PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Microelectrodes”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed1985

Direct measurement of pH in the rat lens by ion-sensitive microelectrodes.

The resting pH of the rat lens was determined using H+-sensitive liquid membrane microelectrodes and found to be 6.89 when measured in a perifusing solution of pH 7.20. The pH of the rat vitreous humour was also measured and was found to be 7.25. Attempts were made to perturb the lens pH by varying the pH of the perifusate. In the presence of alkaline solutions, the lens was able to maintain its resting pH and membrane potential but, upon perfusion with a more acidic solution, the lenticular pH equilibrated with the pH of the bathing solution and the potential depolarized. The internal pH could be manipulated independently of the external pH by perfusing the lens with Ringer solution containing 20 mM ammonium chloride. The ammonium chloride induced a rapid alkalinization and the return to control solution caused a fall in pH to below the normal resting level. The biphasic pH response to ammonium chloride was accompanied by changes in lens transparency and membrane potential.

Ammonium Chloride↗
PubMed1987

Schistosoma mansoni: measurement of Na+ ion activity in the tegument and the extracellular spaces using ion-selective microelectrodes.

Ion-selective microelectrodes were used to measure sodium ion activity (aNa) in the tegument and interstitial spaces in adult male Schistosoma mansoni. In RPMI 1640, aNa averaged 31 +/- 13 mM in the tegument, a value significantly less than that in the bathing medium. In the interstitial spaces, it averaged 72 +/- 17 mM, a value nearly the same as that in the bathing medium. In hypo- or hyperosmotic media, aNa in the interstitial spaces varied by a value commensurate with change in aNa in the medium, but aNa in the tegument was changed by only a small amount. Monensin (10 microM), low temperature (20 C), and ouabain (0.3 to 10 microM) all caused significant increases in aNa in the tegument. Hypo- and hyperosmotic media produced initial weight changes followed by gradual recovery back toward original weights. It is concluded that the schistosome is a volume regulating osmoconformer with osmolality of the extracellular fluid approximating that of the bathing medium, but that within the tegument of the parasite, Na+ concentration is controlled by active transport processes.

Animals↗
PubMed1986

Microelectrode studies of D-glucose- and K+-induced changes in membrane potential of electrofused insulin-producing cells.

In the present study electrical field-induced fusion has been applied to both normal pancreatic islet cells isolated from obese hyperglycemic mice and clonal insulin-producing cells (RINm5F) derived from a transplantable rat insulinoma. The fused cells were then punctured with microelectrodes to measure changes in membrane potential after exposure to stimulatory concentrations of D-glucose or K+. Fused cells of normal islet cellular origin revealed a resting membrane potential of -60 mV and were depolarized by 24 or 27 mV after exposure to 11 mM D-glucose or 30 mM K+. Although D-glucose induced depolarization, it was not possible to establish the existence of an oscillating burst pattern superimposed by action potentials. The resting membrane potential of the fused RINm5F cells was also -60 mV and decreased to -30 mV after exposure to 30 mM K+. As judged from the membrane potential measurements, the reconstitution of the plasma membrane subsequent to electrical breakdown is essentially the same whether the giant cells originated from normal islet cells or RINm5F cells.

Animals↗
PubMed1984

A simple device to aid impalement of cells using conventional microelectrode drives.

Consistent penetration of cell membranes by micropipettes is facilitated by using electrode accelerators or high velocity step drives. Notwithstanding, much intracellular work is still done with conventional mechanical or hydraulic drives; cell membrane penetration is achieved by means of gentle taps on any convenient part of the set up. A remote control device is described which performs this function and is compact enough to be fixed on either the microelectrode holder or the preparation mounting. It consists of a small magnetized rod freely suspended in a pot-core coil. A current pulse through the coil jolts the rod; the inertial reaction of the coil frame provides the sudden movement required by the micropipette tip to overcome the elastic resistance of the cell membrane.

Animals↗
PubMed1975

A single-unit carbon dioxide-oxygen sensing microelectrode system.

