Vergani P, Miosga T, Jarvis S M, Blatt M R
Laboratory of Plant Physiology and Biophysics, Wye College, University of London, Kent, UK.
FEBS Lett. 1997 Apr 1;405(3):337-44. doi: 10.1016/s0014-5793(97)00211-1.
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.
由酿酒酵母基因TOK1编码的酵母钾离子通道的门控，与已克隆的其他外向整流钾离子通道不同，其受膜电压（内膜电位正向）促进，受细胞外钾离子抑制。当在非洲爪蟾卵母细胞中表达时，TOK1p电流强烈向外整流，当外部钾离子浓度（[K+]o）增加到3 mM以上时，其激活与钾离子平衡电位平行移动。对TOK1p电流的分析表明，两个动力学成分对电导及其电压敏感性有贡献。相比之下，电流对[K+]o的敏感性完全包含在缓慢松弛成分中；在[K+]o接近1 mM时降低，并在亚毫摩尔浓度下，TOK1p电导的电压依赖性对[K+]o不敏感。外部铷离子、钾离子通道阻滞剂铯离子和钡离子——但不是钠离子、钙离子或镁离子——在控制TOK1p激活时可替代钾离子，表明阳离子与TOK1p门控的相互作用具有特异性。这些及其他结果表明，外部钾离子作为一种配体使TOK1p通道失活，并且它们暗示了一种由膜电场内单个阳离子结合位点介导的门控过程，但与通透途径不同。
