Microcapillary Electrodes Research Articles

Simultaneous in vivo ascorbate and electrophysiological recordings in rat brain following ischemia/reperfusion

Simultaneous recording of neurochemical signal and electrophysiological activity in the same brain region remains vitally essential to understanding the essences of physiological and pathological events because of the intrinsic chemical and electrical nature of communication between the neurons. However, the difficulty in selectively recording chemical signal with a high temporal resolution in chemically complex central nervous system presents a great challenge for achieving this goal. In this study, we demonstrate a method for simultaneous and real-time recording of ascorbate and electrical signals in live brain by using an integrated dual-mode microelectrode (IDMME), in which a single-walled carbon nanotube (SWNT)-modified carbon fiber microelectrode (CFME) was efficiently integrated with a glass microcapillary electrode. The SWNT-based CFME was served as an electrochemical recording channel to in vivo monitor cerebral ascorbate with a high selectivity and an improved temporal resolution, while the glass microcapillary electrode was employed as an electrophysiological recording channel for single-unit recording in the cerebral system. We found that no reciprocal interference between the two recording channels with the IDMME when constant-potential amperometry was employed for in vivo monitoring of ascorbate. The validity of the IDMME in neurochemical studies was illustrated by concurrently and real-time recording the dynamic changes of cortical ascorbate level and electrophysiological signal in the same brain region of live rats following ischemia/reperfusion. This study essentially offers an effective approach to in vivo monitoring of neurochemical and electrophysiological events in live brain, which is envisaged to be useful for understanding physiological processes involved in brain functions.

Mechanoelectrical transduction in the hydrogel-based biomimetic sensors

The study addresses the phenomenon of mechanoelectrical transduction in polyelectrolyte hydrogels and, in particular, the search of the driving force for the change of the electrical potential of a gel under the applied mechanical stretch. Polyelectrolyte gels of calcium and magnesium salts of polymethacrylic acid were synthesized by the radical polymerization in water solution. Their electrical potential measured by microcapillary electrodes was negative and fall within 100⬜140mV range depending on the nature of a counterion and the networking density of a gel. The rectangular samples (↼10mm in length and 2Ô2mm in cross-section) of gel-based sensors underwent the dynamic axial deformation, and the simultaneous monitoring of their geometrical dimensions and the electrical potential was performed. Sensor elongation resulted in the overall increase of gel volume, and it was always accompanied by the gel potential change toward the depolarization (diminishing of the negative values). Theoretical model based on the assumption of the total electrical charge conservation in the course of the dynamic deformation of a filament was proposed to describe the dependence of the electrical potential of a gel on its volume. Good agreement between the predictions of the model and the experimental trend was shown. The proposed mechanism of mechanoelectrical transduction based on the stretch-dependant volume changes in polyelectrolyte hydrogels might be useful to understand the nature of mechanical sensing in much more complex biological gels like the cell cytoskeleton.

20pm3-PM010 マイクログローコロナによる微量ガスの発光スペクトル測定

This paper presents the emission spectra of micro glow-corona, which is generated at the tip of a micro-capillary electrode with a diameter of 1 μm in Ar, He, and N_2 atmospheres. The spectra are different from reference spectra on the database; some peaks observed in spectra of the glow corona do not appear in the reference spectra, and vice versa.

Single-cell lysis for visual analysis by electron microscopy

The stochastic nature of biological systems makes the study of individual cells a necessity in systems biology. Yet, handling and disruption of single cells and the analysis of the relatively low concentrations of their protein components still challenges available techniques. Transmission electron microscopy (TEM) allows for the analysis of proteins at the single-molecule level. Here, we present a system for single-cell lysis under light microscopy observation, followed by rapid uptake of the cell lysate. Eukaryotic cells were grown on conductively coated glass slides and observed by light microscopy. A custom-designed microcapillary electrode was used to target and lyse individual cells with electrical pulses. Nanoliter volumes were subsequently aspirated into the microcapillary and dispensed onto an electron microscopy grid for TEM inspection. We show, that the cell lysis and preparation method conserves protein structures well and is suitable for visual analysis by TEM.

