Vesicular neurotransmitters exocytosis monitored by amperometry: theoretical quantitative links between experimental current spikes shapes and intravesicular structures.

Single cell amperometry has proven to be a powerful and well-established method for characterizing single vesicular exocytotic events elicited at the level of excitable cells under various experimental conditions. Nevertheless, most of the reported characteristics are descriptive, being mostly concerned with the morphological characteristics of the recorded current spikes (maximum current intensities, released charge, rise and fall times, ) which are certainly important but do not provide sufficient kinetic information on exocytotic mechanisms due to lack of quantitative models. Here, continuing our previous efforts to provide rigorous models rationalizing the kinetic structures of frequently encountered spike types (spikes with unique exponential decay tails and kiss-and-run events), we describe a new theoretical approach enabling a quantitative kinetic modeling of all types of exocytotic events giving rise to current spikes exhibiting exponential decay tails.

Electrochemical Storage of Atomic Hydrogen on Single Layer Graphene.

If hydrogen can be stored and carried safely at a high density, hydrogen-fuel cells offer effective solutions for vehicles. The stable chemisorption of atomic hydrogen on single layer graphene (SLG) seems a perfect solution in this regard, with a theoretical maximum storage capacity of 7.7 wt %.

Intracellular Electrochemical Nanomeasurements Reveal that Exocytosis of Molecules at Living Neurons is Subquantal and Complex.

Since the early work of Bernard Katz, the process of cellular chemical communication through exocytosis, quantal release, has been considered to be all or none. Recent evidence has shown exocytosis to be partial or "subquantal" at single-cell model systems, but there is a need to understand this at communicating nerve cells. Partial release allows nerve cells to control the signal at the site of release during individual events, for which the smaller the fraction released, the greater the range of regulation.

Amperometric Measurements and Dynamic Models Reveal a Mechanism for How Zinc Alters Neurotransmitter Release.

Zinc, a suspected potentiator of learning and memory, is shown to affect exocytotic release and storage in neurotransmitter-containing vesicles. Structural and size analysis of the vesicular dense core and halo using transmission electron microscopy was combined with single-cell amperometry to study the vesicle size changes induced after zinc treatment and to compare these changes to theoretical predictions based on the concept of partial release as opposed to full quantal release. This powerful combined analytical approach establishes the existence of an unsuspected strong link between vesicle structure and exocytotic dynamics, which can be used to explain the mechanism of regulation of synaptic plasticity by Zn through modulation of neurotransmitter release.

Electrochemical Monitoring of ROS/RNS Homeostasis Within Individual Phagolysosomes Inside Single Macrophages.

The existence of a homeostatic mechanism regulating reactive oxygen/nitrogen species (ROS/RNS) amounts inside phagolysosomes has been invoked to account for the efficiency of this process but could not be unambiguously documented. Now, intracellular electrochemical analysis with platinized nanowire electrodes (Pt-NWEs) allowed monitoring ROS/RNS effluxes with sub-millisecond resolution from individual phagolysosomes impacting onto the electrode inserted inside a living macrophage. This shows for the first time that the consumption of ROS/RNS by their oxidation at the nanoelectrode surface stimulates the production of significant ROS/RNS amounts inside phagolysosomes.

Self-Inhibitory Electron Transfer of the Co(III)/Co(II)-Complex Redox Couple at Pristine Carbon Electrode.

Applications of conducting carbon materials for highly efficient electrochemical energy devices require a greater fundamental understanding of heterogeneous electron-transfer (ET) mechanisms. This task, however, is highly challenging experimentally, because an adsorbing carbon surface may easily conceal its intrinsic reactivity through adventitious contamination. Herein, we employ nanoscale scanning electrochemical microscopy (SECM) and cyclic voltammetry to gain new insights into the interplay between heterogeneous ET and adsorption of a Co(III)/Co(II)-complex redox couple at the contamination-free surface of electron-beam-deposited carbon (eC).

'Full fusion' is not ineluctable during vesicular exocytosis of neurotransmitters by endocrine cells.

Vesicular exocytosis is an essential and ubiquitous process in neurons and endocrine cells by which neurotransmitters are released in synaptic clefts or extracellular fluids. It involves the fusion of a vesicle loaded with chemical messengers with the cell membrane through a nanometric fusion pore. In endocrine cells, unless it closes after some flickering ('Kiss-and-Run' events), this initial pore is to expand exponentially, leading to a full integration of the vesicle membrane into the cell membrane-a stage called 'full fusion'.

On the mechanism of electrochemical vesicle cytometry: chromaffin cell vesicles and liposomes.

