Augmentation of nicotinic ␣7 receptor function is considered to be a potential therapeutic strategy aimed at ameliorating cognitive and mnemonic dysfunction in relation to debilitating pathological conditions, such as Alzheimer's disease and schizophrenia. In the present report, a novel positive allosteric modulator of the ␣7 nicotinic acetylcholine receptor (nAChR), 1-(5-chloro-2-hydroxy-phenyl)-3-(2-chloro-5-trifluoromethylphenyl)-urea (NS1738), is described. NS1738 was unable to displace or affect radioligand binding to the agonist binding site of nicotinic receptors, and it was devoid of effect when applied alone in electrophysiological paradigms. However, when applied in the presence of acetylcholine (ACh), NS1738 produced a marked increase in the current flowing through ␣7 nAChRs, as determined in both oocyte electrophysiology and patchclamp recordings from mammalian cells. NS1738 acted by increasing the peak amplitude of ACh-evoked currents at all concentrations; thus, it increased the maximal efficacy of ACh. Oocyte experiments indicated an increase in ACh potency as well. NS1738 had only marginal effects on the desensitization kinetics of ␣7 nAChRs, as determined from patch-clamp studies of both transfected cells and cultured hippocampal neurons. NS1738 was modestly brain-penetrant, and it was demonstrated to counteract a (Ϫ)-scopolamine-induced deficit in acquisition of a water-maze learning task in rats. Moreover, NS1738 improved performance in the rat social recognition test to the same extent as (Ϫ)-nicotine, demonstrating that NS1738 is capable of producing cognitive enhancement in vivo. These data support the notion that ␣7 nAChR allosteric modulation may constitute a novel pharmacological principle for the treatment of cognitive dysfunction.In clinical conditions where it is desirable to augment the function of a particular receptor type, positive allosteric modulation of the receptor in question is frequently considered preferable to classical (orthosteric) agonism. This primarily relies on the fact that actions of positive allosteric modulators are use-dependent, because only receptors activated by the endogenous ligand (agonist) are subject to modulation. Therefore, the temporospatial characteristics of endogenous receptor activation are preserved, and the function of the modulator can be considered as increasing the gain of individual receptor activation events. Agonists, in contrast, tonically activate all receptors. This will lead to a nonphysiological pattern of receptor activation, and it is also well known that prolonged agonist exposure will lead to receptor desensitization and that it affects receptor expression patterns (for review, see Quick and Lester, 2002).The cysteine-loop-containing family of ligand-gated ion channels encompasses anion-preferring receptor channels for ␥-aminobutyric acid (GABA A and GABA C receptors) and glycine as well as cation-preferring receptor channels activated by 5-hydroxytryptamine (5-hydroxytryptamine 3 receptors) and acetylcholine (nicotinic r...
The human intermediate-conductance, Ca2+-activated K+ channel (hIK) was identified by searching the expressed sequence tag database. hIK was found to be identical to two recently cloned K+ channels, hSK4 and hIK1. RNA dot blot analysis showed a widespread tissue expression, with the highest levels in salivary gland, placenta, trachea, and lung. With use of fluorescent in situ hybridization and radiation hybrid mapping, hIK mapped to chromosome 19q13.2 in the same region as the disease Diamond-Blackfan anemia. Stable expression of hIK in HEK-293 cells revealed single Ca2+-activated K+ channels exhibiting weak inward rectification (30 and 11 pS at −100 and +100 mV, respectively). Whole cell recordings showed a noninactivating, inwardly rectifying K+ conductance. Ionic selectivity estimated from bi-ionic reversal potentials gave the permeability ( P K/ P X) sequence K+ = Rb+ (1.0) > Cs+ (10.4) ≫ Na+, Li+, N-methyl-d-glucamine (>51).[Formula: see text] blocked the channel completely. hIK was blocked by the classical inhibitors of the Gardos channel charybdotoxin (IC50 28 nM) and clotrimazole (IC50 153 nM) as well as by nitrendipine (IC50 27 nM), Stichodactyla toxin (IC50 291 nM), margatoxin (IC50 459 nM), miconazole (IC50 785 nM), econazole (IC50 2.4 μM), and cetiedil (IC50 79 μM). Finally, 1-ethyl-2-benzimidazolinone, an opener of the T84 cell IK channel, activated hIK with an EC50 of 74 μM.
