The Journal of Membrane Biology

, Volume 198, Issue 3, pp 177–192

Chloride Channel Function in the Yeast TRK-Potassium Transporters

  • T. Kuroda
  • H. Bihler
  • E. Bashi
  • C. L. Slayman
  • A. Rivetta
Article

DOI: 10.1007/s00232-004-0671-1

Cite this article as:
Kuroda, T., Bihler, H., Bashi, E. et al. J Membrane Biol (2004) 198: 177. doi:10.1007/s00232-004-0671-1

Abstract

The TRK proteins—Trk1p and Trk2p— are the main agents responsible for “active” accumulation of potassium by the yeast Saccharomyces cerevisiae. In previous studies, inward currents measured through those proteins by whole-cell patch-clamping proved very unresponsive to changes of extracellular potassium concentration, although they did increase with extracellular proton concentration—qualitatively as expected for H+ coupling to K+ uptake. These puzzling observations have now been explored in greater detail, with the following major findings: a) the large inward TRK currents are not carried by influx of either K+ or H+, but rather by an efflux of chloride ions; b) with normal expression levels for Trk1p and Trk2p in potassium-replete cells, the inward TRK currents are contributed approximately half by Trk1p and half by Trk2p; but c) strain background strongly influences the absolute magnitude of these currents, which are nearly twice as large in W303-derived spheroplasts as in S288c-derived cells (same cell-size and identical recording conditions); d) incorporation of mutations that increase cell size (deletion of the Golgi calcium pump, Pmr1p) or that upregulate the TRK2 promoter, can further substantially increase the TRK currents; e) removal of intracellular chloride (e.g., replacement by sulfate or gluconate) reveals small inward currents that are K+-dependent and can be enhanced by K+ starvation; and f) finally, the latter currents display two saturating kinetic components, with preliminary estimates of K0.5 at 46 μM [K+]out and 6.8 mM [K+]out, and saturating fluxes of ∼5 mM/min and ∼10 mM/min (referred to intracellular water). These numbers are compatible with the normal K+-transport properties of Trk1p and Trk2p, respectively.

Keywords

Potassium transportTRK proteinsInward rectifierChloride currentPatch clampingSaccharomyces cerevisiae

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • T. Kuroda
    • 1
    • 2
  • H. Bihler
    • 3
  • E. Bashi
    • 1
  • C. L. Slayman
    • 1
  • A. Rivetta
    • 1
  1. 1.Department of Cellular and Molecular PhysiologyYale School of MedicineNew HavenUSA
  2. 2.Department of Microbiology, Faculty of Pharmaceutical SciencesOkayama UniversityOkayamaJapan
  3. 3.Botanisches Institute, Lehrstuhl IUniversität KarlsruheKarlsruheGermany