief tetanizing pulse (tetanus, 20 Hz/20 s) to the preganglionic nerve. The amplitude of the extracellularly recorded postganglionic compound action potential was used as an index of synaptic transmission. Pretreatment with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (10 microM) or L-N(G)-nitro-arginine (10 microM) 30 min before tetanus, inhibited long-term potentiation. The inactive enantiomer of the nitric oxide synthase inhibitor, N(G)-nitro-D-arginine methyl ester (10 microM), failed to inhibit the long-term potentiation when given 30 min before the tetanus. Washout of L-N(G)-nitro-arginine, but not N(G)-nitro-L-arginine methyl ester, resulted in complete recovery of long-term potentiation. The nitric oxide synthase inhibitor had no significant effect on the basal ganglionic neurotransmission or post-tetanic potentiation. Furthermore, established long-term potentiation was blocked by superfusion of ganglia with N(G)-nitro-L-arginine methyl ester 1 h after a tetanus. Pretreatment of ganglia with the nitric oxide donor, sodium nitroprusside (100 microM), or the nitric oxide synthase substrate, L-arginine (1 mM), completely prevented the inhibitory effects of N(G)-nitro-L-arginine methyl ester on the tetanus-induced long-term potentiation. These findings present evidence for a requirement of nitric oxide for the maintenance but not induction of long-term potentiation in rat isolated superior cervical ganglia.
Subject(s)
Action Potentials/physiology , Long-Term Potentiation/physiology , NG-Nitroarginine Methyl Ester/pharmacology , Nitric Oxide/physiology , Nitroarginine/pharmacology , Superior Cervical Ganglion/physiology , Action Potentials/drug effects , Animals , Electric Stimulation , Long-Term Potentiation/drug effects , Male , Nitroprusside/pharmacology , Rats , Rats, Sprague-Dawley , Superior Cervical Ganglion/drug effects , Synapses/drug effects , Synapses/physiology , Synaptic Transmission/drug effects , Synaptic Transmission/physiology , Time FactorsABSTRACT
Long-term potentiation (LTP) of the nicotinic pathway of the superior cervical ganglion (SCG) is remarkably similar to that of the hippocampus which has been shown to involve nitric oxide (NO). We investigated a similar possible involvement of NO in the LTP of the SCG of the rat. Treatment of ganglia with the NO-synthase inhibitor N(G)-nitro-L-arginine (L-NOARG, 10 microM) blocked LTP at the maintenance phase.
