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PubMed1999

A new type of microelectrode for obtaining unitary recordings in the human spinal cord.

OBJECT: In this paper the authors report on the conception and adjustment of a microelectrode used to obtain unitary recordings in the human spinal cord. METHOD: To overcome the difficulties related to intraoperative pulsations of the spinal cord, the authors opted to use a floating microelectrode. Because the recordings are obtained most often from spontaneous activities, it is difficult, with a single microelectrode, to separate spikes from electrical artifacts that are related to the switching of devices. Consequently, the authors designed a dual microelectrode made of two tungsten-in-glass-attached microelectrodes separated by 300 microm. Because the two electrodes cannot obtain recordings in the same neuron, it is possible to distinguish unambiguously spikes (recorded on one tip) from electrical artifacts (recorded simultaneously on the two tips). The dual microelectrode is 2 cm long, with a 20-microm tip length, and 800 to 1200-Ohms impedance. This microelectrode can be implanted "free hand," in the dorsal horn, by using a microsurgical forceps under a surgical microscope. The data analysis is performed off-line with spike sorter hardware. In the dorsal horns in 17 patients who were selected to undergo a dorsal root entry zone (DREZ) rhizotomy to treat various pathological conditions, unitary recordings were obtained using this double microelectrode. The authors recorded 57 neurons in good conditions of stability and isolation. CONCLUSIONS: The microelectrode described in this paper was successfully used to obtain recordings in neurons in more than 85% of the patients. This simplified, floating double microelectrode can therefore be considered for use in microsurgical DREZ rhizotomy to obtain unitary recordings in the human spinal dorsal horn.

Artifacts↗
PubMed2004

Bead-based immunoassays with microelectrode detection.

The suitability of a microelectrode as the detector for a small-volume, bead-based enzyme-labeled immunoassay for later use in a microfluidic device was investigated. The microelectrode helps to overcome consumption of the electroactive species by the electrode (depletion) that is encountered with macroelectrodes such as the rotating disk electrode (RDE) and allows the volume of the detection cell to be reduced. Microelectrodes also allow the chemical reactions to be monitored in real time due to the electrodes' close proximity to the assay site. A bead-based sandwich immunoassay for mouse IgG was developed with alkaline phosphatase (AP) as the enzyme label, p-aminophenyl phosphate (PAPP) as the enzyme substrate, and microelectrode detection. The diffusion coefficient of the product of enzymatic hydrolysis, p-aminophenol (PAP), was determined to be 7.2+/-0.9 x 10(-6) cm(2) s(-1). The detection limits were determined for free (0.52 ng mL(-1)) and bead-bound AP (10 ng mL(-1)). The number of binding sites for AP per bead was calculated to be 9.6 x 10(4) molecules/bead, and under saturation conditions the minimum detectable number of beads was 2500. Lower detection limits could be achieved with the microelectrode than the RDE while maintaining similar reproducibility. The microelectrode also made it possible to work with lower sample volumes (down to 10 microL) than with the RDE (minimum volume of 40 microL). Depletion of PAP was not observed with the microelectrode. The results obtained here with a microelectrode showed great promise for later use of microelectrodes in microfluidic devices with limited sample volumes. RDE detection cannot be used in a microfluidic system due to its complex set-up that includes a motor for rotation.

Alkaline Phosphatase↗
PubMed2004

Fabrication of carbon microelectrodes with a micromolding technique and their use in microchip-based flow analyses.

In this paper, we report a new technique to pattern carbon microelectrodes for use in microfluidics. This technique, termed micromolding of carbon inks, uses poly(dimethylsiloxane)(PDMS) microchannels to define the size of the microelectrode. First, PDMS microchannels of the approximate dimensions desired for the microelectrode are made by soft lithography. The PDMS is then reversibly sealed to a substrate and the microchannels are filled with carbon ink. After a heating step the PDMS mold is removed, leaving a carbon microelectrode with a size slightly smaller than the original PDMS microchannel. The resulting microelectrode (27 microm wide and 6 microm in height) can be reversibly sealed to a PDMS-based flow channel. Fluorescence microscopy showed that no leakage occurred around the chip/electrode seal, even up to flow rates of 10 microL min(-1). The electrode was characterized by microchip-based flow injection analysis. Injections of catechol in Hank's Balanced Salt Solution (pH 7.4), showed a linear response from 2 mM to 10 microM (r(2)= 0.995), with a sensitivity of 56.5 pA microM(-1) and an estimated limit of detection of 2 microM (0.27 picomole, S/N=3). Reproducibility of the electrode response was shown by repeated injections (n= 10) of a 500 microM catechol solution, resulting in a RSD of 4.6%. Finally, selectivity was demonstrated by coating the microelectrode with Nafion, a perfluoronated cation exchange polymer. Dopamine exhibited a response at the modified microelectrode while ascorbic acid was rejected by the Nafion-coating. These electrodes provide inexpensive detectors for microfluidic applications while also being viable alternatives to use of other carbon microelectrode materials, such as carbon fibers. Furthermore, the manner in which the microelectrodes are produced will be of interest to researchers who do not have access to state of the art microfabrication facilities.

