Silanization of glass in the making of ion-sensitive microelectrodes

Nitrazepam and 7-aminonitrazepam studied at the macroscopic and microscopic electrified liquid-liquid interface

Two benzodiazepine type drugs, that is, nitrazepam and 7-aminonitrazepam, were studied at the electrified liquid-liquid interface (eLLI). Both drugs are illicit and act sedative in the human body and moreover are used as date rape drugs. Existence of the diazepine ring in the concerned chemicals structure and one additional amine group (for 7-aminonitrazepam) allows for the molecular charging below their pKa values, and hence, both drugs can cross the eLLI interface upon application of the appropriate value of the Galvani potential difference. Chosen molecules were studied at the macroscopic eLLI formed in the four electrode cell and microscopic eLLI formed within a microtip defined as the single pore having 25 μm in diameter. Microscopic eLLI was formed using only a few μL of the organic and the aqueous phase with the help of a 3D printed cell. Parameters such as limit of detection and voltammetric detection sensitivity are derived from the experimental data. Developed methodology was used to detect nitrazepam in pharmaceutical formulation and both drugs (nitrazepam and 7-aminonitrazepam) in spiked biological fluids (urine and blood).

A Quick and Reproducible Silanization Method by Using Plasma Activation for Hydrophobicity-Based Kinesin Single Molecule Fluorescence-Microscopy Assays

Single-molecule assays often require functionalized surfaces. One approach for microtubule assays renders surfaces hydrophobic and uses amphiphilic blocking agents. However, the optimal hydrophobicity is unclear, protocols take long, produce toxic waste, and are susceptible to failure. Our method uses plasma activation with hydrocarbons for hexamethyldisilazane (HMDS) silanization in the gas phase. We measured the surface hydrophobicity, its effect on how well microtubule filaments were bound to the surface, and the number of nonspecific interactions with kinesin motor proteins. Additionally, we tested and discuss the use of different silanes and activation methods. We found that even weakly hydrophobic surfaces were optimal. Our environmentally friendly method significanty reduced the overall preparation effort and resulted in reproducible, high-quality surfaces with low variability. We expect the method to be applicable to a wide range of other single-molecule assays.

Detection of siloxane thin films on glass substrate using IR ratio-reflectance spectrum

In case of thin films of siloxane obtained from different organo-silane derivatives (alkoxy and chloro) on soda lime silica glass substrates, IR-ATR and IR-SR could not detect the organic functional groups of the coating. This becomes even more problematic for the case of tetraethoxysilane (when fully hydrolyzed), the coating of which possesses the same functional groups as the glass substrate. In this work we propose to employ the so-called ratio-reflectance spectra in the v(Si-O) wavenumber region, where both glass and the siloxane coating give most prominent bands, important for the evaluation of the quality of coating formation and qualitative knowledge on its structure. We show that the reflectance-absorbance spectra obtained from the ratio-reflectance spectra are in direct connection to the structure of the siloxane network which depends not only on the chemical nature of the parent silane, but also on the dipping time and the solvent composition. Some characteristics of the reflectance-absorbance spectra, like the appearance of a two well defined bands at 1110 and 975 cm^-1, can be correlated to the film morphology and bridging oxygen number. We support our conclusions using principal component analysis of reflectance spectra, contact angle, AFM and SEM measurements.

Electrochemical Sensing and Imaging Based on Ion Transfer at Liquid/Liquid Interfaces

Here we review the recent applications of ion transfer (IT) at the interface between two immiscible electrolyte solutions (ITIES) for electrochemical sensing and imaging. In particular, we focus on the development and recent applications of the nanopipet-supported ITIES and double-polymer-modified electrode, which enable the dynamic electrochemical measurements of IT at nanoscopic and macroscopic ITIES, respectively. High-quality IT voltammograms are obtainable using either technique to quantitatively assess the kinetics and dynamic mechanism of IT at the ITIES. Nanopipet-supported ITIES serves as an amperometric tip for scanning electrochemical microscopy to allow for unprecedentedly high-resolution electrochemical imaging. Voltammetric ion sensing at double-polymer-modified electrodes offers high sensitivity and unique multiple-ion selectivity. The promising future applications of these dynamic approaches for bioanalysis and electrochemical imaging are also discussed.

How to make calcium-sensitive minielectrodes

In this protocol we describe how to make and use minielectrodes for measuring [Ca(2+)] in small volumes of solution. The minielectrodes are ~2 mm in diameter and have sufficiently low resistances to be used with a standard pH meter. They are made by dipping polyethylene or borosilicate glass tubes (~5 cm long) in a membrane solution. Although the chemicals used to make these Ca(2+)-sensitive minielectrodes are expensive, they can be used to make hundreds of electrodes, each with a useful life of several months.

How to make calcium-sensitive microelectrodes

Ca(2+)-sensitive microelectrodes (CaSMs) directly measure the pCa at their tip, which can be in a small extracellular space or inside a large and robust cell. They do not add to buffering and do not require expensive equipment. But they are time-consuming to make, require a reference electrode in the same location, and tend to create a leak around the point of insertion. In addition, CaSMs only work well with a tip diameter of >1 μm. In this protocol, we describe how to make and use the electrodes and briefly consider possible problems.

Monitoring ion activities in and around cells using ion-selective liquid-membrane microelectrodes

Determining the effective concentration (i.e., activity) of ions in and around living cells is important to our understanding of the contribution of those ions to cellular function. Moreover, monitoring changes in ion activities in and around cells is informative about the actions of the transporters and/or channels operating in the cell membrane. The activity of an ion can be measured using a glass microelectrode that includes in its tip a liquid-membrane doped with an ion-selective ionophore. Because these electrodes can be fabricated with tip diameters that are less than 1 μm, they can be used to impale single cells in order to monitor the activities of intracellular ions. This review summarizes the history, theory, and practice of ion-selective microelectrode use and brings together a number of classic and recent examples of their usefulness in the realm of physiological study.