A membrane-covered CO2 microelectrode system is described; it consists of a platinum electrode surronded by a ring-shaped Ag-AgCl electrode, both in contact with an electrolyte layer composed 10 minus 3 M/l quinhydrone in 0.1 N KCl. The resulting oxidation-reduction potential is shown to vary linearly with the logarithm of the PCO2 of the medium. Response time for 95% deflection to a step change in PCO2 of 65 mm Hg is about 1 min i.e. considerably less than in the macroelectrode described previously, but stability is decreased at the same time. Since oxygen in concentrations up to about 21% (air) did not influence the CO2 response and the presence of both CO2 (10.33%) and quinhydrone (10 minus 3 M/l) did not alter the oxygen polarogran, this electorde may be used independently as an oxygen electrode as well. Stability and response time for oxygen were similar to those of the Clark electrode. Possibilities and limitations for in vivo estimation of PCO2 and PO2 are discussed.

Carbon Dioxide↗
PubMed1975

The CO2 conductivity electrode, a fast-responding CO2 microelectrode.

A fast-responding CO2 microelectrode system is presented; it consists of a double-lumen polyethylene catheter provided with a stainless steel catheter tip covered by a CO2-permeable membrane, and connected with each lumen separately to a conductivity cell. The catheter is flushed with bidistilled water at constant flow rate and conductivity of inflowing and outflowing water is measured. The change of conductivity in the water leaving the catheter after exposure of the electrode to a medium containing CO2 is related to the PCO2 of the medium. High sensitivity and fast response, both depending on the flow rate of the carrier water, are shown to oppose each other. When cells are placed at a distance of 45 cm from the membrane, response time for 90% deflection is about 10 sec (at flow rates of 5 ml/min), but when located inside the electrode tip at a distance of within 10 mm from the membrane response time is reduced to about 4 sec. Hydrodynamical aspects concerning dispersion of CO2 in the carrier water and reaction kinetics of CO2 hydration are discussed.

Carbon Dioxide↗
PubMed1993

Use of endoscopic biopsies and microelectrodes to study human gastric acid secretion in vitro.

We have investigated the possibility of measuring acid secretion from human gastric mucosa in vitro as a potential pharmacological preparation. We used open-ended 10 microns-tip, lix-based glass microelectrodes to measure the pH of the mucus layer of gastric biopsies superfused with a HEPES buffered solution in an organ bath. With no drugs added the pH of the mucus layer of biopsies from the body of the stomach stayed constant but the pH of antral biopsies fell slightly by a median of 0.12 pH units over 80 min (P < 0.05). Stimulation of the biopsies with 1-100 microM histamine produced a dose-dependent decrease in pH which was significantly greater in biopsies from the gastric body than from the antrum. 500 pM pentagastrin produced a median fall in pH of 1.20 (P < 0.01) which was prevented by the prior addition of 100 microM omeprazole or 10 microM ranitidine. Omeprazole or ranitidine alone produced slight rises in the median pH of 0.47 (P < 0.05) and 0.26 (P < 0.05) units respectively. Those biopsies which were infected with Helicobacter pylori had a slightly elevated initial pH of about 0.2 of a pH unit (P < 0.05). This novel system provides a means to study human gastric acid secretion in vitro and may be valuable in the testing of new drugs on the stomach.

Adolescent↗
PubMed1979

A new moving-coil microelectrode puller.

This paper describes an improved electrode puller for the manufacture of glass microelectrodes or micropipettes. The instrument resembles a conventional horizontal two-stage, solenoid-powered electrode puller but the pull is now developed by a light moving-coil and a fixed permanent magnet, using the principle of the moving-coil loudspeaker. In a conventional puller the force is generated by a solenoid with a massive moving-iron core. In this new puller the moving-coil solenoid responds much more rapidly to changing currents because of its greatly reduced inductance, and a substantial reduction in mass to 25 g, gives more acceleration from a comparable force. The sudden discharge of a capacitor bank through the coil accelerates the glass quickly during the last stage of the pull. This rapid acceleration is of importance in the formation of good electrodes with fine tips. For the prototype, an electronic control unit was constructed which allows the parameters necessary for the manufacture of electrodes to be set and regulated accurately and repeatedly, so that series of electrodes of constant shapes can be made. The length of the electrode shank may be predetermined over a wide range and tip diameters down to 0.08 micron have already been measured. The angle of the taper that supports the tip may be varied from less than 1 to over 6 degrees. The mechanical design of the instrument is comparatively simple, as it has only one moving part, while the relative complexity of the electronic control section should not present any manufacturing difficulties. Although this puller has been used mainly to make single-barrel fine electrodes from borosilicate glass, it is adaptable for other purposes. The extent of the control over the shape of the shank of the electrode renders it particularly suitable for the manufacture of composite, ion-sensitive electrodes.

