Presence of a novel influx pathway for Mg2+ in MDCK cells.
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.
Department of Medicine, University of British Columbia, University Hospital-UBC Site, Vancouver, Canada.
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D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D004285:Dogs; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D007668:Kidney; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects
D002121:Calcium Channel Blockers; D007811:Lanthanum; D008274:Magnesium; D002118:Calcium