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Miniature end plate potentials (MEPPs) were recorded in glyceroltreated muscle fibers with four microelectrodes which were used to determine the passive electrical characteristics of the same fibers. Voltage responses which were computed from miniature end plate currents (MEPCs) and the passive cable properties of a fiber, agreed very closely with experimentally recorded MEPPs confirming the hypothesis that MEPPs spread passively along a muscle fiber. The model was used to analyze the effect of variations in synaptic current and the properties of a muscle fiber on the postsynaptic response. The decrement of MEPPs was exponential for distances up to 1 to 2 mm from an origin but then deviated from the initial exponential. Variations in the growth time of the input current up to 1 msec had little effect on computed MEPPs whereas an increase in the decay time constant caused a significant increase in MEPP amplitude and effective “space constant”. An increase in the internal resistivity of a muscle fiber increased MEPP amplitude at the origin but decreased the effective space constant. The amplitude of MEPPs was inversely proportional to the 1.5 power of the “diameter” of a muscle fiber, and the MEPP space constant increased as the square root of the diameter. The amplitude of MEPPs is not necessarily determined by the “input” resistance of the muscle fiber. Changes in input resistance caused by changes in membrane resistance would have little effect on te amplitude or decrement of MEPPs.

Single unit responses of the cat midbrain tectum to stimuli applied through a microelectrode 500µ rostrally to the recording electrode were recorded extracellularly. The mean latency of both direct and monosynaptic responses was 0.3 msec greater than that for local microstimulation. The responses were identified from their latent and refractory periods, the presence of summation, and the dependence of the firing index on sodium glutamate application to the recorded neuron. Thresholds of synaptic responses were measured during vertical displacement of the stimulating electrode. The experimental relationships can be approximated by parabolic functions. The results indicate that rostrocaudal projections in the midbrain tegmentum are arranged horizontally.

A method is described for the achievement of good adhesion and smooth coating of PTEE (Hostaflon TF) onto tungsten sensory micro needles, which are suitable for human sensory and muscle nerve investigations.

The transepithelial electrical potential difference across rat rena proximal tubule was reinvestigated, using improved techniques. To diminish tip potential artefacts the microelectrodes were filled with HCO3-Ringer's solution instead of 3 molar KCl. The error of the potential measurements with HCO3-Ringer's microelectrodes was tested and was found to be ≤0.5 mV. A significant electrical potential profile was detected along the proximal tubular lumen under free flow. From near zero at the glomerulum the potential difference rose to −1.5 mV, lumen negative, in the first tubular loop at approximately 0.1 to 0.3 mm of tubular length. It decreased then rapidly, changed sign and attained a maximum of ca. 2.0 mV, lumen positive, at 1 mm of tubular length, after which it declined gradually to +1.6 mV in the last accessible loop. The mean of 85 punctures in intermediate and late loops was+1.8, S.D.±0.33 mV, range+1.0 to+3.2 mV. On the basis of perfusion experiments described in the subsequent paper, the lumen-negative potential difference across early loops can be explained as an active transport potential. It is caused by the presence of glucose and amino acids in the glomerular filtrate, which increase the rate of active Na+ absorption over that of active HCO3 − absorption. The lumen-positive potential difference in intermediate and late loops is explained as the sum of a membrane diffusion potential arising from the shift in intratubular Cl− and HCO3 − concentrations and a small lumen-positive active transport potential from H+ secretion/HCO3 − absorption.

Microelectrode studies were performed to produce alternation of coupled beats in the specialized conduction system of the heart and to determine the underlying mechanisms of their production. A typical preparation consisted of a superfused Y-shaped bifurcating segment of canine Purkinje tissue, in which the two branches of the Y were approximately symmetrical and terminated in a functionally communicating bridge of myocardium. Transmembrane potentials were recorded simultaneously from a proximal and a distal location in one branch of the Y. Stimulating the stem of the preparation with 60 pulse pairs/min at a critical coupling interval produced alternation of the coupled beats. Alternate reversal of the proximl-to-distal sequence of activation was observed under these circumstances. This finding probably resulted from alternate antegrade block of the instrumental branch accompanied by retrograde conduction through the accessory pathway offered by the other branch and the common myocardial bridge. The validity of this inference was confirmed by microelectrode exploration and by transection of the retrograde pathway. Analysis of the results demonstrated further that alternating block was also intimately related to the alternation of preceding cycle lengths.

