Protons Activate Homomeric Kir6.2 Channels by Selective Suppression of the Long and Intermediate Closures

Protons Activate Homomeric Kir6.2 Channels by Selective Suppression of the Long and Intermediate... The ATP-sensitive K+ channels (KATP) play an important role in regulating membrane excitability. These channels are regulated by H+ in addition to ATP, ADP, and phospholipids. To understand how protons affect the single-channel properties, Kir6.2DC36 currents were studied in excised inside-out patches. We chose to study the homomeric Kir6.2 channel with 36 amino acids deleted at the C-terminal end, as there are ADP/ATP-binding sites in the SUR subunit, which may obscure the understanding of the channel-gating process. In the absence of ATP, moderate intracellular acidosis (pH 6.8) augmented Popen with small suppression (by ~10%) of the single-channel conductance. The long and intermediate closures were selectively inhibited, leading to a shortening of the mean closed time without significant changes in the mean open time. Stronger acidification (<pH6.2) caused channel rundown. Although similar changes in the single-channel properties were observed in the presence of 1 mM ATP, the Popen-pH relationship curve was shifted by 0.17 pH units toward lower pH levels. ATP had no effect on the inhibition of single-channel conductance during acidosis. Mutation of His175 eliminated the pH effect on the single-channel kinetics, while the single-channel response to acidic pH was retained in the K185E mutant that greatly reduces the ATP sensitivity. These results indicate that Kir6.2DC36 channel gating by protons and ATP relies on two distinct mechanisms opposite to each other, although the pH sensitivity is modulated by ATP. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Protons Activate Homomeric Kir6.2 Channels by Selective Suppression of the Long and Intermediate Closures

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Publisher
Springer Journals
Copyright
Copyright © 2002 by Springer-Verlag New York Inc.
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-002-1029-1
Publisher site
See Article on Publisher Site

Abstract

The ATP-sensitive K+ channels (KATP) play an important role in regulating membrane excitability. These channels are regulated by H+ in addition to ATP, ADP, and phospholipids. To understand how protons affect the single-channel properties, Kir6.2DC36 currents were studied in excised inside-out patches. We chose to study the homomeric Kir6.2 channel with 36 amino acids deleted at the C-terminal end, as there are ADP/ATP-binding sites in the SUR subunit, which may obscure the understanding of the channel-gating process. In the absence of ATP, moderate intracellular acidosis (pH 6.8) augmented Popen with small suppression (by ~10%) of the single-channel conductance. The long and intermediate closures were selectively inhibited, leading to a shortening of the mean closed time without significant changes in the mean open time. Stronger acidification (<pH6.2) caused channel rundown. Although similar changes in the single-channel properties were observed in the presence of 1 mM ATP, the Popen-pH relationship curve was shifted by 0.17 pH units toward lower pH levels. ATP had no effect on the inhibition of single-channel conductance during acidosis. Mutation of His175 eliminated the pH effect on the single-channel kinetics, while the single-channel response to acidic pH was retained in the K185E mutant that greatly reduces the ATP sensitivity. These results indicate that Kir6.2DC36 channel gating by protons and ATP relies on two distinct mechanisms opposite to each other, although the pH sensitivity is modulated by ATP.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Dec 1, 2002

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