Quantification and Localization of Intracellular Free Mg²⁺ in Bovine Chromaffin Cells

Abstract

Magnesium is an essential element for all living systems. The quantification of free intracellular Mg²⁺ concentration ([Mg²⁺]_i) is of utmost importance since changes in its basal value may be an indication of different pathologies due to abnormalities of Mg²⁺ metabolism. In this work we used ³¹P NMR and fluorescence spectroscopy to determine the resting [Mg²⁺]_i in bovine chromaffin cells, a neuron-like cellular model, as well as confocal laser scanning microscopy to study the free Mg²⁺ spatial distribution in these cells. ³¹P NMR spectroscopy did not prove to be effective for the determination of [Mg²⁺]_i in this particular case due to some special morphological and physiological properties of this cell type. A basal [Mg²⁺]_i value of 0.551 ± 0.008 mM was found for these cells using fluorescence spectroscopy and the Mg₂₊-sensitive probe furaptra; this value falls in the concentration range reported in the literature for neurons from different sources. This technique proved to be an accurate and sensitive tool to determine the [Mg²⁺]_i.

lntraceilular free Mg²⁺ seems to be essentially localized in the nucleus and around it, as shown by confocal microscopy with the Mg²⁺-sensitive probe Magnesium Green. It was not possible to derive any conclusion about free Mg²⁺ localization inside the chromaffin granules and/or in the cytoplasm due to the lack of sufficient spatial resolution and to probe compartmentalization.

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