Construction, theory, and practical considerations for using self-referencing of Ca(2+)-selective microelectrodes for monitoring extracellular Ca(2+) gradients

Ca(2+) signaling in the extra- and intracellular domains is linked to Ca(2+) transport across the plasma membrane. Noninvasive monitoring of these resulting extracellular Ca(2+) gradients with self-referencing of Ca(2+)-selective microelectrodes is used for studying Ca(2+) signaling across Kingdoms. The quantitated Ca(2+) flux enables comparison with changes to intracellular [Ca(2+)] measured with other methods and determination of Ca(2+) transport stoichiometry. Here, we review the construction of Ca(2+)-selective microelectrodes, their physical characteristics, and their use in self-referencing mode to calculate Ca(2+) flux. We also discuss potential complications when using them to measure Ca(2+) gradients near the boundary layers of single cells and tissues.

Using fluorometry and ion-sensitive microelectrodes to study the functional expression of heterologously-expressed ion channels and transporters in Xenopus oocytes

The Xenopus laevis oocyte is a model system for the electrophysiological study of exogenous ion transporters. Three main reasons make the oocyte suitable for this purpose: (a) it has a large cell size (approximately 1mm diameter), (b) it has an established capacity to produce-from microinjected mRNAs or cRNAs-exogenous ion transporters with close-to-physiological post-translational modifications and actions, and (c) its membranes contain endogenous ion-transport activities which are usually smaller in magnitude than the activities of exogenously-expressed ion transporters. The expression of ion transporters as green fluorescent protein fusions allows the fluorometric assay of transporter yield in living oocytes. Monitoring of transporter-mediated movement of ions such as Cl(-), H(+) (and hence base equivalents like OH(-) and HCO(3)(-)), K(+), and Na(+) is achieved by positioning the tips of ion-sensitive microelectrodes inside the oocyte and/or at the surface of the oocyte plasma membrane. The use of ion-sensitive electrodes is critical for studying net ion-movements mediated by electroneutral transporters. The combined use of fluorometry and electrophysiology expedites transporter study by allowing measurement of transporter yield prior to electrophysiological study and correlation of relative transporter yield with transport rates.

The cationic composition and pH in the moulting fluid of Porcellio scaber (Crustacea, Isopoda) during calcium carbonate deposit formation and resorption

Before moulting, terrestrial isopods resorb calcium carbonate (CaCO(3)) from the posterior cuticle and store it in sternal deposits. These consist mainly of amorphous calcium carbonate (ACC) spherules that develop within the ecdysial space between the anterior sternal epithelium and the old cuticle. Ions that occur in the moulting fluid, including those required for mineral deposition, are transported from the hemolymph into the ecdysial space by the anterior sternal epithelial cells. The cationic composition of the moulting fluid probably affects mineral deposition and may provide information on the ion-transport activity of the sternal epithelial cells. This study presents the concentrations of inorganic cations within the moulting fluid of the anterior sternites during the late premoult and intramoult stages. The most abundant cation is Na(+) followed by Mg(2+), Ca(2+) and K(+). The concentrations of these ions do not change significantly between the stages whereas the mean pH changed from 8.2 to 6.9 units between mineral deposition in late premoult, and resorption in intramoult, respectively. Measurements of the transepithelial potential show that there is little driving force for passive movements of calcium across the anterior sternal epithelium. The results suggest a possible role of magnesium ions in ACC formation, and a contribution of pH changes to CaCO(3) precipitation and dissolution.

A vacuolar-type H+-ATPase and a Na+/H+exchanger contribute to intracellular pH regulation in cockroach salivary ducts

Cells of the dopaminergically innervated salivary ducts in the cockroach Periplaneta americana have a vacuolar-type H+-ATPase(V-ATPase) of unknown function in their apical membrane. We have studied whether dopamine affects intracellular pH (pHi) in duct cells and whether and to what extent the apical V-ATPase contributes to pHiregulation. pHi measurements with double-barrelled pH-sensitive microelectrodes and the fluorescent dye BCECF have revealed: (1) the steady-state pHi is 7.3±0.1; (2) dopamine induces a dose-dependent acidification up to pH 6.9±0.1 at 1 μmol l–1 dopamine, EC50 at 30 nmol l–1dopamine; (3) V-ATPase inhibition with concanamycin A or Na+-free physiological saline (PS) does not affect the steady-state pHi; (4)concanamycin A, Na+ -free PS and Na+/H+exchange inhibition with 5-(N-ethyl-N-isopropyl)-amiloride(EIPA) each reduce the rate of pHi recovery from a dopamine-induced acidification or an acidification induced by an NH4Cl pulse; (5)pHi recovery after NH4Cl-induced acidification is almost completely blocked by concanamycin A in Na+-free PS or by concanamycin A applied together with EIPA; (6) pHi recovery after dopamine-induced acidification is also completely blocked by concanamycin A in Na+-free PS but only partially blocked by concanamycin A applied together with EIPA. We therefore conclude that the apical V-ATPase and a basolateral Na+/H+ exchange play a minor role in steady-state pHi regulation but contribute both to H+extrusion after an acute dopamine- or NH4Cl-induced acid load.

Fluorescence measurements of serotonin-induced V-ATPase-dependent pH changes at the luminal surface in salivary glands of the blowfly Calliphora vicina

Secretion in blowfly salivary glands is induced by the neurohormone serotonin and powered by a vacuolar-type H(+)-ATPase (V-ATPase) located in the apical membrane of the secretory cells. We have established a microfluorometric method for analysing pH changes at the luminal surface of the secretory epithelial cells by using the fluorescent dye 5-N-hexadecanoyl-aminofluorescein (HAF). After injection of HAF into the lumen of the tubular salivary gland, the fatty acyl chain of the dye molecule partitions into the outer leaflet of the plasma membrane and its pH-sensitive fluorescent moiety is exposed at the cell surface. Confocal imaging has confirmed that HAF distributes over the entire apical membrane of the secretory cells and remains restricted to this membrane domain. Ratiometric analysis of HAF fluorescence demonstrates that serotonin leads to a reversible dose-dependent acidification at the luminal surface. Inhibition by concanamycin A confirms that the serotonin-induced acidification at the luminal surface is due to H(+) transport across the apical membrane via V-ATPase. Measurements with pH-sensitive microelectrodes corroborate a serotonin-induced luminal acidification and demonstrate that luminal pH decreases by about 0.4 pH units at saturating serotonin concentrations. We conclude that ratiometric measurements of HAF fluorescence provide an elegant method for monitoring V-ATPase-dependent H(+) transport in the blowfly salivary gland in vivo and for analysing the spatiotemporal pattern of pH changes at the luminal surface.

