Measurement of free magnesium in perfused and ischemic arrested heart muscle. A quantitative phosphorus-31 nuclear magnetic resonance and multiequilibria analysis.

The concentration of intracellular free Mg2+ in perfused, beating guinea pig hearts has been estimated on the basis of the Mg2+-dependent separation between the alpha- and beta-phosphorus resonances from 31P NMR spectra of intracellular ATP combined with a computer-assisted analysis of the multiequilibria involved. Measurements and calculations are also used to determine the magnitude of any change in free Mg2+ concentration which may occur during the severe acidosis associated with ischemic arrest. We find the concentration of free Mg2+ to be 2.5 +/- 0.7 mM in control hearts. No significant change was observed during ischemic arrest. These results are discussed in relation to other similar measurements in the literature with detailed consideration given to the value of the MgATP stability constant.