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The impermeant ion methylammonium blocks K+ and NH4+ currents through KAT1 channel differently: evidence for ion interaction in channel permeation.

Moroni, Anna and Bardella, L. and Thiel, Gerhard (1998):
The impermeant ion methylammonium blocks K+ and NH4+ currents through KAT1 channel differently: evidence for ion interaction in channel permeation.
In: The Journal of membrane biology, pp. 25-35, 163, (1), ISSN 0022-2631,
[Article]

Abstract

The permeation properties of KAT1, an inward rectifying potassium channel from plant cells, were investigated with different ions in the external medium. With either K+, NH4+ or methylammonium (MA) in the external solution, the channel, expressed in Xenopus oocytes, appeared permeable to K+ and, to a lesser extent, to NH4+ but not to the slightly bigger, methylated analogue of NH4+, MA. Substituting NH4+ for K+ shifted the voltage dependency of channel activation further negative and hastened activation kinetics. This suggests that channel operation depends on the transported substrate. In mixed solution (50 mM K+, 50 mM MA) MA inhibited K+ current in a voltage-independent manner. The maximum block did not exceed 50% of the K+ current. In contrast, when NH4+ was the permeant ion (50 mM NH4+, 50 mM MA) MA caused a voltage-dependent, slowly developing open channel block, achieving complete inhibition at very negative voltages. The latter block could be partially overcome by the addition of K+ in the external solution. The data support a model in which ions, after entering the channel pore, compete with different affinities for binding sites on their permeation pathway.

Item Type: Article
Erschienen: 1998
Creators: Moroni, Anna and Bardella, L. and Thiel, Gerhard
Title: The impermeant ion methylammonium blocks K+ and NH4+ currents through KAT1 channel differently: evidence for ion interaction in channel permeation.
Language: English
Abstract:

The permeation properties of KAT1, an inward rectifying potassium channel from plant cells, were investigated with different ions in the external medium. With either K+, NH4+ or methylammonium (MA) in the external solution, the channel, expressed in Xenopus oocytes, appeared permeable to K+ and, to a lesser extent, to NH4+ but not to the slightly bigger, methylated analogue of NH4+, MA. Substituting NH4+ for K+ shifted the voltage dependency of channel activation further negative and hastened activation kinetics. This suggests that channel operation depends on the transported substrate. In mixed solution (50 mM K+, 50 mM MA) MA inhibited K+ current in a voltage-independent manner. The maximum block did not exceed 50% of the K+ current. In contrast, when NH4+ was the permeant ion (50 mM NH4+, 50 mM MA) MA caused a voltage-dependent, slowly developing open channel block, achieving complete inhibition at very negative voltages. The latter block could be partially overcome by the addition of K+ in the external solution. The data support a model in which ions, after entering the channel pore, compete with different affinities for binding sites on their permeation pathway.

Journal or Publication Title: The Journal of membrane biology
Volume: 163
Number: 1
Divisions: 10 Department of Biology > Plant Membrane Biophysics
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10 Department of Biology
Date Deposited: 22 Jun 2011 07:35
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