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Results for “Microelectrodes”

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At least 235 records · Page 13Linked to original sources

PubMed1980

A triple-barreled microelectrode for simultaneous measurements of intracellular Na+ and K+ activities and membrane potential in biological cells.

A triple-barreled Na+, K+-selective microelectrode was constructed with liquid ion exchangers for Na+ (monensin) and K+ (Corning #477317) to measure the intracellular Na+ and K+ activities ((Na)i and (K)i) of a single cell and its membrane potential (EM), simultaneously. The tip of the triple-barreled assembly was made less than 0.6 micron in outside diameter. Prior to in vivo measurements, some physiochemical properties of microelectrodes were examined in vitro for the slope constant, selectivity coefficient, electrical resistance, and pH effect, as well as measurements of the activity coefficient on ions in blood serum and Ringer solution. Carrying out direct micropunctures on single cells of the sartorius muscle and renal proximal tubule of bullfrogs in vivo, we obtained the following results: (1) In sartorius muscle, the average (Na)i was 14.8 mEq/liter, the (K)i 64.5 mEq/liter, and the EM -86.2 mV. (2) In proximal tubule cells, the average (Na)i, (K)i and EM were 16.8, 63.0 mEq/liter and -65.9 mV, respectively. (3) There were significant correlations in the proximal tubule between (K)i and EM, and inversely between (Na)i and EM, and between (Na)i and (K)i. These facts may somehow be related to both the activity of Na+-K+ exchange pump and the osmotic equilibrium of water across the membrane. Further, several problems inherent in the multibarreled microelectrode were discussed from the practical point of view.

Animals↗

PubMed1979

The measurement of intracellular sodium activities in the bullfrog by means of double-barreled sodium liquid ion-exchanger microelectrodes.

A double-barreled Na+-selective microelectrode was constructed with monensin as a liquid ion exchanger. The HCl-treated monensin was dissolved in a solvent (Corning 477317) at 10% (weight/weight). Internal reference solution of its ionic barrel was mixture of 0.49 M NaCl and 0.01 M KCl, the pH being adjusted to 3 with 0.1 M citrate-HCl buffer, whereas that of the PD barrel was 0.5 M KCl. Average slope and selectivity ratio (Na+/K+) tested on 10 different microelectrodes were -57.5 +/- 1.87 mV/P(Na) (SEM) and 6.7 +/- 0.44, respectively. The electrical resistance was an order of 10(10) ohm and the response time was less than 10 sec. Using this microelectrode, a free flow micropuncture experiment was carried out in the bullfrog kidney and the intracellular Na+ activity as well as the membrane PD was determined on the proximal tubular cell. Average value (+/- SEM, n = 15) for the intracellular Na+ and K+ was 20.7 +/- 1.56 mEq/L and 61.2 +/- 1.16 mEq/L, respectively, and -68.7 +/- 0.88 mV for the peritubular membrane PD. There was a significant negative correlation between Na+ and K+ activities within the cell, i.e., the lower the ionic activity of cellular Na+ was, the higher the cellular K+, and vice versa, the sum of these two being kept nearly constant. The above finding may be somehow related to the isosmosis in the reabsorptive process across the proximal tubular epithelium.

Animals↗

PubMed1992

Comparison of two approaches to measurement of electrical impedance of glass microelectrodes designed for evaluation of temperature changes in biological tissues.

We proposed a temperature sensitive microelectrode for rapid measurements of temperature at the cellular level. In principle, the electrical impedance of the tip of the microelectrode changes with temperature. We designed an impulse measurement system (STEP) sensitive to the above changes of impedance. The system is based on a presettable negative input impedance of the current to a voltage converter. We compared the efficiency of the new STEP with the currently used RAMP system. We found following advantages of the STEP system: i) the danger of high voltage oscillations which could mechanically destroy the microelectrode tip is eliminated; ii) this system provides the opportunity to set the maximum sensitivity of the system according to the measured temperature interval. Moreover, the STEP method makes it possible to measure the resistance by using a sinusoidal stimulation signal which has to be preliminarily compensated by a rectangular signal. The shortest sampling period of the new system represents 0.1 ms with a resolution higher than 0.1 K and sensitivity better than 30 mV/K.

Animals↗

PubMed1991

[Successive detection of cortex oxygen partial pressure with oxygen microelectrodes in cats].

Brain tissue PO2 (PtO2) was successively measured with the new polarographic oxygen microelectrodes in the parietal cortex of ketamine anesthetized cats. This type of oxygen microelectrodes was made from pure platinum wire 0.5 microns in diameter pulled in glass with tip diameter of less than 1.0 micron. Results showed that PtO2 in the superficial gray matter (0-1,000 microns) was markedly higher than that in the white matter (1,001-3,000, 3,001-5,000 microns) in 10 cats. No significant change was observed during successive detecting of PtO2 within 3.0 hours in the cats. It was suggested that we can directly understand the oxygen supply and metabolism of living brain tissue by using the new oxygen microelectrodes.