Background and purpose: Positive modulators of small conductance Ca 2 þ -activated K þ channels (SK1, SK2, and SK3) exert hyperpolarizing effects that influence the activity of excitable and non-excitable cells. The prototype compound 1-EBIO or the more potent compound NS309, do not distinguish between the SK subtypes and they also activate the related intermediate conductance Ca 2 þ -activated K þ channel (IK). This paper demonstrates, for the first time, subtype-selective positive modulation of SK channels. Experimental approach: Using patch clamp and fluorescence techniques we studied the effect of the compound cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA) on recombinant hSK1-3 and hIK channels expressed in HEK293 cells. CyPPA was also tested on SK3 and IK channels endogenously expressed in TE671 and HeLa cells. Key results: CyPPA was found to be a positive modulator of hSK3 (EC 50 ¼ 5.6 7 1.6 mM, efficacy 90 7 1.8 %) and hSK2 (EC 50 ¼ 14 7 4 mM, efficacy 71 7 1.8 %) when measured in inside-out patch clamp experiments. CyPPA was inactive on both hSK1 and hIK channels. At hSK3 channels, CyPPA induced a concentration-dependent increase in the apparent Ca 2 þ -sensitivity of channel activation, changing the EC 50 (Ca 2 þ ) from 429 nM to 59 nM. Conclusions and implications: As a pharmacological tool, CyPPA may be used in parallel with the IK/SK openers 1-EBIO and NS309 to distinguish SK3/SK2-from SK1/IK-mediated pharmacological responses. This is important for the SK2 and SK1 subtypes, since they have overlapping expression patterns in the neocortical and hippocampal regions, and for SK3 and IK channels, since they co-express in certain peripheral tissues.
BACKGROUND AND PURPOSEPositive allosteric modulation of a4b2 nicotinic acetylcholine (nACh) receptors could add a new dimension to the pharmacology and therapeutic approach to these receptors. The novel modulator NS9283 was therefore tested extensively. EXPERIMENTAL APPROACHEffects of NS9283 were evaluated in vitro using fluorescence-based Ca 2+ imaging and electrophysiological voltage clamp experiments in Xenopus oocytes, mammalian cells and thalamocortical neurons. In vivo the compound was tested in models covering a range of cognitive domains in mice and rats. KEY RESULTSNS9283 was shown to increase agonist-evoked response amplitude of (a4)3(b2)2 nACh receptors in electrophysiology paradigms. (a2)3(b2)2, (a2)3(b4)2 and (a4)3(b4)2 were modulated to comparable extents, but no effects were detected at a3-containing or any 2a : 3b stoichiometry nACh receptors. Native nACh receptors in thalamocortical neurons similarly displayed DHbE-sensitive currents that were receptive to modulation. NS9283 had favourable effects on sensory information processing, as shown by reversal of PCP-disrupted pre-pulse inhibition. NS9283 further improved performance in a rat model of episodic memory (social recognition), a rat model of sustained attention (five-choice serial reaction time task) and a rat model of reference memory (Morris water maze). Importantly, the effects in the Morris water maze could be fully reversed with mecamylamine, a blocker of nACh receptors. CONCLUSIONS AND IMPLICATIONSThese results provide compelling evidence that positive allosteric modulators acting at the (a4)3(b2)2 nACh receptors can augment activity across a broad range of cognitive domains, and that a4b2 nACh receptor allosteric modulation therefore constitutes a promising therapeutic approach to symptomatic treatment of cognitive impairment. Abbreviations
1 Three genes encode the small-conductance Ca 2+ -activated K + channels (SK channels). We have stably expressed hSK1 and rSK2 in HEK 293 cells and addressed the pharmacology of these subtypes using whole-cell patch clamp recordings. 2 The bee venom peptide apamin blocked hSK1 as well as rSK2 with IC 50 values of 3.3 nM and 83 pM, respectively. 3 The pharmacological separation between the subtypes was even more prominent when applying the scorpion peptide blocker scyllatoxin, which blocked hSK1 with an IC 50 value of 80 nM and rSK2 at 287 pM. 4 The potent small molecule blockers showed little di erentiation between the channel subtypes. The bis-quinolinium cyclophane UCL 1684 blocked hSK1 with an IC 50 value of 762 pM and rSK2 at 364 pM. The antiseptic compound dequalinium chloride blocked hSK1 and rSK2 with IC 50 values of 444 nM and 162 nM, respectively. 5 The nicotinic acetylcholine receptor antagonist d-tubocurarine was found to block hSK1 and rSK2 with IC 50 values of 27 mM and 17 mM when measured at +80 mV. The inhibition by dtubocurarine was voltage-dependent with increasing a nities at more hyperpolarized potentials. 6 The GABA A receptor antagonist bicuculline methiodide also blocked hSK1 and rSK2 in a voltage-dependent manner with IC 50 values of 15 and 25 mM when measured at +80 mV. 7 In conclusion, the pharmacological separation between SK channel subtypes expressed in mammalian cells is too small to support the notion that the apamin-insensitive afterhyperpolarization of neurones is mediated by hSK1.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.