Fabrication and use of high-speed, concentric h+- and Ca2+-selective microelectrodes suitable for in vitro extracellular recording

Ion-selective microelectrodes (ISMs) have been used extensively in neurophysiological studies. ISMs selective for H(+) and Ca(2+) are notable for their sensitivity and selectivity, but suffer from a slow response time, and susceptibility to noise because of the high electrical resistance of the respective ion exchange cocktails. These drawbacks can be overcome by using a "coaxial" or "concentric" inner micropipette to shunt the bulk of the ion exchanger resistance. This approach was used decades ago to record extracellular [Ca(2+)] transients in cat cortex, but has not been subsequently used. Here, we describe a method for the rapid fabrication of concentric pH- and Ca(2+)-selective microelectrodes useful for extracellular studies in brain slices or other work in vitro. Construction was simplified compared with previous implementations, by using commercially available, thin-walled borosilicate glass, drawing an outer barrel with a rapid taper (similar to a patch pipette), and by use of a quick and reliable silanization procedure. Using a piezoelectric stepper to effect a rapid solution change, the response time constants of the concentric pH and Ca(2+)-electrodes were 14.9 +/- 1.3 and 5.3 +/- 0.90 ms, respectively. Use of these concentric ISMs is demonstrated in rat hippocampal slices. Activity-dependent, extracellular pH, and [Ca(2+)] transients are shown to arise two- to threefold faster, and attain amplitudes two- to fourfold greater, when recorded by concentric versus conventional ISMs. The advantage of concentric ISMs for studies of ion transport and ion diffusion is discussed.

An improved method for constructing and selectively silanizing double-barreled, neutral liquid-carrier, ion-selective microelectrodes

We describe an improved, efficient and reliable method for the vapour-phase silanization of multi-barreled, ion-selective microelectrodes of which the silanized barrel(s) are to be filled with neutral liquid ion-exchanger (LIX). The technique employs a metal manifold to exclusively and simultaneously deliver dimethyldichlorosilane to only the ion-selective barrels of several multi-barreled microelectrodes. Compared to previously published methods the technique requires fewer procedural steps, less handling of individual microelectrodes, improved reproducibility of silanization of the selected microelectrode barrels and employs standard borosilicate tubing rather than the less-conventional theta-type glass. The electrodes remain stable for up to 3 weeks after the silanization procedure. The efficacy of a double-barreled electrode containing a proton ionophore in the ion-selective barrel is demonstrated in situ in the leaf apoplasm of pea (Pisum) and sunflower (Helianthus). Individual leaves were penetrated to depth of approximately 150 microm through the abaxial surface. Microelectrode readings remained stable after multiple impalements without the need for a stabilizing PVC matrix.

Dopamine-induced epithelial K(+) and Na(+) movements in the salivary ducts of Periplaneta americana

K(+)- and Na(+)-selective double-barrelled microelectrodes were used for intracellular and luminal measurements in salivary ducts of Periplaneta americana. The salivary ducts were stimulated with dopamine (10(-6) mol l(-1)). Dopamine decreased intracellular [K(+)] from 112+/-17 mmol l(-1) to 40+/-13 mmol l(-1) (n=6) and increased intracellular [Na(+)] from 22+/-19 mmol l(-1) to 92+/-4 mmol l(-1) (n=6). Luminal [K(+)] was 15+/-3 mmol l(-1) in the unstimulated salivary ducts and increased to 26+/-11 mmol l(-1) upon stimulation with dopamine (n=10). Luminal [Na(+)] was insignificantly increased from 105+/-25 mmol l(-1) to 116+/-22 mmol l(-1) (n=12) by stimulation with dopamine. The potential difference across the basolateral membrane (PD(b)) was depolarized from -65+/-6 mV to -31+/-13 mV (n=12) and the transepithelial potential difference (PD(t)) was hyperpolarized from -13+/-6 mV to -22+/-7 mV (n=22, lumen negative) upon stimulation with dopamine. The re-establishment of prestimulus values of intracellular [K(+)] and [Na(+)] and PD(b) was inhibited by basolateral addition of ouabain (10(-4) mol l(-1)). Furosemide (10(-4) mol l(-1)) in the bath inhibited the dopamine-induced increase in intracellular [Na(+)], the decrease in intracellular [K(+)] and the depolarization of PD(b). We propose a model for dopamine-stimulated ion transport in the salivary ducts involving basolateral Na(+)-K(+)-2Cl(-) cotransport and active extrusion of K(+) via the apical membrane.

Metabolic stress reversibly activates the Drosophila light-sensitive channels TRP and TRPL in vivo

Drosophila transient receptor potential (TRP) is a prototypical member of a novel family of channel proteins underlying phosphoinositide-mediated Ca(2+) entry. Although the initial stages of this signaling cascade are well known, downstream events leading to the opening of the TRP channels are still obscure. In the present study we applied patch-clamp whole-cell recordings and measurements of Ca(2+) concentration by ion-selective microelectrodes in eyes of normal and mutant Drosophila to isolate the TRP and TRP-like (TRPL)-dependent currents. We report that anoxia rapidly and reversibly depolarizes the photoreceptors and induces Ca(2+) influx into these cells in the dark. We further show that openings of the light-sensitive channels, which mediate these effects, can be obtained by mitochondrial uncouplers or by depletion of ATP in photoreceptor cells, whereas the effects of illumination and all forms of metabolic stress were additive. Effects similar to those found in wild-type flies were also found in mutants with strong defects in rhodopsin, Gq-protein, or phospholipase C, thus indicating that the metabolic stress operates at a late stage of the phototransduction cascade. Genetic elimination of both TRP and TRPL channels prevented the effects of anoxia, mitochondrial uncouplers, and depletion of ATP, thus demonstrating that the TRP and TRPL channels are specific targets of metabolic stress. These results shed new light on the properties of the TRP and TRPL channels by showing that a constitutive ATP-dependent process is required to keep these channels closed in the dark, a requirement that would make them sensitive to metabolic stress.

