title: KAT1 inactivates at sub-millimolar concentrations of external potassium.
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 microM. 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.
authors.affiliation: Institute of Botany, Department of Biology, Darmstadt University of Technology, Schnittspahnstrasse 3, D-64287 Darmstadt, Germany.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Hertel
authors.forename: Ferenc
authors.initials: F
authors.lastname: Horváth
authors.forename: Barnabás
authors.initials: B
authors.lastname: Wodala
authors.forename: Annette
authors.initials: A
authors.lastname: Hurst
authors.forename: Anna
authors.initials: A
authors.lastname: Moroni
authors.forename: Gerhard
authors.initials: G
authors.lastname: Thiel
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004553:Electric Conductivity; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D029681:Arabidopsis Proteins; C501210:KAT1 protein, Arabidopsis; D024661:Potassium Channels, Inwardly Rectifying; D011188:Potassium