A Generalized Tip-Membrane Contact Detection Algorithm for Automated Single Cell Electroporation Using Statistical Process Control

This work presents a fully automated method for detecting the contact between a microcapillary tip and a cell membrane based on a statistical process control (SPC) algorithm known as the double-sided cumulative sum (or "cusum"). By analyzing current measurements obtained through a microcapillary electrode, the proposed goal of this system is to determine when tip-to-membrane (tip-membrane) contact occurs using thin adhered cells (e.g., less than 10 μm) for the purposes of fully automated robotic-assisted, single cell electroporation (SCE) - a powerful method of gene transfection. This SPC algorithm is robust against uncontrollable system parameters such as system noise common in electrode-based systems, nonstationary processes, and variations in the physical parameters of cells. The proposed algorithm was successfully demonstrated on adhered mammal cells as small as 4 μm in thickness and using tip-placement velocities from 1 to 8 μm/s. In addition, a novel method of experimentation is described correlating optical measurements between tip-membrane proximity and changes in i <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cct</sub> during the tip-placement sequence.

Lasing to ground state of ions in discharge created plasma in microcapillary

The objective of this paper is to present the results of recent experiments on lasing to ground state in H-like LiIII ions in microcapillary plasma. The experiments were conducted at both Princeton University and NRL. Two methods were used to fill the microcapillaries with plasma: ablation of microcapillary walls when irradiated with a low power laser beam of a few ns duration, or fast electrical discharge. Powerful subpicosecond laser beams (with wavelength of 0.25 μm at Princeton University and 1.053 μm at NRL) were used for longitudinal pumping of microcapillary plasma following by the fast recombination and gain generation in the transition to ground state of hydrogen-like LiIII ions. In these experiments the dependence of the gain on the specific method of the preplasma creation, electric discharge versus low-power laser, pumping laser wavelength (0.248 μm versus 1.053 μm), and the geometry of the experiment (microcapillary dimensions and electrode design) were investigated. Results of these investigations are presented and discussed with the particular emphasis on the experiments with the 1μm subpicosecond laser pumping of discharge-produced microcapillary plasma.

Plasmodesmatal frequency in relation to short‐distance transport and phloem loading in leaves of barley (Hordeum vulgare). Phloem is not loaded directly from the symplast

We investigated the phloem loading pathway in barley, by determining plasmodesmatal frequencies at the electron microscope level for both intermediate and small blade bundles of mature barley leaves. Lucifer yellow was injected intercellularly into bundle sheath, vascular parenchyma, and thin‐walled sieve tubes. Passage of this symplastically transported dye was monitored with an epifluorescence microscope under blue light. Low plasmodesmatal frequencies endarch to the bundle sheath cells are relatively low for most interfaces terminating at the thin‐ and thick‐walled sieve tubes within this C3 species. Lack of connections between vascular parenchyma and sieve tubes, and low frequencies (0.5% plasmodesmata per μm cell wall interface) of connections between vascular parenchyma and companion cells, as well as the very low frequency of pore‐plasmodesmatal connections between companion cells and sieve tubes in small bundles (0.2% plasmodesmata per μm cell wall interface), suggest that the companion cell‐sieve tube complex is symplastically isolated from other vascular parenchyma cells in small bundles.The degree of cellular connectivity and the potential isolation of the companion cell‐sieve tube complex was determined electrophysiologically, using an electrometer coupled to microcapillary electrodes. The less negative cell potential (average –52 mV) from mesophyll to the vascular parenchyma cells contrasted sharply with the more negative potential (–122.5 mV) recorded for the companion cell‐thin‐walled sieve tube complex. Although intercellular injection of lucifer yellow clearly demonstrated rapid (0.75 μm s‐1) longitudinal and radial transport in the bundle sheath‐vascular parenchyma complex, as well as from the bundle sheath through transverse veins to adjacent longitudinal veins, we were neither able to detect nor present unequivocal evidence in support of the symplastic connectivity of the sieve tubes to the vascular parenchyma. Injection of the companion cell‐sieve tube complex, did not demonstrate backward connectivity to the bundle sheath.We conclude that the low plasmodesmatal frequencies, coupled with a two‐domain electropotential zonation configuration, and the negative transport experiments using lucifer yellow, precludes symplastic phloem loading in barley leaves.

