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Short openings in high resolution single channel recordings of mouse nicotinic receptors
Author(s) -
Hallermann Stefan,
Heckmann Sabine,
Dudel Josef,
Heckmann Manfred
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.080606
Subject(s) - pipette , patch clamp , biophysics , chemistry , population , electrophysiology , receptor , amplitude , hyperpolarization (physics) , physics , biology , stereochemistry , neuroscience , optics , biochemistry , nuclear magnetic resonance spectroscopy , demography , sociology
The temporal fine structure of single channel currents was studied to obtain information on how agonists open nicotinic acetylcholine receptor channels. Currents were recorded from mouse myoballs with quartz pipettes in the on‐cell mode of the patch‐clamp technique. With 62 kHz filter cut‐off and root mean square (r.m.s.) noise levels as low as 1.45 pA at 200 mV hyperpolarization, events down to 6 μs duration could be resolved with negligible error rate. Three types of openings with mean durations of 750 μs, 89 μs and 4 μs were identified with 0.1–10 μ m suberyldicholine (SubCh). The relative frequencies of the three types of openings were 84% for long, 5% for medium and 11% for short openings with 1 μ m SubCh. Stability plots and single channel current amplitude comparisons suggest that the three types of openings arise from a homogenous channel population. Above 10 μ m SubCh, the three types of openings could not be discerned because channel openings occurred too closely spaced and open channels were increasingly blocked. Three types of openings can be generated with a mechanistic receptor model with two unequal binding sites, short and medium openings arising from one or the other monoliganded state, and long openings from the fully liganded state of the receptor. Maximum likelihood fitting of the rate constants of this model directly to the sequence of observed open and shut times accurately predicted the main physiological properties of the receptors with 0.1 μ m SubCh. However, fitting recordings with 0.1–10 μ m SubCh simultaneously revealed that this model cannot reproduce the weak influence of SubCh concentration on the proportions of the three types of openings. Therefore we conclude that short and medium openings are unlikely to arise preferentially from one or the other monoliganded state of nicotinic acetylcholine receptor channels.