In:
The Journal of Physiology, Wiley, Vol. 592, No. 12 ( 2014-06-15), p. 2501-2517
Abstract:
High‐resolution patch clamp currents evoked by epibatidine (Ebd), carbamylcholine (CCh) and acetylcholine (ACh) were compared. Ebd binds with 75‐fold higher affinity at αγ than at αδ sites, whereas CCh and ACh prefer αδ sites of nicotinic ACh receptor (nAChR) channels. Similar short (τ O1 ), intermediate (τ O2 ) and long (τ O3 ) types of opening were observed. τ O2 openings were maximally prevalent at low Ebd concentrations, binding at αγ sites, whereas τ O1 openings appear to be generated at αδ sites. Short (∼0.75 ms) bursts of openings (τ B1 ) arise from the αγ site, and long ( 〉 10 ms) bursts (τ B2 ) arise from double liganded receptors. The duration of bursts and of openings within bursts depended on the agonist. Limited by the temporal resolution, the closings within bursts were invariant at 3 μs. Blocking αδ sites with α‐conotoxin M1 (CTx) eliminated both τ O1 and τ B2 and left only τ O2 and the short τ B1 bursts, as expected. Abstract ‘Embryonic’ muscle‐type nicotinic acetylcholine receptor channels (nAChRs) bind ligands at interfaces of α‐ and γ‐ or δ‐subunits. αγ and αδ sites differ in affinity, but their contributions to opening the channel have remained elusive. We compared high‐resolution patch clamp currents evoked by epibatidine (Ebd), carbamylcholine (CCh) and acetylcholine (ACh). Ebd binds with 75‐fold higher affinity at αγ than at αδ sites, whereas CCh and ACh prefer αδ sites. Similar short (τ O1 ), intermediate (τ O2 ) and long (τ O3 ) types of opening were observed with all three agonists. τ O2 openings were maximally prevalent at low Ebd concentrations, binding at αγ sites. By contrast, τ O1 openings appear to be generated at αδ sites. In addition, two types of burst appeared: short bursts of an average of 0.75 ms (τ B1 ) that should arise from the αγ site, and long bursts of 12–25 ms (τ B2 ) in duration arising from double liganded receptors. Limited by the temporal resolution, the closings within bursts were invariant at 3 μs. Corrected for missed closings, in the case of ACh the openings within long bursts lasted 170 μs and those in short bursts about 30 μs. Blocking αδ sites with α‐conotoxin M1 (CTx) eliminated both τ O1 and τ B2 and left only τ O2 and the short τ B1 bursts, as expected. Furthermore we found desensitization when the receptors bound ACh only at the αγ site. When CTx was applied to ‘embryonic’ mouse endplates, monoquantal current rise times were increased, and amplitude and decay time constants were reduced, as expected. Thus the αγ and αδ sites of nAChRs elicit specific channel‐opening patterns.
Type of Medium:
Online Resource
ISSN:
0022-3751
,
1469-7793
DOI:
10.1113/tjp.2014.592.issue-12
DOI:
10.1113/jphysiol.2013.267781
Language:
English
Publisher:
Wiley
Publication Date:
2014
detail.hit.zdb_id:
1475290-6
SSG:
12
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