KCl leakage from microelectrodes and its impact on the membrane parameters of a nonexcitable cell.

Microcapillary electrodes filled with a variety of salt solutions, including 1m KCl, have been used to measure the membrane potentials and resistances of spherical cells from the mycelial fungusNeurospora (cell diameters 15–25 μm, cell volumes 3–8 pl). During impalements with electrodes containing 0.3–1.0m KCl, membrane potential and resistance decayed over a period of 3–10 min. In contrast, electrodes filled with 0.1m KCl gave stable membrane potentials of −180 mV and membrane resistivities of 40 kΩ cm2, values comparable to earlier results from the fungal hyphae. Salt leakage from 1.0m KCl-filled electrodes (tip diameters 0.2–0.3 μm, resistances 50–75 MΩ) occurred at rates of 4–5 fmol sec−1, as indicated by direct intracellular measurements with ion-sensitive microelectrodes. Depending on cell size, such leakage rates could elevate cytoplasmic KCl content at initial rates of 30–170 mM min−1, and actual values as high as 70mm min−1 were observed. Salt leakage and changes in cytoplasmic KCl concentration were reduced five- to sevenfold when impalements were made with electrodes containing 0.1m KCl. The effects on cell membrane parameters of salt leakage from microelectrodes could be attributed to chloride ions. Substitution of the KCl electrolyte with half-molar K2SO4 or Na2SO4 and molar concentrations of K- and Na-MES [potassium and sodium 2-(N-morpholino)ethanesulfonate] gave stable membrane potentials in excess of −200 mV and membrane resistivities greater than 50 kΩ cm2, while the permeant anions NO 3 − and SCN− depressed the membrane parameters in a manner similar to that observed with 1m KCl. Furthermore, modest elevation of cytoplasmic chloride concentration (below ca. 50 mM) affected both membrane potential and resistance in direct proportion to the concentration, and could be quantitatively described by the Constant Field Theory with a fixed membrane permeability (P Cl∼4×10−8 cm sec−1). Higher cytoplasmic chloride levels produced a collapse of the membrane resistance and drastic depolarization in a fashion requiring large changes of membrane permeability. At least for cells with volumes of 10 pl or less, the standard practice of filling electrodes with 1 or 3m KCl should be abandoned. Half-molar (and lower) concentrations of K2SO4 or Na2SO4 are suggested as satisfactory replacements.

Light-induced Changes of the Electrical Potential in Chloroplasts Associated with the Activity of Photosystem I and Photosystem II

The electric potential changes induced by flashing and continuous light were measured with microcapillary electrodes in isolated whole chloroplasts of Peperomia inetallica. In continuous light the chloroplast electrical potential rose in two phases. The initial rapid phase coincided in extent with the flash-induced potential and was insensitive to the electron transfer inhibitor DBMIB. The subsequent phase was relatively slow (20–30 ms) and was inhibited by DBMIB. Electron acceptors of photosystem II (p-phenylendiamine, p-benzoquinone) added to DBMIB-treated chloroplasts produced a suppression of the flash-induced response and a considerable increase in the steady level of the potential in the light. The electrical potential associated with the activity of photosystem II rose in continuous light much more slowly than that associated with the activity of photosystem I alone or the activities of both photosystems. Illumination of chloroplasts with successive flashes at a repetition rate 5 Hz in the presence of oxaloacetate, a terminal acceptor of photosystem I, was accompanied with a gradual decline of the flash-induced potential. The specific role of two photosystems in the light-induced H+ transport and the electrogenesis across the chloroplast thylakoid membranes is discussed.