Animals↗

PubMed2006

[Study on denitrification characteristics of dynamic membrane based on nitrate liquid-membrane microelectrodes].

Nitrate microelectrodes and ORP microelectrodes were fabricated to study the denitrification characteristics of dynamic membrane at different COD loadings. The denitrification process was found at 0.6-1 mm depth beneath the interface of biofilm/bulk. The results of ORP microelectrode also demonstrated that the ORP value in the range of denitrification area was between 88.6 approximately -128.4 mV which was appropriate to denitrification. When the COD loading was 0.45 kg/(m3 x d), the denitrification rate (NO3- -N) was the maximum of 0.6347 x 10(-6 mol/(L x s). With the increase of COD loading, the denitrification area was increasing and two layers with different denitrification rates emerged in the dynamic membrane. The phenomenon implied the effect of organic concentration, oxygen concentration and bacterial competition on the denitrification rate.

Bacteria↗

PubMed1991

[A system for intracellular pH recording in cultured cell with ion-selective microelectrode].

An IBM PC/XT compatible microcomputer based system for recording intracellular pH with ion-selective microelectrodes is described. The method for making ion-selective microelectrodes, the designing ideas of the ion-selective microelectrode amplifier and method for improving the accuracy of measurement are addressed. The performance of the system meets the requirements of experiments. Accuracy of measurement, advantages and disadvantages of the system are discussed.

Cells, Cultured↗

PubMedDate not supplied

Oxygen sensitivity of a multichannel antimony microelectrode for tissue surface oxygen pressure measurements.

The measuring properties of antimony electrodes were improved by the introduction of highly purified crystallographically oriented monocrystalline antimony (COMA). COMA electrodes are sensitive to pH and pO2. For measurements of either pH, pO2, or both, the pH and the pO2 sensitivities must be known and the components of the composite electrode signal must be separable. The oxygen sensitivity of COMA electrodes in vivo have been shown to be higher than in vitro in the pO2 range below 10 kPa. The present study was performed in an animal model to investigate the oxygen sensitivity and to further evaluate the tissue pO2 measuring properties of a miniaturized six channel COMA microelectrode. The results show that the COMA microelectrode has negligible drift, a response time of less than 5 s and high sensitivity and reproducibility for tissue pO2 measurements when the pH part of the electrode signal is eliminated. The oxygen sensitivity found (8.5 +/- 0.4 (mV/pO2) (mean +/- SEM)), is described by a direct linear function in the oxygen tension range studied. It is concluded that tissue pO2 can be calculated after elimination of the pH part of the electrode signal. A multichannel COMA microelectrode possess characteristics suitable for in vivo oxygen measurements and is therefore an interesting complement to traditional tissue oxygen sensors.

Animals↗

PubMed1989

[Manufacturing of K+-potassium microelectrodes for electroretinographic studies].

A method for fabrication of K+-selective microelectrodes for the purposes of elecroretinogram investigations is described. Both one- and two-barrel types of microelectrodes are obtained. The microelectrodes fabricated possess high sensitivity and stability. The values of potassium in corpus vitreous of the frog Rana ridibunda are presented.

Animals↗

PubMed1988

Measurement of cytosolic calcium: ion selective microelectrodes.

Since the Ca2+-selective neutral carrier was introduced in 1972, Ca2+-selective microelectrodes have been made and used for measurement of Ca2+ activity (effective Ca2+ concentration) in the cytoplasm. Over the last several years, application of the technique has provided valuable information about resting levels and changes of cytosolic Ca2+ activity. This article reviews technical aspects of the electrodes, including their construction, calibration, and determination of cytosolic Ca2+ activity. The Ca2+-selective microelectrodes successfully prepared show the voltage responses of about 20 mV between 10(-6) and 10(-7) M Ca2+, and about 10 mV between 10(-7) and 10(-8) M Ca2+ so that they could be used to monitor changes in cytosolic free Ca2+. However, the techniques of the electrodes are still difficult as compared with those of other ion-selective microelectrodes. Some advantages and disadvantages of the techniques are discussed.

Animals↗

PubMed1987

Chloride measurement by microelectrode in cystic fibrosis and normal sweat.

