31P nuclear magnetic resonance and zero-point titration compared for measuring free magnesium concentration in erythrocytes.
Intracellular ionized magnesium concentrations ([Mg2+]i) were measured in erythrocytes by 31P nuclear magnetic resonance (NMR) and zero-point titration in 14 controls and seven patients with renal magnesium loss. The mean intracellular ionized magnesium concentration in controls measured by 31P NMR was 0.20 (SD 0.03) mmol/L cell water, compared with 0.55 (SD 0.12) mmol/L cell water by zero-point titration. Total erythrocyte magnesium content measured with the lysate method was 0.63 mmol/L cell water higher than estimated by 31P NMR, probably because not all magnesium complexes are fully visible to the NMR technique. We found a positive correlation between plasma ultrafiltrable magnesium and [Mg2+]i irrespective of the [Mg2+]i assay used. [Mg2+]i measured with 31P NMR correlated modestly but significantly with [Mg2+]i determined by zero-point titration (r = 0.58, P less than 0.02). Washing erythrocytes before the zero-point titration decreased the ATP content and the cell water fraction, which led to overestimation of [Mg2+]i by zero-point titration. Although absolute values for [Mg2+]i differ with the assay used, both methods determined significantly lower values for [Mg2+]i in patients with isolated renal magnesium loss.
Geven
W B
WB
Department of Pediatrics, University Hospital Nijmegen, University of Nijmegen, The Netherlands.
Vogels-Mentink
G M
GM
Willems
J L
JL
von Os
C H
CH
Hilbers
C W
CW
Joordens
J J
JJ
Rijksen
G
G
Monnens
L A
LA
D000255:Adenosine Triphosphate / Q000097:blood; D004912:Erythrocytes / Q000737:chemistry*; D006801:Humans; D008274:Magnesium / Q000097:blood*; D009682:Magnetic Resonance Spectroscopy; D014462:Ultrafiltration
D000255:Adenosine Triphosphate; D008274:Magnesium