The mechanism of mammalian vesicle rupture onto the surface of a polarized carbon fiber microelectrode during electrochemical vesicle cytometry is investigated. It appears that following adsorption to the surface of the polarized electrode, electroporation leads to the formation of a pore at the interface between a vesicle and the electrode and this is shown to be potential dependent. The chemical cargo is then released through this pore to be oxidized at the electrode surface.

The evidence for open and closed exocytosis as the primary release mechanism.

Exocytosis is the fundamental process by which cells communicate with each other. The events that lead up to the fusion of a vesicle loaded with chemical messenger with the cell membrane were the subject of a Nobel Prize in 2013. However, the processes occurring after the initial formation of a fusion pore are very much still in debate.

Enhancing the Bipolar Redox Cycling Efficiency of Plane-Recessed Microelectrode Arrays by Adding a Chemically Irreversible Interferent.

The individual electrochemical anodic responses of dopamine (DA), epinephrine (EP), and pyrocatechol (CT) were investigated at arrays of recessed gold disk-microelectrodes arrays (MEAs) covered by a gold plane electrode and compared to those of their binary mixture (CT and EP) when the top-plane electrode was operated as a bipolar electrode or as a collector. The interferent species (EP) displays a chemically irreversible wave over the same potential range as the chemically reversible ones of DA or CT. As expected, in the generator-collector (GC) mode, EP did not contribute to the redox cycling amplification that occurred only for DA or CT.

Electrochemical Measurements of Optogenetically Stimulated Quantal Amine Release from Single Nerve Cell Varicosities in Drosophila Larvae.

The nerve terminals found in the body wall of Drosophila melanogaster larvae are readily accessible to experimental manipulation. We used the light-activated ion channel, channelrhodopsin-2, which is expressed by genetic manipulation in Type II varicosities to study octopamine release in Drosophila. We report the development of a method to measure neurotransmitter release from exocytosis events at individual varicosities in the Drosophila larval system by amperometry.

Real-time Monitoring of Discrete Synaptic Release Events and Excitatory Potentials within Self-reconstructed Neuromuscular Junctions.

Chemical synaptic transmission is central to the brain functions. In this regard, real-time monitoring of chemical synaptic transmission during neuronal communication remains a great challenge. In this work, in vivo-like oriented neural networks between superior cervical ganglion (SCG) neurons and their effector smooth muscle cells (SMC) were assembled in a microfluidic device.

Strategy for increasing the electrode density of microelectrode arrays by utilizing bipolar behavior of a metallic film.

Recessed microelectrode arrays and plane-recessed microelectrode arrays (MEAs) with different center-to-center distances are designed and fabricated using lithographic technology. By comparing electrochemical behavior of plane-recessed MEAs with that of recessed MEAs, bipolar phenomenon of the metallic plane film is revealed. Redox cycling can occur when the top plane electrode was floating; that is, the bipolar behavior of the unbiased top plane electrode may perform locally as a collector and enlarge the concentration gradient of Ru(NH3)6Cl3 and thus promote an apparent generator/collector electrochemical response of the microdisk electrode in the MEAs configuration.

Vesicular release of neurotransmitters: converting amperometric measurements into size, dynamics and energetics of initial fusion pores.

Amperometric currents displaying a pre-spike feature (PSF) may be treated so as to lead to precise information about initial fusion pores, viz., about the crucial event initiating neurotransmitter vesicular release in neurons and medullary glands. However, amperometric data alone are not self-sufficient, so their full exploitation requires external calibration to solve the inverse problem.

The association of the original OSHA chemical hazard communication standard with reductions in acute work injuries/illnesses in private industry and the industrial releases of chemical carcinogens.

Background: OSHA predicted the original chemical Hazard Communication Standard (HCS) would cumulatively reduce the lost workday acute injury/illness rate for exposure events by 20% over 20 years and reduce exposure to chemical carcinogens.

Methods: JoinPoint trend software identified changes in the rate of change of BLS rates for days away from work for acute injuries/illnesses during 1992-2009 for manufacturing and nonmanufacturing industries for both chemical, noxious or allergenic injury exposure events and All other exposure events. The annual percent change in the rates was used to adjust observed numbers of cases to estimate their association with the standard.

Theoretical investigation of generator-collector microwell arrays for improving electroanalytical selectivity: application to selective dopamine detection in the presence of ascorbic acid.

Recessed generator-collector assemblies consisting of an array of recessed disks (generator electrodes) with a gold layer (collector electrode) deposited over the top-plane insulator reportedly allow increased selectivity and sensitivity during electrochemical detection of dopamine (DA) in the presence of ascorbic acid (AA), a situation which is frequently encountered. In sensor design, the potential of the disk electrodes is set to the wave plateau of DA, whereas the plane electrode is biased at the irreversible wave plateau of AA before the onset of the DA oxidation wave. Thus, AA is scavenged but DA is allowed to enter the nanocavities to be oxidized at the disk electrodes, and its signal is further amplified by redox cycling between disk and plane electrodes.

