Aa. Very et al., EXPRESSION OF A CLONED PLANT K- ANALYSIS OF MACROSCOPIC CURRENTS( CHANNEL IN XENOPUS OOCYTES ), Plant journal, 7(2), 1995, pp. 321-332
The open reading frame from the Arabidopsis thaliana KAT1 cDNA was clo
ned in a transcription plasmid between the 3' and 5' untranslated regi
ons of a beta-globin cDNA from Xenopus oocyte. The polyadenylated tran
scripts resulting from in vitro transcription gave rise to high levels
of expression of KAT1 channel when injected in Xenopus oocytes. Upon
hyperpolarization, a slow activating current could be recorded, inward
ly- or outwardly-directed, depending on K+ external concentration. Pre
dictions of the voltage-gated channel theory were shown to fit the dat
a well. The equivalent gating charge and the half-activation potential
ranged around 2 and -145 mV, respectively. KAT1 gating characteristic
s did not depend on K+ external concentration nor on external pH in th
e 5.0-7.5 range. KAT1 conductance was, however, increased (40%) when e
xternal pH was decreased from 6.5 to 5.0. The apparent affinity consta
nt of KAT1 for K+ lay in the range 15-30 mM, at external pH 7.4. As fo
r many K+ channels of animal cells, external caesium caused a voltage-
dependent blockage of inward (but not outward) KAT1 current, whereas t
etraethylammonium caused a voltage-independent block of both inward an
d outward KAT1 currents. In conclusion, high levels of expression made
it possible to carry out the first quantitative analysis of KAT1 macr
oscopic currents. KAT1 channel was shown to display features similar t
o those of as yet uncloned inward-rectifying voltage-gated channels de
scribed in both plant cells (namely guard cells) and animal cells.