Aminoglycosides inhibit hormone-stimulated Mg<sup>2+</sup> uptake in mouse distal convoluted tubule cells

Abstract

The clinical use of aminoglycosides often leads to renal magnesium wasting and hypomagnesemia. Of the nephron segments, both the thick ascending limb of Henle's loop and the distal tubule play significant roles in renal magnesium conservation but the distal convoluted tubule exerts the final control of urinary excretion. 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. Peptide hormones, such as parathyroid hormone (PTH), glucagon, calcitonin, and arginine vasopressin (AVP) stimulate Mg 2+ uptake in MDCT cells that is modulated by extracellular polyvalent cations, Ca 2+ and Mg 2+ . The present studies determined the effect of aminoglycosides on parathyroid hormone (PTH)-mediated cAMP formation and Mg 2+ uptake in MDCT cells. Gentamicin, a prototypic aminoglycoside, illicited transient increases in intracellular Ca 2+ from basal levels of 102 ± 13 nM to 713 ± 125 nM, suggesting a receptor-mediated response. In order to determine Mg 2+ transport, 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 1.0 mM MgCl2. The mean rate of Mg 2+ uptake, d((Mg 2+ )i)/dt, was 138 ± 24 nM/s in control MDCT cells. Gentamicin (50 μM) did not affect basal Mg 2+ uptake (105 ± 29 nM/s), but inhibited PTH stimulated Mg 2+ entry, decreasing it from 257 ± 36 nM/s to 108 ± 42 nM/s. This was associated with diminished PTH-stimulated cAMP formation, from 80 ±2 .5 to 23 ±1p mol/mgprotein·5 min. Other aminoglycosides such as tobramycin, streptomycin, and neomycin also inhibited PTH-stimulated Mg 2+ entry and cAMP formation. As these antibiotics are positively charged, the data suggest that aminoglycosides act through an extracellular polyvalent cation-sensing receptor present in distal convoluted tubule cells. We infer from these studies that aminoglycosides inhibit hormone-stimulated Mg 2+ absorption in the distal convoluted tubule that may contribute to the renal magnesium wasting frequently observed with the clinical use of