A novel approach to the simulation of electrochemical mechanisms involving acute reaction fronts at disk and band microelectrodes.

A new simulation algorithm is presented for describing the dynamics of diffusion reactions at the most common microelectrode 1D (planar, cylindrical, spherical) and 2D geometries (band, disk) for electrochemical mechanisms of any complexity and involving fast homogeneous reactions of any kind. A series of typical electrochemical mechanisms that create the most severe simulation difficulties is used to establish the exceptional performance and accuracy of this algorithm, which stem from the combination of (quasi)conformal transformation of space and a new method for auto-adaptive grid compression.

Simple and clear evidence for positive feedback limitation by bipolar behavior during scanning electrochemical microscopy of unbiased conductors.

On the basis of an experimentally validated simple theoretical model, it is demonstrated unambiguously that when an unbiased conductor is probed by a scanning electrochemical tip (scanning electrochemical microscopy, SECM), it performs as a bipolar electrode. Though already envisioned in most recent SECM theories, this phenomenon is generally overlooked in SECM experimental investigations. However, as is shown here, this may alter significantly positive feedback measurements when the probed conductor is not much larger than the tip.

The need for data harmonization--a response to Boden and Ozonoff.

Boden and Ozonoff's undercount estimates in their recent Commentary rely on three assumptions for which no quantitative literature references are provided. Alternatively, we show that findings in both studies and published data indicate lower upper-bound estimates for the undercount range. Am.

The law and incomplete database information as confounders in epidemiologic research on occupational injuries and illnesses.

Background: Capture-recapture studies report undercounting of work injuries/illnesses with days away from work (DAFW) in the Bureau of Labor Statistics annual Survey of Occupational Injuries and Illnesses (BLS SOII) by 25-68% depending on the state and undercounting by various state workers' compensation (WC) systems of eligible claims by 5-35%.

Methods: Statutory/regulatory criteria defining eligible cases are used to adjust counts in the 1998-2001 Minnesota's WC system and the BLS SOII to permit comparison and to evaluate the recent studies. Missing information in the employer database used in the capture-recapture studies is tabulated.

Reconstruction of aperture functions during full fusion in vesicular exocytosis of neurotransmitters.

Individual vesicular exocytosis of adrenaline by dense core vesicles in chromaffin cells is considered here as a paradigm of many situations encountered in biology, nanosciences and drug delivery in which a spherical container releases in the external environment through gradual uncovering of its surface. A procedure for extracting the aperture (opening) function of a biological vesicle fusing with a cell membrane from the released molecular flux of neurotransmitter as monitored by amperometry has been devised based on semi-analytical expressions derived in a former work [C. Amatore, A.

Diffusion from within a spherical body with partially blocked surface: diffusion through a constant surface area.

Diffusion from spherical bodies has been a subject of interest since the earliest times of modern sciences and a few equivalent analytical formulations of the problem are taught in engineering textbooks dealing with cooling rates of hot spheres. However, all these former studies assume that the diffusing material is transferable to/from the surrounding space through the whole surface of the spherical body. Conversely, the development of nanoscience and the improved knowledge of microscopic biological events have evidenced that diffusion from spherical bodies is a ubiquitous problem.

Capacitive and solution resistance effects on voltammetric responses at a disk microelectrode covered with a self-assembled monolayer in the presence of electron hopping.

This article extends our previous works (Amatore, C.; Oleinick, A.; Svir, I.

Electrochemical determination of flow velocity profile in a microfluidic channel from steady-state currents: numerical approach and optimization of electrode layout.

In this article, the numerical approach for flow profile reconstruction in a microfluidic channel equipped with band microelectrodes introduced previously by the authors, based on transient currents, is extended to the exclusive use of steady-state currents. It is shown that, although the currents obey steady state, the flow velocity profile in the channel may be reconstructed rapidly with a high accuracy, provided a sufficient number of electrodes performing under steady state are considered. The present theory demonstrates how the electrode widths and sizes of gaps separating them can be optimized to achieve better performance of the method.

Diffusion with moving boundary on spherical surfaces.

In this work, we illustrate two approaches to the simulation of surface diffusion over a sphere coupled with the formation of a cluster by reactive particles as a paradigm of a wide variety of problems occurring in many areas of nanosciences and biology. The problem is treated using a Brownian motion approach and a numerical solution of the corresponding continuous Fick's laws of diffusion. While being computationally more expensive, the Brownian motion approach allows one to consider a wider range of situations, particularly those corresponding to relatively high concentrations of diffusing particles and the ensuing problem of particle overlap when they are ascribed finite sizes.