Graded potentials and action potentials in the large ocellar interneurons of the bee

The response characteristics to light stimuli of first order ocellar interneurons in the bee (Apis mellifera carnica) were analysed with intracellular recordings. The neurons were identified using intracellular dye injection (Lucifer yellow). The responses of L-(large) neurons can vary. They range from transient graded hyperpolarizations in response to light-On and -Off, (sometimes accompanied by tonic hyperpolarization during the light stimulus), to spontaneous tonic action potentials which are inhibited by light. Some neurons show both hyperpolarizations and action potentials. The varying responses to light stimuli are dependent only on the state of the L-neuron and are not correlated systematically with particular types of L-neurons. The experiments demonstrate that the action potentials are generated within the L-neurons and are not conducted antidromically from other neurons. The amplitude and frequency of the action potentials depend on the membrane potential of the L-neuron. With light stimulation, or application of hyperpolarizing current, spikes can be generated within some of the L-neurons. Presumably non-spiking L-neurons are refractory due to maintained depolarization. They have membrane potentials of about −40 mV. Action potentials in L-neurons were recorded only with high resistance microelectrodes. The vitality of the animal can not be correlated with the occurrence of spikes. Functional significance of spontaneous tonic spike discharges in L-neurons is discussed in the context of behavioural experiments in the bee. It is possible, that a given L-neuron uses either spiking or non-spiking signal transmission depending on the behavioural situation. Although very fine microcapillary electrodes were used, no successful recordings or stainings of S-(small) neurons in the ocellar nerve were achieved. Therefore, results of non-identified ocellar interneurons which have been attributed to S-neurons should be critically reviewed.

Effect of dicyclohexylcarbodiimide on the proton conductance of thylakoid membranes in intact chloroplast

The effects of dicyclohexylcarbodiimide, a potent inhibitor of chloroplast ATPase, on the light-induced electric potential changes in intact chloroplasts of Peperomia metallica and of a hornwort Anthoceros sp. were investigated by means of glass microcapillary electrodes. The characteristics of potential changes induced by flashes or continuous light in chloroplasts of both species are similar except for the phase of potential rise in continuous light, which is clearly biphasic in Anthoceros chloroplasts. Dicyclohexylcarbodiimide at concentration 5 · 10 −5 M completely abolishes the transient potential undershoot in the light-off reaction but has little effect on the peak value of the photoelectric response. The membrane conductance in the light and in the dark was tested by measuring the decay kinetics of flash-generated potential in dark-adapted and preilluminated chloroplasts. In the absence of dicyclohexylcarbodiimide, preillumination causes a significant acceleration of the potential decay. The light-induced changes in the decay kinetics of flash-induced responses were abolished in the presence of dicyclohexylcarbodiimide, whereas the rate of potential decay in dark-adapted chloroplasts was not altered by dicyclohexylcarbodiimide. The results are consistent with the notion that dicyclohexylcarbodiimide diminishes H + conductance of energized thylakoid membranes by interacting with the H + channel of ATPase. The occurrence of a lag (approx. 300 ms) on the plot of potential undershoot (diffusion potential) versus illumination time might suggest the increase in H + permeability coefficient of thylakoid membrane during illumination.

Extracellular potassium activity, intracellular and extracellular potential responses in the spinal cord.