Self-referencing, non-invasive, ion selective electrode for single cell detection of trans-plasma membrane calcium flux

Biological systems have very different internal ion compositions in comparison with their surrounding media. The difference is maintained by transport mechanisms across the plasma membrane and by internal stores. On the plasma membrane, we can classify these mechanisms into three types, pumps, porters, and channels. Channels have been extensively studied, particularly since the advent of the patch clamp technique, which opened new windows into ion channel selectivity and dynamics. Pumps, particularly the plasma membrane Ca(2+)-ATPase, and porters are more illusive. The technique described in this paper, the self-referencing, ion-selective (or Seris) probe, has the ability to monitor the behavior of membrane transport mechanisms, such as the pumps and porters, in near to real-time by non-invasively measuring local extracellular ion gradients with high sensitivity and square micron spatial resolution. The principles behind the self-referencing technique are described with an overview of systems utilizing ion, electrochemical and voltage sensors. Each of these sensors employs the simple expedient of increasing the system resolution by self-referencing and, thereby, removing the drift component inherent to all electrodes. The approach is described in detail, as is the manner in which differential voltage measurements can be converted into a flux value. For the calcium selective probes, we can resolve flux values in the low to sub pmol.cm(-2)s(-1) range. Complications in the use of the liquid ion exchange cocktail are discussed. Applications of the calcium selective probe are given, drawing on examples from the plant sciences, developmental biology, muscle physiology, and the neurosciences.

A nitrite microsensor for profiling environmental biofilms

A highly selective liquid membrane nitrite microsensor based on the hydrophobic ion-carrier aquocyanocobalt(III)-hepta(2-phenylethyl)-cobrynate is described. The sensor has a tip diameter of 10 to 15 (mu)m. The response is log-linear in freshwater down to 1 (mu)M NO(inf2)(sup-) and in seawater to 10 (mu)M NO(inf2)(sup-). A method is described for preparation of relatively large polyvinyl chloride (PVC)-gelled liquid membrane microsensors with a tip diameter of 5 to 15 (mu)m, having a hydrophilic coating on the tip. The coating and increased tip diameter resulted in more sturdy sensors, with a lower detection limit and a more stable signal than uncoated nitrite sensors with a tip diameter of 1 to 3 (mu)m. The coating protects the sensor membrane from detrimental direct contact with biomass and can be used for all PVC-gelled liquid membrane sensors meant for profiling microbial mats, biofilms, and sediments. Thanks to these improvements, liquid membrane sensors can now be used in complex environmental samples and in situ, e.g., in operating bioreactors. Examples of measurements in denitrifying, nitrifying, and nitrifying/denitrifying biofilms from wastewater treatment plants are shown. In all of these biofilms high nitrite concentrations were found in narrow zones of less than 1 mm.

Limulus ventral photoreceptors contain two functionally dissimilar inositol triphosphate-induced calcium release mechanisms

Injections of inositol 1,4,5 triphosphate (InsP3) into Limulus ventral photoreceptors give rise to a rapid depolarization and an elevation of intracellular calcium concentration (Cai). This response to InsP3 is followed by a period of desensitization that persists as long as Cai remains elevated (feedback inhibition). Limulus ventral photoreceptors have two types of lobe: a light-sensitive rhabdomeric lobe (R lobe), and a light-insensitive arhabdomeric lobe (A lobe). Evidence showing the presence of feedback inhibition has been so far demonstrated only in the R lobe. In this study, simultaneous measurements of Cai were made using aequorin and double-barreled calcium-sensitive electrodes in each type of lobe. We carefully checked the location of the R lobe and A lobe by scanning a microspot of light across the whole photoreceptor. We then inserted a double-barreled calcium-sensitive microelectrode with InsP3 in either type of lobe. In the R lobe, injections of InsP3 led to a large Cai increase, a rapid depolarization and feedback inhibition; a brief flash of light induced a rapid depolarization and a Cai increase measured by both aequorin and the calcium-sensitive electrode. In the A lobe, injection of InsP3 led to an increase in Cai measured by the calcium-sensitive electrode but to no depolarization or aequorin luminescence. Further there was no evidence of feedback inhibition in the A lobe; the elevation of Cai caused by the first injection did not desensitize the photoreceptor to a second injection of InsP3 3 s later. To verify that the aequorin and the cell membrane respond to an increase in Cai, we presented a brief flash of light. Following a uniform illumination, there is indeed a typical large luminescence increase and a receptor potential. The calcium-sensitive electrode measures a small and slow Cai increase because its tip is located in the A lobe and it is measuring Ca2+ diffusing from the R lobe. Our observation that the InsP3-induced Cai increase in the A lobe is not apparently accompanied by a subsequent desensitization to InsP3 may suggest that there are more than one type of InsP3 receptor in the same cell. Alternatively, the InsP3 receptor could be the same but some additional factor, which confers feedback inhibition, could be missing in the A lobe.

Ion-selective microelectrodes and diffusion measurements as tools to explore the brain cell microenvironment

The construction and application of liquid-membrane ion-selective microelectrodes (ISM) are described. Recommendations are provided for the selection of appropriate cocktails containing neutral carriers to form the liquid membrane to sense K+, Ca2+, H+ and Na+. The use of charged carriers to sense Cl- and the cation tetramethylammonium (TMA+) is discussed. A detailed protocol is given for constructing double-barreled electrodes (ion-sensor and reference barrel) with tips of 1 micron diameter or more for extracellular ion measurements. The primary results obtained with ISMs in the brain cell microenvironment are briefly surveyed. The theoretical basis for measuring diffusion properties of extracellular space is described. Such measurements enable the estimation of volume fraction (proportion of tissue that is extracellular space) and tortuosity (hindrance of diffusion due to cellular obstructions). A method is given for using TMA+ ISMs in combination with iontophoresis or pressure ejection of TMA+ from a nearby micropipette to measure diffusion properties.