This report discusses overlapping advance control systems in relation to the problems of resolution, compactness, and speed of response which are now present in varying degrees in commercially available rolling diaphragm hydraulic microdrives and which are considerations in certain applications. A mechanical microdrive was first described which achieves resolution (to 0.1 μm) and compactness by mounting a differential-screw translator concentrically within a micrometer screw. A prototype of this microdrive is approximately 6.5 × 6.5 cm, but the design of the unit allows a reduction of diameter to approximately 2 cm with no appreciable loss in resolution. Since the cost of construction is reasonable, this microdrive is a feasible and worthwhile alternative for the advance control of hydraulic systems. The application of piezoelectric transducer (PTZ) devices to impact rapid motion was then discussed: First, it was illustrated how a high load bearing PZT could be placed in series between a mechanical microdrive and a hydraulic system. This allows the wide range positioning capabilities of the mechanical microdrive to effect initial electrode control, while the high speed (“pulsed”) motion of the PZT is reserved to aid in the penetration of small cells or for exceedingly fine position adjustments. In this configuration, the PZT is located so as to avoid the drawbacks produced were such a device to be mounted on the final stage of a hydraulic system where its size would be likely to interfere. Finally, a newly designed PZT device—the inchworm—was described and its application to electrode positioning problems discussed as an additional and new alternative. Under boundary constraints defined by the cost of presently available stepping hydraulic microdrives, the alternatives discussed in this paper are certainly reasonable and the gains in resolution, compactness, and speed may therefore be viewed as attractive bonuses to be had in the event that they are demanded by experimental considerations.

Preparation of bevelled dual-channel glass microelectrodes is described. The bevelled tips overcome some of the problems which complicate intracellular recording. The size of the tip opening is increased, resulting in a lower resistance, which in turn confers greater current-carrying capacity and less noise susceptibility. Bevelling also preserves the sharp point, facilitating tissue penetration and minimizing neuronal trauma. The characteristics of bevelled and unbevelled electrodes filled with 0.5 or 3 M KCI, K Acetate and K 2 SO 4 were similar. Bevelled electrodes were shown to maintain a near constant resistance during current passage, while unbevelled ones showed changes in resistance that were dependent on current magnitude, polarity and duration. Such changes were caused principally by electro-osmosis.

Localized intracellular light-evoked potentials were recorded from the retina of the flyCalliphora erythrocephala by means of very fine tapered glass capillary microelectrodes.

An electrolytic method is described for manufacturing ball-tipped tungsten microelectrodes. The tungsten ball is produced by slowly withdrawing the electrode from the etching solution until the wire mells and tungsten metal forms a ball at the end of the shaft. The size of the ball is related to both the size of the wire shaft and the amount of current being passed. Smaller balled tips are produced when wire of smaller shaft diameter is induced to spark and melt. Higher voltages and larger shaft diameters at sparking yield larger balled tips. Ball-tipped electrodes are produced easily and reliably by this method and require little training. Such electrodes are sturdy and capable of stably recording activity of either single cells or multiple-units with good signal-to-noise ratio. They can record extracellular perikaryal responses from neurons at several levels of the nervous system. Responses of single nerve fibers are not isolated by these electrodes.

The responses of A and C fibres to electrical intradermal stimulation were recorded with microelectrodes inserted percutaneously into intact human skin nerves. Unitary discharges deriving from A fibres were often encountered and sometimes even single C unit deflections were identified. When several C fibres responded to the stimulation, a compact time presentation of the filtered and dot-converted spikes improved the discrimination of individual spikes time-locked to the stimulation, so that unitary C elements could often be identified in the treated records even if the signal-to-noise ratio of the original signals was low. Increases in latency or blockings were traced in both A and C unit responses to repeated excitation, but the influence of repeated activation was more pronounced in thin nerve fibres even at low stimulation frequencies. The decreased excitability of thin nerve endings on repetitive stimulation suggests that not only central factors but also excitation failure in peripheral thin nerve fibres might be responsible for the decrease in pain perception experienced during local intense electrical intradermal stimulation at high frequencies.