Carbon↗
PubMed2005

An array of microactuated microelectrodes for monitoring single-neuronal activity in rodents.

Arrays of microelectrodes used for monitoring single- and multi-neuronal action potentials often fail to record from the same population of neurons over a period of time for several technical and biological reasons. We report here a novel Neural Probe chip with a 3-channel microactuated microelectrode array that will enable precise repositioning of the individual microelectrodes within the brain tissue after implantation. Thermal microactuators and associated microelectrodes in the Neural Probe chip are microfabricated using the Sandia's Ultraplanar Multi-level MEMS Technology (SUMMiTV) process, a 5-layer polysilicon micromachining technology of the Sandia National labs, Albuquerque, NM. The Neural Probe chip enables precise bi-directional positioning of the microelectrodes in the brain with a step resolution in the order of 8.8 microm. The thermal microactuators allow for a linear translation of the microelectrodes of up to 5 mm in either direction making it suitable for positioning microelectrodes in deep structures of a rodent brain. The overall translation in either direction was reduced to approximately 2 mm after insulation of the microelectrodes with epoxy for monitoring multi-unit activity. Single unit recordings were obtained from the somatosensory cortex of adult rats over a period of three days demonstrating the feasibility of this technology. Further optimization of the microelectrode insulation and chip packaging will be necessary before this technology can be validated in chronic experiments.

Action Potentials↗
PubMed1988

Double-barreled K+-selective microelectrodes based on dibenzo-18-crown-6.

Liquid ion-exchanger microelectrodes based on Corning code 477317 K+ exchanger are known to be much more sensitive to quaternary ammonium ions than to K+. In the presence of such cations, the capability of measuring K+ activities with Corning microelectrodes may be seriously impaired. We have developed a neutral carrier K+-selective microelectrode based on the crown ether dibenzo-18-crown-6. The crown ether cocktail contained (wt/wt) 2.3% dibenzo-18-crown-6, 0.8% Na-tetraphenylborate, 30.1% 2-nitrophenylocylether, and 66.8% O-nitrotoluene. Double-barreled crown ether and Corning microelectrodes were calibrated in KCl solutions with or without choline, acetylcholine, tetramethylammonium, imidazole, Na+, tris(hydroxymethyl)aminomethane (Tris), and N-methyl-D-glucamine. Both kinds of microelectrodes showed similar K+ over Na+, Tris, and N-methyl-D-glucamine selectivities. However, crown ether microelectrodes had immensely greater selectivities of K+ over quaternary ammonium ions and imidazole than Corning microelectrodes. Selectivity factors, defined as log K(ij)K, of crown ether microelectrodes with respect to K+ for tetramethylammonium, choline, acetylcholine, and imidazole were -1.92 +/- 0.13, -2.97 +/- 0.03, -1.75 +/- 0.15, and -1.30 +/- 0.20, respectively. Intracellular K+ activities measured in the same Necturus gallbladders with both kinds of microelectrodes did not differ significantly.

Animals↗
PubMed2001

Effects of recording media composition on the responses of Nafion-coated carbon fiber microelectrodes measured using high-speed chronoamperometry.

