Mg2+/Ca2+ sensing inhibits hormone-stimulated Mg2+ uptake in mouse distal convoluted tubule cells

The distal convoluted tubule plays a significant role in renal magnesium conservation. An immortalized mouse distal convoluted tubule (MDCT) cell line has been extensively used to study the cellular mechanisms of magnesium transport in this nephron segment. MDCT cells possess an extracellular polyvalent cation-sensing mechanism responsive to Mg(2+), Ca(2+), and neomycin. The present studies determined the effect of Mg(2+)/Ca(2+) sensing on hormone-mediated cAMP formation and Mg(2+) uptake in MDCT cells. MDCT cells were Mg(2+) depleted by culturing in Mg(2+)-free media for 16 h, and Mg(2+) uptake was measured by microfluorescence after placing the depleted cells in 1.5 mM MgCl(2). The mean rate of Mg(2+) uptake was 164 +/- 5 nM/s in control MDCT cells. Activation of Mg(2+)/Ca(2+) sensing with neomycin did not affect basal Mg(2+) uptake (155 +/- 5 nM/s). We have previously reported that treatment of MDCT cells with either glucagon or arginine vasopressin (AVP) stimulated Mg(2+) entry. In the present studies, the addition of extracellular Mg(2+) or Ca(2+) inhibited glucagon- and AVP-stimulated cAMP formation and Mg(2+) uptake in concentration-dependent manner with half-maximal concentrations of similar to 1.5 and 3.0 mM, respectively. Exogenous cAMP or forskolin stimulated Mg(2+) uptake in the presence of Mg(2+)/Ca(2+) sensing activation. We infer from these studies that Mg(2+)/Ca(2+)-sensing mechanisms located in the distal convoluted tubule may play a role in control of distal magnesium absorption.