Interrelation between renal transport systems of magnesium and calcium

Abstract

Infusion of magnesium chloride markedly increased the excretion of calcium in dogs. A slight but significant increase in the excretion of magnesium occurred following the infusion of calcium chloride. Utilizing the stop-flow technique it was noted that magnesium and calcium achieved minimal concentration ratios in the distal segments of the nephron. Infusion of magnesium chloride during stop-flow studies increased U/P_Ca/U/P_Cr ratios both in the proximal and distal samples. These observations support the postulate that magnesium and calcium compete for a common reabsorptive system in the renal tubules. In several stop-flow experiments Mg²⁸ and Ca⁴⁵ were injected along with inulin 1 or 2 minutes before releasing the ureteral occlusion. Mg²⁸ and Ca⁴⁵ appeared simultaneously in the urine prior to the appearance of inulin, suggesting transtubular flux of these cations. Such observations, while indicating bidirectional movement of these ions across the tubular epithelium, do not imply active or net secretion.