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When glass insulating tungsten microelectrodes are made, the insulating glass is usually drawn apart at an earlier than desired moment leaving a longer uninsulated metallic tip. A simple method for removing the excessively protruded part of the tungsten tip and triming it to any desirable length and shape is described.
The endogenous production of nitric oxide (NO) from the CNS and a peripheral sensory structure (osphradium) of the pulmonate molluscs, Lymnaea stagnalis and Limax sp. as well as from the rat aorta was studied using two different types of NO-sensitive microelectrodes. Both NO-sensitive electrodes gave complementary, but comparable results. From our data it was possible to compile a hierarchy of tissues with respect to estimated NO production: the rat aorta (300-600 nM) > Lymnaea osphradium (100-300 nM) > Lymnaea buccal ganglia (30-100 nM) > Limax protocerebrum (10-50 nM). In the preparations tested the administration of L-arginine (10 nM) caused an increased level of the recorded signals. This effect was suppressed by NG-Nitro-L-arginine (10 nM), an inhibitor of NOS. It may be concluded that NO can be detected directly from the CNS and peripheral tissues of Lymnaea, and rat aorta, despite the limitations of the techniques used. The putative level of NO production in the osphradium is higher than that in areas of the mammalian CNS and can be compared with release from the aorta. The NO release from the buccal ganglia and the protocerebrum was comparable with that of the rat cerebellum. Such high levels of NO production lend themselves to further analysis of the biological role of this molecule in molluscs.
A chamber is described with permanent solution flux aimed for in vivo cytophotometry (microscopy) of the nerve and muscle fibres, and for microelectrode registration of biopotential. Little size and construction peculiarities of the chamber make it possible to use objectives of middle and high magnification and to insert a microinstrument into the fiber.
Localization of the tip of the recording microelectrode with Pontamine Sky Blue 6BX introduced into the tissue iontophoretically was used to study the relationship of the morphological type of the neurone to a given type of elecrographic activity during the epileptic focal discharge. Paroxysmal depolarization shifts (PDSs) and short bursts of spikes in the negative phase of the focal discharge were found to be related to cells of the pyramidal type. Conversely, ovoid cells were active only in quiescent intervals and were inhibited throughout the whole duration of the focal discharge.
It has been shown that dihydropyridines exert a cardioprotective effect during experimental ischemia. This effect is reflected in a reduced K-efflux from the ischemic tissue. Recently we have shown that ischemic K-efflux is largely mediated by ATP-dependent K-channels. Using K-selective microelectrodes we studied the effect of nisoldipine on K-efflux during simulated ischemia (guinea pig papillary muscle immersed in paraffin oil; normal Tyrode solution, HEPES buffered, 100% O2-equilibrated, 37 degrees C). While ischemic K-efflux was Ca-dependent in stimulated preparations, it was independent of extracellular Ca in resting preparations. Our results show that nisoldipine leads to an inhibition of ischemic K-efflux during simulated ischemia. In resting preparations this inhibition is not a direct Ca-antagonistic effect, since withdrawal of extracellular Ca does not inhibit ischemic K-efflux but nisoldipine does. We suggest a direct effect of nisoldipine on the KATP channel which is mainly responsible for ischemic K-loss.