The Lazar Ultra-M chloride-specific microelectrode was evaluated in a series of experiments designed to assess its suitability for the routine determination of human sweat chloride concentrations. NaCl solutions were used to construct a standard curve, and same-day variations in experimental results were less than 1%, while day-to-day variation was also less than 1%. Human sweat collected following pilocarpine iontophoresis was used to compare the chloride concentration measured titrimetrically by a hospital laboratory or by liquid chromatography with the value measured by the microelectrode. There was excellent correlation between each of the methods (r = 0.97). No false positive results were reported in 55 patients whose sweat chloride concentrations ranged from 7 to 43 mmol/l and no false negative values were reported from 6 patients with elevated sweat chloride concentrations (60-124 mmol/l). These results indicate that this new chloride microelectrode offers a simple and reliable method for sweat chloride measurement.

Chlorides↗

PubMed1979

[Semiautomatic regulator for the preparation of microelectrodes for electrophysiology].

This paper describes an electronic device for making metallic microelectrodes to be used for electrophysiological experiments. These microelectrodes are endowed with a small tissue-electrode capacity and a high mechanical strength. The same microelectrodes are applicable for derivation of spikes as in the case of microstimulation of nervous structures during repeated penetrations.

Electrophysiology↗

PubMed1984

[Intracellular activity of Cl- measured with microelectrodes selective for Cl- in superficial epithelial cells of gastric mucosa at "rest"].

Intracellular chloride activity and the electrical membrane potential differences were determined in surface epithelial cells of frog fundic gastric mucosa in resting conditions. Separate measurements were carried out by applying single barreled, (KCl filled), conventional and liquid Cl- -selective microelectrodes. Membrane potentials with respect to the serosal (psi cs) and mucosal surfaces (psi cm) recorded with conventional microelectrodes, were -67 +/- E.S. 1.7 mV and -39.9 mV (as calculated from psi cs and psi T) respectively. The average electrical potential measured with Cl- -selective microelectrodes with respect to the serosal bath (psi Cl-cs) was -30.5 +/- E.S. 1.9 mV which yields an intracellular Cl- activity of 14 mmol/l, a value that is 2.8 times that predicted for an equilibrium distribution across the serosal membrane. On the contrary, Cl- seems to be distributed at equilibrium across the mucosal membrane. These results indicate that Cl- is accumulated across the serosal membrane into gastric cells in an energy requiring step.

Animals↗

PubMed1976

Oxygen microelectrode response to oxygen pressures up to 15 ATA.

Polarographic measurements of oxygen at high pressures were made at 21-22 degrees C with open-type Wood's metal microelectrodes with tip diameter about 5 mu. Although the sensitivity of the individual electrodes ranged from 3.1 x 10(-10) to 8.8 x 10(-12) amps/mm Hg of O2, the oxygen current was always a straight line function of Po2 from 21% O2 at ambient pressure (Po2 = 160 mm Hg) to 100% O2 at 200 psig (Po2 = 11,102 mm Hg). Compression to 200 psig with 100% nitrogen produced no significant change in microelectrode current, showing that the microelectrodes are insensitive to pressure alone.

Microelectrodes↗

PubMed1975

Voltage clamping with a single microelectrode.

A technique is described which allows neurons to be voltage clamped with a single microelectrode, and the advantages of this circuit with respect to conventional bridge techniques are discussed. In this circuit, the single microelectrode is rapidly switched from a current passing to a recording mode. The circuitry consists of: (1) an electronic switch; (2) a high impedance, ultralow input capacity amplifier; (3) a sample-and-hold module; (4) conventional voltage clamping circuitry. The closed electronic switch allows current to flow through the electrode. The switch then opens, and the electrode is in a recording mode. The low input capacity of the preamplifier allows the artifact from the current pulse to rapidly abate, after which time the circuit samples the membrane potential. This cycle is repeated at rates up to 10 kHz. The voltage clamping amplifier senses the output of the sample-and-hold module and adjusts the current pulse amplitude to maintain the desired membrane potential. The system was evaluated in Aplysia neurons by inserting two microelectrodes into a cell. One electrode was used to clamp the cell and the other to independently monitor membrane potential at a remote location in the soma.

Animals↗

PubMed1982

In situ voltammetric microelectrodes: application to the measurement of median eminence catecholamine release during simulated suckling.

