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Potassium Uptake Through the TOK1 K+ Channel in the Budding Yeast
Authors:C. Fairman  X.-L. Zhou  C. Kung
Affiliation:(1) Laboratory of Molecular Biology, University of Wisconsin, 1525 Linden Dr., Madison, WI 53706, USA, US;(2) Department of Genetics, University of Wisconsin, 1525 Linden Dr., Madison, WI 53706, USA, US
Abstract:The current through TOK1 (YKC1), the outward-rectifying K+ channel in Saccharomyces cerevisiae, was amplified by expressing TOK1 from a plasmid driven by a strong constitutive promoter. TOK1 so hyper-expressed could overcome the K+ auxotrophy of a mutant missing the two K+ transporters, TRK1 and TRK2. This trk1Δtrk2Δ double mutant hyperexpressing the TOK1 transgene had a higher internal K+ content than one expressing the empty plasmid. We examined protoplasts of these TOK1-hyperexpressing cells under a patch clamp. Besides the expected K+ outward current activating at membrane potential (V m ) above the K+ equilibrium potential (E K+ ), a small inward current was consistently observed when the V m was slightly below E K+ . The inward and the outward currents are similar in their activation rates, deactivation rates, ion specificities and Ba2+ inhibition, indicating that they flow through the same channel. Thus, the yeast outwardly rectifying K+ channel can take up K+ into yeast cells, at least under certain conditions. Received: 1 October 1998/Revised: 9 December 1998
Keywords:: TOK1 —   YKC1 —   K+ channel —   Yeast —   Patch clamp
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