Red blood cell magnesium concentrations: analytical problems and significance.

In order to assess total magnesium concentrations in human red blood cells (erythrocytes--ErMg), atomic absorption spectrometry (AAS) provides high accuracy and precise method rapid and amenable to automation. Taking care of eliminating the chronic marginal magnesium deficits, normal values of ErMg evaluated through a direct method and expressed as mmol/litre of packed cells are 2.3 +/- 0.24. Inductively coupled plasma-mass spectromettry (ICP-MS) is a multielemental analytical technique. Particle induced x-ray emission (PIXE) also provides multielemental capability, but is time-consuming and costly. Microelectrodes are the gold standard for intracellular Mg2+ measurements. But microelectrodes and fluorescence probes measure the activity of magnesium ions, not the concentrations. Ionized magnesium content of human intact erythrocyte is mainly assessed with the NMR method and with the zero point titration. The concentration of ionized magnesium as estimated by NMR (31P NMR method) was found to be 0.20 +/- 0.02 mmol/litre cell water and with the zero point titration 0.55 +/- 0.12. The uncertainty concerning the two current used techniques for free magnesium determination is worsened by the fact that magnesium inside red cells continually oscillates in vivo. Free magnesium constitutes a small part of total magnesium. Further studies are necessary to assess the importance of its variations in clinical medicine. Efflux of ErMg is controlled through membranous sodium-dependent and sodium-independent pathways and through genetic and neurohormonal regulations. Variations in the total or ionized ErMg do not necessarily mean that similar changes should exist in the magnesium pool. But it remains the basic static cellular magnesium item. Its value will be subsequently enhanced when it takes place among the clinical and paraclinical data of dynamic magnesium investigations.