1,25(OH)2D3 stimulates Mg2+ uptake into MDCT cells: modulation by extracellular Ca2+ and Mg2+

Ritchie G, Kerstan D, Dai LJ, Kang HS, Canaff L, Hendy GN, and Quamme GA:  1,25(OH)2D3 stimulates Mg2+ uptake into MDCT cells: modulation by extracellular Ca2+ and Mg2+. American Journal of Physiology 280:F868-F878, 2001.

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Abstract The distal convoluted tubule plays a significant role in renal magnesium conservation. Although the cells of the distal convoluted tubule possess the vitamin D receptor, little is known about the effects of 1a,25-dihydroxyvitamin D [1,25(OH)2D3] on magnesium transport. In this study, we examined the effect of 1,25(OH)2D3 on distal cellular magnesium uptake and the modulation of this response by extracellular Ca21 and Mg21 in an immortalized mouse distal convoluted tubule (MDCT) cell line. MDCTcells possess the divalent cation-sensing receptor (CaSR) that responds to elevation of extracellular Ca21 and Mg21 concentrations to diminish peptide hormone-stimulated Mg21 uptake. Mg21 uptake rates were determined by microfluorescence in Mg21-depleted MDCT cells. Treatment of MDCT cells with 1,25(OH)2D3 for 16–24 h stimulated basal Mg21 uptake in a concentration-dependent manner from basal levels of 164 6 5 to 210611 nM/s, representing a 2863% change. Pretreatment with actinomycin D or cycloheximide abolished 1,25(OH)2D3- stimulated.Mg21 uptake (154 6 18 nM/s), suggesting that 1,25(OH)2D3 stimulates Mg21 uptake through gene activation and protein synthesis. Elevation of extracellular Ca21 inhibited 1,25(OH)2D3-stimulated Mg21 uptake (143 6 5 nM/s). Preincubation of the cells with an antibody to the CaSR prevented the inhibition by elevated extracellular Ca21 of 1,25(OH)2D3-stimulated Mg21 uptake (202 6 8 nM/s). Treatment with an antisense CaSR mRNA oligodeoxynucleotide also abolished the effects of extracellular Ca21 on 1,25(OH)2D3-responsive Mg21 entry. This showed that elevated extracellular calcium modulates 1,25(OH)2D-mediated responses through the CaSR. In summary, 1,25(OH)2D3 stimulated Mg21 uptake in MDCT cells, and this is dependent on de novo protein synthesis. Elevation of extracellular Ca21, acting via the CaSR, inhibited 1,25(OH)2D3-stimulated Mg21 entry. These data indicate that 1,25(OH)2D3 has important effects on the control of magnesium entry in MDCT cells and these responses can be modulated by extracellular divalent cations.

The distal convoluted tubule plays a significant role in renal
magnesium conservation. Although the cells of the distal convoluted
tubule possess the vitamin D receptor, little is known
about the effects of 1a,25-dihydroxyvitamin D [1,25(OH)2D3] on
magnesium transport. In this study, we examined the effect of
1,25(OH)2D3 on distal cellular magnesium uptake and the modulation
of this response by extracellular Ca21 and Mg21 in an
immortalized mouse distal convoluted tubule (MDCT) cell line.
MDCTcells possess the divalent cation-sensing receptor (CaSR)
that responds to elevation of extracellular Ca21 and Mg21
concentrations to diminish peptide hormone-stimulated Mg21
uptake. Mg21 uptake rates were determined by microfluorescence
in Mg21-depleted MDCT cells. Treatment of MDCT cells
with 1,25(OH)2D3 for 16–24 h stimulated basal Mg21 uptake in
a concentration-dependent manner from basal levels of 164 6 5
to 210611 nM/s, representing a 2863% change. Pretreatment
with actinomycin D or cycloheximide abolished 1,25(OH)2D3-
stimulated.Mg21 uptake (154 6 18 nM/s), suggesting that
1,25(OH)2D3 stimulates Mg21 uptake through gene activation
and protein synthesis. Elevation of extracellular Ca21 inhibited
1,25(OH)2D3-stimulated Mg21 uptake (143 6 5 nM/s). Preincubation
of the cells with an antibody to the CaSR prevented the
inhibition by elevated extracellular Ca21 of 1,25(OH)2D3-stimulated
Mg21 uptake (202 6 8 nM/s). Treatment with an antisense
CaSR mRNA oligodeoxynucleotide also abolished the
effects of extracellular Ca21 on 1,25(OH)2D3-responsive Mg21
entry. This showed that elevated extracellular calcium modulates
1,25(OH)2D-mediated responses through the CaSR. In
summary, 1,25(OH)2D3 stimulated Mg21 uptake in MDCT
cells, and this is dependent on de novo protein synthesis. Elevation
of extracellular Ca21, acting via the CaSR, inhibited
1,25(OH)2D3-stimulated Mg21 entry. These data indicate that
1,25(OH)2D3 has important effects on the control of magnesium
entry in MDCT cells and these responses can be modulated by
extracellular divalent cations.
1a,25-dihydroxyvitamin D; calcium/magnesium-
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