1. Microcapillary electrode assemblies of two or three channels were used to record extracellular and intracellular potentials together with the extracellular activity of potassium ions, from essentially single locations within the substance of the decapitate spinal cord of cats. A liquid ion exchanger filled the tip of the potassium sensing microprobe. Activity was evoked by electrical stimulation of afferent peripheral nerves (ventral roots were cut). 2. Within the substance of the spinal grey matter increments of extracellular potassium activity evoked by repetitive afferent volleys were precisely correlated with magnitudes of sustained shifts of extracellular electric potential. Raising [K+]o from 3 to 4 mM was associated with a negative shift of potential of 2-5 +/- 0-5 mV, regardless of the position of the electrode in the tissue, and regardless of treatment by convulsant or depressant drugs. 3. The spatial distribution of the responses of potassium activity was mapped by the spatial distribution of the negative sustained potential shifts. 4. Depolarization shifts of potential recorded from within neuroglia cells ran parallel with changes of extracellular potassium potential. Even though the magnitude of extracellular sustained potential shifts was precisely correlated with the responses of both extracellular potassium and intracellular glial potentials, the trajectory of sustained potential shifts did not exactly mirror the two other variables. Onset and offset of sustained potential shifts were faster than those of glial potentials or of extracellular potassium. 5. The responses of the true transmembrane potential (intracellular less extracellular potential shifts) of neuroglia cells in the spinal grey matter can fully be described by the Nernst equation. 6. Membrane potentials of neurones, potentials recorded from dorsal root filaments, or from white matter, appeared unrelated to the activity of potassium ions in extracellular fluid. 7. The results are compatible with the suggestions that changes of the membrane potential of spinal neuroglia cells are fully determined by the change of the activity of extracellular potassium, and that glia cells supply most of the current which generates sustained shifts of the extracellular potential of spinal grey matter. The results are hard to reconcile with suggestions that under conditions of moderate excitation (i.e. in the absence of convulsive neuronal activity) changes of extracellular potassium would significantly influence the membrane potential of spinal neurones, or of primary afferent nerve fibres.

The Transport of Potassium to the Xylem Exudate of Ryegrass

The membrane potentials of ryegrass root cells (Evo) were found to be linearly related to the logarithm of the external KC1 concentration ([KC1]0), over the range 0-1 to 20-0 mM. Exuda tion was studied over the same concentration range. The concentration of potassium in the exudate did not vary significantly with [KC1]0 but the rates of movement of water and potassium to the exudate (/h2o and /K respectively) and the electrical potential and electro chemical potential for potassium in the exudate (Exo and ApLx0iK respectively) all tended to de crease as [KC1]0 increased. There was a very highly significant correlation between/K and /Hi0. By rapidly increasing [KC1]0 and following the depolarization, two components of Exo were observed. The first of these was instantaneous and was attributed to Evo of the epidermal cells. The second component, a gradual repolarisation which commenced about 9 min later, was attributed to Evo of the stelar cells. With an additional contribution from electro-osmosis, these two components quantitatively account for Exo. The implications of these data for the mechanism of radial ion transport in roots are discussed and it is concluded that the stelar cells are not exclusively specialized for transport ing potassium into the xylem vessels. INTRODUCTION In the preceding paper (Dunlop, 1973) it was reported that data on the transport properties of cells of ryegrass roots did not support the stelar pump proposed by Lauchli, Spurr, and Epstein (1971) and Pitman (1972). They were consistent with results for maize (Dunlop and Bowling, 1971a) and sunflower (Bowling, 1972) and indicated that there was no specialized mechanism for the radial transport of potassium operating exclusively in the stelar cells. Using their data for membrane potentials, Evo, and potassium concentrations in the xylem exudate, [K]x, of maize roots, Dunlop and Bowling (1971c) were able to calculate values for the electrical potential, Exo, and the electrochemical potentials for potassium, A/ZxoK, and chloride, A/ZxoC1, in the xylem exudate which agreed well with the measured values. They were also able to explain quantitatively the time course of the depolarization of Ex0 caused by an increase in the external KC1 concentration [KC1]0. This supported their model of radial ion transport, which is based upon the uniformity of the ion transport properties of the cells involved. The application of this approach to ryegrass roots is reported in this paper. 5160.1 B This content downloaded from 157.55.39.95 on Sat, 11 Jun 2016 06:38:31 UTC All use subject to http://about.jstor.org/terms 2 Dunlop—Transport of Potassium to the Xylem Exudate of Ryegrass. II MATERIALS AND METHODS Ryegrass seeds (Lolium multiflorum Lam. var. 'Grasslands Paroa') were germinated in distilled water, grown for 4 d in 0-1 mM CaCl2, and then for a further 24 h on the experimental solution (KC1 plus 0-1 mM CaCl2) before being used. Illumination of 4300 lx was provided by fluorescent tubes for 16 h each day. The apical 4-0 cm of roots were excised and sealed into 5 p Microcap microcapillaries with a lanolin-paraffin wax mixture. The Microcaps were adjusted in holders, which contained five roots each, so that the roots were almost completely immersed in the experimental solution. There were 450 ml of solution for each holder and this was maintained at 25 °C and continuously aerated. After 24 h Exo was measured with 3 M KCl-agar micro salt bridges connected to a Keithly model 602 Electrometer by Ag/AgCl wires and coaxial cable. The volume of the exudate was determined by measuring the length of microcapillary it occupied and then diluted to 1-0 ml for potassium analysis by flame photometry. There were between 10 and 20 replicates for each concentration. The membrane potentials of cells between 7 and 15 mm from the root apex were determined with microcapillary electrodes as described in the preceding paper (Dunlop, 1973).