The present study concerns methodological issues of electrochemical recordings using Nafion-coated 30 microm diameter single carbon fiber microelectrodes for high-speed chronoamperometric measurements of biogenic amines. First, the single carbon fiber microelectrodes were coated with Nafion and dried at 85 vs. 200 degrees C and their recording properties were determined. Second, the effects of shifts in solution pH, ionic strength, changes in recording solution levels of Ca(2+) or Mg(2+) and temperature on the recording characteristics and sensitivity of Nafion-coated high temperature dried (200 degrees C) single carbon fiber microelectrodes for measures of dopamine were studied. These studies showed that the high temperature drying of the Nafion produced a microelectrode with better recording properties: higher selectivity for cations versus anions, increased differences between the reduction and oxidation current ratios for the identification of dopamine versus serotonin, and more rapid response times. In addition, these studies demonstrated that the chronoamperometric recordings were insensitive to small changes in pH and divalent cations such as Ca(2+) or Mg(2+). However, increases in ionic strength decreased the sensitivity of the microelectrodes, while increases in temperature produced increases in the sensitivity of the microelectrodes for biogenic amines. These data support that Nafion-coated high temperature (200 degrees C) dried microelectrodes have enhanced recording properties as compared to microelectrodes, which are coated with Nafion and dried at 85 degrees C. In addition, high-speed chronoamperometric recordings of biogenic amines are not affected by solution changes in divalent cations (Ca(2+) or Mg(2+)).

Animals↗
PubMed2004

Fabrication and characterization of nonplanar microelectrode array circuits for use in arthroscopic diagnosis of cartilage diseases.

A process to fabricate nonplanar microelectrode array circuits was developed and the microelectrodes were characterized. These platinum microelectrode arrays are for recording streaming potential signals generated during indentation of articular cartilage. The nonplanar substrate was produced by permanent deformation of a 7-in-diameter circular stainless-steel wafer to form 32 semi-spherical caps (radius of curvature = 4.65 mm and height = 250 microm) at the periphery. The wafer was covered with a 2.5-microm-thick layer of insulating polyimide. Standard microelectronic processes were applied to produce 32 circuits (60 mm long x 4 mm wide) with 37 exposed circular microelectrodes (diameter = 100 microm) centered over each semi-spherical cap. A 2.5-microm-thick photodefinable polyimide layer encapsulated the conducting lines. Capacitances between one microelectrode and either another microelectrode or the metallic substrate were 14.6 +/- 2.0 and 34.4 +/- 3.3 pF, respectively, at 100 Hz. The impedance of the microelectrodes in a 0.15 M saline bath (PBS) was 0.25 +/- 0.08 Mohms while the crosstalk (Vinduced/Vapplied) between two microelectrodes was 0.20 +/- 0.11%, at 100 Hz. Indentation measurements were performed on articular cartilage in vitro showing,streaming potentials that indicate electrode-tissue contact times and generation of streaming potentials.

Animals↗
PubMed2001

Determination of diffusion coefficients of electroactive species in time-of-flight experiments using a microdispenser and microelectrodes.

Two novel methods for the determination of diffusion coefficients of redox species combining the special properties of microdispensing devices and microelectrodes are presented. Both are based on the local application of tiny volumes of the redox-active species by means of a dispenser nozzle at a defined distance from the surface of a microelectrode. The microelectrode, which is inserted through the bottom into an electrochemical cell, is held at a constant potential sufficient to oxidize or reduce the electro-active species under diffusional control. The dispenser, which is filled with the electro-active species, can be positioned by means of micrometer screws over the microelectrode. After dispensing a defined number of droplets near the microelectrode surface, the current through the microelectrode is recorded, usually yielding a peak-shaped curve having a defined time delay between the shooting of the droplets and the maximum current. The time that is necessary to attain maximum current, together with the known distance between two dispensing points, can be used to determine the diffusion coefficient of the electroactive species without knowledge of any system parameters, such as concentration of the redox species, diameter of the electroactive surface or number of transferred electrons. A similar method for the determination of diffusion coefficient of redox species involves a second redox species for calibration purposes. A mixture of both species is shot close to the microelectrode surface. Due to the different formal potentials of the redox species that are used, they can be distinguished in sequential experiments by variation of the potentials that are applied to the microelectrode, and it is thus possible to determine the individual transit times of the redox species independently. The difference in the transit times, together with the known diffusion coefficient of one of the redox species, can be used to calculate the unknown diffusion coefficient of the second one.

Journal Article↗
PubMed1993

A novel combinational pH-PCO2 microelectrode.

