The Impermeant Ion Methylammonium Blocks K+ and NH+ 4 Currents through KAT1 Channel Differently: Evidence for Ion Interaction in Channel Permeation

The Impermeant Ion Methylammonium Blocks K+ and NH+ 4 Currents through KAT1 Channel Differently:... 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+, NH+ 4 or methylammonium (MA) in the external solution, the channel, expressed in Xenopus oocytes, appeared permeable to K+ and, to a lesser extent, to NH+ 4 but not to the slightly bigger, methylated analogue of NH+ 4, MA. Substituting NH+ 4 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 NH+ 4 was the permeant ion (50 mm NH+ 4, 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

The Impermeant Ion Methylammonium Blocks K+ and NH+ 4 Currents through KAT1 Channel Differently: Evidence for Ion Interaction in Channel Permeation

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Publisher
Springer-Verlag
Copyright
Copyright © Inc. by 1998 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s002329900367
Publisher site
See Article on Publisher Site

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+, NH+ 4 or methylammonium (MA) in the external solution, the channel, expressed in Xenopus oocytes, appeared permeable to K+ and, to a lesser extent, to NH+ 4 but not to the slightly bigger, methylated analogue of NH+ 4, MA. Substituting NH+ 4 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 NH+ 4 was the permeant ion (50 mm NH+ 4, 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

The Journal of Membrane BiologySpringer Journals

Published: May 1, 1998

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