Animals↗
PubMed1981

Quantitative ionophoresis of catecholamines using multibarrel carbon fibre microelectrodes.

Carbon fibre microelectrodes can be used to measure the local concentration of ionophoretically ejected catecholamines in vitro or in vivo. The method can also be used to measure the transport number for the materials. The concentration measurement takes about 20 ms and can be repeated at up to about 10 Hz without electrode poisoning or deterioration. This paper describes in detail the methodology of the technique and the apparatus required.

Animals↗
PubMed1981

Two types of bipolar microelectrodes for intraretinal use.

This paper describes in some detail the construction of two types of bipolar microelectrodes that were used in intraretinal recordings from the intact rhesus monkey eye. The first type consists of a glass micropipette with a partly insulated silver paint coating, yielding a recording site located 120 micrometers from the tip of the glass pipette. The second type consists of two coaxial glass micropipettes with a tip distance of 50 micrometers and tip diameter of 10 and 1 micrometer, respectively. The coaxial glass electrode has a better electrical stability than the silver paint electrode and is mechanically stronger. An example of a recording is shown.

Animals↗
PubMed1982

A method for manufacturing long-shanked glass microelectrodes.

A method for manufacturing electrolyte-filled glass microelectrodes with long, non-tapering shanks is described. For this purpose a specially-designed device is used in conjunction with a standard vertical electrode puller. This device acts as a speed controller which maintains a constant speed while pulling the long electrode shank. During the final shaping of the electrode tip the action of the speed controller is bypassed.

Amygdala↗
PubMed1982

A 12-fold microelectrode for recording from vertically aligned cortical neurones.

Twelve glass-coated wire microelectrodes of different lengths permit one to record along a vertical cortical neuron when the penetration angle is 45 degrees. Single units can be isolated at about half of the electrodes. Simultaneous events and spatial activity distributions can be studied; the method saves time, economizes on the use of experimental animals, and is advantageous for teaching.

Animals↗
PubMed1982

A stereotaxic system for independent coordinated positioning of two or three microelectrodes.

This paper describes a straightforward, easily built and relatively inexpensive stereotaxic system that permits independent coordinated positioning of 2 or 3 microelectrodes. This system is ideally suited for situations where the ability to routinely place one electrode at a precise position relative to another is important. Resolution of relative position and interelectrode distance is +/- 50 micrometers. This system should prove useful for the study of local interactions in such neural aggregates as nuclei, motoneuron pools and within and between cortical columns.

Animals↗
PubMed1983

Fiber microelectrodes for electrophysiological recordings.

Methods for the fabrication of tungsten-glass and platinum-rhodium-quartz fiber microelectrodes and of fiber pipettes are described and the electrical and mechanical properties of fiber electrodes are discussed. These properties (minimal tissue damage, good single unit isolation and temporal stability) make them particularly suited for multielectrode recordings from the central nervous system.

Animals↗
PubMed1983

A new microelectrode positioner for electrophysiology in the intact mammalian eye.

This report describes a new microelectrode positioner for intraocular electrophysiology. This positioner provides fine movement along the axis of electrode advance and in two planes at right angles to the axis of advance. Rotation occurs around the scleral insertion point. In addition, this new positioner incorporates a closed chamber system that allows maintenance of constant intraocular pressure (IOP) as well as the ability to set the IOP at any desired level.

Animals↗
PubMed1983

A microelectrode for delivery of defined charge densities.

A procedure is described for fabricating microelectrodes of platinum-30% iridium, insulated with Epoxylite varnish and having beveled ellipsoidal tips obtained by truncating a conical tip at an angle of 30-50 degrees. The geometric surface area of the ellipsoidal facet is reproducible and easily measured. Using these electrodes, neurons in the cerebral cortex of cats have been activated without damage throughout 24 h or more of continuous stimulation at 15-30 microA and charge densities of 150-300 microC/cm2.phase.

Animals↗