Microelectrode and current clamping techniques have been used to investigate the electrical properties of the salt gland of Aegiceras corniculatum Blanco. Three regions of the gland corresponding to the cuticular cap, secretory cells, and the basal cell are distinguishable according to their resting potential and voltage response characteristics. The resting potentials of the secretory cells and basal cells are shown to be markedly negative with respect to the cuticular cap and the surface of the gland. Penetration of the base of the gland always results in a sharp drop in the resting potential. It is also shown that there exists a low resistance pathway from the cuticular region to the underside of the gland which shunts the secretory cells, and that the cuticular cap presents a high electrical resistance. The resting potential and voltage response at various positions in the gland were also measured with variation in leaf illumination. It is shown that the resting potential becomes less negative throughout the gland for the transition light to dark. A similar change in illumination generally produces a rise in voltage response.

In the isolated rabbit hearts the presence of an electrical longitudinal dissociation in the atrial portion of the His bundle was examined by the microelectrode method. Under the normal condition no marked differ-ence was found in the duration of the action potential of the cells at the same transverse level of the His bundle. However, the possibility of separation to at least dual pathways of the His bundle was disclosed, when the arrival time of excitation was observed or when, in addition, the site of stimulation was changed or intracellular stimulation was applied.By passing the current intracellularly into the His bundle the elec-trotonic potential was found to be large in a direction parallel to the running of the His bundle while it was found to be almost zero in a direc-tion perpendicular to it. The longitudinal electrical separation was pre-sumed, however, not to be complete under the normal condition, because the intracellular stimulation of one tract was found to be transmitted to the other tract and the spontaneous activity of one tract was found to be conducted to the other tract. A high potassium content or low sodium content did not increase the longitudinal separation markedly in most cases. But in 1 experiment a high potassium content increased it, showing a possibility that under abnormal conditions a complete longitudinal electrical dissociation may occur.

The Krogh capillary-tissue cylinder arrangement has been modeled and solved to include interaction between the capillary and tissue. Sophisticated, distributed, and simple lumped parameter equations have been used to describe the system. Solutions have been investigated using digital, analog, and hybrid computer techniques. Results from the simulations have been compared with experimental tissue response data obtained with oxygen microelectrodes inserted in the brain of anesthetized, curarized cats. Comparisons indicated that autoregulatory mechanisms play an important role in determining the characteristic tissue oxygen tension response to arteriole oxygen tension upsets. Theoretical control mechanisms have been postulated and superimposed on the capillary-tissue models to explain the temporal behavior of brain oxygen tension during conditions of anoxic-anoxia. Preliminary evidence indicates an active, inhibitory (Protective) mechanism for oxygen in brain. A hybrid computer simulation of interacting regions of brain gives a possible explanation for such a mechanism.

Re-evaluation of microelectrode methodology for the in vitro determination of pH and bicarbonate concentration. The behavior of glass, antimony and quinhydrone microelectrodes was evaluated in an in vitro system in which the pH of 25- to 35-nl droplets of standard bicarbonate solutions (equilibrated with various concentrations of CO 2 gas) and of proximal tubular fluid samples was determined. Whereas measurements with both the glass and quinhydrone microelectrodes closely approximated the theoretical pH, the antimony microelectrodes provided readings from 0.13 to 0.18 pH units below the theoretical values in solutions of 10- to 50-mM bicarbonate gassed with 5% CO 2 . While the antimony microelectrode pH was also invariably lower than glass at 10 and 15% CO 2 , the magnitude of the difference was smallest when the absolute pH of the solution was lowest (low bicarbonate concentration and high P CO 2 ). The relative performances of the electrodes was not altered by the addition of physiological amounts of phosphate to the solution, and similar results to those observed in standard solution were obtained in tubular fluid samples. The failure of the antimony electrode to provide accurate in vitro data raises questions as to its suitability for in vivo application. Reevaluation de la methode de la microelectrode pour la determination in vitro du pH et de la concentration de bicarbonate. Le comportement de microelectrodes de verre, d'antimoine et de quinhydrone at ete evalue dans un systeme in vitro dans lequel le pH de gouttes de 25 a 35 nl de solutions standard de bicarbonate (equilibrees avec des concentrations variables de CO 2 ) et d'echantillons tubulaires proximaux a ete determine. Alors que les determinations obtenues avec les microelectrodes de verre et les microelectrodes a la quinhydrone sont tres proches du pH theorique, les electrodes a l'antimoine donnent des lectures inferieures aux valeurs theoriques de 0,13 a 0,18 unites pH dans des solutions de 10 a 50 mM equilibrees avec du CO 2 5%. Alors que le pH donne par la microelectrode a l'antimoine est toujours inferieur a celui donne par l'electrode de verre a 10 et 15% de CO 2 , l'importance de la difference diminue quand la valeur absolue du pH de la solution est plus faible (concentration basse de bicarbonate et P CO 2 elevee). Les performances relatives des electrodes ne sont pas modifiees par l'addition de quantites physiologiques de phosphate a la solution et des resultats semblables a ceux observes dans les solutions standards sont obtenus pour les echantillons tubulaires. L'impossibilite d'obtenir des valeurs precises in vitro avec l'electrode a l'antimoine pose le probleme de son adequation a des applications in vivo .

