Skip to main content
Article thumbnail
Location of Repository

A Conducting State with Properties of a Slow Inactivated State in a Shaker K+ Channel Mutant

By Riccardo Olcese, Daniel Sigg, Ramon Latorre, Francisco Bezanilla and Enrico Stefani

Abstract

In Shaker K+ channel, the amino terminus deletion Δ6-46 removes fast inactivation (N-type) unmasking a slow inactivation process. In Shaker Δ6-46 (Sh-IR) background, two additional mutations (T449V-I470C) remove slow inactivation, producing a noninactivating channel. However, despite the fact that Sh-IR-T449V-I470C mutant channels remain conductive, prolonged depolarizations (1 min, 0 mV) produce a shift of the QV curve by about −30 mV, suggesting that the channels still undergo the conformational changes typical of slow inactivation. For depolarizations longer than 50 ms, the tail currents measured during repolarization to −90 mV display a slow component that increases in amplitude as the duration of the depolarizing pulse increases. We found that the slow development of the QV shift had a counterpart in the amplitude of the slow component of the ionic tail current that is not present in Sh-IR. During long depolarizations, the time course of both the increase in the slow component of the tail current and the change in voltage dependence of the charge movement could be well fitted by exponential functions with identical time constant of 459 ms. Single channel recordings revealed that after prolonged depolarizations, the channels remain conductive for long periods after membrane repolarization. Nonstationary autocovariance analysis performed on macroscopic current in the T449V-I470C mutant confirmed that a novel open state appears with increasing prepulse depolarization time. These observations suggest that in the mutant studied, a new open state becomes progressively populated during long depolarizations (>50 ms). An appealing interpretation of these results is that the new open state of the mutant channel corresponds to a slow inactivated state of Sh-IR that became conductive

Topics: Original Article
Publisher: The Rockefeller University Press
OAI identifier: oai:pubmedcentral.nih.gov:2217242
Provided by: PubMed Central
Download PDF:
Sorry, we are unable to provide the full text but you may find it at the following location(s):
  • http://www.pubmedcentral.nih.g... (external link)
  • Suggested articles

    Citations

    1. (1998). A mutation in S6 of Shaker potassium channel decreases the K1 affinity of an ion binding site revealing ion–ion interactions in the pore.
    2. (1998). Activation of Shaker potassium channels.
    3. (1994). An engineered cysteine in the external mouth of a K1 channel allows inactivation to be modulated by metal binding.
    4. (1990). Biophysical and molecular mechanisms of Shaker potassium channel inactivation.
    5. (1995). C-type inactivation of a voltage-gated K1 channel occurs by a cooperative mechanism.
    6. (1995). Cooperative subunit interactions in C-type inactivation of K channels.
    7. (1997). Correlation between charge movement and ionic current during slow inactivation in Shaker potassium channels.
    8. (1981). Covariance of nonstationary sodium current fluctuation at the node of Ranvier.
    9. (1982). Distribution and kinetics of membrane dielectric polarization. I. Long-term inactivation of gating currents.
    10. (1996). Dynamic rearrangement of the outer mouth of a K1 channel during gating.
    11. (1993). Effects of external cations and mutations in the pore region on C-type inactivation of Shaker potassium channels. Receptors and Channels.
    12. (1999). Functional consequences of a decreased potassium affinity in a potassium channel pore– ion interactions and C-type inactivation.
    13. (1994). Gating current noise produced by elementary transitions in Shaker potassium channels.
    14. (1994). Gating of Shaker K1 channels: II. The components of gating currents and a model of channel activation.
    15. (1997). How does the W434F mutation block current in Shaker potassium channels?
    16. (1993). Inactivation determined by a single site in K1 pores. Pflügers Arch.
    17. (1998). Inactivation of gating currents of L-type calcium channels. Specific role of the a2d subunit.
    18. (1987). Intramembrane charge movement in frog skeletal muscle fibres. Properties of charge 2.
    19. (1987). Molecular characterization of Shaker, a Drosophila gene that encodes a potassium channel.
    20. (1998). Protein rearrangements underlying slow inactivation of the Shaker K1 channel.
    21. (1983). Relationship between membrane excitability and single channel open-close kinetics.
    22. (1994). Shaker potassium channel gating. I: Transitions near the open state.
    23. (1994). Shaker potassium channel gating. III: Evaluation of kinetic models for activation.
    24. (1996). Slow gating charge immobilization in the human potassium channel Kv 1.5 and its prevention by 4-aminopyridine.
    25. (1998). The cut open oocyte voltage clamp technique. Methods Enzymol.
    26. (1990). The role of divergent amino and carboxyl domains on the inactivation properties of potassium channels derived from the Shaker gene of Drosophila.
    27. (1980). The variance of sodium current fluctuations at the node of Ranvier.
    28. (1997). Trapping of organic163 Olcese et al. blockers by closing of voltage-dependent K1 channels: evidence for a trap door mechanism of activation gating.
    29. (1992). Two classes of gating current from L-type Ca channels in guinea pig ventricular myocytes.
    30. (1991). Two types of inactivation in Shaker K 1 channels: effects of alterations in the carboxy-terminal region.

    To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.