Rhesus monkey alpha 7 nicotinic acetylcholine receptors: Comparisons to human alpha 7 receptors expressed in Xenopus oocytes

Department of Pharmacology and Therapeutics, University of Florida, College of Medicine, Gainesville, 32610, USA.
European Journal of Pharmacology (Impact Factor: 2.53). 12/2005; 524(1-3):11-8. DOI: 10.1016/j.ejphar.2005.08.043
Source: PubMed


An alpha7 nicotinic acetylcholine receptor sequence was cloned from Rhesus monkey (Macaca mulatta). This clone differs from the mature human alpha7 nicotinic acetylcholine receptor in only four amino acids, two of which are in the extracellular domain. The monkey alpha7 nicotinic receptor was characterized in regard to its functional responses to acetylcholine, choline, cytisine, and the experimental alpha7-selective agonists 4OH-GTS-21, TC-1698, and AR-R17779. For all of these agonists, the EC(50) for activation of monkey receptors was uniformly higher than for human receptors. In contrast, the potencies of mecamylamine and MLA for inhibiting monkey and human alpha7 were comparable. Acetylcholine and 4OH-GTS-21 were used to probe the significance of the single point differences in the extracellular domain. Mutants with the two different amino acids in the extracellular domain of the monkey receptor changed to the corresponding sequence of the human receptor had responses to these agonists that were not significantly different in EC(50) from wild-type human alpha7 nicotinic receptors. Monkey alpha7 nicotinic receptors have a serine at residue 171, while the human receptors have an asparagine at this site. Monkey S171N mutants were more like human alpha7 nicotinic receptors, while mutations at the other site (K186R) had relatively little effect. These experiments point toward the basic utility of the monkey receptor as a model for the human alpha7 nicotinic receptor, albeit with the caveat that these receptors will vary in their agonist concentration dependency. They also point to the potential importance of a newly identified sequence element for modeling the specific amino acids involved with receptor activation.

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Available from: Clare Stokes
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    • "We began our investigation of isolated cells obtained from the adrenal glands of M. mulatta monkey by testing three different nAChR agonists, ACh, choline, and 5-I-A-85380. Choline is a full agonist of heterologously expressed M. mulatta α7 nAChRs [37] and is considered to be α7-selective and can be used to assay for the presence of α7 receptors when multiple nAChR subtypes are potentially expressed in a given cell. The compound 5-I-A-85380 has high affinity for heteromeric receptor subtypes that contain the β2 subunit [38] and was chosen with the expectation that receptors that contain this subunit would be preferentially activated. "
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    ABSTRACT: Nicotinic acetylcholine receptors (nAChRs) that contain α6 and β4 subunits have been demonstrated functionally in human adrenal chromaffin cells, rat dorsal root ganglion neurons, and on noradrenergic terminals in the hippocampus of adolescent mice. In human adrenal chromaffin cells, α6β4* nAChRs (the asterisk denotes the possible presence of additional subunits) are the predominant subtype whereas in rodents, the predominant nAChR is the α3β4* subtype. Here we present molecular and pharmacological evidence that chromaffin cells from monkey (Macaca mulatta) also express α6β4* receptors. PCR was used to show the presence of transcripts for α6 and β4 subunits and pharmacological characterization was performed using patch-clamp electrophysiology in combination with α-conotoxins that target the α6β4* subtype. Acetylcholine-evoked currents were sensitive to inhibition by BuIA[T5A,P6O] and MII[H9A,L15A]; α-conotoxins that inhibit α6-containing nAChRs. Two additional agonists were used to probe for the expression of α7 and β2-containing nAChRs. Cells with currents evoked by acetylcholine were relatively unresponsive to the α7-selctive agonist choline but responded to the agonist 5-I-A-85380. These studies provide further insights into the properties of natively expressed α6β4* nAChRs.
    Full-text · Article · Apr 2014 · PLoS ONE
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    • "Simple modifications, such as halogenation, markedly affect binding affinities of nAChRs for cytisine analogues (Chellappan et al., 2006; Fitch et al., 2005; Slater et al., 2003). Reciprocally, modest changes in the presumed agonist-binding pocket of nAChRs can alter cytisine's functional potency (Papke et al., 2005). Further studies of cytisine-based compounds are likely to be informative about the ligand-binding pockets on nAChR and molecular mechanisms involved in nicotine dependence. "
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    ABSTRACT: Cytisine has a molecular structure somewhat similar to that of nicotine and varenicline. The concept for the new smoking cessation drug varenicline was based partly on cytisine. Like varenicline, cytisine is a partial agonist of nicotinic acetylcholine receptors, with high affinity for alpha4beta2 receptors. Cytisine has been used since the 1960s as a smoking cessation drug in Eastern and Central Europe, but has remained largely unnoticed elsewhere. Three placebo-controlled trials, conducted in East and West Germany in the 1960s and 1970s, suggest that cytisine, even with minimal behavioural support, may be effective in aiding smoking cessation. Cytisine tablets are very inexpensive to produce and could be a more affordable treatment than nicotine replacement, bupropion and varenicline. There is however a dearth of scientific research on the properties of cytisine, including safety, abuse liability and efficacy. This paper seeks to identify research priorities for molecular, animal and clinical studies. In particular, new studies are necessary to define the nicotinic receptor interaction profile of cytisine, to establish its pharmacokinetics and pharmacodynamics in humans, to determine whether animals self-administer cytisine, and to ascertain whether cytisine is safe and effective as a smoking cessation drug. Potentially, this research effort, contributing to wider use of an inexpensive drug, could save many lives.
    Full-text · Article · Feb 2008 · Drug and Alcohol Dependence
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    • "The benzylidene anabaseine analogs have also been useful as molecular probes of the ligand binding domains of the 7 nicotinic receptor and 5-HT 3A receptor. Papke and co-workers have demonstrated that DMXBA and its metabolites differ in partial agonist potency and efficacy in rat, monkey, and human 7 nicotinic ACh receptors (Stokes et al., 2004; Papke et al., 2005). In chimeric and point mutant 7 nicotinic ACh receptor electrophysiological studies, this group has shown that residues in loops C, E, and F of the ligand binding domain that differ across species account for the differential pharmacology (Stokes et al., 2004). "
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    Preview · Article · Jun 2006 · Journal of Pharmacology and Experimental Therapeutics
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