title: 31P nuclear magnetic resonance and zero-point titration compared for measuring free magnesium concentration in erythrocytes.
abstract: 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.
authors.affiliation: Department of Pediatrics, University Hospital Nijmegen, University of Nijmegen, The Netherlands.
authors.forename: W B
authors.initials: WB
authors.lastname: Geven
authors.forename: G M
authors.initials: GM
authors.lastname: Vogels-Mentink
authors.forename: J L
authors.initials: JL
authors.lastname: Willems
authors.forename: C H
authors.initials: CH
authors.lastname: von Os
authors.forename: C W
authors.initials: CW
authors.lastname: Hilbers
authors.forename: J J
authors.initials: JJ
authors.lastname: Joordens
authors.forename: G
authors.initials: G
authors.lastname: Rijksen
authors.forename: L A
authors.initials: LA
authors.lastname: Monnens
mesh_terms: D000255:Adenosine Triphosphate / Q000097:blood; D004912:Erythrocytes / Q000737:chemistry*; D006801:Humans; D008274:Magnesium / Q000097:blood*; D009682:Magnetic Resonance Spectroscopy; D014462:Ultrafiltration
chemical_list: D000255:Adenosine Triphosphate; D008274:Magnesium