P. Vergani et al., EXTRACELLULAR K-DEPENDENT INACTIVATION OF THE OUTWARD-RECTIFYING K+ CHANNEL ENCODED BY THE YEAST GENE TOK1( AND BA2+ MEDIATE VOLTAGE), FEBS letters, 405(3), 1997, pp. 337-344
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 r
epressed by extracellular K+. When expressed in Xenopus laevis oocytes
, the TOK1p current rectified strongly outward, its activation shiftin
g in parallel with the K+ equilibrium potential when the external K+ c
oncentration ([K+](0)) was increased above 3 mM. Analysis of the TOK1p
current indicated that two kinetic components contributed to the cond
uctance and the voltage sensitivity of the conductance. By contrast, t
he [K+](0) sensitivity of the current was accommodated entirely within
the slow-relaxing component; it was diminished near 1 mM [K+](0), and
at submillimolar concentrations the voltage dependence of the TOK1p c
onductance was insensitive to [K+](0). External Rb+, the K+ channel bl
ockers Cs+ and Ba2+ - but not Na+, Ca2+ or Mg2+ - substituted for K+ i
n control of TOK1p activation, indicating a specificity in cation inte
raction with the TOK1p gate. These and additional results indicate tha
t external K+ acts as a ligand to inactivate the TOK1p channel, and th
ey implicate a gating process mediated by a single cation binding site
within the membrane electric field, but distinct from the permeation
pathway. (C) 1997 Federation of European Biochemical Societies.