Publikationsdatenbank

Comparison between measured and calculated ionised concentrations in Mg2+/ATP, Mg2+/EDTA and Ca2+/EGTA buffers; influence of changes in temperature, pH and pipetting errors on the ionised concentrations (2007)

Art

Zeitschriftenartikel / wissenschaftlicher Beitrag

Autoren

McGuigan, J. A. S.

Kay, J. W.

Elder, H. Y.

Lüthi, D.

Quelle

Magnesium research

Bandzählung: 20

Heftzählung: 1

Seiten: 72 – 81

ISSN: 0953-1424

Sprache

Englisch

Kontakt

Institut für Veterinär-Physiologie

Oertzenweg 19 b
14163 Berlin
+49 30 838 62600
physiologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

The apparent dissociation constants (Kapp) and total ligand concentrations ([Ligand]T) from extensive published and unpublished macroelectrode measurements for Mg2+/ATP, Mg2+/EDTA and Ca2+/EGTA buffers have been recalculated. These calculations were made feasible by the introduction of an Excel program which reduced the time of calculation for Kapp and [Ligand]T from over an hour to under five minutes. These estimations of Kapp and [Ligand]T allowed, not only a comparison between measured and calculated ionised magnesium and calcium concentrations ([Mg2+] and [Ca2+]) for Mg2+/ATP, Mg2+/EDTA and Ca2+/EGTA buffers but also a comparison amongst calculated values. Calculated [X2]1 values always differed from measured, and calculated values differed amongst themselves by factors of at least 2. These variations cast doubts on the published absolute values for intracellular [Mg2+] estimated by 31P-NMR and the resting values for [Ca2+] in cells. The allowable range for [X2+] in the buffers and consequently for Kapp and [Ligand]T has not been defined, which introduces uncertainties into published absolute values for [X2+]. This paper shows that an upper limit of +/- 10% deviation from the mean value for [X2+] is attainable. This requires the temperature to be maintained within +/- 0.5 degrees C, pH within +/- 0.01 units and pipetting errors of less than 0.25%. Until internationally defined buffer standards are available, the lack of correlation between measured and calculated [X2+] means that measurement of Kapp and [Ligand]T and hence [X2+] is more reliable than calculation.