Localized intracellular potentials from pre- and postsynaptic components in the external plexiform layer of an insect retina

Intracellular potentials from the retina of the flyCalliphora erythrocephala were recorded by means of microcapillary electrodes. The type of cell examined and the exact locus of the recording sites were identified. The potentials were shown to come from the axons of visual cells (presynaptic) and from the axons of monopolar neurons (postsynaptic). The light stimulus employed consisted of step, impulse and sine-wave forms. The presynaptic responses consisted of graded depolarizing potentials while the postsynaptic responses were of a hyperpolarizing type. The former potentials had a slower time course than the postsynaptic potentials and they differed from these latter potentials by another transfer function. Problems were discussed concerning the presynaptic potential in its function as a generator potential for the postsynaptic potentials; and the transduction properties of the synapse. The synapse works as a frequency dependent amplifier with a synaptic delay of 1 msec.

Microelectrode records from a cockroach thoracic ganglion: Synaptic potentials and temporal patterns of spike activity

1. 1. E.p.s.p.s and i.p.s.p.s † † E.p.s.p.s = excitatory postsynaptic potential; i.p.s.p.s = inhibitory post-synaptic potentials. were recorded from cells in the cockroach third thoracic ganglion, using microcapillary electrodes filled with 3 M KCl. 2. 2. Spike response patterns indicating complex integrative activities at the single cell level were also recorded.

The effect of electrolytes of the general formula XCl 2 on the response of the type 1 labellar chemoreceptor of the blowfly, Phormia

An analysis has been made of the electrical responses of the type 1 labellar (‘salt’) chemoreceptor cell of Phormia regina when stimulated with solutions of divalent metal salts. Electrophysiological measurements were made by side-wall penetration of the receptor process with glass microcapillary electrodes. A mean, unstimulated response frequency of 3·3 impulses/sec is totally suppressed by all concentrations of CaCl 2 between 0·05 mM and 100 mM. The characteristic off-discharges following CaCl 2 stimuli (concentrations 0·8 mM to 100 mM) have similar time-courses of spike frequency, but at 0·6 mM, and below, little or no off-discharge can be detected. Suppression of response, with no off-discharge, is attributed to high electrical resistance of the receptor tipchamber rather than to any specific effect of the solute. The time course of off-discharge remains unaffected by the duration of CaCl 2 application between 70 and 500 msec, but is scarcely elicited, or absent, after stimuli of 50 msec or less. Concentrations of CaCl 2≥1 mM are needed to cause hyperpolarization of the receptor membrane. Above 1 mM, the hyperpolarization potential is proportional to the logarithm of the excess concentration of CaCl 2 and may be due to excess Cl − ion on the outside of the receptor membrane. Much higher concentrations of CaCl 2 are needed in mixtures with KCl to suppress the response completely than will arrest unstimulated discharge, e.g. 0·9 M CaCl 2 with 0·8 M KCl. Equal activities of Ba 2+, Sr 2+, Ca 2+, Mg 2+ and Be 2+ as chlorides mixed with KCl in the stimulus solution are able to depress discharge frequency to differing extents. Calcium is most effective, the other cations exerting a diminishing effect as their atomic numbers diverge from that of calcium. Other calcium salts (nitrate, iodide, and acetate) fully suppress the unstimulated response of the type 1 cell at 2, 20, and 100 mM concentrations, further emphasizing the importance of the cation in this effect.

