Chloride channel function in the yeast TRK-potassium transporters

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

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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 Trklp 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 K 0.5 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.

Original languageEnglish
Pages (from-to)177-192
Number of pages16
JournalJournal of Membrane Biology
Volume198
Issue number3
DOIs
Publication statusPublished - Apr 1 2004

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Keywords

  • Chloride current
  • Inward rectifier
  • Patch clamping
  • Potassium transport
  • Saccharomyces cerevisiae
  • TRK proteins

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Cell Biology

Cite this

Kuroda, T., Bihler, H., Bashi, E., Slayman, C. L., & Rivetta, A. (2004). Chloride channel function in the yeast TRK-potassium transporters. Journal of Membrane Biology, 198(3), 177-192. https://doi.org/10.1007/s00232-004-0671-1