Analysis of transmembrane electrical potential across nanofiltration membranes based on electrostatic and steric-hindrance model

2011 ◽  
Vol 36 (1-3) ◽  
pp. 152-163
Author(s):  
Cong-Hui Tu ◽  
Yan-Yan Fang ◽  
Xiao-Lin Wang
Keyword(s):  
Steric Hindrance ◽  
Electrical Potential ◽  
Nanofiltration Membranes ◽  
Transmembrane Electrical Potential

The mitochondrial consequences of uncoupling intact cells depend on the nature of the exogenous substrate

2001 ◽  
Vol 355 (1) ◽  
pp. 231-235 ◽  
Author(s):  
Brigitte SIBILLE ◽  
Céline FILIPPI ◽  
Marie-Astrid PIQUET ◽  
Pascale LECLERCQ ◽  
Eric FONTAINE ◽  
...  
Keyword(s):  
Oxidation Rate ◽  
Marked Decrease ◽  
Electrical Potential ◽  
Atp Synthesis ◽  
Intact Cells ◽  
Isolated Mitochondria ◽  
Exogenous Substrate ◽  
High Oxidation ◽  
Transmembrane Electrical Potential ◽  
Sustained Increase

In isolated mitochondria the consequences of oxidative phosphorylation uncoupling are well defined, whereas in intact cells various effects have been described. Uncoupling liver cells with 2,4-dinitrophenol (DNP) in the presence of dihydroxyacetone (DHA) and ethanol results in a marked decrease in mitochondrial transmembrane electrical potential (∆ψ), ATP/ADP ratios and gluconeogenesis (as an ATP-utilizing process), whereas the increased oxidation rate is limited and transient. Conversely, when DHA is associated with octanoate or proline, DNP addition results in a very large and sustained increase in oxidation rate, whereas the decreases in ∆ψ, ATP/ADP ratios and gluconeogenesis are significantly less when compared with DHA and ethanol. Hence significant energy wastage (high oxidation rate) by uncoupling is achieved only with substrates that are directly oxidized in the mitochondrial matrix. Conversely in the presence of substrates that are first oxidized in the cytosol, uncoupling results in a profound decrease in mitochondrial ∆ψ and ATP synthesis, whereas energy wastage is very limited.

scholarly journals Transport of organic electrolytes with electrostatic and steric-hindrance effects through nanofiltration membranes.

1995 ◽  
Vol 28 (4) ◽  
pp. 372-380 ◽  
Author(s):  
Xiao-Lin Wang ◽  
Toshinori Tsuru ◽  
Masanori Togoh ◽  
Shin-ichi Nakao ◽  
Shoji Kimura
Keyword(s):  
Steric Hindrance ◽  
Nanofiltration Membranes ◽  
Organic Electrolytes

Phosphate transport in kidneys: effect of transmembrane electrical potential

1991 ◽  
Vol 261 (4) ◽  
pp. F663-F669 ◽  
Author(s):  
R. Beliveau ◽  
J. Strevey
Keyword(s):  
Driving Force ◽  
Transmembrane Potential ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Phosphate Transport ◽  
Saturation Curve ◽  
Maximal Velocity ◽  
Transmembrane Electrical Potential ◽  
The Hill ◽  
Phosphate Influx

The effect of a transmembrane electrical potential on phosphate transport by kidney brush-border membrane vesicles was studied. The initial rate of Na(+)-dependent phosphate influx was twice as high as that of efflux. Generation of a negative transmembrane potential had a stimulatory effect on the rate of influx but had no effect on efflux. The Na+ saturation curve for phosphate influx was sigmoidal, and the Hill coefficients were similar, in the presence and absence of a transmembrane potential. The membrane potential increased both the affinity for phosphate and the maximal velocity (Vmax) of the transporter. In the absence of a Na+ gradient, the stimulation by the potential was 1.78-fold. When a proton gradient (in greater than out) was the driving force, the electrical potential stimulated phosphate transport 1.71-fold. Internal Na+ (trans) inhibited phosphate influx whether a potential was present or not. Internal phosphate (trans) stimulated phosphate influx in the absence of a potential but not in its presence. These results indicate that the electrical potential is an important driving force for the Na(+)-phosphate carrier and that the translocation of the carrier is a potential-dependent step.

Sodium and calcium share the electrogenic 2 Na(+)-1 H+ antiporter in crustacean antennal glands

1990 ◽  
Vol 259 (5) ◽  
pp. F758-F767
Author(s):  
G. A. Ahearn ◽  
P. Franco
Keyword(s):  
Driving Forces ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Homarus Americanus ◽  
Competitive Inhibitor ◽  
Hill Coefficient ◽  
Affinity Constant ◽  
Electrical Potential Difference ◽  
Static Head ◽  
Transmembrane Electrical Potential