Microelectrode recordings were made in the binocular portion of the tree shrew striate cortex to determine how orientation selective cells are distributed topographically in area 17 of this species. Seventy-five percent of the cells sampled were activated well by elongated visual stimuli and were quite selective for stimulus orientation. Ninety-five percent of the orientation-selective cells had orientation tuning ranges (Wilson and Sherman, '76) between +/- 5 degrees and +/- 40 degrees from their optimal orientation. Orientation-selective cells with the same or similar optimal orientations were distributed in cortex in a columnar manner (Hubel and Wiesel, '62), as determined from electrode penetrations nearly normal to the cortical surface. Penetrations parallel to the cortical surface revealed a highly ordered representation of optimal stimulus orientation, generally characterized by sequential changes in optimal orientation with electrode movement across the striate cortex. In addition, relatively consistent differences were observed in the rates and patterns of orientation shift on these penetrations depending on the direction of electrode movement across the cortex. Penetrations parallel to the 17--18 border yielded moderate-to-high rates of orientation change (mean slope = 434 degrees/mm), with the changes generally progressing through a complete clockwise or counterclockwise cycle of 180 degrees or more before a major reversal in the direction of orientation shift was encountered. In contrast, penetrations perpendicular to the border yielded low-to-moderate slopes (mean slope = 239 degrees/mm). On these penetrations a more limited range of optimal orientations (< 180 degrees) was usually encountered, due to frequent reversals in the direction of orientation shift. Also, extended regions (100--200) micrometers long) of constant optimal orientation were observed in these penetrations. The different patterns of orientation change found on these orthogonal penetrations across the striate cortex indicate that the orientation column system in this species is anisotropically organized with respect to the 17--18 border. Further, the regions of constant optimal orientation frequently encountered on penetrations perpendicular to the 17--18 border suggest that the anisotropy is subserved by a system of elongated zones of iso-orientation arranged approximately perpendicular to the 17--18 border.
A confocal microspectrometer was used to collect spatially resolved electrochemiluminescence (ECL) spectra from the annihilation reaction between Ru(bpy)3+ and Ru(bpy)3(3+), each species being generated at a platinum band microelectrode and separated by a micrometric insulating gap. The use of a confocal microspectrometer allows in situ photon detection of the ECL reaction with micrometric spatial resolution and observes the concentration distribution of the photon source in the vicinity of the interelectrode gap.
We performed in vitro microelectrode studies in the anconeus muscle biopsy of a 6-week-old infant intoxicated with Clostridium botulinum toxin B. The most striking abnormalities were the severe reduction of the endplate potential (EPP) quantal content and the marked variability of EPP latencies. The increased variability was often limited to a "single quantum" component of the EPP. Neither the amplitudes nor the frequencies of spontaneous miniature endplate potentials (MEEPs) were decreased. However, there was a wide range of amplitudes and frequencies of MEPPs. This unique combination of electrophysiologic findings indicates a severe presynaptic failure of neuromuscular transmission, which appears to result from an impairment of the process of synaptic vesicle release taking place after the stimulus induced influx of calcium into the motor nerve terminals.
Calcium and pH ion-selective microelectrodes are used for the first time to measure chemical activity profiles above laboratory-grown algal biofilms (green alga, Chlorococcum sp). The results are used to calculate the solution composition changes above an actively photosynthesizing biofilm. These changes include the total calcium concentration, degree of supersaturation of the solution with respect to calcite, and the partial pressure of carbon dioxide. Measurements are made in a flow-cell, which was designed to hold the templates on which the biofilms are grown. Measurements show pronounced gradients of pH and calcium concentration, within a distance of approximately 500 μm above the biofilm. The high degree of supersaturation caused by the low concentrations of carbon dioxide near the biofilm surface leads to the precipitation of calcite on the biofilm. SEM micrographs illustrate the close association of calcite crystals with the algal cells. Preliminary results are presented of the precipitation rates estimated from the diffusion flux of calcium at the biofilm surface. The results are in broad agreement with the rates expected from calcite seed growth experiments in similar solution conditions.
During the AC electrokinetic manipulation of particles in suspension on microelectrode structures, strong frequency-dependent fluid flow is observed. The fluid movement is predominant at frequencies below the reciprocal charge relaxation time, with a reproducible pattern occurring close to and across the electrode surface. This paper reports measurements of the fluid velocity as a function of frequency and position across the electrode. Evidence is presented indicating that the flow occurs due to electroosmotic stress arising from the interaction of the electric field and the electrical double layer on the electrodes. The electrode polarization plays a significant role in controlling the frequency dependence of the flow. Copyright 1999 Academic Press.
