AJP - Cell Physiology, Vol 259, Issue 3 C521-C525, Copyright © 1990 by American Physiological Society
Presence of a novel influx pathway for Mg2+ in MDCK cells
G. A. Quamme and L. J. Dai
Department of Medicine, University of British Columbia, University Hospital-UBC Site, Vancouver, Canada.
Basal free Mg2+ concentration was 0.49 +/- 0.03 mM in normal single
Madin-Darby canine kidney (MDCK) cells as measured by fluorescence with the
aid of mag-fura-2. Accordingly, Mg2+ may enter the cell down a
transmembrane electrical gradient. The present study describes some aspects
of Mg2+ entry into the established MDCK cell line. MDCK cells were
Mg2(+)-depleted (0.26 +/- 0.01 mM) by culturing in Mg2(+)-free media for
16-20 h. Cells were subsequently exposed to 5 mM MgCl2, and intracellular
Mg2+ concentration ([Mg2+]i) was monitored with fluorescence. [Mg2+]i
returned to normal basal levels, 0.56 +/- 0.05 mM, with a refill rate of
272 +/- 39 nM/s, n = 4. Mg2+ entry was not changed by 5.0 mM external Ca2+
but was completely inhibited with 5.0 mM La3+. Intracellular Ca2+
concentration was not altered by Mg2+ depletion or during Mg2+ repletion.
Mg2+ uptake was inhibited by verapamil (0 +/- 27 nM/s, n = 3), was
inhibited less so by diltiazem (141 +/- 34 nM/s, n = 3), and was not
affected by nifedipine (300 +/- 53 nM/s, n = 6). These inhibitors were
fully reversible on removal, and [Mg2+]i returned to normal levels. These
data indicate the presence of a unique Mg2+ entry pathway in MDCK cells
that may be important in Mg2+ homeostasis. The model of Mg2+ refill into
Mg2(+)-depleted cells may be useful in other cell types.
