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J Biol Chem, Vol. 275, Issue 14, 10182-10189, April 7, 2000
From the Department of Medicine, University of Texas, Southwestern
Medical Center, Dallas, Texas 75235-8856
ROMK channels are responsible for
K+ secretion in kidney. The activity of ROMK is
regulated by intracellular pH (pHi) with acidification causing
channel closure (effective pKa ~6.9). Recently,
we and others reported that a direct interaction of the channels with
phosphatidyl-4,5-bisphosphate (PIP2) is critical for
opening of the inwardly rectifying K+ channels. Here, we
investigate the relationship between the mechanisms for regulation of
ROMK by PIP2 and by pHi. We find that disruption of
PIP2-ROMK1 interaction not only decreases single-channel open probability (Po) but gives rise to a ROMK1
subconductance state. This state has an increased sensitivity to
intracellular protons (effective pKa shifted to pH
~7.8), such that the subconductance channels are relatively quiescent
at physiological pHi. Open probability for the subconductance
channels can then be increased by intracellular alkalinization to
supra-physiological pH. This increase in Po for
the subconductance channels by alkalinization is not associated with an
increase in PIP2-channel interaction. Thus, direct
interaction with PIP2 is critical for ROMK1 to open at full
conductance. Disruption of this interaction increases pHi
sensitivity for the channels via emergence of the subconductance state.
The control of open probability of ROMK1 by pHi occurs via a
mechanism distinct from the regulation by PIP2.
Phosphatidylinositol 4,5-Bisphosphate and Intracellular pH
Regulate the ROMK1 Potassium Channel via Separate but Interrelated
Mechanisms*
,,
*
This work was supported in part by National Institutes of
Health Grant RO1-DK-54368 (to C.-L. H.) and by a grant-in-aid from the
American Heart Association, National Center.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.
Both authors contributed equally to this work.
§
Supported in part by National Taiwan University and the Ministry of
Education of Taiwan.
¶
Supported in part by National Institutes of Health
Institutional Training Grant T32 DK-07257.
To whom correspondence and reprint requests should be
addressed: Dept. of Medicine, H5-112, MC-8856, UTSW Medical Center, Dallas, TX 75235-8856. Tel.: 214-648-8627; Fax: 214-648-2071; E-mail:chuan1@mednet.swmed.edu.
Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.
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