This paper describes techniques for the fabrication of flexible microelectrodes for recording and stimulation within the human body. The intention of the effort was to develop a prototype microelectrode array for selective electrical stimulation of the cochlear nerve in cases of profound sensory deafness. The prototype array is formed on both sides of a thin-film plastic insulating substrate† and consists of platinum conductor-elements, 0·3 μm thick and 12·7 μm wide, terminating at electrode surfaces, 250 μm wide. Metallisation of the substrate is accomplished by sputtering, and the electrode patterns are defined by photolithographic-etching techniques. Insulation of the array is achieved by dip coating in Silastic. Short term (nonstimulated) animal-tolerance studies indicate that the electrodes are biologically inert. Long-term implant studies are currently in progress, and experiments are planned to determine tissue-reaction and electrolytic-dissolution effects due to prolonged electrical stimulation. Microelectrodes using the fabrication techniques described can be applied, in practically any geometry desired, to the development of functional sensory and motor prostheses. Cet article decrit des techniques de fabrication de microelectrodes flexibles servant a l'enregistrement et a la stimulation a l'interieur du corps humain. Ces travaux avaient pour but de developper le prototype d'un systeme de microelectrode pour la stimulation electrique selective du nerf cochleaire dans les cas de sourdesse sensorielle profonde. Le systeme prototype est forme de part et d'autre d'un film plastique fin d'une substance isolante (Mylar, Teflon ou Parylene) et consiste d'un element conducteur en platine de 0,3 μm d'epaisseur et de 12,7 μm de largeur, se terminant aux surfaces d'electrodes de 250 μm de largeur. La metallisation de la substance se fait par crepitement et es traces de l'electrode sont accomplis par des techniques de gravure photolithographique. L'islolement du systeme se fait par plongee dans un bain de Silastique. Des etudes de tolerance a court terme sur animaux (non stimules) ont indique que l'electrode est biologiquement inerte. Des etudes d'implantation a long terme sont en course, les experiences ont pour intention de determiner les reactions des tissus aux effets de dissolution electrolytique causes par une stimulation electrique prolongee. Les microelectrodes confectionnees d'apres les techniques decrites, peuvent etre appliquees selon pratiquement n'importe quelle geometrie desirees, au developpement de protheses motrices et sensorielles fonctionnelles.

The oculomotor nucleus of the cat was investigated by means of the marking microelectrode technique. By antidromic spike response to stimulation of the respective oculomotor nerve branch, inferior rectus, medial rectus, superior rectus and inferior oblique neurons were identified, and their locations were determined histologically. (1) The antidromic spike latency of 27 inferior rectus units was between 0.4 and 3.0 msec, and the conduction velocity calculated on this group was between 12.0 and 90.0 m/sec. The inferior rectus neurons were predominantly located in the ventro-rostral part of the somatic oculomotor nucleus ipsilateral to the stimulated nerve. (2) The antidromic latency of 39 medial rectus units ranged from 0.5 to 2.1 msec, the conduction velocity along their axons was 14.5 and 64.0 m/sec. The medial rectus neurons were located in the dorsorostral part of the somatic nucleus ipsilateral to the stimulated nerve. (3) The antidromic latency of 17 superior rectus units was between 0.5 and 3.0 msec, and the mean conduction velocity was 27.2 m/sec. The superior rectus neurons were located in the most caudal part of the somatic nucleus contralateral to the stimulated nerve. (4) The antidromic latency of 34 inferior oblique neurons was between 0.4 and 6.6 msec, and the mean conduction velocity was 23.4 m/sec. The inferior oblique neurons were located in the dorsocaudal part of the somatic nucleus ipsilateral to the stimulated nerve.