A possible relationship between KCl symport and basolateral K+-conductance in Necturus gallbladder epithelial cells

1. Apical membrane potential (Va), transepithelial potential (VT), fractional apical voltage ratio (FVa = delta Va/delta VT), tissue resistance (RT), and intracellular Cl- (aiCl) and K+ (aiK) activities were measured in isolated gallbladders maintained between oxygenated bicarbonate-free physiological media (23 degrees C, pH 7.2 or 8.2) in a divided chamber. The basolateral membrane potential (Vb) was calculated from the measured values of Va and VT. 2. Cl- removal from the serosal medium (which should accelerate coupled basolateral KCl exit) significantly depolarized Vb, decreased aiCl, decreased FVa, increased RT, and attenuated the depolarization of Vb (delta Vb) induced by high K+ added to the serosal side. These changes are consistent with a decrease in the K(+)-conductance of the basolateral membrane (gbK). 3. Addition of furosemide (an inhibitor of KCl cotransport) to the serosal medium induced significant increases in Vb, FVa, and high K(+)-induced delta Vb, indicating an increase in gbK. 4. In the presence of serosal furosemide, Cl- removal from the serosal medium did not significantly alter Vb, aiCl or delta Vb from their corresponding values when serosal Cl- was present. 5. Serosal furosemide had no significant effect on aiK and aiCl measured with double-barreled ion-selective microelectrodes. 6. These results suggest the possibility of a reciprocal relationship between gbK and the rate of basolateral KCl cotransport. This may contribute to the maintenance of aiK in gallbladder epithelial cells.

Extracellular K+ in the supraoptic nucleus of the rat during reflex bursting activity by oxytocin neurones

1. We have investigated changes in extracellular potassium concentration [K+]o in the supraoptic nucleus of lactating rats and in particular those that occur during the intense burst of firing by the oxytocin neurones involved in the milk ejection reflex. 2. Double-barrelled K(+)-selective microelectrodes containing a highly selective sensor based on valinomycin were lowered through the exposed cortex towards the supraoptic nucleus (SON) of female rats anaesthetized with urethane. The mean resting [K+]o in the hypothalami of five rats was 2.4 mM, S.D. = 0.3 mM. 3. Where the reference barrel recorded extracellular action potentials from an oxytocin cell, the reflex burst of firing (4 s, typical maximum 50 Hz) was accompanied by a mean increase in [K+]o (delta[K+]o) of 0.22 mM (S.E.M. = 0.02 mM, fifty-seven bursts in eight cells in seven rats). The rise in [K+]o did not begin more than 0.1 s before the onset of the burst, and began to fall from its maximum during the burst. Slow field potentials, indicative of spatial buffering of K+, were undetectable (less than 50 microV). When the electrode was advanced in steps, the amplitudes of both delta[K+]o and the action potential declined steeply to about 10% over a distance of 20 microns: K+ from oxytocin cells appears to be prevented from dispersing freely through the extracellular space of the SON. 4. When the electrode recorded action potentials from a vasopressin cell, delta[K+]o during an oxytocin cell burst was very small: 0.021 mM (S.E.M. = 0.005 mM). At other sites in the SON, where antidromic stimulation evoked a field potential but no action potential, delta[K+]o was 0.047 +/- 0.005 mM. We conclude that the reason oxytocin bursts do not affect vasopressin cells is that [K+]o rises very little around vasopressin cells. A fortiori, since the increases in [K+]o were very small except where action potentials from oxytocin cells were recorded, they can make no significant contribution to synchronizing the onsets of bursts in oxytocin cells that are not contiguous. 5. A standard antidromic stimulation from the pituitary stalk, at 40 Hz for 4 s, which stimulated both oxytocin neurones and vasopressin neurones, caused a delta[K+]o of 0.17-1.8 mM, the variation being mainly from rat to rat. The larger delta[K+]o values were accompanied by slow negative potentials of up to 1.5 mV, there was a gradient in delta[K+]o decreasing towards the pia at the inferior limit of the SON, and there was a slow increase in [K+] in the subarachnoid space.(ABSTRACT TRUNCATED AT 400 WORDS)

Further studies of electrogenic Na+/HCO3- cotransport in glial cells of Necturus optic nerve: regulation of pHi

In the presence of Ba++, an increase in the bath HCO3- at constant CO2 (i.e., variable bath pH) produced a hyperpolarization. The hyperpolarizing effect of adding HCO3-/CO2 at constant bath pH was not significantly affected by the presence of 50 mumol/l strophanthidin. In the absence of Ba++, addition of HCO3-/CO2 at constant bath pH produced a Na(+)-dependent hyperpolarization. Therefore, CO2 movements, electrogenic Na+/K+ pump activity and changes in Ba++ binding do not contribute significantly to the hyperpolarization induced by HCO3-. These results along with the results of previous studies (Astion et al: J Gen Physiol 93:731, 1989) strongly suggest that the hyperpolarization induced by the addition of HCO3- is due to an electrogenic Na+/HCO3- cotransporter, which transports Na+, HCO3- (or its equivalent), and net negative charge across the glial membrane. To study the role of electrogenic Na+/HCO3- cotransport in the regulation of pHi in glial cells, we used intracellular double-barreled, pH-sensitive microelectrodes. At a bath pH of 7.5, the mean initial intracellular pH (pHi) was 7.32 (SD 0.03, n = 6) in HEPES-buffered Ringer's solution and 7.39 (SD 0.1, n = 6) in HCO3-/CO2 buffered solution. These values for pHi are more than 1.2 pH units alkaline to the pHi predicted from a passive distribution of protons; thus, these cells actively regulate pHi. Superfusion and withdrawal of 15 mmol/l NH4+ induced an acidification of 0.2 to 0.3 pH units, which recovered toward the original steady-state pHi.(ABSTRACT TRUNCATED AT 250 WORDS)

Inositol 1,4,5-trisphosphate-induced calcium release in the organelle layers of the stratified, intact egg of Xenopus laevis

Using double-barreled, Ca2(+)-sensitive microelectrodes, we have examined the characteristics of the Ca2+ release by inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) in the various layers of Xenopus laevis eggs in which the organelles had been stratified by centrifugation. Centrifugation of living eggs stratifies the organelles yet retains them in the normal cytoplasmic milieu. The local increase in intracellular free Ca2+ in each layer was directly measured under physiological conditions using theta-tubing, double-barreled, Ca2(+)-sensitive microelectrodes in which one barrel was filled with the Ca2+ sensor and the other was filled with Ins(1,4,5)P3 for microinjection. The two tips of these electrodes were very close to each other (3 microns apart) enabling us to measure the kinetics of both the highly localized intracellular Ca2+ release and its subsequent removal in response to Ins(1,4,5)P3 injection. Upon Ins(1,4,5)P3 injection, the ER-enriched layer exhibited the largest release of Ca2+ in a dosage-dependent manner, whereas the other layers, mitochondria, lipid, and yolk, released 10-fold less Ca2+ in a dosage-independent manner. The removal of released Ca2+ took place within approximately 1 min. The sensitivity to Ins(1,4,5)P3 and the time course of intracellular Ca2+ release in the unstratified (unactivated) egg is nearly identical to that observed in the ER layer of the stratified egg. Our data suggest that the ER is the major organelle of the Ins(1,4,5)P3-sensitive Ca2+ store in the egg of Xenopus laevis.

