ON THE NONINVASIVE MEASUREMENT OF INTRACELLULAR FREE MAGNESIUM BY P-31 NMR-SPECTROSCOPY

  • 1 January 1983
    • journal article
    • research article
    • Vol. 15  (3) , 265-280
Abstract
A noninvasive measurement of the concentration of free Mg2+ in intact cells and tissues using 31P NMR was introduced. To resolve a controversy in the literature concerning the affinity of Mg2+ for ATP used in this procedure, the apparent Kd of MgATP under simulated intracellular conditions was determined by 3 independent magnetic resonance methods, including a newly developed combination procedure for determining this value at intracellular ATP levels. The new combination method, which utilizes 31P NMR to determine the degree of Mg2+ chelation of ATP and the dye antipyrylazo III for optical determination of free Mg2+, yielded a value of (50 .+-. 10) .mu.M for this apparent Kd at pH 7.2 in the presence of 0.15 M K+ and 25.degree. C. Hydroxyquinolines are not satisfactory indicators for optical determination of the Mg2+-nucleotide Kd. A low value of free Mg2+ (< 1 mM) is established for all of the tissues studied, including perfused heart muscle, contrary to a recent report in the literature. Saturating human erythrocytes with Mg2+ results in an .alpha.- and .beta. phosphorus resonance separation for intracellular ATP that is indistinguishable from that observed in a noncellular MgATP control under similar conditions, showing that MgATP resonances in this cell are unaffected by the cellular environment.

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