A novel combinational pH-PCO2 microelectrode based on a neutral carrier hydrogen ion exchanger is described. It is easy to fabricate and allows pH and PCO2 to be measured simultaneously. The microelectrode has a 5-microns tip. The PCO2 microelectrode exhibits a linear response in the range 1.75 x 10(-5)-10(-2) mol/liter with a Nernstian slope of 57.0 mV/decade at 25 degrees C. The detection limit is 10(-5) mol/liter. The pH microelectrode exhibits a linear response in the range pH 4-12 with a Nernstian slope of 60.0 mV/decade at 25 degrees C. The 95% steady-state response time of the PCO2 microelectrode is about 2 min, while it is about 10 s for pH microelectrode. The electromotive force drift is 4.3 mV/h (PCO2) and 2.6 mV/h (pH), respectively. The lifetime is 3 to 4 days. The microelectrode can measure pH and PCO2 in body fluids simultaneously with satisfactory results. It is also a good basic electrode for enzyme microelectrolysis.

Animals↗
PubMed2003

Whole-cell recording of intracellular pH with silanized and oiled patch-type single or double-barreled microelectrodes.

Conventional ion-sensitive microelectrodes cannot be used in small cells, since they create too large an electrical leak at the site of penetration. Membrane potentials can be measured in such cells with the whole-cell configuration of the patch-clamp technique, after obtaining a high-resistance seal (giga-seal) to the cell membrane. Achieving such seals with patch-type microelectrodes silanized and filled with ion-sensitive cocktails has proved very difficult. Since ion-sensitive microelectrodes offer advantages over fluorescent techniques, we have developed a method which enables whole-cell recordings of membrane potential and intracellular pH to be achieved with silanized microelectrodes. We have been able to obtain high-resistance seals with silanized tips by dipping them in mineral oil. We describe the method for both single-barrel and theta-glass double-barreled microelectrodes. Double-barreled microelectrodes can be used to measure and control membrane potential in the whole-cell patch-clamp configuration while also measuring ionic activities with the adjacent barrel. We present illustrative experiments showing intracellular pH recordings in snail neurones and rat dorsal root ganglion cells, and we suggest the method can also be applied to other liquid-sensor ion-sensitive microelectrodes.

Animals↗
PubMed1984

Theory and operation of a single microelectrode voltage clamp.

The theory of operation of a discontinuous single-electrode voltage clamp using an ideal microelectrode (infinite response speed) and fixed (current-passing) duty cycle has been previously described. In this paper, the theory is extended by considering a microelectrode which has a finite response speed, by allowing the duty cycle to be variable, and by considering the clamp noise. Formulate are derived for the relationships between the step response, the steady-state error, the steady-state ripple, and the stability, in terms of the cycling frequency, the duty cycle, the open loop gain, and the electrical resistance and capacitance of the microelectrode and the cell membrane. In addition, the amplification of the microelectrode noise by aliasing is analysed, the error due to incomplete decay of the microelectrode voltage is described, and the accuracy of averaging the peak current measurement is established. To achieve the fastest dynamic response and the smallest steady-state error, the cycling period should be made as small as possible, and the open-loop gain should be as large as possible, consistent with stability. Incomplete decay of the microelectrode voltage destabilizes the clamp, and can introduce a significant clamp error. The choice of duty cycle is a compromise between reducing the noise and the step response time while avoiding design problems in the current output circuit. The output noise is amplified by aliasing. It can be minimized for a given output filter cutoff frequency by keeping the cycling frequency as high as possible, and by the use of an anti-aliasing filter whose cutoff frequency must be set for each microelectrode.

Animals↗
PubMed2004

Ultrastructure at carbon fiber microelectrode implantation sites after acute voltammetric measurements in the striatum of anesthetized rats.

This work seeks to establish the feasibility of characterizing the ultrastructure of brain tissue disruption associated with the implantation of carbon fiber voltammetric microelectrodes. In vivo recording was performed by fast scan cyclic voltammetry in conjunction with carbon fiber microelectrodes (3.5 microm radius) in the striatum of rats anesthetized with chloral hydrate. After 4 h of in vivo recording, the microelectrodes were removed from the brain and the animals underwent intracardial perfusion. Brain tissue was collected and sectioned in the horizontal plane perpendicular to the axis of the microelectrodes. With microelectrodes of a conventional single barreled design, the tissue tracks were often too small to be followed by light microscopy to the point of deepest penetration, which would correspond to the implantation site of the carbon fiber itself. The enlarged tissue tracks formed by the implantation of double barreled electrodes, however, could be followed to their termination by light microscopy. Anatomical mapping was used to identify the fields laying 100 microm deeper than the deepest trace of such tracks. Electron microscopy of these fields revealed a spot of tissue damage presumed to be associated with the implantation site of the carbon fiber microelectrode. The spot of maximal tissue damage had a radius of 2.5 microm and was surrounded by an annular region with a width of 4 microm that contained a mix of healthy and damaged elements. Beyond this annular region, i.e. beyond 6.5 microm from the center of the spot of maximal damage, signs of microelectrode-associated damage were rare and consisted primarily of neurons with darkened cytoplasm.