Na+/H+ exchange in glial cells of Necturus optic nerve

Single and double-barreled pH-sensitive electrodes were used to study intracellular pH (pHi) regulation in glial cells of Necturus optic nerve in the nominal absence of HCO3-/CO2. After the cells were acidified by the addition and withdrawal of NH4+, the pHi recovered toward the original steady-state pHi. The recovery from acidification was Na+-dependent and inhibited by 1 mM amiloride. These results suggest the existence in intact vertebrate glial cells of a Na+/H+ exchanger which functions in acid extrusion.

Chloride enters glial cells and photoreceptors in response to light stimulation in the retina of the honey bee drone

Double-barrelled ion-selective microelectrodes were used to measure free [Cl-] in photoreceptors, extracellular space, and glial cells in superfused slices of drone retina. Tests indicated that with normal superfusate the intracellular electrode signal was due essentially to Cl- and not to some other interfering anion. The results indicate that Cl- is more concentrated in both photoreceptors and glial cells than would be predicted for a passive electrochemical distribution. When the photoreceptors were stimulated by a standard train of 20 ms flashes, 1/s for 90 s, their intracellular free [Cl-] (Cli) rose by 8 +/- 1 mM. At the end of stimulation Cli usually continued to rise for up to a further 2 min and then returned toward the baseline over about 10 min. During light stimulation Cli in the glia rose. The magnitude of the increase was 5.1 +/- 0.4 mM, about half the increase in Ki. In some extracellular recording sites, light stimulation caused [Cl-] to increase and in others to decrease. The mean change was -0.7 mM, SD 6.5 mM. The Cl- that entered the photoreceptors and the glia was presumably made available by the shrinking of the extracellular space. When the cells were depolarized by increasing [K+] in the superfusate from 7.5 mM to 18 mM, Cli increased. The half-time of the change in Cli was longer than the half-time of the depolarization by 10-30 s in the glia and 50-250s in the photoreceptors. During superfusion with 0 Cl- Ringer's solution, the light-induced rise in extracellular [K+] was greater by a factor of 1.4-2.7, and the clearance after the end of the stimulation was slower. The rate of increase in glial Ki during light stimulation fell; the rate of increase of glial Ki caused by superfusion with raised [K+] (in the absence of Cl-) fell more. We conclude that when extracellular [K+] is increased, entry of Cl- into the glia is necessary for part, but not all, of the net uptake of K+. During light stimulation, the observed movement of CL- into glia contributes to homeostasis of extracellular [K+], and the cell swelling associated with movement of Cl- into both glia and photoreceptors contributes to homeostasis of extracellular [Na+].

Spreading depression induced by 100 mM KCl in caudate is blocked by local anesthesia of the substantia nigra

Pressure-ejection of 100 mM KCl was used to induce voltammetric signals in the rat caudate. The signals, detected chronoamperometrically with Nafion-coated carbon fiber microelectrodes, were reproducibly generated at 20-min intervals up to distances of 1600 micron from the KCl stimulus site. Unilateral 6-hydroxydopamine lesions of the substantia nigra (SN) demonstrated that over 90% of the voltammetric signal generated was dopamine. Evaluation of the signal onset at two widely spaced electrodes suggested that injection of nl volumes of 100 mM KCl into the rat caudate generates voltammetric signals which resemble spreading depression (SD) produced by more classical methods (e.g. 1 M KCl). We further investigated this phenomenon by simultaneous evaluation of extracellular K+ ion concentration changes, field potential (FP) and voltammetric signals or multiunit activity following stimulation with 100 mM or 1 M KCl. The results show that the signals generated by 100 mM KCl have many of the attributes of 'classical' SD, although the extracellular K+ ion concentration changes and FP changes were smaller in magnitude. However, the characteristic burst of multiunit activity followed by a marked quiescent period found during 1 M KCl stimulation was not observed with 100 mM KCl stimulation. Furthermore, application of 0.5% lidocaine to the SN reversibly blocked all signals generated by 100 mM KCl in the caudate while similar treatment with up to 2% lidocaine was ineffective when 1 M KCl was used as the stimulus. The results suggest that the signals generated by 100 mM KCl may represent an attenuated form of SD which requires a functioning SN, and that this stimulation could be a useful model for studying neurotransmitter interactions in the propagation of the SD phenomena.

Studies of axon-glial cell interactions and periaxonal K- homeostasis--I. The influence of Na+, K+, Cl- and cholinergic agents on the membrane potential of the adaxonal glia of the crayfish medial giant axon

The ionic basis for the low (-40 mV) resting membrane potential of glial cells surrounding the giant axons of the crayfish and their hyperpolarization by cholinergic agents (to -55 mV) was studied using standard electrophysiological techniques, ionic substitutions and pharmacological agents. The resting membrane potential of the glial cell was depolarized by increasing [K+]o, but the response was not Nernstian. Na+ depletion caused a small depolarization of the glial resting membrane potential, whereas Cl- depletion resulted in a hyperpolarization comparable to that seen with carbachol at various [K+]o. Both furosemide (1 mM) and bumetanide (0.1 mM) produced an 8-10 mV hyperpolarization as compared to 15-17 mV seen with Cl- depletion or carbachol. Carbachol has no further effect on the potential following furosemide treatment or Cl- depletion. After carbachol administration or Cl- depletion the resting membrane potential of the glial cell responded to [K+]o in a more Nernstian manner. The data indicate that the low resting membrane potential of glial cells is due to a combination of a low [K+]i and an outwardly-directed (depolarizing) Cl- electrochemical gradient. Carbachol acts to decrease Cl- conductance, resulting in the hyperpolarization of the glial cell membrane and a decrease in the outwardly-directed K+ electrochemical gradient by approximately two-thirds. We hypothesize that this mechanism for modulation of the glial cell membrane potential and the K+ electrochemical gradient serves to enhance the uptake of K+ by the glial cell transport system.

