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J. Biol. Chem., Vol. 275, Issue 45, 35402-35407, November 10, 2000
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From the Loyola University Chicago, Stritch School of Medicine,
Department of Physiology, Maywood, Illinois 60153
We have investigated the role of
extramitochondrial Na+ for the regulation of
mitochondrial Ca2+ concentration
([Ca2+]m) in permeabilized single vascular
endothelial cells. [Ca2+]m was measured by
loading the cells with the membrane-permeant Ca2+ indicator
fluo-3/AM and subsequent removal of cytoplasmic fluo-3 by surface
membrane permeabilization with digitonin. An elevation of
extramitochondrial Ca2+ resulted in a
dose-dependent increase in the rate of Ca2+
accumulation into mitochondria (k0.5 = 3 µM) via the mitochondrial Ca2+ uniporter. In
the presence of 10 mM extramitochondrial Na+
([Na+]em), repetitive application of brief pulses
of high Ca2+ (2-10 µM) to simulate
cytoplasmic [Ca2+] oscillations caused transient
increases of [Ca2+]m characterized by a fast
rising phase that was followed by a slow decay. Removal of
extramitochondrial Na+ or inhibition of mitochondrial
Na+/Ca2+ exchange with clonazepam blocked
mitochondrial Ca2+ efflux and resulted in a net
accumulation of Ca2+ by the mitochondria. Half-maximal
activation of mitochondrial Na+/Ca2+ exchange
occurred at [Na+]em = 4.4 mM, which
is well within the physiological range of cytoplasmic
[Na+]. This study provides evidence that Ca2+
efflux from the mitochondria in vascular endothelial cells occurs solely via Na+/Ca2+ exchange and emphasizes the
important role of intracellular Na+ for mitochondrial
Ca2+ regulation.
Intracellular Sodium Modulates Mitochondrial Calcium Signaling in
Vascular Endothelial Cells*
*
Financial support was provided by grants from the National
Institutes of Health (HL-51941 and HL-62231) and the American Heart Association National Center (Established Investigator Award 95002520).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.
To whom correspondence should be addressed: Dept. of Physiology,
Loyola University Chicago, 2160 S. First Ave., Maywood, IL 60153.
Tel.: 708-216-1182; Fax: 708-216-6308; E-mail: LBLATTE@LUMC.EDU.
Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.
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