Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents

This Article Full Text Full Text (PDF, 2014K) PPT slides of all figures Alert me when this article is cited Citation Map Services Email this article Similar articles in this journal Similar articles in PubMed Alert me to new content in the JGP Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Zholos, A. V. Articles by Bolton, T. B. Search for Related Content PubMed PubMed Citation Articles by Zholos, A. V. Articles by Bolton, T. B. Social Bookmarking                      What's this?

Effect of Potential on Single-channel Gating

Alexander V. Zholos^1,3, Andrey A. Zholos², and Thomas B. Bolton³

¹ Laboratory of Molecular Pharmacology of Cellular Receptors and Ion Channels, A.A. Bogomoletz Institute of Physiology, Kiev, 01024 Ukraine
² Department of Economical Cybernetics, Taras Shevchenko National University, Kiev, 01033 Ukraine
³ Pharmacology and Clinical Pharmacology Basic Medical Sciences, St. George's Hospital Medical School, London SW17 ORE, UK

Address correspondence to Alexander V. Zholos, Laboratory of Molecular Pharmacology of Cellular Receptors and Ion Channels, A.A. Bogomoletz Institute of Physiology, Kiev, 01024 Ukraine. Fax: (044) 256 2000; email: zholosa{at}sghms.ac.uk

There is little information about the mechanisms by which G-protein–coupled receptors gate ion channels although many ionotropic receptors are well studied. We have investigated gating of the muscarinic cationic channel, which mediates the excitatory effect of acetylcholine in smooth muscles, and proposed a scheme consisting of four pairs of closed and open states. Channel kinetics appeared to be the same in cell-attached or outside-out patches whether the channel was activated by carbachol application or by intracellular dialysis with GTPS. Since in the latter case G-proteins are permanently active, it is concluded that the cationic channel is the major determinant of its own gating, similarly to the K_ACh channel (Ivanova-Nikolova, T.T., and G.E. Breitwieser. 1997. J. Gen. Physiol. 109:245–253). Analysis of adjacent-state dwell times revealed connections between the states that showed features conserved among many other ligand-gated ion channels (e.g., nAChR, BK_Ca channel). Open probability (P_O) of the cationic channel was increased by membrane depolarization consistent with the prominent U-shaped I-V relationship of the muscarinic whole-cell current at negative potentials. Membrane potential affected transitions within each closed-open state pair but had little effect on transitions between pairs; thus, the latter are likely to be caused by interactions of the channel with its ligands, e.g., Ca²⁺ and Go-GTP. Channel activity was highly heterogeneous, as was evident from the prominent cycling behavior when P_O was measured over 5-s intervals. This was related to the variable frequency of openings (as in the K_ACh channel) and, especially, to the number of long openings between consecutive long shuttings. Analysis of the underlying Markov chain in terms of probabilities allowed us to evaluate the contribution of each open state to the integral current (from shortest to longest open state: 0.1, 3, 24, and 73%) as P_O increased 525-fold in three stages.

Key Words: Markov chain • channel kinetics • G-protein • carbachol • smooth muscle

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				T. Sakamoto, T. Unno, T. Kitazawa, T. Taneike, M. Yamada, J. Wess, M. Nishimura, and S. Komori Three distinct muscarinic signalling pathways for cationic channel activation in mouse gut smooth muscle cells J. Physiol., July 1, 2007; 582(1): 41 - 61. [Abstract] [Full Text] [PDF]

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents