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KAT1 inactivates at sub-millimolar concentrations of external potassium

2005; Oxford University Press; Volume: 56; Issue: 422 Linguagem: Inglês

10.1093/jxb/eri307

1460-2431

Brigitte Hertel, Ferenc Horváth, Barnabás Wodala, Annette M. Hurst, Anna Moroni, Gerhard Thiel,

Ion Channels and Receptors

Structural analysis of K+ channel pores suggests that the selectivity filter of the pore is an inherent sensor for extracellular K+ \((\mathrm{K}_{\mathrm{o}}^{{+}});\) channels seem to be inactivated at low \(\mathrm{K}_{\mathrm{o}}^{{+}}\) because of a destabilization of the conducting state and a collapse of the pore. In the present study, the effect of depleting \(\mathrm{K}_{\mathrm{o}}^{{+}}\) on the activity of a plant K+ channel, KAT1, from Arabidopsis thaliana was investigated. This channel is thought to be insensitive to \(\mathrm{K}_{\mathrm{o}}^{{+}}.\) The channel was therefore expressed in mammalian HEK293 cells and measured with patch clamp technology in the whole cell configuration. The effect of \(\mathrm{K}_{\mathrm{o}}^{{+}}\) depletion on channel activity was monitored from the tail currents before, during, and after washing \(\mathrm{K}_{\mathrm{o}}^{{+}}\) from the medium. The data show that a depletion of \(\mathrm{K}_{\mathrm{o}}^{{+}}\) 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 \(\mathrm{K}_{\mathrm{o}}^{{+}}\) could serve as a safety mechanism, which inactivates the channel at low \(\mathrm{K}_{\mathrm{o}}^{{+}}\) and, in this way, prevents leakage of K+ from the cells via this type of channel.