title: Extracellular K+ and Ba2+ mediate voltage-dependent inactivation of the outward-rectifying K+ channel encoded by the yeast gene TOK1.
abstract: Gating of the yeast K+ channel encoded by the Saccharomyces cerevisiae gene TOK1, unlike other outward-rectifying K+ channels that have been cloned, is promoted by membrane voltage (inside positive-going) and repressed by extracellular K+. When expressed in Xenopus laevis oocytes, the TOK1p current rectified strongly outward, its activation shifting in parallel with the K+ equilibrium potential when the external K+ concentration ([K+]o) was increased above 3 mM. Analysis of the TOK1p current indicated that two kinetic components contributed to the conductance and the voltage sensitivity of the conductance. By contrast, the [K+]o sensitivity of the current was accommodated entirely within the slow-relaxing component; it was diminished near 1 mM [K+]o, and at submillimolar concentrations the voltage dependence of the TOK1p conductance was insensitive to [K+]o. External Rb+, the K+ channel blockers Cs+ and Ba2+--but not Na+, Ca2+ or Mg2+--substituted for K+ in control of TOK1p activation, indicating a specificity in cation interaction with the TOK1p gate. These and additional results indicate that external K+ acts as a ligand to inactivate the TOK1p channel, and they implicate a gating process mediated by a single cation binding site within the membrane electric field, but distinct from the permeation pathway.
authors.affiliation: Laboratory of Plant Physiology and Biophysics, Wye College, University of London, Kent, UK.
authors.forename: P
authors.initials: P
authors.lastname: Vergani
authors.forename: T
authors.initials: T
authors.lastname: Miosga
authors.forename: S M
authors.initials: SM
authors.lastname: Jarvis
authors.forename: M R
authors.initials: MR
authors.lastname: Blatt
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology*; D005656:Fungal Proteins / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects; D008024:Ligands; D008564:Membrane Potentials; D009865:Oocytes; D011188:Potassium / Q000494:pharmacology*; D015221:Potassium Channels / Q000502:physiology*; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014982:Xenopus laevis
chemical_list: D005656:Fungal Proteins; D008024:Ligands; D015221:Potassium Channels; D029701:Saccharomyces cerevisiae Proteins; C095220:TOK1 protein, S cerevisiae; D001464:Barium; D011188:Potassium