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JXB Advance Access published online on November 1, 2005
Journal of Experimental Botany, doi:10.1093/jxb/eri307
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© The Author [2005]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved.
Received June 29, 2005
Accepted September 2, 2005

RESEARCH PAPER

KAT1 inactivates at sub-millimolar concentrations of external potassium

Brigitte Hertel 1 *, Ferenc Horváth 2 *, Barnabás Wodala 2, Annette Hurst 1, Anna Moroni 3, and Gerhard Thiel 1*

1 Institute of Botany, Department of Biology, Darmstadt University of Technology, Schnittspahnstraße 3, D-64287 Darmstadt, Germany
2 Department Plant Physiology, University of Szeged, Szeged, Hungary
3 Dipartimento di Biologia and IBF-CNR, Università degli Studi di Milano, Italy

* To whom correspondence should be addressed.
Gerhard Thiel, E-mail: thiel{at}bio.tu-darmstadt.de


  Abstract

Structural analysis of K+ channel pores suggests that the selectivity filter of the pore is an inherent sensor for extracellular K+ (Ko+); channels seem to be inactivated at low Ko+ because of a destabilization of the conducting state and a collapse of the pore. In the present study, the effect of depleting Ko+ on the activity of a plant K+ channel, KAT1, from Arabidopsis thaliana was investigated. This channel is thought to be insensitive to Ko+. The channel was therefore expressed in mammalian HEK293 cells and measured with patch clamp technology in the whole cell configuration. The effect of Ko+ depletion on channel activity was monitored from the tail currents before, during, and after washing Ko+ from the medium. The data show that a depletion of Ko+ results in a decrease in channel conductance, irrespective of whether K+ is simply removed or replaced by either Na+ or Li+. Quantitative analysis suggests that the channel has two binding sites for K+ with the dissociation constant in the order of 20 µM. This high sensitivity of the channel to Ko+ could serve as a safety mechanism, which inactivates the channel at low Ko+ and, in this way, prevents leakage of K+ from the cells via this type of channel.

Keywords: Cation sensitive gating; HEK293 cells; KAT1; potassium affinity.

*These authors contributed equally to this work.


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