Impedance measurements are necessary to determine the passive electrical properties of cells including the equivalent circuits of the several pathways for current flow. Such measurements are usually made with microelectrodes of high impedance (some 15 MOmega) over a wide frequency range (1-10,000 Hz) and so are subject to many errors. An input amplifier has been developed which has negligible phase shift in this frequency range because it uses negative feedback to keep tiny the voltage on top of the microelectrode. An important source of artifact is the extracellular potential produced by capacitive current flow through the wall of the microelectrodes and the effective resistance of the bathing solution. This artifact is reduced some 10 times by shielding the current microelectrode with a conductive paint. The residual artifact is analyzed, measured, and subtracted from our results. The interelectrode coupling capacitance is reduced below 2 x 10(-17) F and can be neglected. Phase and amplitude measurements are made with phase-sensitive detectors insensitive to noise. The entire apparatus is calibrated at different signal to noise ratios and the nature of the extracellular potential is investigated. The phase shift in the last 5-20 mum of the microelectrode tip is shown to be small and quite independent of frequency under several conditions. Experimental measurements of the phase characteristic of muscle fibers in normal Ringer are presented. The improvements in apparatus and the physiological significance of impedance measurements are discussed. It is suggested that the interpretation of impedance measurements is sensitive to small errors and so it is necessary to present objective evidence of the reliability of one's apparatus and measurements.

The resting potential of various parts of the AV nodal regions of an excised rabbit heart was changed by applying constant electrical current with a suction electrode. The membrane potential was recorded with an intracellular microelectrode and the maximum rate of rise of depolarization was computed. The action potential recorded from the AV nodal cell responded to constant current in a manner qualitatively similar to other myocardiums. The relationship between resting potential and amplitude of action potential was expressed by a straight line, while a sigmoidal relationship was observed between the resting potential and the maximum rate of rise of depolarization. Most of the initial current system in alpha region was inactivated at the control membrane potential. The maximum value of the maximum rate of rise of depolarization of alpha region was 30 V/sec which was lower than that of other parts of the nodal region.

Electrolysis measurements have been made on electrodes of platinum, stainless steel, tungsten, iridium, palladium, rhodium, rhenium, gold, tantalum, titanium, zirconium, and some conducting oxides of the tungsten bronze family. Electrodes were immersed in physiologic saline solution and subjected to biphasic rectangular current pulses of various current densities at 50 pps, 24 hours per day for periods up to nine months. Weight loss was recorded at intervals during this time. We conclude that iridium,rhodium, platinum and palladium are extremely resistant to electrolysis under these conditions and electrolysis under 5? thick, made of such materials should have lifetimes on the order of decades. Gold is somewhat poorer but probably acceptable; all the other materials tested, including tungsten and stainless steel, are unacceptable as chronic microelectrode materials.

Explant cultures were prepared from the slow anterior latissimus dorsi muscle and the fast posterior latissimus dorsi muscle of 15 day chick embryos. The morphology and growth pattern of myotubes from the two types of muscle were very similar. Intracellular microelectrode studies did not reveal consistent differences between the myotube types in regard to resting potential, input resistance, input time constant, or ability to produce active electrogenic responses. It is suggested that specific differentiation of the two muscles is determined by their innervation.

An implanted microelectrode technique for recording unit activities from the free-moving cat is described. Stainless steel insect pins electrically sharpened to about 10 μ tip, insulated, are soldered to about 10 cm long lead-off wire. After the electrodes are inserted to predetermined regions in the brain, their lead wires are soldered to a modified 9-pin miniature socket. The electrodes, lead wires and socket were then cemented to the skull with acrylic resin. The socket was fitted to 9-pin miniature plug which contained an input FET stage. We could selectively connect it with one of 8 leads from implanted microelectrodes. The input probe was separated from the main amplifier chassis, the connection made by about 50 cm long flexible lead wires so that the animal could move about freely. This input probe greatly reduced the artifact due to animal movement. The device could thus be used for unit recording from operantly behaving cats.

