The influence of zinc, magnesium, and iron on calcium uptake in brush border membrane vesicles.

The effects of adding increasing concentrations of magnesium (Mg), zinc (Zn), and iron (Fe) on calcium (Ca) uptake into rat brush border membrane vesicles was measured. At ratios of 1:1, based on the RDA, none of these minerals were found to significantly decrease calcium uptake. Mg, however, inhibited Ca uptake at an RDA ratio of 3:1 (Mg:Ca). At higher RDA ratios (Zn:Ca 10:1), Zn also decreased Ca uptake. In a comparison of the molar ratios of the above cations, Zn inhibited Ca uptake the most (0.12:1), possibly by competing directly at high-affinity Ca binding sites. Fe did not decrease Ca uptake but rather demonstrated an enhancing effect at high concentrations (20:1). When mixtures of the above divalent cations were studied, the effects on Ca uptake could largely be explained by the actions of the ions individually.