Catechol-sensitive microelectrodes (10-30 microns) were developed and then used to study the dynamic regulatory role of the prolactin inhibiting factor, dopamine, under conditions of simulated suckling. Current flow resulting from the electrochemical oxidation of catecholamines at the microelectrode surface was linearly related to the concentration of catecholamines present in solution over the range of 5-100 microM. Endogenous catecholamine levels in the rat median eminence were readily detectable and the electrochemical signal corresponding to dopamine release responded in an appropriate manner to various pharmacologic manipulations. We then implanted carbon microelectrodes into the medial median eminence region among capillaries of the primary portal plexus of urethane anesthetized lactating rats. Catecholamine release into the extracellular fluid was electrochemically measured once each minute before, during and after electrical stimulation (15 Hz, 5-30 V, 15 min) of a surgically isolated mammary nerve trunk. This simulated suckling paradigm reliably evoked prolactin secretory episodes qualitatively similar to those observed during suckling of the nipples by the young. During the period of nerve stimulation, a transient (3-5 min) 65% decline in electrochemically detectable catecholamine release was observed. Following cessation of nerve stimulation an oscillatory pattern of catecholamine release was observed with an overall trend toward an increased level of release. This latter observation corresponds with previous reports of increased hypothalamic dopamine turnover during or following suckling and with the increased levels of dopamine measured in hypophysial portal blood following mammary nerve stimulation. The transient nature of the decline of catecholamine release during the nerve stimulation period may explain why a similar observation has not been forth-coming from experiments utilizing the stalk blood collection technique (unless the standard collection periods are considerably shortened). These observations lead us to reject the hypothesis of a mirror image relationship between stalk blood dopamine and peripheral prolactin levels. Instead, we suggest that a transient decline in dopamine secretion coincident with the onset of suckling acts to prepare the pituitary lactotrophs to respond to a prolactin releasing factor which then facilitates prolactin secretion.

Animals↗

PubMed2005

Acoustically fabricated random microelectrode assemblies.

We report the insonation of bismuth, silver, copper and tungsten metal particles suspended in octane in the vicinity of a glassy carbon electrode. AFM and voltammetry reveal that metal particles are immobilised onto the electrode substrate. In the case of bismuth, silver and copper, the possible melting of the metal particles due to the high sonochemical conditions cannot unambiguously be ruled out. However, it is likely that the immobilisation of the metal particles occurs predominantly through mechanical attachment due to the high rates of mass transport, evidenced from the fact that tungsten can be immobilised at a glassy carbon surface which has a melting point (mp 3410 degrees C) outside the likely sonochemical conditions. The immobilised particles are found to be in electrical contact with the glassy carbon electrodes which can then act as random assemblies of microelectrodes. Proof-of-concept for use in electro-analysis is examined for the possible detection of arsenic and cadmium at a silver and bismuth random microelectrode assemblies, respectively. This approach suggests a simple generic methodology for the construction of microelectrode assemblies via abrasive attachment induced by insonation with power ultrasound.

Journal Article↗

PubMed2001

Individually addressable gel-integrated voltammetric microelectrode array for high-resolution measurement of concentration profiles at interfaces.

The application of a novel voltammetric probe, based on an individually addressable gel-integrated microelectrode array (IA-GIME), for real-time, high-spatial resolution concentration profile measurements at interfaces is described. Reliability and validity of steep metal concentration gradients obtained with this novel system have been demonstrated by performing systematic tests at well-controlled liquid-liquid and liquid-solid interfaces. The liquid-liquid interface was formed by two layers of aqueous solutions with different components; only one layer contained trace metal ions (Pb(II) and Cd(II)); the individually addressable microelectrode array was placed at the interface of the liquid-liquid system; the concentration profiles were recorded as function of time; and the effective diffusion coefficients were calculated. The liquid-"solid" interface was formed from an aqueous solution layer overlying a bed of silica particles saturated with an aqueous solution. The sensor array has been used to monitor the diffusion processes of Tl(I) or Pb(II) from the liquid phase to the "solid" phase. The influences of porosity, geometry of the porous media, and complexation between metal ion and silica, on the diffusion processes, have been studied. All these results show that correct diffusion profiles of metal ions at interfaces can be obtained with 200-microm resolution with the IA-GIME. They also demonstrate that, for measurements in "solid" phase, the aforementioned factors must be considered carefully for correct calibration of any electrodes and the gel-integrated microelectrodes are unique tools to enable calibration of the sensors with synthetic solutions.

Journal Article↗

PubMed2002

Detection of hydrogen peroxide at mesoporous platinum microelectrodes.

Mesoporous (H(I)-ePt) platinum microelectrodes electrodeposited from the hexagonal (H(I)) lyotropic liquid crystalline phase are shown to be excellent amperometric sensors for the detection of hydrogen peroxide over a wide range of concentrations. Good reproducibility, high precision, and accuracy of measurements are demonstrated. Mesoporous microelectrodes retain the high rates of mass transport typical of conventional microelectrodes, and their high real surface area greatly enhances their catalytic activity. This unique combination of properties overcomes the limitations of previous amperometric hydrogen peroxide sensors and yields outstanding qualitative and quantitative results.

Journal Article↗