B. Lacombe et Jb. Thibaud, EVIDENCE FOR A MULTIION PORE BEHAVIOR IN THE PLANT POTASSIUM CHANNEL KAT1, The Journal of membrane biology, 166(2), 1998, pp. 91-100
KAT1 is a cloned voltage-gated K+ channel from the plant Arabidopsis t
haliana L., which displays an inward rectification reminiscent of 'ano
malous' rectification of the i(f) pacemaker current recorded in animal
cells. Macroscopic conductance of KAT1 expressed in Xenopus oocytes w
as 5-fold less in pure Rb+ solution than in pure K+ solution, and negl
igible in pure Naf solution. Experiments in different K+/Na+ or K+/Rb mixtures revealed deviations from the principle of independence and n
otably two anomalous effects of the K+/Rb+ Rb+ mole fraction (i.e., th
e ratio [K+]/([K+]+[Rb+])). First, the KAT1 deactivation time constant
was both voltage- and mole fraction-dependent (a so-called 'foot in t
he door' effect was thus observed in KAT1 channel). Second, when plott
ed against the K+/Rb+ mole fraction, KAT1 conductance values passed th
rough a minimum. This minimum is more important for two pore mutants o
f KAT1 (T259S and T260S) that displayed an increase in P-Rb/P-K. These
results are consistent with the idea that KAT1 conduction requires se
veral ions to be present simultaneously within the pore. Therefore, th
is atypical 'green' member of the Shaker superfamily of K+ channels fu
rther shows itself to be an interesting model as well for permeation a
s for gating mechanism studies.