Light-induced oxygen consumption in Limulus ventral photoreceptors does not result from a rise in the intracellular sodium concentration

Illumination of Limulus ventral photoreceptors leads to an increase in the intracellular concentration of sodium, [Na+]i, and to an increase in the consumption of O2 (delta QO2). After a 1-s light flash, it takes approximately 480 s for [Na+]i to return to within 10% of its preillumination level, whereas delta QO2 takes approximately 90 s. Thus, the delta QO2 is complete long before [Na+]i has returned to its resting level. Pressure injection of Na+ into the cell in order to elevate [Na+]i to the same levels as attained by illumination causes a rise in [Na+]i that returns to baseline with the same time course as the light-induced rise in [Na+]i. However, the injection of Na+ does not lead to an increase of the consumption of O2. We conclude that activation of the Na pump by a rise in [Na+]i is not a factor involved in the light-induced activation of O2 consumption in these cells.

Bias current modifies the selectivity of liquid membrane ion-selective microelectrodes

A negative bias potential of up to -80 mV applied to the back of a liquid membrane ion-selective microelectrode containing classical "K+" ion-exchanger was found to make it more selective for millimolar concentrations of K+ over micromolar concentrations of choline, tetramethylammonium, tetraethylammonium and 5-hydroxytryptamine. Conversely, positive bias potential increased severalfold the sensitivity to micromolar concentrations of these ions while decreasing the sensitivity to K+. An increase in response amplitude for millimolar changes of ion concentration was also observed in neutral carrier electrodes for Na+, K+ and Ca2+ with negative bias potential. The various ions caused the resistances of the electrodes to change; these resistance changes contributed to the changes in response amplitude, but there were additional, unexplained, factors. The phenomenon was used to test if the signal from a K+ ion-exchanger microelectrode in extracellular space in bee retina was contaminated by substances other than K+.

Quartz micropipettes for intracellular voltage microelectrodes and ion-selective microelectrodes

We find that quartz is better than borosilicate glass as a material for micropipettes for certain microelectrode applications, including ion-selective microelectrodes of the liquid membrane type. Details are given of a graphite heating element that can be mounted on a standard microelectrode puller and used for making quartz micropipettes. A novel method of silanizing micropipettes is described. Experience with a novel miniature beveller that is fitted on a microscope stage is reported.

The response to monochromatic light flashes of the oxygen consumption of honeybee drone photoreceptors

Local measurements of the fall in oxygen pressure on stimulation of slices of the retina of the honeybee drone by flashes of light were made with oxygen microelectrodes and used to calculate the kinetics of the extra oxygen consumption (delta QO2) induced by each flash. The action spectrum for delta QO2 was obtained from response-intensity curves in response to brief (40 ms) monochromatic light flashes. The action spectrum of receptor potentials was obtained with the same experimental conditions. The two action spectra match closely: they deviate slightly from the photosensitivity spectrum of the drone rhodopsin (R). The deviation is thought to be due to wavelength-dependent light scattering and absorption in the preparation. In these experiments, the visual pigment was first illuminated with orange light, which is known to convert the bistable drone photopigment predominantly to the R state from the metarhodopsin (M) state. When long (300-900 ms) light flashes were used to elicit delta QO2, the responses to different wavelengths could not be matched in time course (as for the short flashes). Flashes producing large R-to-M conversions produced a prolonged delta QO2. The prolongation did not occur after double flashes, which produced both large R-to-M and M-to-R conversions. Similar changes in the length of afterpotentials in the photoreceptor cells and in a long-lasting decrease in photoreceptor intracellular K+ activity were found after long single or double flashes. The results are interpreted to show that the initial event for stimulation by light of metabolism in the drone retina is the same as that for stimulation of electrical responses (i.e., absorption of photons by R). Absorption of photons by M can produce an inhibitory effect on this stimulation.

pO2-dependent distribution of potassium in hippocampal slices of the guinea pig

The distribution of extracellular K+-concentration (cK+s) in 200-1000-micron thick hippocampal slices was studied with ion-selective microelectrodes. In ca. 500-micron thick slices cK+s increased from the surface to the innermost layers by ca. 2 mmol/liter if the pO2 of the bath (pBO2) ranged from 300-600 mm Hg and if the temperature was 28 degrees C. In thicker slices and lowered pO2-values further elevations of cK+s were observed. In vital slices thinner than 500 micron cK+s-values exceeded the potassium-concentration of the bath (cK+B) only when pBO2 was markedly lowered. When pBO2 was reincreased in such thin slices, cK+s rapidly declined and often decreased transiently below ck+B. Similar undershoots of cK+s were observed when cK+B was lowered from high to normal levels. The rapid decline was blocked by hypoxia, ouabain, antimycine and a temperature of 18 degrees C. A stepwise rise of cK+B also caused rapid changes of cK+s in vital thin slices. The rates of changes, however, were hardly affected e.g. by a transient hypoxia. Diffusion did not contribute significantly to these steep changes of cK+s. These rapid distribution modes were widely missing in slices thicker than 500 micron. Therefore in such preparations, the extracellular microenvironment of neurons may markedly differ from the ionic concentrations in the bath.

Procedures for manufacturing double-barrelled ion-sensitive microelectrodes employing liquid sensors

Liquid ion-sensitive/selective sensors are available for most inorganic ions of physiological and biochemical importance. In order to measure intracellular ionic activities in relatively small cells, it is advisable to manufacture and use double-barrelled microelectrodes. Procedures for making two types of double-barrelled ion-sensitive microelectrode are described in detail. Such microelectrodes have been used successfully to measure intracellular K+, Cl- and Na+ activities in retinal horizontal cells of fish and body-wall muscles of insect larvae.

