1. UB-165: a novel nicotinic agonist with subtype selectivity implicates the alpha4beta2* subtype in the modulation of dopamine release from rat striatal synaptosomes.
- Author
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Sharples CG, Kaiser S, Soliakov L, Marks MJ, Collins AC, Washburn M, Wright E, Spencer JA, Gallagher T, Whiteaker P, and Wonnacott S
- Subjects
- Animals, Bacterial Toxins metabolism, Bacterial Toxins pharmacology, Binding, Competitive, Bridged Bicyclo Compounds, Heterocyclic pharmacology, Bridged-Ring Compounds pharmacology, Cells, Cultured, Conotoxins pharmacology, Corpus Striatum drug effects, Cyanobacteria Toxins, Humans, Marine Toxins metabolism, Marine Toxins pharmacology, Microcystins, Neurotoxins metabolism, Neurotoxins pharmacology, Nicotine metabolism, Nicotine pharmacology, Nicotinic Agonists pharmacology, Nicotinic Antagonists pharmacology, Pyridines pharmacology, Rats, Receptors, Nicotinic drug effects, Synaptosomes drug effects, Tropanes, Xenopus, Bridged Bicyclo Compounds, Heterocyclic metabolism, Bridged-Ring Compounds metabolism, Conotoxins metabolism, Corpus Striatum metabolism, Dopamine metabolism, Nicotinic Agonists metabolism, Nicotinic Antagonists metabolism, Pyridines metabolism, Receptors, Nicotinic metabolism, Synaptosomes metabolism
- Abstract
Presynaptic nicotinic acetylcholine receptors (nAChRs) on striatal synaptosomes stimulate dopamine release. Partial inhibition by the alpha3beta2-selective alpha-conotoxin-MII indicates heterogeneity of presynaptic nAChRs on dopamine terminals. We have used this alpha-conotoxin and UB-165, a novel hybrid of epibatidine and anatoxin-a, to address the hypothesis that the alpha-conotoxin-MII-insensitive subtype is composed of alpha4 and beta2 subunits. UB-165 shows intermediate potency, compared with the parent molecules, at alpha4beta2* and alpha3-containing binding sites, and resembles epibatidine in its high discrimination of these sites over alpha7-type and muscle binding sites. (+/-)-Epibatidine, (+/-)-anatoxin-a, and (+/-)-UB-165 stimulated [(3)H]-dopamine release from striatal synaptosomes with EC(50) values of 2.4, 134, and 88 nM, and relative efficacies of 1:0.4:0.2, respectively. alpha-Conotoxin-MII inhibited release evoked by these agonists by 48, 56, and 88%, respectively, suggesting that (+/-)-UB-165 is a very poor agonist at the alpha-conotoxin-MII-insensitive nAChR subtype. In assays of (86)Rb(+) efflux from thalamic synaptosomes, a model of an alpha4beta2* nAChR response, (+/-)-UB-165 was a very weak partial agonist; the low efficacy of (+/-)-UB-165 at alpha4beta2 nAChR was confirmed in Xenopus oocytes expressing various combinations of human nAChR subunits. In contrast, (+/-)-UB-165 and (+/-)-anatoxin-a were similarly efficacious and similarly sensitive to alpha-conotoxin-MII in increasing intracellular Ca(2+) in SH-SY5Y cells, a functional assay for native alpha3-containing nAChR. These data support the involvement of alpha4beta2* nAChR in the presynaptic modulation of striatal dopamine release and illustrate the utility of exploiting a novel partial agonist, together with a selective antagonist, to dissect the functional roles of nAChR subtypes in the brain.
- Published
- 2000