Ionic events

By tradition, electrochemistry has been considered a branch of physical chemistry devoted to macroscopic models and theories. We measure macroscopic currents, electrodic potentials, consumed charges, conductivities, admittance, etc. All of these take place on a macroscopic scale and are the result of multiple molecular, atomic, or ionic events taking place at the electrode/electrolyte interface. Great efforts are being made by electrochemists to show that in a century where the most brilliant star of physical chemistry has been quantum chemistry, electrodes can be studied at an atomic level and elemental electron transfers measured.1 The problem is that elemental electrochemical steps and their kinetics and structural consequences cannot be extrapolated to macroscopic and industrial events without including the structure of the surface electrode. 

WangS, MelkoumianZ, Woodfork KA, CatherC, Davidson AG, Wonderlin WF, Strobl JS (1998) Evidence for an early G1 ionic event necessary for cell cycle progression and survival in the MCF-7 human breast carcinoma cell line. J Cell Physiol... 

Islet Metabolism, Ionic Events and Insulin Secretion. 83... 

ISLET METABOLISM, IONIC EVENTS AND INSULIN SECRETION... 

The sequences of ionic events in the action potential of cardiac cells are descnbed. 

Summary of ionic events associated with stomatal movements... 

Correlation analysis can be performed on internally generated noise in the complete absence of an external excitation function. Because the ionic events... 

Fig. 37. Regression analysis to show the way in which the depolarizations (AV) evoked by cholecystokinin (CCK-8) is related to an associated decrease in membrane resistance R IR). The slope of the line is related to the equilibrium potential of the ionic events which mediate the response of the putative transmitter involved. (From Dodd and Kelly, 1981.)...

Vogalis, F. Hillsley, K. Smith, T. Recording ionic events from cultured, Dil-labehed myenteric neurons in the guinea-pig proximal colon. J. Neurosci Methods 2000, 96, 25-34. 

However, reaction 7 suffers other shortcomings, eg, entropy problems. Other proposals range from trace peroxidic contaminants to ionic mechanisms for generating peroxides (1) to cosmic rays (17). In any event, the initiating reactions are significant only during the induction period (18). 

Fig. 14. The cellular ionic environment depicting representative intracellular ionic concentrations and the equiUbrium potentials, for individual ions. Excitatory and inhibitory events are represented by — and +, respectively. Thus, K" channel agonists and antagonists are inhibitory and excitatory, respectively Ca " channel antagonists and activators are inhibitory and excitatory, respectively.

As it happens, the product Ba is near unity. In particular, it is about one in water if a (the interaction distance) is 3 X 10 10 m. This is not an unreasonable distance. Even if a is somewhat different, the simplification that Ba is nearly unity is a fair approximation, and one that is often made. This is allowed because Ba occurs as a multiplier of fju in the denominator of Eq. (9-39), where this product is invariably less than the unity to which it is added. And the equations for the activity coefficients are in any event reliable only at low ionic strength. For these reasons, and because of the resulting simplification, we shall approximate the expression for the activity coefficient as... 

Because the Na+ and N03 ions appear as both reactants and products, they play no direct role in the reaction. They are spectator ions, ions that are present while the reaction takes place but remain unchanged, like spectators at a sports event. Because spectator ions remain unchanged, we can simplify the chemical equation by canceling them on each side of the arrow in the ionic equation ... 

FIGURE 8.15 The events that take place at the interface of a solid ionic solute and a solvent (water). When the ions at the surface of the solid become hydrated, they move off into the solution. 

Figure 1. Simplified schematic of receptor-mediated signal transduction in neutrophils. Binding of ligand to the receptor activates a guanine-nucleotide-binding protein (G protein), which then stimulates phospholipase C. Phosphatidylinositol 4,5-bis-phosphate is cleaved to produce diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). DAG stimulates protein kinase C. IP3 causes the release of Ca from intracellular stores, which results in an increase in the cytosolic Ca concentration. This increase in Ca may stimulate protein kinase C, calmodulin-dependent protein kinases, and phospholipase A2. Protein phosphorylation events are thought to be important in stimulating degranulation and oxidant production. In addition, ionic fluxes occur across the plasma membrane. It is possible that phospholipase A2 and ionic channels may be governed by G protein interactions. ...

Precellular solute ionization dictates membrane permeability dependence on mucosal pH. Therefore, lumenal or cellular events that affect mucosal microclimate pH may alter the membrane transport of ionizable solutes. The mucosal microclimate pH is defined by a region in the neighborhood of the mucosal membrane in which pH is lower than in the lumenal fluid. This is the result of proton secretion by the enterocytes, for which outward diffusion is slowed by intestinal mucus. (In fact, mucosal secretion of any ion coupled with mucus-restricted diffusion will provide an ionic microclimate.) Important differences in solute transport between experimental systems may be due to differences in intestinal ions and mucus secretion. It might be anticipated that microclimate pH effects would be less pronounced in epithelial cell culture (devoid of goblet cells) transport studies than in whole intestinal tissue. 

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