Calibration of Mg(2+)ࢤselective macroelectrodes down to 1 mumol lߝ1 in intracellular and Ca(2+)ࢤcontaining extracellular solutions

Lüthi, Daniel; Spichiger, Ursula E.; Forster, Ian C.; McGuigan, John A. S.

doi:10.1113/expphysiol.1997.sp004039

Cited by 19 publications

(29 citation statements)

References 8 publications

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“…1 for the estimated [Ca 2+ ] for all four buffers because all lie on the same calibration curve. In view of these findings and previous ones [4,13], it can be concluded that the ligand optimization method accurately estimates the [Ca 2+ ] and [Mg 2+ ] in buffer solutions.…”

Section: Ligand Optimization Methodsmentioning

confidence: 71%

“…First, the ligand optimization method [4] is a robust and accurate method to determine both K app and ligand purity. Second, there is no agreement between calculated and measured [Ca 2+ ] in EGTA, BAPTA, HEDTA, and NTA buffers.…”

Section: Discussionmentioning

confidence: 99%

“…In a review of the various methods to measure the ionized concentrations in buffer solutions [3], the ligand optimization method [4] based on Ca 2+ /Mg 2+ macroelectrodes was shown to be the most accurate. Using this method, it was possible to determine both ligand purity and the [Ca 2+ ] and [Mg 2+ ] in Ca 2+ -EGTA [ethylene glycol-bis(b-aminoethylether)-N,N,N|,N|-tetraacetic acid], Mg 2+ -ATP (adenosine-5 0 -triphosphate), and Mg 2+ -EDTA [2,2 0 ,2 00 ,2 000 -(ethane-1,2-diyldinitrilo)tetraacetic acid] buffers.…”

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confidence: 99%

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Calculated and measured [Ca2+] in buffers used to calibrate Ca2+ macroelectrodes

McGuigan

Stumpff

2013

Analytical Biochemistry

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Section: Ligand Optimization Methodsmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Calculated and measured [Ca2+] in buffers used to calibrate Ca2+ macroelectrodes

McGuigan

Stumpff

2013

Analytical Biochemistry

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“…(: p. 361) described six criteria for an ideal method to measure [X 2+ ] in buffer solutions. Of the seven methods investigated (McGuigan et al., : table 4), only two met all six criteria, namely, the LOM (Lüthi, Spichiger, Forster, & McGuigan, ) and setting concentrations by dilution from 2 mmol l −1 to 10 −7 mol l −1 (Allen, Blinks, & Prendergast, ). The LOM is a routine method and is explained in detail in the Supporting Information.…”

Section: Introductionmentioning

confidence: 99%

Ionized concentrations in Ca²⁺ and Mg²⁺ buffers must be measured, not calculated

McGuigan

Kay

Elder

2020

Experimental Physiology

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New Findings What is the topic of this review?The [Ca2+]/[Mg2+] in buffers are usually calculated using one of eight programs. These all give different values, thus [Ca2+]/[Mg2+] must be measured. What advances does it highlight?The ligand optimization method (LOM) using electrodes is an accurate method to do this. The limitations of the method are described. The LOM has been generalized to include calibration of fluorochromes and aequorin. It is the method of choice to measure intracellular equilibrium constants. Owing to the uncertainties for the values of resting [Ca2+], ∆[Ca2+] and the pK′ values for intracellular Ca2+/Mg2+ binding used in modelling, these values must now be re‐examined critically. Abstract Modelling intracellular regulation of Ca2+/Mg2+ is now an established part of physiology. However, the conclusions drawn from such studies depend on accurate knowledge of intracellular [Ca2+], ∆[Ca2+] and the pK′ values for the intracellular binding of Ca2+/Mg2+. Calculation of [Ca2+]/[Mg2+] in buffers is normal. The eight freely available programs all give different values for the [Ca2+]/[Mg2+] in the buffer solutions, varying by up to a factor of 4.3. As a result, concentrations must be measured. There are two methods to do this, both based on the ligand optimization method (LOM): (1) calibration solutions from 0.5 to 4 mmol l−1; and (2) calibration solutions from 0.1 µmol l−1 to 2 mmol l−1. Both methods can be used to calibrate Ca2+/Mg2+ electrodes. Only Method 2 can be used directly to calibrate fluorochromes and aequorin. Software in the statistical program R to calculate the [Ca2+]/[Mg2+] in buffers is provided for both methods. The LOM has now been generalized for use with electrodes, fluorochromes and aequorin, making it the ideal method to determine the pK′ values for intracellular binding of Ca2+/Mg2+. The [Ca2+]/[Mg2+] in buffers must be measured routinely, which is best done by calibrating electrodes with the LOM and software written in R. If [Ca2+]/[Mg2+] in buffers are calculated, the parameters used in modelling show the same degree of variability as the software programs. Uncritical acceptance of such parameters means that conclusions reached from such studies are relative, not absolute, and must now be re‐examined.

