Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors
We used single-channel kinetic analysis to study the inhibitory effects of tacrine on human adult nicotinic receptors (nAChRs) transiently expressed in HEK 293 cells. Single channel recording from cell-attached patches revealed concentration- and voltage-dependent decreases in mean channel open prob...
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| Format: | Online |
| Language: | English |
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The Rockefeller University Press
2002
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| Online Access: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229521/ |
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pubmed-22295212008-04-16 Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors Prince, Richard J. Pennington, Richard A. Sine, Steven M. Article We used single-channel kinetic analysis to study the inhibitory effects of tacrine on human adult nicotinic receptors (nAChRs) transiently expressed in HEK 293 cells. Single channel recording from cell-attached patches revealed concentration- and voltage-dependent decreases in mean channel open probability produced by tacrine (IC50 4.6 μM at −70 mV, 1.6 μM at −150 mV). Two main effects of tacrine were apparent in the open- and closed-time distributions. First, the mean channel open time decreased with increasing tacrine concentration in a voltage-dependent manner, strongly suggesting that tacrine acts as an open-channel blocker. Second, tacrine produced a new class of closings whose duration increased with increasing tacrine concentration. Concentration dependence of closed-times is not predicted by sequential models of channel block, suggesting that tacrine blocks the nAChR by an unusual mechanism. To probe tacrine's mechanism of action we fitted a series of kinetic models to our data using maximum likelihood techniques. Models incorporating two tacrine binding sites in the open receptor channel gave dramatically improved fits to our data compared with the classic sequential model, which contains one site. Improved fits relative to the sequential model were also obtained with schemes incorporating a binding site in the closed channel, but only if it is assumed that the channel cannot gate with tacrine bound. Overall, the best description of our data was obtained with a model that combined two binding sites in the open channel with a single site in the closed state of the receptor. The Rockefeller University Press 2002-09 /pmc/articles/PMC2229521/ /pubmed/12198092 http://dx.doi.org/10.1085/jgp.20028583 Text en Copyright © 2002, The Rockefeller University Press This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/). |
| repository_type |
Open Access Journal |
| institution_category |
Foreign Institution |
| institution |
US National Center for Biotechnology Information |
| building |
NCBI PubMed |
| collection |
Online Access |
| language |
English |
| format |
Online |
| author |
Prince, Richard J. Pennington, Richard A. Sine, Steven M. |
| spellingShingle |
Prince, Richard J. Pennington, Richard A. Sine, Steven M. Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors |
| author_facet |
Prince, Richard J. Pennington, Richard A. Sine, Steven M. |
| author_sort |
Prince, Richard J. |
| title |
Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors |
| title_short |
Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors |
| title_full |
Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors |
| title_fullStr |
Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors |
| title_full_unstemmed |
Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors |
| title_sort |
mechanism of tacrine block at adult human muscle nicotinic acetylcholine receptors |
| description |
We used single-channel kinetic analysis to study the inhibitory effects of tacrine on human adult nicotinic receptors (nAChRs) transiently expressed in HEK 293 cells. Single channel recording from cell-attached patches revealed concentration- and voltage-dependent decreases in mean channel open probability produced by tacrine (IC50 4.6 μM at −70 mV, 1.6 μM at −150 mV). Two main effects of tacrine were apparent in the open- and closed-time distributions. First, the mean channel open time decreased with increasing tacrine concentration in a voltage-dependent manner, strongly suggesting that tacrine acts as an open-channel blocker. Second, tacrine produced a new class of closings whose duration increased with increasing tacrine concentration. Concentration dependence of closed-times is not predicted by sequential models of channel block, suggesting that tacrine blocks the nAChR by an unusual mechanism. To probe tacrine's mechanism of action we fitted a series of kinetic models to our data using maximum likelihood techniques. Models incorporating two tacrine binding sites in the open receptor channel gave dramatically improved fits to our data compared with the classic sequential model, which contains one site. Improved fits relative to the sequential model were also obtained with schemes incorporating a binding site in the closed channel, but only if it is assumed that the channel cannot gate with tacrine bound. Overall, the best description of our data was obtained with a model that combined two binding sites in the open channel with a single site in the closed state of the receptor. |
| publisher |
The Rockefeller University Press |
| publishDate |
2002 |
| url |
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229521/ |
| _version_ |
1611437924661854208 |