Preparation and use of micro- and macroelectrodes for measurement of transmembrane potentials and ion activities.
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Calcium↗
Biomedical subjects
D Ammann
Publications and source records attributed to D Ammann.
Extra- and intracellular hydrogen ion-selective microelectrode based on neutral carriers with extended pH response range in acid media.
A series of new neutral hydrogen ion carriers suitable for application in H+-selective microelectrodes is presented. One carrier (ETH 1907) proves to be superior to tridodecylamine currently very much in use. Microelectrodes based on ETH 1907 in an optimized membrane composition exhibit a linear dynamic response function from pH 2 to 9 extended into the acidic range, a response time less than or equal to 5 s, and a resistance of about 35 G omega for a tip diameter of about 1 micron. This makes the electrode suitable for measurements at normal physiological intracellular pH as well as in acid physiological media. Measurements using this microelectrode in proximal tubule cells of isolated perfused frog kidney are presented.
Animals↗
Valinomycin-based K+ selective microelectrodes with low electrical membrane resistance.
A valinomycin-based membrane phase for microelectrodes with relatively low electrical membrane resistances is described. Microelectrodes with tip diameters of about 1 micron exhibit resistances of about 10(10) omega. Extremely high K+ selectivities are obtained, e.g. a rejection of Na+ by a factor of 5000 and of acetylcholine by a factor of 3400. At a constant background of 140 and 500 mM Na+, the detection limit of the K+ sensor is at 1.6 X 10(-5) and at 2.5 X 10(-5) M K+, respectively.
Electric Conductivity↗
Intracellular neutral carrier-based Ca2+ microelectrode with subnanomolar detection limit.
In intracellular electrolyte solutions a Ca2+-selective microelectrode based on the synthetic electrically neutral carrier N,N,N',N'-tetracyclohexyl-3-oxapentanediamide (ETH 129) shows an improved detection limit when compared with the so far widely used Ca2+ microelectrodes based on the neutral carrier ETH 1001. Detection limits are found at pCa = 9.2 in Ca2+ buffers containing an intracellular background of K+ (125 mM). Selectivity studies in mixed solutions show a preference of Ca2+ over Na+ of 6 X 10(5), over K+ of 1.6 X 10(6), and over Mg2+ of 5 X 10(6). The microelectrode does not suffer from significant interference by inorganic and organic inhibitors and by lipophilic cations and anions. The low detection limit is unchanged at least during the first eight hours of continuous contact with Ca2+ solutions. The EMF drift during the first hour of use is between 5 and 10 mV and is then reduced to about 1 mV/h. The changes in EMF induced between solution of pCa = 7 and pCa = 8 are reproducible within 24.7 +/- 0.4 mV (SD, n = 8, about 3 h). These electrode characteristics were found for single-barrelled microelectrodes of one micrometer diameter front-filled with a PVC-containing membrane phase. In the absence of poly(vinyl chloride) in the membrane phase irregular EMF response curves were obtained throughout. Preliminary punctures of ferret ventricular muscle cells indicate that the Ca2+ electrode response is not disturbed by the contact of a cytosolic milieu.
Animals↗
Design of ionophores for ion-selective microsensors.
Requirements for a reliable use of liquid membrane microelectrodes are discussed in terms of stability, response time, and lifetime on the basis of membrane technological considerations. The selectivity of H+, Li+, Na+, K+, Mg2+, Ca2+, and Cl- microelectrodes is critically evaluated using the Nikolskii-Eisenman formalism. Recent progress in the design of new ionophores is presented. A novel neutral carrier-based Ca2+-selective microelectrode with a detection limit of about 5 X 10(-10) M Ca2+ at a background of 125 mM K+ has been realized. An neutral carrier-based microelectrode for H+ with extended pH range of the sample solution is now available. Promising developments in the field of Li+-, Mg2+-, and Cl--selective ionophores are discussed.
Animals↗
Cell contamination due to the use of carrier-based microelectrodes.
When using microelectrodes for intracellular ion activity studies, some uncertainties such as interference from cytosolic components at the microelectrode, cell damage, and cell contamination may arise. A model, which treats kinetic processes of the loss of carriers from the membrane phase of microelectrodes into the cytosol and cell membrane, is used for an estimation of the extent and time course of contamination by impaled ion-selective microelectrodes. An isolated model cell consisting of a plasma membrane surrounding a cytosolic milieu is assumed. The results of its considerations represent a worst case situation, in which significant contamination of the cell membrane of such a small isolated single cell might occur during time periods of electrophysiological experiments. In more complex situations, such as in intact tissues, the equilibrium membrane concentrations may be substantially less.
Animals↗
Ion selective liquid membrane electrode for the assay of lithium in blood serum.
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Electrodes↗
Ion-selective membrane electrodes for clinical use.
We review ion-selective solvent polymeric membrane electrodes for clinical use. The particular requirements that the clinical application set on the membrane are discussed in terms of selectivity, stability, lifetime, and response time. The performance of currently available electrodes is reviewed, with consideration of actual problems that arise in clinical practice.
Bicarbonates↗
Neutral carrier sodium ion-selective microelectrode for extracellular studies.
A Na+-selective microelectrode based on a synthetic neutral carrier (ETH 157) is described. The selectivities in respect to K+, Ca2+ and Mg2+ are adequate for extracellular measurements of Na+ activities. Microelectrodes with tip diameters of about 0.7 micron have an electrical resistance of 3 X 10(10) omega and a 90% response time of less than or equal to 3 s. The drift of the potential difference of the Na+-microelectrode cell assembly in aqueous extracellular electrolyte solutions is less than or equal to 0.2 m V/3 h.
Animals↗
Ca2+-selective microelectrodes.
Ca2+-selective microelectrodes based on the synthetic neutral carrier ETH 1001 can be used for quantitative intracellular measurements of resting Ca2+-activities and of slowly changing Ca2+-levels (response time in the order of seconds). Microelectrodes with tip diameters greater than 0.3 micron show selectivities that yield a detection limit between 10(-8) and 10(-7) M Ca2+ in an intracellular background. The Ca2+-activity is obtained together with electrical parameters of the cell (e.g. cell membrane potential and membrane resistance or conductivity). Simultaneous monitoring of other ion-activities is accessible (double- or multi-barrelled microelectrodes). The Ca2+-determination is extremely local, i.e. it probably does not indicate an averaged cytosolic activity in every situation (e.g. localized transients).
Calcium↗
Review: ion-selective electrodes in clinical chemistry.
The theoretic framework of electrode systems and numerical data for use in serum analysis is given. Original literature and recent applications to serum analysis are compiled for different types of sensors. The interactions of various effects and their relevance in the context of the precision that newer instrumentation offers are discussed. Specifically, the following topics are treated: response to interfering ions (Nicolsky Eq.), concentration to activity conversion (Debye-Hückel formalism), and liquid-junction potentials (Henderson Eq.); Debye-Hückel parameters, selectivity factors, and physiologic activity ranges; solid-state, liquid-membrane, and special electrodes; flow-through systems, precision, and stability.
Blood Chemical Analysis↗