title: Cellular mechanisms of chlorothiazide and cellular potassium depletion on Mg2+ uptake in mouse distal convoluted tubule cells.
abstract: The use of the distally-acting diuretic, chlorothiazide, has been reported to have important effects on renal magnesium handling. The cellular mechanisms of chlorothiazide action on Mg2+ uptake was investigated in immortalized mouse distal convoluted tubule (MDCT) cells. Intracellular free Mg2+ concentration was determined by microfluorescence. Mg2+ transport was measured as a function of change in intracellular Mg2+ concentration with time following placement of Mg2+-depleted cells into a buffer containing 1.5 mM magnesium. The uptake rate of Mg2+ into Mg2+-depleted cells was 179 +/- 28 nM/second. Mg2+ uptake was dependent on the membrane voltage as membrane hyperpolarization enhanced uptake whereas depolarization diminished transport. Chlorothiazide increased Mg2+ uptake by 58%, from 179 +/- 28 to 283 +/- 23 nM/second. The ability of chlorothiazide to stimulate Mg2+ uptake in MDCT cells was concentration-dependent and related to the diuretic-induced hyperpolarization of the plasma membrane. These studies support the notion that acute chlorothiazide administration enhances renal magnesium conservation through its effects on Mg2+ transport within the distal convoluted tubule. Since chronic chlorothiazide administration may result in hypokalemia as well as hypomagnesemia, Mg2+ uptake was determined in potassium-depleted MDCT cells. Mg2+ uptake was diminished, 80 +/- 24 nM/second, in potassium depleted cells. Hyperpolarization of the plasma membrane with the cell permanent anion, SCN-, corrected Mg2+ uptake in potassium depleted cells suggesting that the basis for diminished uptake may, in part, be due to depolarization of the membrane voltage. In summary, acute chlorothiazide stimulates Mg2+ transport in MDCT cells. We postulate that chronic chlorothiazide use may lead to hypokalemia that in turn diminishes Mg2+ transport in the distal tubule resulting in urinary magnesium-wasting.
authors.affiliation: Department of Medicine, University of British Columbia, Vancouver, Canada.
authors.forename: L J
authors.initials: LJ
authors.lastname: Dai
authors.forename: P A
authors.initials: PA
authors.lastname: Friedman
authors.forename: G A
authors.initials: GA
authors.lastname: Quamme
mesh_terms: D000818:Animals; D002460:Cell Line; D002740:Chlorothiazide / Q000494:pharmacology*; D004232:Diuretics; D007008:Hypokalemia / Q000139:chemically induced / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007686:Kidney Tubules, Distal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008564:Membrane Potentials; D051379:Mice; D011188:Potassium / Q000378:metabolism*; D049993:Sodium Chloride Symporter Inhibitors / Q000494:pharmacology*
chemical_list: D004232:Diuretics; D049993:Sodium Chloride Symporter Inhibitors; D002740:Chlorothiazide; D008274:Magnesium; D011188:Potassium