The voltage clamp technique is a powerful method for studying the physiology of excitable membrane. This technique has made possible the determination of ionic responses generated by activation of either receptor-mediated or voltage-dependent processes. The development of the whole-cell, 'tight-seal' voltage clamp method has allowed the analysis and examination of membrane physiology at the single cell level. The method allows the characterization of voltage-dependent ionic conductances both at the macroscopic (whole-cell) and at the microscopic (unitary conductance or single channel) level in cells less than 10 micron in diameter, a feat difficult to achieve with 'conventional' fine-tipped micropipettes. In this paper, several methologies used for culturing neuronal and non-neuronal cells in the laboratory are described. A comparison between the two modes of voltage clamp using blunt-tipped 'patch'-microelectrodes, the switching (discontinuous) and the non-switching (continuous) modes, of the Axoclamp-2A amplifier is made. Some results on membrane currents obtained from neuronal and non-neuronal cells using the single electrode whole-cell 'tight-seal' voltage clamp is illustrated. The possible existence of two inactivating K+ currents, one dependent on Ca++ the other is not, is discussed.
Double-barrelled, chloride-selective microelectrodes were used to study mandibular gland acinar cells at rest and during cholinergic stimulation. At rest, intracellular chloride activity was five times the expected equilibrium activity. During sustained stimulation with acetylcholine, chloride activity fell to three times the expected equilibrium activity. Thus, the gradient for chloride exit was reduced in the stimulated cell. These results lead to the conclusion that stimulation increases the permeability of the acinar cell to chloride. Experiments in which extracellular chloride was removed provided evidence that the permeability increase was due to opening of chloride channels located principally in the apical membrane of the acinar cell.
The measurement of chloride activity was studied with Cl- -sensitive ion-exchanger microelectrodes (ISE) in calibrated test solutions stained with commonly used renal test dyes (e.g. Lissamine green SF) or other food or cosmetic dyes. Renal test dyes impair measurements of Cl- activity due to their anionic substitution and were found to increase electrode resistance. Cationic food dyes did not interfere with the Cl- reading of ISE although electrode resistances were increased, too.
The purpose of this study was to characterize the basolateral membrane of the S3 segment of the rabbit proximal tubule using conventional and ion-selective microelectrodes. When compared with results from S1 and S2 segments, S3 cells under control conditions have a more negative basolateral membrane potential (Vbl = -69 mV), a higher relative potassium conductance (tK = 0.6), lower intracellular Na+ activity (ANa = 18.4 mM), and higher intracellular K+ activity (AK = 67.8 mM). No evidence for a conductive sodium-dependent or sodium-independent HCO3- pathway could be demonstrated. The basolateral Na-K pump is inhibited by 10(-4) M ouabain and bath perfusion with a potassium-free (0-K) solution. 0-K perfusion results in ANa = 64.8 mM, AK = 18.5 mM, and Vbl = -28 mV. Basolateral potassium channels are blocked by barium and by acidification of the bathing medium. The relative K+ conductance, as evaluated by increasing bath K+ to 17 mM, is dependent upon the resting Vbl in both S2 and S3 cells. In summary, the basolateral membrane of S3 cells contains a pump-leak system with similar properties to S1 and S2 proximal tubule cells. The absence of conductive bicarbonate pathways results in a hyperpolarized cell and larger Na+ and K+ gradients across the cell borders, which will influence the transport properties and intracellular ion activities in this tubule segment.
