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

Super-resolution microscopy using normal flow decoding and geometric constraints

Prior knowledge about the observed scene provides the key to restoration of frequencies beyond the bandpass of an imaging system (super-resolution). In conjunction with microscopy two super-resolution mechanisms have been mainly reported: analytic continuation of the frequency spectrum, and constrained image deconvolution. This paper describes an alternative approach to super-resolution. Prior knowledge is imposed through geometric and dynamic models of the scene. We illustrate our concept based on the stereo reconstruction of a micropipette moving in close proximity to a stationary target object. Information about the shape and the movement of the pipette is incorporated into the reconstruction algorithm. The algorithm was tested in a microrobot environment, where the pipette tip was tracked at sub-Rayleigh distances to the target. Based on the tracking results, a machine vision module controlled the manipulation of microscopic objects, e.g. latex beads or diamond mono-crystals. In the theoretical part of this paper we prove that knowledge of the form 'the pipette has moved between two consecutive frames of the movie' must result in a twofold increase in resolution. We used the normal flow of an image sequence to decode positional measures from motion evidence. In practice, super-resolution factors between 3 and 5 were obtained. The additional gain originates from the geometric constraints that were imposed upon the stereo reconstruction of the pipette axis.

Proteins and lipids define the diffusional field of nitric oxide

Nitric oxide (NO) fluxes released from the surface of individual activated macrophages or cells localized in small aggregates were measured with a novel polarographic self-referencing microsensor. NO fluxes could be detected at distances from the cells of 100-500 microm. The initial flux and the distance from the cells at which NO could be detected were directly related to the number of cells in the immediate vicinity of the probe releasing NO. Thus, whereas NO fluxes of approximately 1 pmol. cm(-2). s(-1) were measured from individual macrophages, aggregates composed of groups of cells varying in number from 18 to 48 cells produced NO fluxes of between approximately 4 and 10 pmol. cm(-2). s(-1). NO fluxes required the presence of L-arginine. Signals were significantly reduced by the addition of hemoglobin and by N-nitro-L-arginine methyl ester. NO fluxes were greatest when the sensor was placed immediately adjacent to cell membranes and declined as the distance from the cell increased. The NO signal was markedly reduced in the presence of the protein albumin but not by either oxidized or reduced glutathione. A reduction in the NO signal was also noted after the addition of lipid micelles to the culture medium. These results demonstrate that NO can be detected at significant distances from the cell of origin. In addition, both proteins and lipids strongly influence the net movement of free NO from macrophages. This suggests that these tissue components play an important role in regulating the biological activity of NO.

Measurement of chloride flux associated with the myogenic response in rat cerebral arteries

1. Self-referencing ion-selective (SERIS) electrodes were used to measure the temperature and pressure dependence of Cl(-) efflux, during myogenic contraction of pressurized rat cerebral resistance arteries. 2. At room temperature (18-21 degrees C), a small, pressure-independent Cl(-) efflux was measured. On warming to 37 degrees C, arteries developed pressure-dependent myogenic tone, and this was associated with a pressure-dependent increase in Cl(-) efflux (n = 5). 3. Both myogenic tone and the pressure- and temperature-dependent Cl(-) efflux were abolished on application of 10 microM tamoxifen, a Cl(-) channel blocker (IC(50) 3.75 +/- 0.2 microM). Tamoxifen (10 microM) also prevented contraction to 60 mM K(+), suggesting non-specific effects of tamoxifen (n = 5). 4. Myogenic tone was abolished by 2 microM nimodipine, but Cl(-) efflux was unaffected. In the presence of nimodipine, 10 microM tamoxifen still abolished pressure- and temperature-dependent Cl(-) efflux (n = 3). 5. In summary, a Cl(-) efflux can be measured from rat cerebral arteries, with a temperature dependence that is closely correlated with myogenic contraction. We conclude that Cl(-) efflux through Cl(-) channels contributes to the depolarization associated with myogenic contraction.

5-Hydroxytryptamine stimulates net Ca2+ flux in the ventricular muscle of a mollusc (Busycon canaliculatum) during cardioexcitation

Noninvasive, self-referencing calcium (Ca2+) electrodes were used to study the mechanisms by which 5-hydroxytryptamine (5-HT) affects net Ca2+ flux across the sarcolemma of myocytes from ventricular trabeculae (from a marine gastropod, Busycon canaliculatum). Treatment of isolated trabeculae with 5-HT causes a net Ca2+ efflux, which is 30% blocked by verapamil. These findings suggest that the efflux is in part the result of a previous Ca2+ influx through L-type Ca2+ channels and is due to a rapid Ca2+ extrusion mechanism inherent to the sarcolemma of these myocytes. 5-HT-induced net Ca2+ efflux is also reduced by about 40% by treatment with a sodium (Na+)-free, lithium (Li+)-substituted saline, which shuts down the Na-Ca exchanger during Ca2+ extrusion. Cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum (SR) Ca2+ ATPase, almost completely abolishes the 5-HT-induced net Ca2+ efflux, suggesting that the SR rather than the extracellular pool is the primary Ca2+ reservoir serving 5-HT-induced excitation.