Light induced sodium dependent accumulation of calcium and potassium in the extracellular space of bee retina

Intense illumination of long duration induced a large transient increase in extracellular calcium (delta[Ca2+]o) and potassium (delta[K+]o) during and after light in bee retina when measured with ion-selective microelectrodes. Whenever a large delta[Ca2+]o appeared, it was accompanied by a transient afterdepolarization (TA). Both the increase in [Ca2+]o, [K+]o and the TA were reduced or abolished when sodium was replaced by arginine, choline or lithium (Li+) ions. At 0-Na conditions a Na independent decrease in [Ca2+]o was observed during illumination only. A pronounced transient depolarization of the photoreceptor in the dark due to transient anoxia did not result in a significant change in [Ca2+]o. In some retinae the elevated level of [K+]o after light was absent, however a small Na-dependent TA was still observed. The above findings suggest that intense long illumination induces a large Ca2+ influx into the photoreceptors which is followed by Na-dependent Ca2+ efflux due to Na-Ca exchange. The light-induced afterdepolarization arises mainly from K+ accumulation in the extracellular space but partially from the electrogenicity of Na-Ca exchange.

Changes in endolymph chloride concentration following furosemide injection

Endocochlear potential (EP) and chloride concentration in endolymph were monitored with microelectrodes in the basal turn of the cochlea of the chinchilla. After intravenous injection of furosemide (25-100 mg/kg), the EP dropped precipitously and rapidly reached its minimum value, however, the chloride activity in endolymph decreased more gradually. Possible mechanisms for this phenomenon include a reduced electrostatic attraction of chloride ions to the scala media due to a decreased EP and a reduction of passive influx of chloride into endolymph, resulting from a reduction of active inward potassium transport by furosemide.

Submicron tip breakage and silanization control improve ion-selective microelectrodes

Probable causes of failure of otherwise well-constructed liquid ion-exchanger (LIE) micro-electrodes of average tip size less than 0.15 micron were examined. The problem could be attributed to two major variables, both localized at the tip: partial tip occlusion during fabrication prevents the generation of an electromotive force (small or absent slope and/or selectivity, high resistance); or poor hydrophobicity of the tip permits water to displace the resin from the tip (small or absent slope and/or selectivity and low electrode resistance). Controlled dry tip breakage on paper coated with glassine to final tip sizes well below 0.5 micron (confirmed by scanning electron microscopy) improves the yield of usable electrodes severalfold. Adequate silanization of the tip and consequent retention of resin at the tip can be predicted from the contact angles observed at the glass-LIE-backfilling solution interface. Satisfactory silanization can be achieved despite high ambient humidity. No evidence of shunting of Na+-LIE microelectrodes by the glass wall was seen. In the isolated perfused proximal tubule of Ambystoma tigrinum, the mean intracellular Na+ activity recorded by broken-tip electrodes (13.7 +/- 1.9 meq, n = 4) was similar to that recorded by intact electrodes (15.5 +/- 1.1 meq, n = 31).

A simple method for making ion-selective microelectrodes suitable for intracellular recording in vertebrate cells

A simple procedure for manufacturing Cl-, K+, and pH liquid membrane ion-sensitive microelectrodes is presented in detail. Electrodes suitable for recording from the specimen of interest are back-filled with a small amount of silane solution and heated for 5 min on a hot plate at a temperature between 400 and 500 degrees C, after which they are injected with the ion-sensitive resin. The procedure is adaptable to many different glass stocks, e.g., single-barreled, double-barreled, or theta glass, and can be used to produce electrodes having a wide range of tip sizes for recording either extracellular or intracellular ion activities. Another advantage of the method is speed; up to 10 electrodes can be prepared simultaneously, permitting over 40 functional electrodes to be made per hour.

Acid-base properties of human gingival crevicular fluid

The pH of human gingival crevicular fluid (GCF) has been reported by many authors to be very alkaline (pH 7.5 - 8.7). This alkalinity could be explained, at least partially, by the fact that all measurements were performed either at low PCO2 or in the absence of CO2. Therefore, we set up a procedure which allows for measurement of the pH of GCF samples from single inflamed sites at controlled PCO2. At a PCO2 of 4.7 kPa (= 35 mmHg) and at 37 degrees C, the pH was 7.96 +/- 0.10 (SEM, n = 9), a value which differs significantly from the value of 8.38 +/- 0.09 measured in the absence of CO2 in the same samples. The non-bicarbonate buffer value of the sample determined by CO2 titration was 6.0 slykes. It is because this value is low that pH varies so greatly with PCO2. At physiological PCO2, the total buffering power becomes very high above pH 8.0, because of the high bicarbonate concentration.

Construction of K+- and Na+-sensitive theta-microelectrodes with fine tips: an easy method with high yield

A new method is described to prepare theta-microelectrodes with tips up to 0.15 micron diameter controlled under scanning electron microscope. K+- and Na+-sensitive resins were tested. Method features are the following: i) hard drying of the glass, ii) rehydration of one channel and weak wetting of the other with a three-methylchlorosilane solution before pulling, iii) simultaneous presence of water and silane in the two channels during pulling, iv) gradual silanization from the tip to the shank. Selective and conventional channels did not affect each other and no displacements of resins were observed. The change of potential difference of the selective channel was more than -50 mV/decade. Apical membrane potentials and cell Na+ and K+ activities of the epithelial cells of rabbit gall-bladder (cell diameter: 5-10 micron) were measured with these theta-microelectrodes and with single-barrel microelectrodes of similar tip size: results obtained were not significantly different.

Maturation of Xenopus oocytes is not accompanied by electrode-detectable calcium changes

Ca2+-sensitive microelectrodes were used to study changes in cytoplasmic free calcium during progesterone-induced meiotic maturation in Xenopus laevis oocytes. In contrast to previous reports, no changes were detected during the maturation process, although a large activation pulse of Ca2+ was seen when in vitro matured eggs were parthenogenetically activated. The resting level of Ca2+ in the oocytes was 0.14 microM +/- 0.05.

Ca2+-selective microelectrodes

Ca2+-selective microelectrodes based on the synthetic neutral carrier ETH 1001 can be used for quantitative intracellular measurements of resting Ca2+-activities and of slowly changing Ca2+-levels (response time in the order of seconds). Microelectrodes with tip diameters greater than 0.3 micron show selectivities that yield a detection limit between 10(-8) and 10(-7) M Ca2+ in an intracellular background. The Ca2+-activity is obtained together with electrical parameters of the cell (e.g. cell membrane potential and membrane resistance or conductivity). Simultaneous monitoring of other ion-activities is accessible (double- or multi-barrelled microelectrodes). The Ca2+-determination is extremely local, i.e. it probably does not indicate an averaged cytosolic activity in every situation (e.g. localized transients).