The Na+ requirement for active, electrogenic Cl- absorption by Amphiuma small intestine was studied by tracer techniques and double-barreled Cl- -sensitive microelectrodes. Addition of Cl- to a Cl- -free medium bathing in vitro intestinal segments produced a saturable (Km = 5.4 mM) increase in short-circuit current (ISC) which was inhibitable by 1 mM SITS. The selectivity sequence for the anion-evoked current was Cl- = Br- greater than SCN- greater than NO-3 greater than F- = I-. Current evoked by Cl- reached a maximum with increasing medium Na concentration (KM = 12.4 mM). Addition of Na+, as Na gluconate (10 mM), to mucosal and serosal Na+-free media stimulated the Cl- current and simultaneously increased the absorptive Cl- flux (JCl m----s) and net flux ( JClnet ) without changing the secretory Cl- flux ( JCls ----m). Addition of Na+ only to the serosal fluid stimulated JClm ----s much more than Na+ addition only to the mucosal fluid in paired tissues. Serosal DIDS (1 mM) blocked the stimulation. Serosal 10 mM Tris gluconate or choline gluconate failed to stimulate JClm ----s. Intracellular Cl- activity ( aiCl ) in villus epithelial cells was above electrochemical equilibrium indicating active Cl- uptake. Ouabain (1 mM) eliminated Cl- accumulation and reduced the mucosal membrane potential (psi m) over 2 to 3 hr. In contrast, SITS had no effect on Cl- accumulation and hyperpolarized the mucosal membrane. Replacement of serosal Na+ with choline eliminated Cl- accumulation while replacement of mucosal Na+ had no effect. In conclusion by two independent methods active electrogenic Cl- absorption depends on serosal rather than mucosal Na+. It is concluded that Cl- enters the cell via a primary (rheogenic) transport mechanism. At the serosal membrane the Na+ gradient most likely energizes H+ export and regulates mucosal Cl- accumulation perhaps by influencing cell pH or HCO-3 concentration.
On spherical microelectrodes, cyclic staircase voltammograms of reversible redox reactions complicated by the reactant adsorption depend on lateral interactions in the monolayer. Attraction forces increase the separation between the main wave and the post-peak, while the repulsion prevents the resolution of responses of the surface and volume reactions. The theoretical relationships between the dimensionless responses and the dimensionless adsorption constant, the relative surface adsorption capacity, the Frumkin coefficient and the electrode sphericity are given.
Voltammetry with continuously heated microelectrodes yields well-defined sigmoidal current-voltage curves. Unlike hydrodynamic electrodes, the surface temperature of a heated electrode can be adjusted arbitrarily within a certain range. Inside a thermal layer, a virtually stagnant diffusion layer of constant thickness delta(diff) exists. delta(diff )is independent of temperature within a certain range. On the basis of this theory, equations are derived which play a similar role to, for instance, the Levich equation for the rotating disk electrode. Reasonable agreement of the derived relationship with the results from voltammetric experiments is obtained.
Microelectrodes of silver-copper alloys have been evaluated for use in voltammetric analyses. Increased overpotential towards the hydrogen overvoltage reaction (HER) was found as a function of increased copper content in the silver. A study of oxidizing products by cyclic voltammetry (CV) in NaOH solution showed ten anodic and eight cathodic peaks which are described in the present paper. The behaviour of these alloy electrodes is somewhere between pure silver and pure copper electrodes. Differential pulse anodic stripping voltammetry (DPASV) was used to measure zinc, cadmium and lead in ultrapure water only (18 MOmegacm), and good linearity was found for all metals (r (2)=0.998) in the range of 0.5 to 5 ppb with a 600- to 1,200-s plating time. It was additionally found that cadmium and lead were better separated on the alloy electrodes compared to pure silver electrodes. Measurements of nickel were carried out on alloy electrodes by use of adsorptive differential pulse cathodic stripping voltammetry (Ad-DPCSV), and good linearity (r (2)=1.000) was found in the range from 0.5 to 5 ppb with an adsorption time of 120 s. The alloy electrodes were also found to be sensitive to nitrate, and good linearity (r (2)=0.997) was found in the range from 1 mg L(-1) to 100 mg L(-1) using differential pulse voltammetry (DPV) scanning from -450 mV to -1,500 mV. Addition of nitrate in ultrapure water afforded two different peaks related to the successive reductions of nitrate and nitrite. In ammonium buffer solution (pH 8.6) only one peak resulting from reduction of nitrate was observed. Furthermore, the use of alloy electrodes containing 17% Cu was tested in real samples, by installing it in a voltammetric system for monitoring of zinc and lead in a polluted river, the river Deûle, near the town of Douai in northern France. Results were found to be in agreement with parallel measurements carried out by ICP-MS.