Determination of epithelial magnesium transport with stable isotopes.
The inability to adequately determine Mg(2+) flux rates with radiotracer studies has stymied our efforts to understand how magnesium is transported by epithelial cells. To evaluate epithelial Mg(2+) transport, a stable 25Mg isotope was used to measure magnesium uptake into normal and Mg(2+)-depleted Madin-Darby canine kidney (MDCK) cells. 25Mg entry rates were significantly increased in Mg(2+)-depleted cells relative to those cultured in normal magnesium media, 0.5 mM. 25Mg uptake was inhibited by external La(3+) but not Ca(2+) in both normal and Mg(2+)-depleted cells suggesting a specific entry pathway. These results with 25Mg were the same as with microfluorescence determinations using mag-fura-2. We have shown that Mg(2+) entry into epithelial cells reflects transepithelial transport; accordingly, increased Mg(2+) uptake in Mg(2+)-depleted cells provides an important intrinsic control of renal magnesium absorption. Furthermore, these studies indicate that cellular Mg(2+) transport may be quantitated with the use of stable isotopes that may be successfully applied to cells other than epithelia.
Max-Planck-Institut für Chemie, Otto-Hahn-Institut, Mainz, Germany.
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Stegmann
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Quamme
D000818:Animals; D001693:Biological Transport, Active; D003600:Cytosol / Q000378:metabolism; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D011868:Radioisotopes
D011868:Radioisotopes; D008274:Magnesium