Determination of ionized magnesium in platelets and correlation with selected variables

We describe a method for determining the intracellular ionized magnesium concentration (Mg2+]i) in platelets by using the fluorescent probe FURAPTRA. We determined the dissociation constant (KD) of FURAPTRA for Mg2+ (2.26 +/- 0.29 mmol/L), within-day assay variability (CV = 6.8%), among-day intraindividual variability (CV = 11.0%), variability after a 4-h delay in processing the blood specimen (t = 1.2, P >0.2; F = 6.2, P <0.02), and the reference interval (0.23-0.59 mmol/L) for this assay. We also evaluated the correlation between platelet Mg2+]i and concentrations of selected serum electrolytes, proteins, and total cholesterol; age; body mass index; and gender. Only the inverse correlation between platelet Mg2+]i and serum total cholesterol concentration in men was significant (r=-0.66, P <0.005).