Na uptake by short-circuited epithelial brush-border membrane vesicles of Atlantic lobster (Homarus americanus) antennal gland labyrinth was Cl independent, amiloride sensitive, and stimulated by a transmembrane H+ gradient [( H]i greater than [H]o; i is internal, o is external). Na influx (2.5-s uptake) was a sigmoidal function of [Na]o (25-400 mM) when pHi = 5.0 and pHo = 8.0 and followed the Hill equation for binding cooperatively [apparent maximal influx (Jmax) = 271 nmol.mg protein-1.s-1, apparent affinity constant for Na (KNa) = 310 mM Na, and Hill coefficient (n) = 2.41]. Amiloride acted as a competitive inhibitor of Na binding to two external sites with markedly dissimilar apparent amiloride affinities (Ki1 = 14 microM; Ki2 = 1,340 mM). Electrogenic Na-H antiport by these vesicles was demonstrated by equilibrium-shift experiments in which an imposed transmembrane electrical potential difference was the only driving force for exchange. A transport stoichiometry of 2 Na to 1 H was demonstrated with the static-head technique in which a balance of driving forces was attained with 10:1 Na gradient and 100:1 H gradient. External Ca, like amiloride, was a strong competitive inhibitor of Na-H exchange, acting at two sites on the outer vesicular face with markedly different apparent divalent cation affinities (Ki1 = 20 microM; Ki2 = 500 microM). Ca-H exchange by electrogenic Na-H antiporter was demonstrated in complete absence of Na by use of an outward H gradient in presence and absence of amiloride. Both external amiloride (Ki1 = 70 microM; Ki2 = 500 microM) and Na (Ki1 = 12 mM; Ki2 = 380 mM) were competitive inhibitors of Ca-H exchange. These results suggest that the electrogenic 2 Na-1 H exchanger characterized for this crustacean epithelium may also have a role in organismic Ca balance.

Na-dependent L-glutamate transport by eel intestinal BBMV: role of K+ and Cl-

1989 ◽  
Vol 257 (1) ◽  
pp. R180-R188
Author(s):  
P. M. Romano ◽  
G. A. Ahearn ◽  
C. Storelli
Keyword(s):  
Amino Acid ◽  
Glutamate Uptake ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Anguilla Anguilla ◽  
Competitive Inhibitor ◽  
Glutamate Transport ◽  
Electrical Potential Difference ◽  
Intestinal Brush Border Membrane ◽  
Transmembrane Electrical Potential

L-[3H]glutamate uptake into eel (Anguilla anguilla) intestinal brush-border membrane vesicles (BBMV) was a sigmoidal function of extravesicular Na, suggesting that two or more cations accompanied the amino acid during transport. L-[3H]glutamate influx illustrated the following kinetic constants: apparent membrane binding affinity (Kapp) = 0.80 +/- 0.12 mM; influx velocity (Jmax) = 2.61 +/- 0.31 nmol.mg protein-1.min-1; and permeability coefficient (P) = 0.65 +/- 0.10 microliters.mg protein-1. min-1. Results from the imposition of diffusion potentials across vesicle membranes using K-valinomycin or H-carbonyl-cyanide p-chloromethoxyphenylhydrazone suggested that Na-dependent L-glutamate transport was sensitive to transmembrane electrical potential difference. Extravesicular aspartate was a competitive inhibitor of L-[3H]glutamate influx [inhibitory constant (Ki) = 0.28 +/- 0.04 mM]. Intravesicular K and extravesicular Cl ions enhanced maximal amino acid influx and transient L-glutamate accumulation against a concentration gradient (overshoot). Intravesicular K reduced the Kapp of the membrane to L-glutamate, whereas extravesicular Cl increased L-glutamate Jmax. A model for L-[3H]glutamate transport is suggested involving the cotransport of at least two Na and one L-glutamate that is activated by one intravesicular K ion and at least two extravesicular Cl ions.

Electroneutral Na+/H+exchange in brush-border membrane vesicles fromPenaeus japonicus hepatopancreas

1998 ◽  
Vol 274 (2) ◽  
pp. R486-R493 ◽  
Author(s):  
Sebastiano Vilella ◽  
Vincenzo Zonno ◽  
Laura Ingrosso ◽  
Tiziano Verri ◽  
Carlo Storelli
Keyword(s):  
Kinetic Parameters ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Hill Coefficient ◽  
Uptake Kinetic ◽  
Ph Dependent ◽  
Transmembrane Electrical Potential

An electroneutral Na+/H+exchange mechanism (dimethylamiloride inhibitable, Li+ sensitive, and Ca2+ insensitive) was identified in brush-border membrane vesicles (BBMV) from Kuruma prawn hepatopancreas by monitoring Na+-dependent H+ fluxes with the pH-sensitive dye acridine orange and measuring22Na+uptake. Kinetic parameters measured under short-circuited conditions were the Na+ concentration that yielded one-half of the maximal dissipation rate ( F max) of the preset transmembrane ΔpH ( K Na) = 15 ± 2 mM and F max = 3,626 ± 197 Δ F ⋅ min−1 ⋅ mg protein−1, with a Hill coefficient for Na+ of ∼1. In addition, the inhibitory constant for dimethylamiloride was found to be ∼1 μM. The electroneutral nature of the antiporter was assessed in that an inside-negative transmembrane electrical potential neither affected kinetic parameters nor stimulated pH-dependent (intracellular pH > extracellular pH)22Na+uptake. In contrast, electrogenic pH-dependent22Na+uptake was observed in lobster hepatopancreatic BBMV. Substitution of chloride with gluconate resulted in increasing K Na and decreasing Δ F max, which suggests a possible role of chloride in the operational mechanism of the antiporter. These results indicate that a Na+/H+exchanger, resembling the electroneutral Na+/H+antiporter model, is present in hepatopancreatic BBMV from the Kuruma prawn Penaeus japonicus.

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