In situ analysis of pH gradients in mosquito larvae using non-invasive, self-referencing, pH-sensitive microelectrodes

The alkaline environment, pH approximately 11, in the anterior midgut lumen of mosquito larvae is essential for normal nutrition and development. The mechanism of alkalization is, however, unknown. Although evidence from immunohistochemistry, electron microscopy and electrophysiology suggests that a V-ATPase is present in the basal membranes of the epithelial cells, its physiological role in the alkalization process has not been demonstrated. To investigate a possible role of the V-ATPase in lumen alkalization, pH gradients emanating from the hemolymph side of the midgut in semi-intact mosquito larvae were measured using non-invasive, self-referencing, ion-selective microelectrodes (SERIS). Large H+ concentration gradients, with highest concentrations close to the basal membrane (outward [H+] gradients), were found in the anterior midgut, whereas much smaller gradients, with concentrations lowest close to this membrane (inward [H+] gradients), were found in the gastric caeca and posterior midgut. Similar region-specific pH gradients, with consistent anterior-to-posterior profiles, were observed in individuals of two Aedes species, Aedes aegypti from semi-tropical Florida and Aedes canadensis from north-temperate Massachusetts. The gradients remained in a steady state for up to 6 h, the maximum duration of the recordings. Bafilomycin A1 (10(−5), 10(−7)mol × l(−1)) on the hemolymph side greatly diminished the [H+] gradients in the anterior midgut but had no effect on the gradients in the gastric caecum and posterior midgut. These physiological data are consistent with the previous findings noted above. Together, they support the hypothesis that a basal, electrogenic H+ V-ATPase energizes luminal alkalization in the anterior midgut of larval mosquitoes.

Nerve injury induces a rapid efflux of nitric oxide (NO) detected with a novel NO microsensor

An early step in repair of the leech CNS is the appearance of endothelial nitric oxide synthase (eNOS) immunoreactivity and NOS activity, but coincident generation of NO at the lesion after injury has not been shown. This is important because NO can regulate microglial cell motility and axon growth. Indirect measurement of NO with the standard citrulline assay demonstrated that NO was generated within 30 min after nerve cord injury. A polarographic NO-selective self-referencing microelectrode that measures NO flux noninvasively was developed to obtain higher spatial and temporal resolution. With this probe, it was possible to demonstrate that immediately after the leech CNS was injured, NO left the lesion with a mean peak efflux of 803 +/- 99 fmol NO cm(-2) sec(-1). NO efflux exponentially declined to a constant value, as described through the equation f(t) = y(o) + ae(-t/tau), with tau = 117 +/- 30 sec. The constant y(o) = 15.8 +/- 4.5 fmol cm(-2) represents a sustained efflux of NO. Approximately 200 pmol NO cm(-2) is produced at the lesion (n = 8). Thus, injury activates eNOS already present in the CNS and precedes the accumulation of microglia at the lesion, consistent with the hypothesis that NO acts to stop the migrating microglia at the lesion site.

Ion transport in roots: measurement of fluxes using ion-selective microelectrodes to characterize transporter function

The transport of mineral ions into and out of tissues and cells is central to the life of plants. Ion transport and the plasma membrane transporters themselves have been studied using a variety of techniques. In the last 15 years, measurement of specific ion fluxes has contributed to the characterization of transport systems. Progress in molecular genetics is allowing gene identification and controlled expression of transporter molecules. However the molecular expression of transporter gene products must be characterized at the functional level. The ion-selective microelectrode technique to measure specific ion fluxes non-invasively is ideally suited to this purpose. This technique, its theory, its links with others and its application and prospects in plant science, are discussed. Ions studied include hydrogen, potassium, sodium, ammonium, calcium, chloride and nitrate. Applications discussed include: solute ion uptake by roots; gravitropism and other processes in the root cap, meristematic and elongation zones; Nod factor effect on root hairs; osmotic and salt stresses; oscillations; the effects of light and temperature. Studies have included intact roots, leaf mesophyll and other tissues, protoplasts and bacterial biofilms. A multi-ion capability of the technique will greatly assist functional genomics, particularly when coupled with imaging techniques, patch clamping and the use of suitable mutants.