This is the first direct potentiometric determination of intracellular bicarbonate concentration. The new method involves the use of a double-barrelled HCO3 −-selective liquid ion-exchange microelectrode that permits the simultaneous determination of intracellular [HCO3 −] and membrane PD of single cells. The mean in situ intracellular [HCO3 −] of single striated muscle fibers was 4.4±0.3 mM/l in the frog and 12.6±0.6 mM in the rat. Both values are inconsistent with a Donnan equilibrium distribution and can be accounted for by an active HCO3 − influx or an active H+ efflux. During progressive acute hypercapnia there is an accumulative build-up of intracellular bicarbonate in rat skeletal muscle. The increase in intracellular [HCO3 −] with hypercapnia is strictly proportional to the associated increase in plasma [HCO3 −], thus maintaining a constant ratio of extracellular: intracellular [HCO3 −]. Using the directly measured [HCO3 −] in cell water, we calculate a cell pH of 7.00 for frog fibers and of 7.14 for rat fibers, both values being about 1.1 pH units on the alkaline side of those predicted for a Donnan equilibrium distribution of H+ ions across the cell membrane.

A steady current (10·10−10–6·10−9 A) was passed by means of a bridge circuit through a recording microelectrode inserted into a horizontal cell of the turtle retina. Illumination of the retina caused an increase in the resistance of the microelectrode circuit (by 10–80 MΩ), causing a change in the shape of the recorded response of the horizontal cell to light. The change in resistance was shown to take place, not on the cell membrane itself, but inside the cell close to the microelectrode tip. The effect described can be reproduced by passing a current through one barrel of a double-barreled microelectrode alongside the recording barrel, but the strength required for this current was greater than that passed through the recording barrel. If the membrane potential of the horizontal cell was made equal to the equilibrium potential (by means of a steady current passed through extracellular electrodes) the hyperpolarization response to light and the effect of the increase in resistance of the microelectrode circuit disappeared simultaneously. On the other hand, artificial hyperpolarization of the cell membrane caused an increase, but depolarization caused a decrease in the resistance of the microelectrode circuit. It is postulated that the observed effect is due to blocking of the microelectrode tip by an intracellular structure whose resistance varies with a change in membrane potential.

Intracellular potentials in the epithelium of the isolated human cornea were studied with 3 M KCl-filled microelectrodes. The average potential profile increased slightly and reached a maximal value in a depth of about 40 μ from the epithelial surface. The maximal potentials of 27.4±1.5 m V in a closed chamber of the Ussing-Zerahn type and 45.3±1.7 mV in an open chamber were constant up to 180 min after incubation. Using microelectrodes with high resistance the stromal potentials were close to 0 mV. Intracellular potentials were reduced by about 30% 2h after addition of 10−3 M ouabain/l or 10−3 M acetazolamide/l. A significant inhibition could be obtained 30 min after addition of the drugs. Ouabain in a dose of 10−5 M/l showed no inhibitory effect. The data are consistent with the hypothesis of electrolyte transport systems (Na, Cl, HCO3, H) located in the epithelium of the human cornea.

The posterior potential of frog lens has been studied with a microelectrode technique. The lens potential behaved predominantly as a K-electrode, and the slope of the potential for a tenfold change in [K]o, as the product [K]o · [Cl]o was kept constant, was in good agreement with 58 mV predicted from the Nernst equation at high [K]o. The permselectivity of lens membrane towards 90 m m monovalent cations was in the order K + > Rb + > Cs + > NH 4 + . The lens membrane was permeable not only to Cl − but also Br − , I − , NO 3 − , N 3 − , SCN − , ClO 3 − , BrO 3 − , and formate, but not to acetate, propionate, and aspartate. Na + was a much less contributive ion as compared with either K + or Cl − on the lens potential.

Electrical properties of the axon membrane were examined under internal perfusion of squid giant axons with a dilute solution of NaF or CsF. The rate of propagation of the action potential was markedly enhanced when NaCl was added to the external CaCl 2 solution. The membrane conductance both at rest and during the action potential was increased with increasing Na-concentration in the external medium. In the perfusion zone of these axons, the action potentials in different parts of the membrane were found to terminate in a more-or-less spatially random and temporally irregular fashion. When the electric field outside the axon membrane was examined with hyperfine glass-pipette electrodes, small rectangular potential changes of uniform amplitude were observed. The small potential changes, which resemble those obtained by Bean in EIM-treated lipid bilayer, were interpreted as indicating spatial non-uniformity of the axon membrane during excitation. The importance of long-range electric interaction between different parts of the axon membrane is emphasized.

