Vol. 276, Issue 5, C1184-C1192, May 1999
Ni2+ transport by the human
Na+/Ca2+
exchanger expressed in Sf 9 cells
M.
Egger1,
A.
Ruknudin2,3,
E.
Niggli1,
W. J.
Lederer2, and
D. H.
Schulze3
1 Department of Physiology,
University of Bern, CH-3012 Bern, Switzerland;
2 Departments of Physiology
and of Molecular Biology and Biophysics and University of Maryland
Biotechnology Institute, and
3 Department of Microbiology and
Immunology, University of Maryland School of Medicine, Baltimore,
Maryland 21201
The mechanism of
Ni2+ block of the
Na+/Ca2+
exchanger was examined in Sf 9 cells expressing the human heart
Na+/Ca2+
exchanger (NCX1-NACA1). As predicted from the reported actions of
Ni2+, its application reduced
extracellular Na+-dependent
changes in intracellular Ca2+
concentration (measured by fluo 3 fluorescence changes). However, contrary to expectation, the reduced fluorescence was accompanied by
measured
63Ni2+
entry. The
63Ni2+
entry was observed in Sf 9 cells expressing the
Na+/Ca2+
exchanger but not in control cells. The established sequential transport mechanism of the
Na+/Ca2+
exchanger could be compatible with these results if one of the two ion
translocation steps is blocked by
Ni2+ and the other permits
Ni2+ translocation. We conclude
that, because Ni2+ entry was
inhibited by extracellular Ca2+
and enhanced by extracellular Na+,
the Ca2+ translocation step moved
Ni2+, whereas the
Na+ translocation step was
inhibited by Ni2+. A model is
presented to discuss these findings.
heart; nickel ion quench; fluo 3
