Distribution of electric potential and ion transport in the hypocotyl of Vigna sesquipedalis I. Distribution of overall ion concentration and the role of hydrogen ion in generation of potential difference

1970 ◽  
Keyword(s):  
Ion Transport ◽  
Electric Potential ◽  
Potential Difference ◽  
Hydrogen Ion ◽  
Ion Concentration

scholarly journals Electric potential differences across auroral generator interfaces

2013 ◽  
Vol 31 (2) ◽  
pp. 251-261 ◽  
Author(s):  
J. De Keyser ◽  
M. Echim
Keyword(s):  
Electric Field ◽  
High Altitude ◽  
Electric Fields ◽  
Electric Potential ◽  
Equilibrium Configuration ◽  
Potential Difference ◽  
Field Profile ◽  
Electric Potential Difference ◽  
Electric Field Profile

Abstract. Strong localized high-altitude auroral electric fields, such as those observed by Cluster, are often associated with magnetospheric interfaces. The type of high-altitude electric field profile (monopolar, bipolar, or more complicated) depends on the properties of the plasmas on either side of the interface, as well as on the total electric potential difference across the structure. The present paper explores the role of this cross-field electric potential difference in the situation where the interface is a tangential discontinuity. A self-consistent Vlasov description is used to determine the equilibrium configuration for different values of the transverse potential difference. A major observation is that there exist limits to the potential difference, beyond which no equilibrium configuration of the interface can be sustained. It is further demonstrated how the plasma densities and temperatures affect the type of electric field profile in the transition, with monopolar electric fields appearing primarily when the temperature contrast is large. These findings strongly support the observed association of monopolar fields with the plasma sheet boundary. The role of shear flow tangent to the interface is also examined.

scholarly journals THE COLLOIDAL BEHAVIOR OF SERUM GLOBULIN

1922 ◽  
Vol 5 (1) ◽  
pp. 35-44 ◽  
Author(s):  
David I. Hitchcock
Keyword(s):  
Potential Difference ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Serum Globulin ◽  
Hydrogen Ion Concentration ◽  
Egg Albumin ◽  
Electrometric Titration ◽  
Acids And Bases ◽  
Protein Serum ◽  
Colloidal Behavior

1. The globulin prepared from ox serum by dilution and precipitation with carbon dioxide has been found, by electrometric titration experiments, to behave like an amphoteric electrolyte, reacting stoichiometrically with acids and bases. 2. The potential difference developed between a solution of globulin chloride, phosphate, or acetate and a solution of the corresponding acid, free from protein, separated from the globulin by a collodion membrane, was found to be influenced by hydrogen ion concentration and salt concentration in the way predicted by Donnan's theory of membrane equilibrium. In experiments with sodium globulinate and sodium hydroxide it was found that the potential difference could be similarly explained. 3. The osmotic pressure of such solutions could be qualitatively accounted for by the Donnan theory, but exhibited a discrepancy which is explicable by analogy with certain experiments of Loeb on gelatin. 4. The application of Loeb's theory of colloidal behavior, which had previously been found to hold in the case of gelatin, casein, egg albumin, and edestin, has thus been extended to another protein, serum globulin.

scholarly journals Ae4 (Slc4a9) is an electroneutral monovalent cation-dependent Cl−/HCO3− exchanger

2016 ◽  
Vol 147 (5) ◽  
pp. 423-436 ◽  
Author(s):  
Gaspar Peña-Münzenmayer ◽  
Alvin T. George ◽  
Gary E. Shull ◽  
James E. Melvin ◽  
Marcelo A. Catalán
Keyword(s):  
Ion Transport ◽  
Physiological Role ◽  
Acinar Cells ◽  
Monovalent Cation ◽  
Ion Concentration ◽  
Secretory Cells ◽  
Whole Cell ◽  
Na Ions ◽  
Whole Cell Recordings

Ae4 (Slc4a9) belongs to the Slc4a family of Cl−/HCO3− exchangers and Na+-HCO3− cotransporters, but its ion transport cycle is poorly understood. In this study, we find that native Ae4 activity in mouse salivary gland acinar cells supports Na+-dependent Cl−/HCO3− exchange that is comparable with that obtained upon heterologous expression of mouse Ae4 and human AE4 in CHO-K1 cells. Additionally, whole cell recordings and ion concentration measurements demonstrate that Na+ is transported by Ae4 in the same direction as HCO3− (and opposite to that of Cl−) and that ion transport is not associated with changes in membrane potential. We also find that Ae4 can mediate Na+-HCO3− cotransport–like activity under Cl−-free conditions. However, whole cell recordings show that this apparent Na+-HCO3− cotransport activity is in fact electroneutral HCO3−/Na+-HCO3− exchange. Although the Ae4 anion exchanger is thought to regulate intracellular Cl− concentration in exocrine gland acinar cells, our thermodynamic calculations predict that the intracellular Na+, Cl−, and HCO3− concentrations required for Ae4-mediated Cl− influx differ markedly from those reported for acinar secretory cells at rest or under sustained stimulation. Given that K+ ions share many properties with Na+ ions and reach intracellular concentrations of 140–150 mM (essentially the same as extracellular [Na+]), we hypothesize that Ae4 could mediate K+-dependent Cl−/HCO3− exchange. Indeed, we find that Ae4 mediates Cl−/HCO3− exchange activity in the presence of K+ as well as Cs+, Li+, and Rb+. In summary, our results strongly suggest that Ae4 is an electroneutral Cl−/nonselective cation–HCO3− exchanger. We postulate that the physiological role of Ae4 in secretory cells is to promote Cl− influx in exchange for K+(Na+) and HCO3− ions.

scholarly journals Studies in the mechanism of enzyme action. I.—Rôle of the reaction of the medium in fixing the optimum temperature of a ferment

1921 ◽  
Vol 92 (642) ◽  
pp. 1-6 ◽  
Keyword(s):  
Enzyme Activity ◽  
Temperature Effect ◽  
Acid Medium ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Optimum Temperature ◽  
Hydrogen Ion Concentration ◽  
Enzyme Action

Previously, it has been shown for the enzyme maltase —enzyme requiring an acid medium in which to act to best advantage—that increase in the acidity or hydrogen ion concentration of the medium in which the enzyme acts, beyond the optimum acidity, leads to a fall of optimum temperature. The mechanism of his temperature of this temperature effect appears clearly to be due to a certain disablement of the enzyme activity, estimated at the optimum temperature point; which decrease of activity is itself a function of the degree of acidity of the medium in excess of that necessary to produce optimum activation. Being in this way a disablement effect, the question arises whether, by adding to the quantity of enzyme in action, the lowering of optimum temperature which takes place can be controlled. To answer that question, the experiments described in the present paper were undertaken. For the investigation, the enzyme used is the maltase of Aspergillus oryzœ , the same preparation being employed as studied by us in two previous communications, a specially active specimen of takadiastase, purified by repeated solution in water and reprecipitation by alcohol.

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