Electrochemical properties of cation-selective glass microelectrodes made from NAS 27–04 were studied. There was a marked fall in electrical resistance of the microelectrodes stored in 3 M KCl solution (aging). The resistance was in the range of 2×10 7 to 10 9 Ω, which were much lower than those estimated from the electrical resistivity of dry glass for the equivalent dimensions of microelectrode working tips. This fall in resistance was accompanied by an increase in microelectrode selectivity for K + . The low resistance and increased K + selectivity are desirable features that make the microelectrode more suitable for application to biologic studies. The changes in microelectrode resistance and selectivity were interpreted to be due to hydration of the entire thickness of the glass membrane, resulting in a change in the field strength of anionic sites and formation of ionic channels in the glass membrane. Thus, the fall in resistance is explained by decrease in energy barrier, which is equivalent to the activation energy of interaction between the cations and anionic sites in the glass membrane. Some of the microelectrodes showed a transient depolarization that resembled the action potential of a biological membrane. This transient depolarization was associated with the changes in microelectrode resistance and selectivity. The transient depolarizations suggest the temporary development of wide channels in the membrane permitting free movement of hydrated cations according to the bulk electrochemical gradient.

The effect of the cardiac glycoside ouabain in a concentration of 10−4 M on the electrical properties of the Retzius cells in a segmental ganglion of the central nervous system ofHirudomedicinalis was studied by a microelectrode technique. The first phase of the response is depolarization of the cell membrane by 4–11 mV and an increase in the frequency of spontaneous activity with no change in the electrical resistance, both of which develop after about 1 min. The second phase, taking 2–10 min to complete, is characterized by the cessation of spike activity and by a decrease in the resistance of the membrane, and also by the total disappearance of electrical transmission such as is normally observed between the two cells of the ganglion. The response is reversible by prolonged rinsing to remove the ouabain.

THE GLASS ELECTRODE has been historically the means of measuring interstitial pH. Eisenman and his associates [3] have documented it’s performance characteristics. The disadvantages of the glass electrode are its bulk, fragility, and the distance bet,meen the sensing electrode and the reference electrode. More recently, miniature pH electrodes and microelectrodes have become available 11, 2, 4-61 but most of them require special care. The distance between the sensing surface and the reference surface has been reduced in some of these models, but in most, these surfaces are still too widely separated. A new type of electrode utilizing no glass has been developed and is t,he subject of this report. The pH needle electrode (Fig. 1) is of all-metal construction and is contained within an N-gauge hypodermic ncedlc. Although the needle has been made as short as 2 cm, we have chosen 9 cm as a more convenient size. The ele&rode assembly (Fig. 2) consists of a mercury/mercuric oxide (Hg/HgO) or silver/silver chloride (Ag/AgCl) reference surface and an antimony oxide (Sb,O,) pH sensing surface. The needle electrode is a roncent’ric assembly of the pH sensitive film on a stainless steel subsurface and of the reference surface, which is a silver wire conditioned with either mercury or silver

Although microelectrodes have been in use for many years and there is a wealth of literature concerning their fabrication and application, there is little reported on waveform distortion produced by these electrodes. This paper reports experimental studies conducted to determine the effects of ac electrode polarization in microelectrode recording systems. Electrode materials are examined as well as other system factors such as the use of negative-input-capacitance (NIC) preamplifiers, stimulus isolation units (SIU), and electrode contact integrity.

Passive electrical properties (internal conductance, membrane conductance, low frequency capacity, and high frequency capacity obtained from the foot of the action potential) of normal and glycerol-treated muscle of Xenopus were determined with the intracellular microelectrode technique. The results show that the electrical properties of Xenopus muscle are essentially the same as those of frog muscle. Characteristics of the action potential of Xenopus muscle were also similar to those of frog muscle. Twitch tension of glycerol-treated muscle fibers of Xenopus recovered partially when left in normal Ringer for a long time (more than 6 h). Along with the twitch recovery, the membrane capacity increased. Single isolated muscle fibers of Xenopus were subjected to the double sucrose-gap technique. Action potentials under the sucrose gap were not very different from those obtained with the intracellular electrode, except for the sucrose-gap hyperpolarization and a slight tendency toward prolongation of the shape of action potential. Twitch contraction of the artificial node was recorded as a change of force from one end of the fiber under the sucrose gap. From the time-course of the recorded force and the sinusoidal stress-strain relationship at varying frequencies of the resting muscle fiber, the time-course of isotonic shortening of the node was recovered by using Fourier analysis. It was revealed that the recorded twitch force can approximately be regarded as isotonic shortening of the node.

