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J. Biol. Chem., Vol. 276, Issue 17, 13657-13663, April 27, 2001
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From the Multidisciplinary Research Group on Hypertension, Clinical
Research Institute of Montreal, University of Montreal, Montreal,
Quebec H2W 1R7, Canada
Treatment of Madin-Darby canine kidney (MDCK)
cells with the peptide hormone angiotensin II (Ang II) results in an
increase in the concentrations of cytosolic free calcium
([Ca2+]i) and sodium
([Na+]i) with a concomitant decrease in cytosolic
free Mg2+ concentration ([Mg2+]i). In
the present study we demonstrate that this hormone-induced decrease in
[Mg2+]i is independent of
[Ca2+]i but dependent on extracellular
Na+. [Mg2+]i,
[Ca2+]i, and [Na+]i were
measured in Ang II-stimulated MDCK cells by fluorescence digital
imaging using the selective fluoroprobes mag-fura-2AM, fura-2AM, and
sodium-binding benzofuran isophthalate
(acetoxymethyl ester), respectively. Ang II decreased
[Mg2+]i and increased
[Na+]i in a dose-dependent manner.
These effects were inhibited by irbesartan (selective AT1
receptor blocker) but not by PD123319 (selective AT2
receptor blocker). Imipramine and quinidine (putative inhibitors of the
Na+/Mg2+ exchanger) and removal of
extracellular Na+ abrogated Ang II-mediated
[Mg2+]i effects. In cells pretreated with
thapsigargin (reticular Ca2+-ATPase inhibitor), Ang
II-stimulated [Ca2+]i transients were attenuated
(p < 0.01), whereas agonist-induced [Mg2+]i responses were unchanged. Clamping the
[Ca2+]i near 50 nmol/liter with
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) inhibited Ang II-induced
[Ca2+]i increases but failed to alter Ang
II-induced [Mg2+]i responses. Benzamil, a
selective blocker of the Na+/Ca2+ exchanger,
inhibited [Na+]i but not
[Mg2+]i responses. Our data demonstrate that in
MDCK cells, AT1 receptors modulate
[Mg2+]i via a
Na+-dependent Mg2+ transporter that
is not directly related to [Ca2+]i. These data
support the notion that rapid modulation of
[Mg2+]i is not simply a result of
Mg2+ redistribution from intracellular buffering sites by
Ca2+ and provide evidence for the existence of a
Na+-dependent, hormonally regulated transporter
for Mg2+ in renally derived cells.
Angiotensin II Type I Receptor Modulates Intracellular Free
Mg2+ in Renally Derived Cells via
Na+-dependent Ca2+-independent
Mechanisms*
,
*
This study was supported by Grant MT15420 and by a group
grant to the Multidisciplinary Research Group on Hypertension from the
Canadian Institute of Health Research.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.
A scholar of the Canadian Hypertension Society/Canadian Institute
of Health Research. To whom correspondence should be addressed: Clinical Research Inst. of Montreal, 110 Pine Ave. West, Montreal, Quebec H2W 1R7, Canada. Tel.: 514-987-5747; Fax: 514-987-5585; E-mail:
touyzr@ircm.qc.ca.
Copyright © 2001 by The American Society for Biochemistry and Molecular Biology, Inc.
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