Abstract
We identified regions within the N-terminal extracellular domain of α7 nicotinic acetylcholine receptors that affect channel gating. By single-channel analysis of α7 nicotinic acetylcholine receptors currents, we show that the difference in efficacy between the two agonists acetylcholine and 1,1-dimethyl-4-phenylpiperazinium (DMPP) is due to a slower channel activation rate by DMPP. The partial efficacy of DMPP was not caused by channel block or faster desensitization of α7 AChRs by DMPP. In addition, the efficacy and, by inference, the activation rate were found to be voltage dependent. Using chimeras of the two closely related subunits α7 and α8, we map residues that affect channel activation rate and agonist affinity to two different regions of the extracellular domain. Residues that affect channel activation rate are within the sequence 1–179, whereas residues that affect agonist affinity are within the sequence 180–208.
Footnotes
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Send reprint requests to: Dr. Jon Lindstrom, Department of Neuroscience, 217 Stemmler Hall, 36th and Hamilton Walk, University of Pennsylvania Medical School, Philadelphia, PA 19104-6074. E-mail:jslkk{at}mail.med.upenn.edu
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↵1 This work was supported by National Institutes of Health Grants NS33625 (R.A.), NS01903 (G.B.W.), NS10333 (M.E.N.) and NS11323 (J.L.) and by grants from the Muscular Dystrophy Association (J.L.), Council for Tobacco Research, USA, Inc. (J.L.), Smokeless Tobacco Research Council (J.L.) and the Pittsburgh Supercomputing Center through NIH National Center for Research Resources cooperative agreement 2 p41 RR06009. Portions of this work have appeared in abstract form (annual meetings of the Society for Neuroscience, Washington, D.C., 1994; New Orleans, LA, 1997).
- Abbreviations:
- ACh
- acetylcholine
- AChR
- nicotinic acetylcholine receptor
- BAPTA AM
- 1,2-bis (2-aminophenoxy)-ethane-N,N,N′,N′-tetraacetic acid tetrakis (acetyoxymethyl) ester
- DMPP
- 1,1-dimethyl-4-phenylpiperazinium
- EC50
- half-maximally effective concentration of agonist
- EGTA
- ethyleneglycol-bis-(βaminoethyl ether)-N,N,N′,N′-tetraacetic acid
- fc
- filter cut off frequency ≈3 dB
- 5-HT3
- serotonin receptor type 3
- Imax
- peak current maximum
- fc
- filter corner frequency
- HEPES
- N-[2-hydroxyethyl]piperazine-N′-2-ethane sulfonic acid
- MgATP
- adenosine-5′-triphosphate (magnesium salt)
- nH
- Hill coefficient
- M1–M4
- transmembrane domains 1–4
- Tr
- filter rise time
- Received March 27, 1998.
- Accepted June 5, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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Determinants of Channel Gating Located in the N-Terminal Extracellular Domain of Nicotinic α7 Receptor
