Abstract
We are interested in the allosteric modulation of neuronal nicotinic acetylcholine receptors (nAChRs). We have postulated that the anthelmintic morantel (Mor) positively modulates (potentiates) rat α3β2 receptors through a site located at the β(+)/α(−) interface that is homologous to the canonical agonist site (J Neurosci 29:8734–8742, 2009). On this basis, we aimed to determine the site specificity by studying differences in modulation between α3β2 and α4β2 receptors. We also compared modulation by Mor with that of the related compound oxantel (Oxa). Whereas Mor and Oxa each potentiated α3β2 receptors 2-fold at saturating acetylcholine (ACh) concentrations, Mor had no effect on α4β2 receptors, and Oxa inhibited ACh-evoked responses. The inhibition was noncompetitive, but not due to open channel block. Furthermore, the nature and extent of modulation did not depend on subunit stoichiometry. We studied six positions at the α(−) interface that differ between α3 and α4. Two positions (α3Ile57 and α3Thr115) help mediate the effects of the modulators but do not seem to contribute to specificity. Mutations in two others (α3Leu107 and α3Ile117) yielded receptors with appreciable α4-character; that is, Mor potentiation was reduced compared with wild-type α3β2 control and Oxa inhibition was evident. A fifth position (α3Glu113) was unique in that it discriminated between the two compounds, showing no change in Mor potentiation from control but substantial Oxa inhibition. Our work has implications for rational drug design for nicotinic receptors and sheds light on mechanisms of allosteric modulation in nAChRs, especially the subtle differences between potentiation and inhibition.
Footnotes
This work was supported by the National Institutes of Health National Institute of Neurological Disorders and Stroke [Grant 1R15-NS070760–01] (to M.M.L.); the Howard Hughes Medical Institute [Undergraduate Science Education Grant 52006298] (to Grinnell College); and by funding from Grinnell College.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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ABBREVIATIONS:
- nAChR
- nicotinic acetylcholine receptor
- PNU-120596
- N-(5-chloro-2,4-dimethoxyphenyl)-N′-(5-methyl-3-isoxazolyl)-urea
- LY-2087101
- [2-[(4-fluorophenyl)amino]-4-methyl-5-thiazolyl]-3-thienylmethanone
- MTS
- methanethiosulfonate
- OR2
- oocyte Ringer's medium
- Mor
- morantel
- Oxa
- oxantel
- Pyr
- pyrantel.
- Received September 21, 2011.
- Accepted November 4, 2011.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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