Ion distribution and transport in the red marine algae, gracilaria foliifera.

1. Distribution and transport of alkali and halide ions were studied in Gracilaria foliifera, a red marine alga. Ion concentrations, fluxes and rate coefficients were measured with radioisotopes and standard chemical techniques. The intracellular (vacuole) potential was measured with microcapillary electrodes and a high-impedance voltmeter.2. Intracellular ion concentrations were estimated after correcting for 89% tissue water and 19% extracellular space. Intracellular concentrations of the major ions were (meq./kg. cell water): Na+, 66; K+, 680; Cl-, 462. All of the intracellular ions except I- appeared to be completely exchangeable and were probably in solution in the large cell vacuole.3. Nernst equilibrium potentials, calculated for each ion under conditions of approximate flux equilibrium, were (mv.) : Na+, 50; K+, -105; Rb+, -127; Cs+, -85; Cl-, -4; Br-, -14; and I-, +128. Comparison of these values with the measured vacuole potential of -81 mv. suggested active extrusion of Na+ and active uptake of K+, Rb+, Cl- and Br-. Cesium was in approximate electrochemical equilibrium, and the status of I- was uncertain due to some intracellular binding.4. Cation fluxes were stimulated by light and, to a lesser extent, by exogenous substrate (glutamate). Previous exposure to light had a temporary stimulating effect on cation fluxes, provided oxygen was present. Anaerobiosis (nitrogen) depressed both influx and efflux of cations. Rate coefficients for the cation were in the order Na+ > K+ > Rb+,Cs+.5. Anion fluxes were variably affected by light. Chloride uptake was promoted by light, Br- uptake was slightly stimulated, and I- uptake was depressed. Anion efflux, however, was consistently stimulated by light. Anaerobiosis inhibited the uptake of all anions. Rate coefficients for anion fluxes were similar to each other but were generally lower than the rate coefficients for cation fluxes.6. With the exception of I-, neither light nor anaerobiosis had much effect on the steady-state distribution of ions in Gracilaria. The intracellular I- concentration was much higher in the dark than in the light. This was also found in several other seaweeds, and appeared to be due to an increased amount of bound I- in non-photosynthesizing tissues.

Intracellular stimulation myography in man

A new electromyographic technique is described: an intracellular glass microcapillary electrode, introduced and immobilized by means of a thin trocar, is used for simultaneous stimulating and recording in skeletal muscle fibres in man.

Liquid junction and membrane potentials of the squid giant axon.

The potential differences across the squid giant axon membrane, as measured with a series of microcapillary electrodes filled with concentrations of KCl from 0.03 to 3.0 M or sea water, are consistent with a constant membrane potential and the liquid junction potentials calculated by the Henderson equation. The best value for the mobility of an organic univalent ion, such as isethionate, leads to a probably low, but not impossible, axoplasm specific resistance of 1.2 times sea water and to a liquid junction correction of 4 mv. for microelectrodes filled with 3 M KCl. The errors caused by the assumptions of proportional mixing, unity activity coefficients, and a negligible internal fixed charge cannot be estimated but the results suggest that the cumulative effect of them may not be serious.