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J. Biol. Chem., Vol. 276, Issue 16, 12898-12902, April 20, 2001
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From the Department of Biology, Georgia State University,
Atlanta, Georgia 30302-4010
ATP-sensitive K+
(KATP) channels may be regulated by protons in addition to
ATP, phospholipids, and other nucleotides. Such regulation allows a
control of cellular excitability in conditions when pH is low but ATP
concentration is normal. However, whether the KATP changes
its activity with pH alterations remains uncertain. In this
study we showed that the reconstituted KATP was
strongly activated during hypercapnia and intracellular acidosis using whole-cell recordings. Further characterizations in excised patches indicated that channel activity increased with a moderate drop in
intracellular pH and decreased with strong acidification. The channel activation was produced by a direct action of protons on the
Kir6 subunit and relied on a histidine residue that is conserved in all
KATP. The inhibition appeared to be a result of channel
rundown and was not seen in whole-cell recordings. The biphasic
response may explain the contradictory pH sensitivity observed in
cell-endogenous KATP in excised patches. Site-specific mutations of two residues showed that pH and ATP sensitivities were independent of each other. Thus, these results demonstrate that
the proton is a potent activator of the KATP. The
pH-dependent activation may enable the KATP to
control vascular tones, insulin secretion, and neuronal excitability in
several pathophysiologic conditions.
Direct Activation of Cloned KATP Channels by
Intracellular Acidosis*
,,
*
This work was supported by National Institutes of Health
Grant HL58410, American Diabetes Association Grant 01039, and
American Heart Association Grant 9950528N.The costs of publication of this article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
These two authors contributed equally to this work.
§
To whom correspondence should be addressed: Dept. of Biology,
Georgia State University, 24 Peachtree Central Ave., Atlanta, GA
30303-4010. Tel.: 404-651-0913; Fax: 404-651-2509; E-mail: cjiang@gsu.edu.
Copyright © 2001 by The American Society for Biochemistry and Molecular Biology, Inc.
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