Noninvasive measurement of hydrogen and potassium ion flux from single cells and epithelial structures

This review introduces new developments in a technique for measuring the movement of ions across the plasma membrane. With the use of a self-referencing ion-selective (Seris) probe, transport mechanisms can be studied on a variety of preparations ranging from tissues to single cells. In this paper we illustrate this versatility with examples from the vas deferens and inner ear epithelium to large and small single cells represented by mouse single-cell embryos and rat microglia. Potassium and hydrogen ion fluxes are studied and pharmacological manipulation of the signals are reported. The strengths of the self-referencing technique are reviewed with regard to biological applications, and the expansion of self-referencing probes to include electrochemical and enzyme-based sensors is discussed.

Noninvasive measurement of potassium efflux as an early indicator of cell death in mouse embryos

Programmed cell death (apoptosis) occurs in nearly all cell types examined, including mammalian oocytes and embryos, where it may underlie some forms of infertility in humans. Although the molecular machinery participating in apoptosis have been intensely investigated, the accompanying physiological changes have not received similar attention. In this study, a novel electrophysiology technique has been employed to monitor real-time perturbations in the physiology of mouse embryos undergoing apoptosis evoked by hydrogen peroxide, diamide, and staurosporine. Despite differences in their mode of action, these agents evoked a similar early change in cellular physiology; namely, a pronounced, transient, potassium efflux through tetraethylammonium-sensitive potassium channels accompanied by cell shrinkage. Mouse zygotes exposed to 200 microM H(2)O(2) exhibited potassium efflux that elevated the potassium concentration of the media surrounding embryos by 1.4 +/- 0.1 microM. Pretreatment with tetraethylammonium inhibited this increase (0.2 +/- 0.1 microM). Our results indicate that potassium efflux through potassium channels and concurrent cell shrinkage are early indicators of cell death in embryos and that noninvasive measurements of potassium pathophysiology may identify embryos undergoing cell death prior to the manifestation of other morphological or molecular hallmarks of cell death.

Oxidative phosphorylation-dependent and -independent oxygen consumption by individual preimplantation mouse embryos

The self-referencing electrode technique was employed to noninvasively measure gradients of dissolved oxygen in the medium immediately surrounding developing mouse embryos and, thereby, characterized changes in oxygen consumption and utilization during development. A gradient of depleted oxygen surrounded each embryo and could be detected >50 microm from the embryo. Blastocysts depleted the surrounding medium of 0.6+/-0.1 microM of oxygen, whereas early cleavage stage embryos depleted the medium of only 0.3+/-0.1 microM of oxygen, suggesting a twofold increase in oxygen consumption at the blastocyst stage. Mitochondrial oxidative phosphorylation (OXPHOS) accounted for 60-70% of the oxygen consumed by blastocysts, while it accounted for only 30% of the total oxygen consumed by cleavage-stage embryos. The amount of oxygen consumed by non-OXPHOS mechanisms remained relatively constant throughout preimplantation development. By contrast, the amount of oxygen consumed by OXPHOS in blastocysts is greater than that consumed by OXPHOS in cleavage-stage embryos. The amount of oxygen consumed by one-cell embryos was modulated by the absence of pyruvate from the culture medium. Treatment of one-cell embryos and blastocysts with diamide, an agent known to induce cell death in embryos, resulted in a decline in oxygen consumption, such that the medium surrounding dying embryos was not as depleted of oxygen as that surrounding untreated control embryos. Together these results validate the self-referencing electrode technique for analyzing oxygen consumption and utilization by preimplantation embryos and demonstrate that changes in oxygen consumption accompany important physiological events, such as development, response to medium metabolites, or cell death.

Study of calcium signaling in non-excitable cells

The fundamental importance of calcium signaling in the control of cellular physiology is widely recognized. A dramatic illustration of this is the fact that a Medline search for review articles containing the word "calcium" in the title reveals 4,629 hits, whereas the whole body of calcium signaling literature (approximately 2 x 10(6) pages) is more than enough to fill a decent-sized library. Most of this literature deals with calcium signaling in excitable cells types (mainly neurons and muscle cells), but non-excitable cell types are capable of calcium signaling as well. Although calcium fluxes in the latter cell types have attracted much less interest, the literature involved is still vast. Nevertheless, in this review article we hope to contribute some valuable insights to the field. First we shall discuss the experimental techniques available to the researcher interested in calcium signaling in non-excitable cell types with special attention to patch clamp electrophysiology. Subsequently, we shall review some of the results obtained with these techniques by focussing on the calcium-regulating mechanisms in non-excitable cells and discussing the importance of these mechanisms for physiology.