UB-165: a novel nicotinic agonist with subtype selectivity implicates the alpha4beta2* subtype in the modulation of dopamine release from rat striatal synaptosomes.
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.
Sharples
C G
CG
Department of Biology, University of Bath, Bath BA2 7AY, United Kingdom.
Kaiser
S
S
Soliakov
L
L
Marks
M J
MJ
Collins
A C
AC
Washburn
M
M
Wright
E
E
Spencer
J A
JA
Gallagher
T
T
Whiteaker
P
P
Wonnacott
S
S
D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism / Q000494:pharmacology; D001667:Binding, Competitive; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism* / Q000494:pharmacology; D001952:Bridged-Ring Compounds / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D020916:Conotoxins / Q000378:metabolism* / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D000087522:Cyanobacteria Toxins; D004298:Dopamine / Q000378:metabolism*; D006801:Humans; D008387:Marine Toxins / Q000378:metabolism / Q000494:pharmacology; D052998:Microcystins; D009498:Neurotoxins / Q000378:metabolism / Q000494:pharmacology; D009538:Nicotine / Q000378:metabolism / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000378:metabolism* / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000378:metabolism* / Q000494:pharmacology; D011725:Pyridines / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D014326:Tropanes; D014981:Xenopus
C407663:(2-chloro-5-pyridyl)-9-azabicyclo(4.2.1)non-2-ene; D001427:Bacterial Toxins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D001952:Bridged-Ring Compounds; D020916:Conotoxins; D000087522:Cyanobacteria Toxins; D008387:Marine Toxins; D052998:Microcystins; D009498:Neurotoxins; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011725:Pyridines; D011978:Receptors, Nicotinic; D014326:Tropanes; C098872:alpha-conotoxin MII; C403531:nicotinic receptor alpha4beta2; D009538:Nicotine; C509783:anatoxin a; C082748:epibatidine; D004298:Dopamine