Modulation of proton-induced current fluctuations in the human nicotinic acetylcholine receptor channel.
The nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel that switches upon activation from a closed state to a full conducting state. We found that the mutation delta S268K, located at 12' position of the second transmembrane domain of the delta subunit of the human nAChR generates a long-lived intermediate conducting state, from which openings to a wild-type like conductance level occur on a submillisecond time scale. Aiming to understand the interplay between structural changes near the 12' position and channel gating, we investigated the influence of various parameters: different ligands (acetylcholine, choline and epibatidine), ligand concentrations, transmembrane voltages and both fetal and adult nAChRs. Since sojourns in the high conductance state are not fully resolved in time, spectral noise analysis was used as a complement to dwell time analysis to determine the gating rate constants. Open channel current fluctuations are described by a two-state Markov model. The characteristic time of the process is markedly influenced by the ligand and the receptor type, whereas the frequency of openings to the high conductance state increases with membrane hyperpolarization. Conductance changes are discussed with regard to reversible transfer reaction of single protons at the lysine 12' side chain.
Danelon
Christophe
C
Laboratory of Physical Chemistry of Polymers and Membranes, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Grandl
Jörg
J
Hovius
Ruud
R
Vogel
Horst
H
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D018678:Cholinergic Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D008239:Lysine / Q000737:chemistry; D008390:Markov Chains; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D021122:Protein Subunits / Q000378:metabolism; D011522:Protons; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014101:Torpedo / Q000378:metabolism; D014162:Transfection
D018678:Cholinergic Agents; D021122:Protein Subunits; D011522:Protons; D011978:Receptors, Nicotinic; D008239:Lysine