Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Microelectrodes”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,621 records · Page 90Linked to original sources
PubMed1995

The application of in vitro isolation, cryopreservation and patch-clamp microelectrode recording methods to adult rat thymic nurse cells.

Characterisation of the ionic mechanisms possessed by immune cells has begun to reveal a range of transmembrane ion channel properties which may have immunological significance. Since thymic epithelial cells appear to influence selection of the T cell repertoire, understanding their membrane physiology may be of importance. A method is therefore outlined for the targeting of patch-clamp electrophysiological measurements to acutely isolated, fresh and cryopreserved adult rat thymic nurse cells. These cells represent a discrete and predominantly cortical population of epithelium. Cells were separated by enzymatic and mechanical dispersal of thymus, enriched by sedimentation and identified on the basis of their characteristic lympho-epithelial, multi-cellular morphologies. Phase-bright cells retaining this anatomical form survived freezing and the voltage-gated conductances in such cells are described. The merits of this approach include the preparation and storage of mature differentiated phenotypes of immune cells for in vitro studies. Their preservation permits temporal separation of experiments, correlative experimentation on identical samples, optimises cell preparation in terms of cost and labour, and reduces animal and tissue requirements.

Animals↗
PubMed2003

Stimulation of single isolated adult ventricular myocytes within a low volume using a planar microelectrode array.

Microchannels (40- microm wide, 10- microm high, 10-mm long, 70- microm pitch) were patterned in the silicone elastomer, polydimethylsiloxane on a microscope coverslip base. Integrated within each microchamber were individually addressable stimulation electrodes (40- microm wide, 20- microm long, 100-nm thick) and a common central pseudo-reference electrode (60- microm wide, 500- microm long, 100-nm thick). Isolated rabbit ventricular myocytes were introduced into the chamber by micropipetting and subsequently capped with a layer of mineral oil, thus creating limited volumes of saline around individual myocytes that could be varied from 5 nL to 100 pL. Excitation contraction coupling was studied by monitoring myocyte shortening and intracellular Ca(2+) transients (using Fluo-3 fluorescence). The amplitude of stimulated myocyte shortening and Ca(2+) transients remained constant for 90 min in the larger volume (5 nL) configuration, although the shortening (but not the Ca(2+) transient) amplitude gradually decreased to 20% of control within 60 min in the low volume (100 pL) arrangement. These studies indicate a lower limit for the extracellular volume required to stimulate isolated adult cardiac myocytes. Whereas this arrangement could be used to create a screening assay for drugs, individual microchannels (100 pL) can also be used to study the effects of limited extracellular volume on the contractility of single cardiac myocytes.

Animals↗
PubMed1975

Microelectrode study of high grade block in canine Purkinje fibers.

Previous reports from this laboratory described an electrotonic mechanism for simple impulse transmission through blocked segments of canine Purkinje tissue with slow diastolic depolarization assuming a vital role in second degree block. Utilizing an electrical blocking current, a blocked segment of canine Purkinje tissue was produced. Transmembrane events were recorded from blocked segments during higher grades of block (3:1 to complete) to delineate further mechanisms responsible for a periodic distal boundary response. Our results confirm that slow diastolic depolarization is an important determinant in sustaining periodic impulse conduction. Its importance is related to (1) progressive decrease of the resting membrane potential toward threshold at the distal block boundary, and (2) augmentation of the transmitted electrotonic potential in accordance with voltage dependent changes in membrane resistance. These data further lend definition to the distinction between electrotonic, partially active, and active transmembrane potentials. Impulse transmission through a segment of inactivated tissue is electrotonic and slow diastolic depolarization plays an important role in the maintenance of periodic impulse transmission.

Action Potentials↗
PubMed2002

Direct determination of diffusion coefficients of substrate and product by chronoamperometric techniques at microelectrodes for any level of ionic support.

A new method for the determination of the diffusion coefficients of both the substrate, DS, and the product, DP, of an electrode process has been developed. The method proposed is based on the analysis of the transient currents and can be applied to some reactions of the type SzS = PzP + ne and, in contrast to the concept based on the steady-state current, to any ratio of the concentrations of supporting electrolyte and substrate. The diffusion coefficients can be evaluated sequentially from the two parts of the double-potential step chronoamperogram, since the magnitude of the normalized chronoamperometric current of the first step depends on the DS value, while that of the second step is controlled by both DS and DP values. The corresponding, easy-to-use equations and procedures are given in the paper. The equations were derived on the basis of the numerical simulation data. The proposed methods of determination of diffusion coefficients for the substrates and products have been examined experimentally with the charged and uncharged ferrocene derivatives under diffusional and mixed diffusion-migration conditions. Only the chronoamperometric DS values obtained for the substrates could be compared to those determined from the steady-state diffusional current. It was found that for the systems investigated the agreement between these two methods was good. In this limited comparison, the standard deviations for the transient techniques were slightly larger than those obtained for the excess supporting electrolyte steady-state voltammetry.

Journal Article↗
PubMed2003

Characteristic electrochemical responses of polymer microchannel-microelectrode chips.

Polymer microchannel chips (dimension of the channel, 20 microm (depth) x 100 microm (width)) integrated with dual microband electrodes were fabricated by an imprinting method, and their characteristic electrochemical responses were elucidated in detail. A silicon micromachined template fabricated by photolithography and dry etching techniques was used for imprinting. An aqueous solution of a ferrocene derivative was brought into the microchannel by pressure-driven flow, and the electrode responses were studied on the basis of voltammetry and chronoamperometry. A linear sweep voltammetry of 1-hydroxyethylferrocene (FeCp-OH) in water demonstrated that the electrode responses in the microchannel chip were best characterized by one-dimensional diffusion along the channel length, reflecting the structural dimension of the channel. In generation-collection mode experiments, furthermore, a collection efficiency as high as approximately 90% was attained in the microchannel owing to both restricted space and characteristics of solution flow in the channel. It was confirmed that diffusion and solution flow made molecular transport very efficient in the microchannel. The experimental results were also compared with those predicted by computer simulations.

Journal Article↗
PubMed2000

Voltammetric and reference microelectrodes with integrated microchannels for flow through microvoltammetry. 2. Coupling the microcell to a supported liquid membrane preconcentration technique

The paper describes the assembly and functioning of the microvoltammetric cell described in Part 1, with a hollow Fiber Supported Liquid Membrane (HFSLM), for trace metal analysis. Membrane stability, working-electrode behavior, mercury-film lifetime inside the HFSLM, hydrodynamic conditions, as well as transport kinetics of the metal through the SLM have been studied in detail. System calibrations have been performed in the range 5-120 nM Pb(II). The reproducibility and sensitivity of the whole microsystem is discussed as well as limitations and possible improvements.

Journal Article↗
PubMed2006

Electrochemical impedance spectroscopy investigations of a microelectrode behavior in a thin-layer cell: Experimental and theoretical studies.

Electrochemical impedance spectroscopy experiments were performed on a microdisk electrode in a thin-layer cell using a scanning electrochemical microscope for controlling the cell geometry. Experimental data showed that when the thin-layer thickness diminished, an additional low-frequency response appeared. It was ascribed to the radial diffusion of the electroactive species and was strongly dependent on the thin-layer dimensions (both thickness and diameter). Moreover, the numerical simulation of the impedance diagrams by finite element method calculations confirmed this behavior. An equivalent circuit based on a Randles-type circuit was proposed. Thus, the diffusion was described by introducing two electrical elements: one for the spherical diffusion and the other for the radial contribution. A nonlinear Simplex algorithm was used, and this circuit was shown to fit the impedance diagrams with a good accuracy.

Journal Article↗