Acid-base changes alter Mg2+ uptake in mouse distal convoluted tubule cells

Dai LJ, Friedmam PA, and Quamme GA:  Acid-base changes alter Mg2+ uptake in mouse distal  convoluted tubule cells. American Journal of Physiology 272:F759-F766, 1997.

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Abstract Metabolic alkalosis leads to renal magnesium conservation, whereas metabolic acidosis is associated with urinary magnesium wasting. Micropuncture studies suggest that these actions affect magnesium transport in the distal tubule. The cellular mechanisms of acidbase changes were investigated in an immortalized mouse distal convoluted tubule (MDCT) cell line. Intracellular free Mg2+ concentration ([Mg2+]i) was determined by microfluorescence using the Mg2+- responsive dye, mag-fura 2. Mg2+ transport was assessed as a function of change in [Mg2+]i with time following placement of Mg2+-depleted cells into a buffer containing 1.5 mM magnesium. The uptake rate of Mg2+, d( [Mg2+]i)ldt 9 into Mg 2+-depleted cells determined with a buffer solution of pH 7.4 was 178 t 21 nM/s. Mg2+ uptake at pH 8.0 was markedly increased 278 2 35 r&I/s, whereas transport at pH 6.0 was significantly reduced to 121 ? 15 nM/s. Mg2+ uptake at pH 7.4 was not stimulated with 20 or 40 mM bicarbonate, nor were the differences in Mg2+ uptake with pH associated with changes in membrane voltage. Mg2+ uptake was stimulated with membrane hyperpolarization at pH 6.0 but not at pH 8.0. Chlorothiazide (10m4 M), which stimulates Mg2+ uptake by hyperpolarizing the membrane voltage, increased uptake at pH 6.0,59 t 14%, but decreased it at alkaline pH of 8.0, -55 t 3%. Accordingly, MDCT cells become refractory to the stimulating effects of hyperpolarization at alkaline pH values. These studies show that protons may directly affect Mg2+ transport in MDCT cells.

Metabolic alkalosis leads to
renal magnesium conservation, whereas metabolic acidosis is
associated with urinary magnesium wasting. Micropuncture
studies suggest that these actions affect magnesium transport
in the distal tubule. The cellular mechanisms of acidbase
changes were investigated in an immortalized mouse
distal convoluted tubule (MDCT) cell line. Intracellular free
Mg2+ concentration ([Mg2+]i) was determined by microfluorescence
using the Mg2+- responsive dye, mag-fura 2. Mg2+
transport was assessed as a function of change in [Mg2+]i with
time following placement of Mg2+-depleted cells into a buffer
containing 1.5 mM magnesium. The uptake rate of Mg2+,
d( [Mg2+]i)ldt 9 into Mg 2+-depleted cells determined with a
buffer solution of pH 7.4 was 178 t 21 nM/s. Mg2+ uptake at
pH 8.0 was markedly increased 278 2 35 r&I/s, whereas
transport at pH 6.0 was significantly reduced to 121 ? 15
nM/s. Mg2+ uptake at pH 7.4 was not stimulated with 20 or 40
mM bicarbonate, nor were the differences in Mg2+ uptake
with pH associated with changes in membrane voltage. Mg2+
uptake was stimulated with membrane hyperpolarization at
pH 6.0 but not at pH 8.0. Chlorothiazide (10m4 M), which
stimulates Mg2+ uptake by hyperpolarizing the membrane
voltage, increased uptake at pH 6.0,59 t 14%, but decreased
it at alkaline pH of 8.0, -55 t 3%. Accordingly, MDCT cells
become refractory to the stimulating effects of hyperpolarization
at alkaline pH values. These studies show that protons
may directly affect Mg2+ transport in MDCT cells.
intracellular magnesium; fluorescence; acidosis; alkalosis
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