Animals↗
PubMed2005

Single neuronal recordings using surface micromachined polysilicon microelectrodes.

Bulk micromachining techniques of silicon have been used successfully in the past several years to microfabricate microelectrodes for monitoring single neurons in acute and chronic experiments. In this study we report for the first time a novel surface micromachining technique to microfabricate a very thin polysilicon microelectrode that can be used for monitoring single-unit activity in the central nervous system. The microelectrodes are 3 mm long and 50 microm x 3.75 microm in cross-section. Excellent signal to noise ratios in the order of 25-35 dB were obtained while recording neuronal action potentials. The microelectrodes successfully penetrated the brains after a microincision of the dura mater. Chronic implantation of the microprobe for up to 33 days produced only minor gliosis. Since the polysilicon shank acts as a conductor, additional processing steps involved in laying conductor lines on silicon substrates are avoided. Further, surface micromachining allows for fabricating extremely thin microelectrodes which could result in decreased inflammatory responses. We conclude that the polysilicon microelectrode reported here could be a complementary approach to bulk-micromachined silicon microelectrodes for chronic monitoring of single neurons in the central nervous system.

Action Potentials↗
PubMed1998

Pallidotomy lesion locations: significance of microelectrode refinement.

OBJECTIVE: To determine whether stereotactic pallidotomy requires refinement using microelectrode recording to ensure proper lesion placement. METHODS: The experiment approach was based on retrospective comparisons of microelectrode-refined radiofrequency lesion locations with hypothetical unrefined lesion positions. Actual and hypothetical pallidotomy lesions were classified based on their lesion center (thermocoagulative zone) locations and their total lesion areas (surrounding edematous zone) relative to the pallidal target. Assessments were made using postoperative T2-weighted magnetic resonance axial images, which showed both the lesion and globus pallidus (GP). The magnitude of microelectrode refinement from an initial preoperative starting point determined by computed tomography was calculated using stereotactic coordinates and included corrections for the lesioning tract trajectory angle. RESULTS: In all 25 patients, the center of the actual pallidotomy lesion was within the GP. Without microelectrode refinement, 13 of 25 hypothetical lesion positions would have been localized such that the lesion center would not have remained in the GP. In eight cases, microelectrode refinement resulted in no significant change in lesion location, but in one case, microelectrode refinement resulted in lesion center placement away from the GP. CONCLUSION: Kinesthetically driven microelectrode refinement in pallidotomy lesioning seems to be required to ensure proper lesion location within the GP.

Adult↗
PubMed2004

Nanostructured surface modification of ceramic-based microelectrodes to enhance biocompatibility for a direct brain-machine interface.

Many different types of microelectrodes have been developed for use as a direct Brain-Machine Interface (BMI) to chronically recording single neuron action potentials from ensembles of neurons. Unfortunately, the recordings from these microelectrode devices are not consistent and often last for only a few weeks. For most microelectrode types, the loss of these recordings is not due to failure of the electrodes but most likely due to damage to surrounding tissue that results in the formation of nonconductive glial-scar. Since the extracellular matrix consists of nanostructured microtubules, we have postulated that neurons may prefer a more complex surface structure than the smooth surface typical of thin-film microelectrodes. We, therefore, investigated the suitability of a nano-porous silicon surface layer to increase the biocompatibility of our thin film ceramic-insulated multisite electrodes. In-vitro testing demonstrated, for the first time, decreased adhesion of astrocytes and increased extension of neurites from pheochromocytoma cells on porous silicon surfaces compared to smooth silicon sufaces. Moreover, nano-porous surfaces were more biocompatible than macroporous surfaces. Collectively, these results support our hypothesis that nano-porous silicon may be an ideal material to improve biocompatibility of chronically implanted microelectrodes. We next developed a method to apply nano-porous surfaces to ceramic insulated, thin-film, microelectrodes and tested them in vivo. Chronic testing demonstrated that the nano-porous surface modification did not alter the electrical properties of the recording sites and did not interfere with proper functioning of the microelectrodes in vivo.

