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Chloride channel function in the yeast TRK-potassium transporters
1Department of Cellular and Molecular Physiology, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
The Journal of Membrane Biology
|June 25, 2004
Summary
The TRK proteins in yeast facilitate potassium uptake, but surprisingly, their currents are driven by chloride efflux, not potassium or proton influx. These currents are influenced by strain background and cell size, revealing complex transport mechanisms.
Area of Science:
- Molecular and Cellular Biology
- Yeast Physiology
- Ion Transport Mechanisms
Background:
- The TRK proteins (Trk1p and Trk2p) are crucial for active potassium (K+) accumulation in Saccharomyces cerevisiae.
- Previous studies showed TRK currents were unresponsive to extracellular K+ but sensitive to H+ concentration, suggesting H+-K+ coupling.
- These observations presented a puzzle regarding the actual ion transport mechanism.
Purpose of the Study:
- To investigate the underlying mechanism of the puzzling TRK currents in yeast.
- To elucidate the specific ions responsible for the observed inward currents.
- To characterize the factors influencing the magnitude and kinetics of TRK-mediated currents.
Main Methods:
- Whole-cell patch-clamping electrophysiology was employed to measure ion currents.
- Experiments involved manipulating extracellular and intracellular ion concentrations (K+, H+, Cl-).
- Mutant strains affecting cell size (pmr1Δ) and TRK2 expression were analyzed.
Main Results:
- Large inward TRK currents are primarily mediated by chloride (Cl-) efflux, not K+ or H+ influx.
- Both Trk1p and Trk2p contribute equally to TRK currents at normal expression levels.
- Current magnitude is significantly influenced by yeast strain background (W303 vs. S288c) and cell size.
- Mutations increasing cell size or TRK2 expression substantially enhance TRK currents.
- Removal of intracellular Cl- revealed small, K+-dependent inward currents with two saturating kinetic components.
Conclusions:
- Yeast TRK proteins mediate K+ transport indirectly via Cl- efflux.
- TRK current characteristics are modulated by cellular factors including strain background, cell size, and gene expression.
- The identified kinetic components of K+-dependent currents align with known TRK protein transport properties.
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