title: Physiological concentrations of choline activate native alpha7-containing nicotinic acetylcholine receptors in the presence of PNU-120596 [1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)-urea].
abstract: The use of PNU-120596 [1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)-urea], a positive allosteric modulator of alpha7 nicotinic acetylcholine receptor (nAChR), may be beneficial for enhancing cholinergic therapies. However, the effects of PNU-120596 on activation of native alpha7-containing nAChRs by physiological concentrations of choline are not known and were investigated in this study using patch-clamp electrophysiology and histaminergic tuberomammillary neurons in hypothalamic slices. In the presence of PNU-120596, subthreshold (i.e., inactive) physiological concentrations of choline ( approximately 10 microM) elicited repetitive step-like whole-cell responses reminiscent of single ion channel openings that were reversibly blocked by 20 nM methyllycaconitine, a selective alpha7 nAChR antagonist. The effects of choline and PNU-120596 were synergistic as administration of 10 to 40 microM choline or 1 to 4 muM PNU-120596 alone did not elicit responses. In voltage clamp at -60 mV, the persistent activation of alpha7-containing nAChRs by 10 microM choline plus 1 microM PNU-120596 was estimated to produce a sustained influx of Ca(2+) ions at a rate of 8.4 pC/min ( approximately 0.14 pA). In the presence of PNU-120596 in current clamp, transient step-like depolarizations ( approximately 5 mV) enhanced neuronal excitability and triggered voltage-gated conductances; a single opening of an alpha7-containing nAChR channel appeared to transiently depolarize the entire neuron and facilitate spontaneous firing. Therefore, this study tested and confirmed the hypothesis that PNU-120596 enhances the effects of subthreshold concentrations of choline on native alpha7-containing nAChRs, allowing physiological levels of choline to activate these receptors and produce whole-cell responses in the absence of exogenous nicotinic agents. In certain neurological disorders, this activation may be therapeutically beneficial, more efficacious, and safer than treatments with nAChR agonists.
authors.affiliation: Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, IL 62794, USA.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Gusev
authors.forename: Victor V
authors.initials: VV
authors.lastname: Uteshev
mesh_terms: D000157:Aconitine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002794:Choline / Q000378:metabolism / Q000502:physiology*; D004357:Drug Synergism; D005260:Female; D007026:Hypothalamic Area, Lateral / Q000187:drug effects / Q000378:metabolism; D007555:Isoxazoles / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D018722:Nicotinic Agonists / Q000494:pharmacology*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D010671:Phenylurea Compounds / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000187:drug effects*; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C508388:1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)urea; C579165:Chrna7 protein, rat; D007555:Isoxazoles; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D010671:Phenylurea Compounds; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C054634:methyllycaconitine; D002794:Choline; D002118:Calcium; D000157:Aconitine