Action Potentials↗
PubMed1984

Electronic device for microelectrode recordings in epithelial cells.

A device is described that permits continuous measurement of electrophysiological parameters in epithelial tissues in the open-circuit mode. Transepithelial potential (VT) and microelectrode (either conventional or ion-selective) potential (VM) are directly measured. Application of transepithelial current pulses allows continuous monitoring of transepithelial resistance (RT) and the ratio between the changes in VM and VT induced by these pulses. Measurement of this ratio, which under some circumstances reflects the apical fractional resistance of the cellular pathway, is important in assessing membrane damage during microelectrode impalement and/or as an index that the microelectrode tip is inside a cell. This is particularly useful when the change in VM during impalement is small. Application of 0.5-nA current pulses through open-tip microelectrodes allows continuous recording of the microelectrode resistance (RM). In epithelia where the individual cells are electrically coupled this permits acceptable impalements (RM remains nearly constant) to be distinguished from those affected by tip potential artifacts due to plugging of the microelectrode tip (RM increases after penetration of the cell membrane). The device provides compensation for the IR voltage drop in the solution between the potential measuring salt bridges and the epithelial surfaces. The microelectrode electrometer has an input impedance greater than 10(15) and is provided with stray capacitance neutralization.

Electrophysiology↗
PubMed1990

Intracellular calcium measurements with PVC-resin Ca-selective microelectrodes in frog proximal tubules and sartorius muscle fibers.

To measure ion activity of intracellular calcium, (Ca)i, we manufactured a Ca2(+)-selective microelectrode based on a neutral carrier, ETH-1001, with or without polyvinylchloride column (PVC-resin). Before and after cell impalements (n = 7), PVC-resin Ca2(+)-selective microelectrodes exhibited Nernstian slopes in the range of p(Ca) from 3 to 7 (the mean slope constant: 29.1 and 29.4 mV/p(Ca), respectively) and sub-Nernstian slopes between p(Ca) = 7 and 8 (21.6 and 21.1 mV/p(Ca]. Individual detection limits of PVC-resin microelectrodes averaged p(Ca) = 8.5 before and 8.3 after cell impalements. In contrast, the non-PVC-resin microelectrode exhibited a poor response between p(Ca) = 7 and 8 especially after cell impalements. Normal values obtained with the PVC-resin microelectrode for (Ca)i of proximal tubule cells and resting sartorius muscle fibers in the bullfrog averaged 18 +/- 2 (n = 10) and 12 +/- 2 (n = 7) nM (mean +/- S.E., number of observations), respectively. We conclude that 1) the PVC-resin microelectrode is a useful tool for measuring intracellular ion activities, and 2) the values of intracellular Ca2+ activity of the proximal tubule and skeletal muscle fibers measured with this microelectrode are in a lower range among the various values reported before with the other methods.

Animals↗
PubMed2001

An improved Na+-selective microelectrode for intracellular measurements in plant cells.

The high background K+ concentration in plant cells is a problem for intracellular measurements of Na+ using ion-selective microelectrodes. The discrimination between Na+ and K+ of the microelectrode ionophore molecule limits the usefulness of this technique. A new Na+-selective microelectrode with an ionophore incorporating a tetramethoxyethyl ester derivative of p-t-butyl calix[4]arene has been developed. Microelectrodes made with this new sensor have superior selectivity for Na+ over K+ resulting in a lower limit of detection when compared with microelectrodes made using a commercially available ionophore (ETH227). Both types of microelectrodes were insensitive to changes in ionic strength and physiological ranges of pH, but only the calixarene-based electrodes showed no protein interference. To test the suitability of the calixarene-based microelectrodes for measurements in plants, they were used to measure Na+ in epidermal cells in the zone 10-20 mm from the root apex of barley (Hordeum vulgare L.). Seedlings were grown in a nutrient solution containing 200 mM NaCl for 1-6 d. The range of intracellular Na+ activity (a(Na)) measured varied from < or =0.1 mM (limit of detection) to over 100 mM, and these values increased significantly with time. The membrane potential (E(m)) of these cells was variable, but the values became significantly more negative with time, although there was no significant correlation between E(m) and a(Na). These intracellular measurements could not be separated into distinct populations that might be representative of subcellular compartments.

Acetamides↗