Pflügers Archiv - European Journal of Physiology

, Volume 462, Issue 2, pp 315–330

Anion currents in yeast K+ transporters (TRK) characterize a structural homologue of ligand-gated ion channels

Ion Channels, Receptors and Transporters

DOI: 10.1007/s00424-011-0959-9

Cite this article as:
Rivetta, A., Kuroda, T. & Slayman, C. Pflugers Arch - Eur J Physiol (2011) 462: 315. doi:10.1007/s00424-011-0959-9

Abstract

Patch clamp studies of the potassium-transport proteins TRK1,2 in Saccharomyces cerevisiae have revealed large chloride efflux currents: at clamp voltages negative to −100 mV, and intracellular chloride concentrations >10 mM (J. Membr. Biol. 198:177, 2004). Stationary-state current-voltage analysis led to an in-series two-barrier model for chloride activation: the lower barrier (α) being 10–13 kcal/mol located ∼30% into the membrane from the cytoplasmic surface; and the higher one (β) being 12–16 kcal/mol located at the outer surface. Measurements carried out with lyotrophic anions and osmoprotective solutes have now demonstrated the following new properties: (1) selectivity for highly permeant anions changes with extracellular pH; at pHo = 5.5: I ≈ Br > Cl > SCN > NO3, and at pHo 7.5: I ≈ Br > SCN > NO3 > Cl. (2) NO2 acts like “superchoride”, possibly enhancing the channel’s intrinsic permeability to Cl. (3) SCN and NO3 block chloride permeability. (4) The order of selectivity for several slightly permeant anions (at pHo = 5.5 only) is formate > gluconate > acetate >> phosphate−1. (5) All anion conductances are modulated (choked) by osmoprotective solutes. (6) The data and descriptive two-barrier model evoke a hypothetical structure (Biophys. J. 77:789, 1999) consisting of an intramembrane homotetramer of fungal TRK molecules, arrayed radially around a central cluster of four single helices (TM7) from each monomer. (7) That tetrameric cluster would resemble the hydrophobic core of (pentameric) ligand-gated ion channels, and would suggest voltage-modulated hydrophobic gating to underlie anion permeation.

Keywords

TRK proteins Inward rectifier Chloride current Chaotropy Patch clamping Saccharomyces cerevisiae Eyring barriers Facultative channels Ligand-gated ion channels 

Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Alberto Rivetta
    • 1
  • Teruo Kuroda
    • 1
    • 2
  • Clifford Slayman
    • 1
  1. 1.Department of Cellular and Molecular PhysiologyYale School of MedicineNew HavenUSA
  2. 2.Department of Microbiology, Faculty of Pharmaceutical SciencesOkayama UniversityOkayamaJapan

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