Electrodiffusion Phenomena in Neuroscience and the Nernst–Planck–Poisson Equations

This work is aimed to give an electrochemical insight into the ionic transport phenomena in the cellular environment of organized brain tissue. The Nernst–Planck–Poisson (NPP) model is presented, and its applications in the description of electrodiffusion phenomena relevant in nanoscale neurophysiology are reviewed. These phenomena include: the signal propagation in neurons, the liquid junction potential in extracellular space, electrochemical transport in ion channels, the electrical potential distortions invisible to patch-clamp technique, and calcium transport through mitochondrial membrane. The limitations, as well as the extensions of the NPP model that allow us to overcome these limitations, are also discussed.

Burnstock and the legacy of the inhibitory junction potential and P2Y1 receptors

The synaptic event called the inhibitory junction potential (IJP) was arguably one of the more important discoveries made by Burnstock and arguably one of his finer legacies. The discovery of the IJP fundamentally changed how electromechanical coupling was visualised in gastrointestinal smooth muscle. Its discovery also set in motion the search for novel inhibitory neurotransmitters in the enteric nervous system, eventually leading to proposal that ATP or a related nucleotide was a major inhibitory transmitter. The subsequent development of purinergic signalling gave impetus to expanding the classification of surface receptors for extracellular ATP, not only in the GI tract but beyond, and then led to successive phases of medicinal chemistry as the P2 receptor field developed. Ultimately, the discovery of the IJP led to the successful cloning of the first P2Y receptor (chick P2Y1) and expansion of mammalian ATP receptors into two classes: metabotropic P2Y receptors (encompassing P2Y1, P2Y2, P2Y4, P2Y6, P2Y11–14 receptors) and ionotropic P2X receptors (encompassing homomeric P2X1–P2X7 receptors). Here, the causal relationship between the IJP and P2Y1 is explored, setting out the milestones reached and achievements made by Burnstock and his colleagues.

DETERMINATION OF ALKALINITY AND DISSOCIATION CONSTANTS OF HIGH SALINITY WATERS: USE OF F5BC TITRATION FUNCTION

Measurements of parameters expressed in terms of carbonic species such as Alkalinity and Acidity of saline waters do not analyze the influence of external parameters to the titration such as Total free and associated Carbonic Species Concentration, activity coefficient, ion pairing formation and Residual Liquid Junction Potential in pH measurements. This paper shows the development of F5BC titration function based on the titrations developed by Gran (1952) for the carbonate system of natural waters. For practical use, samples of saline watersfrom Pocinhos reservoir in Paraiba were submitted to titration and linear regression analysis. Results showed that F5BC involves F1x and F2x Gran functions determination, respectively, for Alkalinity and Acidity calculations without knowing “a priori” the endpoint of the titration. F5BC also allows the determination of the First and Second Apparent Dissociation Constant of the carbonate system of saline and high ionic strength waters.

Revisiting passivation II: electronic conduction of transition metal oxides, Mott-Schottky plots, and root cause of stainless steel grades and nickel based alloys

The novel views on passivation and passivity are briefly reviewed, with further explanation of some key details. First, the most common polymerisation mechanism directly transforms an insoluble hydroxide into a cross-linked oxide gel. The Al type passivation corresponds to insulating oxides, and this directly leads to a nearly sealed off gel with just a residual access of the electrolyte to the metal surface. In Fe type passivation, the electronic 3d shells are incomplete, which induces a coexistence of bi- and trivalent monomers, and from elsewhere well-known quantum (or magnetic) effects, a complete ordering can suddenly induce an electronic conduction at the interatomic scale. The different grades of stainless steels or Ni based alloys, and a few other paradoxical observations, are thus explained by the required conjunction of magnetic, chemical and electrochemical features. In parallel, any applied polarisation induces a junction potential at the electrolyte boundary, with electric field, ionic space charges, and local electromigration. All are cancelled in the Faraday cage of a conductive gel, but its adaptation to each potential takes some time. Therefore, the alleged “Mott-Schottky” plots do not detect the electronic space charges of a supposedly semiconductor, but just the local ionic space charges induced by artificial polarisations.