A modified method for constructing cation-selective glass membrane microelectrodes is described. The method permits routine fabrication of electrodes with tip diameters less than 1 μ and exposed tip lengths of 2 to 5 μ. These electrodes had tip resistances in the range 107 to 109 ohms and gave stable and reproducible potentials in standard NaCl and KCl solutions. Potentials were unaffected by pH in the range 6 to 8 and satisfactory calibration curves were obtained over the temperature range 15 to 25°C. Pairs of electrodes with different K−Na selectivity coefficients were used to measure K+ and Na+ activities in frog sartorius fibers. In fibers containing normal amounts of these ions, Na+ activitywas much less than would be predicted from chemical analysis of the muscles, assuming that all the apparent muscle Na+ is present in an osmotically active form in the myoplasm. Possible origins of this discrepancy are discussed. Following a 48-hr soak at 5°C in a K-free medium, the apparent Na+ concentration and activity of the fibers both increased and the K+ concentration strongly suggests the existence in normal fibers of at least two intrafiber K+ compartments, both of which exchange with external Na+ but only one of which is detectible by a microelectrode located in the myoplasm. Ca++ appears to exert a strong regulatory effect on Na+−K+ exchange between these compartments and the external medium and on the distribution of intrafiber Na+ and K+ between these compartments.

A technique was developed combining multibarrelled glass microelectrode recordings with local superfusion of the caudate nucleus. Haloperidol had a prolonged reversible blocking action on caudate neurones excited orthodromically by substantia nigra stimulation. These cells were unaffected by microiontophoretic applications of dopamine.

The extension of stripping analysis to the determination of halides with a silver microelectrode was investigated. During the preelectrolysis step, a portion of the halide was deposited by a controlled potential oxidation of the silver electrode. Two methods of stripping the silver halide deposit from the electrode were investigated: electrolysis with constant potential, and electrolysis with linearly varying potential. The quantity of electricity measured in the stripping step was a direct function of the preelectrolysis time and the bulk concentration of halide. The method was applied to iodide solutions as dilute as 4 x 10-8 M.

A new cell with a platinum microelectrode is described: the diffusion layer is renewed by the periodical movement of the electrolyte caused by the displacement of a piston. A magnetic field causes the piston displacement. The diffusion current intensities, both instantaneous and average, may be calculated with a good agreement by the simple equation of spherical diffusion. The cell allows many possibilities of regulation both in the period of the electrode washing and in that during which the electrode is in the stationary electrolyte. Moreover, the flow speed of the solution may be easily regulated. This new cell is particularly interesting for the study of many electrochemical processes characterized by a high redox potential.

Practical methods are described in detail for the construction of tungsten microelectrodes. Straightened 127 μm-diameter tungsten wires are etched to sharp points in KNO2 solution. The sharpened wires are insulated by collapsing borosilicate-glass capillaries onto them in a horizontal pipette puller. A novel technique is described for the removal of insulation from electrode tips by embedding them in a softened bead of solder glass. The bead is then allowed to cool, producing clean fractures of the borosilicate glass at the surface of the bead; the bare, undamaged tip of the electrode is then withdrawn. Electrodes with bare tips from 2 μm to more than 100 μm can be prepared with this method. Finally, the tips are plated with a gold cyanide solution and platinum black. The finished electrodes have tapers of less than 2° and yet are extremely strong. Electrodes with conical plated tips 20 μm long by 6 μm diameter have 1 kHz impedances of less than 1 MΨ.

An attempt is made to provide a deeper understanding, based on physical principles, of the factors that govern (and may limit) use of double-barreled ultra microelectrodes. Equations are developed which relate the geometry and material properties inside and outside the electrodes to their resistance and capacitance parameters in appropriate equivalent circuits. These equations show what to expect of the microelectrode and the direction and amount of change required to improve its performance in a particular application. It is shown that glass leakage resistance between barrels is of the order of 10 13 ohms, but this value creates an error of one percent or less in a measurement of coupling resistance in conventional applications. Temperature changes due to heating by the current inside and just outside the tip become important at current levels above one microampere, and combinations of current and medium resistivity are shown which would produce boiling. The time for the fluid around the tip opening to reach steady-state temperatures is calculated to be significantly less than a microsecond.