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“…Several carriers ETH 5282 [15], ETH 5214 [1a, 20, 22, 32], ETH 5250 [18,28], ETH 7025 [17,21,22,24,29], ETH 3832 [27,33], ETH 5506 [21,33], and the derivative of o-phenanthroline [30], have now been used in potentiometric clinical analysis. The apparent influence of calcium has to be compensated for by numerical techniques for most of the sensors specifically in the extracellular space where the Ca 2þ -exceeds the Mg 2þ -molality by a factor of ca.…”

Section: Introductionmentioning

confidence: 99%

Development of Magnesium-Ion-Selective Microelectrodes Based on a New Neutral Carrier ETHT 5504

Zhang

Fakler

Spichiger³

1998

Electroanalysis

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Two types of magnesium-selective microelectrodes based on a new synthetic neutral carrier ETH T 5504 are presented. One type of microelectrode is applicable to the determination of intracellular free Mg 2þ molality without interference from alkaline or alkaline-earth metal ions versus a typical intracellular ion background of 10 mmol/L NaCl, 100 mmol/L KCl, and 1 mM CaCl 2 . The response function showed a slope of 28.6 Ϯ 0.4 mV (1 SD per decade), and a detection limit at 10 ¹5.1 Ϯ 0.1 mol/L. A magnesium-selective electrode with different composition of the membrane cocktail has been employed for assays of both intracellular and extracellular Mg 2þ -activities, with improved discrimination of Ca 2þ and other physiological cations compared to electrodes based on ETH 1117, ETH 5214 and ETH 7025, respectively. This is the first report where Mg 2þ -selective microelectrodes can be applied to extracellular Mg 2þ -measurements. The microelectrodes based on ETH T 5504 perfectly discriminate the physiological extracellular ion background. Electrodes with tip diameters of typically 1 mm have an average electrical resistance of 3.0 × 10 10 Q, and a response time, t 90 % , of 3 s. The lifetime of the microelectrodes is longer than 1 week and the emf-drift after 1day conditioning period is Յ0.3 mV/ h. An example of measurements of the Mg 2þ -molality in low volumes of specimen is described in this article for blood serum of rats.

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Calibration of Mg(2+)ࢤselective macroelectrodes down to 1 mumol lߝ1 in intracellular and Ca(2+)ࢤcontaining extracellular solutions

Cited by 19 publications

References 8 publications

Calculated and measured [Ca2+] in buffers used to calibrate Ca2+ macroelectrodes

Calculated and measured [Ca2+] in buffers used to calibrate Ca2+ macroelectrodes

Ionized concentrations in Ca²⁺ and Mg²⁺ buffers must be measured, not calculated

Development of Magnesium-Ion-Selective Microelectrodes Based on a New Neutral Carrier ETHT 5504

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Calibration of Mg(2+)ࢤselective macroelectrodes down to 1 mumol lߝ1 in intracellular and Ca(2+)ࢤcontaining extracellular solutions

Cited by 19 publications

References 8 publications

Calculated and measured [Ca2+] in buffers used to calibrate Ca2+ macroelectrodes

Calculated and measured [Ca2+] in buffers used to calibrate Ca2+ macroelectrodes

Ionized concentrations in Ca2+ and Mg2+ buffers must be measured, not calculated

Development of Magnesium-Ion-Selective Microelectrodes Based on a New Neutral Carrier ETHT 5504

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About

Ionized concentrations in Ca²⁺ and Mg²⁺ buffers must be measured, not calculated